919 lines
48 KiB
XML
919 lines
48 KiB
XML
<!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='kernel-how-to'>
|
|
|
|
<title>Working with the Yocto Project Kernel</title>
|
|
|
|
|
|
<section id='actions-org'>
|
|
<title>Introduction</title>
|
|
<para>
|
|
This chapter describes how to accomplish tasks involving a kernel's tree structure.
|
|
The information is designed to help the developer that wants to modify the Yocto
|
|
Project kernel and contribute changes upstream to the Yocto Project.
|
|
The information covers the following:
|
|
<itemizedlist>
|
|
<listitem><para>Tree construction</para></listitem>
|
|
<listitem><para>Build strategies</para></listitem>
|
|
<listitem><para>Workflow examples</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</section>
|
|
|
|
<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
|
|
<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/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.
|
|
</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.
|
|
</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 3.4:
|
|
<literallayout class='monospaced'>
|
|
$ git clone git://git.yoctoproject.org/linux-yocto-3.4
|
|
</literallayout>
|
|
For another example of how to set up a local Git repository of the Yocto Project
|
|
kernel files, see the
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#local-kernel-files'>Yocto Project Kernel</ulink>" bulleted
|
|
item in the Yocto Project Development Manual.
|
|
</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-3.4</filename>:
|
|
<literallayout class='monospaced'>
|
|
$ cd ~/linux-yocto-3.4
|
|
$ git checkout -b meta origin/meta
|
|
</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.
|
|
</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.
|
|
For examples showing how to use Git to inspect kernel commits, see the following sections
|
|
in this chapter.
|
|
<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.
|
|
</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
|
|
<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:
|
|
<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>
|
|
</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:
|
|
<literallayout class='monospaced'>
|
|
<bsp_name>-<kernel_type>.scc
|
|
</literallayout>
|
|
</para></listitem>
|
|
<listitem><para>Once located, the feature description is either compiled into a simple script
|
|
of actions, or into an existing equivalent script that is already part of the
|
|
shipped kernel.</para></listitem>
|
|
<listitem><para>Extra features are appended to the top-level feature description.
|
|
These features can come from the
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
|
|
variable in recipes.</para></listitem>
|
|
<listitem><para>Each extra feature is located, compiled and appended to the script
|
|
as described in step three.</para></listitem>
|
|
<listitem><para>The script is executed to produce a series of <filename>meta-*</filename>
|
|
directories.
|
|
These directories are descriptions of all the branches, tags, patches and configurations that
|
|
need to be applied to the base Git repository to completely create the
|
|
source (build) branch for the new BSP or feature.</para></listitem>
|
|
<listitem><para>The base repository is cloned, and the actions
|
|
listed in the <filename>meta-*</filename> directories are applied to the
|
|
tree.</para></listitem>
|
|
<listitem><para>The Git repository is left with the desired branch checked out and any
|
|
required branching, patching and tagging has been performed.</para></listitem>
|
|
</orderedlist>
|
|
</para>
|
|
<para>
|
|
The kernel tree is now ready for developer consumption to be locally cloned,
|
|
configured, and built into a Yocto Project kernel specific to some target hardware.
|
|
<note><para>The generated <filename>meta-*</filename> directories add to the kernel
|
|
as shipped with the Yocto Project release.
|
|
Any add-ons and configuration data are applied to the end of an existing branch.
|
|
The full repository generation that is found in the
|
|
official Yocto Project kernel repositories at
|
|
<ulink url='&YOCTO_GIT_URL;/cgit.cgi'>http://git.yoctoproject.org/cgit.cgi</ulink>
|
|
is the combination of all supported boards and configurations.</para>
|
|
<para>The technique the Yocto Project team uses is flexible and allows for seamless
|
|
blending of an immutable history with additional patches specific to a
|
|
deployment.
|
|
Any additions to the kernel become an integrated part of the branches.</para>
|
|
</note>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='build-strategy'>
|
|
<title>Build Strategy</title>
|
|
<para>
|
|
Once a local Git repository of the Yocto Project kernel exists on a development system,
|
|
you can consider the compilation phase of kernel development - building a kernel image.
|
|
Some prerequisites exist that are validated by the build process before compilation
|
|
starts:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>The
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink> points
|
|
to the kernel Git repository.</para></listitem>
|
|
<listitem><para>A BSP build branch exists.
|
|
This branch has the following form:
|
|
<literallayout class='monospaced'>
|
|
<kernel_type>/<bsp_name>
|
|
</literallayout></para></listitem>
|
|
</itemizedlist>
|
|
|
|
<para>
|
|
The OpenEmbedded build system makes sure these conditions exist before attempting compilation.
|
|
Other means, however, do exist, such as as bootstrapping a BSP, see
|
|
the "<link linkend='workflow-examples'>Workflow Examples</link>".
|
|
</para>
|
|
|
|
<para>
|
|
Before building a kernel, the build process verifies the tree
|
|
and configures the kernel by processing all of the
|
|
configuration "fragments" specified by feature descriptions in the <filename>.scc</filename>
|
|
files.
|
|
As the features are compiled, associated kernel configuration fragments are noted
|
|
and recorded in the <filename>meta-*</filename> series of directories in their compilation order.
|
|
The fragments are migrated, pre-processed and passed to the Linux Kernel
|
|
Configuration subsystem (<filename>lkc</filename>) as raw input in the form
|
|
of a <filename>.config</filename> file.
|
|
The <filename>lkc</filename> uses its own internal dependency constraints to do the final
|
|
processing of that information and generates the final <filename>.config</filename> file
|
|
that is used during compilation.
|
|
</para>
|
|
|
|
<para>
|
|
Using the board's architecture and other relevant values from the board's template,
|
|
kernel compilation is started and a kernel image is produced.
|
|
</para>
|
|
|
|
<para>
|
|
The other thing that you notice once you configure a kernel is that
|
|
the build process generates a build tree that is separate from your kernel's local Git
|
|
source repository tree.
|
|
This build tree has a name that uses the following form, where
|
|
<filename>${MACHINE}</filename> is the metadata name of the machine (BSP) and "kernel_type" is one
|
|
of the Yocto Project supported kernel types (e.g. "standard"):
|
|
<literallayout class='monospaced'>
|
|
linux-${MACHINE}-<kernel_type>-build
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
The existing support in the <filename>kernel.org</filename> tree achieves this
|
|
default functionality.
|
|
</para>
|
|
|
|
<para>
|
|
This behavior means that all the generated files for a particular machine or BSP are now in
|
|
the build tree directory.
|
|
The files include the final <filename>.config</filename> file, all the <filename>.o</filename>
|
|
files, the <filename>.a</filename> files, and so forth.
|
|
Since each machine or BSP has its own separate build directory in its own separate branch
|
|
of the Git repository, you can easily switch between different builds.
|
|
</para>
|
|
</section>
|
|
|
|
<section id='workflow-examples'>
|
|
<title>Workflow Examples</title>
|
|
|
|
<para>
|
|
As previously noted, the Yocto Project kernel has built-in Git integration.
|
|
However, these utilities are not the only way to work with the kernel repository.
|
|
The Yocto Project has not made changes to Git or to other tools that
|
|
would invalidate alternate workflows.
|
|
Additionally, the way the kernel repository is constructed results in using
|
|
only core Git functionality, thus allowing any number of tools or front ends to use the
|
|
resulting tree.
|
|
</para>
|
|
|
|
<para>
|
|
This section contains several workflow examples.
|
|
Many of the examples use Git commands.
|
|
You can find Git documentation at
|
|
<ulink url='http://git-scm.com/documentation'></ulink>.
|
|
You can find a simple overview of using Git with the Yocto Project in the
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink>"
|
|
section of the Yocto Project Development Manual.
|
|
</para>
|
|
|
|
<section id='change-inspection-kernel-changes-commits'>
|
|
<title>Change Inspection: Changes/Commits</title>
|
|
|
|
<para>
|
|
A common question when working with a kernel is:
|
|
"What changes have been applied to this tree?"
|
|
</para>
|
|
|
|
<para>
|
|
In projects that have a collection of directories that
|
|
contain patches to the kernel, it is possible to inspect or "grep" the contents
|
|
of the directories to get a general feel for the changes.
|
|
This sort of patch inspection is not an efficient way to determine what has been
|
|
done to the kernel.
|
|
The reason it is inefficient is because there are many optional patches that are
|
|
selected based on the kernel type and the feature description.
|
|
Additionally, patches could exist in directories that are not included in the search.
|
|
</para>
|
|
|
|
<para>
|
|
A more efficient way to determine what has changed in the branch is to use
|
|
Git and inspect or search the kernel tree.
|
|
This method gives you a full view of not only the source code modifications,
|
|
but also provides the reasons for the changes.
|
|
</para>
|
|
|
|
<section id='what-changed-in-a-kernel'>
|
|
<title>What Changed in a Kernel?</title>
|
|
|
|
<para>
|
|
Following are a few examples that show how to use Git commands to examine changes.
|
|
Because Git repositories in the Yocto Project do not break existing Git
|
|
functionality, and because there exists many permutations of these types of
|
|
Git commands, many methods exist by which you can discover changes.
|
|
<note>
|
|
In the following examples, unless you provide a commit range,
|
|
<filename>kernel.org</filename> history is blended with Yocto Project
|
|
kernel changes.
|
|
You can form ranges by using branch names from the kernel tree as the
|
|
upper and lower commit markers with the Git commands.
|
|
You can see the branch names through the web interface to the
|
|
Yocto Project source repositories at
|
|
<ulink url='http://git.yoctoproject.org/cgit.cgi'></ulink>.
|
|
For example, the branch names for the <filename>linux-yocto-3.4</filename>
|
|
kernel repository can be seen at
|
|
<ulink url='http://git.yoctoproject.org/cgit.cgi/linux-yocto-3.4/refs/heads'></ulink>.
|
|
</note>
|
|
To see a full range of the changes, use the
|
|
<filename>git whatchanged</filename> command and specify a commit range
|
|
for the branch (<filename><commit>..<commit></filename>).
|
|
</para>
|
|
|
|
<para>
|
|
Here is an example that looks at what has changed in the
|
|
<filename>emenlow</filename> branch of the
|
|
<filename>linux-yocto-3.4</filename> kernel.
|
|
The lower commit range is the commit associated with the
|
|
<filename>standard/base</filename> branch, while
|
|
the upper commit range is the commit associated with the
|
|
<filename>standard/emenlow</filename> branch.
|
|
<literallayout class='monospaced'>
|
|
$ git whatchanged origin/standard/base..origin/standard/emenlow
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
To see a summary of changes use the <filename>git log</filename> command.
|
|
Here is an example using the same branches:
|
|
<literallayout class='monospaced'>
|
|
$ git log --oneline origin/standard/base..origin/standard/emenlow
|
|
</literallayout>
|
|
The <filename>git log</filename> output might be more useful than
|
|
the <filename>git whatchanged</filename> as you get
|
|
a short, one-line summary of each change and not the entire commit.
|
|
</para>
|
|
|
|
<para>
|
|
If you want to see code differences associated with all the changes, use
|
|
the <filename>git diff</filename> command.
|
|
Here is an example:
|
|
<literallayout class='monospaced'>
|
|
$ git diff origin/standard/base..origin/standard/emenlow
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
You can see the commit log messages and the text differences using the
|
|
<filename>git show</filename> command:
|
|
Here is an example:
|
|
<literallayout class='monospaced'>
|
|
$ git show origin/standard/base..origin/standard/emenlow
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
You can create individual patches for each change by using the
|
|
<filename>git format-patch</filename> command.
|
|
Here is an example that that creates patch files for each commit and
|
|
places them in your <filename>Documents</filename> directory:
|
|
<literallayout class='monospaced'>
|
|
$ git format-patch -o $HOME/Documents origin/standard/base..origin/standard/emenlow
|
|
</literallayout>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='show-a-particular-feature-or-branch-change'>
|
|
<title>Show a Particular Feature or Branch Change</title>
|
|
|
|
<para>
|
|
Developers use tags in the Yocto Project kernel tree to divide changes for significant
|
|
features or branches.
|
|
Once you know a particular tag, you can use Git commands
|
|
to show changes associated with the tag and find the branches that contain
|
|
the feature.
|
|
<note>
|
|
Because BSP branch, <filename>kernel.org</filename>, and feature tags are all
|
|
present, there could be many tags.
|
|
</note>
|
|
The <filename>git show <tag></filename> command shows changes that are tagged by
|
|
a feature.
|
|
Here is an example that shows changes tagged by the <filename>systemtap</filename>
|
|
feature:
|
|
<literallayout class='monospaced'>
|
|
$ git show systemtap
|
|
</literallayout>
|
|
You can use the <filename>git branch --contains <tag></filename> command
|
|
to show the branches that contain a particular feature.
|
|
This command shows the branches that contain the <filename>systemtap</filename>
|
|
feature:
|
|
<literallayout class='monospaced'>
|
|
$ git branch --contains systemtap
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
You can use many other comparisons to isolate BSP and kernel changes.
|
|
For example, you can compare against <filename>kernel.org</filename> tags
|
|
such as the <filename>v3.4</filename> tag.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='development-saving-kernel-modifications'>
|
|
<title>Development: Saving Kernel Modifications</title>
|
|
|
|
<para>
|
|
Another common operation is to build a BSP supplied by the Yocto Project, make some
|
|
changes, rebuild, and then test.
|
|
Those local changes often need to be exported, shared or otherwise maintained.
|
|
</para>
|
|
|
|
<para>
|
|
Since the Yocto Project kernel source tree is backed by Git, this activity is
|
|
much easier as compared to with previous releases.
|
|
Because Git tracks file modifications, additions and deletions, it is easy
|
|
to modify the code and later realize that you need to save the changes.
|
|
It is also easy to determine what has changed.
|
|
This method also provides many tools to commit, undo and export those modifications.
|
|
</para>
|
|
|
|
<para>
|
|
This section and its sub-sections, describe general application of Git's
|
|
<filename>push</filename> and <filename>pull</filename> commands, which are used to
|
|
get your changes upstream or source your code from an upstream repository.
|
|
The Yocto Project provides scripts that help you work in a collaborative development
|
|
environment.
|
|
For information on these scripts, see the
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#pushing-a-change-upstream'>Using Scripts to Push a Change
|
|
Upstream and Request a Pull</ulink>" and
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#submitting-a-patch'>Using Email to Submit a Patch</ulink>"
|
|
sections in the Yocto Project Development Manual.
|
|
</para>
|
|
|
|
<para>
|
|
There are many ways to save kernel modifications.
|
|
The technique employed
|
|
depends on the destination for the patches:
|
|
|
|
<itemizedlist>
|
|
<listitem><para>Bulk storage</para></listitem>
|
|
<listitem><para>Internal sharing either through patches or by using Git</para></listitem>
|
|
<listitem><para>External submissions</para></listitem>
|
|
<listitem><para>Exporting for integration into another Source Code
|
|
Manager (SCM)</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
Because of the following list of issues, the destination of the patches also influences
|
|
the method for gathering them:
|
|
|
|
<itemizedlist>
|
|
<listitem><para>Bisectability</para></listitem>
|
|
<listitem><para>Commit headers</para></listitem>
|
|
<listitem><para>Division of subsystems for separate submission or review</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<section id='bulk-export'>
|
|
<title>Bulk Export</title>
|
|
|
|
<para>
|
|
This section describes how you can "bulk" export changes that have not
|
|
been separated or divided.
|
|
This situation works well when you are simply storing patches outside of the kernel
|
|
source repository, either permanently or temporarily, and you are not committing
|
|
incremental changes during development.
|
|
<note>
|
|
This technique is not appropriate for full integration of upstream submission
|
|
because changes are not properly divided and do not provide an avenue for per-change
|
|
commit messages.
|
|
Therefore, this example assumes that changes have not been committed incrementally
|
|
during development and that you simply must gather and export them.
|
|
</note>
|
|
<literallayout class='monospaced'>
|
|
# bulk export of ALL modifications without separation or division
|
|
# of the changes
|
|
|
|
$ git add .
|
|
$ git commit -s -a -m <msg>
|
|
or
|
|
$ git commit -s -a # and interact with $EDITOR
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
The previous operations capture all the local changes in the project source
|
|
tree in a single Git commit.
|
|
And, that commit is also stored in the project's source tree.
|
|
</para>
|
|
|
|
<para>
|
|
Once the changes are exported, you can restore them manually using a template
|
|
or through integration with the <filename>default_kernel</filename>.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section id='incremental-planned-sharing'>
|
|
<title>Incremental/Planned Sharing</title>
|
|
|
|
<para>
|
|
This section describes how to save modifications when you are making incremental
|
|
commits or practicing planned sharing.
|
|
The examples in this section assume that you have incrementally committed
|
|
changes to the tree during development and now need to export them.
|
|
The sections that follow
|
|
describe how you can export your changes internally through either patches or by
|
|
using Git commands.
|
|
</para>
|
|
|
|
<para>
|
|
During development, the following commands are of interest.
|
|
For full Git documentation, refer to the Git documentation at
|
|
<ulink url='http://github.com'></ulink>.
|
|
|
|
<literallayout class='monospaced'>
|
|
# edit a file
|
|
$ vi <path>/file
|
|
# stage the change
|
|
$ git add <path>/file
|
|
# commit the change
|
|
$ git commit -s
|
|
# remove a file
|
|
$ git rm <path>/file
|
|
# commit the change
|
|
$ git commit -s
|
|
|
|
... etc.
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
Distributed development with Git is possible when you use a universally
|
|
agreed-upon unique commit identifier (set by the creator of the commit) that maps to a
|
|
specific change set with a specific parent.
|
|
This identifier is created for you when
|
|
you create a commit, and is re-created when you amend, alter or re-apply
|
|
a commit.
|
|
As an individual in isolation, this is of no interest.
|
|
However, if you
|
|
intend to share your tree with normal Git <filename>push</filename> and
|
|
<filename>pull</filename> operations for
|
|
distributed development, you should consider the ramifications of changing a
|
|
commit that you have already shared with others.
|
|
</para>
|
|
|
|
<para>
|
|
Assuming that the changes have not been pushed upstream, or pulled into
|
|
another repository, you can update both the commit content and commit messages
|
|
associated with development by using the following commands:
|
|
|
|
<literallayout class='monospaced'>
|
|
$ Git add <path>/file
|
|
$ Git commit --amend
|
|
$ Git rebase or Git rebase -i
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
Again, assuming that the changes have not been pushed upstream, and that
|
|
no pending works-in-progress exist (use <filename>git status</filename> to check), then
|
|
you can revert (undo) commits by using the following commands:
|
|
|
|
<literallayout class='monospaced'>
|
|
# remove the commit, update working tree and remove all
|
|
# traces of the change
|
|
$ git reset --hard HEAD^
|
|
# remove the commit, but leave the files changed and staged for re-commit
|
|
$ git reset --soft HEAD^
|
|
# remove the commit, leave file change, but not staged for commit
|
|
$ git reset --mixed HEAD^
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
You can create branches, "cherry-pick" changes, or perform any number of Git
|
|
operations until the commits are in good order for pushing upstream
|
|
or for pull requests.
|
|
After a <filename>push</filename> or <filename>pull</filename> command,
|
|
commits are normally considered
|
|
"permanent" and you should not modify them.
|
|
If the commits need to be changed, you can incrementally do so with new commits.
|
|
These practices follow standard Git workflow and the <filename>kernel.org</filename> best
|
|
practices, which is recommended.
|
|
<note>
|
|
It is recommended to tag or branch before adding changes to a Yocto Project
|
|
BSP or before creating a new one.
|
|
The reason for this recommendation is because the branch or tag provides a
|
|
reference point to facilitate locating and exporting local changes.
|
|
</note>
|
|
</para>
|
|
|
|
<section id='export-internally-via-patches'>
|
|
<title>Exporting Changes Internally by Using Patches</title>
|
|
|
|
<para>
|
|
This section describes how you can extract committed changes from a working directory
|
|
by exporting them as patches.
|
|
Once the changes have been extracted, you can use the patches for upstream submission,
|
|
place them in a Yocto Project template for automatic kernel patching,
|
|
or apply them in many other common uses.
|
|
</para>
|
|
|
|
<para>
|
|
This example shows how to create a directory with sequentially numbered patches.
|
|
Once the directory is created, you can apply it to a repository using the
|
|
<filename>git am</filename> command to reproduce the original commit and all
|
|
the related information such as author, date, commit log, and so forth.
|
|
<note>
|
|
The new commit identifiers (ID) will be generated upon re-application.
|
|
This action reflects that the commit is now applied to an underlying commit
|
|
with a different ID.
|
|
</note>
|
|
<literallayout class='monospaced'>
|
|
# <first-commit> can be a tag if one was created before development
|
|
# began. It can also be the parent branch if a branch was created
|
|
# before development began.
|
|
|
|
$ git format-patch -o <dir> <first commit>..<last commit>
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
In other words:
|
|
<literallayout class='monospaced'>
|
|
# Identify commits of interest.
|
|
|
|
# If the tree was tagged before development
|
|
$ git format-patch -o <save dir> <tag>
|
|
|
|
# If no tags are available
|
|
$ git format-patch -o <save dir> HEAD^ # last commit
|
|
$ git format-patch -o <save dir> HEAD^^ # last 2 commits
|
|
$ git whatchanged # identify last commit
|
|
$ git format-patch -o <save dir> <commit id>
|
|
$ git format-patch -o <save dir> <rev-list>
|
|
</literallayout>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='export-internally-via-git'>
|
|
<title>Exporting Changes Internally by Using Git</title>
|
|
|
|
<para>
|
|
This section describes how you can export changes from a working directory
|
|
by pushing the changes into a master repository or by making a pull request.
|
|
Once you have pushed the changes to the master repository, you can then
|
|
pull those same changes into a new kernel build at a later time.
|
|
</para>
|
|
|
|
<para>
|
|
Use this command form to push the changes:
|
|
<literallayout class='monospaced'>
|
|
$ git push ssh://<master_server>/<path_to_repo>
|
|
<local_branch>:<remote_branch>
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
For example, the following command pushes the changes from your local branch
|
|
<filename>yocto/standard/common-pc/base</filename> to the remote branch with the same name
|
|
in the master repository <filename>//git.mycompany.com/pub/git/kernel-3.4</filename>.
|
|
<literallayout class='monospaced'>
|
|
$ git push ssh://git.mycompany.com/pub/git/kernel-3.4 \
|
|
yocto/standard/common-pc/base:yocto/standard/common-pc/base
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
A pull request entails using the <filename>git request-pull</filename> command to compose
|
|
an email to the
|
|
maintainer requesting that a branch be pulled into the master repository, see
|
|
<ulink url='http://github.com/guides/pull-requests'></ulink> for an example.
|
|
<note>
|
|
Other commands such as <filename>git stash</filename> or branching can also be used to save
|
|
changes, but are not covered in this document.
|
|
</note>
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='export-for-external-upstream-submission'>
|
|
<title>Exporting Changes for External (Upstream) Submission</title>
|
|
|
|
<para>
|
|
This section describes how to export changes for external upstream submission.
|
|
If the patch series is large or the maintainer prefers to pull
|
|
changes, you can submit these changes by using a pull request.
|
|
However, it is common to send patches as an email series.
|
|
This method allows easy review and integration of the changes.
|
|
<note>
|
|
Before sending patches for review be sure you understand the
|
|
community standards for submitting and documenting changes and follow their best practices.
|
|
For example, kernel patches should follow standards such as:
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
<ulink url='http://linux.yyz.us/patch-format.html'></ulink></para></listitem>
|
|
<listitem><para>Documentation/SubmittingPatches (in any linux
|
|
kernel source tree)</para></listitem>
|
|
</itemizedlist>
|
|
</note>
|
|
</para>
|
|
|
|
<para>
|
|
The messages used to commit changes are a large part of these standards.
|
|
Consequently, be sure that the headers for each commit have the required information.
|
|
For information on how to follow the Yocto Project commit message standards, see the
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#how-to-submit-a-change'>How to Submit a
|
|
Change</ulink>" section in the Yocto Project Development Manual.
|
|
</para>
|
|
|
|
<para>
|
|
If the initial commits were not properly documented or do not meet those standards,
|
|
you can re-base by using the <filename>git rebase -i</filename> command to
|
|
manipulate the commits and
|
|
get them into the required format.
|
|
Other techniques such as branching and cherry-picking commits are also viable options.
|
|
</para>
|
|
|
|
<para>
|
|
Once you complete the commits, you can generate the email that sends the patches
|
|
to the maintainer(s) or lists that review and integrate changes.
|
|
The command <filename>git send-email</filename> is commonly used to ensure
|
|
that patches are properly
|
|
formatted for easy application and avoid mailer-induced patch damage.
|
|
</para>
|
|
|
|
<para>
|
|
The following is an example of dumping patches for external submission:
|
|
<literallayout class='monospaced'>
|
|
# dump the last 4 commits
|
|
$ git format-patch --thread -n -o ~/rr/ HEAD^^^^
|
|
$ git send-email --compose --subject '[RFC 0/N] <patch series summary>' \
|
|
--to foo@yoctoproject.org --to bar@yoctoproject.org \
|
|
--cc list@yoctoproject.org ~/rr
|
|
# the editor is invoked for the 0/N patch, and when complete the entire
|
|
# series is sent via email for review
|
|
</literallayout>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='export-for-import-into-other-scm'>
|
|
<title>Exporting Changes for Import into Another SCM</title>
|
|
|
|
<para>
|
|
When you want to export changes for import into another
|
|
Source Code Manager (SCM), you can use any of the previously discussed
|
|
techniques.
|
|
However, if the patches are manually applied to a secondary tree and then
|
|
that tree is checked into the SCM, you can lose change information such as
|
|
commit logs.
|
|
This process is not recommended.
|
|
</para>
|
|
|
|
<para>
|
|
Many SCMs can directly import Git commits, or can translate Git patches so that
|
|
information is not lost.
|
|
Those facilities are SCM-dependent and you should use them whenever possible.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='scm-working-with-the-yocto-project-kernel-in-another-scm'>
|
|
<title>Working with the Yocto Project Kernel in Another SCM</title>
|
|
|
|
<para>
|
|
This section describes kernel development in an SCM other than Git,
|
|
which is not the same as exporting changes to another SCM described earlier.
|
|
For this scenario, you use the OpenEmbedded build system to
|
|
develop the kernel in a different SCM.
|
|
The following must be true for you to accomplish this:
|
|
<itemizedlist>
|
|
<listitem><para>The delivered Yocto Project kernel must be exported into the second
|
|
SCM.</para></listitem>
|
|
<listitem><para>Development must be exported from that secondary SCM into a
|
|
format that can be used by the OpenEmbedded build system.</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<section id='exporting-delivered-kernel-to-scm'>
|
|
<title>Exporting the Delivered Kernel to the SCM</title>
|
|
|
|
<para>
|
|
Depending on the SCM, it might be possible to export the entire Yocto Project
|
|
kernel Git repository, branches and all, into a new environment.
|
|
This method is preferred because it has the most flexibility and potential to maintain
|
|
the meta data associated with each commit.
|
|
</para>
|
|
|
|
<para>
|
|
When a direct import mechanism is not available, it is still possible to
|
|
export a branch (or series of branches) and check them into a new repository.
|
|
</para>
|
|
|
|
<para>
|
|
The following commands illustrate some of the steps you could use to
|
|
import the <filename>yocto/standard/common-pc/base</filename>
|
|
kernel into a secondary SCM:
|
|
<literallayout class='monospaced'>
|
|
$ git checkout yocto/standard/common-pc/base
|
|
$ cd .. ; echo linux/.git > .cvsignore
|
|
$ cvs import -m "initial import" linux MY_COMPANY start
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
You could now relocate the CVS repository and use it in a centralized manner.
|
|
</para>
|
|
|
|
<para>
|
|
The following commands illustrate how you can condense and merge two BSPs into a
|
|
second SCM:
|
|
<literallayout class='monospaced'>
|
|
$ git checkout yocto/standard/common-pc/base
|
|
$ git merge yocto/standard/common-pc-64/base
|
|
# resolve any conflicts and commit them
|
|
$ cd .. ; echo linux/.git > .cvsignore
|
|
$ cvs import -m "initial import" linux MY_COMPANY start
|
|
</literallayout>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='importing-changes-for-build'>
|
|
<title>Importing Changes for the Build</title>
|
|
|
|
<para>
|
|
Once development has reached a suitable point in the second development
|
|
environment, you need to export the changes as patches.
|
|
To export them, place the changes in a recipe and
|
|
automatically apply them to the kernel during patching.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='bsp-creating'>
|
|
<title>Creating a BSP Based on an Existing Similar BSP</title>
|
|
|
|
<para>
|
|
This section overviews the process of creating a BSP based on an
|
|
existing similar BSP.
|
|
The information is introductory in nature and does not provide step-by-step examples.
|
|
For detailed information on how to create a new BSP, 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, or see the
|
|
<ulink url='&YOCTO_WIKI_URL;/wiki/Transcript:_creating_one_generic_Atom_BSP_from_another'>Transcript:_creating_one_generic_Atom_BSP_from_another</ulink>
|
|
wiki page.
|
|
</para>
|
|
|
|
<para>
|
|
The basic steps you need to follow are:
|
|
<orderedlist>
|
|
<listitem><para><emphasis>Make sure you have set up a local Source Directory:</emphasis>
|
|
You must create a local
|
|
<ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
|
|
by either creating a Git repository (recommended) or
|
|
extracting a Yocto Project release tarball.</para></listitem>
|
|
<listitem><para><emphasis>Choose an existing BSP available with the Yocto Project:</emphasis>
|
|
Try to map your board features as closely to the features of a BSP that is
|
|
already supported and exists in the Yocto Project.
|
|
Starting with something as close as possible to your board makes developing
|
|
your BSP easier.
|
|
You can find all the BSPs that are supported and ship with the Yocto Project
|
|
on the Yocto Project's Download page at
|
|
<ulink url='&YOCTO_HOME_URL;/download'></ulink>.</para></listitem>
|
|
<listitem><para><emphasis>Be sure you have the Base BSP:</emphasis>
|
|
You need to either have a local Git repository of the base BSP set up or
|
|
have downloaded and extracted the files from a release BSP tarball.
|
|
Either method gives you access to the BSP source files.</para></listitem>
|
|
<listitem><para><emphasis>Make a copy of the existing BSP, thus isolating your new
|
|
BSP work:</emphasis>
|
|
Copying the existing BSP file structure gives you a new area in which to work.</para></listitem>
|
|
<listitem><para><emphasis>Make configuration and recipe changes to your new BSP:</emphasis>
|
|
Configuration changes involve the files in the BSP's <filename>conf</filename>
|
|
directory.
|
|
Changes include creating a machine-specific configuration file and editing the
|
|
<filename>layer.conf</filename> file.
|
|
The configuration changes identify the kernel you will be using.
|
|
Recipe changes include removing, modifying, or adding new recipe files that
|
|
instruct the build process on what features to include in the image.</para></listitem>
|
|
<listitem><para><emphasis>Prepare for the build:</emphasis>
|
|
Before you actually initiate the build, you need to set up the build environment
|
|
by sourcing the environment initialization script.
|
|
After setting up the environment, you need to make some build configuration
|
|
changes to the <filename>local.conf</filename> and <filename>bblayers.conf</filename>
|
|
files.</para></listitem>
|
|
<listitem><para><emphasis>Build the image:</emphasis>
|
|
The OpenEmbedded build system uses BitBake to create the image.
|
|
You need to decide on the type of image you are going to build (e.g. minimal, base,
|
|
core, sato, and so forth) and then start the build using the <filename>bitbake</filename>
|
|
command.</para></listitem>
|
|
</orderedlist>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='tip-dirty-string'>
|
|
<title>"-dirty" String</title>
|
|
|
|
<para>
|
|
If kernel images are being built with "-dirty" on the end of the version
|
|
string, this simply means that modifications in the source
|
|
directory have not been committed.
|
|
<literallayout class='monospaced'>
|
|
$ git status
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
You can use the above Git command to report modified, removed, or added files.
|
|
You should commit those changes to the tree regardless of whether they will be saved,
|
|
exported, or used.
|
|
Once you commit the changes you need to rebuild the kernel.
|
|
</para>
|
|
|
|
<para>
|
|
To brute force pickup and commit all such pending changes, enter the following:
|
|
<literallayout class='monospaced'>
|
|
$ git add .
|
|
$ git commit -s -a -m "getting rid of -dirty"
|
|
</literallayout>
|
|
</para>
|
|
|
|
<para>
|
|
Next, rebuild the kernel.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
</chapter>
|
|
<!--
|
|
vim: expandtab tw=80 ts=4
|
|
-->
|