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| author | Scott Rifenbark <scott.m.rifenbark@intel.com> | 2012-12-26 14:09:53 -0600 |
|---|---|---|
| committer | Richard Purdie <richard.purdie@linuxfoundation.org> | 2013-01-16 15:59:09 +0000 |
| commit | ea6d5be3ce49a6e64eb8d5fc62e72dc26cc6cb97 (patch) | |
| tree | 3c9e9b3da6bb5116e08421972b19e79a44b58b7c /documentation/kernel-dev | |
| parent | 46b0fc3ec6b4090056560935d35aef26aa3c8ac5 (diff) | |
| download | ast2050-yocto-poky-ea6d5be3ce49a6e64eb8d5fc62e72dc26cc6cb97.zip ast2050-yocto-poky-ea6d5be3ce49a6e64eb8d5fc62e72dc26cc6cb97.tar.gz | |
kernel-dev: First edits to chapter 3 intro and section 3.1.
(From yocto-docs rev: bb640ebcfd99eaf3944711edc813a4bd39aa3753)
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Diffstat (limited to 'documentation/kernel-dev')
| -rw-r--r-- | documentation/kernel-dev/kernel-dev-advanced.xml | 1154 |
1 files changed, 252 insertions, 902 deletions
diff --git a/documentation/kernel-dev/kernel-dev-advanced.xml b/documentation/kernel-dev/kernel-dev-advanced.xml index 9d9aef6..27c082a 100644 --- a/documentation/kernel-dev/kernel-dev-advanced.xml +++ b/documentation/kernel-dev/kernel-dev-advanced.xml @@ -2,916 +2,266 @@ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > -<chapter id='kernel-how-to'> +<chapter id='kernel-dev-advanced'> -<title>Working with the Yocto Project Kernel</title> +<title>Working with Advanced Metadata</title> + <para> + In addition to configuration fragments and patches, the + Yocto Project kernel tools support rich metadata that you can + use to define complex policies and BSP support. + The purpose of the metadata and the tools to manage it, known as + the kern-tools (<filename>kern-tools-native_git.bb</filename>), is + to assist in managing the complexity of the configuration and sources + in support of multiple Board Support Packages (BSPs) and Linux kernel + types. + </para> -<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> + In particular, the kernel tools allow you to specify only what you + must, and nothing more. + Where a complete Linux kernel <filename>.config</filename> includes + all the automatically selected <filename>CONFIG</filename> options, + the configuration fragments only need to contain the highest level + visible <filename>CONFIG</filename> options as presented by the Linux + kernel <filename>menuconfig</filename> system. + This reduces your maintenance effort and allows you + to further separate your configuration in ways that make sense for + your project. + A common split is policy and hardware. + For example, all your kernels might support + the <filename>proc</filename> and <filename>sys</filename> filesystems, + but only specific boards will require sound, USB, or specific drivers. + Specifying these individually allows you to aggregate them + together as needed, but maintain them in only one place. + Similar logic applies to source changes. + </para> + + <para> + Original Text: + <literallayout class='monospaced'> +In addition to configuration fragments and patches, the Yocto Project kernel +tools support rich metadata which you can use to define complex policies and +BSP support. The purpose of the metadata and the tools to manage it, known as +the kern-tools (kern-tools-native_git.bb), is to assist in managing the +complexity of the configuration and sources in support of multiple BSPs and +Linux kernel types. + +In particular, the kernel tools allow you to specify only what you must, and +nothing more. Where a complete Linux kernel .config includes all the +automatically selected CONFIG options, the configuration fragments only need to +contain the highest level visible CONFIG options as presented by the Linux +kernel menuconfig system. This reduces your maintenance effort and allows you +to further separate your configuration in ways that make sense for your project. +A common split is policy and hardware. For example, all your kernels may support +the proc and sys filesystems, but only specific boards will require sound, usb, +or specific drivers. Specifying these individually allows you to aggregate them +together as needed, but maintain them in only one place. Similar logic applies +to source changes. + </literallayout> + </para> + +<section id='using-metadata-in-a-recipe'> + <title>Using Metadata in a Recipe</title> + + <para> + The metadata provided with any linux-yocto style Linux kernel sources + must define a BSP that corresponds to the definition laid out in the + recipe. + A BSP consists of an aggregation of kernel policy and hardware specific + feature enablement. + This can be influenced from within the recipe. + </para> + + <para> + Every linux-yocto style recipe must define the following variable: + <literallayout class='monospaced'> + KMACHINE + </literallayout> + <filename>KMACHINE</filename> is typically set to the same value as + used within the recipe-space BSP definition, such as "routerstationpro" + or "fri2". + However, multiple BSPs can reuse the same <filename>KMACHINE</filename> + name if they are built using the same BSP description. + See section 3.3.5 for more information. + The <filename>meta-intel</filename> "fri2" and "fri2-noemgd" are good + examples of such a situation where each specifies + <filename>KMACHINE</filename> as "fri2". + </para> + + <para> + They may optionally define the following variables: + <literallayout class='monospaced'> + KBRANCH + KERNEL_FEATURES + KBRANCH_DEFAULT + LINUX_KERNEL_TYPE + </literallayout> + <filename>KBRANCH_DEFAULT</filename> defines the default source branch + within the Linux kernel source repository to be used to build the + Linux kernel. + It is used as the default value for <filename>KBRANCH</filename> which + may define an alternate branch, typically with a machine override, + such as: + <literallayout class='monospaced'> + KBRANCH_fri2 = "standard/fri2" + </literallayout> + Unless you specify otherwise, <filename>KBRANCH_DEFAULT</filename> + is initialized to "master". + </para> + + <para> + <filename>LINUX_KERNEL_TYPE</filename> defines the kernel type to be + used in assembling the configuration and defaults to "standard" + if you do not specify otherwise. + Together with <filename>KMACHINE</filename>, this defines the search + arguments used by the Yocto Project Linux kernel tools to find the + appropriate description within the metadata with which to build out + the sources and configuration. + The linux-yocto recipes define "standard", "tiny", and "preempt-rt" + kernel types. + See section 3.3.4 for more inforation on kernel types. </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>${MACHINE}</filename> is the metadata name of the machine (BSP) and "kernel_type" is one - of the Yocto Project supported kernel types (e.g. "standard"): + <para> + During the build, the kern-tools will search for the BSP description + file that most closely matches the <filename>KMACHINE</filename> + and <filename>LINUX_KERNEL_TYPE</filename> passed in from the + recipe. + It will use the first BSP description it finds matching both variables. + Failing that it will issue a warning such as the following: <literallayout class='monospaced'> - linux-${MACHINE}-<kernel_type>-build + WARNING: Can't find any BSP hardware or required configuration fragments. + WARNING: Looked at meta/cfg/broken/fri2-broken/hdw_frags.txt and + meta/cfg/broken/fri2-broken/required_frags.txt in directory: + meta/cfg/broken/fri2-broken </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> + In this example, <filename>KMACHINE</filename> was set to "fri2-broken" + and <filename>LINUX_KERNEL_TYPE</filename> was set to "broken". + </para> + + <para> + It will then search first for the <filename>KMACHINE</filename> and + then for the <filename>LINUX_KERNEL_TYPE</filename>. + If it cannot find a partial match, it will use the + sources from the <filename>KBRANCH</filename> and any configuration + specified in the <filename>SRC_URI</filename>. + </para> + + <para> + <filename>KERNEL_FEATURES</filename> can be used to include features + (configuration fragments, patches, or both) that are not already + included by the <filename>KMACHINE</filename> and + <filename>LINUX_KERNEL_TYPE</filename> combination. + To include a feature specified as "features/netfilter.scc" for example, + specify: + <literallayout class='monospaced'> + KERNEL_FEATURES += "features/netfilter.scc" + </literallayout> + To include a feature called "cfg/sound.scc" just for the + <filename>qemux86</filename> machine, specify: + <literallayout class='monospaced'> + KERNEL_FEATURES_append_qemux86 = "cfg/sound.scc" + </literallayout> + The value of the entries in <filename>KERNEL_FEATURES</filename> + are dependent on their location within the metadata itself. + The examples here are taken from the + <filename>linux-yocto-3.4</filename> repository where "features" + and "cfg" are subdirectories of the <filename>metadata</filename> + directory. + For details, see section 3.3. + <note> + The processing of the these variables has evolved some between the + 0.9 and 1.3 releases of the Yocto Project and associated + kern-tools sources. + The descriptions in this section are accurate for 1.3 and later + releases of the Yocto Project. + </note> + </para> + + <para> + Original Text. + <literallayout class='monospaced'> +The metadata provided with any linux-yocto style Linux kernel sources must +define a BSP that corresponds to the definition laid out in the recipe. A BSP +consists of an aggregation of kernel policy and hardware specific feature +enablement. This can be influenced from within the recipe. + +Every linux-yocto style recipe must define the following variables: + + KMACHINE + +KMACHINE is typically set to the same value as used within the recipe-space BSP +definition, such as "routerstationpro" or "fri2". However, multiple BSPs can +reuse the same KMACHINE name if they are built using the same BSP description +(see 3.3.5). The meta-intel "fri2" and "fri2-noemgd" are good examples of such +a situation where each specifies KMACHINE as "fri2". + +They may optionally define the following variables: + KBRANCH + KERNEL_FEATURES + KBRANCH_DEFAULT + LINUX_KERNEL_TYPE + +KBRANCH_DEFAULT defines the default source branch within the Linux kernel source +repository to be used to build the Linux kernel. It is used as the default value +for KBRANCH which may define an alternate branch, typically with a machine +override, such as: + +KBRANCH_fri2 = "standard/fri2" + +Unless you specify otherwise, KBRANCH_DEFAULT is initialized to "master". + +LINUX_KERNEL_TYPE defines the kernel type to be used in assembling the +configuration and defaults to "standard" if you do not specify otherwise. +Together with KMACHINE, this defines the search arguments used by the Yocto +Project Linux kernel tools to find the appropriate description within the +metadata with which to build out the sources and configuration. The linux-yocto +recipes define "standard", "tiny", and "preempt-rt" kernel types. See 3.3.4 for +more inforation on kernel types. + +During the build, the kern-tools will search for the BSP description file that +most closely matches the KMACHINE and LINUX_KERNEL_TYPE passed in from the +recipe. It will use the first BSP description it finds matching both variables. +Failing that it will issue a warning such as the following: + + WARNING: Can't find any BSP hardware or required configuration fragments. + WARNING: Looked at meta/cfg/broken/fri2-broken/hdw_frags.txt and + meta/cfg/broken/fri2-broken/required_frags.txt in directory: + meta/cfg/broken/fri2-broken + + In this example KMACHINE was set to "fri2-broken" and LINUX_KERNEL_TYPE + was set to "broken". + +It will then search first for the KMACHINE and then +for the LINUX_KERNEL_TYPE. If it cannot find a partial match, it will use the +sources from the KBRANCH and any configuration specified in the SRC_URI. + +KERNEL_FEATURES can be used to include features (configuration fragments, +patches, or both) that are not already included by the KMACHINE and +LINUX_KERNEL_TYPE combination. To include a feature specified as +"features/netfilter.scc" for example, specify: + +KERNEL_FEATURES += "features/netfilter.scc" + +To include a feature called "cfg/sound.scc" just for the qemux86 machine, +specify: + +KERNEL_FEATURES_append_qemux86 = "cfg/sound.scc" + +The value of the entries in KERNEL_FEATURES are dependent on their location +within the metadata itself. The examples here are taken from the +linux-yocto-3.4 repository where "features" and "cfg" are subdirectories of the +metadata directory. For details, see 3.3. + + Note: The processing of the these variables has evolved some between the + 0.9 and 1.3 releases of the Yocto Project and associated + kern-tools sources. The above is accurate for 1.3 and later + releases of the Yocto Project. + </literallayout> + </para> +</section> + </chapter> <!-- vim: expandtab tw=80 ts=4 |
