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kernel-dev: Minor updates to the "Kernel Maintenance" appendix.

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(From yocto-docs rev: eabeff4611d447be12af64f0f44c218c69da3409)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark 2017-10-03 08:50:52 -07:00 committed by Richard Purdie
parent 214c692889
commit 398a00a74c
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documentation/kernel-dev/kernel-dev-maint-appx.xml
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<section id='tree-construction'>
<title>Tree Construction</title>
<para>
This section describes construction of the Yocto Project kernel source repositories
as accomplished by the Yocto Project team to create kernel repositories.
These kernel repositories are found under the heading "Yocto Linux Kernel" at
This section describes construction of the Yocto Project kernel
source repositories as accomplished by the Yocto Project team to
create Yocto Linux kernel repositories.
These kernel repositories are found under the heading "Yocto Linux
Kernel" at
<ulink url='&YOCTO_GIT_URL;/cgit.cgi'>&YOCTO_GIT_URL;/cgit.cgi</ulink>
and can be shipped as part of a Yocto Project release.
The team creates these repositories by
compiling and executing the set of feature descriptions for every BSP
and feature in the product.
and are shipped as part of a Yocto Project release.
The team creates these repositories by compiling and executing the
set of feature descriptions for every BSP and feature in the
product.
Those feature descriptions list all necessary patches,
configuration, branching, tagging and feature divisions found in a kernel.
Thus, the Yocto Project kernel repository (or tree) is built.
configurations, branches, tags, and feature divisions found in a
Yocto Linux kernel.
Thus, the Yocto Project Linux kernel repository (or tree) is built.
</para>
<para>
The existence of this tree allows you to access and clone a particular
Yocto Project kernel repository and use it to build images based on their configurations
and features.
The existence of this tree allows you to access and clone a
particular Yocto Project Linux kernel repository and use it to
build images based on their configurations and features.
</para>
<para>
You can find the files used to describe all the valid features and BSPs
in the Yocto Project kernel in any clone of the Yocto Project kernel source repository
Git tree.
For example, the following command clones the Yocto Project baseline kernel that
branched off of <filename>linux.org</filename> version 3.19:
You can find the files used to describe all the valid features and
BSPs in the Yocto Project Linux kernel in any clone of the Yocto
Project Linux kernel source repository Git tree.
For example, the following command clones the Yocto Project
baseline Linux kernel that branches off
<filename>linux.org</filename> version 4.12:
<literallayout class='monospaced'>
$ git clone git://git.yoctoproject.org/linux-yocto-3.19
$ git clone git://git.yoctoproject.org/linux-yocto-4.12
</literallayout>
For more information on how to set up a local Git repository of
the Yocto Project kernel files, see the
the Yocto Project Linux kernel files, see the
"<link linkend='preparing-the-build-host-to-work-on-the-kernel'>Preparing the Build Host to Work on the Kernel</link>"
section.
</para>
<para>
Once you have cloned the kernel Git repository on your local machine, you can
switch to the <filename>meta</filename> branch within the repository.
Here is an example that assumes the local Git repository for the kernel is in
a top-level directory named <filename>linux-yocto-3.19</filename>:
Once you have cloned the kernel Git repository on your local
machine, you can discover the branches that are avilable in the
repository using the following Git command:
<literallayout class='monospaced'>
$ cd linux-yocto-3.19
$ git checkout -b meta origin/meta
$ git branch -a
</literallayout>
Once you have checked out and switched to the <filename>meta</filename> branch,
you can see a snapshot of all the kernel configuration and feature descriptions that are
used to build that particular kernel repository.
These descriptions are in the form of <filename>.scc</filename> files.
Checking out a branch allows you to work with a particular
Yocto Linux kernel.
For example, the following command checks out the
<filename>standard/beagleboard</filename> branch of the
repository:
<literallayout class='monospaced'>
$ cd linux-yocto-4.12
$ git checkout -b my-kernel-4.12 standard/beagleboard
</literallayout>
Once you have checked out and switched to the
<filename>standard/beagleboard</filename> branch,
you can see a snapshot of all the kernel source files used to
used to build that particular Yocto Linux kernel for that
particular board.
</para>
<para>
You should realize, however, that browsing your local kernel repository
for feature descriptions and patches is not an effective way to determine what is in a
particular kernel branch.
Instead, you should use Git directly to discover the changes in a branch.
Using Git is an efficient and flexible way to inspect changes to the kernel.
To see the features and configurations for a particular Yocto
Linux kernel, you need to examine the
<filename>yocto-kernel-cache</filename> Git repository.
Branches in the <filename>yocto-kernel-cache</filename> repository
correspond to Yocto Linux kernel versions (e.g.
<filename>yocto-4.12</filename>).
Branches contain descriptions in the form of
<filename>.scc</filename> and <filename>.cfg</filename> files.
</para>
<para>
You should realize, however, that browsing your local
<filename>yocto-kernel-cache</filename> repository for feature
descriptions and patches is not an effective way to determine what
is in a particular kernel branch.
Instead, you should use Git directly to discover the changes in
a branch.
Using Git is an efficient and flexible way to inspect changes to
the kernel.
<note>
Ground up reconstruction of the complete kernel tree is an action only taken by the
Yocto Project team during an active development cycle.
When you create a clone of the kernel Git repository, you are simply making it
efficiently available for building and development.
Ground up reconstruction of the complete kernel tree is an
action only taken by the Yocto Project team during an active
development cycle.
When you create a clone of the kernel Git repository, you are
simply making it efficiently available for building and
development.
</note>
</para>
<para>
The following steps describe what happens when the Yocto Project Team constructs
the Yocto Project kernel source Git repository (or tree) found at
The following steps describe what happens when the Yocto Project
Team constructs the Yocto Project kernel source Git repository
(or tree) found at
<ulink url='&YOCTO_GIT_URL;/cgit.cgi'></ulink> given the
introduction of a new top-level kernel feature or BSP.
These are the actions that effectively create the tree
that includes the new feature, patch or BSP:
<orderedlist>
<listitem><para>A top-level kernel feature is passed to the kernel build subsystem.
Normally, this feature is a BSP for a particular kernel type.</para></listitem>
<listitem><para>The file that describes the top-level feature is located by searching
these system directories:
<listitem><para>
A top-level kernel feature is passed to the kernel build
subsystem.
Normally, this feature is a BSP for a particular kernel
type.
</para></listitem>
<listitem><para>
The file that describes the top-level feature is located
by searching these system directories:
<itemizedlist>
<listitem><para>The in-tree kernel-cache directories, which are located
in <filename>meta/cfg/kernel-cache</filename></para></listitem>
<listitem><para>Areas pointed to by <filename>SRC_URI</filename> statements
found in recipes</para></listitem>
<listitem><para>
The in-tree kernel-cache directories, which are
located in
<filename>yocto-kernel-cache/cfg/kernel-cache</filename>
</para></listitem>
<listitem><para>
Areas pointed to by <filename>SRC_URI</filename>
statements found in recipes
</para></listitem>
</itemizedlist>
For a typical build, the target of the search is a
feature description in an <filename>.scc</filename> file
whose name follows this format:
I AM HERE
<literallayout class='monospaced'>
<replaceable>bsp_name</replaceable>-<replaceable>kernel_type</replaceable>.scc
</literallayout>