From d2e540116f1cc0bf93b7ed6f4828c56ab909489e Mon Sep 17 00:00:00 2001 From: Scott Rifenbark Date: Mon, 29 Nov 2010 07:28:51 -0800 Subject: documentation/kernel-manual/yocto-project-kernel-manual.xml: Removed this file so manual could be structured into a book with chapters. Signed-off-by: Scott Rifenbark --- .../kernel-manual/yocto-project-kernel-manual.xml | 2305 -------------------- 1 file changed, 2305 deletions(-) delete mode 100644 documentation/kernel-manual/yocto-project-kernel-manual.xml (limited to 'documentation') diff --git a/documentation/kernel-manual/yocto-project-kernel-manual.xml b/documentation/kernel-manual/yocto-project-kernel-manual.xml deleted file mode 100644 index c0747b2540..0000000000 --- a/documentation/kernel-manual/yocto-project-kernel-manual.xml +++ /dev/null @@ -1,2305 +0,0 @@ - - - - -Yocto Project Kernel Architecture and Use Manual - -
- Introduction - - Yocto Project presents the kernel as a fully patched, history-clean git - repository. - The git tree represents the selected features, board support, - and configurations extensively tested by Yocto Project. - The Yocto Project kernel allows the end user to leverage community - best practices to seamlessly manage the development, build and debug cycles. - - - This manual describes the Yocto Project kernel by providing information - on its history, organization, benefits, and use. - The manual consists of two sections: - - Concepts - Describes concepts behind the kernel. - You will understand how the kernel is organized and why it is organized in - the way it is. You will understand the benefits of the kernel's organization - and the mechanisms used to work with the kernel and how to apply it in your - design process. - Using the Kernel - Describes best practices and "how-to" information - that lets you put the kernel to practical use. Some examples are "How to Build a - Project Specific Tree", "How to Examine Changes in a Branch", and "Saving Kernel - Modifications." - - - - For more information on the kernel, see the following links: - - - - - - - You can find more information on Yocto Project by visiting the website at - . - - -
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- Concepts - - This section provides conceptual information about the Yocto Project kernel: - - Kernel Goals - Yocto Project Kernel Development and Maintenance Overview - Kernel Architecture - Kernel Tools - - -
- Kernel Goals - - The complexity of embedded kernel design has increased dramatically. - Whether it is managing multiple implementations of a particular feature or tuning and - optimizing board specific features, flexibility and maintainability are key concerns. - The Yocto Project Linux kernel is presented with the embedded - developer's needs in mind and has evolved to assist in these key concerns. - For example, prior methods such as applying hundreds of patches to an extracted - tarball have been replaced with proven techniques that allow easy inspection, - bisection and analysis of changes. - Application of these techniques also creates a platform for performing integration and - collaboration with the thousands of upstream development projects. - - - With all these considerations in mind, the Yocto Project kernel and development team - strives to attain these goals: - - Allow the end user to leverage community best practices to seamlessly - manage the development, build and debug cycles. - Create a platform for performing integration and collaboration with the - thousands of upstream development projects that exist. - Provide mechanisms that support many different work flows, front-ends and - management techniques. - Deliver the most up-to-date kernel possible while still ensuring that - the baseline kernel is the the most stable official release. - Include major technological features as part of Yocto Project's up-rev - strategy. - Present a git tree, that just like the upstream kernel.org tree, has a - clear and continuous history. - Deliver a key set of supported kernel types, where each type is tailored - to a specific use case (i.g. networking, consumer, devices, and so forth). - Employ a git branching strategy that from a customer's point of view - results in a linear path from the baseline kernel.org, through a select group of features and - ends with their BSP-specific commits. - - -
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- Yocto Project Kernel Development and Maintenance Overview - - Yocto Project kernel, like other kernels, is based off the Linux kernel release - from . - At the beginning of our major development cycle, we choose our Yocto Project kernel - based on factors like release timing, the anticipated release timing of "final" (i.e. non "rc") - upstream kernel.org versions, and Yocto Project feature requirements. - Typically this will be a kernel that is in the - final stages of development by the community (i.e. still in the release - candidate or "rc" phase) and not yet a final release. - But by being in the final stages of external development, we know that the - kernel.org final release will clearly land within the early stages of - the Yocto Project development window. - - - This balance allows us to deliver the most up-to-date kernel - as possible, while still ensuring that we have a stable official release as - our baseline kernel version. - - - The following figure represents the overall place the Yocto Project kernel fills. - - - - - - In the figure the ultimate source for the Yocto Project kernel is a released kernel - from kernel.org. - In addition to a foundational kernel from kernel.org the commercially released - Yocto Project kernel contains a mix of important new mainline - developments, non-mainline developments, Board Support Package (BSP) developments, - and custom features. - These additions result in a commercially released Yocto Project kernel that caters - to specific embedded designer needs for targeted hardware. - - - Once a Yocto Project kernel is officially released the Yocto Project team goes into - their next development cycle, or "uprev" cycle. - It is important to note that the most sustainable and stable way - to include feature development upstream is through a kernel uprev process. - Back-porting of hundreds of individual fixes and minor features from various - kernel versions is not sustainable and can easily compromise quality. - During the uprev cycle, the Yocto Project team uses an ongoing analysis of - kernel development, BSP support, and release timing to select the best - possible kernel.org version. - The team continually monitors community kernel - development to look for significant features of interest. - The illustration depicts this by showing the team looking back to kernel.org for new features, - BSP features, and significant bug fixes. - The team does consider back-porting large features if they have a significant advantage. - User or community demand can also trigger a back-port or creation of new - functionality in the Yocto Project baseline kernel during the uprev cycle. - - - Generally speaking, every new kernel both adds features and introduces new bugs. - These consequences are the basic properties of upstream kernel development and are - managed by the Yocto Project team's kernel strategy. - It is the Yocto Project team's policy to not back-port minor features to the released kernel. - They only consider back-porting significant technological jumps - and, that is done - after a complete gap analysis. - The reason for this policy is that simply back-porting any small to medium sized change - from an evolving kernel can easily create mismatches, incompatibilities and very - subtle errors. - - - These policies result in both a stable and a cutting - edge kernel that mixes forward ports of existing features and significant and critical - new functionality. - Forward porting functionality in the Yocto Project kernel can be thought of as a - "micro uprev." - The many “micro uprevs” produce a kernel version with a mix of - important new mainline, non-mainline, BSP developments and feature integrations. - This kernel gives insight into new features and allows focused - amounts of testing to be done on the kernel, which prevents - surprises when selecting the next major uprev. - The quality of these cutting edge kernels is evolving and the kernels are used in very special - cases for BSP and feature development. - -
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- Kernel Architecture - - This section describes the architecture of the Yocto Project kernel and provides information - on the mechanisms used to achieve that architecture. - - -
- Overview - - As mentioned earlier, a key goal of Yocto Project is to present the developer with - a kernel that has a clear and continuous history that is visible to the user. - The architecture and mechanisms used achieve that goal in a manner similar to the - upstream kernel.org. - - - - You can think of the Yocto Project kernel as consisting of a baseline kernel with - added features logically structured on top of the baseline. - The features are tagged and organized by way of a branching strategy implemented by the - source code manager (SCM) git. - The result is that the user has the ability to see the added features and - the commits that make up those features. - In addition to being able to see added features, the user can also view the history of what - made up the baseline kernel as well. - - - The following illustration shows the conceptual Yocto Project kernel. - - - - - - In the illustration, the "kernel.org Branch Point" marks the specific spot (or release) from - which the Yocto Project kernel is created. From this point "up" in the tree features and - differences are organized and tagged. - - - The "Yocto Project Baseline Kernel" contains functionality that is common to every kernel - type and BSP that is organized further up the tree. Placing these common features in the - tree this way means features don't have to be duplicated along individual branches of the - structure. - - - From the Yocto Project Baseline Kernel branch points represent specific functionality - for individual BSPs as well as real-time kernels. - The illustration represents this through three BSP-specific branches and a real-time - kernel branch. - Each branch represents some unique functionality for the BSP or a real-time kernel. - - - The real-time kernel branch has common features for all real-time kernels and contains - more branches for individual BSP-specific real-time kernels. - The illustration shows three branches as an example. - Each branch points the way to specific, unique features for a respective real-time - kernel as they apply to a given BSP. - - - The resulting tree structure presents a clear path of markers (or branches) to the user - that for all practical purposes is the kernel needed for any given set of requirements. - -
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- Branching Strategy and Workflow - - The Yocto Project team creates kernel branches at points where functionality is - no longer shared and thus, needs to be isolated. - For example, board-specific incompatibilities would require different functionality - and would require a branch to separate the features. - Likewise, for specific kernel features the same branching strategy is used. - This branching strategy results in a tree that has features organized to be specific - for particular functionality, single kernel types, or a subset of kernel types. - This strategy results in not having to store the same feature twice internally in the - tree. - Rather we store the unique differences required to apply the feature onto the kernel type - in question. - - - BSP-specific code additions are handled in a similar manner to kernel-specific additions. - Some BSPs only make sense given certain kernel types. - So, for these types, we create branches off the end of that kernel type for all - of the BSPs that are supported on that kernel type. - From the perspective of the tools that create the BSP branch, the BSP is really no - different than a feature. - Consequently, the same branching strategy applies to BSPs as it does to features. - So again, rather than store the BSP twice, only the unique differences for the BSP across - the supported multiple kernels are uniquely stored. - - - While this strategy results in a tree with a significant number of branches, it is - important to realize that from the customer's point of view, there is a linear - path that travels from the baseline kernel.org, through a select group of features and - ends with their BSP-specific commits. - In other words, the divisions of the kernel are transparent and are not relevant - to the developer on a day-to-day basis. - From the customer's perspective, this is the "master" branch. - They do not need not be aware of the existence of any other branches at all. - Of course there is value in the existence of these branches - in the tree, should a person decide to explore them. - For example, a comparison between two BSPs at either the commit level or at the line-by-line - code diff level is now a trivial operation. - - - Working with the kernel as a structured tree follows recognized community best practices. - In particular, the kernel as shipped with the product should be - considered an 'upstream source' and viewed as a series of - historical and documented modifications (commits). - These modifications represent the development and stabilization done - by the Yocto Project kernel development team. - - - Because commits only change at significant release points in the product life cycle, - developers can work on a branch created - from the last relevant commit in the shipped Yocto Project kernel. - As mentioned previously, the structure is transparent to the user - because the kernel tree is left in this state after cloning and building the kernel. - -
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- Source Code Manager - git - - The Source Code Manager (SCM) is git and it is the obvious mechanism for meeting the - previously mentioned goals. - Not only is it the SCM for kernel.org but git continues to grow in popularity and - supports many different work flows, front-ends and management techniques. - - - It should be noted that you can use as much, or as little, of what git has to offer - as is appropriate to your project. - -
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- Kernel Tools - -Since most standard workflows involve moving forward with an existing tree by -continuing to add and alter the underlying baseline, the tools that manage -Yocto Project's kernel construction are largely hidden from the developer to -present a simplified view of the kernel for ease of use. - - -The fundamental properties of the tools that manage and construct the -kernel are: - - the ability to group patches into named, reusable features - to allow top down control of included features - the binding of kernel configuration to kernel patches/features - the presentation of a seamless git repository that blends Yocto Project value with the kernel.org history and development - - - -
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- How to Get Things Accomplished with the Kernel - - This section describes how to accomplish tasks involving the kernel's tree structure. - The information covers the following: - - Tree construction - Build strategies - - Workflow examples - Source Code Manager (SCM) - - BSP creation - Patching - Updating BSP patches and configuration - - "dirty" string - - - - -
- Tree Construction - -The Yocto Project kernel repository, as shipped with the product, is created 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 the kernel. - - -The files used to describe all the valid features and BSPs in the Yocto Project -kernel can be found in any clone of the kernel git tree. The directory -wrs/cfg/kernel-cache/ is a snapshot of all the kernel configuration and -feature descriptions (.scc) that were used to build the kernel repository. -It should however be noted, that browsing the snapshot of feature -descriptions and patches is not an effective way to determine what is in a -particular kernel branch. Using git directly to get insight into the changes -in a branch is more efficient and a more flexible way to inspect changes to -the kernel. Examples of using git to inspect kernel commits are in the -following sections. - - -As a reminder, it is envisioned that a ground up reconstruction of the -complete kernel tree is an action only taken by Yocto Project team during an -active development cycle. When an end user creates a project, it takes -advantage of this complete tree in order to efficiently place a git tree -within their project. - - -The general flow of the project specific kernel tree construction is as follows: - - a top level kernel feature is passed to the kernel build subsystem, - normally this is a BSP for a particular kernel type. - - the file that describes the top level feature is located by searching - system directories: - - - the kernel-cache under linux/wrs/cfg/kernel-cache - - recipe SRC_URIs - - - - In a typical build a feature description of the format: - <bsp name>-<kernel type>.scc is the target of the search. - - - once located, the feature description is compiled into a simple script - of actions, or an existing equivalent script which was part of the - shipped kernel is located. - - extra features are appended to the top level feature description. Extra - features can come from the KERNEL_FEATURES variable in recipes. - - each extra feature is located, compiled and appended to the script from - step #3 - - the script is executed, and a meta-series is produced. The meta-series - is a description of all the branches, tags, patches and configuration that - need to be applied to the base git repository to completely create the - "bsp_name-kernel_type". - - the base repository is cloned, and the actions - listed in the meta-series are applied to the tree. - - the git repository is left with the desired branch checked out and any - required branching, patching and tagging has been performed. - - - - -The tree is now ready for configuration and compilation. Those two topics will -be covered below. - - -The end user generated meta-series adds 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 linux-2.6-windriver.git is the combination of all - supported boards and configurations. - - - -This technique is flexible and allows the seamless blending of an immutable -history with additional deployment specific patches. Any additions to the -kernel become an integrated part of the branches. - - - - - -A summary of end user tree construction activities follow: - - compile and link a full top-down kernel description from feature descriptions - execute the complete description to generate a meta-series - interpret the meta-series to create a customized git repository for the - board - migrate configuration fragments and configure the kernel - checkout the BSP branch and build - - -
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- Build Strategy - -There are some prerequisites that must be met before starting the compilation -phase of the kernel build system: - - - There must be a kernel git repository indicated in the SRC_URI. - There must be a branch <bsp name>-<kernel type>. - - - -These are typically met by running tree construction/patching phase of the -build system, but can be achieved by other means. Examples of alternate work -flows such as bootstrapping a BSP are provided below. - - -Before building a kernel it is configured by processing all of the -configuration "fragments" specified by the scc feature descriptions. As the -features are compiled, associated kernel configuration fragments are noted -and recorded in the meta-series in their compilation order. The -fragments are migrated, pre-processed and passed to the Linux Kernel -Configuration subsystem (lkc) as raw input in the form of a .config file. -The lkc uses its own internal dependency constraints to do the final -processing of that information and generates the final .config that will -be used during compilation. - - -Kernel compilation is started, using the board's architecture and other -relevant values from the board template, and a kernel image is produced. - - -The other thing that you will first see once you configure a kernel is that -it will generate a build tree that is separate from your git source tree. -This build dir will be called "linux-<BSPname>-<kerntype>-build" where -kerntype is one of standard kernel types. This functionality is done by making -use of the existing support that is within the kernel.org tree by default. - - -What this means, is that all the generated files (that includes the final -".config" itself, all ".o" and ".a" etc) are now in this directory. Since -the git source tree can contain any number of BSPs, all on their own branch, -you now can easily switch between builds of BSPs as well, since each one also -has their own separate build directory. - -
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- Workflow Examples - - -As previously noted, the Yocto Project kernel has built in git/guilt -integration, but these utilities are not the only way to work with the kernel -repository. Yocto Project has not made changes to git, or other tools that -invalidate alternate workflows. Additionally, the way the kernel repository -is constructed uses only core git functionality allowing any number of tools -or front ends to use the resulting tree. - -This section contains several workflow examples. - - -
- Change Inspection: Kernel Changes/Commits - -A common question when working with a BSP/kernel is: "What changes have been applied to this tree?" - - -In some projects, where a collection of directories that -contained patches to the kernel, those patches could be inspected, grep'd or -otherwise used to get a general feeling for changes. This sort of patch -inspection is not an efficient way to determine what has been done to the -kernel, since there are many optional patches that are selected based on the -kernel type and feature description, not to mention patches that are actually -in directories that are not being searched. - - -A more effective way to determine what has changed in the kernel is to use -git and inspect / search the kernel tree. This is a full view of not only the -source code modifications, but the reasoning behind the changes. - -
- What Changed in a BSP? - -These examples could continue for some time, since the Yocto Project git -repository doesn't break existing git functionality and there are nearly -endless permutations of those commands. Also note that unless a commit range -is given (<kernel type>..<bsp>-<kernel type>), kernel.org history is blended -with Yocto Project changes - - - # full description of the changes - > git whatchanged <kernel type>..<bsp>-<kernel type> - > eg: git whatchanged standard..common_pc-standard - - # summary of the changes - > git log ‐‐pretty=oneline ‐‐abbrev-commit <kernel type>..<bsp>-<kernel type> - - # source code changes (one combined diff) - > git diff <kernel type>..<bsp>-<kernel type> - > git show <kernel type>..<bsp>-<kernel type> - - # dump individual patches per commit - > git format-patch -o <dir> <kernel type>..<bsp>-<kernel type> - - # determine the change history of a particular file - > git whatchanged <path to file> - - # determine the commits which touch each line in a file - > git blame <path to file> - -
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- Show a Particular Feature or Branch Change - -Significant features or branches are tagged in the Yocto Project tree to divide -changes. Remember to first determine (or add) the tag of interest. Note: -there will be many tags, since each BSP branch is tagged, kernel.org tags and -feature tags are all present. - - - # show the changes tagged by a feature - > git show <tag> - > eg: git show yaffs2 - - # determine which branches contain a feature - > git branch ‐‐contains <tag> - - # show the changes in a kernel type - > git whatchanged wrs_base..<kernel type> - > eg: git whatchanged wrs_base..standard - - -Many other comparisons can be done to isolate BSP changes, such as comparing -to kernel.org tags (v2.6.27.18, etc), per subsystem comparisons (git -whatchanged mm) or many other types of checks. - -
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- Development: Saving Kernel Modifications - -Another common operation is to build a Yocto Project supplied BSP, make some -changes, rebuild and test. Those local changes often need to be exported, -shared or otherwise maintained. - - -Since the Yocto Project kernel source tree is backed by git, this activity is -greatly simplified and is much easier than in previous releases. git tracks -file modifications, additions and deletions, which allows the developer to -modify the code and later realize that the changes should be saved, and -easily determine what was changed. It also provides many tools to commit, -undo and export those modifications. - - -There are many ways to perform this action, and the technique employed -depends on the destination for the patches, which could be any of: - - bulk storage - internal sharing either through patches or using git - external submission - export for integration into another SCM - - - -The destination of the patches also incluences the method of gathering them -due to issues such as: - - bisectability - commit headers - division of subsystems for separate submission / review - - - -
- Bulk Export - -If patches are simply being stored outside of the kernel source repository, -either permanently or temporarily, then there are several methods that can be -used. - - -Note the "bulk" in this discussion, these techniques are not appropriate for -full integration of upstream submission, since they do not properly divide -changes or provide an avenue for per-change commit messages. This example -assumes that changes have not been committed incrementally during development -and simply must be gathered and exported. - - # bulk export of ALL modifications without separation or division - # of the changes - - > git add . - > git commit -s -a -m >commit message< - or - > git commit -s -a # and interact with $EDITOR - - - -These operations have captured 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. - - -Once exported, those changes can then be restored manually, via a template or -through integration with the default_kernel. Those topics are covered in -future sections. - -
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- Incremental/Planned Sharing - -Note: unlike the previous "bulk" section, the following examples assume that -changes have been incrementally committed to the tree during development and -now are being exported. - - -During development the following commands will be of interest, but for full -git documentation refer to the git man pages or an online resource such as -http://github.com - - # 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. - - - -Distributed development with git is possible by having a universally agreed -upon unique commit identifier (set by the creator of the commit) mapping to a -specific changeset with a specific parent. This ID is created for you when -you create a commit, and will be re-created when you amend/alter or re-apply -a commit. As an individual in isolation, this is of no interest, but if you -intend to share your tree with normal git push/pull operations for -distributed development, you should consider the ramifications of changing a -commit that you've already shared with others. - - -Assuming that the changes have *not* been pushed upstream, or pulled into -another repository, both the commit content and commit messages associated -with development can be update via: - - > git add >path</file - > git commit ‐‐amend - > git rebase or git rebase -i - - - -Again, assuming that the changes have *not* been pushed upstream, and that -there are no pending works in progress (use "git status" to check) then -commits can be reverted (undone) via: - - # 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^ - - - -Branches can be created, changes cherry-picked or any number of git -operations performed until the commits are in good order for pushing upstream -or pull requests. After a push or pull, commits are normally considered -'permanent' and should not be modified, only incrementally changed in new -commits. This is standard "git" workflow and Yocto Project recommends the -kernel.org best practices. - -It is recommend to tag or branch before adding changes to a Yocto Project - BSP (or creating a new one), since the branch or tag provides a - reference point to facilitate locating and exporting local changes. - - -
- Export Internally Via Patches - -Committed changes can be extracted from a working directory by exporting them -as patches. Those patches can be used for upstream submission, placed in a -Yocto Project template for automatic kernel patching or many other common uses. - - - # >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> - - - - - In other words: - - # 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> - - - - -The result is a directory with sequentially numbered patches, that when -applied to a repository using "git am", will reproduce the original commit -and all related information (author, date, commit log, etc) will be -preserved. Note that new commit IDs will be generated upon reapplication, -reflecting that the commit is now applied to an underlying commit with a -different ID. - - -
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- Export Internally Via git - -Committed changes can also be exported from a working directory by pushing -(or by making a pull request) the changes into a master repository. Those -same change can then be pulled into a new kernel build at a later time using this command form: - - git push ssh://<master server>/<path to repo> <local branch>:<remote branch> - -For example: - - > push ssh://git.mycompany.com/pub/git/kernel-2.6.27 common_pc-standard:common_pc-standard - -A pull request entails using "git request-pull" to compose an email to the -maintainer requesting that a branch be pulled into the master repository, see -http://github.com/guides/pull-requests for an example. - - -Other commands such as 'git stash' or branching can also be used to save -changes, but are not covered in this document. - - -See the section "importing from another SCM" for how a git push to the -default_kernel, can be used to automatically update the builds of all users -of a central git repository. - -
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- Export for External (Upstream) Submission - -If patches are to be sent for external submission, they can be done via a -pull request if the patch series is large or the maintainer prefers to pull -changes. But commonly, patches are sent as email series for easy review and -integration. - - -Before sending patches for review ensure that you understand the -standard of the community in question and follow their best practices. For -example, kernel patches should follow standards such as: - - - - Documentation/SubmittingPatches (in any linux kernel source tree) - - - -The messages used to commit changes are a large part of these standards, so -ensure that the headers for each commit have the required information. If the -initial commits were not properly documented or don't meet those standards -rebasing via git rebase -i offer an opportunity to manipulate the commits and -get them into the required format. Other techniques such as branching and -cherry picking commits are also viable options. - - -Once complete, patches are sent via email to the maintainer(s) or lists that -review and integrate changes. "git send-email" is commonly used to ensure -that patches are properly formatted for easy application and avoid mailer -induced patch damage. - - -An example of dumping patches for external submission follows: - - # 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 - - -
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- Export for Import into Other SCM - -Using any one of the previously discussed techniques, commits can be exported -as patches for import into another SCM. Note however, that if those patches -are manually applied to a secondary tree and then that secondary tree is -checked into the SCM, then it often results in lost information (like commit -logs) and so it is not recommended. - - -Many SCMs can directly import git commits, or can translate git patches to -not lose information. Those facilities are SCM dependent and should be used -whenever possible. - -
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- SCM: Working with the Yocto Project Kernel in Another SCM - -This is not the same as the exporting of patches to another SCM, but instead -is concerned with kernel development that is done completely in another -environment, but built with the Yocto Project build system. In this scenario two -things must happen: - - The delivered Yocto Project kernel must be exported into the second - SCM. - Development must be exported from that secondary SCM into a - format that can be used by the Yocto Project build system. - - -
- Exporting Delivered Kernel to SCM - -Depending on the SCM it may be possible to export the entire Yocto Project -kernel git repository, branches and all, into a new environment. This is the -preferred method, since it has the most flexibility and potential to maintain -the meta data associated with each commit. - - -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. - - -The following commands illustrate some of the steps that could be used to -import the common_pc-standard kernel into a secondary SCM - - > git checkout common_pc-standard - > cd .. ; echo linux/.git > .cvsignore - > cvs import -m "initial import" linux MY_COMPANY start - -The CVS repo could now be relocated and used in a centralized manner. - - -The following commands illustrate how two BSPs could be condensed and merged -into a second SCM: - - > git checkout common_pc-standard - > git merge cav_ebt5800-standard - # resolve any conflicts and commit them - > cd .. ; echo linux/.git > .cvsignore - > cvs import -m "initial import" linux MY_COMPANY start - - -
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- Importing Changes for Build - -Once development has reached a suitable point in the second development -environment, changes can either be exported as patches or imported into git -directly (if a conversion/import mechanism is available for the SCM). - - -If changes are exported as patches, they can be placed in a recipe and -automatically applied to the kernel during patching. - - -
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- BSP: Creating - - This section provides an example for creating a BSP based on an existing, and hopefully, - similar one. - Follow these steps and keep in mind your particular situation and differences: - - Get a machine configuration file that matches your machine. - You can start with something in meta/conf/machine. - Or, meta-emenlow/conf/machine has an example in its own layer. - The most up-to-date machines that are probably most similar to yours and that you might want - to look at are meta/conf/machine/atom-pc.conf and - meta-emenlow/conf/machine/emenlow.conf. - Both of these were either just added or upgraded to use the Yocto Project kernel - at . - The main difference between them is that "emenlow" is in its own layer. - It is in its own layer because it needs extra machine-specific packages such as its - own video driver and other supporting packages. - The "atom-pc" is simpler and does not need any special packages - everything it needs can - be specified in the configuration file. - The "atom-pc" machine also supports all of Asus eee901, Acer Aspire One, Toshiba NB305, - and the Intel® Embedded Development Board 1-N450 with no changes. - If you want to make minor changes to support a slightly different machine, you can - create a new configuration file for it and add it alongside the others. - You might consider keeping the common stuff separate and including it. - Similarly, you can also use multiple configuration files for different machines even - if you do it as a separate layer like meta-emenlow. - As an example consider this: - - Copy meta-emenlow - Fix or remove anything you do not need. - For this example the only thing left was the kernel directory with a linux-yocto_git.bbappend - file (linux-yocto is the kernel listed in - meta-crownbay/conf/machine/crownbay.conf. - Finally, a new entry to the build/donf/bblayers.conf was added so the - new layer could be found by Bitbake. - - - Get an image with a working kernel built. - For the kernel to compile successfully, you need to create a branch in the git repository - specifically named for your machine. - So first create a bare clone of the Yocto Project git repository, and then create a - local clone of that: - - $ git clone ‐‐bare git://git.pokylinux.org/linux-2.6-windriver.git - linux-2.6-windriver.git - $ git clone linux-2.6-windriver.git linux-2.6-windriver - - - Now create a branch in the local clone and push it to the bare clone: - - $ git checkout -b crownbay-standard origin/standard $ git push origin crownbay-standard:crownbay-standard - - - At this point, your git tree should be set up well enough to compile. - Point the build at the new kernel git tree. - You can do this by commenting out the SRC_URI variable in - meta/recipes-kernel/linux/linux-yocto_git.bb and using a SRC_URI - that points to your new bare git tree. - You should also be able to do this in linux-yocto_git.bbappend in the layer: - - # To use a staged, on-disk bare clone of a Wind River Kernel, use a variant of the - # below SRC_URI = "git://///path/to/kernel/default_kernel.git;fullclone=1" - # - SRC_URI = "git://git.pokylinux.org/linux-2.6-windriver.git;protocol=git;fullclone=1;branch=${KBRANCH};name=machine -\ - git://git.pokylinux.org/linux-2.6-windriver.git;protocol=git;noclone=1;branch=wrs_meta;name=meta" - - - After doing that, select the machine in build/conf/local.conf: - - # - MACHINE ?= "crownbay" - # - - - You should now be able to build and boot an image with the new kernel: - - $ bitbake poky-image-sato-live - - - Of course, that will give you a kernel with the default config, which is probably - not what you want. - If you just want to set some kernel config options, you can do that by putting them in a files. - For example inserting the following into some .cfg file: - - CONFIG_NETDEV_1000=y - CONFIG_E1000E=y - - - And, another .cfg file would contain: - - CONFIG_LOG_BUF_SHIFT=18 - - http://git.pokylinux.org/cgit/cgit.cgi/linux-2.6-windriver/ - - SRC_URI_append_crownbay = " file://some.cfg \ - file://other.cfg \ - " - - - You could also add these directly to the git repo's wrs_meta branch as well. - However, the former method is probably easier. - If you're also adding patches to the kernel, you can do the same thing. - Put your patches in the SRC_URI as well (plus .cfg for their kernel config options if needed). - Practically speaking, to generate the patches, you'd go to the source in the build tree: - - build/tmp/work/crownbay-poky-linux/linux-yocto-2.6.34+git0+d1cd5c80ee97e81e130be8c3de3965b770f320d6_0+ -0431115c9d720fee5bb105f6a7411efb4f851d26-r13/linux - - - Then, modify the code there, using quilt to save the changes, and recompile - (bitbake -c compile -f) - until it works. - Once you have the final patch from quilt, copy it to the - SRC_URI location, and it should be - applied the next time you do a clean build. - Of course, since you have a branch for the BSP in git, it would be better to put it there instead. - For example, in this case, commit the patch to the crownbay-standard branch, and during the - next build it will be applied from there. - - -
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- "-dirty" String - -If kernel images are being built with -dirty on the end of the version -string, this simply means that there are modification in the source -directory that haven't been committed. - - > git status - - - -The above git command will indicate modified, removed or added files. Those changes should -be committed to the tree (even if they will never be saved, or exported -for future use) and the kernel rebuilt. - - -To brute force pickup and commit all such pending changes enter the following: - - > git add . - > git commit -s -a -m "getting rid of -dirty" - - - -And then rebuild the kernel - -
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- Kernel: Transition Kernel Layer - -In order to temporarily use a different base kernel in Yocto Project -Linux 3.0 you need to do the following: - - Create a custom kernel layer. - Create a git repository of the transition kernel. - - - -Once those requirements are met multiple boards and kernels can -be built. The cost of setup is only paid once and then additional -BSPs and options can be added. - - -This creates a transition kernel layer to evaluate functionality -of some other kernel with the goal of easing transition to an -integrated and validated Yocto Project kernel. - - - - - - - - - -
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