diff --git a/documentation/kernel-manual/kernel-concepts.xml b/documentation/kernel-manual/kernel-concepts.xml index eede5a2e59..bcda78c4e1 100644 --- a/documentation/kernel-manual/kernel-concepts.xml +++ b/documentation/kernel-manual/kernel-concepts.xml @@ -46,12 +46,14 @@ the baseline kernel is 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. + Present a kernel Git repository that, similar to 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.e. 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 + to a specific use case (e.g. networking, consumer, devices, and so forth). + Employ a Git branching strategy that, from a developer'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. @@ -60,27 +62,29 @@
Yocto Project Kernel Development and Maintenance Overview - Yocto Project kernel, like other kernels, is based off the Linux kernel release + The 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 + At the beginning of a major development cycle, the Yocto Project team + chooses its Yocto Project kernel + based on factors like release timing, the anticipated release timing of final + upstream kernel.org versions, and Yocto Project feature requirements. + Typically, the kernel chosen is in the + final stages of development by the community. + In other words, the kernel is in the release + candidate or "rc" phase and not yet a final release. + But, by being in the final stages of external development, the team knows that the + kernel.org final release will clearly be 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. + This balance allows the team to deliver the most up-to-date kernel + as possible, while still ensuring that the team has a stable official release as + the baseline kernel version. 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 released + from kernel.org. + In addition to a foundational kernel from kernel.org, the released Yocto Project kernel contains a mix of important new mainline developments, non-mainline developments (when there is no alternative), Board Support Package (BSP) developments, @@ -88,37 +92,21 @@ 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 while continuing maintenance on the + Once a Yocto Project kernel is officially released, the Yocto Project team goes into + their next development cycle, or "uprev" cycle, while still continuing maintenance on the released kernel. 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. + Back-porting 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. + possible kernel.org version. The team continually monitors community kernel development to look for significant features of interest. - 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. @@ -130,7 +118,7 @@ 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 + The reason for this policy is that back-porting any small to medium sized change from an evolving kernel can easily create mismatches, incompatibilities and very subtle errors. @@ -163,18 +151,23 @@ 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. - + 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. + source code manager (SCM) Git. + For information on Git as applied to the Yocto Project, see the + "Git" + section in The + Yocto Project Development Manual. + + 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. + made up the baseline kernel. The following illustration shows the conceptual Yocto Project kernel. @@ -183,18 +176,20 @@ - 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. + 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 + 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 + 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. @@ -209,8 +204,9 @@ 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. + The resulting tree structure presents a clear path of markers (or branches) to the + developer that, for all practical purposes, is the kernel needed for any given set + of requirements.
@@ -221,50 +217,52 @@ 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. + 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. + This strategy also results in not having to store the same feature twice + internally in the tree. + Rather, the kernel team stores the unique differences required to apply the + feature onto the kernel type in question. + + The Yocto Project team strives to place features in the tree such that they can be + shared by all boards and kernel types where possible. + However, during development cycles or when large features are merged, + the team cannot always follow this practice. + In those cases, the team uses isolated branches to merge features. + - - The Yocto Project team strives to place features in the tree such that they can be - shared by all boards and kernel types where possible. - However, during development cycles or when large features are merged this practice - cannot always be followed. - In those cases isolated branches are used for feature merging. - 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 + So, for these types, the team creates 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. + So again, rather than store the BSP twice, the team only stores the unique + differences for the BSP across the supported multiple kernels. While this strategy can result in a tree with a significant number of branches, it is - important to realize that from the user'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. + important to realize that from the developer'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 user'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 + From the developer's perspective, this path is the "master" branch. + The developer does 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. + 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 + 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. @@ -273,7 +271,7 @@ 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 + As mentioned previously, the structure is transparent to the developer because the kernel tree is left in this state after cloning and building the kernel. @@ -281,20 +279,26 @@
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. + The Source Code Manager (SCM) is Git. + This SCM 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. You can find documentation on Git at . - Also, the Yocto Project Development manual has an introduction to Git and describes a - minimal set of commands that allow you to be functional with Git. + You can also get an introduction to Git as it applies to the Yocto Project in the + "Git" + section in The + Yocto Project Development Manual. + This section overviews Git and describes a minimal set of commands that allow you to be + functional using Git. + + You can use as much, or as little, of what Git has to offer to accomplish what + you need for your project. + You do not have to be a "Git Master" in order to use it with the Yocto Project. + - - 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. -
@@ -307,17 +311,19 @@ present a simplified view of the kernel for ease of use. - The fundamental properties of the tools that manage and construct the - Yocto Project kernel are: + Fundamentally, the kernel tools that manage and construct the + Yocto Project kernel accomplish the following: Group patches into named, reusable features. - Allow top down control of included features. - Bind kernel configuration to kernel patches and features. + Allow top-down control of included features. + Bind kernel configurations to kernel patches and features. Present a seamless Git repository that blends Yocto Project value - with the kernel.org history and development. + with the kernel.org history and development. Workflow examples - @@ -35,65 +24,73 @@
Tree Construction - The Yocto Project kernel repository, as shipped with the product, is created by + This section describes construction of the Yocto Project kernel repositories as accomplished + by the Yocto Project team to create kernel repositories, which are found at + http://git.yoctoproject.org/cgit.cgi, + that 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 the kernel. Thus, the Yocto Project kernel repository (or tree) is built. - The existence of this tree allows you to build images based on your configurations + + + The existence of this tree allows you to access and clone a particular + Linux Yocto kernel repository and use it to build images based on their configurations and features. - You can find the files used to describe all the valid features and BSPs in the Yocto Project - kernel in any clone of the kernel Git tree. + You can find the files used to describe all the valid features and BSPs + in the Yocto Project kernel in any clone of the Linux Yocto kernel source repository Git tree. For example, the following command clones the Yocto Project baseline kernel that - branched off of linux.org version 2.6.37: + branched off of linux.org version 3.0: - $ git clone http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-2.6.37 - - After you switch to the meta branch within the repository - you can see a snapshot of all the kernel configuration and feature descriptions that are + $ git clone git://git.yoctoproject.org/linux-yocto-3.0 + + For another example of how to set up a local Git repository of the Linux Yocto + kernel files, see the + "Linux Yocto Kernel" bulleted item in + The Yocto Project Development Manual. + + + Once the Git repository is set up on your local machine, you can switch to the + meta branch within the repository. + Here, you can see a snapshot of all the kernel configuration and feature descriptions that are used to build the kernel repository. These descriptions are in the form of .scc files. - You should realize, however, that browsing the snapshot of feature + You should realize, however, that browsing your local snapshot of 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. + 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. + + Ground up reconstruction of the complete kernel tree is an action only taken by the + Yocto Project team during an active development cycle. + When you create a clone of the kernel Git repository, you are simply making it + efficiently available for building and development. + - - Ground up reconstruction of the complete kernel tree is an action only taken by the - Yocto Project team during an active development cycle. - Creating a project simply clones this tree to make it efficiently available for building - and development. - - The following steps describe what happens during tree construction given the introduction - of a new top-level kernel feature or BSP. + The following steps describe what happens when the Yocto kernel team constructs + the kernel tree 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: A top-level kernel feature is passed to the kernel build subsystem. - Normally, this is a BSP for a particular kernel type. - + Normally, this feature is a BSP for a particular kernel type. The file that describes the top-level feature is located by searching these system directories: - The in-tree kernel-cache directories, which are located in meta/cfg/kernel-cache - Areas pointed to by SRC_URI statements found in recipes - - For a typical build, the target of the search is a feature description in an .scc file whose name follows this format: @@ -101,85 +98,60 @@ <bsp_name>-<kernel_type>.scc - 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. - Extra features are appended to the top-level feature description. These features can come from the KERNEL_FEATURES variable in recipes. - Each extra feature is located, compiled and appended to the script as described in step three. - - The script is executed to produce a meta-series. - The meta-series is a description of all the branches, tags, patches and configurations that + The script is executed to produce a series of meta-* + 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. - The base repository is cloned, and the actions - listed in the meta-series are applied to the tree. - + listed in the meta-* directories 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. + The kernel tree is now ready for developer consumption to be locally cloned, + configured, and built into a Linux Yocto kernel specific to some target hardware. + The generated meta-* 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 + http://git.yoctoproject.org/cgit.cgi + is the combination of all supported boards and configurations. + The technique the Yocto Project team uses is flexible and allows for seamless + blending of an immutable history with additional deployment specific patches. + Any additions to the kernel become an integrated part of the branches. + - - 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 - official Yocto Project kernel repositories is the combination of all - supported boards and configurations. - - This technique is flexible and allows for seamless blending of an immutable - history with additional deployment specific patches. - Any additions to the kernel become an integrated part of the branches. - - - - -
Build Strategy - There are some prerequisites that must be met before starting the compilation + Once a local Git repository of the Linux Yocto kernel exists on a development system, + you can consider the compilation phase of kernel development - building a kernel image. + Some prerequisites exist 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 BSP build branch - <bsp name>-<kernel type> in 0.9 or - <kernel type>/<bsp name> in 1.0. + The SRC_URI must point to the kernel Git + repository. + A BSP build branch must exist. + This branch has the following form: + + <kernel_type>/<bsp_name> + @@ -187,15 +159,15 @@ A summary of end user tree construction activities follow: of the build system. However, other means do exist. For examples of alternate workflows such as bootstrapping a BSP, see - the Workflow Examples section in this manual. + the "Workflow Examples". - Before building a kernel it is configured by processing all of the - configuration "fragments" specified by feature descriptions in the scc + Before building a kernel, the build process configures the kernel by processing all of the + configuration "fragments" specified by feature descriptions in the .scc files. As the features are compiled, associated kernel configuration fragments are noted - and recorded in the meta-series in their compilation order. + and recorded in the meta-* series of directories 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. @@ -205,201 +177,47 @@ A summary of end user tree construction activities follow: - Using the board's architecture and other relevant values from the board's template - the Kernel compilation is started and a kernel image is produced. + Using the board's architecture and other relevant values from the board's template, + kernel compilation is started 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 tree has the name using the following form: + + 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 + ${MACHINE} is the metadata name of the machine (BSP) and "kernel_type" is one + of the Yocto Project supported kernel types (e.g. "standard"): - linux-<BSPname>-<kerntype>-build + linux-${MACHINE}-<kernel_type>-build - "kerntype" is one of the standard kernel types. - The existing support in the kernel.org tree achieves this default functionality. + The existing support in the kernel.org tree achieves this + default functionality. - What this means, is that all the generated files for a particular BSP are now in this directory. - The files include the final .config, all the .o + What this means, is that all the generated files for a particular machine or BSP are now in + the build tree directory. + The files include the final .config file, all the .o files, the .a files, and so forth. - Since each BSP has its own separate build directory in its own separate branch - of the Git tree you can easily switch between different BSP builds. + 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.
- - - -
Workflow Examples 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. - Yocto Project has not made changes to Git or to other tools that + 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 + only core Git functionality, thus allowing any number of tools or front ends to use the resulting tree. @@ -417,7 +235,7 @@ repository. In projects that have a collection of directories that - contain patches to the kernel it is possible to inspect or "grep" the contents + 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. @@ -441,15 +259,12 @@ repository. Note that because the Yocto Project Git repository does not break existing Git functionality and because there exists many permutations of these types of commands there are many more methods to discover changes. - - - - Unless you provide a commit range - (<kernel-type>..<bsp>-<kernel-type>), kernel.org history - is blended with Yocto Project changes. - - - + + Unless you provide a commit range + (<kernel-type>..<bsp>-<kernel-type>), kernel.org history + is blended with Yocto Project changes. + + # full description of the changes > git whatchanged <kernel type>..<kernel type>/<bsp> > eg: git whatchanged yocto/standard/base..yocto/standard/common-pc/base @@ -469,7 +284,8 @@ repository. # determine the commits which touch each line in a file > git blame <path to file> - + +
@@ -479,13 +295,11 @@ repository. Significant features or branches are tagged in the Yocto Project tree to divide changes. Remember to first determine (or add) the tag of interest. - - - - Because BSP branch, kernel.org, and feature tags are all present, there are many tags. - - - + + Because BSP branch, kernel.org, and feature tags are all + present, there could be many tags. + + # show the changes tagged by a feature > git show <tag> > eg: git show yaffs2 @@ -496,11 +310,13 @@ repository. # show the changes in a kernel type > git whatchanged yocto/base..<kernel type> > eg: git whatchanged yocto/base..yocto/standard/base - + + You can use many other comparisons to isolate BSP changes. - For example, you can compare against kernel.org tags (e.g. v2.6.27.18, etc), or + For example, you can compare against kernel.org tags + (e.g. v2.6.27.18, etc), or you can compare against subsystems (e.g. git whatchanged mm).
@@ -510,8 +326,8 @@ repository. Development: Saving Kernel Modifications - Another common operation is to build a BSP supplied by Yocto Project, make some - changes, rebuild and then test. + 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. @@ -519,7 +335,7 @@ repository. 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 the changes should be saved. + 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. @@ -529,45 +345,43 @@ repository. The technique employed depends on the destination for the patches: - - Bulk storage - Internal sharing either through patches or by using Git - External submissions - Exporting for integration into another SCM - + + Bulk storage + Internal sharing either through patches or by using Git + External submissions + Exporting for integration into another Source Code + Manager (SCM) + Because of the following list of issues, the destination of the patches also influences the method for gathering them: - - Bisectability - Commit headers - Division of subsystems for separate submission or review - + + Bisectability + Commit headers + Division of subsystems for separate submission or review +
Bulk Export - This section describes how you can export in "bulk" changes that have not + 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. - - - - 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. - - - + + 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. + + # bulk export of ALL modifications without separation or division # of the changes @@ -575,7 +389,8 @@ repository. > git commit -s -a -m >commit message< or > git commit -s -a # and interact with $EDITOR - + + The previous operations capture all the local changes in the project source @@ -596,18 +411,19 @@ repository. This section describes how to save modifications when you are making incremental commits or practicing planned sharing. - The examples in this section assume that changes have been incrementally committed - to the tree during development and now need to be exported. The sections that follow + 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. - During development the following commands are of interest. - For full Git documentation, refer to the Git man pages or to an online resource such - as . + During development, the following commands are of interest. + For full Git documentation, refer to the Git documentation at + . - + # edit a file > vi >path</file # stage the change @@ -620,11 +436,11 @@ repository. > git commit -s ... etc. - + - Distributed development with git is possible when you use a universally + 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 @@ -632,7 +448,8 @@ repository. a commit. As an individual in isolation, this is of no interest. However, if you - intend to share your tree with normal git push and pull operations for + intend to share your tree with normal Git push and + pull operations for distributed development, you should consider the ramifications of changing a commit that you have already shared with others. @@ -642,19 +459,19 @@ repository. another repository, you can update both the commit content and commit messages associated with development by using the following commands: - + > 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 - no pending works-in-progress exist (use git status to check) then + no pending works-in-progress exists (use git status to check), then you can revert (undo) commits by using the following commands: - + # remove the commit, update working tree and remove all # traces of the change > git reset --hard HEAD^ @@ -662,26 +479,26 @@ repository. > git reset --soft HEAD^ # remove the commit, leave file change, but not staged for commit > git reset --mixed HEAD^ - + - You can create branches, "cherry-pick" changes or perform any number of Git + 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 push or pull, commits are normally considered + After a push or pull command, + commits are normally considered "permanent" and you should not modify them. - If they need to be changed you can incrementally do so with new commits. - These practices follow the standard Git workflow and the kernel.org best + If the commits need to be changed, you can incrementally do so with new commits. + These practices follow standard Git workflow and the kernel.org best practices, which Yocto Project recommends. + + 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. + - - - 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. -
Exporting Changes Internally by Using Patches @@ -699,27 +516,23 @@ repository. Once the directory is created, you can apply it to a repository using the git am command to reproduce the original commit and all the related information such as author, date, commit log, and so forth. - - - - 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. - - - - + + 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. + + # <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 @@ -731,13 +544,8 @@ repository. > git whatchanged # identify last commit > git format-patch -o <save dir> <commit id> > git format-patch -o <save dir> <rev-list> - + - -
@@ -746,44 +554,38 @@ repository. 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 in the master repository you can then + Once you have pushed the changes in the master repository, you can then pull those same changes into a new kernel build at a later time. Use this command form to push the changes: - + > git push ssh://<master_server>/<path_to_repo> <local_branch>:<remote_branch> - + For example, the following command pushes the changes from your local branch yocto/standard/common-pc/base to the remote branch with the same name - in the master repository //git.mycompany.com/pub/git/kernel-2.6.37. - - > git push ssh://git.mycompany.com/pub/git/kernel-2.6.37 \ + in the master repository //git.mycompany.com/pub/git/kernel-3.0. + + > git push ssh://git.mycompany.com/pub/git/kernel-3.0 \ yocto/standard/common-pc/base:yocto/standard/common-pc/base - + - A pull request entails using git request-pull to compose an email to the + 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 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. + - - - Other commands such as git stash or branching can also be used to save - changes, but are not covered in this document. - - -
@@ -794,26 +596,29 @@ repository. 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 sent patches as an email series. + However, it is common to send patches as an email series. This method allows easy review and integration of the changes. + + 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: + + + + + + Documentation/SubmittingPatches (in any linux + kernel source tree) + + - - 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: - - - - Documentation/SubmittingPatches (in any linux kernel source tree) - - - 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. If the initial commits were not properly documented or do not meet those standards, - you can re-base by using the git rebase -i command to manipulate the commits and + you can re-base by using the git rebase -i 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. @@ -821,13 +626,14 @@ repository. 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 git send-email is commonly used to ensure that patches are properly + The command git send-email is commonly used to ensure + that patches are properly formatted for easy application and avoid mailer-induced patch damage. The following is an example of dumping patches for external submission: - + # dump the last 4 commits > git format-patch --thread -n -o ~/rr/ HEAD^^^^ > git send-email --compose --subject '[RFC 0/N] <patch series summary>' \ @@ -835,7 +641,7 @@ repository. --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 - + @@ -844,12 +650,12 @@ repository. When you want to export changes for import into another - Source Code Manager (SCM) you can use any of the previously discussed + 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 + that tree is checked into the SCM, you can lose change information such as commit logs. - Yocto Project does not recommend this process. + The Yocto Project does not recommend this process. @@ -864,16 +670,16 @@ repository. Working with the Yocto Project Kernel in Another SCM - This section describes kernel development in another SCM, which is not the same - as exporting changes to another SCM. - For this scenario you use the Yocto Project build system to + 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 Yocto Project build system to develop the kernel in a different SCM. The following must be true for you to accomplish this: The delivered Yocto Project kernel must be exported into the second - SCM. + SCM. Development must be exported from that secondary SCM into a - format that can be used by the Yocto Project build system. + format that can be used by the Yocto Project build system. @@ -881,7 +687,7 @@ repository. Exporting the Delivered Kernel to the SCM - Depending on the SCM it might be possible to export the entire Yocto Project + 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. @@ -894,12 +700,13 @@ repository. The following commands illustrate some of the steps you could use to - import the yocto/standard/common-pc/base kernel into a secondary SCM: - + import the yocto/standard/common-pc/base + kernel into a secondary SCM: + > git checkout yocto/standard/common-pc/base > cd .. ; echo linux/.git > .cvsignore > cvs import -m "initial import" linux MY_COMPANY start - + @@ -908,13 +715,13 @@ repository. The following commands illustrate how you can condense and merge two BSPs into a second SCM: - + > 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 - + @@ -924,112 +731,12 @@ repository. 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 + To export them, place the changes in a recipe and automatically apply them to the kernel during patching. - - - - -
Creating a BSP Based on an Existing Similar BSP @@ -1037,19 +744,21 @@ That's it. Configure and build. 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 BSP given an existing similar BSP - see the Yocto Project Development Manual [NEED LINK] or the - + For detailed information on how to create a BSP given an existing similar BSP, see + the "BSP Development Example" appendix in + The + Yocto Project Development Manual, or see the + Transcript:_creating_one_generic_Atom_BSP_from_another wiki page. The basic steps you need to follow are: - Make sure you have the Yocto Project source tree available. + Make sure you have the Yocto Project source tree available: You should either create a Yocto Project Git repository (recommended), or you should get the Yocto Project release tarball and extract it. - Choose an existing BSP available with the Yocto Project. + Choose an existing BSP available with the Yocto Project: 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 @@ -1057,13 +766,14 @@ That's it. Configure and build. You can find all the BSPs that are supported and ship with the Yocto Project on the Yocto Project's Download page at . - Be sure you have the Base BSP. + Be sure you have the Base BSP: You need to either have the Yocto Project Git repository set up or download the tarball of the base BSP. Either method gives you access to the BSP source files. - Make a copy of the existing BSP, thus isolating your new BSP work. + Make a copy of the existing BSP, thus isolating your new + BSP work: Copying the existing BSP structure gives you a new area in which to work. - Make configuration and recipe changes to your new BSP. + Make configuration and recipe changes to your new BSP: Configuration changes involve the files in the BSP's conf directory. Changes include creating a machine-specific configuration file and editing the @@ -1071,13 +781,13 @@ That's it. Configure and build. 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. - Prepare for the build. - Before you actually initiate the build you need to set up the build environment + Prepare for the build: + 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 + After setting up the environment, you need to make some build configuration changes to the local.conf and bblayers.conf files. - Build the image. + Build the image: The Yocto Project uses the BitBake tool 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 bitbake @@ -1086,746 +796,6 @@ That's it. Configure and build.
- - - - - - - - -
"-dirty" String @@ -1839,14 +809,14 @@ This section shows an example of transforms: - You can use the Git command above to report modified, removed, or added files. + 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. - To brute force pickup and commit all such pending changes enter the following: + To brute force pickup and commit all such pending changes, enter the following: > git add . > git commit -s -a -m "getting rid of -dirty" @@ -1857,206 +827,7 @@ This section shows an example of transforms: Next, rebuild the kernel.
- - - - - - - - - - - - - - - - - - - -