diff options
| author | Scott Rifenbark <scott.m.rifenbark@intel.com> | 2010-11-24 08:31:55 -0800 |
|---|---|---|
| committer | Saul Wold <Saul.Wold@intel.com> | 2010-12-10 22:01:07 -0800 |
| commit | 000f052765577826907ff1e3f758bab3a0724d74 (patch) | |
| tree | d24d2bcb667aae24a63be1b5184ef2f29580d60b | |
| parent | aa583453935a13618f0068fdf8d6d3205725ec54 (diff) | |
| download | openembedded-core-000f052765577826907ff1e3f758bab3a0724d74.tar.gz openembedded-core-000f052765577826907ff1e3f758bab3a0724d74.tar.bz2 openembedded-core-000f052765577826907ff1e3f758bab3a0724d74.tar.xz openembedded-core-000f052765577826907ff1e3f758bab3a0724d74.zip | |
documentation/kerenl-manual: New directory and files for kernel manual.
This is the first draft of the Yocto Project Kernel manual. The
manual consists of two sections: concepts and a practical section that
has examples. It is based of Bruce Ashfield's kernel theory paper.
This first draft has been re-written and organized through the
concepts section. The remainder was just placed in as-is due to
time constraints for getting some kernel documentation up on the website.
The manual still needs scrubbing and organization in the latter half.
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
| -rw-r--r-- | documentation/kernel-manual/Makefile | 32 | ||||
| -rwxr-xr-x | documentation/kernel-manual/figures/kernel-architecture-overview.png | bin | 0 -> 40778 bytes | |||
| -rwxr-xr-x | documentation/kernel-manual/figures/kernel-big-picture.png | bin | 0 -> 173130 bytes | |||
| -rwxr-xr-x | documentation/kernel-manual/figures/yocto-project-transp.png | bin | 0 -> 8626 bytes | |||
| -rw-r--r-- | documentation/kernel-manual/style.css | 967 | ||||
| -rw-r--r-- | documentation/kernel-manual/yocto-project-kernal-manual-customization.xsl | 8 | ||||
| -rw-r--r-- | documentation/kernel-manual/yocto-project-kernal-manual.xml | 2175 |
7 files changed, 3182 insertions, 0 deletions
diff --git a/documentation/kernel-manual/Makefile b/documentation/kernel-manual/Makefile new file mode 100644 index 000000000..701bddfa7 --- /dev/null +++ b/documentation/kernel-manual/Makefile @@ -0,0 +1,32 @@ +XSLTOPTS = --stringparam html.stylesheet style.css \ + --xinclude + +XSL_BASE_URI = http://docbook.sourceforge.net/release/xsl/current +XSL_XHTML_URI = $(XSL_BASE_URI)/xhtml/docbook.xsl + +all: html tarball + +## +# These URI should be rewritten by your distribution's xml catalog to +# match your localy installed XSL stylesheets. + +html: +# See http://www.sagehill.net/docbookxsl/HtmlOutput.html + +# xsltproc $(XSLTOPTS) -o yocto-project-qs.html $(XSL_XHTML_URI) yocto-project-qs.xml + xsltproc $(XSLTOPTS) -o yocto-project-kernal-manual.html yocto-project-kernal-manual-customization.xsl yocto-project-kernal-manual.xml + +tarball: html + tar -cvzf yocto-project-kernal-manual.tgz yocto-project-kernal-manual.html style.css figures/yocto-project-transp.png figures/kernel-big-picture.png figures/kernel-architecture-overview.png + +validate: + xmllint --postvalid --xinclude --noout yocto-project-kernal-manual.xml + +OUTPUTS = yocto-project-kernal-manual.tgz yocto-project-kernal-manual.html +SOURCES = *.png *.xml *.css + +publish: + scp -r $(OUTPUTS) $(SOURCES) o-hand.com:/srv/www/pokylinux.org/doc/ + +clean: + rm -f $(OUTPUTS) diff --git a/documentation/kernel-manual/figures/kernel-architecture-overview.png b/documentation/kernel-manual/figures/kernel-architecture-overview.png Binary files differnew file mode 100755 index 000000000..cdf908526 --- /dev/null +++ b/documentation/kernel-manual/figures/kernel-architecture-overview.png diff --git a/documentation/kernel-manual/figures/kernel-big-picture.png b/documentation/kernel-manual/figures/kernel-big-picture.png Binary files differnew file mode 100755 index 000000000..49bac618e --- /dev/null +++ b/documentation/kernel-manual/figures/kernel-big-picture.png diff --git a/documentation/kernel-manual/figures/yocto-project-transp.png b/documentation/kernel-manual/figures/yocto-project-transp.png Binary files differnew file mode 100755 index 000000000..31d2b147f --- /dev/null +++ b/documentation/kernel-manual/figures/yocto-project-transp.png diff --git a/documentation/kernel-manual/style.css b/documentation/kernel-manual/style.css new file mode 100644 index 000000000..d100b69fc --- /dev/null +++ b/documentation/kernel-manual/style.css @@ -0,0 +1,967 @@ +/* + Generic XHTML / DocBook XHTML CSS Stylesheet. + + Browser wrangling and typographic design by + Oyvind Kolas / pippin@gimp.org + + Customised for Poky by + Matthew Allum / mallum@o-hand.com + + Thanks to: + Liam R. E. Quin + William Skaggs + Jakub Steiner + + Structure + --------- + + The stylesheet is divided into the following sections: + + Positioning + Margins, paddings, width, font-size, clearing. + Decorations + Borders, style + Colors + Colors + Graphics + Graphical backgrounds + Nasty IE tweaks + Workarounds needed to make it work in internet explorer, + currently makes the stylesheet non validating, but up until + this point it is validating. + Mozilla extensions + Transparency for footer + Rounded corners on boxes + +*/ + + + /*************** / + / Positioning / +/ ***************/ + +body { + font-family: Verdana, Sans, sans-serif; + + min-width: 640px; + width: 80%; + margin: 0em auto; + padding: 2em 5em 5em 5em; + color: #333; +} + +.reviewer { + color: red; +} + +h1,h2,h3,h4,h5,h6,h7 { + font-family: Arial, Sans; + color:#999999; + clear: both; +} + +h1 { + font-size: 2em; + text-align: left; + padding: 0em 0em 0em 0em; + margin: 2em 0em 0em 0em; +} + +h2.subtitle { + margin: 0.10em 0em 3.0em 0em; 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+} + +ul li p { + text-align: left; +} + +table { + width :100%; +} + +th { + padding: 0.25em; + text-align: left; + font-weight: normal; + vertical-align: top; +} + +td { + padding: 0.25em; + vertical-align: top; +} + +p a[id] { + margin: 0px; + padding: 0px; + display: inline; + background-image: none; +} + +a { + text-decoration: underline; + color: #444; +} + +pre { + overflow: auto; +} + +a:hover { + text-decoration: underline; + /*font-weight: bold;*/ +} + + +div.informalfigure, +div.informalexample, +div.informaltable, +div.figure, +div.table, +div.example { + margin: 1em 0em; + padding: 1em; + page-break-inside: avoid; +} + + +div.informalfigure p.title b, +div.informalexample p.title b, +div.informaltable p.title b, +div.figure p.title b, +div.example p.title b, +div.table p.title b{ + padding-top: 0em; + margin-top: 0em; + font-size: 100%; + font-weight: normal; +} + +.mediaobject .caption, +.mediaobject .caption p { + text-align: center; + font-size: 80%; + padding-top: 0.5em; 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+ background-attachment: fixed; +} + +*/ +h1, +h2, +h3, +h4, +h5, +h6, +h7{ +} + +/* +Example of how to stick an image as part of the title. + +div.article .titlepage .title +{ + background-image: url("figures/white-on-black.png"); + background-position: center; + background-repeat: repeat-x; +} +*/ + +div.preface .titlepage .title, +div.colophon .title, +div.chapter .titlepage .title, +div.article .titlepage .title +{ +} + +div.section div.section .titlepage .title, +div.sect2 .titlepage .title { + background: none; +} + + +h1.title { + background-color: transparent; + background-image: url("figures/yocto-project-bw.png"); + background-repeat: no-repeat; + height: 256px; + text-indent: -9000px; + overflow:hidden; +} + +h2.subtitle { + background-color: transparent; + text-indent: -9000px; + overflow:hidden; + width: 0px; + display: none; +} + + /*************************************** / + / pippin.gimp.org specific alterations / +/ ***************************************/ + +/* +div.heading, div.navheader { + color: #777; + font-size: 80%; + padding: 0; + margin: 0; + text-align: left; + position: absolute; + top: 0px; + left: 0px; + width: 100%; + height: 50px; + background: url('/gfx/heading_bg.png') transparent; + background-repeat: repeat-x; + background-attachment: fixed; + border: none; +} + +div.heading a { + color: #444; +} + +div.footing, div.navfooter { + border: none; + color: #ddd; + font-size: 80%; + text-align:right; + + width: 100%; + padding-top: 10px; + position: absolute; + bottom: 0px; + left: 0px; + + background: url('/gfx/footing_bg.png') transparent; +} +*/ + + + + /****************** / + / nasty ie tweaks / +/ ******************/ + +/* +div.heading, div.navheader { + width:expression(document.body.clientWidth + "px"); +} + +div.footing, div.navfooter { + width:expression(document.body.clientWidth + "px"); + margin-left:expression("-5em"); +} +body { + padding:expression("4em 5em 0em 5em"); +} +*/ + + /**************************************** / + / mozilla vendor specific css extensions / +/ ****************************************/ +/* +div.navfooter, div.footing{ + -moz-opacity: 0.8em; 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+} diff --git a/documentation/kernel-manual/yocto-project-kernal-manual-customization.xsl b/documentation/kernel-manual/yocto-project-kernal-manual-customization.xsl new file mode 100644 index 000000000..8e6ea34dd --- /dev/null +++ b/documentation/kernel-manual/yocto-project-kernal-manual-customization.xsl @@ -0,0 +1,8 @@ +<?xml version='1.0'?> +<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns="http://www.w3.org/1999/xhtml" xmlns:fo="http://www.w3.org/1999/XSL/Format" version="1.0"> + + <xsl:import href="http://docbook.sourceforge.net/release/xsl/current/xhtml/docbook.xsl" /> + + <xsl:param name="generate.toc" select="'article nop'"></xsl:param> + +</xsl:stylesheet> diff --git a/documentation/kernel-manual/yocto-project-kernal-manual.xml b/documentation/kernel-manual/yocto-project-kernal-manual.xml new file mode 100644 index 000000000..b1693500f --- /dev/null +++ b/documentation/kernel-manual/yocto-project-kernal-manual.xml @@ -0,0 +1,2175 @@ +<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" +"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + +<article id='intro'> + <imagedata fileref="figures/yocto-project-transp.png" width="6in" depth="1in" align="right" scale="25" /> + +<section id='fake-title'> + <title>Yocto Project Kernel Architecture and Use Manual</title> +</section> + +<section id='introduction'> + <title>Introduction</title> + <para> + 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. + </para> + <para> + This manual describes the Yocto Project kernel by providing information + on its history, organization, benefits, and use. + The manual consists of two sections: + <itemizedlist> + <listitem><para>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.</para></listitem> + <listitem><para>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."</para></listitem> + </itemizedlist> + </para> + <para> + For more information on the kernel, see the following links: + <itemizedlist> + <listitem><para><ulink url='http://ldn.linuxfoundation.org/book/1-a-guide-kernel-development-process'></ulink></para></listitem> + <listitem><para><ulink url='http://userweb.kernel.org/~akpm/stuff/tpp.txt'></ulink></para></listitem> + <listitem><para><ulink url='http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob_plain;f=Documentation/HOWTO;hb=HEAD'></ulink></para></listitem> + </itemizedlist> + <para> + You can find more information on Yocto Project by visiting the website at + <ulink url='http://www.yoctoproject.org'></ulink>. + </para> + </para> +</section> + +<section id='concepts'> + <title>Concepts</title> + <para> + This section provides conceptual information about the Yocto Project kernel: + <itemizedlist> + <listitem><para>Kernel Goals</para></listitem> + <listitem><para>Yocto Project Kernel Development and Maintenance Overview</para></listitem> + <listitem><para>Kernel Architecture</para></listitem> + <listitem><para>Kernel Tools</para></listitem> + </itemizedlist> + </para> + <section id='kernel-goals'> + <title>Kernel Goals</title> + <para> + 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. + </para> + <para> + With all these considerations in mind, the Yocto Project kernel and development team + strives to attain these goals: + <itemizedlist> + <listitem><para>Allow the end user to leverage community best practices to seamlessly + manage the development, build and debug cycles.</para></listitem> + <listitem><para>Create a platform for performing integration and collaboration with the + thousands of upstream development projects that exist.</para></listitem> + <listitem><para>Provide mechanisms that support many different work flows, front-ends and + management techniques.</para></listitem> + <listitem><para>Deliver the most up-to-date kernel possible while still ensuring that + the baseline kernel is the the most stable official release.</para></listitem> + <listitem><para>Include major technological features as part of Yocto Project's up-rev + strategy.</para></listitem> + <listitem><para>Present a git tree, that just like the upstream kernel.org tree, has a + clear and continuous history.</para></listitem> + <listitem><para>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).</para></listitem> + <listitem><para>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.</para></listitem> + </itemizedlist> + </para> + </section> + + <section id='kernel-big-picture'> + <title>Yocto Project Kernel Development and Maintenance Overview</title> + <para> + Yocto Project kernel, like other kernels, is based off the Linux kernel release + from <ulink url='http://www.kernel.org'></ulink>. + 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. + </para> + <para> + 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. + </para> + <para> + The following figure represents the overall place the Yocto Project kernel fills. + </para> + <para> + <imagedata fileref="figures/kernel-big-picture.png" width="6in" depth="4in" align="center" scale="100" /> + </para> + <para> + 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. + </para> + <para> + 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. + </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 simply 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 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. + </para> + </section> + + <section id='kernel-architecture'> + <title>Kernel Architecture</title> + <para> + This section describes the architecture of the Yocto Project kernel 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 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. + + </para> + <para> + 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. + </para> + <para> + The following illustration shows the conceptual Yocto Project kernel. + </para> + <para> + <imagedata fileref="figures/kernel-architecture-overview.png" width="6in" depth="4in" 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 don't 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> + 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 user + 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. + 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. + </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, 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. + </para> + <para> + 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. + </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 user + 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 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. + </para> + <note><para> + 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. + </para></note> + </section> + </section> + + <section id='kernel-tools'> + <title>Kernel Tools</title> + <para> +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. +</para> +<para> +The fundamental properties of the tools that manage and construct the +kernel are: +<itemizedlist> + <listitem><para>the ability to group patches into named, reusable features</para></listitem> + <listitem><para>to allow top down control of included features</para></listitem> + <listitem><para>the binding of kernel configuration to kernel patches/features</para></listitem> + <listitem><para>the presentation of a seamless git repository that blends Yocto Project value with the kernel.org history and development</para></listitem> +</itemizedlist> +</para> +<para> +The tools that construct a kernel tree will be discussed later in this +document. The following tools form the foundation of the Yocto Project +kernel toolkit: +<itemizedlist> + <listitem><para>git : distributed revision control system created by Linus Torvalds</para></listitem> + <listitem><para>guilt: quilt on top of git</para></listitem> + <listitem><para>*cfg : kernel configuration management and classification</para></listitem> + <listitem><para>kgit*: Yocto Project kernel tree creation and management tools</para></listitem> + <listitem><para>scc : series & configuration compiler</para></listitem> +</itemizedlist> +</para> + </section> +</section> + + + + +<!-- <section id='concepts2'> + <title>Kernel Concepts</title> + <itemizedlist> + <listitem><para>What tools and commands are used with the kernel.</para></listitem> + <listitem><para>Source Control Manager (SCM).</para></listitem> + <listitem><para>What are some workflows that you can apply using the kernel.</para></listitem> + </itemizedlist> +</section> --> + +<section id='actions'> + <title>How to get things accomplished with the kernel</title> + <para> + This section describes how to accomplish tasks involving the kernel's tree structure. + The information covers the following: + <itemizedlist> + <listitem><para>Tree construction</para></listitem> + <listitem><para>Build strategies</para></listitem> + <listitem><para>Series & Configuration Compiler</para></listitem> + <listitem><para>kgit</para></listitem> + <listitem><para>Workflow examples</para></listitem> + <listitem><para>Source Code Manager (SCM)</para></listitem> + <listitem><para>Board Support Package (BSP) template migration</para></listitem> + <listitem><para>BSP creation</para></listitem> + <listitem><para>Patching</para></listitem> + <listitem><para>Updating BSP patches and configuration</para></listitem> + <listitem><para>guilt</para></listitem> + <listitem><para>scc file example</para></listitem> + <listitem><para>"dirty" string</para></listitem> + <listitem><para>Transition kernel layer</para></listitem> + </itemizedlist> + </para> + + <section id='tree-construction'> + <title>Tree Construction</title> + <para> +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. +</para> +<para> +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. +</para> +<para> +As a reminder, it is envisioned that a ground up reconstruction of the +complete kernel tree is an action only taken by Yocto Project staff 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. +</para> +<para> +The general flow of the project specific kernel tree construction is as follows: +<orderedlist> + <listitem><para>a top level kernel feature is passed to the kernel build subsystem, + normally this is a BSP for a particular kernel type.</para></listitem> + + <listitem><para>the file that describes the top level feature is located by searching + system directories:</para> + + <itemizedlist> + <listitem><para>the kernel-cache under linux/wrs/cfg/kernel-cache</para></listitem> + <listitem><para>kernel-*-cache directories in layers</para></listitem> + <listitem><para>configured and default templates</para></listitem> + </itemizedlist> + + <para>In a typical build a feature description of the format: + <bsp name>-<kernel type>.scc is the target of the search. + </para></listitem> + + <listitem><para>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.</para></listitem> + + <listitem><para>extra features are appended to the top level feature description. Extra + features can come from the command line, the configure script or + templates.</para></listitem> + + <listitem><para>each extra feature is located, compiled and appended to the script from + step #3</para></listitem> + + <listitem><para>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".</para></listitem> + + <listitem><para>the base repository (normally kernel.org) is cloned, and the actions + listed in the meta-series are applied to the tree.</para></listitem> + + <listitem><para>the git repository is left with the desired branch checked out and any + required branching, patching and tagging has been performed.</para></listitem> +</orderedlist> +</para> + +<para> +The tree is now ready for configuration and compilation. Those two topics will +be covered below. +</para> + +<note><para>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. +</para></note> + +<para> +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. +</para> + +<note><para>It is key that feature descriptions indicate if any branches are + required, since the build system cannot automatically decide where a + BSP should branch or if that branch point needs a name with + significance. There is a single restriction enforced by the compilation + phase: + </para> + <para>A BSP must create a branch of the format <bsp name>-<kernel type>.</para> + + <para>This means that all merged/support BSPs must indicate where to start + its branch from, with the right name, in its .scc files. The scc + section describes the available branching commands in more detail. + </para> +</note> + +<para> +A summary of end user tree construction activities follow: +<itemizedlist> + <listitem><para>compile and link a full top-down kernel description from feature descriptions</para></listitem> + <listitem><para>execute the complete description to generate a meta-series</para></listitem> + <listitem><para>interpret the meta-series to create a customized git repository for the + board</para></listitem> + <listitem><para>migrate configuration fragments and configure the kernel</para></listitem> + <listitem><para>checkout the BSP branch and build</para></listitem> +</itemizedlist> +</para> + </section> + + <section id='build-strategy'> + <title>Build Strategy</title> +<para> +There are some prerequisites that must be met before starting the compilation +phase of the kernel build system: +</para> +<itemizedlist> + <listitem><para>There must be a kernel git repository indicated in the SRC_URI.</para></listitem> + <listitem><para>There must be a branch <bsp name>-<kernel type>.</para></listitem> +</itemizedlist> + +<para> +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. +</para> +<para> +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. +</para> +<para> +Kernel compilation is started, using the board's architecture and other +relevant values from the board template, and a kernel image is produced. +</para> +<para> +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, cg`` +e, etc. This functionality is done by making +use of the existing support that is within the kernel.org tree by default. +</para> +<para> +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. +</para> + </section> + + <section id='scc'> + <title>Series & Configuration Compiler (SCC)</title> +<para> +In early versions of the product, kernel patches were simply listed in a flat +file called "patches.list", and then quilt was added as a tool to help +traverse this list, which in quilt terms was called a "series" file. +</para> +<para> +Before the 2.0 release, it was already apparent that a static series file was +too inflexible, and that the series file had to become more dynamic and rely +on certain state (like kernel type) in order to determine whether a patch was +to be used or not. The 2.0 release already made use of some stateful +construction of series files, but since the delivery mechanism was unchanged +(tar + patches + series files), most people were not aware of anything really +different. The 3.0 release continues with this stateful construction of +series files, but since the delivery mechanism is changed (git + branches) it +now is more apparent to people. +</para> +<para> +As was previously mentioned, scc is a "series and configuration +compiler". Its role is to combine feature descriptions into a format that can +be used to generate a meta-series. A meta series contains all the required +information to construct a complete set of branches that are required to +build a desired board and feature set. The meta series is interpreted by the +kgit tools to create a git repository that could be built. +</para> +<para> +To illustrate how scc works, a feature description must first be understood. +A feature description is simply a small bash shell script that is executed by +scc in a controlled environment. Each feature description describes a set of +operations that add patches, modify existing patches or configure the +kernel. It is key that feature descriptions can include other features, and +hence allow the division of patches and configuration into named, reusable +containers. +</para> +<para> +Each feature description can use any of the following valid scc commands: +<itemizedlist> + <listitem><para>shell constructs: bash conditionals and other utilities can be used in a feature + description. During compilation, the working directory is the feature + description itself, so any command that is "raw shell" and not from the + list of supported commands, can not directly modify a git repository.</para></listitem> + + <listitem><para>patch <relative path>/<patch name>: outputs a patch to be included in a feature's patch set. Only the name of + the patch is supplied, the path is calculated from the currently set + patch directory, which is normally the feature directory itself.</para></listitem> + + <listitem><para>patch_trigger >condition< >action< <tgt>: indicate that a trigger should be set to perform an action on a + patch.</para> + +<para>The conditions can be: + + <itemizedlist> + <listitem><para>arch:<comma separated arch list or "all"></para></listitem> + <listitem><para>plat:<comma separated platform list or "all"></para></listitem> + </itemizedlist></para> +<para>The action can be: + <itemizedlist> + <listitem><para>exclude: This is used in exceptional situations where a patch + cannot be applied for certain reasons (arch or platform). + When the trigger is satisfied the patch will be removed from + the patch list.</para></listitem> + <listitem><para>include: This is used to include a patch only for a specific trigger. + Like exclude, this should only be used when necessary. + It takes 1 argument, the patch to include.</para></listitem> + </itemizedlist></para></listitem> + + <listitem><para>include <feature name> [after <feature>]: includes a feature for processing. The feature is "expanded" at the + position of the include directive. This means that any patches, + configuration or sub-includes of the feature will appear in the final + series before the commands that follow the include.</para> + <para> + include searches the include directories for a matching feature name, + include directories are passed to scc by the caller using -I <path> and + is transparent to the feature script. This means that <feature name> must + be relative to one of the search paths. For example, if + /opt/kernel-cache/feat/sched.scc is to be included and scc is invoked + with -I /opt/kernel-cache, then a feature would issue "include + feat/sched.scc" to include the feature. +</para> +<para> + The optional "after" directive allows a feature to modify the existing + order of includes and insert a feature after the named feature is + processed. Note: the "include foo after bar" must be issued before "bar" + is processed, so is normally only used by a new top level feature to + modify the order of features in something it is including.</para></listitem> + + <listitem><para>exclude <feature name>: Indicates that a particular feature should *not* be included even if an + 'include' directive is found. The exclude must be issued before the + include is processed, so is normally only used by a new top level feature + to modify the order of features in something it is including.</para></listitem> + + <listitem><para>git <command>: Issues any git command during tree construction. Note: this command is + not validated/sanitized so care must be taken to not damage the + tree. This can be used to script branching, tagging, pulls or other git + operations.</para></listitem> + + <listitem><para>dir <directory>: changes the working directory for "patch" directives. This can be used to + shorten a long sequence of patches by not requiring a common relative + directory to be issued each time.</para></listitem> + + <listitem><para>kconf <type> <fragment name>: associates a kernel config frag with the feature. + <type> can be + "hardware" or "non-hardware" and is used by the kernel configuration + subsystem to audit configuration. <fragment name> is the name of a file + in the current feature directory that contains a series of kernel + configuration options. There is no restriction on the chosen fragment + name, although a suffix of ".cfg" is recommended. Multiple fragment + specifications are supported.</para></listitem> + + <listitem><para>branch <branch name>: creates a branch in the tree. All subsequent patch commands will be + applied to the new branch and changes isolated from the rest of the + repository.</para></listitem> + + <listitem><para>scc_leaf <base feature> <branch name>: Performs a combination feature include and branch. This is mainly a + convenience directive, but has significance to some build system bindings + as a sentinel to indicate that this intends to create a branch that is + valid for kernel compilation.</para></listitem> + + <listitem><para>tag <tag name>: Tags the tree. The tag will be applied in processing order, so will + be after already applied patches and precede patches yet to be applied.</para></listitem> + + <listitem><para>define <var> <value>: Creates a variable with a particular value that can be used in subsequent + feature descriptions.</para></listitem> +</itemizedlist> + +</para> + </section> + + <section id='kgit-tools'> + <title>kgit Tools</title> +<para> +The kgit tools are responsible for constructing and maintaining the Wind +River kernel repository. These activities include importing, exporting, and +applying patches as well as sanity checking and branch management. From the +developers perspective, the kgit tools are hidden and rarely require +interactive use. But one tool in particular that warrants further description +is "kgit-meta". +</para> +<para> +kgit-meta is the actual application of feature description(s) to a kernel repo. +In other words, it is responsible for interpreting the meta series generated +from a scc compiled script. As a result, kgit-meta is coupled to the set of +commands permitted in a .scc feature description (listed in the scc section). +kgit-meta understands both the meta series format and how to use git and +guilt to modify a base git repository. It processes a meta-series line by +line, branching, tagging, patching and tracking changes that are made to the +base git repository. +</para> +<para> +Once kgit-meta has processed a meta-series, it leaves the repository with the +last branch checked out, and creates the necessary guilt infrastructure to +inspect the tree, or add to it via using guilt. As was previously mentioned, +guilt is not required, but is provided as a convenience. Other utilities such +as quilt, stgit, git or others can also be used to manipulate the git +repository. +</para> + </section> + + <section id='workflow-examples'> + <title>Workflow Examples</title> + + <para> +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.</para> +<para> +This section contains several workflow examples. +</para> + + <section id='change-inspection-kernel-changes-commits'> + <title>Change Inspection: Kernel Changes/Commits</title> +<para> +A common question when working with a BSP/kernel is: "What changes have been applied to this tree?" +</para> +<para> +In previous Yocto Project releases, there were 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. +</para> +<para> +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. +</para> + <section id='what-changed-in-a-bsp'> + <title>What Changed in a BSP?</title> +<para> +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 +</para> +<literallayout class='monospaced'> + # 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> +</literallayout> + </section> + + <section id='show-a-particular-feature-or-branch-change'> + <title>Show a Particular Feature or Branch Change</title> +<para> +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. +</para> +<literallayout class='monospaced'> + # 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 +</literallayout> +<para> +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. +</para> + </section> + </section> + + <section id='development-saving-kernel-modifications'> + <title>Development: Saving Kernel Modifications</title> +<para> +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. +</para> +<para> +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. +</para> +<para> +There are many ways to perform this action, and the technique employed +depends on the destination for the patches, which could be any of: +<itemizedlist> + <listitem><para>bulk storage</para></listitem> + <listitem><para>internal sharing either through patches or using git</para></listitem> + <listitem><para>external submission</para></listitem> + <listitem><para>export for integration into another SCM</para></listitem> +</itemizedlist> +</para> +<para> +The destination of the patches also incluences the method of gathering them +due to issues such as: +<itemizedlist> + <listitem><para>bisectability</para></listitem> + <listitem><para>commit headers</para></listitem> + <listitem><para>division of subsystems for separate submission / review</para></listitem> +</itemizedlist> +</para> + + <section id='bulk-export'> + <title>Bulk Export</title> +<para> +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. +</para> +<para> +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. +<literallayout class='monospaced'> + # 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 +</literallayout> +</para> +<para> +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. +</para> +<para> +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. +</para> + </section> + + <section id='incremental-planned-sharing'> + <title>Incremental/Planned Sharing</title> +<para> +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. +</para> +<para> +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 +<literallayout class='monospaced'> + # edit a file + > vi >path</file + # stage the change + > git add >path</file + # commit the change + > git commit -s + # remove a file + > git rm >path</file + # commit the change + > git commit -s + + ... etc. +</literallayout> +</para> +<para> +Distributed development with git is possible 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. +</para> +<para> +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: +<literallayout class='monospaced'> + > git add >path</file + > git commit ‐‐amend + > git rebase or git rebase -i +</literallayout> +</para> +<para> +Again, assuming that the changes have *not* been pushed upstream, and that +there are no pending works in progress (use "git status" to check) then +commits can be reverted (undone) via: +<literallayout class='monospaced'> + # remove the commit, update working tree and remove all + # traces of the change + > git reset ‐‐hard HEAD^ + # remove the commit, but leave the files changed and staged for re-commit + > git reset ‐‐soft HEAD^ + # remove the commit, leave file change, but not staged for commit + > git reset ‐‐mixed HEAD^ +</literallayout> +</para> +<para> +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. +</para> +<note><para>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. +</para></note> + + <section id='export-internally-via-patches'> + <title>Export Internally Via Patches</title> +<para> +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. + +<literallayout class='monospaced'> + # >first commit> can be a tag if one was created before development + # began. It can also be the parent branch if a branch was created + # before development began. + + > git format-patch -o <dir> <first commit>..<last commit> +</literallayout> +</para> + +<para> + In other words: +<literallayout class='monospaced'> + # identify commits of interest. + + # if the tree was tagged before development + > git format-patch -o <save dir> <tag> + + # if no tags are available + > git format-patch -o <save dir> HEAD^ # last commit + > git format-patch -o <save dir> HEAD^^ # last 2 commits + > git whatchanged # identify last commit + > git format-patch -o <save dir> <commit id> + > git format-patch -o <save dir> <rev-list> +</literallayout> +</para> + +<para> +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. +</para> +<para> +See the "template patching" example for how to use the patches to +automatically apply to a new kernel build. +</para> + </section> + + <section id='export-internally-via-git'> + <title>Export Internally Via git</title> +<para> +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: +<literallayout class='monospaced'> + git push ssh://<master server>/<path to repo> <local branch>:<remote branch> +</literallayout> +For example: +<literallayout class='monospaced'> + > push ssh://openlinux.windriver.com/pub/git/kernel-2.6.27 common_pc-standard:common_pc-standard +</literallayout> +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. +</para> +<para> +Other commands such as 'git stash' or branching can also be used to save +changes, but are not covered in this document. +</para> +<para> +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. +</para> + </section> + </section> + + <section id='export-for-external-upstream-submission'> + <title>Export for External (Upstream) Submission</title> +<para> +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. +</para> +<note><para> +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: +<itemizedlist> + <listitem><para><ulink url='http://userweb.kernel.org/~akpm/stuff/tpp.txt'></ulink></para></listitem> + <listitem><para><ulink url='http://linux.yyz.us/patch-format.html'></ulink></para></listitem> + <listitem><para>Documentation/SubmittingPatches (in any linux kernel source tree)</para></listitem> +</itemizedlist> +</para></note> +<para> +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. +</para> +<para> +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. +</para> +<para> +An example of dumping patches for external submission follows: +<literallayout class='monospaced'> + # dump the last 4 commits + > git format-patch ‐‐thread -n -o ~/rr/ HEAD^^^^ + > git send-email ‐‐compose ‐‐subject '[RFC 0/N] <patch series summary>' \ + ‐‐to foo@yoctoproject.org ‐‐to bar@yoctoproject.org \ + ‐‐cc list@yoctoproject.org ~/rr + # the editor is invoked for the 0/N patch, and when complete the entire + # series is sent via email for review +</literallayout> +</para> + </section> + + <section id='export-for-import-into-other-scm'> + <title>Export for Import into Other SCM</title> +<para> +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. +</para> +<para> +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. +</para> + </section> + </section> + + <section id='scm-working-with-the-yocto-project-kernel-in-another-scm'> + <title>SCM: Working with the Yocto Project Kernel in Another SCM</title> +<para> +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: +<itemizedlist> + <listitem><para>The delivered Yocto Project kernel must be exported into the second + SCM.</para></listitem> + <listitem><para>Development must be exported from that secondary SCM into a + format that can be used by the Yocto Project build system.</para></listitem> +</itemizedlist> +</para> + <section id='exporting-delivered-kernel-to-scm'> + <title>Exporting Delivered Kernel to SCM</title> +<para> +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. +</para> +<para> +When a direct import mechanism is not available, it is still possible to +export a branch (or series of branches) and check them into a new +repository. +</para> +<para> +The following commands illustrate some of the steps that could be used to +import the common_pc-standard kernel into a secondary SCM +<literallayout class='monospaced'> + > git checkout common_pc-standard + > cd .. ; echo linux/.git > .cvsignore + > cvs import -m "initial import" linux MY_COMPANY start +</literallayout> +The CVS repo could now be relocated and used in a centralized manner. +</para> +<para> +The following commands illustrate how two BSPs could be condensed and merged +into a second SCM: +<literallayout class='monospaced'> + > 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 +</literallayout> +</para> + </section> + + <section id='importing-changes-for-build'> + <title>Importing Changes for Build</title> +<para> +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). +</para> +If changes are exported as patches, they can be placed in a template and +automatically applied to the kernel during patching. See the template patch +example for details. +<para> +</para> +If changes are imported directly into git, they must be propagated to the +wrll-linux-2.6.27/git/default_kernel bare clone of each individual build +to be present when the kernel is checked out. +<para> +The following example illustrates one variant of this workflow: +<literallayout class='monospaced'> + # on master git repository + > cd linux-2.6.27 + > git tag -d common_pc-standard-mark + > git pull ssh://<foo>@<bar>/pub/git/kernel-2.6.27 common_pc-standard:common_pc-standard + > git tag common_pc-standard-mark + + # on each build machine (or NFS share, etc) + > cd wrll-linux-2.6.27/git/default_kernel + > git fetch ssh://<foo>@<master server>/pub/git/kernel-2.6.27 + + # in the build, perform a from-scratch build of Linux and the new changes + # will be checked out and built. + > make linux +</literallayout> +</para> + </section> + </section> + + <section id='bsp-template-migration-from-2'> + <title>BSP: Template Migration from 2.0</title> +<para> +The move to a git-backed kernel build system in 3.0 introduced a small new +requirement for any BSP that is not integrated into the GA release of the +product: branching information. +</para> +<para> +As was previously mentioned in the background sections, branching information +is always required, since the kernel build system cannot make intelligent +branching decisions and must rely on the developer. This branching +information is provided via a .scc file. +</para> +<para> +A BSP template in 2.0 contained build system information (config.sh, etc) and +kernel patching information in the 'linux' subdirectory. The same holds true +in 3.0, with only minor changes in the kernel patching directory. +The ".smudge" files are now ".scc" files and now contain a full description + of the kernel branching, patching and configuration for the BSP. Where in + 2.0, they only contained kernel patching information. +</para> +<para> +The following illustrates the migration of a simple 2.0 BSP template to the +new 3.0 kernel build system. +</para> +<note><para> +Note: all operations are from the root of a customer layer. +</para></note> +<literallayout class='monospaced'> + templates/ + `‐‐ board + `‐‐ my_board + |‐‐ config.sh + |‐‐ include + `‐‐ linux + `‐‐ 2.6.x + |‐‐ knl-base.cfg + |‐‐ bsp.patch + `‐‐ my_bsp.smudge + + > mv templates/board/my_board/linux/2.6.x/* templates/board/my_board/linux + > rm -rf templates/board/my_board/linux/2.6.x/ + > mv templates/board/my_board/linux/my_bsp.smudge \ + templates/board/my_board/linux/my_bsp-standard.scc + > echo "kconf hardware knl-base.cfg" >> \ + templates/board/my_board/linux/my_bsp-standard.scc + > vi templates/board/my_board/linux/my_bsp-standard.scc + # add the following at the top of the file + scc_leaf ktypes/standard my_bsp-standard + + templates/ + `‐‐ board + `‐‐ my_board + |‐‐ config.sh + |‐‐ include + `‐‐ linux + |‐‐ knl-base.cfg + |‐‐ bsp.patch + `‐‐ my_bsp-standard.scc +</literallayout> +<para> +That's it. Configure and build. +</para> +<note><para>There is a naming convention for the .scc file, which allows the build + system to locate suitable feature descriptions for a board: +</para></note> +<literallayout class='monospaced'> + <bsp name>-<kernel type>.scc +</literallayout> +<para> + if this naming convention isn't followed your feature description will + not be located and a build error thrown. +</para> + </section> + + <section id='bsp-creating-a-new-bsp'> + <title>BSP: Creating a New BSP</title> +<para> +Although it is obvious that the structure of a new BSP uses the migrated +directory structure from the previous example,the first question is whether +or not the BSP is started from scratch. +</para> +<para> +If Yocto Project has a similar BSP, it is often easier to clone and update, +rather than start from scratch. If the mainline kernel has support, it is +easier to branch from the -standard kernel and begin development (and not be +concerned with undoing existing changes). This section covers both options. +</para> +<para> +In almost every scenario, the LDAT build system bindings must be completed +before either cloning or starting a new BSP from scratch. This is simply +because the board template files are required to configure a project/build +and create the necessary environment to begin working directly with the +kernel. If it is desired to start immediately with kernel development and +then add LDAT bindings, see the "bootstrapping a BSP" section. +</para> + <section id='creating-from-scratch'> + <title>Creating the BSP from Scratch</title> +<para> +To create the BSP from scratch you need to do the following: +<orderedlist> + <listitem><para>Create a board template for the new BSP in a layer.</para></listitem> + <listitem><para>Configure a build with the board.</para></listitem> + <listitem><para>Configure a kernel.</para></listitem> +</orderedlist> +</para> +<para> +Following is an example showing all three steps. You start by creating a board template for the new BSP in a layer. +<literallayout class='monospaced'> + templates/ + `‐‐ board + `‐‐ my_bsp + |‐‐ include + |‐‐ config.sh + `‐‐ linux + |‐‐ my_bsp.cfg + `‐‐ my_bsp-standard.scc + + > cat config.sh + TARGET_BOARD="my_bsp" + TARGET_LINUX_LINKS="bzImage" + TARGET_SUPPORTED_KERNEL="standard" + TARGET_SUPPORTED_ROOTFS="glibc_std" + BANNER="This BSP is *NOT* supported" + TARGET_PROCFAM="pentium4" + TARGET_PLATFORMS="GPP" + + > cat include + cpu/x86_32_i686 + karch/i386 + + > cat linux/my_bsp-standard.scc + scc_leaf ktypes/standard/standard.scc my_bsp-standard + + > cat linux/my_bsp.cfg + CONFIG_X86=y + CONFIG_SMP=y + CONFIG_VT=y + # etc, etc, etc +</literallayout> +</para> +<para> +Something like the following can now be added to a board build, and +a project can be started: +<literallayout class='monospaced'> + ‐‐enable-board=my_bsp \ + ‐‐with-layer=custom_bsp +</literallayout> +</para> +<para> +Now you can configure a kernel: +<literallayout class='monospaced'> + > make -C build linux.config +</literallayout> +</para> +<para> +You now have a kernel tree, which is branched and has no patches, ready for +development. +</para> + </section> + + <section id='cloning-an-existing-bsp'> + <title>Cloning an Existing BSP</title> +<para> +Cloning an existing BSP from the shipped product is similar to the "from +scratch" option and there are two distinct ways to achieve this goal: +<itemizedlist> + <listitem><para>Create a board template for the new BSP in a layer.</para></listitem> + <listitem><para>Clone the .scc and board config.</para></listitem> +</itemizedlist> +</para> +<para> +The first method is similar to the from scratch BSP where you create a board template for the new +BSP. Although in this case, copying an existing board template from +wrll-wrlinux/templates/board would be appropriate, since we are cloning an +existing BSP. Edit the config.sh, include and other board options for the new +BSP. +</para> +<para> +The second method is to clone the .scc and board config. +To do this, in the newly created board template, create a linux subdirectory and export +the .scc and configuration from the source BSP in the published Yocto Project +kernel. During construction, all of the configuration and patches were +captured, so it is simply a matter of extracting them. +</para> +<para> +Extraction can be accomplished using four different techniques: +<itemizedlist> + <listitem><para>Config and patches from the bare default_kernel.</para></listitem> + <listitem><para>Clone default_kernel and checkout wrs_base.</para></listitem> + <listitem><para>Clone default_kernel and checkout BSP branch.</para></listitem> + <listitem><para>Branch from the Yocto Project BSP.</para></listitem> +</itemizedlist> +</para> +<para> +Technique 1: config and patches from the bare default_kernel +<literallayout class='monospaced'> + > cd layers/wrll-linux-2.6.27/git/default_kernel + > git show checkpoint_end | filterdiff -i '*common_pc*' | patch -s -p2 -d /tmp + + # This will create two directories: cfg and patches. + + > cd /tmp/cfg/kernel-cache/bsp/common_pc/ + + # This directory contains all the patches and .scc files used to construct + # the BSP in the shipped tree. Copy the patches to the new BSP template, + # and add them to the .scc file created above. See "template patching" if + # more details are required. +</literallayout> +</para> +<para> +Technique 2: clone default_kernel and checkout wrs_base +<literallayout class='monospaced'> + > git clone layers/wrll-linux-2.6.27/git/default_kernel windriver-2.6.27 + > cd windriver-2.6.27 + > git checkout wrs_base + > cd wrs/cfg/kernel-cache/bsp/common_pc + +# again, this directory has all the patches and .scc files used to construct +# the BSP +</literallayout> +</para> +<para> +Technique 3: clone default_kernel and checkout BSP branch +<literallayout class='monospaced'> + > git clone layers/wrll-linux-2.6.27/git/default_kernel windriver-2.6.27 + > cd windriver-2.6.27 + > git checkout common_pc-standard + > git whatchanged + # browse patches and determine which ones are of interest, say there are + # 3 patches of interest + > git format-patch -o <path to BSP template>/linux HEAD^^^ + # update the .scc file to add the patches, see "template patches" if + # more details are required +</literallayout> +</para> +<para> +Technique #4: branch from the Yocto Project BSP +<note><para>This is potentially the most "different" technique, but is actually + the easiest to support and leverages the infrastructure. rtcore BSPs + are created in a similar manner to this. +</para></note> +</para> +<para> +In this technique the .scc file in the board template is slightly different + and indicates that the BSP should branch after the base Yocto Project BSP + of the correct kernel type, so to start a new BSP that inherits the + kernel patches of the common_pc-standard, the following would be done: +<literallayout class='monospaced'> + > cat linux/my_bsp-standard.scc + scc_leaf bsp/common_pc/common_pc-standard.scc my_bsp-standard +</literallayout> +</para> +<para> + And only kernel configuration (not patches) need be contained in the + board template. +</para> +<para> + This has the advantage of automatically picking up updates to the BSP + and not duplicating any patches for a similar board. +</para> + </section> + + <section id='bsp-bootstrapping'> + <title>BSP: Bootstrapping</title> +<para> +The previous examples created the board templates and configured a build +before beginning work on a new BSP. It is also possible for advanced users to +simply treat the Yocto Project git repository as an upstream source and begin +BSP development directly on the repository. This is the closest match to how +the kernel community at large would operate. +</para> +<para> +Two techniques exist to accomplish this: +</para> +<para> +Technique 1: upstream workflow +<literallayout class='monospaced'> + > git clone layers/wrll-linux-2.6.27/git/default_kernel windriver-2.6.27 + > cd windriver-2.6.27 + > git checkout -b my_bsp-standard common_pc-standard + + # edit files, import patches, generally do BSP development + + # at this point we can create the BSP template, and export the kernel + # changes using one of the techniques discussed in that section. For + # example, It is possible to push these changes, directly into the + # default_kernel and never directly manipulate or export patch files +</literallayout> +</para> +<para> +Technique 2: Yocto Project kernel build workflow +</para> +<para> + Create the BSP branch from the appropriate kernel type +<literallayout class='monospaced'> + > cd linux + # the naming convention for auto-build is <bsp>-<kernel type> + > git checkout -b my_bsp-standard standard +</literallayout> +</para> +<para> +Make changes, import patches, etc. +<literallayout class='monospaced'> + > ../../host-cross/bin/guilt init + # 'wrs/patches/my_bsp-standard' has now been created to + # manage the branches patches + + # option 1: edit files, guilt import + > ../../host-cross/bin/guilt new extra-version.patch + > vi Makefile + > ../../host-cross/bin/guilt refresh + # add a header + > ../../host-cross/bin/guilt header -e + # describe the patch using best practices, like the example below: + + ‐‐‐>‐‐‐>‐‐‐> cut here + From: Bruce Ashfield <bruce.ashfield@windriver.com> + + Adds an extra version to the kernel + + Modify the main EXTRAVERSION to show our bsp name + + Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com> + ‐‐‐>‐‐‐>‐‐‐> cut here + + # option 2: import patches + > git am <patch> + or + > git apply <patch> + > git add <files> + > git commit -s + + # configure the board, save relevant options + > make ARCH=<arch> menuconfig + + # save the cfg changes for reconfiguration + > mkdir wrs/cfg/<cache>/my_bsp + > vi wrs/cfg/<cache>/my_bsp/my_bsp.cfg + + # classify the patches + > ../../host-cross/bin/kgit classify create <kernel-foo-cache>/my_bsp/my_bsp + # test build + > cd .. + > make linux TARGET_BOARD=my_bsp kprofile=my_bsp use_current_branch=1 +</literallayout> +</para> +<para> + Assuming the patches have been exported to the correct location, Future + builds will now find the board, apply the patches to the base tree and make + the relevant branches and structures and the special build options are no + longer required. +</para> + </section> + </section> + + <section id='patching'> + <title>Patching</title> +<para> +The most common way to apply patches to the kernel is via a template. +However, for more advanced applications (such as the sharing of patches between +multiple sub-features) it is possible to patch the kernel-cache. +This section covers both scenarios. +</para> + <section id='patching-template'> + <title>Patching: Template</title> +<para> +kernel +templates follow the same rules as any LDAT template. A directory should be +created in a recognized template location, with a 'linux' subdirectory. The +'linux' directory triggers LDAT to pass the dir as a potential patch location +to the kernel build system. Any .scc files found in that directory, will be +automatically appended to the end of the BSP branch (for the configured +board). +</para> +<para> +This behavior is essentially the same since previous product +releases. The only exception is the use of ".scc", which allows kernel +configuration AND patches to be applied in a template. +</para> +<note><para> +If creating a full template is not required, a .scc file can be placed at +the top of the build, along with configuration and patches. The build +system will pickup the .scc and add it onto the patch list automatically +</para></note> +<para> +As an example, consider a simple template to update a BP: +<literallayout class='monospaced'> + > cat templates/feature/extra_version/linux/extra_version.scc + patch 0001-extraversion-add-Wind-River-identifier.patch +</literallayout> +</para> +<para> +To illustrate how the previous template patch was created, the following +steps were performed: +<literallayout class='monospaced'> + > cd <board build>/build/linux + > vi Makefile + # modify EXTRAVERSION to have a unique string + > git commit -s -m "extraversion: add Yocto Project identifier" Makefile + > git format-patch -o <path to layer>/templates/feature/extra_version/linux/ + > echo "patch 0001-extraversion-add-Wind-River-identifier.patch" > \ + <path to layer>/templates/feature/extra_version/linux/extra_version.scc +</literallayout> +</para> +<para> +This next example creates a template with a linux subdirectory, just as we + always have for previous releases. +<literallayout class='monospaced'> + > mkdir templates/features/my_feature/linux +</literallayout> +</para> +<para> + In that directory place your feature description, your + patch and configuration (if required). +<literallayout class='monospaced'> + > ls templates/features/my_feature/linux + + version.patch + my_feature.scc + my_feature.cfg +</literallayout> +</para> +<para> + The .scc file describes the patches, configuration and + where in the patch order the feature should be inserted. +<literallayout class='monospaced'> + patch version.patch + kconf non-hardware my_feature.cfg +</literallayout> +</para> +<para> + Configure your build with the new template +<literallayout class='monospaced'> + ‐‐with-template=features/my_feature +</literallayout> +</para> +<para> +Build the kernel +<literallayout class='monospaced'> + > make linux +</literallayout> +</para> + </section> + + <section id='patching-kernel-cache'> + <title>Patching: Kernel Cache</title> +<para> +As previously mentioned, this example is included for completeness, and is for more advanced +applications (such as the sharing of patches between multiple sub-features). +Most patching should be done via templates, since that interface is +guaranteed not to change and the kernel-cache interface carries no such +guarantee. +</para> +<para> +At the top of a layer, create a kernel cache. The build system will recognize +any directory of the name 'kernel-*-cache' as a kernel cache. +<literallayout class='monospaced'> + > cd <my layer> + >mkdir kernel-temp-cache +</literallayout> +</para> +<para> +Make a directory with the BSP +<literallayout class='monospaced'> + > mkdir kernel-temp-cache + > mkdir kernel-temp-cache/my_feat +</literallayout> +</para> +<para> +Create the feature files as they were in technique #1 +<literallayout class='monospaced'> + > echo "patch my_patch.path" > kernel-temp-cache/my_feat/my_feature.scc +</literallayout> +</para> +<para> +Configure the build with the feature added to the kernel type +<literallayout class='monospaced'> + ‐‐with-kernel=standard+my_feat/my_feature.scc +</literallayout> +</para> +<para> +Build the kernel +<literallayout class='monospaced'> + > make linux +</literallayout> +</para> + </section> + </section> + + <section id='bsp-updating-patches-and-configuration'> + <title>BSP: Updating Patches and Configuration</title> +<para> +As was described in the "template patching" example, it is simple +to add patches to a BSP via a template, but often, it is desirable +to experiment and test patches before committing them to a template. +You can do this by modifying the BSP source. +</para> +<para> +Start as follows: +<literallayout class='monospaced'> + > cd linux + > git checkout <bspname>-<kernel name> + + > git am <patch> +</literallayout> +</para> +<para> +Or you can do this: +<literallayout class='monospaced'> + > kgit-import -t patch <patch> + + > cd .. + > make linux +</literallayout> +</para> +<para> +For details on conflict resolution and patch application, see the +git manual, or other suitable online references. +<literallayout class='monospaced'> + > git am <mbox> + # conflict + > git apply ‐‐reject .git/rebase-apply/0001 + # resolve conflict + > git am ‐‐resolved (or git am ‐‐skip, git am ‐‐abort) + # continue until complete +</literallayout> +</para> +<para> +Here is another example: +<literallayout class='monospaced'> + # merge the patches + # 1) single patch + > git am <mbox> + > git apply <patch< + > kgit import -t patch <patch> + + # 2) multiple patches + > git am <mbox> + > kgit import -t dir <dir> + + # if kgit -t dir is used, a patch resolution cycle such + # as this can be used: + + > kgit import -t dir <dir> + # locate rejects and resolve + # options: + > wiggle ‐‐replace <path to file> <path to reject> + > guilt refresh + or + > # manual resolution + > git add <files> + > git commit -s + or + > git apply ‐‐reject .git/rebase-apply/0001 + > git add <files> + > git am ‐‐resolved + or + > # merge tool of choice + + # continue series: + + > kgit import -t dir <dir> + or + > git am ‐‐continue +</literallayout> +</para> +<para> +Once all the patches have been tested and are satisfactory, they +should be exported via the techniques described in "saving kernel +modifications." +</para> +<para> +Once the kernel has been patched and configured for a BSP, it's +configuration commonly needs to be modified. This can be done by +running [menu|x]config on the kernel tree, or working with +configuration fragments. +</para> +<para> +Using menuconfig, the operation is as follows: +<literallayout class='monospaced'> + > make linux.menuconfig + > make linux.rebuild +</literallayout> +</para> +<para> +Once complete, the changes are in linux-<bsp>-<kernel type>-build/.config. +To permanently save these changes, compare the .config before and after the +menuconfig, and place those changes in a configuration fragment in the +template of your choice. +</para> +<para> +Using configuration fragments, the operation is as follows (using the +si_is8620 as an example BSP): +<literallayout class='monospaced'> + > vi linux/wrs/cfg/kernel-cache/bsp/si_is8620/si_is8620.cfg + > make linux.reconfig + > make linux.rebuild +</literallayout> +</para> +<para> +The modified configuration fragment can simply be copied out of the +linux/wrs/.. directory and placed in the appropriate template for future +application. +</para> + </section> + + <section id='tools-guilt'> + <title>Tools: guilt</title> +<para> +Yocto Project has guilt integrated as a kernel tool; therefore users that are +familiar with quilt may wish to use this tool to pop, push and refresh +their patches. Note: guilt should only be used for local operations, once +a set of changes has been pushed or pulled, they should no longer be popped +or refresh by guilt, since popping, refreshing and re-pushing patches +changes their commit IDs and creating non-fast forward branches. +</para> +<para> +The following example illustrates how to add patches a Yocto Project +BSP branch via guilt: +<literallayout class='monospaced'> + > cd build/linux + > git checkout common_pc-standard + > guilt new extra.patch + # edit files, make changes, etc + > guilt refresh + > guilt top + extra.patch + + # export that patch to an external location + > kgit export -p top /tmp +</literallayout> +</para> +<para> +Other guilt operations of interest are: +<literallayout class='monospaced'> + > guilt push, guilt push -a + > guilt pop + > guilt applied, guilt unapplied + > guilt top + > guilt refresh + > guilt header -e + > guilt next +</literallayout> +</para> +<note><para> +Guilt only uses git commands and git plumbing to perform its operations, +anything that guilt does can also be done using git directly. It is provided +as a convenience utility, but is not required and the developer can use whatever +tools or workflow they wish. +</para></note> +<para> +The following builds from the above instructions to show how guilt can be +used to assist in getting your BSP kernel patches ready. You should follow +the above instructions up to and including 'make linux.config'. In this +example I will create a new commit (patch) from scratch and import another +fictitious patch from some external public git tree (ie, a commit with full +message, signoff etc.). Please ensure you have host-cross/bin in your path. +<literallayout class='monospaced'> + %> cd linux + %> guilt-init + %> guilt-new -m fill_me_in_please first_one.patch + %> touch somefile.txt + %> guilt-add somefile.txt + %> guilt-header -e + %> guilt-refresh + %> guilt-import path_to_some_patch/patch_filename + %> guilt-push +</literallayout> +</para> +<para> +Here are a few notes about the above: +<itemizedlist> + <listitem><para>guilt-header -e ‐‐ this will open editing of the patch header in + EDITOR. As with a git commit the first line is the short log and + should be just that short and concise message about the commit. Follow + the short log with lines of text that will be the long description but + note Do not put a blank line after the short log. As usual you will + want to follow this with a blank line and then a signoff line.</para></listitem> + + <listitem><para>The last line in the example above has 2 dots on the end. If you + don't add the 2 periods on the end guilt will think you are sending + just one patch. The wrong one!</para></listitem> + + <listitem><para>The advantage to using guilt over not using guilt is that if you have a + review comment in the first patch (first_one.patch in the case of this + example) it is very easy to use guilt to pop the other patches off + allowing you to make the necessary changes without having to use more + inventive git type strategies.</para></listitem> +</itemizedlist> +</para> + </section> + + <section id='tools-scc-file-example'> + <title>Tools: scc File Example</title> +<para> +This section provides some scc file examples: leaf node, 'normal' mode, and transforms. +</para> + <section id='leaf-node'> + <title>Leaf Node</title> +<para> +The following example is a BSP branch with no child branches - a leaf on the tree. +<literallayout class='monospaced'> + # these are optional, but allow standalone tree construction + define WRS_BOARD <name> + define WRS_KERNEL <kern type> + define WRS_ARCH <arch> + + scc_leaf ktypes/standard common_pc-standard + # ^ ^ + # +‐‐ parent + branch name + + include common_pc.scc + # ^ + # +‐‐‐ include another feature +</literallayout> +</para> + </section> + + <section id='normal-mode'> + <title>'Normal' Mode</title> +<para> +Here is an example of 'normal' mode: +<literallayout class='monospaced'> + # +‐‐‐‐ name of file to read + # v + kconf hardware common_pc.cfg + # ^ ^ + # | +‐‐ 'type: hardware or non-hardware + # | + # +‐‐‐ kernel config + + # patches + patch 0002-atl2-add-atl2-driver.patch + patch 0003-net-remove-LLTX-in-atl2-driver.patch + patch 0004-net-add-net-poll-support-for-atl2-driver.patch +</literallayout> +</para> + + </section> + + <section id='transforms'> + <title>Transforms</title> +<para> +This section shows an example of transforms: +<literallayout class='monospaced'> + # either of the next two options will trigger an 'auto' + # branch from existing ones, since they change the commit + # order and hence must construct their own branch + + # this changes the order of future includes, if the + # passed feature is detected, the first feature is + # included AFTER it + include features/rt/rt.scc after features/kgdb/kgdb + # this also changes the order of existing branches + # this prevents the named feature from ever being + # included + exclude features/dynamic_ftrace/dynamic_ftrace.scc + + # inherit the standard kernel + include ktypes/standard/standard + + + # LTT supplies this, so we don't want the sub-chunk from RT. + patch_trigger arch:all exclude ftrace-upstream-tracepoints.patch + # ...but we still want the one unique tracepoint it added. + patch tracepoint-add-for-sched_resched_task.patch + + # these will change the named patches in the series into + # <patch name>.patch.<feature name> + # where the substituted patch is in this directory + patch_trigger arch:all ctx_mod dynamic_printk.patch + patch_trigger arch:all ctx_mod 0001-Implement-futex-macros-for-ARM.patch + # unconditionally exclude a patch + patch_trigger arch:all exclude ftrace-fix-ARM-crash.patch +</literallayout> +</para> + </section> + </section> + + <section id='tip-dirty-string'> + <title>"-dirty" String</title> +<para> +If kernel images are being built with -dirty on the end of the version +string, this simply means that there are modification in the source +directory that haven't been committed. +<literallayout class='monospaced'> + > git status +</literallayout> +</para> +<para> +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. +</para> +<para> +To brute force pickup and commit all such pending changes enter the following: +<literallayout class='monospaced'> + > git add . + > git commit -s -a -m "getting rid of -dirty" +</literallayout> +</para> +<para> +And then rebuild the kernel +</para> + </section> + + <section id='kernel-transition-kernel-layer'> + <title>Kernel: Transition Kernel Layer</title> +<para> +In order to temporarily use a different base kernel in Yocto Project +Linux 3.0 you need to do the following: +<orderedlist> + <listitem><para>Create a custom kernel layer.</para></listitem> + <listitem><para>Create a git repository of the transition kernel.</para></listitem> +</orderedlist> +</para> +<para> +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. +</para> +<para> +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. +</para> +<para> +The next few sections describe the process: +</para> + <section id='creating-a-custom-kernel-layer'> + <title>Creating a Custom Kernel Layer</title> +<para> +The custom kernel layer must have the following minimum +elements: +<itemizedlist> + <listitem><para>An include of the shipped Yocto Project kernel layer.</para></listitem> + <listitem><para>A kernel-cache with an override of the standard kernel type.</para></listitem> +</itemizedlist> +</para> +<para> +This allows the inheritance of the kernel build infrastructure, +while overriding the list of patches that should be applied to +the base kernel. +</para> +<para> +The kernel layer can optionally include an override to the base +Yocto Project Linux BSP to inhibit the application of BSP specific +patches. If a custom BSP is being used, this is not required. +</para> + </section> + + <section id='git-repo-of-the-transition-kernel'> + <title>git Repo of the Transition Kernel</title> +<para> +The kernel build system requires a base kernel repository to +seed the build process. This repository must be found in the +same layer as the build infrastructure (i.e wrll-linux-2.6.27) +in the 'git' subdir, with the name 'default_kernel' +</para> +<para>Since Yocto Project Linux ships with a default_kernel +(the validated Yocto Project kernel) in the wrll-linux-2.6.27 +kernel layer, that must be removed and replaced with the +transition kernel. +</para> +<para>If the Yocto Project install cannot be directly modified +with the new default kernel, then the path to the transition +kernel layer's 'git' subdir must be passed to the build +process via: +<programlisting> +linux_GIT_BASE=<absolute path to layer>/git +</programlisting> +</para> +<para> +If the transition kernel has not been delivered via git, +then a git repo should be created, and bare cloned into +place. Creating this repository is as simple as: +<literallayout class='monospaced'> + > tar zxvf temp_kernel.tgz + > cd temp_kernel + > git init + > git add . + > git commit -a -m "Transition kernel baseline" + + 'temp_kernel' can now be cloned into place via: + + > cd <path to git base>/git + > git clone ‐‐bare <path to temp_kernel/temp_kernel default_kernel +</literallayout> +</para> + </section> + + <section id='building-the-kernel'> + <title>Building the Kernel</title> +<para> +Once these prerequisites have been met, the kernel can be +built with: +<literallayout class='monospaced'> + > make linux +</literallayout> +</para> +<para> +The new base kernel will be cloned into place and have any patches +indicated in the transition kernel's cache (or templates) applied. +The kernel build will detect the non-Yocto Project base repo and +use the HEAD of the tree for the build. +</para> + </section> + + <section id='example'> + <title>Example</title> +<para> +This example creates a kernel layer to build the latest +kernel.org tree as the 'common_pc' BSP. +<literallayout class='monospaced'> + > cd <path to layers> + > mkdir wrll-linux-my_version + > cd wrll-linux-my_version + > echo "wrll-linux-2.6.27" > include + > mkdir -p kernel-cache/ktypes/standard + > mkdir -p kernel-cache/bsp/common_pc + > echo "v2.6.29" > kernel-cache/kver + > echo "branch common_pc-standard" > kernel-cache/bsp/common_pc/common_pc.scc + > echo "kconf hardware common_pc.cfg" >> kernel-cache/bsp/common_pc/common_pc.scc + > echo "CONFIG_FOO=y" > kernel-cache/bsp/common_pc/common_pc.cfg + > mkdir git + > cd git + > git clone ‐‐bare git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git default_kernel +</literallayout> +</para> +<para> +Configure a build to use the new layer. This means that: +<literallayout class='monospaced'> + ‐‐enable-kernel-version=my_version +</literallayout> +</para> +<para> +Should be used to override the shipped default. +</para> +<para> +To build the kernel: +<literallayout class='monospaced'> + > cd build + > make linux_GIT_BASE=<layer path>/wrll-linux-my_version/git linux +</literallayout> +</para> +<para> +If this is to build without some user intervention (passing of the +GIT_BASE), you must do the clone into the wrll-linux-2.6.27/git directory. +</para> +<note><para>Unless you define valid "hardware.kcf" and "non-hardware.kcf" some +non fatal warnings will be seen. They can be fixed by populating these +files in the kernel-cache with valid hardware and non hardware config +options. +</para></note> + </section> + </section> + </section> + + + + + +<!-- <itemizedlist> + <listitem><para>Introduction to this section.</para></listitem> + <listitem><para>Constructing a project-specific kernel tree.</para></listitem> + <listitem><para>Building the kernel.</para></listitem> + <listitem><para>Seeing what has changed.</para></listitem> + <listitem><para>Seeing what has changed in a particular branch.</para></listitem> + <listitem><para>Modifying the kernel.</para></listitem> + <listitem><para>Saving modifications.</para></listitem> + <listitem><para>Storing patches outside of the kernel source repository (bulk export).</para></listitem> + <listitem><para>Working with incremental changes.</para></listitem> + <listitem><para>Extracting commited changes from a working directory (exporting internally through + patches.</para></listitem> + <listitem><para>Pushing commited changes.</para></listitem> + <listitem><para>Exporting for external (upstream) submission.</para></listitem> + <listitem><para>Exporting for import into another Source Control Manager (SCM).</para></listitem> + <listitem><para>Working with the Yocto Project kernel in another SCM.</para> + <itemizedlist> + <listitem><para>Exporting the delivered kernel to an SCM.</para></listitem> + <listitem><para>Importing changed for the build.</para></listitem> + </itemizedlist></listitem> + <listitem><para>Migrating templates from version 2.0.</para></listitem> + <listitem><para>Creating a new Board Support Package (BSP).</para> + <itemizedlist> + <listitem><para>Creating from scratch.</para></listitem> + <listitem><para>Cloning.</para></listitem> + </itemizedlist></listitem> + <listitem><para>BSP bootstrapping.</para></listitem> + <listitem><para>Applying patches to the kernel through a template.</para></listitem> + <listitem><para>Applying patches to the kernel without using a template.</para></listitem> + <listitem><para>Updating patches and configurations for a BSP.</para></listitem> + <listitem><para>Using guilt to add and export patches.</para></listitem> + <listitem><para>Using scc.</para></listitem> + <listitem><para>Building a 'dirty' image.</para></listitem> + <listitem><para>Temporarily using a different base kernel.</para></listitem> + <listitem><para>Creating a custom kernel layer.</para></listitem> + <listitem><para>Creating the git repository of the transition kernel.</para></listitem> + </itemizedlist> --> + + +</section> + +</article> +<!-- +vim: expandtab tw=80 ts=4 +--> |
