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diff --git a/yocto-poky/documentation/kernel-dev/kernel-dev-concepts-appx.xml b/yocto-poky/documentation/kernel-dev/kernel-dev-concepts-appx.xml deleted file mode 100644 index ac91749cd..000000000 --- a/yocto-poky/documentation/kernel-dev/kernel-dev-concepts-appx.xml +++ /dev/null @@ -1,253 +0,0 @@ -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" -"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" -[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] > - -<appendix id='kernel-dev-concepts-appx'> -<title>Advanced Kernel Concepts</title> - - <section id='kernel-big-picture'> - <title>Yocto Project Kernel Development and Maintenance</title> - <para> - Kernels available through the Yocto Project, like other kernels, are based off the Linux - kernel releases from <ulink url='http://www.kernel.org'></ulink>. - At the beginning of a major development cycle, the Yocto Project team - chooses its kernel based on factors such as release timing, the anticipated release - timing of final upstream <filename>kernel.org</filename> 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 - <filename>kernel.org</filename> final release will clearly be within the early stages of - the Yocto Project development window. - </para> - <para> - This balance allows the team to deliver the most up-to-date kernel - possible, while still ensuring that the team has a stable official release for - the baseline Linux kernel version. - </para> - <para> - The ultimate source for kernels available through the Yocto Project are released kernels - from <filename>kernel.org</filename>. - In addition to a foundational kernel from <filename>kernel.org</filename>, the - kernels available contain a mix of important new mainline - developments, non-mainline developments (when there is no alternative), - Board Support Package (BSP) developments, - and custom features. - These additions result in a commercially released Yocto Project Linux kernel that caters - to specific embedded designer needs for targeted hardware. - </para> - <para> - Once a kernel is officially released, the Yocto Project team goes into - their next development cycle, or upward revision (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 hundreds of individual fixes and minor features from various - kernel versions is not sustainable and can easily compromise quality. - </para> - <para> - 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 <filename>kernel.org</filename> 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. - </para> - <para> - 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 back-porting any small to medium sized change - from an evolving kernel can easily create mismatches, incompatibilities and very - subtle errors. - </para> - <para> - 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 kernels available through 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 leading edge - feature and BSP development. - </para> - </section> - - <section id='kernel-architecture'> - <title>Kernel Architecture</title> - <para> - This section describes the architecture of the kernels available through the - Yocto Project and provides information - on the mechanisms used to achieve that architecture. - </para> - - <section id='architecture-overview'> - <title>Overview</title> - <para> - As mentioned earlier, a key goal of the 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 <filename>kernel.org</filename>. - </para> - <para> - You can think of a Yocto Project kernel as consisting of a baseline Linux 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. - For information on Git as applied to the Yocto Project, see the - "<ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink>" section in the - Yocto Project Development Manual. - </para> - <para> - 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. - </para> - <para> - The following illustration shows the conceptual Yocto Project kernel. - </para> - <para> - <imagedata fileref="figures/kernel-architecture-overview.png" width="6in" depth="7in" align="center" scale="100" /> - </para> - <para> - 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. - </para> - <para> - 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 do not have to be duplicated along individual branches of the - structure. - </para> - <para> - 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. - </para> - <para> - In this example structure, 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. - </para> - <para> - 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. - </para> - </section> - - <section id='branching-and-workflow'> - <title>Branching Strategy and Workflow</title> - <para> - 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. - </para> - <para> - 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 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. - <note> - 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. - </note> - </para> - <para> - 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, 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, the team only stores the unique - differences for the BSP across the supported multiple kernels. - </para> - <para> - While this strategy can result in a tree with a significant number of branches, it is - important to realize that from the developer's point of view, there is a linear - path that travels from the baseline <filename>kernel.org</filename>, 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 developer's perspective, this path is the "master" branch. - The developer does not need to 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 <filename>diff</filename> level is now a trivial operation. - </para> - <para> - 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. - </para> - <para> - 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 developer - because the kernel tree is left in this state after cloning and building the kernel. - </para> - </section> - - <section id='source-code-manager-git'> - <title>Source Code Manager - Git</title> - <para> - 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 <filename>kernel.org</filename> but, - Git continues to grow in popularity and supports many different work flows, - front-ends and management techniques. - </para> - <para> - You can find documentation on Git at <ulink url='http://git-scm.com/documentation'></ulink>. - You can also get an introduction to Git as it applies to the Yocto Project in the - "<ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink>" - section in the Yocto Project Development Manual. - These referenced sections overview Git and describe a minimal set of - commands that allows you to be functional using Git. - <note> - 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. - </note> - </para> - </section> - </section> -</appendix> -<!-- -vim: expandtab tw=80 ts=4 ---> |
