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poky/documentation/dev-manual/dev-manual-common-tasks.xml
Scott Rifenbark d0c89b6d59 dev-manual: Updates to "Using .bbappend Files in Your Layer" 
I did some rewriting for clarity in the "Using .bbappend Files
in Your Layer" section.  The section needed to be retitled so
focus on the layer aspect of .bbappend files.  Also, while I
was in there, I did more work on the prose in general.

Also had to fix some links in the bsp, kernel, and ref manuals
that linked into the section whose name I changes.

(From yocto-docs rev: 27003c525a05ffa2f810a038c7c8f96bb7535986)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
2017-09-02 00:52:56 +01:00

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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
<chapter id='extendpoky'>
<title>Common Tasks</title>
<para>
This chapter describes fundamental procedures such as creating layers,
adding new software packages, extending or customizing images,
porting work to new hardware (adding a new machine), and so forth.
You will find that the procedures documented here occur often in the
development cycle using the Yocto Project.
</para>
<section id="understanding-and-creating-layers">
<title>Understanding and Creating Layers</title>
<para>
The OpenEmbedded build system supports organizing
<link linkend='metadata'>Metadata</link> into multiple layers.
Layers allow you to isolate different types of customizations from
each other.
You might find it tempting to keep everything in one layer when
working on a single project.
However, the more modular your Metadata, the easier
it is to cope with future changes.
</para>
<para>
To illustrate how layers are used to keep things modular, consider
machine customizations.
These types of customizations typically reside in a special layer,
rather than a general layer, called a Board Support Package (BSP)
Layer.
Furthermore, the machine customizations should be isolated from
recipes and Metadata that support a new GUI environment,
for example.
This situation gives you a couple of layers: one for the machine
configurations, and one for the GUI environment.
It is important to understand, however, that the BSP layer can
still make machine-specific additions to recipes within the GUI
environment layer without polluting the GUI layer itself
with those machine-specific changes.
You can accomplish this through a recipe that is a BitBake append
(<filename>.bbappend</filename>) file, which is described later
in this section.
<note>
For general information on BSP layer structure, see the
<ulink url='&YOCTO_DOCS_BSP_URL;#bsp'>Board Support Packages (BSP) - Developer's Guide</ulink>.
</note>
</para>
<para>
</para>
<section id='yocto-project-layers'>
<title>Layers</title>
<para>
The <link linkend='source-directory'>Source Directory</link>
contains both general layers and BSP
layers right out of the box.
You can easily identify layers that ship with a
Yocto Project release in the Source Directory by their
folder names.
Folders that represent layers typically have names that begin with
the string <filename>meta-</filename>.
<note>
It is not a requirement that a layer name begin with the
prefix <filename>meta-</filename>, but it is a commonly
accepted standard in the Yocto Project community.
</note>
For example, when you set up the Source Directory structure,
you will see several layers:
<filename>meta</filename>,
<filename>meta-skeleton</filename>,
<filename>meta-selftest</filename>,
<filename>meta-poky</filename>, and
<filename>meta-yocto-bsp</filename>.
Each of these folders represents a distinct layer.
</para>
<para>
As another example, if you set up a local copy of the
<filename>meta-intel</filename> Git repository
and then explore the folder of that general layer,
you will discover many Intel-specific BSP layers inside.
For more information on BSP layers, see the
"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
section in the Yocto Project Board Support Package (BSP)
Developer's Guide.
</para>
</section>
<section id='creating-your-own-layer'>
<title>Creating Your Own Layer</title>
<para>
It is very easy to create your own layers to use with the
OpenEmbedded build system.
The Yocto Project ships with scripts that speed up creating
general layers and BSP layers.
This section describes the steps you perform by hand to create
a layer so that you can better understand them.
For information about the layer-creation scripts, see the
"<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
section in the Yocto Project Board Support Package (BSP)
Developer's Guide and the
"<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
section further down in this manual.
</para>
<para>
Follow these general steps to create your layer without the aid of a script:
<orderedlist>
<listitem><para><emphasis>Check Existing Layers:</emphasis>
Before creating a new layer, you should be sure someone
has not already created a layer containing the Metadata
you need.
You can see the
<ulink url='http://layers.openembedded.org/layerindex/layers/'><filename>OpenEmbedded Metadata Index</filename></ulink>
for a list of layers from the OpenEmbedded community
that can be used in the Yocto Project.
</para></listitem>
<listitem><para><emphasis>Create a Directory:</emphasis>
Create the directory for your layer.
While not strictly required, prepend the name of the
folder with the string <filename>meta-</filename>.
For example:
<literallayout class='monospaced'>
meta-mylayer
meta-GUI_xyz
meta-mymachine
</literallayout>
</para></listitem>
<listitem><para><emphasis>Create a Layer Configuration
File:</emphasis>
Inside your new layer folder, you need to create a
<filename>conf/layer.conf</filename> file.
It is easiest to take an existing layer configuration
file and copy that to your layer's
<filename>conf</filename> directory and then modify the
file as needed.</para>
<para>The
<filename>meta-yocto-bsp/conf/layer.conf</filename> file
demonstrates the required syntax:
<literallayout class='monospaced'>
# We have a conf and classes directory, add to BBPATH
BBPATH .= ":${LAYERDIR}"
# We have recipes-* directories, add to BBFILES
BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
${LAYERDIR}/recipes-*/*/*.bbappend"
BBFILE_COLLECTIONS += "yoctobsp"
BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
BBFILE_PRIORITY_yoctobsp = "5"
LAYERVERSION_yoctobsp = "3"
</literallayout></para>
<para>Here is an explanation of the example:
<itemizedlist>
<listitem><para>The configuration and
classes directory is appended to
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>.
<note>
All non-distro layers, which include all BSP
layers, are expected to append the layer
directory to the
<filename>BBPATH</filename>.
On the other hand, distro layers, such as
<filename>meta-poky</filename>, can choose
to enforce their own precedence over
<filename>BBPATH</filename>.
For an example of that syntax, see the
<filename>layer.conf</filename> file for
the <filename>meta-poky</filename> layer.
</note></para></listitem>
<listitem><para>The recipes for the layers are
appended to
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'>BBFILES</ulink></filename>.
</para></listitem>
<listitem><para>The
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</ulink></filename>
variable is then appended with the layer name.
</para></listitem>
<listitem><para>The
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PATTERN'>BBFILE_PATTERN</ulink></filename>
variable is set to a regular expression and is
used to match files from
<filename>BBFILES</filename> into a particular
layer.
In this case,
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
is used to make <filename>BBFILE_PATTERN</filename> match within the
layer's path.</para></listitem>
<listitem><para>The
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'>BBFILE_PRIORITY</ulink></filename>
variable then assigns a priority to the layer.
Applying priorities is useful in situations
where the same recipe might appear in multiple
layers and allows you to choose the layer
that takes precedence.</para></listitem>
<listitem><para>The
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERVERSION'>LAYERVERSION</ulink></filename>
variable optionally specifies the version of a
layer as a single number.</para></listitem>
</itemizedlist></para>
<para>Note the use of the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
variable, which expands to the directory of the current
layer.</para>
<para>Through the use of the <filename>BBPATH</filename>
variable, BitBake locates class files
(<filename>.bbclass</filename>),
configuration files, and files that are included
with <filename>include</filename> and
<filename>require</filename> statements.
For these cases, BitBake uses the first file that
matches the name found in <filename>BBPATH</filename>.
This is similar to the way the <filename>PATH</filename>
variable is used for binaries.
It is recommended, therefore, that you use unique
class and configuration
filenames in your custom layer.</para></listitem>
<listitem><para><emphasis>Add Content:</emphasis> Depending
on the type of layer, add the content.
If the layer adds support for a machine, add the machine
configuration in a <filename>conf/machine/</filename>
file within the layer.
If the layer adds distro policy, add the distro
configuration in a <filename>conf/distro/</filename>
file within the layer.
If the layer introduces new recipes, put the recipes
you need in <filename>recipes-*</filename>
subdirectories within the layer.
<note>In order to be compliant with the Yocto Project,
a layer must contain a
<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout-readme'>README file.</ulink>
</note>
</para></listitem>
<listitem><para>
<emphasis>Optionally Test for Compatibility:</emphasis>
If you want permission to use the Yocto Project
Compatibility logo with your layer or application that
uses your layer, perform the steps to apply for
compatibility.
See the
"<link linkend='making-sure-your-layer-is-compatible-with-yocto-project'>Making Sure Your Layer is Compatible With Yocto Project</link>"
section for more information.
</para></listitem>
</orderedlist>
</para>
</section>
<section id='best-practices-to-follow-when-creating-layers'>
<title>Best Practices to Follow When Creating Layers</title>
<para>
To create layers that are easier to maintain and that will
not impact builds for other machines, you should consider the
information in the following sections.
</para>
<section id='avoid-overlaying-entire-recipes'>
<title>Avoid "Overlaying" Entire Recipes</title>
<para>
Avoid "overlaying" entire recipes from other layers in your
configuration.
In other words, do not copy an entire recipe into your
layer and then modify it.
Rather, use an append file (<filename>.bbappend</filename>)
to override
only those parts of the original recipe you need to modify.
</para>
</section>
<section id='avoid-duplicating-include-files'>
<title>Avoid Duplicating Include Files</title>
<para>
Avoid duplicating include files.
Use append files (<filename>.bbappend</filename>)
for each recipe
that uses an include file.
Or, if you are introducing a new recipe that requires
the included file, use the path relative to the original
layer directory to refer to the file.
For example, use
<filename>require recipes-core/</filename><replaceable>package</replaceable><filename>/</filename><replaceable>file</replaceable><filename>.inc</filename>
instead of <filename>require </filename><replaceable>file</replaceable><filename>.inc</filename>.
If you're finding you have to overlay the include file,
it could indicate a deficiency in the include file in
the layer to which it originally belongs.
If this is the case, you should try to address that
deficiency instead of overlaying the include file.
For example, you could address this by getting the
maintainer of the include file to add a variable or
variables to make it easy to override the parts needing
to be overridden.
</para>
</section>
<section id='structure-your-layers'>
<title>Structure Your Layers</title>
<para>
Proper use of overrides within append files and placement
of machine-specific files within your layer can ensure that
a build is not using the wrong Metadata and negatively
impacting a build for a different machine.
Following are some examples:
<itemizedlist>
<listitem><para><emphasis>Modifying Variables to Support
a Different Machine:</emphasis>
Suppose you have a layer named
<filename>meta-one</filename> that adds support
for building machine "one".
To do so, you use an append file named
<filename>base-files.bbappend</filename> and
create a dependency on "foo" by altering the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
variable:
<literallayout class='monospaced'>
DEPENDS = "foo"
</literallayout>
The dependency is created during any build that
includes the layer
<filename>meta-one</filename>.
However, you might not want this dependency
for all machines.
For example, suppose you are building for
machine "two" but your
<filename>bblayers.conf</filename> file has the
<filename>meta-one</filename> layer included.
During the build, the
<filename>base-files</filename> for machine
"two" will also have the dependency on
<filename>foo</filename>.</para>
<para>To make sure your changes apply only when
building machine "one", use a machine override
with the <filename>DEPENDS</filename> statement:
<literallayout class='monospaced'>
DEPENDS_one = "foo"
</literallayout>
You should follow the same strategy when using
<filename>_append</filename> and
<filename>_prepend</filename> operations:
<literallayout class='monospaced'>
DEPENDS_append_one = " foo"
DEPENDS_prepend_one = "foo "
</literallayout>
As an actual example, here's a line from the recipe
for gnutls, which adds dependencies on
"argp-standalone" when building with the musl C
library:
<literallayout class='monospaced'>
DEPENDS_append_libc-musl = " argp-standalone"
</literallayout>
<note>
Avoiding "+=" and "=+" and using
machine-specific
<filename>_append</filename>
and <filename>_prepend</filename> operations
is recommended as well.
</note></para></listitem>
<listitem><para><emphasis>Place Machine-Specific Files
in Machine-Specific Locations:</emphasis>
When you have a base recipe, such as
<filename>base-files.bb</filename>, that
contains a
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
statement to a file, you can use an append file
to cause the build to use your own version of
the file.
For example, an append file in your layer at
<filename>meta-one/recipes-core/base-files/base-files.bbappend</filename>
could extend
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
using
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
as follows:
<literallayout class='monospaced'>
FILESEXTRAPATHS_prepend := "${THISDIR}/${BPN}:"
</literallayout>
The build for machine "one" will pick up your
machine-specific file as long as you have the
file in
<filename>meta-one/recipes-core/base-files/base-files/</filename>.
However, if you are building for a different
machine and the
<filename>bblayers.conf</filename> file includes
the <filename>meta-one</filename> layer and
the location of your machine-specific file is
the first location where that file is found
according to <filename>FILESPATH</filename>,
builds for all machines will also use that
machine-specific file.</para>
<para>You can make sure that a machine-specific
file is used for a particular machine by putting
the file in a subdirectory specific to the
machine.
For example, rather than placing the file in
<filename>meta-one/recipes-core/base-files/base-files/</filename>
as shown above, put it in
<filename>meta-one/recipes-core/base-files/base-files/one/</filename>.
Not only does this make sure the file is used
only when building for machine "one", but the
build process locates the file more quickly.</para>
<para>In summary, you need to place all files
referenced from <filename>SRC_URI</filename>
in a machine-specific subdirectory within the
layer in order to restrict those files to
machine-specific builds.</para></listitem>
</itemizedlist>
</para>
</section>
<section id='other-recommendations'>
<title>Other Recommendations</title>
<para>
We also recommend the following:
<itemizedlist>
<listitem><para>If you want permission to use the
Yocto Project Compatibility logo with your layer
or application that uses your layer, perform the
steps to apply for compatibility.
See the
"<link linkend='making-sure-your-layer-is-compatible-with-yocto-project'>Making Sure Your Layer is Compatible With Yocto Project</link>"
section for more information.
</para></listitem>
<listitem><para>Store custom layers in a Git repository
that uses the
<filename>meta-<replaceable>layer_name</replaceable></filename> format.
</para></listitem>
<listitem><para>Clone the repository alongside other
<filename>meta</filename> directories in the
<link linkend='source-directory'>Source Directory</link>.
</para></listitem>
</itemizedlist>
Following these recommendations keeps your Source Directory and
its configuration entirely inside the Yocto Project's core
base.
</para>
</section>
</section>
<section id='making-sure-your-layer-is-compatible-with-yocto-project'>
<title>Making Sure Your Layer is Compatible With Yocto Project</title>
<para>
When you create a layer used with the Yocto Project, it is
advantageous to make sure that the layer interacts well with
existing Yocto Project layers (i.e. the layer is compatible
with the Yocto Project).
Ensuring compatibility makes the layer easy to be consumed
by others in the Yocto Project community and allows you
permission to use the Yocto Project Compatibility logo.
</para>
<para>
Version 1.0 of the Yocto Project Compatibility Program has
been in existence for a number of releases.
This version of the program consists of the layer application
process that requests permission to use the Yocto Project
Compatibility logo for your layer and application.
You can find version 1.0 of the form at
<ulink url='https://www.yoctoproject.org/webform/yocto-project-compatible-registration'></ulink>.
To be granted permission to use the logo, you need to be able
to answer "Yes" to the questions or have an acceptable
explanation for any questions answered "No".
</para>
<para>
A second version (2.0) of the Yocto Project Compatibility
Program is currently under development.
Included as part of version 2.0 (and currently available) is
the <filename>yocto-compat-layer.py</filename> script.
When run against a layer, this script tests the layer against
tighter constraints based on experiences of how layers have
worked in the real world and where pitfalls have been found.
</para>
<para>
Part of the 2.0 version of the program that is not currently
available but is in development is an updated compatibility
application form.
This updated form, among other questions, specifically
asks if your layer has passed the test using the
<filename>yocto-compat-layer.py</filename> script.
<note><title>Tip</title>
Even though the updated application form is currently
unavailable for version 2.0 of the Yocto Project
Compatibility Program, the
<filename>yocto-compat-layer.py</filename> script is
available in OE-Core.
You can use the script to assess the status of your
layers in advance of the 2.0 release of the program.
</note>
</para>
<para>
The remainder of this section presents information on the
version 1.0 registration form and on the
<filename>yocto-compat-layer.py</filename> script.
</para>
<section id='yocto-project-compatibility-program-application'>
<title>Yocto Project Compatibility Program Application</title>
<para>
Use the 1.0 version of the form to apply for your
layer's compatibility approval.
Upon successful application, you can use the Yocto
Project Compatibility logo with your layer and the
application that uses your layer.
</para>
<para>
To access the form, use this link:
<ulink url='https://www.yoctoproject.org/webform/yocto-project-compatible-registration'></ulink>.
Follow the instructions on the form to complete your
application.
</para>
<para>
The application consists of the following sections:
<itemizedlist>
<listitem><para>
<emphasis>Contact Information:</emphasis>
Provide your contact information as the fields
require.
Along with your information, provide the
released versions of the Yocto Project for which
your layer is compatible.
</para></listitem>
<listitem><para>
<emphasis>Acceptance Criteria:</emphasis>
Provide "Yes" or "No" answers for each of the
items in the checklist.
Space exists at the bottom of the form for any
explanations for items for which you answered "No".
</para></listitem>
<listitem><para>
<emphasis>Recommendations:</emphasis>
Provide answers for the questions regarding Linux
kernel use and build success.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='yocto-compat-layer-py-script'>
<title><filename>yocto-compat-layer.py</filename> Script</title>
<para>
The <filename>yocto-compat-layer.py</filename> script,
which is currently available, provides you a way to
assess how compatible your layer is with the Yocto
Project.
You should run this script prior to using the form to
apply for compatibility as described in the previous
section.
<note>
Because the script is part of the 2.0 release of the
Yocto Project Compatibility Program, you are not
required to successfully run your layer against it
in order to be granted compatibility status.
However, it is a good idea as it promotes
well-behaved layers and gives you an idea of where your
layer stands regarding compatibility.
</note>
</para>
<para>
The script divides tests into three areas: COMMON, BSD,
and DISTRO.
For example, given a distribution layer (DISTRO), the
layer must pass both the COMMON and DISTRO related tests.
Furthermore, if your layer is a BSP layer, the layer must
pass the COMMON and BSP set of tests.
</para>
<para>
To execute the script, enter the following commands from
your build directory:
<literallayout class='monospaced'>
$ source oe-init-build-env
$ yocto-compat-layer.py <replaceable>your_layer_directory</replaceable>
</literallayout>
Be sure to provide the actual directory for your layer
as part of the command.
</para>
<para>
Entering the command causes the script to determine the
type of layer and then to execute a set of specific
tests against the layer.
The following list overviews the test:
<itemizedlist>
<listitem><para>
<filename>common.test_readme</filename>:
Tests if a <filename>README</filename> file
exists in the layer and the file is not empty.
</para></listitem>
<listitem><para>
<filename>common.test_parse</filename>:
Tests to make sure that BitBake can parse the
files without error (i.e.
<filename>bitbake -p</filename>).
</para></listitem>
<listitem><para>
<filename>common.test_show_environment</filename>:
Tests that the global or per-recipe environment
is in order without errors (i.e.
<filename>bitbake -e</filename>).
</para></listitem>
<listitem><para>
<filename>common.test_signatures</filename>:
Tests to be sure that BSP and DISTRO layers do not
come with recipes that change signatures.
</para></listitem>
<listitem><para>
<filename>bsp.test_bsp_defines_machines</filename>:
Tests if a BSP layer has machine configurations.
</para></listitem>
<listitem><para>
<filename>bsp.test_bsp_no_set_machine</filename>:
Tests to ensure a BSP layer does not set the
machine when the layer is added.
</para></listitem>
<listitem><para>
<filename>distro.test_distro_defines_distros</filename>:
Tests if a DISTRO layer has distro configurations.
</para></listitem>
<listitem><para>
<filename>distro.test_distro_no_set_distro</filename>:
Tests to ensure a DISTRO layer does not set the
distribution when the layer is added.
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
<section id='enabling-your-layer'>
<title>Enabling Your Layer</title>
<para>
Before the OpenEmbedded build system can use your new layer,
you need to enable it.
To enable your layer, simply add your layer's path to the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'>BBLAYERS</ulink></filename>
variable in your <filename>conf/bblayers.conf</filename> file,
which is found in the
<link linkend='build-directory'>Build Directory</link>.
The following example shows how to enable a layer named
<filename>meta-mylayer</filename>:
<literallayout class='monospaced'>
LCONF_VERSION = "6"
BBPATH = "${TOPDIR}"
BBFILES ?= ""
BBLAYERS ?= " \
$HOME/poky/meta \
$HOME/poky/meta-poky \
$HOME/poky/meta-yocto-bsp \
$HOME/poky/meta-mylayer \
"
</literallayout>
</para>
<para>
BitBake parses each <filename>conf/layer.conf</filename> file
as specified in the <filename>BBLAYERS</filename> variable
within the <filename>conf/bblayers.conf</filename> file.
During the processing of each
<filename>conf/layer.conf</filename> file, BitBake adds the
recipes, classes and configurations contained within the
particular layer to the source directory.
</para>
</section>
<section id='using-bbappend-files'>
<title>Using .bbappend Files in Your Layer</title>
<para>
A recipe that appends Metadata to another recipe is called a
BitBake append file.
A BitBake append file uses the <filename>.bbappend</filename>
file type suffix, while the corresponding recipe to which
Metadata is being appended uses the <filename>.bb</filename>
file type suffix.
</para>
<para>
You can use a <filename>.bbappend</filename> file in your
layer to make additions or changes to the content of another
layer's recipe without having to copy the other layer's
recipe into your layer.
Your <filename>.bbappend</filename> file resides in your layer,
while the main <filename>.bb</filename> recipe file to
which you are appending Metadata resides in a different layer.
</para>
<para>
Being able to append information to an existing recipe not only
avoids duplication, but also automatically applies recipe
changes from a different layer into your layer.
If you were copying recipes, you would have to manually merge
changes as they occur.
</para>
<para>
When you create an append file, you must use the same root
name as the corresponding recipe file.
For example, the append file
<filename>someapp_&DISTRO;.bbappend</filename> must apply to
<filename>someapp_&DISTRO;.bb</filename>.
This means the original recipe and append file names are
version number-specific.
If the corresponding recipe is renamed to update to a newer
version, you must also rename and possibly update
the corresponding <filename>.bbappend</filename> as well.
During the build process, BitBake displays an error on starting
if it detects a <filename>.bbappend</filename> file that does
not have a corresponding recipe with a matching name.
See the
<ulink url='&YOCTO_DOCS_REF_URL;#var-BB_DANGLINGAPPENDS_WARNONLY'><filename>BB_DANGLINGAPPENDS_WARNONLY</filename></ulink>
variable for information on how to handle this error.
</para>
<para>
As an example, consider the main formfactor recipe and a
corresponding formfactor append file both from the
<link linkend='source-directory'>Source Directory</link>.
Here is the main formfactor recipe, which is named
<filename>formfactor_0.0.bb</filename> and located in the
"meta" layer at
<filename>meta/recipes-bsp/formfactor</filename>:
<literallayout class='monospaced'>
SUMMARY = "Device formfactor information"
SECTION = "base"
LICENSE = "MIT"
LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
PR = "r45"
SRC_URI = "file://config file://machconfig"
S = "${WORKDIR}"
PACKAGE_ARCH = "${MACHINE_ARCH}"
INHIBIT_DEFAULT_DEPS = "1"
do_install() {
# Install file only if it has contents
install -d ${D}${sysconfdir}/formfactor/
install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
if [ -s "${S}/machconfig" ]; then
install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
fi
} </literallayout>
In the main recipe, note the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
variable, which tells the OpenEmbedded build system where to
find files during the build.
</para>
<para>
Following is the append file, which is named
<filename>formfactor_0.0.bbappend</filename> and is from the
Raspberry Pi BSP Layer named
<filename>meta-raspberrypi</filename>.
The file is in the layer at
<filename>recipes-bsp/formfactor</filename>:
<literallayout class='monospaced'>
FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
</literallayout>
</para>
<para>
By default, the build system uses the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
variable to locate files.
This append file extends the locations by setting the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
variable.
Setting this variable in the <filename>.bbappend</filename>
file is the most reliable and recommended method for adding
directories to the search path used by the build system
to find files.
</para>
<para>
The statement in this example extends the directories to
include
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-THISDIR'><filename>THISDIR</filename></ulink><filename>}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>,
which resolves to a directory named
<filename>formfactor</filename> in the same directory
in which the append file resides (i.e.
<filename>meta-raspberrypi/recipes-bsp/formfactor</filename>.
This implies that you must have the supporting directory
structure set up that will contain any files or patches you
will be including from the layer.
</para>
<para>
Using the immediate expansion assignment operator
<filename>:=</filename> is important because of the reference
to <filename>THISDIR</filename>.
The trailing colon character is important as it ensures that
items in the list remain colon-separated.
<note>
<para>
BitBake automatically defines the
<filename>THISDIR</filename> variable.
You should never set this variable yourself.
Using "_prepend" as part of the
<filename>FILESEXTRAPATHS</filename> ensures your path
will be searched prior to other paths in the final
list.
</para>
<para>
Also, not all append files add extra files.
Many append files simply exist to add build options
(e.g. <filename>systemd</filename>).
For these cases, your append file would not even
use the <filename>FILESEXTRAPATHS</filename> statement.
</para>
</note>
</para>
</section>
<section id='prioritizing-your-layer'>
<title>Prioritizing Your Layer</title>
<para>
Each layer is assigned a priority value.
Priority values control which layer takes precedence if there
are recipe files with the same name in multiple layers.
For these cases, the recipe file from the layer with a higher
priority number takes precedence.
Priority values also affect the order in which multiple
<filename>.bbappend</filename> files for the same recipe are
applied.
You can either specify the priority manually, or allow the
build system to calculate it based on the layer's dependencies.
</para>
<para>
To specify the layer's priority manually, use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
variable.
For example:
<literallayout class='monospaced'>
BBFILE_PRIORITY_mylayer = "1"
</literallayout>
</para>
<note>
<para>It is possible for a recipe with a lower version number
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
in a layer that has a higher priority to take precedence.</para>
<para>Also, the layer priority does not currently affect the
precedence order of <filename>.conf</filename>
or <filename>.bbclass</filename> files.
Future versions of BitBake might address this.</para>
</note>
</section>
<section id='managing-layers'>
<title>Managing Layers</title>
<para>
You can use the BitBake layer management tool to provide a view
into the structure of recipes across a multi-layer project.
Being able to generate output that reports on configured layers
with their paths and priorities and on
<filename>.bbappend</filename> files and their applicable
recipes can help to reveal potential problems.
</para>
<para>
Use the following form when running the layer management tool.
<literallayout class='monospaced'>
$ bitbake-layers <replaceable>command</replaceable> [<replaceable>arguments</replaceable>]
</literallayout>
The following list describes the available commands:
<itemizedlist>
<listitem><para><filename><emphasis>help:</emphasis></filename>
Displays general help or help on a specified command.
</para></listitem>
<listitem><para><filename><emphasis>show-layers:</emphasis></filename>
Shows the current configured layers.
</para></listitem>
<listitem><para><filename><emphasis>show-recipes:</emphasis></filename>
Lists available recipes and the layers that provide them.
</para></listitem>
<listitem><para><filename><emphasis>show-overlayed:</emphasis></filename>
Lists overlayed recipes.
A recipe is overlayed when a recipe with the same name
exists in another layer that has a higher layer
priority.
</para></listitem>
<listitem><para><filename><emphasis>show-appends:</emphasis></filename>
Lists <filename>.bbappend</filename> files and the
recipe files to which they apply.
</para></listitem>
<listitem><para><filename><emphasis>show-cross-depends:</emphasis></filename>
Lists dependency relationships between recipes that
cross layer boundaries.
</para></listitem>
<listitem><para><filename><emphasis>add-layer:</emphasis></filename>
Adds a layer to <filename>bblayers.conf</filename>.
</para></listitem>
<listitem><para><filename><emphasis>remove-layer:</emphasis></filename>
Removes a layer from <filename>bblayers.conf</filename>
</para></listitem>
<listitem><para><filename><emphasis>flatten:</emphasis></filename>
Flattens the layer configuration into a separate output
directory.
Flattening your layer configuration builds a "flattened"
directory that contains the contents of all layers,
with any overlayed recipes removed and any
<filename>.bbappend</filename> files appended to the
corresponding recipes.
You might have to perform some manual cleanup of the
flattened layer as follows:
<itemizedlist>
<listitem><para>Non-recipe files (such as patches)
are overwritten.
The flatten command shows a warning for these
files.
</para></listitem>
<listitem><para>Anything beyond the normal layer
setup has been added to the
<filename>layer.conf</filename> file.
Only the lowest priority layer's
<filename>layer.conf</filename> is used.
</para></listitem>
<listitem><para>Overridden and appended items from
<filename>.bbappend</filename> files need to be
cleaned up.
The contents of each
<filename>.bbappend</filename> end up in the
flattened recipe.
However, if there are appended or changed
variable values, you need to tidy these up
yourself.
Consider the following example.
Here, the <filename>bitbake-layers</filename>
command adds the line
<filename>#### bbappended ...</filename> so that
you know where the following lines originate:
<literallayout class='monospaced'>
...
DESCRIPTION = "A useful utility"
...
EXTRA_OECONF = "--enable-something"
...
#### bbappended from meta-anotherlayer ####
DESCRIPTION = "Customized utility"
EXTRA_OECONF += "--enable-somethingelse"
</literallayout>
Ideally, you would tidy up these utilities as
follows:
<literallayout class='monospaced'>
...
DESCRIPTION = "Customized utility"
...
EXTRA_OECONF = "--enable-something --enable-somethingelse"
...
</literallayout></para></listitem>
</itemizedlist></para></listitem>
</itemizedlist>
</para>
</section>
<section id='creating-a-general-layer-using-the-yocto-layer-script'>
<title>Creating a General Layer Using the yocto-layer Script</title>
<para>
The <filename>yocto-layer</filename> script simplifies
creating a new general layer.
<note>
For information on BSP layers, see the
"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
section in the Yocto Project Board Specific (BSP)
Developer's Guide.
</note>
The default mode of the script's operation is to prompt you for
information needed to generate the layer:
<itemizedlist>
<listitem><para>The layer priority.
</para></listitem>
<listitem><para>Whether or not to create a sample recipe.
</para></listitem>
<listitem><para>Whether or not to create a sample
append file.
</para></listitem>
</itemizedlist>
</para>
<para>
Use the <filename>yocto-layer create</filename> sub-command
to create a new general layer.
In its simplest form, you can create a layer as follows:
<literallayout class='monospaced'>
$ yocto-layer create mylayer
</literallayout>
The previous example creates a layer named
<filename>meta-mylayer</filename> in the current directory.
</para>
<para>
As the <filename>yocto-layer create</filename> command runs,
default values for the prompts appear in brackets.
Pressing enter without supplying anything for the prompts
or pressing enter and providing an invalid response causes the
script to accept the default value.
Once the script completes, the new layer
is created in the current working directory.
The script names the layer by prepending
<filename>meta-</filename> to the name you provide.
</para>
<para>
Minimally, the script creates the following within the layer:
<itemizedlist>
<listitem><para><emphasis>The <filename>conf</filename>
directory:</emphasis>
This directory contains the layer's configuration file.
The root name for the file is the same as the root name
your provided for the layer (e.g.
<filename><replaceable>layer</replaceable>.conf</filename>).
</para></listitem>
<listitem><para><emphasis>The
<filename>COPYING.MIT</filename> file:</emphasis>
The copyright and use notice for the software.
</para></listitem>
<listitem><para><emphasis>The <filename>README</filename>
file:</emphasis>
A file describing the contents of your new layer.
</para></listitem>
</itemizedlist>
</para>
<para>
If you choose to generate a sample recipe file, the script
prompts you for the name for the recipe and then creates it
in <filename><replaceable>layer</replaceable>/recipes-example/example/</filename>.
The script creates a <filename>.bb</filename> file and a
directory, which contains a sample
<filename>helloworld.c</filename> source file, along with
a sample patch file.
If you do not provide a recipe name, the script uses
"example".
</para>
<para>
If you choose to generate a sample append file, the script
prompts you for the name for the file and then creates it
in <filename><replaceable>layer</replaceable>/recipes-example-bbappend/example-bbappend/</filename>.
The script creates a <filename>.bbappend</filename> file and a
directory, which contains a sample patch file.
If you do not provide a recipe name, the script uses
"example".
The script also prompts you for the version of the append file.
The version should match the recipe to which the append file
is associated.
</para>
<para>
The easiest way to see how the <filename>yocto-layer</filename>
script works is to experiment with the script.
You can also read the usage information by entering the
following:
<literallayout class='monospaced'>
$ yocto-layer help
</literallayout>
</para>
<para>
Once you create your general layer, you must add it to your
<filename>bblayers.conf</filename> file.
Here is an example where a layer named
<filename>meta-mylayer</filename> is added:
<literallayout class='monospaced'>
BBLAYERS = ?" \
/usr/local/src/yocto/meta \
/usr/local/src/yocto/meta-poky \
/usr/local/src/yocto/meta-yocto-bsp \
/usr/local/src/yocto/meta-mylayer \
"
</literallayout>
Adding the layer to this file enables the build system to
locate the layer during the build.
</para>
</section>
</section>
<section id='usingpoky-extend-customimage'>
<title>Customizing Images</title>
<para>
You can customize images to satisfy particular requirements.
This section describes several methods and provides guidelines for each.
</para>
<section id='usingpoky-extend-customimage-localconf'>
<title>Customizing Images Using <filename>local.conf</filename></title>
<para>
Probably the easiest way to customize an image is to add a
package by way of the <filename>local.conf</filename>
configuration file.
Because it is limited to local use, this method generally only
allows you to add packages and is not as flexible as creating
your own customized image.
When you add packages using local variables this way, you need
to realize that these variable changes are in effect for every
build and consequently affect all images, which might not
be what you require.
</para>
<para>
To add a package to your image using the local configuration
file, use the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
variable with the <filename>_append</filename> operator:
<literallayout class='monospaced'>
IMAGE_INSTALL_append = " strace"
</literallayout>
Use of the syntax is important - specifically, the space between
the quote and the package name, which is
<filename>strace</filename> in this example.
This space is required since the <filename>_append</filename>
operator does not add the space.
</para>
<para>
Furthermore, you must use <filename>_append</filename> instead
of the <filename>+=</filename> operator if you want to avoid
ordering issues.
The reason for this is because doing so unconditionally appends
to the variable and avoids ordering problems due to the
variable being set in image recipes and
<filename>.bbclass</filename> files with operators like
<filename>?=</filename>.
Using <filename>_append</filename> ensures the operation takes
affect.
</para>
<para>
As shown in its simplest use,
<filename>IMAGE_INSTALL_append</filename> affects all images.
It is possible to extend the syntax so that the variable
applies to a specific image only.
Here is an example:
<literallayout class='monospaced'>
IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
</literallayout>
This example adds <filename>strace</filename> to the
<filename>core-image-minimal</filename> image only.
</para>
<para>
You can add packages using a similar approach through the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'>CORE_IMAGE_EXTRA_INSTALL</ulink></filename>
variable.
If you use this variable, only
<filename>core-image-*</filename> images are affected.
</para>
</section>
<section id='usingpoky-extend-customimage-imagefeatures'>
<title>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and
<filename>EXTRA_IMAGE_FEATURES</filename></title>
<para>
Another method for customizing your image is to enable or
disable high-level image features by using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
variables.
Although the functions for both variables are nearly equivalent,
best practices dictate using <filename>IMAGE_FEATURES</filename>
from within a recipe and using
<filename>EXTRA_IMAGE_FEATURES</filename> from within
your <filename>local.conf</filename> file, which is found in the
<link linkend='build-directory'>Build Directory</link>.
</para>
<para>
To understand how these features work, the best reference is
<filename>meta/classes/core-image.bbclass</filename>.
This class lists out the available
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
of which most map to package groups while some, such as
<filename>debug-tweaks</filename> and
<filename>read-only-rootfs</filename>, resolve as general
configuration settings.
</para>
<para>
In summary, the file looks at the contents of the
<filename>IMAGE_FEATURES</filename> variable and then maps
or configures the feature accordingly.
Based on this information, the build system automatically
adds the appropriate packages or configurations to the
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
variable.
Effectively, you are enabling extra features by extending the
class or creating a custom class for use with specialized image
<filename>.bb</filename> files.
</para>
<para>
Use the <filename>EXTRA_IMAGE_FEATURES</filename> variable
from within your local configuration file.
Using a separate area from which to enable features with
this variable helps you avoid overwriting the features in the
image recipe that are enabled with
<filename>IMAGE_FEATURES</filename>.
The value of <filename>EXTRA_IMAGE_FEATURES</filename> is added
to <filename>IMAGE_FEATURES</filename> within
<filename>meta/conf/bitbake.conf</filename>.
</para>
<para>
To illustrate how you can use these variables to modify your
image, consider an example that selects the SSH server.
The Yocto Project ships with two SSH servers you can use
with your images: Dropbear and OpenSSH.
Dropbear is a minimal SSH server appropriate for
resource-constrained environments, while OpenSSH is a
well-known standard SSH server implementation.
By default, the <filename>core-image-sato</filename> image
is configured to use Dropbear.
The <filename>core-image-full-cmdline</filename> and
<filename>core-image-lsb</filename> images both
include OpenSSH.
The <filename>core-image-minimal</filename> image does not
contain an SSH server.
</para>
<para>
You can customize your image and change these defaults.
Edit the <filename>IMAGE_FEATURES</filename> variable
in your recipe or use the
<filename>EXTRA_IMAGE_FEATURES</filename> in your
<filename>local.conf</filename> file so that it configures the
image you are working with to include
<filename>ssh-server-dropbear</filename> or
<filename>ssh-server-openssh</filename>.
</para>
<note>
See the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
section in the Yocto Project Reference Manual for a complete
list of image features that ship with the Yocto Project.
</note>
</section>
<section id='usingpoky-extend-customimage-custombb'>
<title>Customizing Images Using Custom .bb Files</title>
<para>
You can also customize an image by creating a custom recipe
that defines additional software as part of the image.
The following example shows the form for the two lines you need:
<literallayout class='monospaced'>
IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"
inherit core-image
</literallayout>
</para>
<para>
Defining the software using a custom recipe gives you total
control over the contents of the image.
It is important to use the correct names of packages in the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
variable.
You must use the OpenEmbedded notation and not the Debian notation for the names
(e.g. <filename>glibc-dev</filename> instead of <filename>libc6-dev</filename>).
</para>
<para>
The other method for creating a custom image is to base it on an existing image.
For example, if you want to create an image based on <filename>core-image-sato</filename>
but add the additional package <filename>strace</filename> to the image,
copy the <filename>meta/recipes-sato/images/core-image-sato.bb</filename> to a
new <filename>.bb</filename> and add the following line to the end of the copy:
<literallayout class='monospaced'>
IMAGE_INSTALL += "strace"
</literallayout>
</para>
</section>
<section id='usingpoky-extend-customimage-customtasks'>
<title>Customizing Images Using Custom Package Groups</title>
<para>
For complex custom images, the best approach for customizing
an image is to create a custom package group recipe that is
used to build the image or images.
A good example of a package group recipe is
<filename>meta/recipes-core/packagegroups/packagegroup-base.bb</filename>.
</para>
<para>
If you examine that recipe, you see that the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename>
variable lists the package group packages to produce.
The <filename>inherit packagegroup</filename> statement
sets appropriate default values and automatically adds
<filename>-dev</filename>, <filename>-dbg</filename>, and
<filename>-ptest</filename> complementary packages for each
package specified in the <filename>PACKAGES</filename>
statement.
<note>
The <filename>inherit packages</filename> should be
located near the top of the recipe, certainly before
the <filename>PACKAGES</filename> statement.
</note>
</para>
<para>
For each package you specify in <filename>PACKAGES</filename>,
you can use
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'>RDEPENDS</ulink></filename>
and
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'>RRECOMMENDS</ulink></filename>
entries to provide a list of packages the parent task package
should contain.
You can see examples of these further down in the
<filename>packagegroup-base.bb</filename> recipe.
</para>
<para>
Here is a short, fabricated example showing the same basic
pieces:
<literallayout class='monospaced'>
DESCRIPTION = "My Custom Package Groups"
inherit packagegroup
PACKAGES = "\
packagegroup-custom-apps \
packagegroup-custom-tools \
"
RDEPENDS_packagegroup-custom-apps = "\
dropbear \
portmap \
psplash"
RDEPENDS_packagegroup-custom-tools = "\
oprofile \
oprofileui-server \
lttng-tools"
RRECOMMENDS_packagegroup-custom-tools = "\
kernel-module-oprofile"
</literallayout>
</para>
<para>
In the previous example, two package group packages are created with their dependencies and their
recommended package dependencies listed: <filename>packagegroup-custom-apps</filename>, and
<filename>packagegroup-custom-tools</filename>.
To build an image using these package group packages, you need to add
<filename>packagegroup-custom-apps</filename> and/or
<filename>packagegroup-custom-tools</filename> to
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>.
For other forms of image dependencies see the other areas of this section.
</para>
</section>
<section id='usingpoky-extend-customimage-image-name'>
<title>Customizing an Image Hostname</title>
<para>
By default, the configured hostname (i.e.
<filename>/etc/hostname</filename>) in an image is the
same as the machine name.
For example, if
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
equals "qemux86", the configured hostname written to
<filename>/etc/hostname</filename> is "qemux86".
</para>
<para>
You can customize this name by altering the value of the
"hostname" variable in the
<filename>base-files</filename> recipe using either
an append file or a configuration file.
Use the following in an append file:
<literallayout class='monospaced'>
hostname="myhostname"
</literallayout>
Use the following in a configuration file:
<literallayout class='monospaced'>
hostname_pn-base-files = "myhostname"
</literallayout>
</para>
<para>
Changing the default value of the variable "hostname" can be
useful in certain situations.
For example, suppose you need to do extensive testing on an
image and you would like to easily identify the image
under test from existing images with typical default
hostnames.
In this situation, you could change the default hostname to
"testme", which results in all the images using the name
"testme".
Once testing is complete and you do not need to rebuild the
image for test any longer, you can easily reset the default
hostname.
</para>
<para>
Another point of interest is that if you unset the variable,
the image will have no default hostname in the filesystem.
Here is an example that unsets the variable in a
configuration file:
<literallayout class='monospaced'>
hostname_pn-base-files = ""
</literallayout>
Having no default hostname in the filesystem is suitable for
environments that use dynamic hostnames such as virtual
machines.
</para>
</section>
</section>
<section id='new-recipe-writing-a-new-recipe'>
<title>Writing a New Recipe</title>
<para>
Recipes (<filename>.bb</filename> files) are fundamental components
in the Yocto Project environment.
Each software component built by the OpenEmbedded build system
requires a recipe to define the component.
This section describes how to create, write, and test a new
recipe.
<note>
For information on variables that are useful for recipes and
for information about recipe naming issues, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-varlocality-recipe-required'>Required</ulink>"
section of the Yocto Project Reference Manual.
</note>
</para>
<section id='new-recipe-overview'>
<title>Overview</title>
<para>
The following figure shows the basic process for creating a
new recipe.
The remainder of the section provides details for the steps.
<imagedata fileref="figures/recipe-workflow.png" width="6in" depth="7in" align="center" scalefit="1" />
</para>
</section>
<section id='new-recipe-locate-or-automatically-create-a-base-recipe'>
<title>Locate or Automatically Create a Base Recipe</title>
<para>
You can always write a recipe from scratch.
However, three choices exist that can help you quickly get a
start on a new recipe:
<itemizedlist>
<listitem><para>
<emphasis><filename>devtool add</filename>:</emphasis>
A command that assists in creating a recipe and
an environment conducive to development.
</para></listitem>
<listitem><para>
<emphasis><filename>recipetool create</filename>:</emphasis>
A command provided by the Yocto Project that automates
creation of a base recipe based on the source
files.
</para></listitem>
<listitem><para>
<emphasis>Existing Recipes:</emphasis>
Location and modification of an existing recipe that is
similar in function to the recipe you need.
</para></listitem>
</itemizedlist>
</para>
<section id='new-recipe-creating-the-base-recipe-using-devtool'>
<title>Creating the Base Recipe Using <filename>devtool add</filename></title>
<para>
The <filename>devtool add</filename> command uses the same
logic for auto-creating the recipe as
<filename>recipetool create</filename>, which is listed
below.
Additionally, however, <filename>devtool add</filename>
sets up an environment that makes it easy for you to
patch the source and to make changes to the recipe as
is often necessary when adding a recipe to build a new
piece of software to be included in a build.
</para>
<para>
You can find a complete description of the
<filename>devtool add</filename> command in the
"<link linkend='use-devtool-to-integrate-new-code'>Use <filename>devtool add</filename> to Add an Application</link>"
section.
</para>
</section>
<section id='new-recipe-creating-the-base-recipe-using-recipetool'>
<title>Creating the Base Recipe Using <filename>recipetool create</filename></title>
<para>
<filename>recipetool create</filename> automates creation
of a base recipe given a set of source code files.
As long as you can extract or point to the source files,
the tool will construct a recipe and automatically
configure all pre-build information into the recipe.
For example, suppose you have an application that builds
using Autotools.
Creating the base recipe using
<filename>recipetool</filename> results in a recipe
that has the pre-build dependencies, license requirements,
and checksums configured.
</para>
<para>
To run the tool, you just need to be in your
<link linkend='build-directory'>Build Directory</link>
and have sourced the build environment setup script
(i.e.
<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>oe-init-build-env</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>).
Here is the basic <filename>recipetool</filename> syntax:
<note>
Running <filename>recipetool -h</filename> or
<filename>recipetool create -h</filename> produces the
Python-generated help, which presented differently
than what follows here.
</note>
<literallayout class='monospaced'>
recipetool -h
recipetool create [-h]
recipetool [-d] [-q] [--color auto | always | never ] create -o <replaceable>OUTFILE</replaceable> [-m] [-x <replaceable>EXTERNALSRC</replaceable>] <replaceable>source</replaceable>
-d Enables debug output.
-q Outputs only errors (quiet mode).
--color Colorizes the output automatically, always, or never.
-h Displays Python generated syntax for recipetool.
create Causes recipetool to create a base recipe. The create
command is further defined with these options:
-o <replaceable>OUTFILE</replaceable> Specifies the full path and filename for the generated
recipe.
-m Causes the recipe to be machine-specific rather than
architecture-specific (default).
-x <replaceable>EXTERNALSRC</replaceable> Fetches and extracts source files from <replaceable>source</replaceable>
and places them in <replaceable>EXTERNALSRC</replaceable>.
<replaceable>source</replaceable> must be a URL.
-h Displays Python-generated syntax for create.
<replaceable>source</replaceable> Specifies the source code on which to base the
recipe.
</literallayout>
</para>
<para>
Running <filename>recipetool create -o</filename>&nbsp;<replaceable>OUTFILE</replaceable>
creates the base recipe and locates it properly in the
layer that contains your source files.
Following are some syntax examples:
</para>
<para>
Use this syntax to generate a recipe based on <replaceable>source</replaceable>.
Once generated, the recipe resides in the existing source
code layer:
<literallayout class='monospaced'>
recipetool create -o <replaceable>OUTFILE</replaceable>&nbsp;<replaceable>source</replaceable>
</literallayout>
Use this syntax to generate a recipe using code that you
extract from <replaceable>source</replaceable>.
The extracted code is placed in its own layer defined
by <replaceable>EXTERNALSRC</replaceable>.
<literallayout class='monospaced'>
recipetool create -o <replaceable>OUTFILE</replaceable> -x <replaceable>EXTERNALSRC</replaceable> <replaceable>source</replaceable>
</literallayout>
Use this syntax to generate a recipe based on <replaceable>source</replaceable>.
The options direct <filename>recipetool</filename> to
generate debugging information.
Once generated, the recipe resides in the existing source
code layer:
<literallayout class='monospaced'>
recipetool create -d -o <replaceable>OUTFILE</replaceable> <replaceable>source</replaceable>
</literallayout>
</para>
</section>
<section id='new-recipe-locating-and-using-a-similar-recipe'>
<title>Locating and Using a Similar Recipe</title>
<para>
Before writing a recipe from scratch, it is often useful to
discover whether someone else has already written one that
meets (or comes close to meeting) your needs.
The Yocto Project and OpenEmbedded communities maintain many
recipes that might be candidates for what you are doing.
You can find a good central index of these recipes in the
<ulink url='http://layers.openembedded.org'>OpenEmbedded metadata index</ulink>.
</para>
<para>
Working from an existing recipe or a skeleton recipe is the
best way to get started.
Here are some points on both methods:
<itemizedlist>
<listitem><para><emphasis>Locate and modify a recipe that
is close to what you want to do:</emphasis>
This method works when you are familiar with the
current recipe space.
The method does not work so well for those new to
the Yocto Project or writing recipes.</para>
<para>Some risks associated with this method are
using a recipe that has areas totally unrelated to
what you are trying to accomplish with your recipe,
not recognizing areas of the recipe that you might
have to add from scratch, and so forth.
All these risks stem from unfamiliarity with the
existing recipe space.</para></listitem>
<listitem><para><emphasis>Use and modify the following
skeleton recipe:</emphasis>
If for some reason you do not want to use
<filename>recipetool</filename> and you cannot
find an existing recipe that is close to meeting
your needs, you can use the following structure to
provide the fundamental areas of a new recipe.
<literallayout class='monospaced'>
DESCRIPTION = ""
HOMEPAGE = ""
LICENSE = ""
SECTION = ""
DEPENDS = ""
LIC_FILES_CHKSUM = ""
SRC_URI = ""
</literallayout>
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
<section id='new-recipe-storing-and-naming-the-recipe'>
<title>Storing and Naming the Recipe</title>
<para>
Once you have your base recipe, you should put it in your
own layer and name it appropriately.
Locating it correctly ensures that the OpenEmbedded build
system can find it when you use BitBake to process the
recipe.
</para>
<itemizedlist>
<listitem><para><emphasis>Storing Your Recipe:</emphasis>
The OpenEmbedded build system locates your recipe
through the layer's <filename>conf/layer.conf</filename>
file and the
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'><filename>BBFILES</filename></ulink>
variable.
This variable sets up a path from which the build system can
locate recipes.
Here is the typical use:
<literallayout class='monospaced'>
BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
${LAYERDIR}/recipes-*/*/*.bbappend"
</literallayout>
Consequently, you need to be sure you locate your new recipe
inside your layer such that it can be found.</para>
<para>You can find more information on how layers are
structured in the
"<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>"
section.</para></listitem>
<listitem><para><emphasis>Naming Your Recipe:</emphasis>
When you name your recipe, you need to follow this naming
convention:
<literallayout class='monospaced'>
<replaceable>basename</replaceable>_<replaceable>version</replaceable>.bb
</literallayout>
Use lower-cased characters and do not include the reserved
suffixes <filename>-native</filename>,
<filename>-cross</filename>, <filename>-initial</filename>,
or <filename>-dev</filename> casually (i.e. do not use them
as part of your recipe name unless the string applies).
Here are some examples:
<literallayout class='monospaced'>
cups_1.7.0.bb
gawk_4.0.2.bb
irssi_0.8.16-rc1.bb
</literallayout></para></listitem>
</itemizedlist>
</section>
<section id='understanding-recipe-syntax'>
<title>Understanding Recipe Syntax</title>
<para>
Understanding recipe file syntax is important for
writing recipes.
The following list overviews the basic items that make up a
BitBake recipe file.
For more complete BitBake syntax descriptions, see the
"<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>"
chapter of the BitBake User Manual.
<itemizedlist>
<listitem><para><emphasis>Variable Assignments and Manipulations:</emphasis>
Variable assignments allow a value to be assigned to a
variable.
The assignment can be static text or might include
the contents of other variables.
In addition to the assignment, appending and prepending
operations are also supported.</para>
<para>The following example shows some of the ways
you can use variables in recipes:
<literallayout class='monospaced'>
S = "${WORKDIR}/postfix-${PV}"
CFLAGS += "-DNO_ASM"
SRC_URI_append = " file://fixup.patch"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Functions:</emphasis>
Functions provide a series of actions to be performed.
You usually use functions to override the default
implementation of a task function or to complement
a default function (i.e. append or prepend to an
existing function).
Standard functions use <filename>sh</filename> shell
syntax, although access to OpenEmbedded variables and
internal methods are also available.</para>
<para>The following is an example function from the
<filename>sed</filename> recipe:
<literallayout class='monospaced'>
do_install () {
autotools_do_install
install -d ${D}${base_bindir}
mv ${D}${bindir}/sed ${D}${base_bindir}/sed
rmdir ${D}${bindir}/
}
</literallayout>
It is also possible to implement new functions that
are called between existing tasks as long as the
new functions are not replacing or complementing the
default functions.
You can implement functions in Python
instead of shell.
Both of these options are not seen in the majority of
recipes.</para></listitem>
<listitem><para><emphasis>Keywords:</emphasis>
BitBake recipes use only a few keywords.
You use keywords to include common
functions (<filename>inherit</filename>), load parts
of a recipe from other files
(<filename>include</filename> and
<filename>require</filename>) and export variables
to the environment (<filename>export</filename>).</para>
<para>The following example shows the use of some of
these keywords:
<literallayout class='monospaced'>
export POSTCONF = "${STAGING_BINDIR}/postconf"
inherit autoconf
require otherfile.inc
</literallayout>
</para></listitem>
<listitem><para><emphasis>Comments:</emphasis>
Any lines that begin with the hash character
(<filename>#</filename>) are treated as comment lines
and are ignored:
<literallayout class='monospaced'>
# This is a comment
</literallayout>
</para></listitem>
</itemizedlist>
</para>
<para>
This next list summarizes the most important and most commonly
used parts of the recipe syntax.
For more information on these parts of the syntax, you can
reference the
<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>
chapter in the BitBake User Manual.
<itemizedlist>
<listitem><para><emphasis>Line Continuation: <filename>\</filename></emphasis> -
Use the backward slash (<filename>\</filename>)
character to split a statement over multiple lines.
Place the slash character at the end of the line that
is to be continued on the next line:
<literallayout class='monospaced'>
VAR = "A really long \
line"
</literallayout>
<note>
You cannot have any characters including spaces
or tabs after the slash character.
</note>
</para></listitem>
<listitem><para>
<emphasis>Using Variables: <filename>${...}</filename></emphasis> -
Use the <filename>${<replaceable>VARNAME</replaceable>}</filename> syntax to
access the contents of a variable:
<literallayout class='monospaced'>
SRC_URI = "${SOURCEFORGE_MIRROR}/libpng/zlib-${PV}.tar.gz"
</literallayout>
<note>
It is important to understand that the value of a
variable expressed in this form does not get
substituted automatically.
The expansion of these expressions happens
on-demand later (e.g. usually when a function that
makes reference to the variable executes).
This behavior ensures that the values are most
appropriate for the context in which they are
finally used.
On the rare occasion that you do need the variable
expression to be expanded immediately, you can use
the <filename>:=</filename> operator instead of
<filename>=</filename> when you make the
assignment, but this is not generally needed.
</note>
</para></listitem>
<listitem><para><emphasis>Quote All Assignments: <filename>"<replaceable>value</replaceable>"</filename></emphasis> -
Use double quotes around the value in all variable
assignments.
<literallayout class='monospaced'>
VAR1 = "${OTHERVAR}"
VAR2 = "The version is ${PV}"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Conditional Assignment: <filename>?=</filename></emphasis> -
Conditional assignment is used to assign a value to
a variable, but only when the variable is currently
unset.
Use the question mark followed by the equal sign
(<filename>?=</filename>) to make a "soft" assignment
used for conditional assignment.
Typically, "soft" assignments are used in the
<filename>local.conf</filename> file for variables
that are allowed to come through from the external
environment.
</para>
<para>Here is an example where
<filename>VAR1</filename> is set to "New value" if
it is currently empty.
However, if <filename>VAR1</filename> has already been
set, it remains unchanged:
<literallayout class='monospaced'>
VAR1 ?= "New value"
</literallayout>
In this next example, <filename>VAR1</filename>
is left with the value "Original value":
<literallayout class='monospaced'>
VAR1 = "Original value"
VAR1 ?= "New value"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Appending: <filename>+=</filename></emphasis> -
Use the plus character followed by the equals sign
(<filename>+=</filename>) to append values to existing
variables.
<note>
This operator adds a space between the existing
content of the variable and the new content.
</note></para>
<para>Here is an example:
<literallayout class='monospaced'>
SRC_URI += "file://fix-makefile.patch"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Prepending: <filename>=+</filename></emphasis> -
Use the equals sign followed by the plus character
(<filename>=+</filename>) to prepend values to existing
variables.
<note>
This operator adds a space between the new content
and the existing content of the variable.
</note></para>
<para>Here is an example:
<literallayout class='monospaced'>
VAR =+ "Starts"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Appending: <filename>_append</filename></emphasis> -
Use the <filename>_append</filename> operator to
append values to existing variables.
This operator does not add any additional space.
Also, the operator is applied after all the
<filename>+=</filename>, and
<filename>=+</filename> operators have been applied and
after all <filename>=</filename> assignments have
occurred.
</para>
<para>The following example shows the space being
explicitly added to the start to ensure the appended
value is not merged with the existing value:
<literallayout class='monospaced'>
SRC_URI_append = " file://fix-makefile.patch"
</literallayout>
You can also use the <filename>_append</filename>
operator with overrides, which results in the actions
only being performed for the specified target or
machine:
<literallayout class='monospaced'>
SRC_URI_append_sh4 = " file://fix-makefile.patch"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Prepending: <filename>_prepend</filename></emphasis> -
Use the <filename>_prepend</filename> operator to
prepend values to existing variables.
This operator does not add any additional space.
Also, the operator is applied after all the
<filename>+=</filename>, and
<filename>=+</filename> operators have been applied and
after all <filename>=</filename> assignments have
occurred.
</para>
<para>The following example shows the space being
explicitly added to the end to ensure the prepended
value is not merged with the existing value:
<literallayout class='monospaced'>
CFLAGS_prepend = "-I${S}/myincludes "
</literallayout>
You can also use the <filename>_prepend</filename>
operator with overrides, which results in the actions
only being performed for the specified target or
machine:
<literallayout class='monospaced'>
CFLAGS_prepend_sh4 = "-I${S}/myincludes "
</literallayout>
</para></listitem>
<listitem><para><emphasis>Overrides:</emphasis> -
You can use overrides to set a value conditionally,
typically based on how the recipe is being built.
For example, to set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-KBRANCH'><filename>KBRANCH</filename></ulink>
variable's value to "standard/base" for any target
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
except for qemuarm where it should be set to
"standard/arm-versatile-926ejs", you would do the
following:
<literallayout class='monospaced'>
KBRANCH = "standard/base"
KBRANCH_qemuarm = "standard/arm-versatile-926ejs"
</literallayout>
Overrides are also used to separate alternate values
of a variable in other situations.
For example, when setting variables such as
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
that are specific to individual packages produced by
a recipe, you should always use an override that
specifies the name of the package.
</para></listitem>
<listitem><para><emphasis>Indentation:</emphasis>
Use spaces for indentation rather than than tabs.
For shell functions, both currently work.
However, it is a policy decision of the Yocto Project
to use tabs in shell functions.
Realize that some layers have a policy to use spaces
for all indentation.
</para></listitem>
<listitem><para><emphasis>Using Python for Complex Operations: <filename>${@<replaceable>python_code</replaceable>}</filename></emphasis> -
For more advanced processing, it is possible to use
Python code during variable assignments (e.g.
search and replacement on a variable).</para>
<para>You indicate Python code using the
<filename>${@<replaceable>python_code</replaceable>}</filename>
syntax for the variable assignment:
<literallayout class='monospaced'>
SRC_URI = "ftp://ftp.info-zip.org/pub/infozip/src/zip${@d.getVar('PV',1).replace('.', '')}.tgz
</literallayout>
</para></listitem>
<listitem><para><emphasis>Shell Function Syntax:</emphasis>
Write shell functions as if you were writing a shell
script when you describe a list of actions to take.
You should ensure that your script works with a generic
<filename>sh</filename> and that it does not require
any <filename>bash</filename> or other shell-specific
functionality.
The same considerations apply to various system
utilities (e.g. <filename>sed</filename>,
<filename>grep</filename>, <filename>awk</filename>,
and so forth) that you might wish to use.
If in doubt, you should check with multiple
implementations - including those from BusyBox.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='new-recipe-running-a-build-on-the-recipe'>
<title>Running a Build on the Recipe</title>
<para>
Creating a new recipe is usually an iterative process that
requires using BitBake to process the recipe multiple times in
order to progressively discover and add information to the
recipe file.
</para>
<para>
Assuming you have sourced a build environment setup script (i.e.
<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>)
and you are in the
<link linkend='build-directory'>Build Directory</link>,
use BitBake to process your recipe.
All you need to provide is the
<filename><replaceable>basename</replaceable></filename> of the recipe as described
in the previous section:
<literallayout class='monospaced'>
$ bitbake <replaceable>basename</replaceable>
</literallayout>
</para>
<para>
During the build, the OpenEmbedded build system creates a
temporary work directory for each recipe
(<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>)
where it keeps extracted source files, log files, intermediate
compilation and packaging files, and so forth.
</para>
<para>
The path to the per-recipe temporary work directory depends
on the context in which it is being built.
The quickest way to find this path is to have BitBake return it
by running the following:
<literallayout class='monospaced'>
$ bitbake -e <replaceable>basename</replaceable> | grep ^WORKDIR=
</literallayout>
As an example, assume a Source Directory top-level folder named
<filename>poky</filename>, a default Build Directory at
<filename>poky/build</filename>, and a
<filename>qemux86-poky-linux</filename> machine target system.
Furthermore, suppose your recipe is named
<filename>foo_1.3.0.bb</filename>.
In this case, the work directory the build system uses to
build the package would be as follows:
<literallayout class='monospaced'>
poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0
</literallayout>
Inside this directory you can find sub-directories such as
<filename>image</filename>, <filename>packages-split</filename>,
and <filename>temp</filename>.
After the build, you can examine these to determine how well
the build went.
<note>
You can find log files for each task in the recipe's
<filename>temp</filename> directory (e.g.
<filename>poky/build/tmp/work/qemux86-poky-linux/foo/1.3.0-r0/temp</filename>).
Log files are named <filename>log.<replaceable>taskname</replaceable></filename>
(e.g. <filename>log.do_configure</filename>,
<filename>log.do_fetch</filename>, and
<filename>log.do_compile</filename>).
</note>
</para>
<para>
You can find more information about the build process in the
"<ulink url='&YOCTO_DOCS_REF_URL;#closer-look'>A Closer Look at the Yocto Project Development Environment</ulink>"
chapter of the Yocto Project Reference Manual.
</para>
</section>
<section id='new-recipe-fetching-code'>
<title>Fetching Code</title>
<para>
The first thing your recipe must do is specify how to fetch
the source files.
Fetching is controlled mainly through the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
variable.
Your recipe must have a <filename>SRC_URI</filename> variable
that points to where the source is located.
For a graphical representation of source locations, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#sources-dev-environment'>Sources</ulink>"
section in the Yocto Project Reference Manual.
</para>
<para>
The
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>
task uses the prefix of each entry in the
<filename>SRC_URI</filename> variable value to determine which
fetcher to use to get your source files.
It is the <filename>SRC_URI</filename> variable that triggers
the fetcher.
The
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
task uses the variable after source is fetched to apply
patches.
The OpenEmbedded build system uses
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESOVERRIDES'><filename>FILESOVERRIDES</filename></ulink>
for scanning directory locations for local files in
<filename>SRC_URI</filename>.
</para>
<para>
The <filename>SRC_URI</filename> variable in your recipe must
define each unique location for your source files.
It is good practice to not hard-code pathnames in an URL used
in <filename>SRC_URI</filename>.
Rather than hard-code these paths, use
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
which causes the fetch process to use the version specified in
the recipe filename.
Specifying the version in this manner means that upgrading the
recipe to a future version is as simple as renaming the recipe
to match the new version.
</para>
<para>
Here is a simple example from the
<filename>meta/recipes-devtools/cdrtools/cdrtools-native_3.01a20.bb</filename>
recipe where the source comes from a single tarball.
Notice the use of the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
variable:
<literallayout class='monospaced'>
SRC_URI = "ftp://ftp.berlios.de/pub/cdrecord/alpha/cdrtools-${PV}.tar.bz2"
</literallayout>
</para>
<para>
Files mentioned in <filename>SRC_URI</filename> whose names end
in a typical archive extension (e.g. <filename>.tar</filename>,
<filename>.tar.gz</filename>, <filename>.tar.bz2</filename>,
<filename>.zip</filename>, and so forth), are automatically
extracted during the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
task.
For another example that specifies these types of files, see
the
"<link linkend='new-recipe-autotooled-package'>Autotooled Package</link>"
section.
</para>
<para>
Another way of specifying source is from an SCM.
For Git repositories, you must specify
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
and you should specify
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
to include the revision with
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>.
Here is an example from the recipe
<filename>meta/recipes-kernel/blktrace/blktrace_git.bb</filename>:
<literallayout class='monospaced'>
SRCREV = "d6918c8832793b4205ed3bfede78c2f915c23385"
PR = "r6"
PV = "1.0.5+git${SRCPV}"
SRC_URI = "git://git.kernel.dk/blktrace.git \
file://ldflags.patch"
</literallayout>
</para>
<para>
If your <filename>SRC_URI</filename> statement includes
URLs pointing to individual files fetched from a remote server
other than a version control system, BitBake attempts to
verify the files against checksums defined in your recipe to
ensure they have not been tampered with or otherwise modified
since the recipe was written.
Two checksums are used:
<filename>SRC_URI[md5sum]</filename> and
<filename>SRC_URI[sha256sum]</filename>.
</para>
<para>
If your <filename>SRC_URI</filename> variable points to
more than a single URL (excluding SCM URLs), you need to
provide the <filename>md5</filename> and
<filename>sha256</filename> checksums for each URL.
For these cases, you provide a name for each URL as part of
the <filename>SRC_URI</filename> and then reference that name
in the subsequent checksum statements.
Here is an example:
<literallayout class='monospaced'>
SRC_URI = "${DEBIAN_MIRROR}/main/a/apmd/apmd_3.2.2.orig.tar.gz;name=tarball \
${DEBIAN_MIRROR}/main/a/apmd/apmd_${PV}.diff.gz;name=patch"
SRC_URI[tarball.md5sum] = "b1e6309e8331e0f4e6efd311c2d97fa8"
SRC_URI[tarball.sha256sum] = "7f7d9f60b7766b852881d40b8ff91d8e39fccb0d1d913102a5c75a2dbb52332d"
SRC_URI[patch.md5sum] = "57e1b689264ea80f78353519eece0c92"
SRC_URI[patch.sha256sum] = "7905ff96be93d725544d0040e425c42f9c05580db3c272f11cff75b9aa89d430"
</literallayout>
</para>
<para>
Proper values for <filename>md5</filename> and
<filename>sha256</filename> checksums might be available
with other signatures on the download page for the upstream
source (e.g. <filename>md5</filename>,
<filename>sha1</filename>, <filename>sha256</filename>,
<filename>GPG</filename>, and so forth).
Because the OpenEmbedded build system only deals with
<filename>sha256sum</filename> and <filename>md5sum</filename>,
you should verify all the signatures you find by hand.
</para>
<para>
If no <filename>SRC_URI</filename> checksums are specified
when you attempt to build the recipe, or you provide an
incorrect checksum, the build will produce an error for each
missing or incorrect checksum.
As part of the error message, the build system provides
the checksum string corresponding to the fetched file.
Once you have the correct checksums, you can copy and paste
them into your recipe and then run the build again to continue.
<note>
As mentioned, if the upstream source provides signatures
for verifying the downloaded source code, you should
verify those manually before setting the checksum values
in the recipe and continuing with the build.
</note>
</para>
<para>
This final example is a bit more complicated and is from the
<filename>meta/recipes-sato/rxvt-unicode/rxvt-unicode_9.20.bb</filename>
recipe.
The example's <filename>SRC_URI</filename> statement identifies
multiple files as the source files for the recipe: a tarball, a
patch file, a desktop file, and an icon.
<literallayout class='monospaced'>
SRC_URI = "http://dist.schmorp.de/rxvt-unicode/Attic/rxvt-unicode-${PV}.tar.bz2 \
file://xwc.patch \
file://rxvt.desktop \
file://rxvt.png"
</literallayout>
</para>
<para>
When you specify local files using the
<filename>file://</filename> URI protocol, the build system
fetches files from the local machine.
The path is relative to the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
variable and searches specific directories in a certain order:
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink><filename>}</filename>,
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}</filename>,
and <filename>files</filename>.
The directories are assumed to be subdirectories of the
directory in which the recipe or append file resides.
For another example that specifies these types of files, see the
"<link linkend='new-recipe-single-c-file-package-hello-world'>Single .c File Package (Hello World!)</link>"
section.
</para>
<para>
The previous example also specifies a patch file.
Patch files are files whose names usually end in
<filename>.patch</filename> or <filename>.diff</filename> but
can end with compressed suffixes such as
<filename>diff.gz</filename> and
<filename>patch.bz2</filename>, for example.
The build system automatically applies patches as described
in the
"<link linkend='new-recipe-patching-code'>Patching Code</link>" section.
</para>
</section>
<section id='new-recipe-unpacking-code'>
<title>Unpacking Code</title>
<para>
During the build, the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>
task unpacks the source with
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>
pointing to where it is unpacked.
</para>
<para>
If you are fetching your source files from an upstream source
archived tarball and the tarball's internal structure matches
the common convention of a top-level subdirectory named
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink><filename>}-${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink><filename>}</filename>,
then you do not need to set <filename>S</filename>.
However, if <filename>SRC_URI</filename> specifies to fetch
source from an archive that does not use this convention,
or from an SCM like Git or Subversion, your recipe needs to
define <filename>S</filename>.
</para>
<para>
If processing your recipe using BitBake successfully unpacks
the source files, you need to be sure that the directory
pointed to by <filename>${S}</filename> matches the structure
of the source.
</para>
</section>
<section id='new-recipe-patching-code'>
<title>Patching Code</title>
<para>
Sometimes it is necessary to patch code after it has been
fetched.
Any files mentioned in <filename>SRC_URI</filename> whose
names end in <filename>.patch</filename> or
<filename>.diff</filename> or compressed versions of these
suffixes (e.g. <filename>diff.gz</filename> are treated as
patches.
The
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
task automatically applies these patches.
</para>
<para>
The build system should be able to apply patches with the "-p1"
option (i.e. one directory level in the path will be stripped
off).
If your patch needs to have more directory levels stripped off,
specify the number of levels using the "striplevel" option in
the <filename>SRC_URI</filename> entry for the patch.
Alternatively, if your patch needs to be applied in a specific
subdirectory that is not specified in the patch file, use the
"patchdir" option in the entry.
</para>
<para>
As with all local files referenced in
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
using <filename>file://</filename>, you should place
patch files in a directory next to the recipe either
named the same as the base name of the recipe
(<ulink url='&YOCTO_DOCS_REF_URL;#var-BP'><filename>BP</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink>)
or "files".
</para>
</section>
<section id='new-recipe-licensing'>
<title>Licensing</title>
<para>
Your recipe needs to have both the
<ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
variables:
<itemizedlist>
<listitem><para><emphasis><filename>LICENSE</filename>:</emphasis>
This variable specifies the license for the software.
If you do not know the license under which the software
you are building is distributed, you should go to the
source code and look for that information.
Typical files containing this information include
<filename>COPYING</filename>,
<filename>LICENSE</filename>, and
<filename>README</filename> files.
You could also find the information near the top of
a source file.
For example, given a piece of software licensed under
the GNU General Public License version 2, you would
set <filename>LICENSE</filename> as follows:
<literallayout class='monospaced'>
LICENSE = "GPLv2"
</literallayout></para>
<para>The licenses you specify within
<filename>LICENSE</filename> can have any name as long
as you do not use spaces, since spaces are used as
separators between license names.
For standard licenses, use the names of the files in
<filename>meta/files/common-licenses/</filename>
or the <filename>SPDXLICENSEMAP</filename> flag names
defined in <filename>meta/conf/licenses.conf</filename>.
</para></listitem>
<listitem><para><emphasis><filename>LIC_FILES_CHKSUM</filename>:</emphasis>
The OpenEmbedded build system uses this variable to
make sure the license text has not changed.
If it has, the build produces an error and it affords
you the chance to figure it out and correct the problem.
</para>
<para>You need to specify all applicable licensing
files for the software.
At the end of the configuration step, the build process
will compare the checksums of the files to be sure
the text has not changed.
Any differences result in an error with the message
containing the current checksum.
For more explanation and examples of how to set the
<filename>LIC_FILES_CHKSUM</filename> variable, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</ulink>"
section in the Yocto Project Reference Manual.</para>
<para>To determine the correct checksum string, you
can list the appropriate files in the
<filename>LIC_FILES_CHKSUM</filename> variable with
incorrect md5 strings, attempt to build the software,
and then note the resulting error messages that will
report the correct md5 strings.
See the
"<link linkend='new-recipe-fetching-code'>Fetching Code</link>"
section for additional information.
</para>
<para>
Here is an example that assumes the software has a
<filename>COPYING</filename> file:
<literallayout class='monospaced'>
LIC_FILES_CHKSUM = "file://COPYING;md5=xxx"
</literallayout>
When you try to build the software, the build system
will produce an error and give you the correct string
that you can substitute into the recipe file for a
subsequent build.
</para></listitem>
</itemizedlist>
</para>
<!--
<para>
For trying this out I created a new recipe named
<filename>htop_1.0.2.bb</filename> and put it in
<filename>poky/meta/recipes-extended/htop</filename>.
There are two license type statements in my very simple
recipe:
<literallayout class='monospaced'>
LICENSE = ""
LIC_FILES_CHKSUM = ""
SRC_URI[md5sum] = ""
SRC_URI[sha256sum] = ""
</literallayout>
Evidently, you need to run a <filename>bitbake -c cleanall htop</filename>.
Next, you delete or comment out the two <filename>SRC_URI</filename>
lines at the end and then attempt to build the software with
<filename>bitbake htop</filename>.
Doing so causes BitBake to report some errors and and give
you the actual strings you need for the last two
<filename>SRC_URI</filename> lines.
Prior to this, you have to dig around in the home page of the
source for <filename>htop</filename> and determine that the
software is released under GPLv2.
You can provide that in the <filename>LICENSE</filename>
statement.
Now you edit your recipe to have those two strings for
the <filename>SRC_URI</filename> statements:
<literallayout class='monospaced'>
LICENSE = "GPLv2"
LIC_FILES_CHKSUM = ""
SRC_URI = "${SOURCEFORGE_MIRROR}/htop/htop-${PV}.tar.gz"
SRC_URI[md5sum] = "0d01cca8df3349c74569cefebbd9919e"
SRC_URI[sha256sum] = "ee60657b044ece0df096c053060df7abf3cce3a568ab34d260049e6a37ccd8a1"
</literallayout>
At this point, you can build the software again using the
<filename>bitbake htop</filename> command.
There is just a set of errors now associated with the
empty <filename>LIC_FILES_CHKSUM</filename> variable now.
</para>
-->
</section>
<section id='new-dependencies'>
<title>Dependencies</title>
<para>
Most software packages have a short list of other packages
that they require, which are called dependencies.
These dependencies fall into two main categories: build-time
dependencies, which are required when the software is built;
and runtime dependencies, which are required to be installed
on the target in order for the software to run.
</para>
<para>
Within a recipe, you specify build-time dependencies using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
variable.
Although nuances exist, items specified in
<filename>DEPENDS</filename> should be names of other recipes.
It is important that you specify all build-time dependencies
explicitly.
If you do not, due to the parallel nature of BitBake's
execution, you can end up with a race condition where the
dependency is present for one task of a recipe (e.g.
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>)
and then gone when the next task runs (e.g.
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>).
</para>
<para>
Another consideration is that configure scripts might
automatically check for optional dependencies and enable
corresponding functionality if those dependencies are found.
This behavior means that to ensure deterministic results and
thus avoid more race conditions, you need to either explicitly
specify these dependencies as well, or tell the configure
script explicitly to disable the functionality.
If you wish to make a recipe that is more generally useful
(e.g. publish the recipe in a layer for others to use),
instead of hard-disabling the functionality, you can use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG'><filename>PACKAGECONFIG</filename></ulink>
variable to allow functionality and the corresponding
dependencies to be enabled and disabled easily by other
users of the recipe.
</para>
<para>
Similar to build-time dependencies, you specify runtime
dependencies through a variable -
<ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
which is package-specific.
All variables that are package-specific need to have the name
of the package added to the end as an override.
Since the main package for a recipe has the same name as the
recipe, and the recipe's name can be found through the
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
variable, then you specify the dependencies for the main
package by setting <filename>RDEPENDS_${PN}</filename>.
If the package were named <filename>${PN}-tools</filename>,
then you would set <filename>RDEPENDS_${PN}-tools</filename>,
and so forth.
</para>
<para>
Some runtime dependencies will be set automatically at
packaging time.
These dependencies include any shared library dependencies
(i.e. if a package "example" contains "libexample" and
another package "mypackage" contains a binary that links to
"libexample" then the OpenEmbedded build system will
automatically add a runtime dependency to "mypackage" on
"example").
See the
"<ulink url='&YOCTO_DOCS_REF_URL;#automatically-added-runtime-dependencies'>Automatically Added Runtime Dependencies</ulink>"
in the Yocto Project Reference Manual for further details.
</para>
</section>
<section id='new-recipe-configuring-the-recipe'>
<title>Configuring the Recipe</title>
<para>
Most software provides some means of setting build-time
configuration options before compilation.
Typically, setting these options is accomplished by running a
configure script with some options, or by modifying a build
configuration file.
<note>
As of Yocto Project Release 1.7, some of the core recipes
that package binary configuration scripts now disable the
scripts due to the scripts previously requiring error-prone
path substitution.
The OpenEmbedded build system uses
<filename>pkg-config</filename> now, which is much more
robust.
You can find a list of the <filename>*-config</filename>
scripts that are disabled list in the
"<ulink url='&YOCTO_DOCS_REF_URL;#migration-1.7-binary-configuration-scripts-disabled'>Binary Configuration Scripts Disabled</ulink>"
section in the Yocto Project Reference Manual.
</note>
</para>
<para>
A major part of build-time configuration is about checking for
build-time dependencies and possibly enabling optional
functionality as a result.
You need to specify any build-time dependencies for the
software you are building in your recipe's
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
value, in terms of other recipes that satisfy those
dependencies.
You can often find build-time or runtime
dependencies described in the software's documentation.
</para>
<para>
The following list provides configuration items of note based
on how your software is built:
<itemizedlist>
<listitem><para><emphasis>Autotools:</emphasis>
If your source files have a
<filename>configure.ac</filename> file, then your
software is built using Autotools.
If this is the case, you just need to worry about
modifying the configuration.</para>
<para>When using Autotools, your recipe needs to inherit
the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
class and your recipe does not have to contain a
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
task.
However, you might still want to make some adjustments.
For example, you can set
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink>
to pass any needed configure options that are specific
to the recipe.</para></listitem>
<listitem><para><emphasis>CMake:</emphasis>
If your source files have a
<filename>CMakeLists.txt</filename> file, then your
software is built using CMake.
If this is the case, you just need to worry about
modifying the configuration.</para>
<para>When you use CMake, your recipe needs to inherit
the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
class and your recipe does not have to contain a
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
task.
You can make some adjustments by setting
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></ulink>
to pass any needed configure options that are specific
to the recipe.</para></listitem>
<listitem><para><emphasis>Other:</emphasis>
If your source files do not have a
<filename>configure.ac</filename> or
<filename>CMakeLists.txt</filename> file, then your
software is built using some method other than Autotools
or CMake.
If this is the case, you normally need to provide a
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
task in your recipe
unless, of course, there is nothing to configure.
</para>
<para>Even if your software is not being built by
Autotools or CMake, you still might not need to deal
with any configuration issues.
You need to determine if configuration is even a required step.
You might need to modify a Makefile or some configuration file
used for the build to specify necessary build options.
Or, perhaps you might need to run a provided, custom
configure script with the appropriate options.</para>
<para>For the case involving a custom configure
script, you would run
<filename>./configure --help</filename> and look for
the options you need to set.</para></listitem>
</itemizedlist>
</para>
<para>
Once configuration succeeds, it is always good practice to
look at the <filename>log.do_configure</filename> file to
ensure that the appropriate options have been enabled and no
additional build-time dependencies need to be added to
<filename>DEPENDS</filename>.
For example, if the configure script reports that it found
something not mentioned in <filename>DEPENDS</filename>, or
that it did not find something that it needed for some
desired optional functionality, then you would need to add
those to <filename>DEPENDS</filename>.
Looking at the log might also reveal items being checked for,
enabled, or both that you do not want, or items not being found
that are in <filename>DEPENDS</filename>, in which case
you would need to look at passing extra options to the
configure script as needed.
For reference information on configure options specific to the
software you are building, you can consult the output of the
<filename>./configure --help</filename> command within
<filename>${S}</filename> or consult the software's upstream
documentation.
</para>
</section>
<section id='new-recipe-using-headers-to-interface-with-devices'>
<title>Using Headers to Interface with Devices</title>
<para>
If your recipe builds an application that needs to
communicate with some device or needs an API into a custom
kernel, you will need to provide appropriate header files.
Under no circumstances should you ever modify the existing
<filename>meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc</filename>
file.
These headers are used to build <filename>libc</filename> and
must not be compromised with custom or machine-specific
header information.
If you customize <filename>libc</filename> through modified
headers all other applications that use
<filename>libc</filename> thus become affected.
<note><title>Warning</title>
Never copy and customize the <filename>libc</filename>
header file (i.e.
<filename>meta/recipes-kernel/linux-libc-headers/linux-libc-headers.inc</filename>).
</note>
The correct way to interface to a device or custom kernel is
to use a separate package that provides the additional headers
for the driver or other unique interfaces.
When doing so, your application also becomes responsible for
creating a dependency on that specific provider.
</para>
<para>
Consider the following:
<itemizedlist>
<listitem><para>
Never modify
<filename>linux-libc-headers.inc</filename>.
Consider that file to be part of the
<filename>libc</filename> system, and not something
you use to access the kernel directly.
You should access <filename>libc</filename> through
specific <filename>libc</filename> calls.
</para></listitem>
<listitem><para>
Applications that must talk directly to devices
should either provide necessary headers themselves,
or establish a dependency on a special headers package
that is specific to that driver.
</para></listitem>
</itemizedlist>
</para>
<para>
For example, suppose you want to modify an existing header
that adds I/O control or network support.
If the modifications are used by a small number programs,
providing a unique version of a header is easy and has little
impact.
When doing so, bear in mind the guidelines in the previous
list.
<note>
If for some reason your changes need to modify the behavior
of the <filename>libc</filename>, and subsequently all
other applications on the system, use a
<filename>.bbappend</filename> to modify the
<filename>linux-kernel-headers.inc</filename> file.
However, take care to not make the changes
machine specific.
</note>
</para>
<para>
Consider a case where your kernel is older and you need
an older <filename>libc</filename> ABI.
The headers installed by your recipe should still be a
standard mainline kernel, not your own custom one.
</para>
<para>
When you use custom kernel headers you need to get them from
<ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_KERNEL_DIR'><filename>STAGING_KERNEL_DIR</filename></ulink>,
which is the directory with kernel headers that are
required to build out-of-tree modules.
Your recipe will also need the following:
<literallayout class='monospaced'>
do_configure[depends] += "virtual/kernel:do_shared_workdir"
</literallayout>
</para>
</section>
<section id='new-recipe-compilation'>
<title>Compilation</title>
<para>
During a build, the <filename>do_compile</filename> task
happens after source is fetched, unpacked, and configured.
If the recipe passes through <filename>do_compile</filename>
successfully, nothing needs to be done.
</para>
<para>
However, if the compile step fails, you need to diagnose the
failure.
Here are some common issues that cause failures.
<note>
For cases where improper paths are detected for
configuration files or for when libraries/headers cannot
be found, be sure you are using the more robust
<filename>pkg-config</filename>.
See the note in section
"<link linkend='new-recipe-configuring-the-recipe'>Configuring the Recipe</link>"
for additional information.
</note>
<itemizedlist>
<listitem><para><emphasis>Parallel build failures:</emphasis>
These failures manifest themselves as intermittent
errors, or errors reporting that a file or directory
that should be created by some other part of the build
process could not be found.
This type of failure can occur even if, upon inspection,
the file or directory does exist after the build has
failed, because that part of the build process happened
in the wrong order.</para>
<para>To fix the problem, you need to either satisfy
the missing dependency in the Makefile or whatever
script produced the Makefile, or (as a workaround)
set
<ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
to an empty string:
<literallayout class='monospaced'>
PARALLEL_MAKE = ""
</literallayout></para>
<para>
For information on parallel Makefile issues, see the
"<link linkend='debugging-parallel-make-races'>Debugging Parallel Make Races</link>"
section.
</para></listitem>
<listitem><para><emphasis>Improper host path usage:</emphasis>
This failure applies to recipes building for the target
or <filename>nativesdk</filename> only.
The failure occurs when the compilation process uses
improper headers, libraries, or other files from the
host system when cross-compiling for the target.
</para>
<para>To fix the problem, examine the
<filename>log.do_compile</filename> file to identify
the host paths being used (e.g.
<filename>/usr/include</filename>,
<filename>/usr/lib</filename>, and so forth) and then
either add configure options, apply a patch, or do both.
</para></listitem>
<listitem><para><emphasis>Failure to find required
libraries/headers:</emphasis>
If a build-time dependency is missing because it has
not been declared in
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
or because the dependency exists but the path used by
the build process to find the file is incorrect and the
configure step did not detect it, the compilation
process could fail.
For either of these failures, the compilation process
notes that files could not be found.
In these cases, you need to go back and add additional
options to the configure script as well as possibly
add additional build-time dependencies to
<filename>DEPENDS</filename>.</para>
<para>Occasionally, it is necessary to apply a patch
to the source to ensure the correct paths are used.
If you need to specify paths to find files staged
into the sysroot from other recipes, use the variables
that the OpenEmbedded build system provides
(e.g.
<filename>STAGING_BINDIR</filename>,
<filename>STAGING_INCDIR</filename>,
<filename>STAGING_DATADIR</filename>, and so forth).
<!--
(e.g.
<ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_BINDIR'><filename>STAGING_BINDIR</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_INCDIR'><filename>STAGING_INCDIR</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_DATADIR'><filename>STAGING_DATADIR</filename></ulink>,
and so forth).
-->
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='new-recipe-installing'>
<title>Installing</title>
<para>
During <filename>do_install</filename>, the task copies the
built files along with their hierarchy to locations that
would mirror their locations on the target device.
The installation process copies files from the
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>,
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink><filename>}</filename>,
and
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename>
directories to the
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
directory to create the structure as it should appear on the
target system.
</para>
<para>
How your software is built affects what you must do to be
sure your software is installed correctly.
The following list describes what you must do for installation
depending on the type of build system used by the software
being built:
<itemizedlist>
<listitem><para><emphasis>Autotools and CMake:</emphasis>
If the software your recipe is building uses Autotools
or CMake, the OpenEmbedded build
system understands how to install the software.
Consequently, you do not have to have a
<filename>do_install</filename> task as part of your
recipe.
You just need to make sure the install portion of the
build completes with no issues.
However, if you wish to install additional files not
already being installed by
<filename>make install</filename>, you should do this
using a <filename>do_install_append</filename> function
using the install command as described in
the "Manual" bulleted item later in this list.
</para></listitem>
<listitem><para><emphasis>Other (using
<filename>make install</filename>):</emphasis>
You need to define a
<filename>do_install</filename> function in your
recipe.
The function should call
<filename>oe_runmake install</filename> and will likely
need to pass in the destination directory as well.
How you pass that path is dependent on how the
<filename>Makefile</filename> being run is written
(e.g. <filename>DESTDIR=${D}</filename>,
<filename>PREFIX=${D}</filename>,
<filename>INSTALLROOT=${D}</filename>, and so forth).
</para>
<para>For an example recipe using
<filename>make install</filename>, see the
"<link linkend='new-recipe-makefile-based-package'>Makefile-Based Package</link>"
section.</para></listitem>
<listitem><para><emphasis>Manual:</emphasis>
You need to define a
<filename>do_install</filename> function in your
recipe.
The function must first use
<filename>install -d</filename> to create the
directories under
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>.
Once the directories exist, your function can use
<filename>install</filename> to manually install the
built software into the directories.</para>
<para>You can find more information on
<filename>install</filename> at
<ulink url='http://www.gnu.org/software/coreutils/manual/html_node/install-invocation.html'></ulink>.
</para></listitem>
</itemizedlist>
</para>
<para>
For the scenarios that do not use Autotools or
CMake, you need to track the installation
and diagnose and fix any issues until everything installs
correctly.
You need to look in the default location of
<filename>${D}</filename>, which is
<filename>${WORKDIR}/image</filename>, to be sure your
files have been installed correctly.
</para>
<note><title>Notes</title>
<itemizedlist>
<listitem><para>
During the installation process, you might need to
modify some of the installed files to suit the target
layout.
For example, you might need to replace hard-coded paths
in an initscript with values of variables provided by
the build system, such as replacing
<filename>/usr/bin/</filename> with
<filename>${bindir}</filename>.
If you do perform such modifications during
<filename>do_install</filename>, be sure to modify the
destination file after copying rather than before
copying.
Modifying after copying ensures that the build system
can re-execute <filename>do_install</filename> if
needed.
</para></listitem>
<listitem><para>
<filename>oe_runmake install</filename>, which can be
run directly or can be run indirectly by the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-cmake'><filename>cmake</filename></ulink>
classes, runs <filename>make install</filename> in
parallel.
Sometimes, a Makefile can have missing dependencies
between targets that can result in race conditions.
If you experience intermittent failures during
<filename>do_install</filename>, you might be able to
work around them by disabling parallel Makefile
installs by adding the following to the recipe:
<literallayout class='monospaced'>
PARALLEL_MAKEINST = ""
</literallayout>
See
<ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename></ulink>
for additional information.
</para></listitem>
</itemizedlist>
</note>
</section>
<section id='new-recipe-enabling-system-services'>
<title>Enabling System Services</title>
<para>
If you want to install a service, which is a process that
usually starts on boot and runs in the background, then
you must include some additional definitions in your recipe.
</para>
<para>
If you are adding services and the service initialization
script or the service file itself is not installed, you must
provide for that installation in your recipe using a
<filename>do_install_append</filename> function.
If your recipe already has a <filename>do_install</filename>
function, update the function near its end rather than
adding an additional <filename>do_install_append</filename>
function.
</para>
<para>
When you create the installation for your services, you need
to accomplish what is normally done by
<filename>make install</filename>.
In other words, make sure your installation arranges the output
similar to how it is arranged on the target system.
</para>
<para>
The OpenEmbedded build system provides support for starting
services two different ways:
<itemizedlist>
<listitem><para><emphasis>SysVinit:</emphasis>
SysVinit is a system and service manager that
manages the init system used to control the very basic
functions of your system.
The init program is the first program
started by the Linux kernel when the system boots.
Init then controls the startup, running and shutdown
of all other programs.</para>
<para>To enable a service using SysVinit, your recipe
needs to inherit the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-update-rc.d'><filename>update-rc.d</filename></ulink>
class.
The class helps facilitate safely installing the
package on the target.</para>
<para>You will need to set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PACKAGES'><filename>INITSCRIPT_PACKAGES</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_NAME'><filename>INITSCRIPT_NAME</filename></ulink>,
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITSCRIPT_PARAMS'><filename>INITSCRIPT_PARAMS</filename></ulink>
variables within your recipe.</para></listitem>
<listitem><para><emphasis>systemd:</emphasis>
System Management Daemon (systemd) was designed to
replace SysVinit and to provide
enhanced management of services.
For more information on systemd, see the systemd
homepage at
<ulink url='http://freedesktop.org/wiki/Software/systemd/'></ulink>.
</para>
<para>To enable a service using systemd, your recipe
needs to inherit the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-systemd'><filename>systemd</filename></ulink>
class.
See the <filename>systemd.bbclass</filename> file
located in your
<link linkend='source-directory'>Source Directory</link>.
section for more information.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='new-recipe-packaging'>
<title>Packaging</title>
<para>
Successful packaging is a combination of automated processes
performed by the OpenEmbedded build system and some
specific steps you need to take.
The following list describes the process:
<itemizedlist>
<listitem><para><emphasis>Splitting Files</emphasis>:
The <filename>do_package</filename> task splits the
files produced by the recipe into logical components.
Even software that produces a single binary might
still have debug symbols, documentation, and other
logical components that should be split out.
The <filename>do_package</filename> task ensures
that files are split up and packaged correctly.
</para></listitem>
<listitem><para><emphasis>Running QA Checks</emphasis>:
The
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-insane'><filename>insane</filename></ulink>
class adds a step to
the package generation process so that output quality
assurance checks are generated by the OpenEmbedded
build system.
This step performs a range of checks to be sure the
build's output is free of common problems that show
up during runtime.
For information on these checks, see the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-insane'><filename>insane</filename></ulink>
class and the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-qa-checks'>QA Error and Warning Messages</ulink>"
chapter in the Yocto Project Reference Manual.
</para></listitem>
<listitem><para><emphasis>Hand-Checking Your Packages</emphasis>:
After you build your software, you need to be sure
your packages are correct.
Examine the
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/packages-split</filename>
directory and make sure files are where you expect
them to be.
If you discover problems, you can set
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>,
<filename>do_install(_append)</filename>, and so forth as
needed.
</para></listitem>
<listitem><para><emphasis>Splitting an Application into Multiple Packages</emphasis>:
If you need to split an application into several
packages, see the
"<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
section for an example.
</para></listitem>
<listitem><para><emphasis>Installing a Post-Installation Script</emphasis>:
For an example showing how to install a
post-installation script, see the
"<link linkend='new-recipe-post-installation-scripts'>Post-Installation Scripts</link>"
section.
</para></listitem>
<listitem><para><emphasis>Marking Package Architecture</emphasis>:
Depending on what your recipe is building and how it
is configured, it might be important to mark the
packages produced as being specific to a particular
machine, or to mark them as not being specific to
a particular machine or architecture at all.</para>
<para>By default, packages apply to any machine with the
same architecture as the target machine.
When a recipe produces packages that are
machine-specific (e.g. the
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
value is passed into the configure script or a patch
is applied only for a particular machine), you should
mark them as such by adding the following to the
recipe:
<literallayout class='monospaced'>
PACKAGE_ARCH = "${MACHINE_ARCH}"
</literallayout></para>
<para>On the other hand, if the recipe produces packages
that do not contain anything specific to the target
machine or architecture at all (e.g. recipes
that simply package script files or configuration
files), you should use the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-allarch'><filename>allarch</filename></ulink>
class to do this for you by adding this to your
recipe:
<literallayout class='monospaced'>
inherit allarch
</literallayout>
Ensuring that the package architecture is correct is
not critical while you are doing the first few builds
of your recipe.
However, it is important in order
to ensure that your recipe rebuilds (or does not
rebuild) appropriately in response to changes in
configuration, and to ensure that you get the
appropriate packages installed on the target machine,
particularly if you run separate builds for more
than one target machine.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='new-sharing-files-between-recipes'>
<title>Sharing Files Between Recipes</title>
<para>
Recipes often need to use files provided by other recipes on
the build host.
For example, an application linking to a common library needs
access to the library itself and its associated headers.
The way this access is accomplished is by populating sysroot
with files.
Each recipe has two sysroots in its work directory, one for
target files
(<filename>recipe-sysroot</filename>) and one for files that
are native to the build host
(<filename>recipe-sysroot-native</filename>).
<note>
You could find the term "staging" used within the Yocto
project regarding files populating sysroot (e.g. the
<ulink url='&YOCTO_DOCS_REF_URL;#var-STAGING_DIR'><filename>STAGING_DIR</filename></ulink>
variable).
</note>
</para>
<para>
Recipes should never populate the sysroot directly (i.e. write
files into sysroot).
Instead, files should be installed into standard locations
during the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
task within the
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
directory.
The reason for this limitation is that almost all files that
populate the sysroot are cataloged in manifests in order to
ensure the files can be removed later when a recipe is either
modified or removed.
Thus, the sysroot is able to remain free from stale files.
</para>
<para>
A subset of the files installed by the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
task are used by the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></ulink>
task as defined by the the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SYSROOT_DIRS'><filename>SYSROOT_DIRS</filename></ulink>
variable to automatically populate the sysroot.
It is possible to modify the list of directories that populate
the sysroot.
The following example shows how you could add the
<filename>/opt</filename> directory to the list of
directories:
<literallayout class='monospaced'>
SYSROOT_DIRS += "/opt"
</literallayout>
</para>
<para>
for a more complete description of the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></ulink>
task and its associated functions, see the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-staging'><filename>staging</filename></ulink>
class.
</para>
</section>
<section id='properly-versioning-pre-release-recipes'>
<title>Properly Versioning Pre-Release Recipes</title>
<para>
Sometimes the name of a recipe can lead to versioning
problems when the recipe is upgraded to a final release.
For example, consider the
<filename>irssi_0.8.16-rc1.bb</filename> recipe file in
the list of example recipes in the
"<link linkend='new-recipe-storing-and-naming-the-recipe'>Storing and Naming the Recipe</link>"
section.
This recipe is at a release candidate stage (i.e.
"rc1").
When the recipe is released, the recipe filename becomes
<filename>irssi_0.8.16.bb</filename>.
The version change from <filename>0.8.16-rc1</filename>
to <filename>0.8.16</filename> is seen as a decrease by the
build system and package managers, so the resulting packages
will not correctly trigger an upgrade.
</para>
<para>
In order to ensure the versions compare properly, the
recommended convention is to set
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
within the recipe to
"<replaceable>previous_version</replaceable>+<replaceable>current_version</replaceable>".
You can use an additional variable so that you can use the
current version elsewhere.
Here is an example:
<literallayout class='monospaced'>
REALPV = "0.8.16-rc1"
PV = "0.8.15+${REALPV}"
</literallayout>
</para>
</section>
<section id='new-recipe-post-installation-scripts'>
<title>Post-Installation Scripts</title>
<para>
Post-installation scripts run immediately after installing
a package on the target or during image creation when a
package is included in an image.
To add a post-installation script to a package, add a
<filename>pkg_postinst_</filename><replaceable>PACKAGENAME</replaceable><filename>()</filename> function to
the recipe file (<filename>.bb</filename>) and replace
<replaceable>PACKAGENAME</replaceable> with the name of the package
you want to attach to the <filename>postinst</filename>
script.
To apply the post-installation script to the main package
for the recipe, which is usually what is required, specify
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
in place of <replaceable>PACKAGENAME</replaceable>.
</para>
<para>
A post-installation function has the following structure:
<literallayout class='monospaced'>
pkg_postinst_<replaceable>PACKAGENAME</replaceable>() {
# Commands to carry out
}
</literallayout>
</para>
<para>
The script defined in the post-installation function is
called when the root filesystem is created.
If the script succeeds, the package is marked as installed.
If the script fails, the package is marked as unpacked and
the script is executed when the image boots again.
<note>
Any RPM post-installation script that runs on the target
should return a 0 exit code.
RPM does not allow non-zero exit codes for these scripts,
and the RPM package manager will cause the package to fail
installation on the target.
</note>
</para>
<para>
Sometimes it is necessary for the execution of a
post-installation script to be delayed until the first boot.
For example, the script might need to be executed on the
device itself.
To delay script execution until boot time, use the following
structure in the post-installation script:
<literallayout class='monospaced'>
pkg_postinst_<replaceable>PACKAGENAME</replaceable>() {
if [ x"$D" = "x" ]; then
# Actions to carry out on the device go here
else
exit 1
fi
}
</literallayout>
</para>
<para>
The previous example delays execution until the image boots
again because the environment variable <filename>D</filename>
points to the directory containing the image when
the root filesystem is created at build time but is unset
when executed on the first boot.
</para>
<para>
If you have recipes that use <filename>pkg_postinst</filename>
scripts and they require the use of non-standard native
tools that have dependencies during rootfs construction, you
need to use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_WRITE_DEPS'><filename>PACKAGE_WRITE_DEPS</filename></ulink>
variable in your recipe to list these tools.
If you do not use this variable, the tools might be missing and
execution of the post-installation script is deferred until
first boot.
Deferring the script to first boot is undesirable and for
read-only rootfs impossible.
</para>
<note>
Equivalent support for pre-install, pre-uninstall, and
post-uninstall scripts exist by way of
<filename>pkg_preinst</filename>,
<filename>pkg_prerm</filename>, and
<filename>pkg_postrm</filename>, respectively.
These scrips work in exactly the same way as does
<filename>pkg_postinst</filename> with the exception that they
run at different times.
Also, because of when they run, they are not applicable to
being run at image creation time like
<filename>pkg_postinst</filename>.
</note>
</section>
<section id='new-recipe-testing'>
<title>Testing</title>
<para>
The final step for completing your recipe is to be sure that
the software you built runs correctly.
To accomplish runtime testing, add the build's output
packages to your image and test them on the target.
</para>
<para>
For information on how to customize your image by adding
specific packages, see the
"<link linkend='usingpoky-extend-customimage'>Customizing Images</link>"
section.
</para>
</section>
<section id='new-recipe-testing-examples'>
<title>Examples</title>
<para>
To help summarize how to write a recipe, this section provides
some examples given various scenarios:
<itemizedlist>
<listitem><para>Recipes that use local files</para></listitem>
<listitem><para>Using an Autotooled package</para></listitem>
<listitem><para>Using a Makefile-based package</para></listitem>
<listitem><para>Splitting an application into multiple packages</para></listitem>
<listitem><para>Adding binaries to an image</para></listitem>
</itemizedlist>
</para>
<section id='new-recipe-single-c-file-package-hello-world'>
<title>Single .c File Package (Hello World!)</title>
<para>
Building an application from a single file that is stored
locally (e.g. under <filename>files</filename>) requires
a recipe that has the file listed in the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
variable.
Additionally, you need to manually write the
<filename>do_compile</filename> and
<filename>do_install</filename> tasks.
The <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
variable defines the directory containing the source code,
which is set to
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
in this case - the directory BitBake uses for the build.
<literallayout class='monospaced'>
SUMMARY = "Simple helloworld application"
SECTION = "examples"
LICENSE = "MIT"
LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
SRC_URI = "file://helloworld.c"
S = "${WORKDIR}"
do_compile() {
${CC} helloworld.c -o helloworld
}
do_install() {
install -d ${D}${bindir}
install -m 0755 helloworld ${D}${bindir}
}
</literallayout>
</para>
<para>
By default, the <filename>helloworld</filename>,
<filename>helloworld-dbg</filename>, and
<filename>helloworld-dev</filename> packages are built.
For information on how to customize the packaging process,
see the
"<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application into Multiple Packages</link>"
section.
</para>
</section>
<section id='new-recipe-autotooled-package'>
<title>Autotooled Package</title>
<para>
Applications that use Autotools such as <filename>autoconf</filename> and
<filename>automake</filename> require a recipe that has a source archive listed in
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> and
also inherit the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink>
class, which contains the definitions of all the steps
needed to build an Autotool-based application.
The result of the build is automatically packaged.
And, if the application uses NLS for localization, packages with local information are
generated (one package per language).
Following is one example: (<filename>hello_2.3.bb</filename>)
<literallayout class='monospaced'>
SUMMARY = "GNU Helloworld application"
SECTION = "examples"
LICENSE = "GPLv2+"
LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"
inherit autotools gettext
</literallayout>
</para>
<para>
The variable
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</ulink></filename>
is used to track source license changes as described in the
"<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</ulink>" section.
You can quickly create Autotool-based recipes in a manner similar to the previous example.
</para>
</section>
<section id='new-recipe-makefile-based-package'>
<title>Makefile-Based Package</title>
<para>
Applications that use GNU <filename>make</filename> also require a recipe that has
the source archive listed in
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
You do not need to add a <filename>do_compile</filename> step since by default BitBake
starts the <filename>make</filename> command to compile the application.
If you need additional <filename>make</filename> options, you should store them in the
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'><filename>EXTRA_OEMAKE</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink>
variables.
BitBake passes these options into the GNU <filename>make</filename> invocation.
Note that a <filename>do_install</filename> task is still required.
Otherwise, BitBake runs an empty <filename>do_install</filename> task by default.
</para>
<para>
Some applications might require extra parameters to be passed to the compiler.
For example, the application might need an additional header path.
You can accomplish this by adding to the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink></filename> variable.
The following example shows this:
<literallayout class='monospaced'>
CFLAGS_prepend = "-I ${S}/include "
</literallayout>
</para>
<para>
In the following example, <filename>mtd-utils</filename> is a makefile-based package:
<literallayout class='monospaced'>
SUMMARY = "Tools for managing memory technology devices"
SECTION = "base"
DEPENDS = "zlib lzo e2fsprogs util-linux"
HOMEPAGE = "http://www.linux-mtd.infradead.org/"
LICENSE = "GPLv2+"
LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"
# Use the latest version at 26 Oct, 2013
SRCREV = "9f107132a6a073cce37434ca9cda6917dd8d866b"
SRC_URI = "git://git.infradead.org/mtd-utils.git \
file://add-exclusion-to-mkfs-jffs2-git-2.patch \
"
PV = "1.5.1+git${SRCPV}"
S = "${WORKDIR}/git"
EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' 'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"
do_install () {
oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} INCLUDEDIR=${includedir}
}
PACKAGES =+ "mtd-utils-jffs2 mtd-utils-ubifs mtd-utils-misc"
FILES_mtd-utils-jffs2 = "${sbindir}/mkfs.jffs2 ${sbindir}/jffs2dump ${sbindir}/jffs2reader ${sbindir}/sumtool"
FILES_mtd-utils-ubifs = "${sbindir}/mkfs.ubifs ${sbindir}/ubi*"
FILES_mtd-utils-misc = "${sbindir}/nftl* ${sbindir}/ftl* ${sbindir}/rfd* ${sbindir}/doc* ${sbindir}/serve_image ${sbindir}/recv_image"
PARALLEL_MAKE = ""
BBCLASSEXTEND = "native"
</literallayout>
</para>
</section>
<section id='splitting-an-application-into-multiple-packages'>
<title>Splitting an Application into Multiple Packages</title>
<para>
You can use the variables
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> and
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink></filename>
to split an application into multiple packages.
</para>
<para>
Following is an example that uses the <filename>libxpm</filename> recipe.
By default, this recipe generates a single package that contains the library along
with a few binaries.
You can modify the recipe to split the binaries into separate packages:
<literallayout class='monospaced'>
require xorg-lib-common.inc
SUMMARY = "Xpm: X Pixmap extension library"
LICENSE = "BSD"
LIC_FILES_CHKSUM = "file://COPYING;md5=51f4270b012ecd4ab1a164f5f4ed6cf7"
DEPENDS += "libxext libsm libxt"
PE = "1"
XORG_PN = "libXpm"
PACKAGES =+ "sxpm cxpm"
FILES_cxpm = "${bindir}/cxpm"
FILES_sxpm = "${bindir}/sxpm"
</literallayout>
</para>
<para>
In the previous example, we want to ship the <filename>sxpm</filename>
and <filename>cxpm</filename> binaries in separate packages.
Since <filename>bindir</filename> would be packaged into the main
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
package by default, we prepend the <filename>PACKAGES</filename>
variable so additional package names are added to the start of list.
This results in the extra <filename>FILES_*</filename>
variables then containing information that define which files and
directories go into which packages.
Files included by earlier packages are skipped by latter packages.
Thus, the main <filename>PN</filename> package
does not include the above listed files.
</para>
</section>
<section id='packaging-externally-produced-binaries'>
<title>Packaging Externally Produced Binaries</title>
<para>
Sometimes, you need to add pre-compiled binaries to an
image.
For example, suppose that binaries for proprietary code
exist, which are created by a particular division of a
company.
Your part of the company needs to use those binaries as
part of an image that you are building using the
OpenEmbedded build system.
Since you only have the binaries and not the source code,
you cannot use a typical recipe that expects to fetch the
source specified in
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
and then compile it.
</para>
<para>
One method is to package the binaries and then install them
as part of the image.
Generally, it is not a good idea to package binaries
since, among other things, it can hinder the ability to
reproduce builds and could lead to compatibility problems
with ABI in the future.
However, sometimes you have no choice.
</para>
<para>
The easiest solution is to create a recipe that uses
the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-bin-package'><filename>bin_package</filename></ulink>
class and to be sure that you are using default locations
for build artifacts.
In most cases, the <filename>bin_package</filename> class
handles "skipping" the configure and compile steps as well
as sets things up to grab packages from the appropriate
area.
In particular, this class sets <filename>noexec</filename>
on both the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
tasks, sets
<filename>FILES_${PN}</filename> to "/" so that it picks
up all files, and sets up a
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
task, which effectively copies all files from
<filename>${S}</filename> to <filename>${D}</filename>.
The <filename>bin_package</filename> class works well when
the files extracted into <filename>${S}</filename> are
already laid out in the way they should be laid out
on the target.
For more information on these variables, see the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>,
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink>
variables in the Yocto Project Reference Manual's variable
glossary.
<note><title>Notes</title>
<itemizedlist>
<listitem><para>
Using
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
is a good idea even for components distributed
in binary form, and is often necessary for
shared libraries.
For a shared library, listing the library
dependencies in
<filename>DEPENDS</filename> makes sure that
the libraries are available in the staging
sysroot when other recipes link against the
library, which might be necessary for
successful linking.
</para></listitem>
<listitem><para>
Using <filename>DEPENDS</filename> also
allows runtime dependencies between packages
to be added automatically.
See the
"<ulink url='&YOCTO_DOCS_REF_URL;#automatically-added-runtime-dependencies'>Automatically Added Runtime Dependencies</ulink>"
section in the Yocto Project Reference Manual
for more information.
</para></listitem>
</itemizedlist>
</note>
</para>
<para>
If you cannot use the <filename>bin_package</filename>
class, you need to be sure you are doing the following:
<itemizedlist>
<listitem><para>
Create a recipe where the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink>
tasks do nothing:
It is usually sufficient to just not define these
tasks in the recipe, because the default
implementations do nothing unless a Makefile is
found in
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink><filename>}</filename>.
</para>
<para>If
<filename>${S}</filename> might contain a Makefile,
or if you inherit some class that replaces
<filename>do_configure</filename> and
<filename>do_compile</filename> with custom
versions, then you can use the
<filename>[</filename><ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'><filename>noexec</filename></ulink><filename>]</filename>
flag to turn the tasks into no-ops, as follows:
<literallayout class='monospaced'>
do_configure[noexec] = "1"
do_compile[noexec] = "1"
</literallayout>
Unlike
<ulink url='&YOCTO_DOCS_BB_URL;#deleting-a-task'><filename>deleting the tasks</filename></ulink>,
using the flag preserves the dependency chain from
the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>,
and
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink>
tasks to the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
task.
</para></listitem>
<listitem><para>Make sure your
<filename>do_install</filename> task installs the
binaries appropriately.
</para></listitem>
<listitem><para>Ensure that you set up
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink>
(usually
<filename>FILES_${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>)
to point to the files you have installed, which of
course depends on where you have installed them
and whether those files are in different locations
than the defaults.
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
<section id="following-recipe-style-guidelines">
<title>Following Recipe Style Guidelines</title>
<para>
When writing recipes, it is good to conform to existing
style guidelines.
The
<ulink url='http://www.openembedded.org/wiki/Styleguide'>OpenEmbedded Styleguide</ulink>
wiki page provides rough guidelines for preferred recipe style.
</para>
<para>
It is common for existing recipes to deviate a bit from this
style.
However, aiming for at least a consistent style is a good idea.
Some practices, such as omitting spaces around
<filename>=</filename> operators in assignments or ordering
recipe components in an erratic way, are widely seen as poor
style.
</para>
</section>
</section>
<section id="platdev-newmachine">
<title>Adding a New Machine</title>
<para>
Adding a new machine to the Yocto Project is a straightforward
process.
This section describes how to add machines that are similar
to those that the Yocto Project already supports.
<note>
Although well within the capabilities of the Yocto Project,
adding a totally new architecture might require
changes to <filename>gcc/glibc</filename> and to the site
information, which is beyond the scope of this manual.
</note>
</para>
<para>
For a complete example that shows how to add a new machine,
see the
"<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
section in the Yocto Project Board Support Package (BSP) Developer's Guide.
</para>
<section id="platdev-newmachine-conffile">
<title>Adding the Machine Configuration File</title>
<para>
To add a new machine, you need to add a new machine
configuration file to the layer's
<filename>conf/machine</filename> directory.
This configuration file provides details about the device
you are adding.
</para>
<para>
The OpenEmbedded build system uses the root name of the
machine configuration file to reference the new machine.
For example, given a machine configuration file named
<filename>crownbay.conf</filename>, the build system
recognizes the machine as "crownbay".
</para>
<para>
The most important variables you must set in your machine
configuration file or include from a lower-level configuration
file are as follows:
<itemizedlist>
<listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_ARCH'>TARGET_ARCH</ulink></filename>
(e.g. "arm")</para></listitem>
<listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</ulink>_virtual/kernel</filename>
</para></listitem>
<listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'>MACHINE_FEATURES</ulink></filename>
(e.g. "apm screen wifi")</para></listitem>
</itemizedlist>
</para>
<para>
You might also need these variables:
<itemizedlist>
<listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLES'>SERIAL_CONSOLES</ulink></filename>
(e.g. "115200;ttyS0 115200;ttyS1")</para></listitem>
<listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'>KERNEL_IMAGETYPE</ulink></filename>
(e.g. "zImage")</para></listitem>
<listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'>IMAGE_FSTYPES</ulink></filename>
(e.g. "tar.gz jffs2")</para></listitem>
</itemizedlist>
</para>
<para>
You can find full details on these variables in the reference
section.
You can leverage existing machine <filename>.conf</filename>
files from <filename>meta-yocto-bsp/conf/machine/</filename>.
</para>
</section>
<section id="platdev-newmachine-kernel">
<title>Adding a Kernel for the Machine</title>
<para>
The OpenEmbedded build system needs to be able to build a kernel
for the machine.
You need to either create a new kernel recipe for this machine,
or extend an existing kernel recipe.
You can find several kernel recipe examples in the
Source Directory at
<filename>meta/recipes-kernel/linux</filename>
that you can use as references.
</para>
<para>
If you are creating a new kernel recipe, normal recipe-writing
rules apply for setting up a
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
Thus, you need to specify any necessary patches and set
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
to point at the source code.
You need to create a <filename>do_configure</filename> task that
configures the unpacked kernel with a
<filename>defconfig</filename> file.
You can do this by using a <filename>make defconfig</filename>
command or, more commonly, by copying in a suitable
<filename>defconfig</filename> file and then running
<filename>make oldconfig</filename>.
By making use of <filename>inherit kernel</filename> and
potentially some of the <filename>linux-*.inc</filename> files,
most other functionality is centralized and the defaults of the
class normally work well.
</para>
<para>
If you are extending an existing kernel recipe, it is usually
a matter of adding a suitable <filename>defconfig</filename>
file.
The file needs to be added into a location similar to
<filename>defconfig</filename> files used for other machines
in a given kernel recipe.
A possible way to do this is by listing the file in the
<filename>SRC_URI</filename> and adding the machine to the
expression in
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</ulink></filename>:
<literallayout class='monospaced'>
COMPATIBLE_MACHINE = '(qemux86|qemumips)'
</literallayout>
For more information on <filename>defconfig</filename> files,
see the
"<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
section in the Yocto Project Linux Kernel Development Manual.
</para>
</section>
<section id="platdev-newmachine-formfactor">
<title>Adding a Formfactor Configuration File</title>
<para>
A formfactor configuration file provides information about the
target hardware for which the image is being built and information that
the build system cannot obtain from other sources such as the kernel.
Some examples of information contained in a formfactor configuration file include
framebuffer orientation, whether or not the system has a keyboard,
the positioning of the keyboard in relation to the screen, and
the screen resolution.
</para>
<para>
The build system uses reasonable defaults in most cases.
However, if customization is
necessary, you need to create a <filename>machconfig</filename> file
in the <filename>meta/recipes-bsp/formfactor/files</filename>
directory.
This directory contains directories for specific machines such as
<filename>qemuarm</filename> and <filename>qemux86</filename>.
For information about the settings available and the defaults, see the
<filename>meta/recipes-bsp/formfactor/files/config</filename> file found in the
same area.
</para>
<para>
Following is an example for "qemuarm" machine:
<literallayout class='monospaced'>
HAVE_TOUCHSCREEN=1
HAVE_KEYBOARD=1
DISPLAY_CAN_ROTATE=0
DISPLAY_ORIENTATION=0
#DISPLAY_WIDTH_PIXELS=640
#DISPLAY_HEIGHT_PIXELS=480
#DISPLAY_BPP=16
DISPLAY_DPI=150
DISPLAY_SUBPIXEL_ORDER=vrgb
</literallayout>
</para>
</section>
</section>
<section id='platdev-building-targets-with-multiple-configurations'>
<title>Building Targets with Multiple Configurations</title>
<para>
Bitbake also has functionality that allows you to build
multiple targets at the same time, where each target uses
a different configuration.
</para>
<para>
In order to accomplish this, you setup each of the configurations
you need to use in parallel by placing the configuration files in
your current build directory alongside the usual
<filename>local.conf</filename> file.
</para>
<para>
Follow these guidelines to create an environment that supports
multiple configurations:
<itemizedlist>
<listitem><para>
<emphasis>Create Configuration Files</emphasis>:
You need to create a single configuration file for each
configuration for which you want to add support.
These files would contain lines such as the following:
<literallayout class='monospaced'>
MACHINE = "A"
</literallayout>
The files would contain any other variables that can
be set and built in the same directory.
<note>
You can change the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
to not conflict.
</note></para>
<para>
Furthermore, the configuration file must be located in the
current build directory in a directory named
<filename>multiconfig</filename> under the build's
<filename>conf</filename> directory where
<filename>local.conf</filename> resides.
The reason for this restriction is because the
<filename>BBPATH</filename> variable is not constructed
until the layers are parsed.
Consequently, using the configuration file as a
pre-configuration file is not possible unless it is
located in the current working directory.
</para></listitem>
<listitem><para>
<emphasis>Add the BitBake Multi-Config Variable to you Local Configuration File</emphasis>:
Use the
<filename>BBMULTICONFIG</filename>
variable in your <filename>conf/local.conf</filename>
configuration file to specify each separate configuration.
For example, the following line tells BitBake it should load
<filename>conf/multiconfig/configA.conf</filename>,
<filename>conf/multiconfig/configB.conf</filename>, and
<filename>conf/multiconfig/configC.conf</filename>.
<literallayout class='monospaced'>
BBMULTICONFIG = "configA configB configC"
</literallayout>
</para></listitem>
<listitem><para>
<emphasis>Launch BitBake</emphasis>:
Use the following BitBake command form to launch the
build:
<literallayout class='monospaced'>
$ bitbake [multiconfig:<replaceable>multiconfigname</replaceable>:]<replaceable>target</replaceable> [[[multiconfig:<replaceable>multiconfigname</replaceable>:]<replaceable>target</replaceable>] ... ]
</literallayout>
Following is an example that supports building a minimal
image for configuration A alongside a standard
<filename>core-image-sato</filename>, which takes its
configuration from <filename>local.conf</filename>:
<literallayout class='monospaced'>
$ bitbake multiconfig:configA:core-image-minimal core-image-sato
</literallayout>
</para></listitem>
</itemizedlist>
</para>
<para>
Support for multiple configurations in this current release of
the Yocto Project (&DISTRO_NAME; &DISTRO;) has some known issues:
<itemizedlist>
<listitem><para>
No inter-multi-configuration dependencies exist.
</para></listitem>
<listitem><para>
Shared State (sstate) optimizations do not exist.
Consequently, if the build uses the same object twice
in, for example, two different
<filename>TMPDIR</filename> directories, the build
will either load from an existing sstate cache at the
start or build the object twice.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id="platdev-working-with-libraries">
<title>Working With Libraries</title>
<para>
Libraries are an integral part of your system.
This section describes some common practices you might find
helpful when working with libraries to build your system:
<itemizedlist>
<listitem><para><link linkend='including-static-library-files'>How to include static library files</link>
</para></listitem>
<listitem><para><link linkend='combining-multiple-versions-library-files-into-one-image'>How to use the Multilib feature to combine multiple versions of library files into a single image</link>
</para></listitem>
<listitem><para><link linkend='installing-multiple-versions-of-the-same-library'>How to install multiple versions of the same library in parallel on the same system</link>
</para></listitem>
</itemizedlist>
</para>
<section id='including-static-library-files'>
<title>Including Static Library Files</title>
<para>
If you are building a library and the library offers static linking, you can control
which static library files (<filename>*.a</filename> files) get included in the
built library.
</para>
<para>
The <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
and <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES_*</filename></ulink>
variables in the
<filename>meta/conf/bitbake.conf</filename> configuration file define how files installed
by the <filename>do_install</filename> task are packaged.
By default, the <filename>PACKAGES</filename> variable includes
<filename>${PN}-staticdev</filename>, which represents all static library files.
<note>
Some previously released versions of the Yocto Project
defined the static library files through
<filename>${PN}-dev</filename>.
</note>
Following is part of the BitBake configuration file, where
you can see how the static library files are defined:
<literallayout class='monospaced'>
PACKAGE_BEFORE_PN ?= ""
PACKAGES = "${PN}-dbg ${PN}-staticdev ${PN}-dev ${PN}-doc ${PN}-locale ${PACKAGE_BEFORE_PN} ${PN}"
PACKAGES_DYNAMIC = "^${PN}-locale-.*"
FILES = ""
FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
${sysconfdir} ${sharedstatedir} ${localstatedir} \
${base_bindir}/* ${base_sbindir}/* \
${base_libdir}/*${SOLIBS} \
${base_prefix}/lib/udev/rules.d ${prefix}/lib/udev/rules.d \
${datadir}/${BPN} ${libdir}/${BPN}/* \
${datadir}/pixmaps ${datadir}/applications \
${datadir}/idl ${datadir}/omf ${datadir}/sounds \
${libdir}/bonobo/servers"
FILES_${PN}-bin = "${bindir}/* ${sbindir}/*"
FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
${datadir}/gnome/help"
SECTION_${PN}-doc = "doc"
FILES_SOLIBSDEV ?= "${base_libdir}/lib*${SOLIBSDEV} ${libdir}/lib*${SOLIBSDEV}"
FILES_${PN}-dev = "${includedir} ${FILES_SOLIBSDEV} ${libdir}/*.la \
${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
${datadir}/aclocal ${base_libdir}/*.o \
${libdir}/${BPN}/*.la ${base_libdir}/*.la"
SECTION_${PN}-dev = "devel"
ALLOW_EMPTY_${PN}-dev = "1"
RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"
FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a ${libdir}/${BPN}/*.a"
SECTION_${PN}-staticdev = "devel"
RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
</literallayout>
</para>
</section>
<section id="combining-multiple-versions-library-files-into-one-image">
<title>Combining Multiple Versions of Library Files into One Image</title>
<para>
The build system offers the ability to build libraries with different
target optimizations or architecture formats and combine these together
into one system image.
You can link different binaries in the image
against the different libraries as needed for specific use cases.
This feature is called "Multilib."
</para>
<para>
An example would be where you have most of a system compiled in 32-bit
mode using 32-bit libraries, but you have something large, like a database
engine, that needs to be a 64-bit application and uses 64-bit libraries.
Multilib allows you to get the best of both 32-bit and 64-bit libraries.
</para>
<para>
While the Multilib feature is most commonly used for 32 and 64-bit differences,
the approach the build system uses facilitates different target optimizations.
You could compile some binaries to use one set of libraries and other binaries
to use a different set of libraries.
The libraries could differ in architecture, compiler options, or other
optimizations.
</para>
<para>
Several examples exist in the
<filename>meta-skeleton</filename> layer found in the
<link linkend='source-directory'>Source Directory</link>:
<itemizedlist>
<listitem><para><filename>conf/multilib-example.conf</filename>
configuration file</para></listitem>
<listitem><para><filename>conf/multilib-example2.conf</filename>
configuration file</para></listitem>
<listitem><para><filename>recipes-multilib/images/core-image-multilib-example.bb</filename>
recipe</para></listitem>
</itemizedlist>
</para>
<section id='preparing-to-use-multilib'>
<title>Preparing to Use Multilib</title>
<para>
User-specific requirements drive the Multilib feature.
Consequently, there is no one "out-of-the-box" configuration that likely
exists to meet your needs.
</para>
<para>
In order to enable Multilib, you first need to ensure your recipe is
extended to support multiple libraries.
Many standard recipes are already extended and support multiple libraries.
You can check in the <filename>meta/conf/multilib.conf</filename>
configuration file in the
<link linkend='source-directory'>Source Directory</link> to see how this is
done using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
variable.
Eventually, all recipes will be covered and this list will
not be needed.
</para>
<para>
For the most part, the Multilib class extension works automatically to
extend the package name from <filename>${PN}</filename> to
<filename>${MLPREFIX}${PN}</filename>, where <filename>MLPREFIX</filename>
is the particular multilib (e.g. "lib32-" or "lib64-").
Standard variables such as
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-RPROVIDES'><filename>RPROVIDES</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>, and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES_DYNAMIC'><filename>PACKAGES_DYNAMIC</filename></ulink>
are automatically extended by the system.
If you are extending any manual code in the recipe, you can use the
<filename>${MLPREFIX}</filename> variable to ensure those names are extended
correctly.
This automatic extension code resides in <filename>multilib.bbclass</filename>.
</para>
</section>
<section id='using-multilib'>
<title>Using Multilib</title>
<para>
After you have set up the recipes, you need to define the actual
combination of multiple libraries you want to build.
You accomplish this through your <filename>local.conf</filename>
configuration file in the
<link linkend='build-directory'>Build Directory</link>.
An example configuration would be as follows:
<literallayout class='monospaced'>
MACHINE = "qemux86-64"
require conf/multilib.conf
MULTILIBS = "multilib:lib32"
DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
IMAGE_INSTALL_append = " lib32-glib-2.0"
</literallayout>
This example enables an
additional library named <filename>lib32</filename> alongside the
normal target packages.
When combining these "lib32" alternatives, the example uses "x86" for tuning.
For information on this particular tuning, see
<filename>meta/conf/machine/include/ia32/arch-ia32.inc</filename>.
</para>
<para>
The example then includes <filename>lib32-glib-2.0</filename>
in all the images, which illustrates one method of including a
multiple library dependency.
You can use a normal image build to include this dependency,
for example:
<literallayout class='monospaced'>
$ bitbake core-image-sato
</literallayout>
You can also build Multilib packages specifically with a command like this:
<literallayout class='monospaced'>
$ bitbake lib32-glib-2.0
</literallayout>
</para>
</section>
<section id='additional-implementation-details'>
<title>Additional Implementation Details</title>
<para>
Generic implementation details as well as details that are
specific to package management systems exist.
Following are implementation details that exist regardless
of the package management system:
<itemizedlist>
<listitem><para>The typical convention used for the
class extension code as used by
Multilib assumes that all package names specified
in
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
that contain <filename>${PN}</filename> have
<filename>${PN}</filename> at the start of the name.
When that convention is not followed and
<filename>${PN}</filename> appears at
the middle or the end of a name, problems occur.
</para></listitem>
<listitem><para>The
<ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_VENDOR'><filename>TARGET_VENDOR</filename></ulink>
value under Multilib will be extended to
"-<replaceable>vendor</replaceable>ml<replaceable>multilib</replaceable>"
(e.g. "-pokymllib32" for a "lib32" Multilib with
Poky).
The reason for this slightly unwieldy contraction
is that any "-" characters in the vendor
string presently break Autoconf's
<filename>config.sub</filename>, and
other separators are problematic for different
reasons.
</para></listitem>
</itemizedlist>
</para>
<para>
For the RPM Package Management System, the following implementation details
exist:
<itemizedlist>
<listitem><para>A unique architecture is defined for the Multilib packages,
along with creating a unique deploy folder under
<filename>tmp/deploy/rpm</filename> in the
<link linkend='build-directory'>Build Directory</link>.
For example, consider <filename>lib32</filename> in a
<filename>qemux86-64</filename> image.
The possible architectures in the system are "all", "qemux86_64",
"lib32_qemux86_64", and "lib32_x86".</para></listitem>
<listitem><para>The <filename>${MLPREFIX}</filename> variable is stripped from
<filename>${PN}</filename> during RPM packaging.
The naming for a normal RPM package and a Multilib RPM package in a
<filename>qemux86-64</filename> system resolves to something similar to
<filename>bash-4.1-r2.x86_64.rpm</filename> and
<filename>bash-4.1.r2.lib32_x86.rpm</filename>, respectively.
</para></listitem>
<listitem><para>When installing a Multilib image, the RPM backend first
installs the base image and then installs the Multilib libraries.
</para></listitem>
<listitem><para>The build system relies on RPM to resolve the identical files in the
two (or more) Multilib packages.</para></listitem>
</itemizedlist>
</para>
<para>
For the IPK Package Management System, the following implementation details exist:
<itemizedlist>
<listitem><para>The <filename>${MLPREFIX}</filename> is not stripped from
<filename>${PN}</filename> during IPK packaging.
The naming for a normal RPM package and a Multilib IPK package in a
<filename>qemux86-64</filename> system resolves to something like
<filename>bash_4.1-r2.x86_64.ipk</filename> and
<filename>lib32-bash_4.1-rw_x86.ipk</filename>, respectively.
</para></listitem>
<listitem><para>The IPK deploy folder is not modified with
<filename>${MLPREFIX}</filename> because packages with and without
the Multilib feature can exist in the same folder due to the
<filename>${PN}</filename> differences.</para></listitem>
<listitem><para>IPK defines a sanity check for Multilib installation
using certain rules for file comparison, overridden, etc.
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
<section id='installing-multiple-versions-of-the-same-library'>
<title>Installing Multiple Versions of the Same Library</title>
<para>
Situations can exist where you need to install and use
multiple versions of the same library on the same system
at the same time.
These situations almost always exist when a library API
changes and you have multiple pieces of software that
depend on the separate versions of the library.
To accommodate these situations, you can install multiple
versions of the same library in parallel on the same system.
</para>
<para>
The process is straightforward as long as the libraries use
proper versioning.
With properly versioned libraries, all you need to do to
individually specify the libraries is create separate,
appropriately named recipes where the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink> part of the
name includes a portion that differentiates each library version
(e.g.the major part of the version number).
Thus, instead of having a single recipe that loads one version
of a library (e.g. <filename>clutter</filename>), you provide
multiple recipes that result in different versions
of the libraries you want.
As an example, the following two recipes would allow the
two separate versions of the <filename>clutter</filename>
library to co-exist on the same system:
<literallayout class='monospaced'>
clutter-1.6_1.6.20.bb
clutter-1.8_1.8.4.bb
</literallayout>
Additionally, if you have other recipes that depend on a given
library, you need to use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
variable to create the dependency.
Continuing with the same example, if you want to have a recipe
depend on the 1.8 version of the <filename>clutter</filename>
library, use the following in your recipe:
<literallayout class='monospaced'>
DEPENDS = "clutter-1.8"
</literallayout>
</para>
</section>
</section>
<section id='enabling-gobject-introspection-support'>
<title>Enabling GObject Introspection Support</title>
<para>
<ulink url='https://wiki.gnome.org/Projects/GObjectIntrospection'>GObject introspection</ulink>
is the standard mechanism for accessing GObject-based software
from runtime environments.
GObject is a feature of the GLib library that provides an object
framework for the GNOME desktop and related software.
GObject Introspection adds information to GObject that allows
objects created within it to be represented across different
programming languages.
If you want to construct GStreamer pipelines using Python, or
control UPnP infrastructure using Javascript and GUPnP,
GObject introspection is the only way to do it.
</para>
<para>
This section describes the Yocto Project support for generating
and packaging GObject introspection data.
GObject introspection data is a description of the
API provided by libraries built on top of GLib framework,
and, in particular, that framework's GObject mechanism.
GObject Introspection Repository (GIR) files go to
<filename>-dev</filename> packages,
<filename>typelib</filename> files go to main packages as they
are packaged together with libraries that are introspected.
</para>
<para>
The data is generated when building such a library, by linking
the library with a small executable binary that asks the library
to describe itself, and then executing the binary and
processing its output.
</para>
<para>
Generating this data in a cross-compilation environment
is difficult because the library is produced for the target
architecture, but its code needs to be executed on the build host.
This problem is solved with the OpenEmbedded build system by
running the code through QEMU, which allows precisely that.
Unfortunately, QEMU does not always work perfectly as mentioned
in the xxx section.
</para>
<section id='enabling-the-generation-of-introspection-data'>
<title>Enabling the Generation of Introspection Data</title>
<para>
Enabling the generation of introspection data (GIR files)
in your library package involves the following:
<orderedlist>
<listitem><para>
Inherit the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-gobject-introspection'><filename>gobject-introspection</filename></ulink>
class.
</para></listitem>
<listitem><para>
Make sure introspection is not disabled anywhere in
the recipe or from anything the recipe includes.
Also, make sure that "gobject-introspection-data" is
not in
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>
and that "qemu-usermode" is not in
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
If either of these conditions exist, nothing will
happen.
</para></listitem>
<listitem><para>
Try to build the recipe.
If you encounter build errors that look like
something is unable to find
<filename>.so</filename> libraries, check where these
libraries are located in the source tree and add
the following to the recipe:
<literallayout class='monospaced'>
GIR_EXTRA_LIBS_PATH = "${B}/<replaceable>something</replaceable>/.libs"
</literallayout>
<note>
See recipes in the <filename>oe-core</filename>
repository that use that
<filename>GIR_EXTRA_LIBS_PATH</filename> variable
as an example.
</note>
</para></listitem>
<listitem><para>
Look for any other errors, which probably mean that
introspection support in a package is not entirely
standard, and thus breaks down in a cross-compilation
environment.
For such cases, custom-made fixes are needed.
A good place to ask and receive help in these cases
is the
<ulink url='&YOCTO_DOCS_REF_URL;#resources-mailinglist'>Yocto Project mailing lists</ulink>.
</para></listitem>
</orderedlist>
<note>
Using a library that no longer builds against the latest
Yocto Project release and prints introspection related
errors is a good candidate for the previous procedure.
</note>
</para>
</section>
<section id='disabling-the-generation-of-introspection-data'>
<title>Disabling the Generation of Introspection Data</title>
<para>
You might find that you do not want to generate
introspection data.
Or, perhaps QEMU does not work on your build host and
target architecture combination.
If so, you can use either of the following methods to
disable GIR file generations:
<itemizedlist>
<listitem><para>
Add the following to your distro configuration:
<literallayout class='monospaced'>
DISTRO_FEATURES_BACKFILL_CONSIDERED = "gobject-introspection-data"
</literallayout>
Adding this statement disables generating
introspection data using QEMU but will still enable
building introspection tools and libraries
(i.e. building them does not require the use of QEMU).
</para></listitem>
<listitem><para>
Add the following to your machine configuration:
<literallayout class='monospaced'>
MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"
</literallayout>
Adding this statement disables the use of QEMU
when building packages for your machine.
Currently, this feature is used only by introspection
recipes and has the same effect as the previously
described option.
<note>
Future releases of the Yocto Project might have
other features affected by this option.
</note>
</para></listitem>
</itemizedlist>
If you disable introspection data, you can still
obtain it through other means such as copying the data
from a suitable sysroot, or by generating it on the
target hardware.
The OpenEmbedded build system does not currently
provide specific support for these techniques.
</para>
</section>
<section id='testing-that-introspection-works-in-an-image'>
<title>Testing that Introspection Works in an Image</title>
<para>
Use the following procedure to test if generating
introspection data is working in an image:
<orderedlist>
<listitem><para>
Make sure that "gobject-introspection-data" is not in
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>
and that "qemu-usermode" is not in
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES_BACKFILL_CONSIDERED'><filename>MACHINE_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
</para></listitem>
<listitem><para>
Build <filename>core-image-sato</filename>.
</para></listitem>
<listitem><para>
Launch a Terminal and then start Python in the
terminal.
</para></listitem>
<listitem><para>
Enter the following in the terminal:
<literallayout class='monospaced'>
>>> from gi.repository import GLib
>>> GLib.get_host_name()
</literallayout>
</para></listitem>
<listitem><para>
For something a little more advanced, enter the
following:
<literallayout class='monospaced'>
http://python-gtk-3-tutorial.readthedocs.org/en/latest/introduction.html
</literallayout>
</para></listitem>
</orderedlist>
</para>
</section>
<section id='known-issues'>
<title>Known Issues</title>
<para>
The following know issues exist for
GObject Introspection Support:
<itemizedlist>
<listitem><para>
<filename>qemu-ppc64</filename> immediately crashes.
Consequently, you cannot build introspection data on
that architecture.
</para></listitem>
<listitem><para>
x32 is not supported by QEMU.
Consequently, introspection data is disabled.
</para></listitem>
<listitem><para>
musl causes transient GLib binaries to crash on
assertion failures.
Consequently, generating introspection data is
disabled.
</para></listitem>
<listitem><para>
Because QEMU is not able to run the binaries correctly,
introspection is disabled for some specific packages
under specific architectures (e.g.
<filename>gcr</filename>,
<filename>libsecret</filename>, and
<filename>webkit</filename>).
</para></listitem>
<listitem><para>
QEMU usermode might not work properly when running
64-bit binaries under 32-bit host machines.
In particular, "qemumips64" is known to not work under
i686.
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
<section id='dev-optionally-using-an-external-toolchain'>
<title>Optionally Using an External Toolchain</title>
<para>
You might want to use an external toolchain as part of your
development.
If this is the case, the fundamental steps you need to accomplish
are as follows:
<itemizedlist>
<listitem><para>
Understand where the installed toolchain resides.
For cases where you need to build the external toolchain,
you would need to take separate steps to build and install
the toolchain.
</para></listitem>
<listitem><para>
Make sure you add the layer that contains the toolchain to
your <filename>bblayers.conf</filename> file through the
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
variable.
</para></listitem>
<listitem><para>
Set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNAL_TOOLCHAIN'><filename>EXTERNAL_TOOLCHAIN</filename></ulink>
variable in your <filename>local.conf</filename> file
to the location in which you installed the toolchain.
</para></listitem>
</itemizedlist>
A good example of an external toolchain used with the Yocto Project
is <trademark class='registered'>Mentor Graphics</trademark>
Sourcery G++ Toolchain.
You can see information on how to use that particular layer in the
<filename>README</filename> file at
<ulink url='http://github.com/MentorEmbedded/meta-sourcery/'></ulink>.
You can find further information by reading about the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TCMODE'><filename>TCMODE</filename></ulink>
variable in the Yocto Project Reference Manual's variable glossary.
</para>
</section>
<section id='creating-partitioned-images'>
<title>Creating Partitioned Images</title>
<para>
Creating an image for a particular hardware target using the
OpenEmbedded build system does not necessarily mean you can boot
that image as is on your device.
Physical devices accept and boot images in various ways depending
on the specifics of the device.
Usually, information about the hardware can tell you what image
format the device requires.
Should your device require multiple partitions on an SD card, flash,
or an HDD, you can use the OpenEmbedded Image Creator,
Wic, to create the properly partitioned image.
</para>
<para>
You can generate partitioned images
(<replaceable>image</replaceable><filename>.wic</filename>)
two ways: using the OpenEmbedded build system and by running
the OpenEmbedded Image Creator Wic directly.
The former way is preferable as it is easier to use and understand.
</para>
<section id='creating-wic-images-oe'>
<title>Creating Partitioned Images</title>
<para>
The OpenEmbedded build system can generate
partitioned images the same way as it generates
any other image type.
To generate a partitioned image, you need to modify
two variables.
<itemizedlist>
<listitem><para>
Include "wic" as part of the
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></ulink>
variable.
</para></listitem>
<listitem><para>
Include the name of the
<link linkend='openembedded-kickstart-wks-reference'>wic kickstart file</link>
as part of the
<ulink url='&YOCTO_DOCS_REF_URL;#var-WKS_FILE'><filename>WKS_FILE</filename></ulink>
variable
</para></listitem>
</itemizedlist>
Further steps to generate a partitioned image
are the same as for any other image type.
For information on image types, see the
"<link linkend='building-images'>Building Images</link>"
section.
</para>
</section>
<section id='create-wic-images-wic'>
<title>Using OpenEmbedded Image Creator Wic to Generate Partitioned Images</title>
<para>
The <filename>wic</filename> command generates partitioned
images from existing OpenEmbedded build artifacts.
Image generation is driven by partitioning commands
contained in an Openembedded kickstart file
(<filename>.wks</filename>) specified either directly on
the command line or as one of a selection of canned
<filename>.wks</filename> files as shown with the
<filename>wic list images</filename> command in the
"<link linkend='using-a-provided-kickstart-file'>Using an Existing Kickstart File</link>"
section.
When you apply the command to a given set of build
artifacts, the result is an image or set of images that
can be directly written onto media and used on a particular
system.
</para>
<para>
The <filename>wic</filename> command and the infrastructure
it is based on is by definition incomplete.
The purpose of the command is to allow the generation of
customized images, and as such, was designed to be
completely extensible through a plug-in interface.
See the
"<link linkend='openembedded-kickstart-plugins'>Plug-ins</link>"
section for information on these plug-ins.
</para>
<para>
This section provides some background information on Wic,
describes what you need to have in
place to run the tool, provides instruction on how to use
the <filename>wic</filename> utility,
and provides several examples.
</para>
<section id='wic-background'>
<title>Background</title>
<para>
This section provides some background on the
<filename>wic</filename> utility.
While none of this information is required to use
Wic, you might find it interesting.
<itemizedlist>
<listitem><para>
The name "Wic" is derived from OpenEmbedded
Image Creator (oeic).
The "oe" diphthong in "oeic" was promoted to the
letter "w", because "oeic" is both difficult to
remember and to pronounce.
</para></listitem>
<listitem><para>
Wic is loosely based on the
Meego Image Creator (<filename>mic</filename>)
framework.
The Wic implementation has been
heavily modified to make direct use of OpenEmbedded
build artifacts instead of package installation and
configuration, which are already incorporated within
the OpenEmbedded artifacts.
</para></listitem>
<listitem><para>
Wic is a completely independent
standalone utility that initially provides
easier-to-use and more flexible replacements for an
existing functionality in OE Core's
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-image-live'><filename>image-live</filename></ulink>
class and <filename>mkefidisk.sh</filename> script.
The difference between
Wic and those examples is
that with Wic the
functionality of those scripts is implemented
by a general-purpose partitioning language, which is
based on Redhat kickstart syntax.</para></listitem>
</itemizedlist>
</para>
</section>
<section id='wic-requirements'>
<title>Requirements</title>
<para>
In order to use the <filename>wic</filename> utility
with the OpenEmbedded Build system, your system needs
to meet the following requirements:
<itemizedlist>
<listitem><para>The Linux distribution on your
development host must support the Yocto Project.
See the
"<ulink url='&YOCTO_DOCS_REF_URL;#detailed-supported-distros'>Supported Linux Distributions</ulink>"
section in the Yocto Project Reference Manual for
the list of distributions that support the
Yocto Project.
</para></listitem>
<listitem><para>
The standard system utilities, such as
<filename>cp</filename>, must be installed on your
development host system.
</para></listitem>
<listitem><para>
You need to have the build artifacts already
available, which typically means that you must
have already created an image using the
Openembedded build system (e.g.
<filename>core-image-minimal</filename>).
While it might seem redundant to generate an image
in order to create an image using
Wic, the current version of
Wic requires the artifacts
in the form generated by the build system.
</para></listitem>
<listitem><para>
You must build several native tools, which are tools
built to run on the build system:
<literallayout class='monospaced'>
$ bitbake parted-native dosfstools-native mtools-native
</literallayout>
</para></listitem>
<listitem><para>
You must have sourced one of the build environment
setup scripts (i.e.
<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>)
found in the
<link linkend='build-directory'>Build Directory</link>.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='wic-getting-help'>
<title>Getting Help</title>
<para>
You can get general help for the <filename>wic</filename>
command by entering the <filename>wic</filename> command
by itself or by entering the command with a help argument
as follows:
<literallayout class='monospaced'>
$ wic -h
$ wic --help
</literallayout>
</para>
<para>
Currently, Wic supports two commands:
<filename>create</filename> and <filename>list</filename>.
You can get help for these commands as follows:
<literallayout class='monospaced'>
$ wic help <replaceable>command</replaceable>
with <replaceable>command</replaceable> being either
<filename>create</filename> or <filename>list</filename>.
</literallayout>
</para>
<para>
You can also get detailed help on a number of topics
from the help system.
The output of <filename>wic --help</filename>
displays a list of available help
topics under a "Help topics" heading.
You can have the help system display the help text for
a given topic by prefacing the topic with
<filename>wic help</filename>:
<literallayout class='monospaced'>
$ wic help <replaceable>help_topic</replaceable>
</literallayout>
</para>
<para>
You can find out more about the images
Wic creates using the existing
kickstart files with the following form of the command:
<literallayout class='monospaced'>
$ wic list <replaceable>image</replaceable> help
</literallayout>
with <filename><replaceable>image</replaceable></filename>
being either <filename>directdisk</filename> or
<filename>mkefidisk</filename>.
</para>
</section>
<section id='operational-modes'>
<title>Operational Modes</title>
<para>
You can use Wic in two different
modes, depending on how much control you need for
specifying the Openembedded build artifacts that are
used for creating the image: Raw and Cooked:
<itemizedlist>
<listitem><para>
<emphasis>Raw Mode:</emphasis>
You explicitly specify build artifacts through
command-line arguments.
</para></listitem>
<listitem><para>
<emphasis>Cooked Mode:</emphasis>
The current
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
setting and image name are used to automatically
locate and provide the build artifacts.
</para></listitem>
</itemizedlist>
</para>
<para>
Regardless of the mode you use, you need to have the build
artifacts ready and available.
Additionally, the environment must be set up using the
<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>
script found in the
<link linkend='build-directory'>Build Directory</link>.
</para>
<section id='raw-mode'>
<title>Raw Mode</title>
<para>
The general form of the
<filename>wic</filename> command in raw mode is:
<literallayout class='monospaced'>
$ wic create <replaceable>image_name</replaceable>.wks [<replaceable>options</replaceable>] [...]
Where:
<replaceable>image_name</replaceable>.wks
An OpenEmbedded kickstart file. You can provide
your own custom file or use a file from a set of
existing files as described by further options.
-o <replaceable>OUTDIR</replaceable>, --outdir=<replaceable>OUTDIR</replaceable>
The name of a directory in which to create image.
-i <replaceable>PROPERTIES_FILE</replaceable>, --infile=<replaceable>PROPERTIES_FILE</replaceable>
The name of a file containing the values for image
properties as a JSON file.
-e <replaceable>IMAGE_NAME</replaceable>, --image-name=<replaceable>IMAGE_NAME</replaceable>
The name of the image from which to use the artifacts
(e.g. <filename>core-image-sato</filename>).
-r <replaceable>ROOTFS_DIR</replaceable>, --rootfs-dir=<replaceable>ROOTFS_DIR</replaceable>
The path to the <filename>/rootfs</filename> directory to use as the
<filename>.wks</filename> rootfs source.
-b <replaceable>BOOTIMG_DIR</replaceable>, --bootimg-dir=<replaceable>BOOTIMG_DIR</replaceable>
The path to the directory containing the boot artifacts
(e.g. <filename>/EFI</filename> or <filename>/syslinux</filename>) to use as the <filename>.wks</filename> bootimg
source.
-k <replaceable>KERNEL_DIR</replaceable>, --kernel-dir=<replaceable>KERNEL_DIR</replaceable>
The path to the directory containing the kernel to use
in the <filename>.wks</filename> boot image.
-n <replaceable>NATIVE_SYSROOT</replaceable>, --native-sysroot=<replaceable>NATIVE_SYSROOT</replaceable>
The path to the native sysroot containing the tools to use
to build the image.
-s, --skip-build-check
Skips the build check.
-D, --debug
Output debug information.
</literallayout>
<note>
You do not need root privileges to run
Wic.
In fact, you should not run as root when using the
utility.
</note>
</para>
</section>
<section id='cooked-mode'>
<title>Cooked Mode</title>
<para>
The general form of the <filename>wic</filename> command
using Cooked Mode is:
<literallayout class='monospaced'>
$ wic create <replaceable>kickstart_file</replaceable> -e <replaceable>image_name</replaceable>
Where:
<replaceable>kickstart_file</replaceable>
An OpenEmbedded kickstart file. You can provide your own
custom file or a supplied file.
<replaceable>image_name</replaceable>
Specifies the image built using the OpenEmbedded build
system.
</literallayout>
This form is the simplest and most user-friendly, as it
does not require specifying all individual parameters.
All you need to provide is your own
<filename>.wks</filename> file or one provided with the
release.
</para>
</section>
</section>
<section id='using-a-provided-kickstart-file'>
<title>Using an Existing Kickstart File</title>
<para>
If you do not want to create your own
<filename>.wks</filename> file, you can use an existing
file provided by the Wic installation.
Use the following command to list the available files:
<literallayout class='monospaced'>
$ wic list images
directdisk Create a 'pcbios' direct disk image
mkefidisk Create an EFI disk image
</literallayout>
When you use an existing file, you do not have to use the
<filename>.wks</filename> extension.
Here is an example in Raw Mode that uses the
<filename>directdisk</filename> file:
<literallayout class='monospaced'>
$ wic create directdisk -r <replaceable>rootfs_dir</replaceable> -b <replaceable>bootimg_dir</replaceable> \
-k <replaceable>kernel_dir</replaceable> -n <replaceable>native_sysroot</replaceable>
</literallayout>
</para>
<para>
Here are the actual partition language commands
used in the <filename>mkefidisk.wks</filename> file to
generate an image:
<literallayout class='monospaced'>
# short-description: Create an EFI disk image
# long-description: Creates a partitioned EFI disk image that the user
# can directly dd to boot media.
part /boot --source bootimg-efi --ondisk sda --label msdos --active --align 1024
part / --source rootfs --ondisk sda --fstype=ext3 --label platform --align 1024
part swap --ondisk sda --size 44 --label swap1 --fstype=swap
bootloader --timeout=10 --append="rootwait rootfstype=ext3 console=ttyPCH0,115200 console=tty0 vmalloc=256MB snd-hda-intel.enable_msi=0"
</literallayout>
</para>
</section>
<section id='wic-usage-examples'>
<title>Examples</title>
<para>
This section provides several examples that show how to use
the <filename>wic</filename> utility.
All the examples assume the list of requirements in the
"<link linkend='wic-requirements'>Requirements</link>"
section have been met.
The examples assume the previously generated image is
<filename>core-image-minimal</filename>.
</para>
<section id='generate-an-image-using-a-provided-kickstart-file'>
<title>Generate an Image using an Existing Kickstart File</title>
<para>
This example runs in Cooked Mode and uses the
<filename>mkefidisk</filename> kickstart file:
<literallayout class='monospaced'>
$ wic create mkefidisk -e core-image-minimal
Checking basic build environment...
Done.
Creating image(s)...
Info: The new image(s) can be found here:
<replaceable>current_directory</replaceable>/build/mkefidisk-201310230946-sda.direct
The following build artifacts were used to create the image(s):
ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/minnow-poky-linux/core-image-minimal/1.0-r0/rootfs
BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/work/minnow-poky-linux/core-image-minimal/1.0-r0/core-image-minimal-1.0/hddimg
KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/minnow/usr/src/kernel
NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux
The image(s) were created using OE kickstart file:
/home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/mkefidisk.wks
</literallayout>
The previous example shows the easiest way to create
an image by running in Cooked Mode and using the
<filename>-e</filename> option with an existing
kickstart file.
All that is necessary is to specify the image used to
generate the artifacts.
Your <filename>local.conf</filename> needs to have the
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
variable set to the machine you are using, which is
"minnow" in this example.
</para>
<para>
The output specifies the exact image created as well as
where it was created, which is in the current
directory by default.
The output also names the artifacts used and the exact
<filename>.wks</filename> script that was used to
generate the image.
<note>
You should always verify the details provided in the
output to make sure that the image was indeed
created exactly as expected.
</note>
</para>
<para>
Continuing with the example, you can now write the
image to a USB stick, or whatever media for which you
built your image, and boot the resulting media.
You can write the image by using
<filename>bmaptool</filename> or
<filename>dd</filename>:
<literallayout class='monospaced'>
$ oe-run-native bmaptool copy build/mkefidisk-201310230946-sda.direct /dev/sd<replaceable>X</replaceable>
</literallayout>
or
<literallayout class='monospaced'>
$ sudo dd if=build/mkefidisk-201310230946-sda.direct of=/dev/sd<replaceable>X</replaceable>
</literallayout>
<note>
For more information on how to use the
<filename>bmaptool</filename> to flash a device
with an image, see the
"<link linkend='flashing-images-using-bmaptool'>Flashing Images Using <filename>bmaptool</filename></link>"
section.
</note>
</para>
</section>
<section id='using-a-modified-kickstart-file'>
<title>Using a Modified Kickstart File</title>
<para>
Because partitioned image creation is
driven by the kickstart file, it is easy to affect
image creation by changing the parameters in the file.
This next example demonstrates that through modification
of the <filename>directdisk</filename> kickstart file.
</para>
<para>
As mentioned earlier, you can use the command
<filename>wic list images</filename> to show the list
of existing kickstart files.
The directory in which these files reside is
<filename>scripts/lib/image/canned-wks/</filename>
located in the
<link linkend='source-directory'>Source Directory</link>.
Because the available files reside in this directory,
you can create and add your own custom files to the
directory.
Subsequent use of the
<filename>wic list images</filename> command would then
include your kickstart files.
</para>
<para>
In this example, the existing
<filename>directdisk</filename> file already does most
of what is needed.
However, for the hardware in this example, the image
will need to boot from <filename>sdb</filename> instead
of <filename>sda</filename>, which is what the
<filename>directdisk</filename> kickstart file uses.
</para>
<para>
The example begins by making a copy of the
<filename>directdisk.wks</filename> file in the
<filename>scripts/lib/image/canned-wks</filename>
directory and then by changing the lines that specify
the target disk from which to boot.
<literallayout class='monospaced'>
$ cp /home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisk.wks \
/home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisksdb.wks
</literallayout>
Next, the example modifies the
<filename>directdisksdb.wks</filename> file and changes
all instances of "<filename>--ondisk sda</filename>"
to "<filename>--ondisk sdb</filename>".
The example changes the following two lines and leaves
the remaining lines untouched:
<literallayout class='monospaced'>
part /boot --source bootimg-pcbios --ondisk sdb --label boot --active --align 1024
part / --source rootfs --ondisk sdb --fstype=ext3 --label platform --align 1024
</literallayout>
Once the lines are changed, the example generates the
<filename>directdisksdb</filename> image.
The command points the process at the
<filename>core-image-minimal</filename> artifacts for
the Next Unit of Computing (nuc)
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
the <filename>local.conf</filename>.
<literallayout class='monospaced'>
$ wic create directdisksdb -e core-image-minimal
Checking basic build environment...
Done.
Creating image(s)...
Info: The new image(s) can be found here:
<replaceable>current_directory</replaceable>/build/directdisksdb-201310231131-sdb.direct
The following build artifacts were used to create the image(s):
ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/nuc-poky-linux/core-image-minimal/1.0-r0/rootfs
BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/nuc/usr/share
KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/nuc/usr/src/kernel
NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux
The image(s) were created using OE kickstart file:
/home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisksdb.wks
</literallayout>
Continuing with the example, you can now directly
<filename>dd</filename> the image to a USB stick, or
whatever media for which you built your image,
and boot the resulting media:
<literallayout class='monospaced'>
$ sudo dd if=build/directdisksdb-201310231131-sdb.direct of=/dev/sdb
86018+0 records in
86018+0 records out
44041216 bytes (44 MB) copied, 13.0734 s, 3.4 MB/s
[trz at empanada tmp]$ sudo eject /dev/sdb
</literallayout>
</para>
</section>
<section id='creating-an-image-based-on-core-image-minimal-and-crownbay-noemgd'>
<title>Creating an Image Based on <filename>core-image-minimal</filename> and <filename>crownbay-noemgd</filename></title>
<para>
This example creates an image based on
<filename>core-image-minimal</filename> and a
<filename>crownbay-noemgd</filename>
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
that works right out of the box.
<literallayout class='monospaced'>
$ wic create directdisk -e core-image-minimal
Checking basic build environment...
Done.
Creating image(s)...
Info: The new image(s) can be found here:
<replaceable>current_directory</replaceable>/build/directdisk-201309252350-sda.direct
The following build artifacts were used to create the image(s):
ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs
BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share
KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
The image(s) were created using OE kickstart file:
/home/trz/yocto/yocto-image/scripts/lib/image/canned-wks/directdisk.wks
</literallayout>
</para>
</section>
<section id='using-a-modified-kickstart-file-and-running-in-raw-mode'>
<title>Using a Modified Kickstart File and Running in Raw Mode</title>
<para>
This next example manually specifies each build artifact
(runs in Raw Mode) and uses a modified kickstart file.
The example also uses the <filename>-o</filename> option
to cause Wic to create the output
somewhere other than the default output directory,
which is the current directory:
<literallayout class='monospaced'>
$ wic create ~/test.wks -o /home/trz/testwic --rootfs-dir \
/home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs \
--bootimg-dir /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share \
--kernel-dir /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel \
--native-sysroot /home/trz/yocto/yocto-image/build/tmp/sysroots/x86_64-linux
Creating image(s)...
Info: The new image(s) can be found here:
/home/trz/testwic/build/test-201309260032-sda.direct
The following build artifacts were used to create the image(s):
ROOTFS_DIR: /home/trz/yocto/yocto-image/build/tmp/work/crownbay_noemgd-poky-linux/core-image-minimal/1.0-r0/rootfs
BOOTIMG_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/share
KERNEL_DIR: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
NATIVE_SYSROOT: /home/trz/yocto/yocto-image/build/tmp/sysroots/crownbay-noemgd/usr/src/kernel
The image(s) were created using OE kickstart file:
/home/trz/test.wks
</literallayout>
For this example,
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
did not have to be specified in the
<filename>local.conf</filename> file since the
artifact is manually specified.
</para>
</section>
</section>
<section id='openembedded-kickstart-plugins'>
<title>Plug-ins</title>
<para>
Plug-ins allow Wic functionality to
be extended and specialized by users.
This section documents the plug-in interface, which is
currently restricted to source plug-ins.
</para>
<para>
Source plug-ins provide a mechanism to customize
various aspects of the image generation process in
Wic, mainly the contents of
partitions.
The plug-ins provide a mechanism for mapping values
specified in <filename>.wks</filename> files using the
<filename>--source</filename> keyword to a
particular plug-in implementation that populates a
corresponding partition.
<note>
If you use plug-ins that have build-time dependencies
(e.g. native tools, bootloaders, and so forth)
when building a Wic image, you need to specify those
dependencies using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-WKS_FILE_DEPENDS'><filename>WKS_FILE_DEPENDS</filename></ulink>
variable.
</note>
</para>
<para>
A source plug-in is created as a subclass of
<filename>SourcePlugin</filename>.
The plug-in file containing it is added to
<filename>scripts/lib/wic/plugins/source/</filename> to
make the plug-in implementation available to the
Wic implementation.
For more information, see
<filename>scripts/lib/wic/pluginbase.py</filename>.
</para>
<para>
Source plug-ins can also be implemented and added by
external layers.
As such, any plug-ins found in a
<filename>scripts/lib/wic/plugins/source/</filename>
directory in an external layer are also made
available.
</para>
<para>
When the Wic implementation needs
to invoke a partition-specific implementation, it looks
for the plug-in that has the same name as the
<filename>--source</filename> parameter given to
that partition.
For example, if the partition is set up as follows:
<literallayout class='monospaced'>
part /boot --source bootimg-pcbios ...
</literallayout>
The methods defined as class members of the plug-in
having the matching <filename>bootimg-pcbios.name</filename>
class member are used.
</para>
<para>
To be more concrete, here is the plug-in definition that
matches a
<filename>--source bootimg-pcbios</filename> usage,
along with an example
method called by the Wic implementation
when it needs to invoke an implementation-specific
partition-preparation function:
<literallayout class='monospaced'>
class BootimgPcbiosPlugin(SourcePlugin):
name = 'bootimg-pcbios'
@classmethod
def do_prepare_partition(self, part, ...)
</literallayout>
If the subclass itself does not implement a function, a
default version in a superclass is located and
used, which is why all plug-ins must be derived from
<filename>SourcePlugin</filename>.
</para>
<para>
The <filename>SourcePlugin</filename> class defines the
following methods, which is the current set of methods
that can be implemented or overridden by
<filename>--source</filename> plug-ins.
Any methods not implemented by a
<filename>SourcePlugin</filename> subclass inherit the
implementations present in the
<filename>SourcePlugin</filename> class.
For more information, see the
<filename>SourcePlugin</filename> source for details:
</para>
<para>
<itemizedlist>
<listitem><para>
<emphasis><filename>do_prepare_partition()</filename>:</emphasis>
Called to do the actual content population for a
partition.
In other words, the method prepares the final
partition image that is incorporated into the
disk image.
</para></listitem>
<listitem><para>
<emphasis><filename>do_configure_partition()</filename>:</emphasis>
Called before
<filename>do_prepare_partition()</filename>.
This method is typically used to create custom
configuration files for a partition (e.g. syslinux
or grub configuration files).
</para></listitem>
<listitem><para>
<emphasis><filename>do_install_disk()</filename>:</emphasis>
Called after all partitions have been prepared and
assembled into a disk image.
This method provides a hook to allow finalization
of a disk image, (e.g. writing an MBR).
</para></listitem>
<listitem><para>
<emphasis><filename>do_stage_partition()</filename>:</emphasis>
Special content-staging hook called before
<filename>do_prepare_partition()</filename>.
This method is normally empty.</para>
<para>Typically, a partition just uses the passed-in
parameters (e.g. the unmodified value of
<filename>bootimg_dir</filename>).
However, in some cases things might need to be
more tailored.
As an example, certain files might additionally
need to be taken from
<filename>bootimg_dir + /boot</filename>.
This hook allows those files to be staged in a
customized fashion.
<note>
<filename>get_bitbake_var()</filename>
allows you to access non-standard variables
that you might want to use for this.
</note>
</para></listitem>
</itemizedlist>
</para>
<para>
This scheme is extensible.
Adding more hooks is a simple matter of adding more
plug-in methods to <filename>SourcePlugin</filename> and
derived classes.
The code that then needs to call the plug-in methods uses
<filename>plugin.get_source_plugin_methods()</filename>
to find the method or methods needed by the call.
Retrieval of those methods is accomplished
by filling up a dict with keys
containing the method names of interest.
On success, these will be filled in with the actual
methods.
Please see the Wic
implementation for examples and details.
</para>
</section>
<section id='openembedded-kickstart-wks-reference'>
<title>OpenEmbedded Kickstart (<filename>.wks</filename>) Reference</title>
<para>
The current Wic implementation supports
only the basic kickstart partitioning commands:
<filename>partition</filename> (or <filename>part</filename>
for short) and <filename>bootloader</filename>.
<note>
Future updates will implement more commands and options.
If you use anything that is not specifically
supported, results can be unpredictable.
</note>
</para>
<para>
The following is a list of the commands, their syntax,
and meanings.
The commands are based on the Fedora
kickstart versions but with modifications to
reflect Wic capabilities.
You can see the original documentation for those commands
at the following links:
<itemizedlist>
<listitem><para>
<ulink url='http://fedoraproject.org/wiki/Anaconda/Kickstart#part_or_partition'>http://fedoraproject.org/wiki/Anaconda/Kickstart#part_or_partition</ulink>
</para></listitem>
<listitem><para>
<ulink url='http://fedoraproject.org/wiki/Anaconda/Kickstart#bootloader'>http://fedoraproject.org/wiki/Anaconda/Kickstart#bootloader</ulink>
</para></listitem>
</itemizedlist>
</para>
<section id='command-part-or-partition'>
<title>Command: part or partition</title>
<para>
Either of these commands create a partition on the system
and use the following syntax:
<literallayout class='monospaced'>
part [<replaceable>mntpoint</replaceable>]
partition [<replaceable>mntpoint</replaceable>]
</literallayout>
If you do not provide
<replaceable>mntpoint</replaceable>, Wic creates a
partition but does not mount it.
</para>
<para>
The
<filename><replaceable>mntpoint</replaceable></filename>
is where the partition will be mounted and must be of
one of the following forms:
<itemizedlist>
<listitem><para>
<filename>/<replaceable>path</replaceable></filename>:
For example, "/", "/usr", or "/home"
</para></listitem>
<listitem><para>
<filename>swap</filename>:
The created partition is used as swap space.
</para></listitem>
</itemizedlist>
</para>
<para>
Specifying a <replaceable>mntpoint</replaceable> causes
the partition to automatically be mounted.
Wic achieves this by adding entries to the filesystem
table (fstab) during image generation.
In order for wic to generate a valid fstab, you must
also provide one of the <filename>--ondrive</filename>,
<filename>--ondisk</filename>, or
<filename>--use-uuid</filename> partition options as
part of the command.
Here is an example using "/" as the mountpoint.
The command uses "--ondisk" to force the partition onto
the <filename>sdb</filename> disk:
<literallayout class='monospaced'>
part / --source rootfs --ondisk sdb --fstype=ext3 --label platform --align 1024
</literallayout>
</para>
<para>
Here is a list that describes other supported options
you can use with the <filename>part</filename> and
<filename>partition</filename> commands:
<itemizedlist>
<listitem><para>
<emphasis><filename>--size</filename>:</emphasis>
The minimum partition size in MBytes.
Specify an integer value such as 500.
Do not append the number with "MB".
You do not need this option if you use
<filename>--source</filename>.
</para></listitem>
<listitem><para>
<emphasis><filename>--source</filename>:</emphasis>
This option is a
Wic-specific option that
names the source of the data that populates
the partition.
The most common value for this option is
"rootfs", but you can use any value that maps to
a valid source plug-in.
For information on the source plug-ins, see the
"<link linkend='openembedded-kickstart-plugins'>Plug-ins</link>"
section.</para>
<para>If you use
<filename>--source rootfs</filename>,
Wic creates a partition as
large as needed and to fill it with the contents
of the root filesystem pointed to by the
<filename>-r</filename> command-line option
or the equivalent rootfs derived from the
<filename>-e</filename> command-line
option.
The filesystem type used to create the
partition is driven by the value of the
<filename>--fstype</filename> option
specified for the partition.
See the entry on
<filename>--fstype</filename> that
follows for more information.
</para>
<para>If you use
<filename>--source <replaceable>plugin-name</replaceable></filename>,
Wic creates a partition as
large as needed and fills it with the contents
of the partition that is generated by the
specified plug-in name using the data pointed
to by the <filename>-r</filename> command-line
option or the equivalent rootfs derived from the
<filename>-e</filename> command-line
option.
Exactly what those contents and filesystem type
end up being are dependent on the given plug-in
implementation.
</para>
<para>If you do not use the
<filename>--source</filename> option, the
<filename>wic</filename> command creates an
empty partition.
Consequently, you must use the
<filename>--size</filename> option to specify
the size of the empty partition.
</para></listitem>
<listitem><para>
<emphasis><filename>--ondisk</filename> or <filename>--ondrive</filename>:</emphasis>
Forces the partition to be created on a
particular disk.
</para></listitem>
<listitem><para>
<emphasis><filename>--fstype</filename>:</emphasis>
Sets the file system type for the partition.
Valid values are:
<itemizedlist>
<listitem><para><filename>ext4</filename>
</para></listitem>
<listitem><para><filename>ext3</filename>
</para></listitem>
<listitem><para><filename>ext2</filename>
</para></listitem>
<listitem><para><filename>btrfs</filename>
</para></listitem>
<listitem><para><filename>squashfs</filename>
</para></listitem>
<listitem><para><filename>swap</filename>
</para></listitem>
</itemizedlist>
</para></listitem>
<listitem><para>
<emphasis><filename>--fsoptions</filename>:</emphasis>
Specifies a free-form string of options to be
used when mounting the filesystem.
This string will be copied into the
<filename>/etc/fstab</filename> file of the
installed system and should be enclosed in
quotes.
If not specified, the default string
is "defaults".
</para></listitem>
<listitem><para>
<emphasis><filename>--label label</filename>:</emphasis>
Specifies the label to give to the filesystem to
be made on the partition.
If the given label is already in use by another
filesystem, a new label is created for the
partition.
</para></listitem>
<listitem><para>
<emphasis><filename>--active</filename>:</emphasis>
Marks the partition as active.
</para></listitem>
<listitem><para>
<emphasis><filename>--align (in KBytes)</filename>:</emphasis>
This option is a
Wic-specific option that
says to start a partition on an
<replaceable>x</replaceable> KBytes
boundary.</para></listitem>
<listitem><para>
<emphasis><filename>--no-table</filename>:</emphasis>
This option is a
Wic-specific option.
Using the option reserves space for the
partition and causes it to become populated.
However, the partition is not added to the
partition table.
</para></listitem>
<listitem><para>
<emphasis><filename>--extra-space</filename>:</emphasis>
This option is a
Wic-specific option that
adds extra space after the space filled by the
content of the partition.
The final size can go beyond the size specified
by the <filename>--size</filename> option.
The default value is 10 Mbytes.
</para></listitem>
<listitem><para>
<emphasis><filename>--overhead-factor</filename>:</emphasis>
This option is a
Wic-specific option that
multiplies the size of the partition by the
option's value.
You must supply a value greater than or equal to
"1".
The default value is "1.3".
</para></listitem>
<listitem><para>
<emphasis><filename>--part-type</filename>:</emphasis>
This option is a
Wic-specific option that
specifies the partition type globally
unique identifier (GUID) for GPT partitions.
You can find the list of partition type GUIDs
at
<ulink url='http://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs'></ulink>.
</para></listitem>
<listitem><para>
<emphasis><filename>--use-uuid</filename>:</emphasis>
This option is a
Wic-specific option that
causes Wic to generate a
random GUID for the partition.
The generated identifier is used in the
bootloader configuration to specify the root
partition.
</para></listitem>
<listitem><para>
<emphasis><filename>--uuid</filename>:</emphasis>
This option is a
Wic-specific
option that specifies the partition UUID.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='command-bootloader'>
<title>Command: bootloader</title>
<para>
This command specifies how the bootloader should be
configured and supports the following options:
<note>
Bootloader functionality and boot partitions are
implemented by the various
<filename>--source</filename>
plug-ins that implement bootloader functionality.
The bootloader command essentially provides a
means of modifying bootloader configuration.
</note>
<itemizedlist>
<listitem><para>
<emphasis><filename>--timeout</filename>:</emphasis>
Specifies the number of seconds before the
bootloader times out and boots the default
option.
</para></listitem>
<listitem><para>
<emphasis><filename>--append</filename>:</emphasis>
Specifies kernel parameters.
These parameters will be added to the syslinux
<filename>APPEND</filename> or
<filename>grub</filename> kernel command line.
</para></listitem>
<listitem><para>
<emphasis><filename>--configfile</filename>:</emphasis>
Specifies a user-defined configuration file for
the bootloader.
You can provide a full pathname for the file or
a file that exists in the
<filename>canned-wks</filename> folder.
This option overrides all other bootloader
options.
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
</section>
</section>
<section id='building-an-initramfs-image'>
<title>Building an Initial RAM Filesystem (initramfs) Image</title>
<para>
initramfs is the successor of Initial RAM Disk (initrd).
It is a "copy in and out" (cpio) archive of the initial file system
that gets loaded into memory during the Linux startup process.
Because Linux uses the contents of the archive during
initialization, the initramfs needs to contain all of the device
drivers and tools needed to mount the final root filesystem.
</para>
<para>
To build an initramfs image and bundle it into the kernel, set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink>
variable in your <filename>local.conf</filename> file, and set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE'><filename>INITRAMFS_IMAGE</filename></ulink>
variable in your <filename>machine.conf</filename> file:
<literallayout class='monospaced'>
INITRAMFS_IMAGE_BUNDLE = "1"
INITRAMFS_IMAGE = "<replaceable>image_recipe_name</replaceable>"
</literallayout>
Setting the <filename>INITRAMFS_IMAGE_BUNDLE</filename>
flag causes the initramfs created by the recipe and defined by
<filename>INITRAMFS_IMAGE</filename> to be unpacked into the
<filename>${B}/usr/</filename> directory.
The unpacked initramfs is then passed to the kernel's
<filename>Makefile</filename> using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-CONFIG_INITRAMFS_SOURCE'><filename>CONFIG_INITRAMFS_SOURCE</filename></ulink>
variable, allowing initramfs to be built in to the kernel
normally.
<note>
The preferred method is to use the
<filename>INITRAMFS_IMAGE</filename> variable rather than the
<filename>INITRAMFS_TASK</filename> variable.
Setting <filename>INITRAMFS_TASK</filename> is supported for
backward compatibility.
However, use of this variable has circular dependency
problems.
See the
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_IMAGE_BUNDLE'><filename>INITRAMFS_IMAGE_BUNDLE</filename></ulink>
variable for additional information on these dependency
problems.
</note>
</para>
<para>
The recipe that <filename>INITRAMFS_IMAGE</filename>
points to must produce a <filename>.cpio.gz</filename>,
<filename>.cpio.tar</filename>, <filename>.cpio.lz4</filename>,
<filename>.cpio.lzma</filename>, or
<filename>.cpio.xz</filename> file.
You can ensure you produce one of these <filename>.cpio.*</filename>
files by setting the
<ulink url='&YOCTO_DOCS_REF_URL;#var-INITRAMFS_FSTYPES'><filename>INITRAMFS_FSTYPES</filename></ulink>
variable in your configuration file to one or more of the above
file types.
<note>
If you add items to the initramfs image by way of its recipe,
you should use
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_INSTALL'><filename>PACKAGE_INSTALL</filename></ulink>
rather than
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>.
<filename>PACKAGE_INSTALL</filename> gives more direct control
of what is added to the image as compared to the defaults you
might not necessarily want that are set by the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-image'><filename>image</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-core-image'><filename>core-image</filename></ulink>
classes.
</note>
</para>
</section>
<section id='configuring-the-kernel'>
<title>Configuring the Kernel</title>
<para>
Configuring the Yocto Project kernel consists of making sure the
<filename>.config</filename> file has all the right information
in it for the image you are building.
You can use the <filename>menuconfig</filename> tool and
configuration fragments to make sure your
<filename>.config</filename> file is just how you need it.
You can also save known configurations in a
<filename>defconfig</filename> file that the build system can use
for kernel configuration.
</para>
<para>
This section describes how to use <filename>menuconfig</filename>,
create and use configuration fragments, and how to interactively
modify your <filename>.config</filename> file to create the
leanest kernel configuration file possible.
</para>
<para>
For more information on kernel configuration, see the
"<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
section in the Yocto Project Linux Kernel Development Manual.
</para>
<section id='using-menuconfig'>
<title>Using&nbsp;&nbsp;<filename>menuconfig</filename></title>
<para>
The easiest way to define kernel configurations is to set them through the
<filename>menuconfig</filename> tool.
This tool provides an interactive method with which
to set kernel configurations.
For general information on <filename>menuconfig</filename>, see
<ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
</para>
<para>
To use the <filename>menuconfig</filename> tool in the Yocto Project development
environment, you must launch it using BitBake.
Thus, the environment must be set up using the
<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#structure-memres-core-script'><filename>oe-init-build-env-memres</filename></ulink>
script found in the
<link linkend='build-directory'>Build Directory</link>.
You must also be sure of the state of your build in the
<link linkend='source-directory'>Source Directory</link>.
The following commands run <filename>menuconfig</filename>
assuming the Source Directory's top-level folder is
<filename>~/poky</filename>:
<literallayout class='monospaced'>
$ cd poky
$ source oe-init-build-env
$ bitbake linux-yocto -c kernel_configme -f
$ bitbake linux-yocto -c menuconfig
</literallayout>
Once <filename>menuconfig</filename> comes up, its standard
interface allows you to interactively examine and configure
all the kernel configuration parameters.
After making your changes, simply exit the tool and save your
changes to create an updated version of the
<filename>.config</filename> configuration file.
</para>
<para>
Consider an example that configures the <filename>linux-yocto-3.14</filename>
kernel.
The OpenEmbedded build system recognizes this kernel as
<filename>linux-yocto</filename>.
Thus, the following commands from the shell in which you previously sourced the
environment initialization script cleans the shared state cache and the
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
directory and then runs <filename>menuconfig</filename>:
<literallayout class='monospaced'>
$ bitbake linux-yocto -c menuconfig
</literallayout>
</para>
<para>
Once <filename>menuconfig</filename> launches, use the interface
to navigate through the selections to find the configuration settings in
which you are interested.
For example, consider the <filename>CONFIG_SMP</filename> configuration setting.
You can find it at <filename>Processor Type and Features</filename> under
the configuration selection <filename>Symmetric Multi-processing Support</filename>.
After highlighting the selection, use the arrow keys to select or deselect
the setting.
When you are finished with all your selections, exit out and save them.
</para>
<para>
Saving the selections updates the <filename>.config</filename> configuration file.
This is the file that the OpenEmbedded build system uses to configure the
kernel during the build.
You can find and examine this file in the Build Directory in
<filename>tmp/work/</filename>.
The actual <filename>.config</filename> is located in the area where the
specific kernel is built.
For example, if you were building a Linux Yocto kernel based on the
Linux 3.14 kernel and you were building a QEMU image targeted for
<filename>x86</filename> architecture, the
<filename>.config</filename> file would be located here:
<literallayout class='monospaced'>
poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.14.11+git1+84f...
...656ed30-r1/linux-qemux86-standard-build
</literallayout>
<note>
The previous example directory is artificially split and many of the characters
in the actual filename are omitted in order to make it more readable.
Also, depending on the kernel you are using, the exact pathname
for <filename>linux-yocto-3.14...</filename> might differ.
</note>
</para>
<para>
Within the <filename>.config</filename> file, you can see the kernel settings.
For example, the following entry shows that symmetric multi-processor support
is not set:
<literallayout class='monospaced'>
# CONFIG_SMP is not set
</literallayout>
</para>
<para>
A good method to isolate changed configurations is to use a combination of the
<filename>menuconfig</filename> tool and simple shell commands.
Before changing configurations with <filename>menuconfig</filename>, copy the
existing <filename>.config</filename> and rename it to something else,
use <filename>menuconfig</filename> to make
as many changes as you want and save them, then compare the renamed configuration
file against the newly created file.
You can use the resulting differences as your base to create configuration fragments
to permanently save in your kernel layer.
<note>
Be sure to make a copy of the <filename>.config</filename> and don't just
rename it.
The build system needs an existing <filename>.config</filename>
from which to work.
</note>
</para>
</section>
<section id='creating-a-defconfig-file'>
<title>Creating a&nbsp;&nbsp;<filename>defconfig</filename> File</title>
<para>
A <filename>defconfig</filename> file is simply a
<filename>.config</filename> renamed to "defconfig".
You can use a <filename>defconfig</filename> file
to retain a known set of kernel configurations from which the
OpenEmbedded build system can draw to create the final
<filename>.config</filename> file.
<note>
Out-of-the-box, the Yocto Project never ships a
<filename>defconfig</filename> or
<filename>.config</filename> file.
The OpenEmbedded build system creates the final
<filename>.config</filename> file used to configure the
kernel.
</note>
</para>
<para>
To create a <filename>defconfig</filename>, start with a
complete, working Linux kernel <filename>.config</filename>
file.
Copy that file to the appropriate
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
directory in your layer's
<filename>recipes-kernel/linux</filename> directory, and rename
the copied file to "defconfig".
Then, add the following lines to the linux-yocto
<filename>.bbappend</filename> file in your layer:
<literallayout class='monospaced'>
FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
SRC_URI += "file://defconfig"
</literallayout>
The
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
tells the build system how to search for the file, while the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
extends the
<ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
variable (search directories) to include the
<filename>${PN}</filename> directory you created to hold the
configuration changes.
<note>
The build system applies the configurations from the
<filename>defconfig</filename> file before applying any
subsequent configuration fragments.
The final kernel configuration is a combination of the
configurations in the <filename>defconfig</filename>
file and any configuration fragments you provide.
You need to realize that if you have any configuration
fragments, the build system applies these on top of and
after applying the existing defconfig file configurations.
</note>
For more information on configuring the kernel, see the
"<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
and
"<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'>Generating Configuration Files</ulink>"
sections, both in the Yocto Project Linux Kernel Development
Manual.
</para>
</section>
<section id='creating-config-fragments'>
<title>Creating Configuration Fragments</title>
<para>
Configuration fragments are simply kernel options that appear in a file
placed where the OpenEmbedded build system can find and apply them.
Syntactically, the configuration statement is identical to what would appear
in the <filename>.config</filename> file, which is in the
<link linkend='build-directory'>Build Directory</link>:
<literallayout class='monospaced'>
tmp/work/<replaceable>arch</replaceable>-poky-linux/linux-yocto-<replaceable>release_specific_string</replaceable>/linux-<replaceable>arch</replaceable>-<replaceable>build_type</replaceable>
</literallayout>
</para>
<para>
It is simple to create a configuration fragment.
For example, issuing the following from the shell creates a configuration fragment
file named <filename>my_smp.cfg</filename> that enables multi-processor support
within the kernel:
<literallayout class='monospaced'>
$ echo "CONFIG_SMP=y" >> my_smp.cfg
</literallayout>
<note>
All configuration fragment files must use the
<filename>.cfg</filename> extension in order for the
OpenEmbedded build system to recognize them as a
configuration fragment.
</note>
</para>
<para>
Where do you put your configuration fragment files?
You can place these files in the same area pointed to by
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
The OpenEmbedded build system picks up the configuration and
adds it to the kernel's configuration.
For example, suppose you had a set of configuration options
in a file called <filename>myconfig.cfg</filename>.
If you put that file inside a directory named
<filename>linux-yocto</filename> that resides in the same
directory as the kernel's append file and then add a
<filename>SRC_URI</filename> statement such as the following
to the kernel's append file, those configuration options
will be picked up and applied when the kernel is built.
<literallayout class='monospaced'>
SRC_URI += "file://myconfig.cfg"
</literallayout>
</para>
<para>
As mentioned earlier, you can group related configurations into multiple files and
name them all in the <filename>SRC_URI</filename> statement as well.
For example, you could group separate configurations specifically for Ethernet and graphics
into their own files and add those by using a <filename>SRC_URI</filename> statement like the
following in your append file:
<literallayout class='monospaced'>
SRC_URI += "file://myconfig.cfg \
file://eth.cfg \
file://gfx.cfg"
</literallayout>
</para>
</section>
<section id='fine-tuning-the-kernel-configuration-file'>
<title>Fine-Tuning the Kernel Configuration File</title>
<para>
You can make sure the <filename>.config</filename> file is as lean or efficient as
possible by reading the output of the kernel configuration fragment audit,
noting any issues, making changes to correct the issues, and then repeating.
</para>
<para>
As part of the kernel build process, the
<filename>do_kernel_configcheck</filename> task runs.
This task validates the kernel configuration by checking the final
<filename>.config</filename> file against the input files.
During the check, the task produces warning messages for the following
issues:
<itemizedlist>
<listitem><para>Requested options that did not make the final
<filename>.config</filename> file.</para></listitem>
<listitem><para>Configuration items that appear twice in the same
configuration fragment.</para></listitem>
<listitem><para>Configuration items tagged as "required" that were overridden.
</para></listitem>
<listitem><para>A board overrides a non-board specific option.</para></listitem>
<listitem><para>Listed options not valid for the kernel being processed.
In other words, the option does not appear anywhere.</para></listitem>
</itemizedlist>
<note>
The <filename>do_kernel_configcheck</filename> task can
also optionally report if an option is overridden during
processing.
</note>
</para>
<para>
For each output warning, a message points to the file
that contains a list of the options and a pointer to the
configuration fragment that defines them.
Collectively, the files are the key to streamlining the
configuration.
</para>
<para>
To streamline the configuration, do the following:
<orderedlist>
<listitem><para>Start with a full configuration that you
know works - it builds and boots successfully.
This configuration file will be your baseline.
</para></listitem>
<listitem><para>Separately run the
<filename>do_kernel_configme</filename> and
<filename>do_kernel_configcheck</filename> tasks.
</para></listitem>
<listitem><para>Take the resulting list of files from the
<filename>do_kernel_configcheck</filename> task
warnings and do the following:
<itemizedlist>
<listitem><para>
Drop values that are redefined in the fragment
but do not change the final
<filename>.config</filename> file.
</para></listitem>
<listitem><para>
Analyze and potentially drop values from the
<filename>.config</filename> file that override
required configurations.
</para></listitem>
<listitem><para>
Analyze and potentially remove non-board
specific options.
</para></listitem>
<listitem><para>
Remove repeated and invalid options.
</para></listitem>
</itemizedlist></para></listitem>
<listitem><para>
After you have worked through the output of the kernel
configuration audit, you can re-run the
<filename>do_kernel_configme</filename> and
<filename>do_kernel_configcheck</filename> tasks to
see the results of your changes.
If you have more issues, you can deal with them as
described in the previous step.
</para></listitem>
</orderedlist>
</para>
<para>
Iteratively working through steps two through four eventually yields
a minimal, streamlined configuration file.
Once you have the best <filename>.config</filename>, you can build the Linux
Yocto kernel.
</para>
</section>
<section id='determining-hardware-and-non-hardware-features-for-the-kernel-configuration-audit-phase'>
<title>Determining Hardware and Non-Hardware Features for the Kernel Configuration Audit Phase</title>
<para>
This section describes part of the kernel configuration audit
phase that most developers can ignore.
During this part of the audit phase, the contents of the final
<filename>.config</filename> file are compared against the
fragments specified by the system.
These fragments can be system fragments, distro fragments,
or user specified configuration elements.
Regardless of their origin, the OpenEmbedded build system
warns the user if a specific option is not included in the
final kernel configuration.
</para>
<para>
In order to not overwhelm the user with configuration warnings,
by default the system only reports on missing "hardware"
options because a missing hardware option could mean a boot
failure or that important hardware is not available.
</para>
<para>
To determine whether or not a given option is "hardware" or
"non-hardware", the kernel Metadata contains files that
classify individual or groups of options as either hardware
or non-hardware.
To better show this, consider a situation where the
Yocto Project kernel cache contains the following files:
<literallayout class='monospaced'>
kernel-cache/features/drm-psb/hardware.cfg
kernel-cache/features/kgdb/hardware.cfg
kernel-cache/ktypes/base/hardware.cfg
kernel-cache/bsp/mti-malta32/hardware.cfg
kernel-cache/bsp/fsl-mpc8315e-rdb/hardware.cfg
kernel-cache/bsp/qemu-ppc32/hardware.cfg
kernel-cache/bsp/qemuarma9/hardware.cfg
kernel-cache/bsp/mti-malta64/hardware.cfg
kernel-cache/bsp/arm-versatile-926ejs/hardware.cfg
kernel-cache/bsp/common-pc/hardware.cfg
kernel-cache/bsp/common-pc-64/hardware.cfg
kernel-cache/features/rfkill/non-hardware.cfg
kernel-cache/ktypes/base/non-hardware.cfg
kernel-cache/features/aufs/non-hardware.kcf
kernel-cache/features/ocf/non-hardware.kcf
kernel-cache/ktypes/base/non-hardware.kcf
kernel-cache/ktypes/base/hardware.kcf
kernel-cache/bsp/qemu-ppc32/hardware.kcf
</literallayout>
The following list provides explanations for the various
files:
<itemizedlist>
<listitem><para><filename>hardware.kcf</filename>:
Specifies a list of kernel Kconfig files that contain
hardware options only.
</para></listitem>
<listitem><para><filename>non-hardware.kcf</filename>:
Specifies a list of kernel Kconfig files that contain
non-hardware options only.
</para></listitem>
<listitem><para><filename>hardware.cfg</filename>:
Specifies a list of kernel
<filename>CONFIG_</filename> options that are hardware,
regardless of whether or not they are within a Kconfig
file specified by a hardware or non-hardware
Kconfig file (i.e. <filename>hardware.kcf</filename> or
<filename>non-hardware.kcf</filename>).
</para></listitem>
<listitem><para><filename>non-hardware.cfg</filename>:
Specifies a list of kernel
<filename>CONFIG_</filename> options that are
not hardware, regardless of whether or not they are
within a Kconfig file specified by a hardware or
non-hardware Kconfig file (i.e.
<filename>hardware.kcf</filename> or
<filename>non-hardware.kcf</filename>).
</para></listitem>
</itemizedlist>
Here is a specific example using the
<filename>kernel-cache/bsp/mti-malta32/hardware.cfg</filename>:
<literallayout class='monospaced'>
CONFIG_SERIAL_8250
CONFIG_SERIAL_8250_CONSOLE
CONFIG_SERIAL_8250_NR_UARTS
CONFIG_SERIAL_8250_PCI
CONFIG_SERIAL_CORE
CONFIG_SERIAL_CORE_CONSOLE
CONFIG_VGA_ARB
</literallayout>
The kernel configuration audit automatically detects these
files (hence the names must be exactly the ones discussed here),
and uses them as inputs when generating warnings about the
final <filename>.config</filename> file.
</para>
<para>
A user-specified kernel Metadata repository, or recipe space
feature, can use these same files to classify options that are
found within its <filename>.cfg</filename> files as hardware
or non-hardware, to prevent the OpenEmbedded build system from
producing an error or warning when an option is not in the
final <filename>.config</filename> file.
</para>
</section>
</section>
<section id="patching-the-kernel">
<title>Patching the Kernel</title>
<para>
Patching the kernel involves changing or adding configurations to an existing kernel,
changing or adding recipes to the kernel that are needed to support specific hardware features,
or even altering the source code itself.
<note>
You can use the <filename>yocto-kernel</filename> script
found in the <link linkend='source-directory'>Source Directory</link>
under <filename>scripts</filename> to manage kernel patches and configuration.
See the "<ulink url='&YOCTO_DOCS_BSP_URL;#managing-kernel-patches-and-config-items-with-yocto-kernel'>Managing kernel Patches and Config Items with yocto-kernel</ulink>"
section in the Yocto Project Board Support Packages (BSP) Developer's Guide for
more information.</note>
</para>
<para>
This example creates a simple patch by adding some QEMU emulator console
output at boot time through <filename>printk</filename> statements in the kernel's
<filename>calibrate.c</filename> source code file.
Applying the patch and booting the modified image causes the added
messages to appear on the emulator's console.
</para>
<para>
The example assumes a clean build exists for the <filename>qemux86</filename>
machine in a
<link linkend='source-directory'>Source Directory</link>
named <filename>poky</filename>.
Furthermore, the <link linkend='build-directory'>Build Directory</link> is
<filename>build</filename> and is located in <filename>poky</filename> and
the kernel is based on the Linux 3.4 kernel.
</para>
<para>
Also, for more information on patching the kernel, see the
"<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#applying-patches'>Applying Patches</ulink>"
section in the Yocto Project Linux Kernel Development Manual.
</para>
<section id='create-a-layer-for-your-changes'>
<title>Create a Layer for your Changes</title>
<para>
The first step is to create a layer so you can isolate your
changes.
Rather than use the <filename>yocto-layer</filename> script
to create the layer, this example steps through the process
by hand.
If you want information on the script that creates a general
layer, see the
"<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
section.
</para>
<para>
These two commands create a directory you can use for your
layer:
<literallayout class='monospaced'>
$ cd ~/poky
$ mkdir meta-mylayer
</literallayout>
Creating a directory that follows the Yocto Project layer naming
conventions sets up the layer for your changes.
The layer is where you place your configuration files, append
files, and patch files.
To learn more about creating a layer and filling it with the
files you need, see the "<link linkend='understanding-and-creating-layers'>Understanding
and Creating Layers</link>" section.
</para>
</section>
<section id='finding-the-kernel-source-code'>
<title>Finding the Kernel Source Code</title>
<para>
Each time you build a kernel image, the kernel source code is fetched
and unpacked into the following directory:
<literallayout class='monospaced'>
${S}/linux
</literallayout>
See the "<link linkend='finding-the-temporary-source-code'>Finding Temporary Source Code</link>"
section and the
<ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> variable
for more information about where source is kept during a build.
</para>
<para>
For this example, we are going to patch the
<filename>init/calibrate.c</filename> file
by adding some simple console <filename>printk</filename> statements that we can
see when we boot the image using QEMU.
</para>
</section>
<section id='creating-the-patch'>
<title>Creating the Patch</title>
<para>
Two methods exist by which you can create the patch:
<link linkend='using-devtool-in-your-workflow'><filename>devtool</filename></link> and
<link linkend='using-a-quilt-workflow'>Quilt</link>.
For kernel patches, the Git workflow is more appropriate.
This section assumes the Git workflow and shows the steps specific to
this example.
<orderedlist>
<listitem><para><emphasis>Change the working directory</emphasis>:
Change to where the kernel source code is before making
your edits to the <filename>calibrate.c</filename> file:
<literallayout class='monospaced'>
$ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
</literallayout>
Because you are working in an established Git repository,
you must be in this directory in order to commit your changes
and create the patch file.
<note>The <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink> and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> variables
represent the version and revision for the
<filename>linux-yocto</filename> recipe.
The <filename>PV</filename> variable includes the Git meta and machine
hashes, which make the directory name longer than you might
expect.
</note></para></listitem>
<listitem><para><emphasis>Edit the source file</emphasis>:
Edit the <filename>init/calibrate.c</filename> file to have the
following changes:
<literallayout class='monospaced'>
void calibrate_delay(void)
{
unsigned long lpj;
static bool printed;
int this_cpu = smp_processor_id();
printk("*************************************\n");
printk("* *\n");
printk("* HELLO YOCTO KERNEL *\n");
printk("* *\n");
printk("*************************************\n");
if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
.
.
.
</literallayout></para></listitem>
<listitem><para><emphasis>Stage and commit your changes</emphasis>:
These Git commands display the modified file, stage it, and then
commit the file:
<literallayout class='monospaced'>
$ git status
$ git add init/calibrate.c
$ git commit -m "calibrate: Add printk example"
</literallayout></para></listitem>
<listitem><para><emphasis>Generate the patch file</emphasis>:
This Git command creates the a patch file named
<filename>0001-calibrate-Add-printk-example.patch</filename>
in the current directory.
<literallayout class='monospaced'>
$ git format-patch -1
</literallayout>
</para></listitem>
</orderedlist>
</para>
</section>
<section id='set-up-your-layer-for-the-build'>
<title>Set Up Your Layer for the Build</title>
<para>These steps get your layer set up for the build:
<orderedlist>
<listitem><para><emphasis>Create additional structure</emphasis>:
Create the additional layer structure:
<literallayout class='monospaced'>
$ cd ~/poky/meta-mylayer
$ mkdir conf
$ mkdir recipes-kernel
$ mkdir recipes-kernel/linux
$ mkdir recipes-kernel/linux/linux-yocto
</literallayout>
The <filename>conf</filename> directory holds your configuration files, while the
<filename>recipes-kernel</filename> directory holds your append file and
your patch file.</para></listitem>
<listitem><para><emphasis>Create the layer configuration file</emphasis>:
Move to the <filename>meta-mylayer/conf</filename> directory and create
the <filename>layer.conf</filename> file as follows:
<literallayout class='monospaced'>
# We have a conf and classes directory, add to BBPATH
BBPATH .= ":${LAYERDIR}"
# We have recipes-* directories, add to BBFILES
BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
${LAYERDIR}/recipes-*/*/*.bbappend"
BBFILE_COLLECTIONS += "mylayer"
BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"
BBFILE_PRIORITY_mylayer = "5"
</literallayout>
Notice <filename>mylayer</filename> as part of the last three
statements.</para></listitem>
<listitem><para><emphasis>Create the kernel recipe append file</emphasis>:
Move to the <filename>meta-mylayer/recipes-kernel/linux</filename> directory and create
the <filename>linux-yocto_3.4.bbappend</filename> file as follows:
<literallayout class='monospaced'>
FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
SRC_URI += "file://0001-calibrate-Add-printk-example.patch"
</literallayout>
The <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
and <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
statements enable the OpenEmbedded build system to find the patch file.
For more information on using append files, see the
"<link linkend='using-bbappend-files'>Using .bbappend Files in Your Layer</link>"
section.
</para></listitem>
<listitem><para><emphasis>Put the patch file in your layer</emphasis>:
Move the <filename>0001-calibrate-Add-printk-example.patch</filename> file to
the <filename>meta-mylayer/recipes-kernel/linux/linux-yocto</filename>
directory.</para></listitem>
</orderedlist>
</para>
</section>
<section id='set-up-for-the-build'>
<title>Set Up for the Build</title>
<para>
Do the following to make sure the build parameters are set up for the example.
Once you set up these build parameters, they do not have to change unless you
change the target architecture of the machine you are building:
<itemizedlist>
<listitem><para><emphasis>Build for the correct target architecture:</emphasis> Your
selected <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
definition within the <filename>local.conf</filename> file in the
<link linkend='build-directory'>Build Directory</link>
specifies the target architecture used when building the Linux kernel.
By default, <filename>MACHINE</filename> is set to
<filename>qemux86</filename>, which specifies a 32-bit
<trademark class='registered'>Intel</trademark> Architecture
target machine suitable for the QEMU emulator.</para></listitem>
<listitem><para><emphasis>Identify your <filename>meta-mylayer</filename>
layer:</emphasis> The
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
variable in the
<filename>bblayers.conf</filename> file found in the
<filename>poky/build/conf</filename> directory needs to have the path to your local
<filename>meta-mylayer</filename> layer.
By default, the <filename>BBLAYERS</filename> variable contains paths to
<filename>meta</filename>, <filename>meta-poky</filename>, and
<filename>meta-yocto-bsp</filename> in the
<filename>poky</filename> Git repository.
Add the path to your <filename>meta-mylayer</filename> location:
<literallayout class='monospaced'>
BBLAYERS ?= " \
$HOME/poky/meta \
$HOME/poky/meta-poky \
$HOME/poky/meta-yocto-bsp \
$HOME/poky/meta-mylayer \
"
</literallayout></para></listitem>
</itemizedlist>
</para>
</section>
<section id='build-the-modified-qemu-kernel-image'>
<title>Build the Modified QEMU Kernel Image</title>
<para>
The following steps build your modified kernel image:
<orderedlist>
<listitem><para><emphasis>Be sure your build environment is initialized</emphasis>:
Your environment should be set up since you previously sourced
the
<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
script.
If it is not, source the script again from <filename>poky</filename>.
<literallayout class='monospaced'>
$ cd ~/poky
$ source &OE_INIT_FILE;
</literallayout>
</para></listitem>
<listitem><para><emphasis>Clean up</emphasis>:
Be sure to clean the shared state out by using BitBake
to run from within the Build Directory the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>
task as follows:
<literallayout class='monospaced'>
$ bitbake -c cleansstate linux-yocto
</literallayout></para>
<para>
<note>
Never remove any files by hand from the
<filename>tmp/deploy</filename>
directory inside the
<link linkend='build-directory'>Build Directory</link>.
Always use the various BitBake clean tasks to
clear out previous build artifacts.
For information on the clean tasks, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-clean'><filename>do_clean</filename></ulink>",
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleanall'><filename>do_cleanall</filename></ulink>",
and
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-cleansstate'><filename>do_cleansstate</filename></ulink>"
sections all in the Yocto Project Reference
Manual.
</note>
</para></listitem>
<listitem><para><emphasis>Build the image</emphasis>:
Next, build the kernel image using this command:
<literallayout class='monospaced'>
$ bitbake -k linux-yocto
</literallayout></para></listitem>
</orderedlist>
</para>
</section>
<section id='boot-the-image-and-verify-your-changes'>
<title>Boot the Image and Verify Your Changes</title>
<para>
These steps boot the image and allow you to see the changes
<orderedlist>
<listitem><para><emphasis>Boot the image</emphasis>:
Boot the modified image in the QEMU emulator
using this command:
<literallayout class='monospaced'>
$ runqemu qemux86
</literallayout></para></listitem>
<listitem><para><emphasis>Verify the changes</emphasis>:
Log into the machine using <filename>root</filename> with no password and then
use the following shell command to scroll through the console's boot output.
<literallayout class='monospaced'>
# dmesg | less
</literallayout>
You should see the results of your <filename>printk</filename> statements
as part of the output.</para></listitem>
</orderedlist>
</para>
</section>
</section>
<section id='making-images-more-secure'>
<title>Making Images More Secure</title>
<para>
Security is of increasing concern for embedded devices.
Consider the issues and problems discussed in just this
sampling of work found across the Internet:
<itemizedlist>
<listitem><para><emphasis>
"<ulink url='https://www.schneier.com/blog/archives/2014/01/security_risks_9.html'>Security Risks of Embedded Systems</ulink>"</emphasis>
by Bruce Schneier
</para></listitem>
<listitem><para><emphasis>
"<ulink url='http://internetcensus2012.bitbucket.org/paper.html'>Internet Census 2012</ulink>"</emphasis>
by Carna Botnet</para></listitem>
<listitem><para><emphasis>
"<ulink url='http://elinux.org/images/6/6f/Security-issues.pdf'>Security Issues for Embedded Devices</ulink>"</emphasis>
by Jake Edge
</para></listitem>
</itemizedlist>
</para>
<para>
When securing your image is of concern, there are steps, tools,
and variables that you can consider to help you reach the
security goals you need for your particular device.
Not all situations are identical when it comes to making an
image secure.
Consequently, this section provides some guidance and suggestions
for consideration when you want to make your image more secure.
<note>
Because the security requirements and risks are
different for every type of device, this section cannot
provide a complete reference on securing your custom OS.
It is strongly recommended that you also consult other sources
of information on embedded Linux system hardening and on
security.
</note>
</para>
<section id='general-considerations'>
<title>General Considerations</title>
<para>
General considerations exist that help you create more
secure images.
You should consider the following suggestions to help
make your device more secure:
<itemizedlist>
<listitem><para>
Scan additional code you are adding to the system
(e.g. application code) by using static analysis
tools.
Look for buffer overflows and other potential
security problems.
</para></listitem>
<listitem><para>
Pay particular attention to the security for
any web-based administration interface.
</para>
<para>Web interfaces typically need to perform
administrative functions and tend to need to run with
elevated privileges.
Thus, the consequences resulting from the interface's
security becoming compromised can be serious.
Look for common web vulnerabilities such as
cross-site-scripting (XSS), unvalidated inputs,
and so forth.</para>
<para>As with system passwords, the default credentials
for accessing a web-based interface should not be the
same across all devices.
This is particularly true if the interface is enabled
by default as it can be assumed that many end-users
will not change the credentials.
</para></listitem>
<listitem><para>
Ensure you can update the software on the device to
mitigate vulnerabilities discovered in the future.
This consideration especially applies when your
device is network-enabled.
</para></listitem>
<listitem><para>
Ensure you remove or disable debugging functionality
before producing the final image.
For information on how to do this, see the
"<link linkend='considerations-specific-to-the-openembedded-build-system'>Considerations Specific to the OpenEmbedded Build System</link>"
section.
</para></listitem>
<listitem><para>
Ensure you have no network services listening that
are not needed.
</para></listitem>
<listitem><para>
Remove any software from the image that is not needed.
</para></listitem>
<listitem><para>
Enable hardware support for secure boot functionality
when your device supports this functionality.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='security-flags'>
<title>Security Flags</title>
<para>
The Yocto Project has security flags that you can enable that
help make your build output more secure.
The security flags are in the
<filename>meta/conf/distro/include/security_flags.inc</filename>
file in your
<link linkend='source-directory'>Source Directory</link>
(e.g. <filename>poky</filename>).
<note>
Depending on the recipe, certain security flags are enabled
and disabled by default.
</note>
</para>
<para>
<!--
The GCC/LD flags in <filename>security_flags.inc</filename>
enable more secure code generation.
By including the <filename>security_flags.inc</filename>
file, you enable flags to the compiler and linker that cause
them to generate more secure code.
<note>
The GCC/LD flags are enabled by default in the
<filename>poky-lsb</filename> distribution.
</note>
-->
Use the following line in your
<filename>local.conf</filename> file or in your custom
distribution configuration file to enable the security
compiler and linker flags for your build:
<literallayout class='monospaced'>
require conf/distro/include/security_flags.inc
</literallayout>
</para>
</section>
<section id='considerations-specific-to-the-openembedded-build-system'>
<title>Considerations Specific to the OpenEmbedded Build System</title>
<para>
You can take some steps that are specific to the
OpenEmbedded build system to make your images more secure:
<itemizedlist>
<listitem><para>
Ensure "debug-tweaks" is not one of your selected
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>.
When creating a new project, the default is to provide you
with an initial <filename>local.conf</filename> file that
enables this feature using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink> variable with the line:
<literallayout class='monospaced'>
EXTRA_IMAGE_FEATURES = "debug-tweaks"
</literallayout>
To disable that feature, simply comment out that line in your
<filename>local.conf</filename> file, or
make sure <filename>IMAGE_FEATURES</filename> does not contain
"debug-tweaks" before producing your final image.
Among other things, leaving this in place sets the
root password as blank, which makes logging in for
debugging or inspection easy during
development but also means anyone can easily log in
during production.
</para></listitem>
<listitem><para>
It is possible to set a root password for the image
and also to set passwords for any extra users you might
add (e.g. administrative or service type users).
When you set up passwords for multiple images or
users, you should not duplicate passwords.
</para>
<para>
To set up passwords, use the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers</filename></ulink>
class, which is the preferred method.
For an example on how to set up both root and user
passwords, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-extrausers'><filename>extrausers.bbclass</filename></ulink>"
section.
<note>
When adding extra user accounts or setting a
root password, be cautious about setting the
same password on every device.
If you do this, and the password you have set
is exposed, then every device is now potentially
compromised.
If you need this access but want to ensure
security, consider setting a different,
random password for each device.
Typically, you do this as a separate step after
you deploy the image onto the device.
</note>
</para></listitem>
<listitem><para>
Consider enabling a Mandatory Access Control (MAC)
framework such as SMACK or SELinux and tuning it
appropriately for your device's usage.
You can find more information in the
<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/meta-selinux/'><filename>meta-selinux</filename></ulink>
layer.
</para></listitem>
</itemizedlist>
</para>
<para>
</para>
</section>
<section id='tools-for-hardening-your-image'>
<title>Tools for Hardening Your Image</title>
<para>
The Yocto Project provides tools for making your image
more secure.
You can find these tools in the
<filename>meta-security</filename> layer of the
<ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi'>Yocto Project Source Repositories</ulink>.
</para>
</section>
</section>
<section id='creating-your-own-distribution'>
<title>Creating Your Own Distribution</title>
<para>
When you build an image using the Yocto Project and
do not alter any distribution
<link linkend='metadata'>Metadata</link>, you are creating a
Poky distribution.
If you wish to gain more control over package alternative
selections, compile-time options, and other low-level
configurations, you can create your own distribution.
</para>
<para>
To create your own distribution, the basic steps consist of
creating your own distribution layer, creating your own
distribution configuration file, and then adding any needed
code and Metadata to the layer.
The following steps provide some more detail:
<itemizedlist>
<listitem><para><emphasis>Create a layer for your new distro:</emphasis>
Create your distribution layer so that you can keep your
Metadata and code for the distribution separate.
It is strongly recommended that you create and use your own
layer for configuration and code.
Using your own layer as compared to just placing
configurations in a <filename>local.conf</filename>
configuration file makes it easier to reproduce the same
build configuration when using multiple build machines.
See the
"<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
section for information on how to quickly set up a layer.
</para></listitem>
<listitem><para><emphasis>Create the distribution configuration file:</emphasis>
The distribution configuration file needs to be created in
the <filename>conf/distro</filename> directory of your
layer.
You need to name it using your distribution name
(e.g. <filename>mydistro.conf</filename>).
<note>
The
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
variable in your
<filename>local.conf</filename> file determines the
name of your distribution.
</note></para>
<para>You can split out parts of your configuration file
into include files and then "require" them from within
your distribution configuration file.
Be sure to place the include files in the
<filename>conf/distro/include</filename> directory of
your layer.
A common example usage of include files would be to
separate out the selection of desired version and revisions
for individual recipes.
</para>
<para>Your configuration file needs to set the following
required variables:
<literallayout class='monospaced'>
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_NAME'><filename>DISTRO_NAME</filename></ulink>
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_VERSION'><filename>DISTRO_VERSION</filename></ulink>
</literallayout>
These following variables are optional and you typically
set them from the distribution configuration file:
<literallayout class='monospaced'>
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RDEPENDS'><filename>DISTRO_EXTRA_RDEPENDS</filename></ulink>
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RRECOMMENDS'><filename>DISTRO_EXTRA_RRECOMMENDS</filename></ulink>
<ulink url='&YOCTO_DOCS_REF_URL;#var-TCLIBC'><filename>TCLIBC</filename></ulink>
</literallayout>
<tip>
If you want to base your distribution configuration file
on the very basic configuration from OE-Core, you
can use
<filename>conf/distro/defaultsetup.conf</filename> as
a reference and just include variables that differ
as compared to <filename>defaultsetup.conf</filename>.
Alternatively, you can create a distribution
configuration file from scratch using the
<filename>defaultsetup.conf</filename> file
or configuration files from other distributions
such as Poky or Angstrom as references.
</tip></para></listitem>
<listitem><para><emphasis>Provide miscellaneous variables:</emphasis>
Be sure to define any other variables for which you want to
create a default or enforce as part of the distribution
configuration.
You can include nearly any variable from the
<filename>local.conf</filename> file.
The variables you use are not limited to the list in the
previous bulleted item.</para></listitem>
<listitem><para><emphasis>Point to Your distribution configuration file:</emphasis>
In your <filename>local.conf</filename> file in the
<link linkend='build-directory'>Build Directory</link>,
set your
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
variable to point to your distribution's configuration file.
For example, if your distribution's configuration file is
named <filename>mydistro.conf</filename>, then you point
to it as follows:
<literallayout class='monospaced'>
DISTRO = "mydistro"
</literallayout></para></listitem>
<listitem><para><emphasis>Add more to the layer if necessary:</emphasis>
Use your layer to hold other information needed for the
distribution:
<itemizedlist>
<listitem><para>Add recipes for installing
distro-specific configuration files that are not
already installed by another recipe.
If you have distro-specific configuration files
that are included by an existing recipe, you should
add an append file (<filename>.bbappend</filename>)
for those.
For general information and recommendations
on how to add recipes to your layer, see the
"<link linkend='creating-your-own-layer'>Creating Your Own Layer</link>"
and
"<link linkend='best-practices-to-follow-when-creating-layers'>Best Practices to Follow When Creating Layers</link>"
sections.</para></listitem>
<listitem><para>Add any image recipes that are specific
to your distribution.</para></listitem>
<listitem><para>Add a <filename>psplash</filename>
append file for a branded splash screen.
For information on append files, see the
"<link linkend='using-bbappend-files'>Using .bbappend Files in Your Layer</link>"
section.</para></listitem>
<listitem><para>Add any other append files to make
custom changes that are specific to individual
recipes.</para></listitem>
</itemizedlist></para></listitem>
</itemizedlist>
</para>
</section>
<section id='creating-a-custom-template-configuration-directory'>
<title>Creating a Custom Template Configuration Directory</title>
<para>
If you are producing your own customized version
of the build system for use by other users, you might
want to customize the message shown by the setup script or
you might want to change the template configuration files (i.e.
<filename>local.conf</filename> and
<filename>bblayers.conf</filename>) that are created in
a new build directory.
</para>
<para>
The OpenEmbedded build system uses the environment variable
<filename>TEMPLATECONF</filename> to locate the directory
from which it gathers configuration information that ultimately
ends up in the
<link linkend='build-directory'>Build Directory's</link>
<filename>conf</filename> directory.
By default, <filename>TEMPLATECONF</filename> is set as
follows in the <filename>poky</filename> repository:
<literallayout class='monospaced'>
TEMPLATECONF=${TEMPLATECONF:-meta-poky/conf}
</literallayout>
This is the directory used by the build system to find templates
from which to build some key configuration files.
If you look at this directory, you will see the
<filename>bblayers.conf.sample</filename>,
<filename>local.conf.sample</filename>, and
<filename>conf-notes.txt</filename> files.
The build system uses these files to form the respective
<filename>bblayers.conf</filename> file,
<filename>local.conf</filename> file, and display the list of
BitBake targets when running the setup script.
</para>
<para>
To override these default configuration files with
configurations you want used within every new
Build Directory, simply set the
<filename>TEMPLATECONF</filename> variable to your directory.
The <filename>TEMPLATECONF</filename> variable is set in the
<filename>.templateconf</filename> file, which is in the
top-level
<link linkend='source-directory'>Source Directory</link>
folder (e.g. <filename>poky</filename>).
Edit the <filename>.templateconf</filename> so that it can locate
your directory.
</para>
<para>
Best practices dictate that you should keep your
template configuration directory in your custom distribution layer.
For example, suppose you have a layer named
<filename>meta-mylayer</filename> located in your home directory
and you want your template configuration directory named
<filename>myconf</filename>.
Changing the <filename>.templateconf</filename> as follows
causes the OpenEmbedded build system to look in your directory
and base its configuration files on the
<filename>*.sample</filename> configuration files it finds.
The final configuration files (i.e.
<filename>local.conf</filename> and
<filename>bblayers.conf</filename> ultimately still end up in
your Build Directory, but they are based on your
<filename>*.sample</filename> files.
<literallayout class='monospaced'>
TEMPLATECONF=${TEMPLATECONF:-meta-mylayer/myconf}
</literallayout>
</para>
<para>
Aside from the <filename>*.sample</filename> configuration files,
the <filename>conf-notes.txt</filename> also resides in the
default <filename>meta-poky/conf</filename> directory.
The scripts that set up the build environment
(i.e.
<ulink url="&YOCTO_DOCS_REF_URL;#structure-core-script"><filename>&OE_INIT_FILE;</filename></ulink>
and
<ulink url="&YOCTO_DOCS_REF_URL;#structure-memres-core-script"><filename>oe-init-build-env-memres</filename></ulink>)
use this file to display BitBake targets as part of the script
output.
Customizing this <filename>conf-notes.txt</filename> file is a
good way to make sure your list of custom targets appears
as part of the script's output.
</para>
<para>
Here is the default list of targets displayed as a result of
running either of the setup scripts:
<literallayout class='monospaced'>
You can now run 'bitbake &lt;target&gt;'
Common targets are:
core-image-minimal
core-image-sato
meta-toolchain
meta-ide-support
</literallayout>
</para>
<para>
Changing the listed common targets is as easy as editing your
version of <filename>conf-notes.txt</filename> in your
custom template configuration directory and making sure you
have <filename>TEMPLATECONF</filename> set to your directory.
</para>
</section>
<section id='building-a-tiny-system'>
<title>Building a Tiny System</title>
<para>
Very small distributions have some significant advantages such
as requiring less on-die or in-package memory (cheaper), better
performance through efficient cache usage, lower power requirements
due to less memory, faster boot times, and reduced development
overhead.
Some real-world examples where a very small distribution gives
you distinct advantages are digital cameras, medical devices,
and small headless systems.
</para>
<para>
This section presents information that shows you how you can
trim your distribution to even smaller sizes than the
<filename>poky-tiny</filename> distribution, which is around
5 Mbytes, that can be built out-of-the-box using the Yocto Project.
</para>
<section id='tiny-system-overview'>
<title>Overview</title>
<para>
The following list presents the overall steps you need to
consider and perform to create distributions with smaller
root filesystems, achieve faster boot times, maintain your critical
functionality, and avoid initial RAM disks:
<itemizedlist>
<listitem><para>
<link linkend='goals-and-guiding-principles'>Determine your goals and guiding principles.</link>
</para></listitem>
<listitem><para>
<link linkend='understand-what-gives-your-image-size'>Understand what contributes to your image size.</link>
</para></listitem>
<listitem><para>
<link linkend='trim-the-root-filesystem'>Reduce the size of the root filesystem.</link>
</para></listitem>
<listitem><para>
<link linkend='trim-the-kernel'>Reduce the size of the kernel.</link>
</para></listitem>
<listitem><para>
<link linkend='remove-package-management-requirements'>Eliminate packaging requirements.</link>
</para></listitem>
<listitem><para>
<link linkend='look-for-other-ways-to-minimize-size'>Look for other ways to minimize size.</link>
</para></listitem>
<listitem><para>
<link linkend='iterate-on-the-process'>Iterate on the process.</link>
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='goals-and-guiding-principles'>
<title>Goals and Guiding Principles</title>
<para>
Before you can reach your destination, you need to know
where you are going.
Here is an example list that you can use as a guide when
creating very small distributions:
<itemizedlist>
<listitem><para>Determine how much space you need
(e.g. a kernel that is 1 Mbyte or less and
a root filesystem that is 3 Mbytes or less).
</para></listitem>
<listitem><para>Find the areas that are currently
taking 90% of the space and concentrate on reducing
those areas.
</para></listitem>
<listitem><para>Do not create any difficult "hacks"
to achieve your goals.</para></listitem>
<listitem><para>Leverage the device-specific
options.</para></listitem>
<listitem><para>Work in a separate layer so that you
keep changes isolated.
For information on how to create layers, see
the "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>" section.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='understand-what-gives-your-image-size'>
<title>Understand What Contributes to Your Image Size</title>
<para>
It is easiest to have something to start with when creating
your own distribution.
You can use the Yocto Project out-of-the-box to create the
<filename>poky-tiny</filename> distribution.
Ultimately, you will want to make changes in your own
distribution that are likely modeled after
<filename>poky-tiny</filename>.
<note>
To use <filename>poky-tiny</filename> in your build,
set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
variable in your
<filename>local.conf</filename> file to "poky-tiny"
as described in the
"<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
section.
</note>
</para>
<para>
Understanding some memory concepts will help you reduce the
system size.
Memory consists of static, dynamic, and temporary memory.
Static memory is the TEXT (code), DATA (initialized data
in the code), and BSS (uninitialized data) sections.
Dynamic memory represents memory that is allocated at runtime:
stacks, hash tables, and so forth.
Temporary memory is recovered after the boot process.
This memory consists of memory used for decompressing
the kernel and for the <filename>__init__</filename>
functions.
</para>
<para>
To help you see where you currently are with kernel and root
filesystem sizes, you can use two tools found in the
<link linkend='source-directory'>Source Directory</link> in
the <filename>scripts/tiny/</filename> directory:
<itemizedlist>
<listitem><para><filename>ksize.py</filename>: Reports
component sizes for the kernel build objects.
</para></listitem>
<listitem><para><filename>dirsize.py</filename>: Reports
component sizes for the root filesystem.</para></listitem>
</itemizedlist>
This next tool and command help you organize configuration
fragments and view file dependencies in a human-readable form:
<itemizedlist>
<listitem><para><filename>merge_config.sh</filename>:
Helps you manage configuration files and fragments
within the kernel.
With this tool, you can merge individual configuration
fragments together.
The tool allows you to make overrides and warns you
of any missing configuration options.
The tool is ideal for allowing you to iterate on
configurations, create minimal configurations, and
create configuration files for different machines
without having to duplicate your process.</para>
<para>The <filename>merge_config.sh</filename> script is
part of the Linux Yocto kernel Git repositories
(i.e. <filename>linux-yocto-3.14</filename>,
<filename>linux-yocto-3.10</filename>,
<filename>linux-yocto-3.8</filename>, and so forth)
in the
<filename>scripts/kconfig</filename> directory.</para>
<para>For more information on configuration fragments,
see the
"<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'>Generating Configuration Files</ulink>"
section of the Yocto Project Linux Kernel Development
Manual and the "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>"
section, which is in this manual.</para></listitem>
<listitem><para><filename>bitbake -u taskexp -g <replaceable>bitbake_target</replaceable></filename>:
Using the BitBake command with these options brings up
a Dependency Explorer from which you can view file
dependencies.
Understanding these dependencies allows you to make
informed decisions when cutting out various pieces of the
kernel and root filesystem.</para></listitem>
</itemizedlist>
</para>
</section>
<section id='trim-the-root-filesystem'>
<title>Trim the Root Filesystem</title>
<para>
The root filesystem is made up of packages for booting,
libraries, and applications.
To change things, you can configure how the packaging happens,
which changes the way you build them.
You can also modify the filesystem itself or select a different
filesystem.
</para>
<para>
First, find out what is hogging your root filesystem by running the
<filename>dirsize.py</filename> script from your root directory:
<literallayout class='monospaced'>
$ cd <replaceable>root-directory-of-image</replaceable>
$ dirsize.py 100000 > dirsize-100k.log
$ cat dirsize-100k.log
</literallayout>
You can apply a filter to the script to ignore files under
a certain size.
The previous example filters out any files below 100 Kbytes.
The sizes reported by the tool are uncompressed, and thus
will be smaller by a relatively constant factor in a
compressed root filesystem.
When you examine your log file, you can focus on areas of the
root filesystem that take up large amounts of memory.
</para>
<para>
You need to be sure that what you eliminate does not cripple
the functionality you need.
One way to see how packages relate to each other is by using
the Dependency Explorer UI with the BitBake command:
<literallayout class='monospaced'>
$ cd <replaceable>image-directory</replaceable>
$ bitbake -u taskexp -g <replaceable>image</replaceable>
</literallayout>
Use the interface to select potential packages you wish to
eliminate and see their dependency relationships.
</para>
<para>
When deciding how to reduce the size, get rid of packages that
result in minimal impact on the feature set.
For example, you might not need a VGA display.
Or, you might be able to get by with <filename>devtmpfs</filename>
and <filename>mdev</filename> instead of
<filename>udev</filename>.
</para>
<para>
Use your <filename>local.conf</filename> file to make changes.
For example, to eliminate <filename>udev</filename> and
<filename>glib</filename>, set the following in the
local configuration file:
<literallayout class='monospaced'>
VIRTUAL-RUNTIME_dev_manager = ""
</literallayout>
</para>
<para>
Finally, you should consider exactly the type of root
filesystem you need to meet your needs while also reducing
its size.
For example, consider <filename>cramfs</filename>,
<filename>squashfs</filename>, <filename>ubifs</filename>,
<filename>ext2</filename>, or an <filename>initramfs</filename>
using <filename>initramfs</filename>.
Be aware that <filename>ext3</filename> requires a 1 Mbyte
journal.
If you are okay with running read-only, you do not need this
journal.
</para>
<note>
After each round of elimination, you need to rebuild your
system and then use the tools to see the effects of your
reductions.
</note>
</section>
<section id='trim-the-kernel'>
<title>Trim the Kernel</title>
<para>
The kernel is built by including policies for hardware-independent
aspects.
What subsystems do you enable?
For what architecture are you building?
Which drivers do you build by default?
<note>You can modify the kernel source if you want to help
with boot time.
</note>
</para>
<para>
Run the <filename>ksize.py</filename> script from the top-level
Linux build directory to get an idea of what is making up
the kernel:
<literallayout class='monospaced'>
$ cd <replaceable>top-level-linux-build-directory</replaceable>
$ ksize.py > ksize.log
$ cat ksize.log
</literallayout>
When you examine the log, you will see how much space is
taken up with the built-in <filename>.o</filename> files for
drivers, networking, core kernel files, filesystem, sound,
and so forth.
The sizes reported by the tool are uncompressed, and thus
will be smaller by a relatively constant factor in a compressed
kernel image.
Look to reduce the areas that are large and taking up around
the "90% rule."
</para>
<para>
To examine, or drill down, into any particular area, use the
<filename>-d</filename> option with the script:
<literallayout class='monospaced'>
$ ksize.py -d > ksize.log
</literallayout>
Using this option breaks out the individual file information
for each area of the kernel (e.g. drivers, networking, and
so forth).
</para>
<para>
Use your log file to see what you can eliminate from the kernel
based on features you can let go.
For example, if you are not going to need sound, you do not
need any drivers that support sound.
</para>
<para>
After figuring out what to eliminate, you need to reconfigure
the kernel to reflect those changes during the next build.
You could run <filename>menuconfig</filename> and make all your
changes at once.
However, that makes it difficult to see the effects of your
individual eliminations and also makes it difficult to replicate
the changes for perhaps another target device.
A better method is to start with no configurations using
<filename>allnoconfig</filename>, create configuration
fragments for individual changes, and then manage the
fragments into a single configuration file using
<filename>merge_config.sh</filename>.
The tool makes it easy for you to iterate using the
configuration change and build cycle.
</para>
<para>
Each time you make configuration changes, you need to rebuild
the kernel and check to see what impact your changes had on
the overall size.
</para>
</section>
<section id='remove-package-management-requirements'>
<title>Remove Package Management Requirements</title>
<para>
Packaging requirements add size to the image.
One way to reduce the size of the image is to remove all the
packaging requirements from the image.
This reduction includes both removing the package manager
and its unique dependencies as well as removing the package
management data itself.
</para>
<para>
To eliminate all the packaging requirements for an image,
be sure that "package-management" is not part of your
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
statement for the image.
When you remove this feature, you are removing the package
manager as well as its dependencies from the root filesystem.
</para>
</section>
<section id='look-for-other-ways-to-minimize-size'>
<title>Look for Other Ways to Minimize Size</title>
<para>
Depending on your particular circumstances, other areas that you
can trim likely exist.
The key to finding these areas is through tools and methods
described here combined with experimentation and iteration.
Here are a couple of areas to experiment with:
<itemizedlist>
<listitem><para><filename>glibc</filename>:
In general, follow this process:
<orderedlist>
<listitem><para>Remove <filename>glibc</filename>
features from
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
that you think you do not need.</para></listitem>
<listitem><para>Build your distribution.
</para></listitem>
<listitem><para>If the build fails due to missing
symbols in a package, determine if you can
reconfigure the package to not need those
features.
For example, change the configuration to not
support wide character support as is done for
<filename>ncurses</filename>.
Or, if support for those characters is needed,
determine what <filename>glibc</filename>
features provide the support and restore the
configuration.
</para></listitem>
<listitem><para>Rebuild and repeat the process.
</para></listitem>
</orderedlist></para></listitem>
<listitem><para><filename>busybox</filename>:
For BusyBox, use a process similar as described for
<filename>glibc</filename>.
A difference is you will need to boot the resulting
system to see if you are able to do everything you
expect from the running system.
You need to be sure to integrate configuration fragments
into Busybox because BusyBox handles its own core
features and then allows you to add configuration
fragments on top.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='iterate-on-the-process'>
<title>Iterate on the Process</title>
<para>
If you have not reached your goals on system size, you need
to iterate on the process.
The process is the same.
Use the tools and see just what is taking up 90% of the root
filesystem and the kernel.
Decide what you can eliminate without limiting your device
beyond what you need.
</para>
<para>
Depending on your system, a good place to look might be
Busybox, which provides a stripped down
version of Unix tools in a single, executable file.
You might be able to drop virtual terminal services or perhaps
ipv6.
</para>
</section>
</section>
<section id='building-images-for-more-than-one-machine'>
<title>Building Images for More than One Machine</title>
<para>
A common scenario developers face is creating images for several
different machines that use the same software environment.
In this situation, it is tempting to set the
tunings and optimization flags for each build specifically for
the targeted hardware (i.e. "maxing out" the tunings).
Doing so can considerably add to build times and package feed
maintenance collectively for the machines.
For example, selecting tunes that are extremely specific to a
CPU core used in a system might enable some micro optimizations
in GCC for that particular system but would otherwise not gain
you much of a performance difference across the other systems
as compared to using a more general tuning across all the builds
(e.g. setting
<ulink url='var-DEFAULTTUNE'><filename>DEFAULTTUNE</filename></ulink>
specifically for each machine's build).
Rather than "max out" each build's tunings, you can take steps that
cause the OpenEmbedded build system to reuse software across the
various machines where it makes sense.
</para>
<para>
If build speed and package feed maintenance are considerations,
you should consider the points in this section that can help you
optimize your tunings to best consider build times and package
feed maintenance.
<itemizedlist>
<listitem><para><emphasis>Share the Build Directory:</emphasis>
If at all possible, share the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
across builds.
The Yocto Project supports switching between different
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
values in the same <filename>TMPDIR</filename>.
This practice is well supported and regularly used by
developers when building for multiple machines.
When you use the same <filename>TMPDIR</filename> for
multiple machine builds, the OpenEmbedded build system can
reuse the existing native and often cross-recipes for
multiple machines.
Thus, build time decreases.
<note>
If
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
settings change or fundamental configuration settings
such as the filesystem layout, you need to work with
a clean <filename>TMPDIR</filename>.
Sharing <filename>TMPDIR</filename> under these
circumstances might work but since it is not
guaranteed, you should use a clean
<filename>TMPDIR</filename>.
</note>
</para></listitem>
<listitem><para><emphasis>Enable the Appropriate Package Architecture:</emphasis>
By default, the OpenEmbedded build system enables three
levels of package architectures: "all", "tune" or "package",
and "machine".
Any given recipe usually selects one of these package
architectures (types) for its output.
Depending for what a given recipe creates packages, making
sure you enable the appropriate package architecture can
directly impact the build time.</para>
<para>A recipe that just generates scripts can enable
"all" architecture because there are no binaries to build.
To specifically enable "all" architecture, be sure your
recipe inherits the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-allarch'><filename>allarch</filename></ulink>
class.
This class is useful for "all" architectures because it
configures many variables so packages can be used across
multiple architectures.</para>
<para>If your recipe needs to generate packages that are
machine-specific or when one of the build or runtime
dependencies is already machine-architecture dependent,
which makes your recipe also machine-architecture dependent,
make sure your recipe enables the "machine" package
architecture through the
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_ARCH'><filename>MACHINE_ARCH</filename></ulink>
variable:
<literallayout class='monospaced'>
PACKAGE_ARCH = "${MACHINE_ARCH}"
</literallayout>
When you do not specifically enable a package
architecture through the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>,
The OpenEmbedded build system defaults to the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TUNE_PKGARCH'><filename>TUNE_PKGARCH</filename></ulink>
setting:
<literallayout class='monospaced'>
PACKAGE_ARCH = "${TUNE_PKGARCH}"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Choose a Generic Tuning File if Possible:</emphasis>
Some tunes are more generic and can run on multiple targets
(e.g. an <filename>armv5</filename> set of packages could
run on <filename>armv6</filename> and
<filename>armv7</filename> processors in most cases).
Similarly, <filename>i486</filename> binaries could work
on <filename>i586</filename> and higher processors.
You should realize, however, that advances on newer
processor versions would not be used.</para>
<para>If you select the same tune for several different
machines, the OpenEmbedded build system reuses software
previously built, thus speeding up the overall build time.
Realize that even though a new sysroot for each machine is
generated, the software is not recompiled and only one
package feed exists.
</para></listitem>
<listitem><para><emphasis>Manage Granular Level Packaging:</emphasis>
Sometimes cases exist where injecting another level
of package architecture beyond the three higher levels
noted earlier can be useful.
For example, consider the <filename>emgd</filename>
graphics stack in the
<filename>meta-intel</filename> layer.
In this layer, a subset of software exists that is
compiled against something different from the rest of the
generic packages.
You can examine the key code in the
<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Source Repositories</ulink>
"daisy" branch in
<filename>classes/emgd-gl.bbclass</filename>.
For a specific set of packages, the code redefines
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>.
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_EXTRA_ARCHS'><filename>PACKAGE_EXTRA_ARCHS</filename></ulink>
is then appended with this extra tune name in
<filename>meta-intel-emgd.inc</filename>.
The result is that when searching for packages, the
build system uses a four-level search and the packages
in this new level are preferred as compared to the standard
tune.
The overall result is that the build system reuses most
software from the common tune except for specific cases
as needed.
</para></listitem>
<listitem><para><emphasis>Use Tools to Debug Issues:</emphasis>
Sometimes you can run into situations where software is
being rebuilt when you think it should not be.
For example, the OpenEmbedded build system might not be
using shared state between machines when you think it
should be.
These types of situations are usually due to references
to machine-specific variables such as
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLE'><filename>SERIAL_CONSOLE</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-XSERVER'><filename>XSERVER</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'><filename>MACHINE_FEATURES</filename></ulink>,
and so forth in code that is supposed to only be
tune-specific or when the recipe depends
(<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-RSUGGESTS'><filename>RSUGGESTS</filename></ulink>,
and so forth) on some other recipe that already has
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>
defined as "${MACHINE_ARCH}".
<note>
Patches to fix any issues identified are most welcome
as these issues occasionally do occur.
</note></para>
<para>For such cases, you can use some tools to help you
sort out the situation:
<itemizedlist>
<listitem><para><emphasis><filename>sstate-diff-machines.sh</filename>:</emphasis>
You can find this tool in the
<filename>scripts</filename> directory of the
Source Repositories.
See the comments in the script for information on
how to use the tool.
</para></listitem>
<listitem><para><emphasis>BitBake's "-S printdiff" Option:</emphasis>
Using this option causes BitBake to try to
establish the closest signature match it can
(e.g. in the shared state cache) and then run
<filename>bitbake-diffsigs</filename> over the
matches to determine the stamps and delta where
these two stamp trees diverge.
</para></listitem>
</itemizedlist>
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='working-with-packages'>
<title>Working with Packages</title>
<para>
This section describes a few tasks that involve packages:
<itemizedlist>
<listitem><para>
<link linkend='excluding-packages-from-an-image'>Excluding packages from an image</link>
</para></listitem>
<listitem><para>
<link linkend='incrementing-a-binary-package-version'>Incrementing a binary package version</link>
</para></listitem>
<listitem><para>
<link linkend='handling-optional-module-packaging'>Handling optional module packaging</link>
</para></listitem>
<listitem><para>
<link linkend='using-runtime-package-management'>Using Runtime Package Management</link>
</para></listitem>
<listitem><para>
<link linkend='testing-packages-with-ptest'>Setting up and running package test (ptest)</link>
</para></listitem>
</itemizedlist>
</para>
<section id='excluding-packages-from-an-image'>
<title>Excluding Packages from an Image</title>
<para>
You might find it necessary to prevent specific packages
from being installed into an image.
If so, you can use several variables to direct the build
system to essentially ignore installing recommended packages
or to not install a package at all.
</para>
<para>
The following list introduces variables you can use to
prevent packages from being installed into your image.
Each of these variables only works with IPK and RPM
package types.
Support for Debian packages does not exist.
Also, you can use these variables from your
<filename>local.conf</filename> file or attach them to a
specific image recipe by using a recipe name override.
For more detail on the variables, see the descriptions in the
Yocto Project Reference Manual's glossary chapter.
<itemizedlist>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-BAD_RECOMMENDATIONS'><filename>BAD_RECOMMENDATIONS</filename></ulink>:
Use this variable to specify "recommended-only"
packages that you do not want installed.
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-NO_RECOMMENDATIONS'><filename>NO_RECOMMENDATIONS</filename></ulink>:
Use this variable to prevent all "recommended-only"
packages from being installed.
</para></listitem>
<listitem><para><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_EXCLUDE'><filename>PACKAGE_EXCLUDE</filename></ulink>:
Use this variable to prevent specific packages from
being installed regardless of whether they are
"recommended-only" or not.
You need to realize that the build process could
fail with an error when you
prevent the installation of a package whose presence
is required by an installed package.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='incrementing-a-binary-package-version'>
<title>Incrementing a Package Version</title>
<para>
This section provides some background on how binary package
versioning is accomplished and presents some of the services,
variables, and terminology involved.
</para>
<para>
In order to understand binary package versioning, you need
to consider the following:
<itemizedlist>
<listitem><para>
Binary Package: The binary package that is eventually
built and installed into an image.
</para></listitem>
<listitem><para>
Binary Package Version: The binary package version
is composed of two components - a version and a
revision.
<note>
Technically, a third component, the "epoch" (i.e.
<ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>)
is involved but this discussion for the most part
ignores <filename>PE</filename>.
</note>
The version and revision are taken from the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
variables, respectively.
</para></listitem>
<listitem><para>
<filename>PV</filename>: The recipe version.
<filename>PV</filename> represents the version of the
software being packaged.
Do not confuse <filename>PV</filename> with the
binary package version.
</para></listitem>
<listitem><para>
<filename>PR</filename>: The recipe revision.
</para></listitem>
<listitem><para>
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>:
The OpenEmbedded build system uses this string
to help define the value of <filename>PV</filename>
when the source code revision needs to be included
in it.
</para></listitem>
<listitem><para>
<ulink url='https://wiki.yoctoproject.org/wiki/PR_Service'>PR Service</ulink>:
A network-based service that helps automate keeping
package feeds compatible with existing package
manager applications such as RPM, APT, and OPKG.
</para></listitem>
</itemizedlist>
</para>
<para>
Whenever the binary package content changes, the binary package
version must change.
Changing the binary package version is accomplished by changing
or "bumping" the <filename>PR</filename> and/or
<filename>PV</filename> values.
Increasing these values occurs one of two ways:
<itemizedlist>
<listitem><para>Automatically using a Package Revision
Service (PR Service).
</para></listitem>
<listitem><para>Manually incrementing the
<filename>PR</filename> and/or
<filename>PV</filename> variables.
</para></listitem>
</itemizedlist>
</para>
<para>
Given a primary challenge of any build system and its users
is how to maintain a package feed that is compatible with
existing package manager applications such as RPM, APT, and
OPKG, using an automated system is much preferred over a
manual system.
In either system, the main requirement is that binary package
version numbering increases in a linear fashion and that a
number of version components exist that support that linear
progression.
For information on how to ensure package revisioning remains
linear, see the
"<link linkend='automatically-incrementing-a-binary-package-revision-number'>Automatically Incrementing a Binary Package Revision Number</link>"
section.
</para>
<para>
The following three sections provide related information on the
PR Service, the manual method for "bumping"
<filename>PR</filename> and/or <filename>PV</filename>, and
on how to ensure binary package revisioning remains linear.
</para>
<section id='working-with-a-pr-service'>
<title>Working With a PR Service</title>
<para>
As mentioned, attempting to maintain revision numbers in the
<ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>
is error prone, inaccurate, and causes problems for people
submitting recipes.
Conversely, the PR Service automatically generates
increasing numbers, particularly the revision field,
which removes the human element.
<note>
For additional information on using a PR Service, you
can see the
<ulink url='&YOCTO_WIKI_URL;/wiki/PR_Service'>PR Service</ulink>
wiki page.
</note>
</para>
<para>
The Yocto Project uses variables in order of
decreasing priority to facilitate revision numbering (i.e.
<ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
for epoch, version, and revision, respectively).
The values are highly dependent on the policies and
procedures of a given distribution and package feed.
</para>
<para>
Because the OpenEmbedded build system uses
"<ulink url='&YOCTO_DOCS_REF_URL;#checksums'>signatures</ulink>",
which are unique to a given build, the build system
knows when to rebuild packages.
All the inputs into a given task are represented by a
signature, which can trigger a rebuild when different.
Thus, the build system itself does not rely on the
<filename>PR</filename>, <filename>PV</filename>, and
<filename>PE</filename> numbers to trigger a rebuild.
The signatures, however, can be used to generate
these values.
</para>
<para>
The PR Service works with both
<filename>OEBasic</filename> and
<filename>OEBasicHash</filename> generators.
The value of <filename>PR</filename> bumps when the
checksum changes and the different generator mechanisms
change signatures under different circumstances.
</para>
<para>
As implemented, the build system includes values from
the PR Service into the <filename>PR</filename> field as
an addition using the form "<filename>.x</filename>" so
<filename>r0</filename> becomes <filename>r0.1</filename>,
<filename>r0.2</filename> and so forth.
This scheme allows existing <filename>PR</filename> values
to be used for whatever reasons, which include manual
<filename>PR</filename> bumps, should it be necessary.
</para>
<para>
By default, the PR Service is not enabled or running.
Thus, the packages generated are just "self consistent".
The build system adds and removes packages and
there are no guarantees about upgrade paths but images
will be consistent and correct with the latest changes.
</para>
<para>
The simplest form for a PR Service is for it to exist
for a single host development system that builds the
package feed (building system).
For this scenario, you can enable a local PR Service by
setting
<ulink url='&YOCTO_DOCS_REF_URL;#var-PRSERV_HOST'><filename>PRSERV_HOST</filename></ulink>
in your <filename>local.conf</filename> file in the
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
<literallayout class='monospaced'>
PRSERV_HOST = "localhost:0"
</literallayout>
Once the service is started, packages will automatically
get increasing <filename>PR</filename> values and
BitBake takes care of starting and stopping the server.
</para>
<para>
If you have a more complex setup where multiple host
development systems work against a common, shared package
feed, you have a single PR Service running and it is
connected to each building system.
For this scenario, you need to start the PR Service using
the <filename>bitbake-prserv</filename> command:
<literallayout class='monospaced'>
bitbake-prserv --host <replaceable>ip</replaceable> --port <replaceable>port</replaceable> --start
</literallayout>
In addition to hand-starting the service, you need to
update the <filename>local.conf</filename> file of each
building system as described earlier so each system
points to the server and port.
</para>
<para>
It is also recommended you use build history, which adds
some sanity checks to binary package versions, in
conjunction with the server that is running the PR Service.
To enable build history, add the following to each building
system's <filename>local.conf</filename> file:
<literallayout class='monospaced'>
# It is recommended to activate "buildhistory" for testing the PR service
INHERIT += "buildhistory"
BUILDHISTORY_COMMIT = "1"
</literallayout>
For information on build history, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#maintaining-build-output-quality'>Maintaining Build Output Quality</ulink>"
section in the Yocto Project Reference Manual.
</para>
<note>
<para>
The OpenEmbedded build system does not maintain
<filename>PR</filename> information as part of the
shared state (sstate) packages.
If you maintain an sstate feed, its expected that either
all your building systems that contribute to the sstate
feed use a shared PR Service, or you do not run a PR
Service on any of your building systems.
Having some systems use a PR Service while others do
not leads to obvious problems.
</para>
<para>
For more information on shared state, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#shared-state-cache'>Shared State Cache</ulink>"
section in the Yocto Project Reference Manual.
</para>
</note>
</section>
<section id='manually-bumping-pr'>
<title>Manually Bumping PR</title>
<para>
The alternative to setting up a PR Service is to manually
"bump" the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
variable.
</para>
<para>
If a committed change results in changing the package
output, then the value of the PR variable needs to be
increased (or "bumped") as part of that commit.
For new recipes you should add the <filename>PR</filename>
variable and set its initial value equal to "r0", which is
the default.
Even though the default value is "r0", the practice of
adding it to a new recipe makes it harder to forget to bump
the variable when you make changes to the recipe in future.
</para>
<para>
If you are sharing a common <filename>.inc</filename> file
with multiple recipes, you can also use the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-INC_PR'>INC_PR</ulink></filename>
variable to ensure that the recipes sharing the
<filename>.inc</filename> file are rebuilt when the
<filename>.inc</filename> file itself is changed.
The <filename>.inc</filename> file must set
<filename>INC_PR</filename> (initially to "r0"), and all
recipes referring to it should set <filename>PR</filename>
to "${INC_PR}.0" initially, incrementing the last number
when the recipe is changed.
If the <filename>.inc</filename> file is changed then its
<filename>INC_PR</filename> should be incremented.
</para>
<para>
When upgrading the version of a binary package, assuming the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'>PV</ulink></filename>
changes, the <filename>PR</filename> variable should be
reset to "r0" (or "${INC_PR}.0" if you are using
<filename>INC_PR</filename>).
</para>
<para>
Usually, version increases occur only to binary packages.
However, if for some reason <filename>PV</filename> changes
but does not increase, you can increase the
<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PE'>PE</ulink></filename>
variable (Package Epoch).
The <filename>PE</filename> variable defaults to "0".
</para>
<para>
Binary package version numbering strives to follow the
<ulink url='http://www.debian.org/doc/debian-policy/ch-controlfields.html'>
Debian Version Field Policy Guidelines</ulink>.
These guidelines define how versions are compared and what
"increasing" a version means.
</para>
</section>
<section id='automatically-incrementing-a-binary-package-revision-number'>
<title>Automatically Incrementing a Package Version Number</title>
<para>
When fetching a repository, BitBake uses the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink>
variable to determine the specific source code revision
from which to build.
You set the <filename>SRCREV</filename> variable to
<ulink url='&YOCTO_DOCS_REF_URL;#var-AUTOREV'><filename>AUTOREV</filename></ulink>
to cause the OpenEmbedded build system to automatically use the
latest revision of the software:
<literallayout class='monospaced'>
SRCREV = "${AUTOREV}"
</literallayout>
</para>
<para>
Furthermore, you need to reference <filename>SRCPV</filename>
in <filename>PV</filename> in order to automatically update
the version whenever the revision of the source code
changes.
Here is an example:
<literallayout class='monospaced'>
PV = "1.0+git${SRCPV}"
</literallayout>
The OpenEmbedded build system substitutes
<filename>SRCPV</filename> with the following:
<literallayout class='monospaced'>
AUTOINC+<replaceable>source_code_revision</replaceable>
</literallayout>
The build system replaces the <filename>AUTOINC</filename> with
a number.
The number used depends on the state of the PR Service:
<itemizedlist>
<listitem><para>
If PR Service is enabled, the build system increments
the number, which is similar to the behavior of
<ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>.
This behavior results in linearly increasing package
versions, which is desirable.
Here is an example:
<literallayout class='monospaced'>
hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
hello-world-git_0.0+git1+dd2f5c3565-r0.0_armv7a-neon.ipk
</literallayout>
</para></listitem>
<listitem><para>
If PR Service is not enabled, the build system
replaces the <filename>AUTOINC</filename>
placeholder with zero (i.e. "0").
This results in changing the package version since
the source revision is included.
However, package versions are not increased linearly.
Here is an example:
<literallayout class='monospaced'>
hello-world-git_0.0+git0+b6558dd387-r0.0_armv7a-neon.ipk
hello-world-git_0.0+git0+dd2f5c3565-r0.0_armv7a-neon.ipk
</literallayout>
</para></listitem>
</itemizedlist>
</para>
<para>
In summary, the OpenEmbedded build system does not track the
history of binary package versions for this purpose.
<filename>AUTOINC</filename>, in this case, is comparable to
<filename>PR</filename>.
If PR server is not enabled, <filename>AUTOINC</filename>
in the package version is simply replaced by "0".
If PR server is enabled, the build system keeps track of the
package versions and bumps the number when the package
revision changes.
</para>
</section>
</section>
<section id='handling-optional-module-packaging'>
<title>Handling Optional Module Packaging</title>
<para>
Many pieces of software split functionality into optional
modules (or plug-ins) and the plug-ins that are built
might depend on configuration options.
To avoid having to duplicate the logic that determines what
modules are available in your recipe or to avoid having
to package each module by hand, the OpenEmbedded build system
provides functionality to handle module packaging dynamically.
</para>
<para>
To handle optional module packaging, you need to do two things:
<itemizedlist>
<listitem><para>Ensure the module packaging is actually
done.</para></listitem>
<listitem><para>Ensure that any dependencies on optional
modules from other recipes are satisfied by your recipe.
</para></listitem>
</itemizedlist>
</para>
<section id='making-sure-the-packaging-is-done'>
<title>Making Sure the Packaging is Done</title>
<para>
To ensure the module packaging actually gets done, you use
the <filename>do_split_packages</filename> function within
the <filename>populate_packages</filename> Python function
in your recipe.
The <filename>do_split_packages</filename> function
searches for a pattern of files or directories under a
specified path and creates a package for each one it finds
by appending to the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
variable and setting the appropriate values for
<filename>FILES_packagename</filename>,
<filename>RDEPENDS_packagename</filename>,
<filename>DESCRIPTION_packagename</filename>, and so forth.
Here is an example from the <filename>lighttpd</filename>
recipe:
<literallayout class='monospaced'>
python populate_packages_prepend () {
lighttpd_libdir = d.expand('${libdir}')
do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
'lighttpd-module-%s', 'Lighttpd module for %s',
extra_depends='')
}
</literallayout>
The previous example specifies a number of things in the
call to <filename>do_split_packages</filename>.
<itemizedlist>
<listitem><para>A directory within the files installed
by your recipe through <filename>do_install</filename>
in which to search.</para></listitem>
<listitem><para>A regular expression used to match module
files in that directory.
In the example, note the parentheses () that mark
the part of the expression from which the module
name should be derived.</para></listitem>
<listitem><para>A pattern to use for the package names.
</para></listitem>
<listitem><para>A description for each package.
</para></listitem>
<listitem><para>An empty string for
<filename>extra_depends</filename>, which disables
the default dependency on the main
<filename>lighttpd</filename> package.
Thus, if a file in <filename>${libdir}</filename>
called <filename>mod_alias.so</filename> is found,
a package called <filename>lighttpd-module-alias</filename>
is created for it and the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DESCRIPTION'><filename>DESCRIPTION</filename></ulink>
is set to "Lighttpd module for alias".</para></listitem>
</itemizedlist>
</para>
<para>
Often, packaging modules is as simple as the previous
example.
However, more advanced options exist that you can use
within <filename>do_split_packages</filename> to modify its
behavior.
And, if you need to, you can add more logic by specifying
a hook function that is called for each package.
It is also perfectly acceptable to call
<filename>do_split_packages</filename> multiple times if
you have more than one set of modules to package.
</para>
<para>
For more examples that show how to use
<filename>do_split_packages</filename>, see the
<filename>connman.inc</filename> file in the
<filename>meta/recipes-connectivity/connman/</filename>
directory of the <filename>poky</filename>
<link linkend='yocto-project-repositories'>source repository</link>.
You can also find examples in
<filename>meta/classes/kernel.bbclass</filename>.
</para>
<para>
Following is a reference that shows
<filename>do_split_packages</filename> mandatory and
optional arguments:
<literallayout class='monospaced'>
Mandatory arguments
root
The path in which to search
file_regex
Regular expression to match searched files.
Use parentheses () to mark the part of this
expression that should be used to derive the
module name (to be substituted where %s is
used in other function arguments as noted below)
output_pattern
Pattern to use for the package names. Must
include %s.
description
Description to set for each package. Must
include %s.
Optional arguments
postinst
Postinstall script to use for all packages
(as a string)
recursive
True to perform a recursive search - default
False
hook
A hook function to be called for every match.
The function will be called with the following
arguments (in the order listed):
f
Full path to the file/directory match
pkg
The package name
file_regex
As above
output_pattern
As above
modulename
The module name derived using file_regex
extra_depends
Extra runtime dependencies (RDEPENDS) to be
set for all packages. The default value of None
causes a dependency on the main package
(${PN}) - if you do not want this, pass empty
string '' for this parameter.
aux_files_pattern
Extra item(s) to be added to FILES for each
package. Can be a single string item or a list
of strings for multiple items. Must include %s.
postrm
postrm script to use for all packages (as a
string)
allow_dirs
True to allow directories to be matched -
default False
prepend
If True, prepend created packages to PACKAGES
instead of the default False which appends them
match_path
match file_regex on the whole relative path to
the root rather than just the file name
aux_files_pattern_verbatim
Extra item(s) to be added to FILES for each
package, using the actual derived module name
rather than converting it to something legal
for a package name. Can be a single string item
or a list of strings for multiple items. Must
include %s.
allow_links
True to allow symlinks to be matched - default
False
summary
Summary to set for each package. Must include %s;
defaults to description if not set.
</literallayout>
</para>
</section>
<section id='satisfying-dependencies'>
<title>Satisfying Dependencies</title>
<para>
The second part for handling optional module packaging
is to ensure that any dependencies on optional modules
from other recipes are satisfied by your recipe.
You can be sure these dependencies are satisfied by
using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES_DYNAMIC'><filename>PACKAGES_DYNAMIC</filename></ulink> variable.
Here is an example that continues with the
<filename>lighttpd</filename> recipe shown earlier:
<literallayout class='monospaced'>
PACKAGES_DYNAMIC = "lighttpd-module-.*"
</literallayout>
The name specified in the regular expression can of
course be anything.
In this example, it is <filename>lighttpd-module-</filename>
and is specified as the prefix to ensure that any
<ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
and <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>
on a package name starting with the prefix are satisfied
during build time.
If you are using <filename>do_split_packages</filename>
as described in the previous section, the value you put in
<filename>PACKAGES_DYNAMIC</filename> should correspond to
the name pattern specified in the call to
<filename>do_split_packages</filename>.
</para>
</section>
</section>
<section id='using-runtime-package-management'>
<title>Using Runtime Package Management</title>
<para>
During a build, BitBake always transforms a recipe into one or
more packages.
For example, BitBake takes the <filename>bash</filename> recipe
and currently produces the <filename>bash-dbg</filename>,
<filename>bash-staticdev</filename>,
<filename>bash-dev</filename>, <filename>bash-doc</filename>,
<filename>bash-locale</filename>, and
<filename>bash</filename> packages.
Not all generated packages are included in an image.
</para>
<para>
In several situations, you might need to update, add, remove,
or query the packages on a target device at runtime
(i.e. without having to generate a new image).
Examples of such situations include:
<itemizedlist>
<listitem><para>
You want to provide in-the-field updates to deployed
devices (e.g. security updates).
</para></listitem>
<listitem><para>
You want to have a fast turn-around development cycle
for one or more applications that run on your device.
</para></listitem>
<listitem><para>
You want to temporarily install the "debug" packages
of various applications on your device so that
debugging can be greatly improved by allowing
access to symbols and source debugging.
</para></listitem>
<listitem><para>
You want to deploy a more minimal package selection of
your device but allow in-the-field updates to add a
larger selection for customization.
</para></listitem>
</itemizedlist>
</para>
<para>
In all these situations, you have something similar to a more
traditional Linux distribution in that in-field devices
are able to receive pre-compiled packages from a server for
installation or update.
Being able to install these packages on a running,
in-field device is what is termed "runtime package
management".
</para>
<para>
In order to use runtime package management, you
need a host/server machine that serves up the pre-compiled
packages plus the required metadata.
You also need package manipulation tools on the target.
The build machine is a likely candidate to act as the server.
However, that machine does not necessarily have to be the
package server.
The build machine could push its artifacts to another machine
that acts as the server (e.g. Internet-facing).
</para>
<para>
A simple build that targets just one device produces
more than one package database.
In other words, the packages produced by a build are separated
out into a couple of different package groupings based on
criteria such as the target's CPU architecture, the target
board, or the C library used on the target.
For example, a build targeting the <filename>qemuarm</filename>
device produces the following three package databases:
<filename>all</filename>, <filename>armv5te</filename>, and
<filename>qemuarm</filename>.
If you wanted your <filename>qemuarm</filename> device to be
aware of all the packages that were available to it,
you would need to point it to each of these databases
individually.
In a similar way, a traditional Linux distribution usually is
configured to be aware of a number of software repositories
from which it retrieves packages.
</para>
<para>
Using runtime package management is completely optional and
not required for a successful build or deployment in any
way.
But if you want to make use of runtime package management,
you need to do a couple things above and beyond the basics.
The remainder of this section describes what you need to do.
</para>
<section id='runtime-package-management-build'>
<title>Build Considerations</title>
<para>
This section describes build considerations of which you
need to be aware in order to provide support for runtime
package management.
</para>
<para>
When BitBake generates packages, it needs to know
what format or formats to use.
In your configuration, you use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>
variable to specify the format:
<orderedlist>
<listitem><para>
Open the <filename>local.conf</filename> file
inside your
<link linkend='build-directory'>Build Directory</link>
(e.g. <filename>~/poky/build/conf/local.conf</filename>).
</para></listitem>
<listitem><para>
Select the desired package format as follows:
<literallayout class='monospaced'>
PACKAGE_CLASSES ?= “package_<replaceable>packageformat</replaceable>”
</literallayout>
where <replaceable>packageformat</replaceable>
can be "ipk", "rpm", and "deb", which are the
supported package formats.
<note>
Because the Yocto Project supports three
different package formats, you can set the
variable with more than one argument.
However, the OpenEmbedded build system only
uses the first argument when creating an image
or Software Development Kit (SDK).
</note>
</para></listitem>
</orderedlist>
</para>
<para>
If you would like your image to start off with a basic
package database containing the packages in your current
build as well as to have the relevant tools available on the
target for runtime package management, you can include
"package-management" in the
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
variable.
Including "package-management" in this
configuration variable ensures that when the image
is assembled for your target, the image includes
the currently-known package databases as well as
the target-specific tools required for runtime
package management to be performed on the target.
However, this is not strictly necessary.
You could start your image off without any databases
but only include the required on-target package
tool(s).
As an example, you could include "opkg" in your
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
variable if you are using the IPK package format.
You can then initialize your target's package database(s)
later once your image is up and running.
</para>
<para>
Whenever you perform any sort of build step that can
potentially generate a package or modify an existing
package, it is always a good idea to re-generate the
package index with:
<literallayout class='monospaced'>
$ bitbake package-index
</literallayout>
Realize that it is not sufficient to simply do the
following:
<literallayout class='monospaced'>
$ bitbake <replaceable>some-package</replaceable> package-index
</literallayout>
The reason for this restriction is because BitBake does not
properly schedule the <filename>package-index</filename>
target fully after any other target has completed.
Thus, be sure to run the package update step separately.
</para>
<para>
You can use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>,
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
variables to pre-configure target images to use a package
feed.
If you do not define these variables, then manual steps
as described in the subsequent sections are necessary to
configure the target.
You should set these variables before building the image
in order to produce a correctly configured image.
</para>
<para>
When your build is complete, your packages reside in the
<filename>${TMPDIR}/deploy/<replaceable>packageformat</replaceable></filename>
directory.
For example, if
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink><filename>}</filename>
is <filename>tmp</filename> and your selected package type
is IPK, then your IPK packages are available in
<filename>tmp/deploy/ipk</filename>.
</para>
</section>
<section id='runtime-package-management-server'>
<title>Host or Server Machine Setup</title>
<para>
Although other protocols are possible, a server using HTTP
typically serves packages.
If you want to use HTTP, then set up and configure a
web server such as Apache 2, lighttpd, or
SimpleHTTPServer on the machine serving the packages.
</para>
<para>
To keep things simple, this section describes how to set
up a SimpleHTTPServer web server to share package feeds
from the developer's machine.
Although this server might not be the best for a production
environment, the setup is simple and straight forward.
Should you want to use a different server more suited for
production (e.g. Apache 2, Lighttpd, or Nginx), take the
appropriate steps to do so.
</para>
<para>
From within the build directory where you have built an
image based on your packaging choice (i.e. the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>
setting), simply start the server.
The following example assumes a build directory of
<filename>~/poky/build/tmp/deploy/rpm</filename> and a
<filename>PACKAGE_CLASSES</filename> setting of
"package_rpm":
<literallayout class='monospaced'>
$ cd ~/poky/build/tmp/deploy/rpm
$ python -m SimpleHTTPServer
</literallayout>
</para>
</section>
<section id='runtime-package-management-target'>
<title>Target Setup</title>
<para>
Setting up the target differs depending on the
package management system.
This section provides information for RPM, IPK, and DEB.
</para>
<section id='runtime-package-management-target-rpm'>
<title>Using RPM</title>
<para>
The <filename>dnf</filename> application performs
runtime package management of RPM packages.
You must perform an initial setup for
<filename>dnf</filename> on the target machine
if the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>,
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
variables have not been set or the target image was
built before the variables were set.
</para>
<para>
As an example, assume the target is able to use the
following package databases:
<filename>all</filename>, <filename>i586</filename>,
and <filename>qemux86</filename> from a server named
<filename>my.server</filename>.
You must inform <filename>dnf</filename> of the
availability of these databases by creating a
<filename>/etc/yum.repos.d/oe-packages.repo</filename>
file with the following content:
<literallayout class='monospaced'>
[oe-packages]
baseurl="http://my.server/rpm/i586 http://my.server/rpm/qemux86 http://my.server/rpm/all"
</literallayout>
From the target machine, fetch the repository:
<literallayout class='monospaced'>
# dnf makecache
</literallayout>
After everything is set up, <filename>dnf</filename>
is able to find, install, and upgrade packages from
the specified repository.
<note>
See the
<ulink url='http://dnf.readthedocs.io/en/latest/'>DNF documentation</ulink>
for additional information.
</note>
</para>
</section>
<section id='runtime-package-management-target-ipk'>
<title>Using IPK</title>
<para>
The <filename>opkg</filename> application performs
runtime package management of IPK packages.
You must perform an initial setup for
<filename>opkg</filename> on the target machine
if the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>, and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
variables have not been set or the target image was
built before the variables were set.
</para>
<para>
The <filename>opkg</filename> application uses
configuration files to find available package
databases.
Thus, you need to create a configuration file inside
the <filename>/etc/opkg/</filename> direction, which
informs <filename>opkg</filename> of any repository
you want to use.
</para>
<para>
As an example, suppose you are serving packages from a
<filename>ipk/</filename> directory containing the
<filename>i586</filename>,
<filename>all</filename>, and
<filename>qemux86</filename> databases through an
HTTP server named <filename>my.server</filename>.
On the target, create a configuration file
(e.g. <filename>my_repo.conf</filename>) inside the
<filename>/etc/opkg/</filename> directory containing
the following:
<literallayout class='monospaced'>
src/gz all http://my.server/ipk/all
src/gz i586 http://my.server/ipk/i586
src/gz qemux86 http://my.server/ipk/qemux86
</literallayout>
Next, instruct <filename>opkg</filename> to fetch
the repository information:
<literallayout class='monospaced'>
# opkg update
</literallayout>
The <filename>opkg</filename> application is now able
to find, install, and upgrade packages from the
specified repository.
</para>
</section>
<section id='runtime-package-management-target-deb'>
<title>Using DEB</title>
<para>
The <filename>apt</filename> application performs
runtime package management of DEB packages.
This application uses a source list file to find
available package databases.
You must perform an initial setup for
<filename>apt</filename> on the target machine
if the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_ARCHS'><filename>PACKAGE_FEED_ARCHS</filename></ulink>,
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_BASE_PATHS'><filename>PACKAGE_FEED_BASE_PATHS</filename></ulink>, and
<ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_FEED_URIS'><filename>PACKAGE_FEED_URIS</filename></ulink>
variables have not been set or the target image was
built before the variables were set.
</para>
<para>
To inform <filename>apt</filename> of the repository
you want to use, you might create a list file (e.g.
<filename>my_repo.list</filename>) inside the
<filename>/etc/apt/sources.list.d/</filename>
directory.
As an example, suppose you are serving packages from a
<filename>deb/</filename> directory containing the
<filename>i586</filename>,
<filename>all</filename>, and
<filename>qemux86</filename> databases through an
HTTP server named <filename>my.server</filename>.
The list file should contain:
<literallayout class='monospaced'>
deb http://my.server/deb/all ./
deb http://my.server/deb/i586 ./
deb http://my.server/deb/qemux86 ./
</literallayout>
Next, instruct the <filename>apt</filename>
application to fetch the repository information:
<literallayout class='monospaced'>
# apt-get update
</literallayout>
After this step, <filename>apt</filename> is able
to find, install, and upgrade packages from the
specified repository.
</para>
</section>
</section>
</section>
<section id='generating-and-using-signed-packages'>
<title>Generating and Using Signed Packages</title>
<para>
In order to add security to RPM packages used during a build,
you can take steps to securely sign them.
Once a signature is verified, the OpenEmbedded build system
can use the package in the build.
If security fails for a signed package, the build system
aborts the build.
</para>
<para>
This section describes how to sign RPM packages during a build
and how to use signed package feeds (repositories) when
doing a build.
</para>
<section id='signing-rpm-packages'>
<title>Signing RPM Packages</title>
<para>
To enable signing RPM packages, you must set up the
following configurations in either your
<filename>local.config</filename> or
<filename>distro.config</filename> file:
<literallayout class='monospaced'>
# Inherit sign_rpm.bbclass to enable signing functionality
INHERIT += " sign_rpm"
# Define the GPG key that will be used for signing.
RPM_GPG_NAME = "<replaceable>key_name</replaceable>"
# Provide passphrase for the key
RPM_GPG_PASSPHRASE = "<replaceable>passphrase</replaceable>"
</literallayout>
<note>
Be sure to supply appropriate values for both
<replaceable>key_name</replaceable> and
<replaceable>passphrase</replaceable>
</note>
Aside from the
<filename>RPM_GPG_NAME</filename> and
<filename>RPM_GPG_PASSPHRASE</filename> variables in the
previous example, two optional variables related to signing
exist:
<itemizedlist>
<listitem><para>
<emphasis><filename>GPG_BIN</filename>:</emphasis>
Specifies a <filename>gpg</filename> binary/wrapper
that is executed when the package is signed.
</para></listitem>
<listitem><para>
<emphasis><filename>GPG_PATH</filename>:</emphasis>
Specifies the <filename>gpg</filename> home
directory used when the package is signed.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='processing-package-feeds'>
<title>Processing Package Feeds</title>
<para>
In addition to being able to sign RPM packages, you can
also enable the OpenEmbedded build system to be able to
handle previously signed package feeds for IPK
packages.
<note>
The OpenEmbedded build system does not currently
support signed DPKG or RPM package feeds.
</note>
The steps you need to take to enable signed package feed
use are similar to the steps used to sign RPM packages.
You must define the following in your
<filename>local.config</filename> or
<filename>distro.config</filename> file:
<literallayout class='monospaced'>
INHERIT += "sign_package_feed"
PACKAGE_FEED_GPG_NAME = "<replaceable>key_name</replaceable>"
PACKAGE_FEED_GPG_PASSPHRASE_FILE = "<replaceable>path_to_file_containing_passphrase</replaceable>"
</literallayout>
For signed package feeds, the passphrase must exist in a
separate file, which is pointed to by the
<filename>PACKAGE_FEED_GPG_PASSPHRASE_FILE</filename>
variable.
Regarding security, keeping a plain text passphrase out of
the configuration is more secure.
</para>
<para>
Aside from the
<filename>PACKAGE_FEED_GPG_NAME</filename> and
<filename>PACKAGE_FEED_GPG_PASSPHRASE_FILE</filename>
variables, three optional variables related to signed
package feeds exist:
<itemizedlist>
<listitem><para>
<emphasis><filename>GPG_BIN</filename>:</emphasis>
Specifies a <filename>gpg</filename> binary/wrapper
that is executed when the package is signed.
</para></listitem>
<listitem><para>
<emphasis><filename>GPG_PATH</filename>:</emphasis>
Specifies the <filename>gpg</filename> home
directory used when the package is signed.
</para></listitem>
<listitem><para>
<emphasis><filename>PACKAGE_FEED_GPG_SIGNATURE_TYPE</filename>:</emphasis>
Specifies the type of <filename>gpg</filename>
signature.
This variable applies only to RPM and IPK package
feeds.
Allowable values for the
<filename>PACKAGE_FEED_GPG_SIGNATURE_TYPE</filename>
are "ASC", which is the default and specifies ascii
armored, and "BIN", which specifies binary.
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
<section id='testing-packages-with-ptest'>
<title>Testing Packages With ptest</title>
<para>
A Package Test (ptest) runs tests against packages built
by the OpenEmbedded build system on the target machine.
A ptest contains at least two items: the actual test, and
a shell script (<filename>run-ptest</filename>) that starts
the test.
The shell script that starts the test must not contain
the actual test - the script only starts the test.
On the other hand, the test can be anything from a simple
shell script that runs a binary and checks the output to
an elaborate system of test binaries and data files.
</para>
<para>
The test generates output in the format used by
Automake:
<literallayout class='monospaced'>
<replaceable>result</replaceable>: <replaceable>testname</replaceable>
</literallayout>
where the result can be <filename>PASS</filename>,
<filename>FAIL</filename>, or <filename>SKIP</filename>,
and the testname can be any identifying string.
</para>
<para>
For a list of Yocto Project recipes that are already
enabled with ptest, see the
<ulink url='https://wiki.yoctoproject.org/wiki/Ptest'>Ptest</ulink>
wiki page.
<note>
A recipe is "ptest-enabled" if it inherits the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-ptest'><filename>ptest</filename></ulink>
class.
</note>
</para>
<section id='adding-ptest-to-your-build'>
<title>Adding ptest to Your Build</title>
<para>
To add package testing to your build, add the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
variables to your <filename>local.conf</filename> file,
which is found in the
<link linkend='build-directory'>Build Directory</link>:
<literallayout class='monospaced'>
DISTRO_FEATURES_append = " ptest"
EXTRA_IMAGE_FEATURES += "ptest-pkgs"
</literallayout>
Once your build is complete, the ptest files are installed
into the
<filename>/usr/lib/<replaceable>package</replaceable>/ptest</filename>
directory within the image, where
<filename><replaceable>package</replaceable></filename>
is the name of the package.
</para>
</section>
<section id='running-ptest'>
<title>Running ptest</title>
<para>
The <filename>ptest-runner</filename> package installs a
shell script that loops through all installed ptest test
suites and runs them in sequence.
Consequently, you might want to add this package to
your image.
</para>
</section>
<section id='getting-your-package-ready'>
<title>Getting Your Package Ready</title>
<para>
In order to enable a recipe to run installed ptests
on target hardware,
you need to prepare the recipes that build the packages
you want to test.
Here is what you have to do for each recipe:
<itemizedlist>
<listitem><para><emphasis>Be sure the recipe
inherits the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-ptest'><filename>ptest</filename></ulink>
class:</emphasis>
Include the following line in each recipe:
<literallayout class='monospaced'>
inherit ptest
</literallayout>
</para></listitem>
<listitem><para><emphasis>Create <filename>run-ptest</filename>:</emphasis>
This script starts your test.
Locate the script where you will refer to it
using
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
Here is an example that starts a test for
<filename>dbus</filename>:
<literallayout class='monospaced'>
#!/bin/sh
cd test
make -k runtest-TESTS
</literallayout>
</para></listitem>
<listitem><para><emphasis>Ensure dependencies are
met:</emphasis>
If the test adds build or runtime dependencies
that normally do not exist for the package
(such as requiring "make" to run the test suite),
use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
variables in your recipe in order for the package
to meet the dependencies.
Here is an example where the package has a runtime
dependency on "make":
<literallayout class='monospaced'>
RDEPENDS_${PN}-ptest += "make"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Add a function to build the
test suite:</emphasis>
Not many packages support cross-compilation of
their test suites.
Consequently, you usually need to add a
cross-compilation function to the package.
</para>
<para>Many packages based on Automake compile and
run the test suite by using a single command
such as <filename>make check</filename>.
However, the host <filename>make check</filename>
builds and runs on the same computer, while
cross-compiling requires that the package is built
on the host but executed for the target
architecture (though often, as in the case for
ptest, the execution occurs on the host).
The built version of Automake that ships with the
Yocto Project includes a patch that separates
building and execution.
Consequently, packages that use the unaltered,
patched version of <filename>make check</filename>
automatically cross-compiles.</para>
<para>Regardless, you still must add a
<filename>do_compile_ptest</filename> function to
build the test suite.
Add a function similar to the following to your
recipe:
<literallayout class='monospaced'>
do_compile_ptest() {
oe_runmake buildtest-TESTS
}
</literallayout>
</para></listitem>
<listitem><para><emphasis>Ensure special configurations
are set:</emphasis>
If the package requires special configurations
prior to compiling the test code, you must
insert a <filename>do_configure_ptest</filename>
function into the recipe.
</para></listitem>
<listitem><para><emphasis>Install the test
suite:</emphasis>
The <filename>ptest</filename> class
automatically copies the file
<filename>run-ptest</filename> to the target and
then runs make <filename>install-ptest</filename>
to run the tests.
If this is not enough, you need to create a
<filename>do_install_ptest</filename> function and
make sure it gets called after the
"make install-ptest" completes.
</para></listitem>
</itemizedlist>
</para>
</section>
</section>
</section>
<section id='working-with-source-files'>
<title>Working with Source Files</title>
<para>
The OpenEmbedded build system works with source files located
through the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
variable.
When you build something using BitBake, a big part of the operation
is locating and downloading all the source tarballs.
For images, downloading all the source for various packages can
take a significant amount of time.
</para>
<para>
This section presents information for working with source
files that can lead to more efficient use of resources and
time.
</para>
<section id='setting-up-effective-mirrors'>
<title>Setting up Effective Mirrors</title>
<para>
As mentioned, a good deal that goes into a Yocto Project
build is simply downloading all of the source tarballs.
Maybe you have been working with another build system
(OpenEmbedded or Angstrom) for which you have built up a
sizable directory of source tarballs.
Or, perhaps someone else has such a directory for which you
have read access.
If so, you can save time by adding statements to your
configuration file so that the build process checks local
directories first for existing tarballs before checking the
Internet.
</para>
<para>
Here is an efficient way to set it up in your
<filename>local.conf</filename> file:
<literallayout class='monospaced'>
SOURCE_MIRROR_URL ?= "file:///home/you/your-download-dir/"
INHERIT += "own-mirrors"
BB_GENERATE_MIRROR_TARBALLS = "1"
# BB_NO_NETWORK = "1"
</literallayout>
</para>
<para>
In the previous example, the
<ulink url='&YOCTO_DOCS_REF_URL;#var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></ulink>
variable causes the OpenEmbedded build system to generate
tarballs of the Git repositories and store them in the
<ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>
directory.
Due to performance reasons, generating and storing these
tarballs is not the build system's default behavior.
</para>
<para>
You can also use the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PREMIRRORS'><filename>PREMIRRORS</filename></ulink>
variable.
For an example, see the variable's glossary entry in the
Yocto Project Reference Manual.
</para>
</section>
<section id='getting-source-files-and-suppressing-the-build'>
<title>Getting Source Files and Suppressing the Build</title>
<para>
Another technique you can use to ready yourself for a
successive string of build operations, is to pre-fetch
all the source files without actually starting a build.
This technique lets you work through any download issues
and ultimately gathers all the source files into your
download directory
<ulink url='&YOCTO_DOCS_REF_URL;#structure-build-downloads'><filename>build/downloads</filename></ulink>,
which is located with
<ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>.
</para>
<para>
Use the following BitBake command form to fetch all the
necessary sources without starting the build:
<literallayout class='monospaced'>
$ bitbake -c fetchall <replaceable>target</replaceable>
</literallayout>
This variation of the BitBake command guarantees that you
have all the sources for that BitBake target should you
disconnect from the Internet and want to do the build
later offline.
</para>
</section>
</section>
<section id="building-software-from-an-external-source">
<title>Building Software from an External Source</title>
<para>
By default, the OpenEmbedded build system uses the
<link linkend='build-directory'>Build Directory</link> when
building source code.
The build process involves fetching the source files, unpacking
them, and then patching them if necessary before the build takes
place.
</para>
<para>
Situations exist where you might want to build software from source
files that are external to and thus outside of the
OpenEmbedded build system.
For example, suppose you have a project that includes a new BSP with
a heavily customized kernel.
And, you want to minimize exposing the build system to the
development team so that they can focus on their project and
maintain everyone's workflow as much as possible.
In this case, you want a kernel source directory on the development
machine where the development occurs.
You want the recipe's
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
variable to point to the external directory and use it as is, not
copy it.
</para>
<para>
To build from software that comes from an external source, all you
need to do is inherit the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc</filename></ulink>
class and then set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC'><filename>EXTERNALSRC</filename></ulink>
variable to point to your external source code.
Here are the statements to put in your
<filename>local.conf</filename> file:
<literallayout class='monospaced'>
INHERIT += "externalsrc"
EXTERNALSRC_pn-<replaceable>myrecipe</replaceable> = "<replaceable>path-to-your-source-tree</replaceable>"
</literallayout>
</para>
<para>
This next example shows how to accomplish the same thing by setting
<filename>EXTERNALSRC</filename> in the recipe itself or in the
recipe's append file:
<literallayout class='monospaced'>
EXTERNALSRC = "<replaceable>path</replaceable>"
EXTERNALSRC_BUILD = "<replaceable>path</replaceable>"
</literallayout>
<note>
In order for these settings to take effect, you must globally
or locally inherit the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc</filename></ulink>
class.
</note>
</para>
<para>
By default, <filename>externalsrc.bbclass</filename> builds
the source code in a directory separate from the external source
directory as specified by
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC'><filename>EXTERNALSRC</filename></ulink>.
If you need to have the source built in the same directory in
which it resides, or some other nominated directory, you can set
<ulink url='&YOCTO_DOCS_REF_URL;#var-EXTERNALSRC_BUILD'><filename>EXTERNALSRC_BUILD</filename></ulink>
to point to that directory:
<literallayout class='monospaced'>
EXTERNALSRC_BUILD_pn-<replaceable>myrecipe</replaceable> = "<replaceable>path-to-your-source-tree</replaceable>"
</literallayout>
</para>
</section>
<section id="selecting-an-initialization-manager">
<title>Selecting an Initialization Manager</title>
<para>
By default, the Yocto Project uses SysVinit as the initialization
manager.
However, support also exists for systemd,
which is a full replacement for init with
parallel starting of services, reduced shell overhead and other
features that are used by many distributions.
</para>
<para>
If you want to use SysVinit, you do
not have to do anything.
But, if you want to use systemd, you must
take some steps as described in the following sections.
</para>
<section id='using-systemd-exclusively'>
<title>Using systemd Exclusively</title>
<para>
Set the these variables in your distribution configuration
file as follows:
<literallayout class='monospaced'>
DISTRO_FEATURES_append = " systemd"
VIRTUAL-RUNTIME_init_manager = "systemd"
</literallayout>
You can also prevent the SysVinit
distribution feature from
being automatically enabled as follows:
<literallayout class='monospaced'>
DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"
</literallayout>
Doing so removes any redundant SysVinit scripts.
</para>
<para>
To remove initscripts from your image altogether,
set this variable also:
<literallayout class='monospaced'>
VIRTUAL-RUNTIME_initscripts = ""
</literallayout>
</para>
<para>
For information on the backfill variable, see
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>.
</para>
</section>
<section id='using-systemd-for-the-main-image-and-using-sysvinit-for-the-rescue-image'>
<title>Using systemd for the Main Image and Using SysVinit for the Rescue Image</title>
<para>
Set these variables in your distribution configuration
file as follows:
<literallayout class='monospaced'>
DISTRO_FEATURES_append = " systemd"
VIRTUAL-RUNTIME_init_manager = "systemd"
</literallayout>
Doing so causes your main image to use the
<filename>packagegroup-core-boot.bb</filename> recipe and
systemd.
The rescue/minimal image cannot use this package group.
However, it can install SysVinit
and the appropriate packages will have support for both
systemd and SysVinit.
</para>
</section>
</section>
<section id="selecting-dev-manager">
<title>Selecting a Device Manager</title>
<para>
The Yocto Project provides multiple ways to manage the device
manager (<filename>/dev</filename>):
<itemizedlist>
<listitem><para><emphasis>Persistent and Pre-Populated<filename>/dev</filename>:</emphasis>
For this case, the <filename>/dev</filename> directory
is persistent and the required device nodes are created
during the build.
</para></listitem>
<listitem><para><emphasis>Use <filename>devtmpfs</filename> with a Device Manager:</emphasis>
For this case, the <filename>/dev</filename> directory
is provided by the kernel as an in-memory file system and
is automatically populated by the kernel at runtime.
Additional configuration of device nodes is done in user
space by a device manager like
<filename>udev</filename> or
<filename>busybox-mdev</filename>.
</para></listitem>
</itemizedlist>
</para>
<section id="static-dev-management">
<title>Using Persistent and Pre-Populated<filename>/dev</filename></title>
<para>
To use the static method for device population, you need to
set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
variable to "0" as follows:
<literallayout class='monospaced'>
USE_DEVFS = "0"
</literallayout>
</para>
<para>
The content of the resulting <filename>/dev</filename>
directory is defined in a Device Table file.
The
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_DEVICE_TABLES'><filename>IMAGE_DEVICE_TABLES</filename></ulink>
variable defines the Device Table to use and should be set
in the machine or distro configuration file.
Alternatively, you can set this variable in your
<filename>local.conf</filename> configuration file.
</para>
<para>
If you do not define the
<filename>IMAGE_DEVICE_TABLES</filename> variable, the default
<filename>device_table-minimal.txt</filename> is used:
<literallayout class='monospaced'>
IMAGE_DEVICE_TABLES = "device_table-mymachine.txt"
</literallayout>
</para>
<para>
The population is handled by the <filename>makedevs</filename>
utility during image creation:
</para>
</section>
<section id="devtmpfs-dev-management">
<title>Using <filename>devtmpfs</filename> and a Device Manager</title>
<para>
To use the dynamic method for device population, you need to
use (or be sure to set) the
<ulink url='&YOCTO_DOCS_REF_URL;#var-USE_DEVFS'><filename>USE_DEVFS</filename></ulink>
variable to "1", which is the default:
<literallayout class='monospaced'>
USE_DEVFS = "1"
</literallayout>
With this setting, the resulting <filename>/dev</filename>
directory is populated by the kernel using
<filename>devtmpfs</filename>.
Make sure the corresponding kernel configuration variable
<filename>CONFIG_DEVTMPFS</filename> is set when building
you build a Linux kernel.
</para>
<para>
All devices created by <filename>devtmpfs</filename> will be
owned by <filename>root</filename> and have permissions
<filename>0600</filename>.
</para>
<para>
To have more control over the device nodes, you can use a
device manager like <filename>udev</filename> or
<filename>busybox-mdev</filename>.
You choose the device manager by defining the
<filename>VIRTUAL-RUNTIME_dev_manager</filename> variable
in your machine or distro configuration file.
Alternatively, you can set this variable in your
<filename>local.conf</filename> configuration file:
<literallayout class='monospaced'>
VIRTUAL-RUNTIME_dev_manager = "udev"
# Some alternative values
# VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
# VIRTUAL-RUNTIME_dev_manager = "systemd"
</literallayout>
</para>
</section>
</section>
<section id="platdev-appdev-srcrev">
<title>Using an External SCM</title>
<para>
If you're working on a recipe that pulls from an external Source
Code Manager (SCM), it is possible to have the OpenEmbedded build
system notice new recipe changes added to the SCM and then build
the resulting packages that depend on the new recipes by using
the latest versions.
This only works for SCMs from which it is possible to get a
sensible revision number for changes.
Currently, you can do this with Apache Subversion (SVN), Git, and
Bazaar (BZR) repositories.
</para>
<para>
To enable this behavior, the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
of the recipe needs to reference
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRCPV'><filename>SRCPV</filename></ulink>.
Here is an example:
<literallayout class='monospaced'>
PV = "1.2.3+git${SRCPV}"
</literallayout>
Then, you can add the following to your
<filename>local.conf</filename>:
<literallayout class='monospaced'>
SRCREV_pn-<replaceable>PN</replaceable> = "${AUTOREV}"
</literallayout>
<ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>
is the name of the recipe for which you want to enable automatic source
revision updating.
</para>
<para>
If you do not want to update your local configuration file, you can
add the following directly to the recipe to finish enabling
the feature:
<literallayout class='monospaced'>
SRCREV = "${AUTOREV}"
</literallayout>
</para>
<para>
The Yocto Project provides a distribution named
<filename>poky-bleeding</filename>, whose configuration
file contains the line:
<literallayout class='monospaced'>
require conf/distro/include/poky-floating-revisions.inc
</literallayout>
This line pulls in the listed include file that contains
numerous lines of exactly that form:
<literallayout class='monospaced'>
#SRCREV_pn-opkg-native ?= "${AUTOREV}"
#SRCREV_pn-opkg-sdk ?= "${AUTOREV}"
#SRCREV_pn-opkg ?= "${AUTOREV}"
#SRCREV_pn-opkg-utils-native ?= "${AUTOREV}"
#SRCREV_pn-opkg-utils ?= "${AUTOREV}"
SRCREV_pn-gconf-dbus ?= "${AUTOREV}"
SRCREV_pn-matchbox-common ?= "${AUTOREV}"
SRCREV_pn-matchbox-config-gtk ?= "${AUTOREV}"
SRCREV_pn-matchbox-desktop ?= "${AUTOREV}"
SRCREV_pn-matchbox-keyboard ?= "${AUTOREV}"
SRCREV_pn-matchbox-panel-2 ?= "${AUTOREV}"
SRCREV_pn-matchbox-themes-extra ?= "${AUTOREV}"
SRCREV_pn-matchbox-terminal ?= "${AUTOREV}"
SRCREV_pn-matchbox-wm ?= "${AUTOREV}"
SRCREV_pn-settings-daemon ?= "${AUTOREV}"
SRCREV_pn-screenshot ?= "${AUTOREV}"
.
.
.
</literallayout>
These lines allow you to experiment with building a
distribution that tracks the latest development source
for numerous packages.
<note><title>Caution</title>
The <filename>poky-bleeding</filename> distribution
is not tested on a regular basis.
Keep this in mind if you use it.
</note>
</para>
</section>
<section id='creating-a-read-only-root-filesystem'>
<title>Creating a Read-Only Root Filesystem</title>
<para>
Suppose, for security reasons, you need to disable
your target device's root filesystem's write permissions
(i.e. you need a read-only root filesystem).
Or, perhaps you are running the device's operating system
from a read-only storage device.
For either case, you can customize your image for
that behavior.
</para>
<note>
Supporting a read-only root filesystem requires that the system and
applications do not try to write to the root filesystem.
You must configure all parts of the target system to write
elsewhere, or to gracefully fail in the event of attempting to
write to the root filesystem.
</note>
<section id='creating-the-root-filesystem'>
<title>Creating the Root Filesystem</title>
<para>
To create the read-only root filesystem, simply add the
"read-only-rootfs" feature to your image.
Using either of the following statements in your
image recipe or from within the
<filename>local.conf</filename> file found in the
<link linkend='build-directory'>Build Directory</link>
causes the build system to create a read-only root filesystem:
<literallayout class='monospaced'>
IMAGE_FEATURES = "read-only-rootfs"
</literallayout>
or
<literallayout class='monospaced'>
EXTRA_IMAGE_FEATURES += "read-only-rootfs"
</literallayout>
</para>
<para>
For more information on how to use these variables, see the
"<link linkend='usingpoky-extend-customimage-imagefeatures'>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and <filename>EXTRA_IMAGE_FEATURES</filename></link>"
section.
For information on the variables, see
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>.
</para>
</section>
<section id='post-installation-scripts'>
<title>Post-Installation Scripts</title>
<para>
It is very important that you make sure all
post-Installation (<filename>pkg_postinst</filename>) scripts
for packages that are installed into the image can be run
at the time when the root filesystem is created during the
build on the host system.
These scripts cannot attempt to run during first-boot on the
target device.
With the "read-only-rootfs" feature enabled,
the build system checks during root filesystem creation to make
sure all post-installation scripts succeed.
If any of these scripts still need to be run after the root
filesystem is created, the build immediately fails.
These build-time checks ensure that the build fails
rather than the target device fails later during its
initial boot operation.
</para>
<para>
Most of the common post-installation scripts generated by the
build system for the out-of-the-box Yocto Project are engineered
so that they can run during root filesystem creation
(e.g. post-installation scripts for caching fonts).
However, if you create and add custom scripts, you need
to be sure they can be run during this file system creation.
</para>
<para>
Here are some common problems that prevent
post-installation scripts from running during root filesystem
creation:
<itemizedlist>
<listitem><para>
<emphasis>Not using $D in front of absolute
paths:</emphasis>
The build system defines
<filename>$</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink>
when the root filesystem is created.
Furthermore, <filename>$D</filename> is blank when the
script is run on the target device.
This implies two purposes for <filename>$D</filename>:
ensuring paths are valid in both the host and target
environments, and checking to determine which
environment is being used as a method for taking
appropriate actions.
</para></listitem>
<listitem><para>
<emphasis>Attempting to run processes that are
specific to or dependent on the target
architecture:</emphasis>
You can work around these attempts by using native
tools, which run on the host system,
to accomplish the same tasks, or
by alternatively running the processes under QEMU,
which has the <filename>qemu_run_binary</filename>
function.
For more information, see the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-qemu'><filename>qemu</filename></ulink>
class.</para></listitem>
</itemizedlist>
</para>
</section>
<section id='areas-with-write-access'>
<title>Areas With Write Access</title>
<para>
With the "read-only-rootfs" feature enabled,
any attempt by the target to write to the root filesystem at
runtime fails.
Consequently, you must make sure that you configure processes
and applications that attempt these types of writes do so
to directories with write access (e.g.
<filename>/tmp</filename> or <filename>/var/run</filename>).
</para>
</section>
</section>
<section id="performing-automated-runtime-testing">
<title>Performing Automated Runtime Testing</title>
<para>
The OpenEmbedded build system makes available a series of automated
tests for images to verify runtime functionality.
You can run these tests on either QEMU or actual target hardware.
Tests are written in Python making use of the
<filename>unittest</filename> module, and the majority of them
run commands on the target system over SSH.
This section describes how you set up the environment to use these
tests, run available tests, and write and add your own tests.
</para>
<para>
For information on the test and QA infrastructure available
within the Yocto Project, see the
"<ulink url='&YOCTO_DOCS_REF_URL;#testing-and-quality-assurance'>Testing and Quality Assurance</ulink>"
section in the Yocto Project Reference Manual.
</para>
<section id='enabling-tests'>
<title>Enabling Tests</title>
<para>
Depending on whether you are planning to run tests using
QEMU or on the hardware, you have to take
different steps to enable the tests.
See the following subsections for information on how to
enable both types of tests.
</para>
<section id='qemu-image-enabling-tests'>
<title>Enabling Runtime Tests on QEMU</title>
<para>
In order to run tests, you need to do the following:
<itemizedlist>
<listitem><para><emphasis>Set up to avoid interaction
with <filename>sudo</filename> for networking:</emphasis>
To accomplish this, you must do one of the
following:
<itemizedlist>
<listitem><para>Add
<filename>NOPASSWD</filename> for your user
in <filename>/etc/sudoers</filename> either for
all commands or just for
<filename>runqemu-ifup</filename>.
You must provide the full path as that can
change if you are using multiple clones of the
source repository.
<note>
On some distributions, you also need to
comment out "Defaults requiretty" in
<filename>/etc/sudoers</filename>.
</note></para></listitem>
<listitem><para>Manually configure a tap interface
for your system.</para></listitem>
<listitem><para>Run as root the script in
<filename>scripts/runqemu-gen-tapdevs</filename>,
which should generate a list of tap devices.
This is the option typically chosen for
Autobuilder-type environments.
</para></listitem>
</itemizedlist></para></listitem>
<listitem><para><emphasis>Set the
<filename>DISPLAY</filename> variable:</emphasis>
You need to set this variable so that you have an X
server available (e.g. start
<filename>vncserver</filename> for a headless machine).
</para></listitem>
<listitem><para><emphasis>Be sure your host's firewall
accepts incoming connections from
192.168.7.0/24:</emphasis>
Some of the tests (in particular DNF tests) start
an HTTP server on a random high number port,
which is used to serve files to the target.
The DNF module serves
<filename>${WORKDIR}/oe-rootfs-repo</filename>
so it can run DNF channel commands.
That means your host's firewall
must accept incoming connections from 192.168.7.0/24,
which is the default IP range used for tap devices
by <filename>runqemu</filename>.</para></listitem>
<listitem><para><emphasis>Be sure your host has the
correct packages installed:</emphasis>
Depending your host's distribution, you need
to have the following packages installed:
<itemizedlist>
<listitem><para>Ubuntu and Debian:
<filename>sysstat</filename> and
<filename>iproute2</filename>
</para></listitem>
<listitem><para>OpenSUSE:
<filename>sysstat</filename> and
<filename>iproute2</filename>
</para></listitem>
<listitem><para>Fedora:
<filename>sysstat</filename> and
<filename>iproute</filename>
</para></listitem>
<listitem><para>CentOS:
<filename>sysstat</filename> and
<filename>iproute</filename>
</para></listitem>
</itemizedlist>
</para></listitem>
</itemizedlist>
</para>
<para>
Once you start running the tests, the following happens:
<orderedlist>
<listitem><para>A copy of the root filesystem is written
to <filename>${WORKDIR}/testimage</filename>.
</para></listitem>
<listitem><para>The image is booted under QEMU using the
standard <filename>runqemu</filename> script.
</para></listitem>
<listitem><para>A default timeout of 500 seconds occurs
to allow for the boot process to reach the login prompt.
You can change the timeout period by setting
<ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_QEMUBOOT_TIMEOUT'><filename>TEST_QEMUBOOT_TIMEOUT</filename></ulink>
in the <filename>local.conf</filename> file.
</para></listitem>
<listitem><para>Once the boot process is reached and the
login prompt appears, the tests run.
The full boot log is written to
<filename>${WORKDIR}/testimage/qemu_boot_log</filename>.
</para></listitem>
<listitem><para>Each test module loads in the order found
in <filename>TEST_SUITES</filename>.
You can find the full output of the commands run over
SSH in
<filename>${WORKDIR}/testimgage/ssh_target_log</filename>.
</para></listitem>
<listitem><para>If no failures occur, the task running the
tests ends successfully.
You can find the output from the
<filename>unittest</filename> in the task log at
<filename>${WORKDIR}/temp/log.do_testimage</filename>.
</para></listitem>
</orderedlist>
</para>
</section>
<section id='hardware-image-enabling-tests'>
<title>Enabling Runtime Tests on Hardware</title>
<para>
The OpenEmbedded build system can run tests on real
hardware, and for certain devices it can also deploy
the image to be tested onto the device beforehand.
</para>
<para>
For automated deployment, a "master image" is installed
onto the hardware once as part of setup.
Then, each time tests are to be run, the following
occurs:
<orderedlist>
<listitem><para>The master image is booted into and
used to write the image to be tested to
a second partition.
</para></listitem>
<listitem><para>The device is then rebooted using an
external script that you need to provide.
</para></listitem>
<listitem><para>The device boots into the image to be
tested.
</para></listitem>
</orderedlist>
</para>
<para>
When running tests (independent of whether the image
has been deployed automatically or not), the device is
expected to be connected to a network on a
pre-determined IP address.
You can either use static IP addresses written into
the image, or set the image to use DHCP and have your
DHCP server on the test network assign a known IP address
based on the MAC address of the device.
</para>
<para>
In order to run tests on hardware, you need to set
<filename>TEST_TARGET</filename> to an appropriate value.
For QEMU, you do not have to change anything, the default
value is "QemuTarget".
For running tests on hardware, the following options exist:
<itemizedlist>
<listitem><para><emphasis>"SimpleRemoteTarget":</emphasis>
Choose "SimpleRemoteTarget" if you are going to
run tests on a target system that is already
running the image to be tested and is available
on the network.
You can use "SimpleRemoteTarget" in conjunction
with either real hardware or an image running
within a separately started QEMU or any
other virtual machine manager.
</para></listitem>
<listitem><para><emphasis>"Systemd-bootTarget":</emphasis>
Choose "Systemd-bootTarget" if your hardware is
an EFI-based machine with
<filename>systemd-boot</filename> as bootloader and
<filename>core-image-testmaster</filename>
(or something similar) is installed.
Also, your hardware under test must be in a
DHCP-enabled network that gives it the same IP
address for each reboot.</para>
<para>If you choose "Systemd-bootTarget", there are
additional requirements and considerations.
See the
"<link linkend='selecting-systemd-boottarget'>Selecting Systemd-bootTarget</link>"
section, which follows, for more information.
</para></listitem>
<listitem><para><emphasis>"BeagleBoneTarget":</emphasis>
Choose "BeagleBoneTarget" if you are deploying
images and running tests on the BeagleBone
"Black" or original "White" hardware.
For information on how to use these tests, see the
comments at the top of the BeagleBoneTarget
<filename>meta-yocto-bsp/lib/oeqa/controllers/beaglebonetarget.py</filename>
file.
</para></listitem>
<listitem><para><emphasis>"EdgeRouterTarget":</emphasis>
Choose "EdgeRouterTarget" is you are deploying
images and running tests on the Ubiquiti Networks
EdgeRouter Lite.
For information on how to use these tests, see the
comments at the top of the EdgeRouterTarget
<filename>meta-yocto-bsp/lib/oeqa/controllers/edgeroutertarget.py</filename>
file.
</para></listitem>
<listitem><para><emphasis>"GrubTarget":</emphasis>
Choose the "supports deploying images and running
tests on any generic PC that boots using GRUB.
For information on how to use these tests, see the
comments at the top of the GrubTarget
<filename>meta-yocto-bsp/lib/oeqa/controllers/grubtarget.py</filename>
file.
</para></listitem>
<listitem><para><emphasis>"<replaceable>your-target</replaceable>":</emphasis>
Create your own custom target if you want to run
tests when you are deploying images and running
tests on a custom machine within your BSP layer.
To do this, you need to add a Python unit that
defines the target class under
<filename>lib/oeqa/controllers/</filename> within
your layer.
You must also provide an empty
<filename>__init__.py</filename>.
For examples, see files in
<filename>meta-yocto-bsp/lib/oeqa/controllers/</filename>.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='selecting-systemd-boottarget'>
<title>Selecting Systemd-bootTarget</title>
<para>
If you did not set <filename>TEST_TARGET</filename> to
"Systemd-bootTarget", then you do not need any information
in this section.
You can skip down to the
"<link linkend='qemu-image-running-tests'>Running Tests</link>"
section.
</para>
<para>
If you did set <filename>TEST_TARGET</filename> to
"Systemd-bootTarget", you also need to perform a one-time
setup of your master image by doing the following:
<orderedlist>
<listitem><para><emphasis>Set <filename>EFI_PROVIDER</filename>:</emphasis>
Be sure that <filename>EFI_PROVIDER</filename>
is as follows:
<literallayout class='monospaced'>
EFI_PROVIDER = "systemd-boot"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Build the master image:</emphasis>
Build the <filename>core-image-testmaster</filename>
image.
The <filename>core-image-testmaster</filename>
recipe is provided as an example for a
"master" image and you can customize the image
recipe as you would any other recipe.
</para>
<para>Here are the image recipe requirements:
<itemizedlist>
<listitem><para>Inherits
<filename>core-image</filename>
so that kernel modules are installed.
</para></listitem>
<listitem><para>Installs normal linux utilities
not busybox ones (e.g.
<filename>bash</filename>,
<filename>coreutils</filename>,
<filename>tar</filename>,
<filename>gzip</filename>, and
<filename>kmod</filename>).
</para></listitem>
<listitem><para>Uses a custom
Initial RAM Disk (initramfs) image with a
custom installer.
A normal image that you can install usually
creates a single rootfs partition.
This image uses another installer that
creates a specific partition layout.
Not all Board Support Packages (BSPs)
can use an installer.
For such cases, you need to manually create
the following partition layout on the
target:
<itemizedlist>
<listitem><para>First partition mounted
under <filename>/boot</filename>,
labeled "boot".
</para></listitem>
<listitem><para>The main rootfs
partition where this image gets
installed, which is mounted under
<filename>/</filename>.
</para></listitem>
<listitem><para>Another partition
labeled "testrootfs" where test
images get deployed.
</para></listitem>
</itemizedlist>
</para></listitem>
</itemizedlist>
</para></listitem>
<listitem><para><emphasis>Install image:</emphasis>
Install the image that you just built on the target
system.
</para></listitem>
</orderedlist>
</para>
<para>
The final thing you need to do when setting
<filename>TEST_TARGET</filename> to "Systemd-bootTarget" is
to set up the test image:
<orderedlist>
<listitem><para><emphasis>Set up your <filename>local.conf</filename> file:</emphasis>
Make sure you have the following statements in
your <filename>local.conf</filename> file:
<literallayout class='monospaced'>
IMAGE_FSTYPES += "tar.gz"
INHERIT += "testimage"
TEST_TARGET = "Systemd-bootTarget"
TEST_TARGET_IP = "192.168.2.3"
</literallayout>
</para></listitem>
<listitem><para><emphasis>Build your test image:</emphasis>
Use BitBake to build the image:
<literallayout class='monospaced'>
$ bitbake core-image-sato
</literallayout>
</para></listitem>
</orderedlist>
</para>
</section>
<section id='power-control'>
<title>Power Control</title>
<para>
For most hardware targets other than SimpleRemoteTarget,
you can control power:
<itemizedlist>
<listitem><para>
You can use
<filename>TEST_POWERCONTROL_CMD</filename>
together with
<filename>TEST_POWERCONTROL_EXTRA_ARGS</filename>
as a command that runs on the host and does power
cycling.
The test code passes one argument to that command:
off, on or cycle (off then on).
Here is an example that could appear in your
<filename>local.conf</filename> file:
<literallayout class='monospaced'>
TEST_POWERCONTROL_CMD = "powercontrol.exp test 10.11.12.1 nuc1"
</literallayout>
In this example, the expect script does the
following:
<literallayout class='monospaced'>
ssh test@10.11.12.1 "pyctl nuc1 <replaceable>arg</replaceable>"
</literallayout>
It then runs a Python script that controls power
for a label called <filename>nuc1</filename>.
<note>
You need to customize
<filename>TEST_POWERCONTROL_CMD</filename>
and
<filename>TEST_POWERCONTROL_EXTRA_ARGS</filename>
for your own setup.
The one requirement is that it accepts
"on", "off", and "cycle" as the last argument.
</note>
</para></listitem>
<listitem><para>
When no command is defined, it connects to the
device over SSH and uses the classic reboot command
to reboot the device.
Classic reboot is fine as long as the machine
actually reboots (i.e. the SSH test has not
failed).
It is useful for scenarios where you have a simple
setup, typically with a single board, and where
some manual interaction is okay from time to time.
</para></listitem>
</itemizedlist>
If you have no hardware to automatically perform power
control but still wish to experiment with automated
hardware testing, you can use the dialog-power-control
script that shows a dialog prompting you to perform the
required power action.
This script requires either KDialog or Zenity to be
installed.
To use this script, set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_POWERCONTROL_CMD'><filename>TEST_POWERCONTROL_CMD</filename></ulink>
variable as follows:
<literallayout class='monospaced'>
TEST_POWERCONTROL_CMD = "${COREBASE}/scripts/contrib/dialog-power-control"
</literallayout>
</para>
</section>
<section id='serial-console-connection'>
<title>Serial Console Connection</title>
<para>
For test target classes requiring a serial console
to interact with the bootloader (e.g. BeagleBoneTarget,
EdgeRouterTarget, and GrubTarget), you need to
specify a command to use to connect to the serial console
of the target machine by using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SERIALCONTROL_CMD'><filename>TEST_SERIALCONTROL_CMD</filename></ulink>
variable and optionally the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SERIALCONTROL_EXTRA_ARGS'><filename>TEST_SERIALCONTROL_EXTRA_ARGS</filename></ulink>
variable.
</para>
<para>
These cases could be a serial terminal program if the
machine is connected to a local serial port, or a
<filename>telnet</filename> or
<filename>ssh</filename> command connecting to a remote
console server.
Regardless of the case, the command simply needs to
connect to the serial console and forward that connection
to standard input and output as any normal terminal
program does.
For example, to use the picocom terminal program on
serial device <filename>/dev/ttyUSB0</filename>
at 115200bps, you would set the variable as follows:
<literallayout class='monospaced'>
TEST_SERIALCONTROL_CMD = "picocom /dev/ttyUSB0 -b 115200"
</literallayout>
For local devices where the serial port device disappears
when the device reboots, an additional "serdevtry" wrapper
script is provided.
To use this wrapper, simply prefix the terminal command
with
<filename>${COREBASE}/scripts/contrib/serdevtry</filename>:
<literallayout class='monospaced'>
TEST_SERIALCONTROL_CMD = "${COREBASE}/scripts/contrib/serdevtry picocom -b
115200 /dev/ttyUSB0"
</literallayout>
</para>
</section>
</section>
<section id="qemu-image-running-tests">
<title>Running Tests</title>
<para>
You can start the tests automatically or manually:
<itemizedlist>
<listitem><para><emphasis>Automatically running tests:</emphasis>
To run the tests automatically after the
OpenEmbedded build system successfully creates an image,
first set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_IMAGE'><filename>TEST_IMAGE</filename></ulink>
variable to "1" in your <filename>local.conf</filename>
file in the
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
<literallayout class='monospaced'>
TEST_IMAGE = "1"
</literallayout>
Next, build your image.
If the image successfully builds, the tests will be
run:
<literallayout class='monospaced'>
bitbake core-image-sato
</literallayout></para></listitem>
<listitem><para><emphasis>Manually running tests:</emphasis>
To manually run the tests, first globally inherit the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-testimage*'><filename>testimage</filename></ulink>
class by editing your <filename>local.conf</filename>
file:
<literallayout class='monospaced'>
INHERIT += "testimage"
</literallayout>
Next, use BitBake to run the tests:
<literallayout class='monospaced'>
bitbake -c testimage <replaceable>image</replaceable>
</literallayout></para></listitem>
</itemizedlist>
</para>
<para>
All test files reside in
<filename>meta/lib/oeqa/runtime</filename> in the
<link linkend='source-directory'>Source Directory</link>.
A test name maps directly to a Python module.
Each test module may contain a number of individual tests.
Tests are usually grouped together by the area
tested (e.g tests for systemd reside in
<filename>meta/lib/oeqa/runtime/systemd.py</filename>).
</para>
<para>
You can add tests to any layer provided you place them in the
proper area and you extend
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>
in the <filename>local.conf</filename> file as normal.
Be sure that tests reside in
<filename><replaceable>layer</replaceable>/lib/oeqa/runtime</filename>.
<note>
Be sure that module names do not collide with module names
used in the default set of test modules in
<filename>meta/lib/oeqa/runtime</filename>.
</note>
</para>
<para>
You can change the set of tests run by appending or overriding
<ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SUITES'><filename>TEST_SUITES</filename></ulink>
variable in <filename>local.conf</filename>.
Each name in <filename>TEST_SUITES</filename> represents a
required test for the image.
Test modules named within <filename>TEST_SUITES</filename>
cannot be skipped even if a test is not suitable for an image
(e.g. running the RPM tests on an image without
<filename>rpm</filename>).
Appending "auto" to <filename>TEST_SUITES</filename> causes the
build system to try to run all tests that are suitable for the
image (i.e. each test module may elect to skip itself).
</para>
<para>
The order you list tests in <filename>TEST_SUITES</filename>
is important and influences test dependencies.
Consequently, tests that depend on other tests should be added
after the test on which they depend.
For example, since the <filename>ssh</filename> test
depends on the
<filename>ping</filename> test, "ssh" needs to come after
"ping" in the list.
The test class provides no re-ordering or dependency handling.
<note>
Each module can have multiple classes with multiple test
methods.
And, Python <filename>unittest</filename> rules apply.
</note>
</para>
<para>
Here are some things to keep in mind when running tests:
<itemizedlist>
<listitem><para>The default tests for the image are defined
as:
<literallayout class='monospaced'>
DEFAULT_TEST_SUITES_pn-<replaceable>image</replaceable> = "ping ssh df connman syslog xorg scp vnc date rpm dnf dmesg"
</literallayout></para></listitem>
<listitem><para>Add your own test to the list of the
by using the following:
<literallayout class='monospaced'>
TEST_SUITES_append = " mytest"
</literallayout></para></listitem>
<listitem><para>Run a specific list of tests as follows:
<literallayout class='monospaced'>
TEST_SUITES = "test1 test2 test3"
</literallayout>
Remember, order is important.
Be sure to place a test that is dependent on another test
later in the order.</para></listitem>
</itemizedlist>
</para>
</section>
<section id="exporting-tests">
<title>Exporting Tests</title>
<para>
You can export tests so that they can run independently of
the build system.
Exporting tests is required if you want to be able to hand
the test execution off to a scheduler.
You can only export tests that are defined in
<ulink url='&YOCTO_DOCS_REF_URL;#var-TEST_SUITES'><filename>TEST_SUITES</filename></ulink>.
</para>
<para>
If your image is already built, make sure the following are set
in your <filename>local.conf</filename> file:
<literallayout class='monospaced'>
INHERIT +="testexport"
TEST_TARGET_IP = "<replaceable>IP-address-for-the-test-target</replaceable>"
TEST_SERVER_IP = "<replaceable>IP-address-for-the-test-server</replaceable>"
</literallayout>
You can then export the tests with the following BitBake
command form:
<literallayout class='monospaced'>
$ bitbake <replaceable>image</replaceable> -c testexport
</literallayout>
Exporting the tests places them in the
<link linkend='build-directory'>Build Directory</link> in
<filename>tmp/testexport/</filename><replaceable>image</replaceable>,
which is controlled by the
<filename>TEST_EXPORT_DIR</filename> variable.
</para>
<para>
You can now run the tests outside of the build environment:
<literallayout class='monospaced'>
$ cd tmp/testexport/<replaceable>image</replaceable>
$ ./runexported.py testdata.json
</literallayout>
</para>
<para>
Here is a complete example that shows IP addresses and uses
the <filename>core-image-sato</filename> image:
<literallayout class='monospaced'>
INHERIT +="testexport"
TEST_TARGET_IP = "192.168.7.2"
TEST_SERVER_IP = "192.168.7.1"
</literallayout>
Use BitBake to export the tests:
<literallayout class='monospaced'>
$ bitbake core-image-sato -c testexport
</literallayout>
Run the tests outside of the build environment using the
following:
<literallayout class='monospaced'>
$ cd tmp/testexport/core-image-sato
$ ./runexported.py testdata.json
</literallayout>
</para>
</section>
<section id="qemu-image-writing-new-tests">
<title>Writing New Tests</title>
<para>
As mentioned previously, all new test files need to be in the
proper place for the build system to find them.
New tests for additional functionality outside of the core
should be added to the layer that adds the functionality, in
<filename><replaceable>layer</replaceable>/lib/oeqa/runtime</filename>
(as long as
<ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>
is extended in the layer's
<filename>layer.conf</filename> file as normal).
Just remember the following:
<itemizedlist>
<listitem><para>Filenames need to map directly to test
(module) names.
</para></listitem>
<listitem><para>Do not use module names that
collide with existing core tests.
</para></listitem>
<listitem><para>Minimally, an empty
<filename>__init__.py</filename> file must exist
in the runtime directory.
</para></listitem>
</itemizedlist>
</para>
<para>
To create a new test, start by copying an existing module
(e.g. <filename>syslog.py</filename> or
<filename>gcc.py</filename> are good ones to use).
Test modules can use code from
<filename>meta/lib/oeqa/utils</filename>, which are helper
classes.
</para>
<note>
Structure shell commands such that you rely on them and they
return a single code for success.
Be aware that sometimes you will need to parse the output.
See the <filename>df.py</filename> and
<filename>date.py</filename> modules for examples.
</note>
<para>
You will notice that all test classes inherit
<filename>oeRuntimeTest</filename>, which is found in
<filename>meta/lib/oetest.py</filename>.
This base class offers some helper attributes, which are
described in the following sections:
</para>
<section id='qemu-image-writing-tests-class-methods'>
<title>Class Methods</title>
<para>
Class methods are as follows:
<itemizedlist>
<listitem><para><emphasis><filename>hasPackage(pkg)</filename>:</emphasis>
Returns "True" if <filename>pkg</filename> is in the
installed package list of the image, which is based
on the manifest file that is generated during the
<filename>do_rootfs</filename> task.
</para></listitem>
<listitem><para><emphasis><filename>hasFeature(feature)</filename>:</emphasis>
Returns "True" if the feature is in
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id='qemu-image-writing-tests-class-attributes'>
<title>Class Attributes</title>
<para>
Class attributes are as follows:
<itemizedlist>
<listitem><para><emphasis><filename>pscmd</filename>:</emphasis>
Equals "ps -ef" if <filename>procps</filename> is
installed in the image.
Otherwise, <filename>pscmd</filename> equals
"ps" (busybox).
</para></listitem>
<listitem><para><emphasis><filename>tc</filename>:</emphasis>
The called test context, which gives access to the
following attributes:
<itemizedlist>
<listitem><para><emphasis><filename>d</filename>:</emphasis>
The BitBake datastore, which allows you to
use stuff such as
<filename>oeRuntimeTest.tc.d.getVar("VIRTUAL-RUNTIME_init_manager")</filename>.
</para></listitem>
<listitem><para><emphasis><filename>testslist</filename> and <filename>testsrequired</filename>:</emphasis>
Used internally.
The tests do not need these.
</para></listitem>
<listitem><para><emphasis><filename>filesdir</filename>:</emphasis>
The absolute path to
<filename>meta/lib/oeqa/runtime/files</filename>,
which contains helper files for tests meant
for copying on the target such as small
files written in C for compilation.
</para></listitem>
<listitem><para><emphasis><filename>target</filename>:</emphasis>
The target controller object used to deploy
and start an image on a particular target
(e.g. QemuTarget, SimpleRemote, and
Systemd-bootTarget).
Tests usually use the following:
<itemizedlist>
<listitem><para><emphasis><filename>ip</filename>:</emphasis>
The target's IP address.
</para></listitem>
<listitem><para><emphasis><filename>server_ip</filename>:</emphasis>
The host's IP address, which is
usually used by the DNF test
suite.
</para></listitem>
<listitem><para><emphasis><filename>run(cmd, timeout=None)</filename>:</emphasis>
The single, most used method.
This command is a wrapper for:
<filename>ssh root@host "cmd"</filename>.
The command returns a tuple:
(status, output), which are what
their names imply - the return code
of "cmd" and whatever output
it produces.
The optional timeout argument
represents the number of seconds the
test should wait for "cmd" to
return.
If the argument is "None", the
test uses the default instance's
timeout period, which is 300
seconds.
If the argument is "0", the test
runs until the command returns.
</para></listitem>
<listitem><para><emphasis><filename>copy_to(localpath, remotepath)</filename>:</emphasis>
<filename>scp localpath root@ip:remotepath</filename>.
</para></listitem>
<listitem><para><emphasis><filename>copy_from(remotepath, localpath)</filename>:</emphasis>
<filename>scp root@host:remotepath localpath</filename>.
</para></listitem>
</itemizedlist></para></listitem>
</itemizedlist></para></listitem>
</itemizedlist>
</para>
</section>
<section id='qemu-image-writing-tests-instance-attributes'>
<title>Instance Attributes</title>
<para>
A single instance attribute exists, which is
<filename>target</filename>.
The <filename>target</filename> instance attribute is
identical to the class attribute of the same name, which
is described in the previous section.
This attribute exists as both an instance and class
attribute so tests can use
<filename>self.target.run(cmd)</filename> in instance
methods instead of
<filename>oeRuntimeTest.tc.target.run(cmd)</filename>.
</para>
</section>
</section>
<section id='installing-packages-in-the-dut-without-the-package-manager'>
<title>Installing Packages in the DUT Without the Package Manager</title>
<para>
When a test requires a package built by BitBake, it is possible
to install that package.
Installing the package does not require a package manager be
installed in the device under test (DUT).
It does, however, require an SSH connection and the target must
be using the <filename>sshcontrol</filename> class.
<note>
This method uses <filename>scp</filename> to copy files
from the host to the target, which causes permissions and
special attributes to be lost.
</note>
</para>
<para>
A JSON file is used to define the packages needed by a test.
This file must be in the same path as the file used to define
the tests.
Furthermore, the filename must map directly to the test
module name with a <filename>.json</filename> extension.
</para>
<para>
The JSON file must include an object with the test name as
keys of an object or an array.
This object (or array of objects) uses the following data:
<itemizedlist>
<listitem><para>"pkg" - A mandatory string that is the
name of the package to be installed.
</para></listitem>
<listitem><para>"rm" - An optional boolean, which defaults
to "false", that specifies to remove the package after
the test.
</para></listitem>
<listitem><para>"extract" - An optional boolean, which
defaults to "false", that specifies if the package must
be extracted from the package format.
When set to "true", the package is not automatically
installed into the DUT.
</para></listitem>
</itemizedlist>
</para>
<para>
Following is an example JSON file that handles test "foo"
installing package "bar" and test "foobar" installing
packages "foo" and "bar".
Once the test is complete, the packages are removed from the
DUT.
<literallayout class='monospaced'>
{
"foo": {
"pkg": "bar"
},
"foobar": [
{
"pkg": "foo",
"rm": true
},
{
"pkg": "bar",
"rm": true
}
]
}
</literallayout>
</para>
</section>
</section>
<section id="platdev-gdb-remotedebug">
<title>Debugging With the GNU Project Debugger (GDB) Remotely</title>
<para>
GDB allows you to examine running programs, which in turn helps you to understand and fix problems.
It also allows you to perform post-mortem style analysis of program crashes.
GDB is available as a package within the Yocto Project and is
installed in SDK images by default.
See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter
in the Yocto Project Reference Manual for a description of these images.
You can find information on GDB at <ulink url="http://sourceware.org/gdb/"/>.
</para>
<tip>
For best results, install debug (<filename>-dbg</filename>) packages
for the applications you are going to debug.
Doing so makes extra debug symbols available that give you more
meaningful output.
</tip>
<para>
Sometimes, due to memory or disk space constraints, it is not possible
to use GDB directly on the remote target to debug applications.
These constraints arise because GDB needs to load the debugging information and the
binaries of the process being debugged.
Additionally, GDB needs to perform many computations to locate information such as function
names, variable names and values, stack traces and so forth - even before starting the
debugging process.
These extra computations place more load on the target system and can alter the
characteristics of the program being debugged.
</para>
<para>
To help get past the previously mentioned constraints, you can use
gdbserver, which runs on the remote target and does not load any
debugging information from the debugged process.
Instead, a GDB instance processes the debugging information that is run on a
remote computer - the host GDB.
The host GDB then sends control commands to gdbserver to make it stop or start the debugged
program, as well as read or write memory regions of that debugged program.
All the debugging information loaded and processed as well
as all the heavy debugging is done by the host GDB.
Offloading these processes gives the gdbserver running on the target a chance to remain
small and fast.
</para>
<para>
Because the host GDB is responsible for loading the debugging information and
for doing the necessary processing to make actual debugging happen,
you have to make sure the host can access the unstripped binaries complete
with their debugging information and also be sure the target is compiled with no optimizations.
The host GDB must also have local access to all the libraries used by the
debugged program.
Because gdbserver does not need any local debugging information, the binaries on
the remote target can remain stripped.
However, the binaries must also be compiled without optimization
so they match the host's binaries.
</para>
<para>
To remain consistent with GDB documentation and terminology, the binary being debugged
on the remote target machine is referred to as the "inferior" binary.
For documentation on GDB see the
<ulink url="http://sourceware.org/gdb/documentation/">GDB site</ulink>.
</para>
<para>
The following steps show you how to debug using the GNU project
debugger.
<orderedlist>
<listitem><para>
<emphasis>Configure your build system to construct the
companion debug filesystem:</emphasis></para>
<para>In your <filename>local.conf</filename> file, set
the following:
<literallayout class='monospaced'>
IMAGE_GEN_DEBUGFS = "1"
IMAGE_FSTYPES_DEBUGFS = "tar.bz2"
</literallayout>
These options cause the OpenEmbedded build system
to generate a special companion filesystem fragment,
which contains the matching source and debug symbols to
your deployable filesystem.
The build system does this by looking at what is in the
deployed filesystem, and pulling the corresponding
<filename>-dbg</filename> packages.</para>
<para>The companion debug filesystem is not a complete
filesystem, but only contains the debug fragments.
This filesystem must be combined with the full filesystem
for debugging.
Subsequent steps in this procedure show how to combine
the partial filesystem with the full filesystem.
</para></listitem>
<listitem><para>
<emphasis>Configure the system to include gdbserver in
the target filesystem:</emphasis></para>
<para>Make the following addition in either your
<filename>local.conf</filename> file or in an image
recipe:
<literallayout class='monospaced'>
IMAGE_INSTALL_append = “ gdbserver"
</literallayout>
The change makes sure the <filename>gdbserver</filename>
package is included.
</para></listitem>
<listitem><para>
<emphasis>Build the environment:</emphasis></para>
<para>Use the following command to construct the image and
the companion Debug Filesystem:
<literallayout class='monospaced'>
$ bitbake <replaceable>image</replaceable>
</literallayout>
Build the cross GDB component and make it available
for debugging.
Build the SDK that matches the image.
Building the SDK is best for a production build
that can be used later for debugging, especially
during long term maintenance:
<literallayout class='monospaced'>
$ bitbake -c populate_sdk <replaceable>image</replaceable>
</literallayout></para>
<para>Alternatively, you can build the minimal
toolchain components that match the target.
Doing so creates a smaller than typical SDK and only
contains a minimal set of components with which to
build simple test applications, as well as run the
debugger:
<literallayout class='monospaced'>
$ bitbake meta-toolchain
</literallayout></para>
<para>A final method is to build Gdb itself within
the build system:
<literallayout class='monospaced'>
$ bitbake gdb-cross-<replaceable>architecture</replaceable>
</literallayout>
Doing so produces a temporary copy of
<filename>cross-gdb</filename> you can use for
debugging during development.
While this is the quickest approach, the two previous
methods in this step are better when considering
long-term maintenance strategies.
<note>
If you run
<filename>bitbake gdb-cross</filename>, the
OpenEmbedded build system suggests the actual
image (e.g. <filename>gdb-cross-i586</filename>).
The suggestion is usually the actual name you want
to use.
</note>
</para></listitem>
<listitem><para>
<emphasis>Set up the</emphasis>&nbsp;<filename>debugfs</filename></para>
<para>Run the following commands to set up the
<filename>debugfs</filename>:
<literallayout class='monospaced'>
$ mkdir debugfs
$ cd debugfs
$ tar xvfj <replaceable>build-dir</replaceable>/tmp-glibc/deploy/images/<replaceable>machine</replaceable>/<replaceable>image</replaceable>.rootfs.tar.bz2
$ tar xvfj <replaceable>build-dir</replaceable>/tmp-glibc/deploy/images/<replaceable>machine</replaceable>/<replaceable>image</replaceable>-dbg.rootfs.tar.bz2
</literallayout>
</para></listitem>
<listitem><para>
<emphasis>Set up GDB</emphasis></para>
<para>Install the SDK (if you built one) and then
source the correct environment file.
Sourcing the environment file puts the SDK in your
<filename>PATH</filename> environment variable.</para>
<para>If you are using the build system, Gdb is
located in
<replaceable>build-dir</replaceable>/tmp/sysroots/<replaceable>host</replaceable>/usr/bin/<replaceable>architecture</replaceable>/<replaceable>architecture</replaceable>-gdb
</para></listitem>
<listitem><para>
<emphasis>Boot the target:</emphasis></para>
<para>For information on how to run QEMU, see the
<ulink url='http://wiki.qemu.org/Documentation/GettingStartedDevelopers'>QEMU Documentation</ulink>.
<note>
Be sure to verify that your host can access the
target via TCP.
</note>
</para></listitem>
<listitem><para>
<emphasis>Debug a program:</emphasis></para>
<para>Debugging a program involves running gdbserver
on the target and then running Gdb on the host.
The example in this step debugs
<filename>gzip</filename>:
<literallayout class='monospaced'>
root@qemux86:~# gdbserver localhost:1234 /bin/gzip —help
</literallayout>
For additional gdbserver options, see the
<ulink url='https://www.gnu.org/software/gdb/documentation/'>GDB Server Documentation</ulink>.
</para>
<para>After running gdbserver on the target, you need
to run Gdb on the host and configure it and connect to
the target.
Use these commands:
<literallayout class='monospaced'>
$ cd <replaceable>directory-holding-the-debugfs-directory</replaceable>
$ <replaceable>arch</replaceable>-gdb
(gdb) set sysroot debugfs
(gdb) set substitute-path /usr/src/debug debugfs/usr/src/debug
(gdb) target remote <replaceable>IP-of-target</replaceable>:1234
</literallayout>
At this point, everything should automatically load
(i.e. matching binaries, symbols and headers).
<note>
The Gdb <filename>set</filename> commands in the
previous example can be placed into the users
<filename>~/.gdbinit</filename> file.
Upon starting, Gdb automatically runs whatever
commands are in that file.
</note>
</para></listitem>
<listitem><para>
<emphasis>Deploying without a full image
rebuild:</emphasis></para>
<para>In many cases, during development you want a
quick method to deploy a new binary to the target and
debug it, without waiting for a full image build.
</para>
<para>One approach to solving this situation is to
just build the component you want to debug.
Once you have built the component, copy the
executable directly to both the target and the
host <filename>debugfs</filename>.</para>
<para>If the binary is processed through the debug
splitting in OpenEmbedded, you should also
copy the debug items (i.e. <filename>.debug</filename>
contents and corresponding
<filename>/usr/src/debug</filename> files)
from the work directory.
Here is an example:
<literallayout class='monospaced'>
$ bitbake bash
$ bitbake -c devshell bash
$ cd ..
$ scp packages-split/bash/bin/bash <replaceable>target</replaceable>:/bin/bash
$ cp -a packages-split/bash-dbg/* <replaceable>path</replaceable>/debugfs
</literallayout>
</para></listitem>
</orderedlist>
</para>
</section>
<!--
<section id='platdev-gdb-remotedebug-setup'>
<title>Set Up the Cross-Development Debugging Environment</title>
<para>
Before you can initiate a remote debugging session, you need
to be sure you have set up the cross-development environment,
toolchain, and sysroot.
The <ulink url='&YOCTO_DOCS_SDK_URL;#sdk-intro'>Yocto Project Software Development Kit (SDK) Developer's Guide</ulink>
describes this process.
</para>
</section>
<section id="platdev-gdb-remotedebug-launch-gdbserver">
<title>Launch gdbserver on the Target</title>
<para>
Make sure gdbserver is installed on the target.
If it is not, install the package
<filename>gdbserver</filename>, which needs the
<filename>libthread-db1</filename> package.
</para>
<para>
Here is an example, that when entered from the host,
connects to the target and launches gdbserver in order to
"debug" a binary named <filename>helloworld</filename>:
<literallayout class='monospaced'>
$ gdbserver localhost:2345 /usr/bin/helloworld
</literallayout>
gdbserver should now be listening on port 2345 for debugging
commands coming from a remote GDB process that is running on
the host computer.
Communication between gdbserver and the host GDB are done
using TCP.
To use other communication protocols, please refer to the
<ulink url='http://www.gnu.org/software/gdb/'>Gdbserver documentation</ulink>.
</para>
</section>
<section id="platdev-gdb-remotedebug-launch-gdb">
<title>Launch GDB on the Host Computer</title>
<para>
Running GDB on the host computer takes a number of stages, which
this section describes.
</para>
<section id="platdev-gdb-remotedebug-launch-gdb-buildcross">
<title>Build the Cross-GDB Package</title>
<para>
A suitable GDB cross-binary is required that runs on your
host computer but also knows about the the ABI of the
remote target.
You can get this binary from the
<link linkend='cross-development-toolchain'>Cross-Development Toolchain</link>.
Here is an example where the toolchain has been installed
in the default directory
<filename>/opt/poky/&DISTRO;</filename>:
<literallayout class='monospaced'>
/opt/poky/&DISTRO;/sysroots/i686-pokysdk-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gdb
</literallayout>
where <filename>arm</filename> is the target architecture
and <filename>linux-gnueabi</filename> is the target ABI.
</para>
<para>
Alternatively, you can use BitBake to build the
<filename>gdb-cross</filename> binary.
Here is an example:
<literallayout class='monospaced'>
$ bitbake gdb-cross
</literallayout>
Once the binary is built, you can find it here:
<literallayout class='monospaced'>
tmp/sysroots/<replaceable>host-arch</replaceable>/usr/bin/<replaceable>target-platform</replaceable>/<replaceable>target-abi</replaceable>-gdb
</literallayout>
</para>
</section>
<section id='create-the-gdb-initialization-file'>
<title>Create the GDB Initialization File and Point to Your Root Filesystem</title>
<para>
Aside from the GDB cross-binary, you also need a GDB
initialization file in the same top directory in which
your binary resides.
When you start GDB on your host development system, GDB
finds this initialization file and executes all the
commands within.
For information on the <filename>.gdbinit</filename>, see
"<ulink url='http://sourceware.org/gdb/onlinedocs/gdb/'>Debugging with GDB</ulink>",
which is maintained by
<ulink url='http://www.sourceware.org'>sourceware.org</ulink>.
</para>
<para>
You need to add a statement in the
<filename>~/.gdbinit</filename> file that points to your
root filesystem.
Here is an example that points to the root filesystem for
an ARM-based target device:
<literallayout class='monospaced'>
set sysroot ~/sysroot_arm
</literallayout>
</para>
</section>
<section id="platdev-gdb-remotedebug-launch-gdb-launchhost">
<title>Launch the Host GDB</title>
<para>
Before launching the host GDB, you need to be sure
you have sourced the cross-debugging environment script,
which if you installed the root filesystem in the default
location is at <filename>/opt/poky/&DISTRO;</filename>
and begins with the string "environment-setup".
For more information, see the
<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-manual'>Yocto Project Software Development Kit (SDK) Developer's
Guide</ulink>.
</para>
<para>
Finally, switch to the directory where the binary resides
and run the <filename>cross-gdb</filename> binary.
Provide the binary file you are going to debug.
For example, the following command continues with the
example used in the previous section by loading
the <filename>helloworld</filename> binary as well as the
debugging information:
<literallayout class='monospaced'>
$ arm-poky-linux-gnuabi-gdb helloworld
</literallayout>
The commands in your <filename>.gdbinit</filename> execute
and the GDB prompt appears.
</para>
</section>
</section>
<section id='platdev-gdb-connect-to-the-remote-gdb-server'>
<title>Connect to the Remote GDB Server</title>
<para>
From the target, you need to connect to the remote GDB
server that is running on the host.
You need to specify the remote host and port.
Here is the command continuing with the example:
<literallayout class='monospaced'>
target remote 192.168.7.2:2345
</literallayout>
</para>
</section>
<section id="platdev-gdb-remotedebug-launch-gdb-using">
<title>Use the Debugger</title>
<para>
You can now proceed with debugging as normal - as if you were debugging
on the local machine.
For example, to instruct GDB to break in the "main" function and then
continue with execution of the inferior binary use the following commands
from within GDB:
<literallayout class='monospaced'>
(gdb) break main
(gdb) continue
</literallayout>
</para>
<para>
For more information about using GDB, see the project's online documentation at
<ulink url="http://sourceware.org/gdb/download/onlinedocs/"/>.
</para>
</section>
</section>
-->
<section id='debugging-with-the-gnu-project-debugger-gdb-on-the-target'>
<title>Debugging with the GNU Project Debugger (GDB) on the Target</title>
<para>
The previous section addressed using GDB remotely for debugging
purposes, which is the most usual case due to the inherent
hardware limitations on many embedded devices.
However, debugging in the target hardware itself is also possible
with more powerful devices.
This section describes what you need to do in order to support
using GDB to debug on the target hardware.
</para>
<para>
To support this kind of debugging, you need do the following:
<itemizedlist>
<listitem><para>
Ensure that GDB is on the target.
You can do this by adding "gdb" to
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>:
<literallayout class='monospaced'>
IMAGE_INSTALL_append = " gdb"
</literallayout>
Alternatively, you can add "tools-debug" to
<ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>:
<literallayout class='monospaced'>
IMAGE_FEATURES_append = " tools-debug"
</literallayout>
</para></listitem>
<listitem><para>
Ensure that debug symbols are present.
You can make sure these symbols are present by installing
<filename>-dbg</filename>:
<literallayout class='monospaced'>
IMAGE_INSTALL_append = " <replaceable>packagename</replaceable>-dbg"
</literallayout>
Alternatively, you can do the following to include all the
debug symbols:
<literallayout class='monospaced'>
IMAGE_FEATURES_append = " dbg-pkgs"
</literallayout>
</para></listitem>
</itemizedlist>
<note>
To improve the debug information accuracy, you can reduce the
level of optimization used by the compiler.
For example, when adding the following line to your
<filename>local.conf</filename> file, you will reduce
optimization from
<ulink url='&YOCTO_DOCS_REF_URL;#var-FULL_OPTIMIZATION'><filename>FULL_OPTIMIZATION</filename></ulink>
of "-O2" to
<ulink url='&YOCTO_DOCS_REF_URL;#var-DEBUG_OPTIMIZATION'><filename>DEBUG_OPTIMIZATION</filename></ulink>
of "-O -fno-omit-frame-pointer":
<literallayout class='monospaced'>
DEBUG_BUILD = "1"
</literallayout>
Consider that this will reduce the application's performance
and is recommended only for debugging purposes.
</note>
</para>
</section>
<section id='debugging-parallel-make-races'>
<title>Debugging Parallel Make Races</title>
<para>
A parallel <filename>make</filename> race occurs when the build
consists of several parts that are run simultaneously and
a situation occurs when the output or result of one
part is not ready for use with a different part of the build that
depends on that output.
Parallel make races are annoying and can sometimes be difficult
to reproduce and fix.
However, some simple tips and tricks exist that can help
you debug and fix them.
This section presents a real-world example of an error encountered
on the Yocto Project autobuilder and the process used to fix it.
<note>
If you cannot properly fix a <filename>make</filename> race
condition, you can work around it by clearing either the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
or
<ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKEINST'><filename>PARALLEL_MAKEINST</filename></ulink>
variables.
</note>
</para>
<section id='the-failure'>
<title>The Failure</title>
<para>
For this example, assume that you are building an image that
depends on the "neard" package.
And, during the build, BitBake runs into problems and
creates the following output.
<note>
This example log file has longer lines artificially
broken to make the listing easier to read.
</note>
If you examine the output or the log file, you see the
failure during <filename>make</filename>:
<literallayout class='monospaced'>
| DEBUG: SITE files ['endian-little', 'bit-32', 'ix86-common', 'common-linux', 'common-glibc', 'i586-linux', 'common']
| DEBUG: Executing shell function do_compile
| NOTE: make -j 16
| make --no-print-directory all-am
| /bin/mkdir -p include/near
| /bin/mkdir -p include/near
| /bin/mkdir -p include/near
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/types.h include/near/types.h
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/log.h include/near/log.h
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/plugin.h include/near/plugin.h
| /bin/mkdir -p include/near
| /bin/mkdir -p include/near
| /bin/mkdir -p include/near
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/tag.h include/near/tag.h
| /bin/mkdir -p include/near
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/adapter.h include/near/adapter.h
| /bin/mkdir -p include/near
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/ndef.h include/near/ndef.h
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/tlv.h include/near/tlv.h
| /bin/mkdir -p include/near
| /bin/mkdir -p include/near
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/setting.h include/near/setting.h
| /bin/mkdir -p include/near
| /bin/mkdir -p include/near
| /bin/mkdir -p include/near
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/device.h include/near/device.h
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/nfc_copy.h include/near/nfc_copy.h
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/snep.h include/near/snep.h
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/version.h include/near/version.h
| ln -s /home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/work/i586-poky-linux/neard/
0.14-r0/neard-0.14/include/dbus.h include/near/dbus.h
| ./src/genbuiltin nfctype1 nfctype2 nfctype3 nfctype4 p2p > src/builtin.h
| i586-poky-linux-gcc -m32 -march=i586 --sysroot=/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/
build/build/tmp/sysroots/qemux86 -DHAVE_CONFIG_H -I. -I./include -I./src -I./gdbus -I/home/pokybuild/
yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/glib-2.0
-I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/
lib/glib-2.0/include -I/home/pokybuild/yocto-autobuilder/yocto-slave/nightly-x86/build/build/
tmp/sysroots/qemux86/usr/include/dbus-1.0 -I/home/pokybuild/yocto-autobuilder/yocto-slave/
nightly-x86/build/build/tmp/sysroots/qemux86/usr/lib/dbus-1.0/include -I/home/pokybuild/yocto-autobuilder/
yocto-slave/nightly-x86/build/build/tmp/sysroots/qemux86/usr/include/libnl3
-DNEAR_PLUGIN_BUILTIN -DPLUGINDIR=\""/usr/lib/near/plugins"\"
-DCONFIGDIR=\""/etc/neard\"" -O2 -pipe -g -feliminate-unused-debug-types -c
-o tools/snep-send.o tools/snep-send.c
| In file included from tools/snep-send.c:16:0:
| tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
| #include &lt;near/dbus.h&gt;
| ^
| compilation terminated.
| make[1]: *** [tools/snep-send.o] Error 1
| make[1]: *** Waiting for unfinished jobs....
| make: *** [all] Error 2
| ERROR: oe_runmake failed
</literallayout>
</para>
</section>
<section id='reproducing-the-error'>
<title>Reproducing the Error</title>
<para>
Because race conditions are intermittent, they do not
manifest themselves every time you do the build.
In fact, most times the build will complete without problems
even though the potential race condition exists.
Thus, once the error surfaces, you need a way to reproduce it.
</para>
<para>
In this example, compiling the "neard" package is causing the
problem.
So the first thing to do is build "neard" locally.
Before you start the build, set the
<ulink url='&YOCTO_DOCS_REF_URL;#var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></ulink>
variable in your <filename>local.conf</filename> file to
a high number (e.g. "-j 20").
Using a high value for <filename>PARALLEL_MAKE</filename>
increases the chances of the race condition showing up:
<literallayout class='monospaced'>
$ bitbake neard
</literallayout>
</para>
<para>
Once the local build for "neard" completes, start a
<filename>devshell</filename> build:
<literallayout class='monospaced'>
$ bitbake neard -c devshell
</literallayout>
For information on how to use a
<filename>devshell</filename>, see the
"<link linkend='platdev-appdev-devshell'>Using a Development Shell</link>"
section.
</para>
<para>
In the <filename>devshell</filename>, do the following:
<literallayout class='monospaced'>
$ make clean
$ make tools/snep-send.o
</literallayout>
The <filename>devshell</filename> commands cause the failure
to clearly be visible.
In this case, a missing dependency exists for the "neard"
Makefile target.
Here is some abbreviated, sample output with the
missing dependency clearly visible at the end:
<literallayout class='monospaced'>
i586-poky-linux-gcc -m32 -march=i586 --sysroot=/home/scott-lenovo/......
.
.
.
tools/snep-send.c
In file included from tools/snep-send.c:16:0:
tools/../src/near.h:41:23: fatal error: near/dbus.h: No such file or directory
#include &lt;near/dbus.h&gt;
^
compilation terminated.
make: *** [tools/snep-send.o] Error 1
$
</literallayout>
</para>
</section>
<section id='creating-a-patch-for-the-fix'>
<title>Creating a Patch for the Fix</title>
<para>
Because there is a missing dependency for the Makefile
target, you need to patch the
<filename>Makefile.am</filename> file, which is generated
from <filename>Makefile.in</filename>.
You can use Quilt to create the patch:
<literallayout class='monospaced'>
$ quilt new parallelmake.patch
Patch patches/parallelmake.patch is now on top
$ quilt add Makefile.am
File Makefile.am added to patch patches/parallelmake.patch
</literallayout>
For more information on using Quilt, see the
"<link linkend='using-a-quilt-workflow'>Using Quilt in Your Workflow</link>"
section.
</para>
<para>
At this point you need to make the edits to
<filename>Makefile.am</filename> to add the missing
dependency.
For our example, you have to add the following line
to the file:
<literallayout class='monospaced'>
tools/snep-send.$(OBJEXT): include/near/dbus.h
</literallayout>
</para>
<para>
Once you have edited the file, use the
<filename>refresh</filename> command to create the patch:
<literallayout class='monospaced'>
$ quilt refresh
Refreshed patch patches/parallelmake.patch
</literallayout>
Once the patch file exists, you need to add it back to the
originating recipe folder.
Here is an example assuming a top-level
<link linkend='source-directory'>Source Directory</link>
named <filename>poky</filename>:
<literallayout class='monospaced'>
$ cp patches/parallelmake.patch poky/meta/recipes-connectivity/neard/neard
</literallayout>
The final thing you need to do to implement the fix in the
build is to update the "neard" recipe (i.e.
<filename>neard-0.14.bb</filename>) so that the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
statement includes the patch file.
The recipe file is in the folder above the patch.
Here is what the edited <filename>SRC_URI</filename>
statement would look like:
<literallayout class='monospaced'>
SRC_URI = "${KERNELORG_MIRROR}/linux/network/nfc/${BPN}-${PV}.tar.xz \
file://neard.in \
file://neard.service.in \
file://parallelmake.patch \
"
</literallayout>
</para>
<para>
With the patch complete and moved to the correct folder and
the <filename>SRC_URI</filename> statement updated, you can
exit the <filename>devshell</filename>:
<literallayout class='monospaced'>
$ exit
</literallayout>
</para>
</section>
<section id='testing-the-build'>
<title>Testing the Build</title>
<para>
With everything in place, you can get back to trying the
build again locally:
<literallayout class='monospaced'>
$ bitbake neard
</literallayout>
This build should succeed.
</para>
<para>
Now you can open up a <filename>devshell</filename> again
and repeat the clean and make operations as follows:
<literallayout class='monospaced'>
$ bitbake neard -c devshell
$ make clean
$ make tools/snep-send.o
</literallayout>
The build should work without issue.
</para>
<para>
As with all solved problems, if they originated upstream, you
need to submit the fix for the recipe in OE-Core and upstream
so that the problem is taken care of at its source.
See the
"<link linkend='how-to-submit-a-change'>How to Submit a Change</link>"
section for more information.
</para>
</section>
</section>
<section id='maintaining-open-source-license-compliance-during-your-products-lifecycle'>
<title>Maintaining Open Source License Compliance During Your Product's Lifecycle</title>
<para>
One of the concerns for a development organization using open source
software is how to maintain compliance with various open source
licensing during the lifecycle of the product.
While this section does not provide legal advice or
comprehensively cover all scenarios, it does
present methods that you can use to
assist you in meeting the compliance requirements during a software
release.
</para>
<para>
With hundreds of different open source licenses that the Yocto
Project tracks, it is difficult to know the requirements of each
and every license.
However, the requirements of the major FLOSS licenses can begin
to be covered by
assuming that three main areas of concern exist:
<itemizedlist>
<listitem><para>Source code must be provided.</para></listitem>
<listitem><para>License text for the software must be
provided.</para></listitem>
<listitem><para>Compilation scripts and modifications to the
source code must be provided.
</para></listitem>
</itemizedlist>
There are other requirements beyond the scope of these
three and the methods described in this section
(e.g. the mechanism through which source code is distributed).
</para>
<para>
As different organizations have different methods of complying with
open source licensing, this section is not meant to imply that
there is only one single way to meet your compliance obligations,
but rather to describe one method of achieving compliance.
The remainder of this section describes methods supported to meet the
previously mentioned three requirements.
Once you take steps to meet these requirements,
and prior to releasing images, sources, and the build system,
you should audit all artifacts to ensure completeness.
<note>
The Yocto Project generates a license manifest during
image creation that is located
in <filename>${DEPLOY_DIR}/licenses/<replaceable>image_name-datestamp</replaceable></filename>
to assist with any audits.
</note>
</para>
<section id='providing-the-source-code'>
<title>Providing the Source Code</title>
<para>
Compliance activities should begin before you generate the
final image.
The first thing you should look at is the requirement that
tops the list for most compliance groups - providing
the source.
The Yocto Project has a few ways of meeting this
requirement.
</para>
<para>
One of the easiest ways to meet this requirement is
to provide the entire
<ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>
used by the build.
This method, however, has a few issues.
The most obvious is the size of the directory since it includes
all sources used in the build and not just the source used in
the released image.
It will include toolchain source, and other artifacts, which
you would not generally release.
However, the more serious issue for most companies is accidental
release of proprietary software.
The Yocto Project provides an
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-archiver'><filename>archiver</filename></ulink>
class to help avoid some of these concerns.
</para>
<para>
Before you employ <filename>DL_DIR</filename> or the
<filename>archiver</filename> class, you need to decide how
you choose to provide source.
The source <filename>archiver</filename> class can generate
tarballs and SRPMs and can create them with various levels of
compliance in mind.
</para>
<para>
One way of doing this (but certainly not the only way) is to
release just the source as a tarball.
You can do this by adding the following to the
<filename>local.conf</filename> file found in the
<link linkend='build-directory'>Build Directory</link>:
<literallayout class='monospaced'>
INHERIT += "archiver"
ARCHIVER_MODE[src] = "original"
</literallayout>
During the creation of your image, the source from all
recipes that deploy packages to the image is placed within
subdirectories of
<filename>DEPLOY_DIR/sources</filename> based on the
<ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
for each recipe.
Releasing the entire directory enables you to comply with
requirements concerning providing the unmodified source.
It is important to note that the size of the directory can
get large.
</para>
<para>
A way to help mitigate the size issue is to only release
tarballs for licenses that require the release of
source.
Let us assume you are only concerned with GPL code as
identified by running the following script:
<literallayout class='monospaced'>
# Script to archive a subset of packages matching specific license(s)
# Source and license files are copied into sub folders of package folder
# Must be run from build folder
#!/bin/bash
src_release_dir="source-release"
mkdir -p $src_release_dir
for a in tmp/deploy/sources/*; do
for d in $a/*; do
# Get package name from path
p=`basename $d`
p=${p%-*}
p=${p%-*}
# Only archive GPL packages (update *GPL* regex for your license check)
numfiles=`ls tmp/deploy/licenses/$p/*GPL* 2> /dev/null | wc -l`
if [ $numfiles -gt 1 ]; then
echo Archiving $p
mkdir -p $src_release_dir/$p/source
cp $d/* $src_release_dir/$p/source 2> /dev/null
mkdir -p $src_release_dir/$p/license
cp tmp/deploy/licenses/$p/* $src_release_dir/$p/license 2> /dev/null
fi
done
done </literallayout>
At this point, you could create a tarball from the
<filename>gpl_source_release</filename> directory and
provide that to the end user.
This method would be a step toward achieving compliance
with section 3a of GPLv2 and with section 6 of GPLv3.
</para>
</section>
<section id='providing-license-text'>
<title>Providing License Text</title>
<para>
One requirement that is often overlooked is inclusion
of license text.
This requirement also needs to be dealt with prior to
generating the final image.
Some licenses require the license text to accompany
the binary.
You can achieve this by adding the following to your
<filename>local.conf</filename> file:
<literallayout class='monospaced'>
COPY_LIC_MANIFEST = "1"
COPY_LIC_DIRS = "1"
LICENSE_CREATE_PACKAGE = "1"
</literallayout>
Adding these statements to the configuration file ensures
that the licenses collected during package generation
are included on your image.
<note>
<para>Setting all three variables to "1" results in the
image having two copies of the same license file.
One copy resides in
<filename>/usr/share/common-licenses</filename> and
the other resides in
<filename>/usr/share/license</filename>.</para>
<para>The reason for this behavior is because
<ulink url='&YOCTO_DOCS_REF_URL;#var-COPY_LIC_DIRS'><filename>COPY_LIC_DIRS</filename></ulink>
and
<ulink url='&YOCTO_DOCS_REF_URL;#var-COPY_LIC_MANIFEST'><filename>COPY_LIC_MANIFEST</filename></ulink>
add a copy of the license when the image is built but do
not offer a path for adding licenses for newly installed
packages to an image.
<ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_CREATE_PACKAGE'><filename>LICENSE_CREATE_PACKAGE</filename></ulink>
adds a separate package and an upgrade path for adding
licenses to an image.</para>
</note>
</para>
<para>
As the source <filename>archiver</filename> class has already
archived the original
unmodified source that contains the license files,
you would have already met the requirements for inclusion
of the license information with source as defined by the GPL
and other open source licenses.
</para>
</section>
<section id='providing-compilation-scripts-and-source-code-modifications'>
<title>Providing Compilation Scripts and Source Code Modifications</title>
<para>
At this point, we have addressed all we need to
prior to generating the image.
The next two requirements are addressed during the final
packaging of the release.
</para>
<para>
By releasing the version of the OpenEmbedded build system
and the layers used during the build, you will be providing both
compilation scripts and the source code modifications in one
step.
</para>
<para>
If the deployment team has a
<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP layer</ulink>
and a distro layer, and those those layers are used to patch,
compile, package, or modify (in any way) any open source
software included in your released images, you
might be required to release those layers under section 3 of
GPLv2 or section 1 of GPLv3.
One way of doing that is with a clean
checkout of the version of the Yocto Project and layers used
during your build.
Here is an example:
<literallayout class='monospaced'>
# We built using the &DISTRO_NAME_NO_CAP; branch of the poky repo
$ git clone -b &DISTRO_NAME_NO_CAP; git://git.yoctoproject.org/poky
$ cd poky
# We built using the release_branch for our layers
$ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
$ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
# clean up the .git repos
$ find . -name ".git" -type d -exec rm -rf {} \;
</literallayout>
One thing a development organization might want to consider
for end-user convenience is to modify
<filename>meta-poky/conf/bblayers.conf.sample</filename> to
ensure that when the end user utilizes the released build
system to build an image, the development organization's
layers are included in the <filename>bblayers.conf</filename>
file automatically:
<literallayout class='monospaced'>
# LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
# changes incompatibly
LCONF_VERSION = "6"
BBPATH = "${TOPDIR}"
BBFILES ?= ""
BBLAYERS ?= " \
##OEROOT##/meta \
##OEROOT##/meta-poky \
##OEROOT##/meta-yocto-bsp \
##OEROOT##/meta-mylayer \
"
</literallayout>
Creating and providing an archive of the
<link linkend='metadata'>Metadata</link> layers
(recipes, configuration files, and so forth)
enables you to meet your
requirements to include the scripts to control compilation
as well as any modifications to the original source.
</para>
</section>
</section>
<section id='using-the-error-reporting-tool'>
<title>Using the Error Reporting Tool</title>
<para>
The error reporting tool allows you to
submit errors encountered during builds to a central database.
Outside of the build environment, you can use a web interface to
browse errors, view statistics, and query for errors.
The tool works using a client-server system where the client
portion is integrated with the installed Yocto Project
<link linkend='source-directory'>Source Directory</link>
(e.g. <filename>poky</filename>).
The server receives the information collected and saves it in a
database.
</para>
<para>
A live instance of the error reporting server exists at
<ulink url='http://errors.yoctoproject.org'></ulink>.
This server exists so that when you want to get help with
build failures, you can submit all of the information on the
failure easily and then point to the URL in your bug report
or send an email to the mailing list.
<note>
If you send error reports to this server, the reports become
publicly visible.
</note>
</para>
<section id='enabling-and-using-the-tool'>
<title>Enabling and Using the Tool</title>
<para>
By default, the error reporting tool is disabled.
You can enable it by inheriting the
<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-report-error'><filename>report-error</filename></ulink>
class by adding the following statement to the end of
your <filename>local.conf</filename> file in your
<link linkend='build-directory'>Build Directory</link>.
<literallayout class='monospaced'>
INHERIT += "report-error"
</literallayout>
</para>
<para>
By default, the error reporting feature stores information in
<filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LOG_DIR'><filename>LOG_DIR</filename></ulink><filename>}/error-report</filename>.
However, you can specify a directory to use by adding the following
to your <filename>local.conf</filename> file:
<literallayout class='monospaced'>
ERR_REPORT_DIR = "path"
</literallayout>
Enabling error reporting causes the build process to collect
the errors and store them in a file as previously described.
When the build system encounters an error, it includes a
command as part of the console output.
You can run the command to send the error file to the server.
For example, the following command sends the errors to an
upstream server:
<literallayout class='monospaced'>
$ send-error-report /home/brandusa/project/poky/build/tmp/log/error-report/error_report_201403141617.txt
</literallayout>
In the previous example, the errors are sent to a public
database available at
<ulink url='http://errors.yoctoproject.org'></ulink>, which is
used by the entire community.
If you specify a particular server, you can send the errors
to a different database.
Use the following command for more information on available
options:
<literallayout class='monospaced'>
$ send-error-report --help
</literallayout>
</para>
<para>
When sending the error file, you are prompted to review the
data being sent as well as to provide a name and optional
email address.
Once you satisfy these prompts, the command returns a link
from the server that corresponds to your entry in the database.
For example, here is a typical link:
<literallayout class='monospaced'>
http://errors.yoctoproject.org/Errors/Details/9522/
</literallayout>
Following the link takes you to a web interface where you can
browse, query the errors, and view statistics.
</para>
</section>
<section id='disabling-the-tool'>
<title>Disabling the Tool</title>
<para>
To disable the error reporting feature, simply remove or comment
out the following statement from the end of your
<filename>local.conf</filename> file in your
<link linkend='build-directory'>Build Directory</link>.
<literallayout class='monospaced'>
INHERIT += "report-error"
</literallayout>
</para>
</section>
<section id='setting-up-your-own-error-reporting-server'>
<title>Setting Up Your Own Error Reporting Server</title>
<para>
If you want to set up your own error reporting server, you
can obtain the code from the Git repository at
<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/error-report-web/'></ulink>.
Instructions on how to set it up are in the README document.
</para>
</section>
</section>
</chapter>
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