2176 lines
94 KiB
XML
2176 lines
94 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article id='intro'>
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<imagedata fileref="figures/yocto-project-transp.png" width="6in" depth="1in" align="right" scale="25" />
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<section id='fake-title'>
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<title>Yocto Project Kernel Architecture and Use Manual</title>
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</section>
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<section id='introduction'>
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<title>Introduction</title>
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<para>
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Yocto Project presents the kernel as a fully patched, history-clean git
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repository.
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The git tree represents the selected features, board support,
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and configurations extensively tested by Yocto Project.
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The Yocto Project kernel allows the end user to leverage community
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best practices to seamlessly manage the development, build and debug cycles.
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</para>
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<para>
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This manual describes the Yocto Project kernel by providing information
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on its history, organization, benefits, and use.
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The manual consists of two sections:
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<itemizedlist>
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<listitem><para>Concepts - Describes concepts behind the kernel.
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You will understand how the kernel is organized and why it is organized in
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the way it is. You will understand the benefits of the kernel's organization
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and the mechanisms used to work with the kernel and how to apply it in your
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design process.</para></listitem>
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<listitem><para>Using the Kernel - Describes best practices and "how-to" information
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that lets you put the kernel to practical use. Some examples are "How to Build a
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Project Specific Tree", "How to Examine Changes in a Branch", and "Saving Kernel
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Modifications."</para></listitem>
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</itemizedlist>
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</para>
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<para>
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For more information on the kernel, see the following links:
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<itemizedlist>
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<listitem><para><ulink url='http://ldn.linuxfoundation.org/book/1-a-guide-kernel-development-process'></ulink></para></listitem>
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<listitem><para><ulink url='http://userweb.kernel.org/~akpm/stuff/tpp.txt'></ulink></para></listitem>
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<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>
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</itemizedlist>
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<para>
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You can find more information on Yocto Project by visiting the website at
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<ulink url='http://www.yoctoproject.org'></ulink>.
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</para>
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</para>
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</section>
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<section id='concepts'>
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<title>Concepts</title>
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<para>
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This section provides conceptual information about the Yocto Project kernel:
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<itemizedlist>
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<listitem><para>Kernel Goals</para></listitem>
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<listitem><para>Yocto Project Kernel Development and Maintenance Overview</para></listitem>
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<listitem><para>Kernel Architecture</para></listitem>
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<listitem><para>Kernel Tools</para></listitem>
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</itemizedlist>
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</para>
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<section id='kernel-goals'>
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<title>Kernel Goals</title>
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<para>
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The complexity of embedded kernel design has increased dramatically.
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Whether it is managing multiple implementations of a particular feature or tuning and
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optimizing board specific features, flexibility and maintainability are key concerns.
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The Yocto Project Linux kernel is presented with the embedded
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developer's needs in mind and has evolved to assist in these key concerns.
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For example, prior methods such as applying hundreds of patches to an extracted
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tarball have been replaced with proven techniques that allow easy inspection,
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bisection and analysis of changes.
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Application of these techniques also creates a platform for performing integration and
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collaboration with the thousands of upstream development projects.
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</para>
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<para>
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With all these considerations in mind, the Yocto Project kernel and development team
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strives to attain these goals:
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<itemizedlist>
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<listitem><para>Allow the end user to leverage community best practices to seamlessly
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manage the development, build and debug cycles.</para></listitem>
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<listitem><para>Create a platform for performing integration and collaboration with the
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thousands of upstream development projects that exist.</para></listitem>
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<listitem><para>Provide mechanisms that support many different work flows, front-ends and
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management techniques.</para></listitem>
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<listitem><para>Deliver the most up-to-date kernel possible while still ensuring that
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the baseline kernel is the the most stable official release.</para></listitem>
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<listitem><para>Include major technological features as part of Yocto Project's up-rev
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strategy.</para></listitem>
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<listitem><para>Present a git tree, that just like the upstream kernel.org tree, has a
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clear and continuous history.</para></listitem>
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<listitem><para>Deliver a key set of supported kernel types, where each type is tailored
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to a specific use case (i.g. networking, consumer, devices, and so forth).</para></listitem>
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<listitem><para>Employ a git branching strategy that from a customer's point of view
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results in a linear path from the baseline kernel.org, through a select group of features and
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ends with their BSP-specific commits.</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='kernel-big-picture'>
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<title>Yocto Project Kernel Development and Maintenance Overview</title>
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<para>
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Yocto Project kernel, like other kernels, is based off the Linux kernel release
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from <ulink url='http://www.kernel.org'></ulink>.
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At the beginning of our major development cycle, we choose our Yocto Project kernel
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based on factors like release timing, the anticipated release timing of "final" (i.e. non "rc")
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upstream kernel.org versions, and Yocto Project feature requirements.
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Typically this will be a kernel that is in the
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final stages of development by the community (i.e. still in the release
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candidate or "rc" phase) and not yet a final release.
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But by being in the final stages of external development, we know that the
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kernel.org final release will clearly land within the early stages of
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the Yocto Project development window.
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</para>
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<para>
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This balance allows us to deliver the most up-to-date kernel
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as possible, while still ensuring that we have a stable official release as
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our baseline kernel version.
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</para>
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<para>
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The following figure represents the overall place the Yocto Project kernel fills.
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</para>
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<para>
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<imagedata fileref="figures/kernel-big-picture.png" width="6in" depth="4in" align="center" scale="100" />
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</para>
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<para>
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In the figure the ultimate source for the Yocto Project kernel is a released kernel
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from kernel.org.
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In addition to a foundational kernel from kernel.org the commercially released
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Yocto Project kernel contains a mix of important new mainline
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developments, non-mainline developments, Board Support Package (BSP) developments,
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and custom features.
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These additions result in a commercially released Yocto Project kernel that caters
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to specific embedded designer needs for targeted hardware.
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</para>
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<para>
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Once a Yocto Project kernel is officially released the Yocto Project team goes into
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their next development cycle, or "uprev" cycle.
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It is important to note that the most sustainable and stable way
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to include feature development upstream is through a kernel uprev process.
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Back-porting of hundreds of individual fixes and minor features from various
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kernel versions is not sustainable and can easily compromise quality.
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During the uprev cycle, the Yocto Project team uses an ongoing analysis of
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kernel development, BSP support, and release timing to select the best
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possible kernel.org version.
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The team continually monitors community kernel
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development to look for significant features of interest.
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The illustration depicts this by showing the team looking back to kernel.org for new features,
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BSP features, and significant bug fixes.
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The team does consider back-porting large features if they have a significant advantage.
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User or community demand can also trigger a back-port or creation of new
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functionality in the Yocto Project baseline kernel during the uprev cycle.
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</para>
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<para>
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Generally speaking, every new kernel both adds features and introduces new bugs.
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These consequences are the basic properties of upstream kernel development and are
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managed by the Yocto Project team's kernel strategy.
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It is the Yocto Project team's policy to not back-port minor features to the released kernel.
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They only consider back-porting significant technological jumps - and, that is done
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after a complete gap analysis.
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The reason for this policy is that simply back-porting any small to medium sized change
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from an evolving kernel can easily create mismatches, incompatibilities and very
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subtle errors.
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</para>
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<para>
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These policies result in both a stable and a cutting
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edge kernel that mixes forward ports of existing features and significant and critical
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new functionality.
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Forward porting functionality in the Yocto Project kernel can be thought of as a
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"micro uprev."
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The many “micro uprevs” produce a kernel version with a mix of
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important new mainline, non-mainline, BSP developments and feature integrations.
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This kernel gives insight into new features and allows focused
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amounts of testing to be done on the kernel, which prevents
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surprises when selecting the next major uprev.
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The quality of these cutting edge kernels is evolving and the kernels are used in very special
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cases for BSP and feature development.
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</para>
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</section>
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<section id='kernel-architecture'>
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<title>Kernel Architecture</title>
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<para>
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This section describes the architecture of the Yocto Project kernel and provides information
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on the mechanisms used to achieve that architecture.
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</para>
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<section id='architecture-overview'>
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<title>Overview</title>
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<para>
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As mentioned earlier, a key goal of Yocto Project is to present the developer with
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a kernel that has a clear and continuous history that is visible to the user.
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The architecture and mechanisms used achieve that goal in a manner similar to the
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upstream kernel.org.
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</para>
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<para>
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You can think of the Yocto Project kernel as consisting of a baseline kernel with
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added features logically structured on top of the baseline.
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The features are tagged and organized by way of a branching strategy implemented by the
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source code manager (SCM) git.
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The result is that the user has the ability to see the added features and
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the commits that make up those features.
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In addition to being able to see added features, the user can also view the history of what
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made up the baseline kernel as well.
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</para>
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<para>
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The following illustration shows the conceptual Yocto Project kernel.
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</para>
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<para>
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<imagedata fileref="figures/kernel-architecture-overview.png" width="6in" depth="4in" align="center" scale="100" />
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</para>
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<para>
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In the illustration, the "kernel.org Branch Point" marks the specific spot (or release) from
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which the Yocto Project kernel is created. From this point "up" in the tree features and
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differences are organized and tagged.
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</para>
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<para>
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The "Yocto Project Baseline Kernel" contains functionality that is common to every kernel
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type and BSP that is organized further up the tree. Placing these common features in the
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tree this way means features don't have to be duplicated along individual branches of the
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structure.
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</para>
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<para>
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From the Yocto Project Baseline Kernel branch points represent specific functionality
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for individual BSPs as well as real-time kernels.
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The illustration represents this through three BSP-specific branches and a real-time
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kernel branch.
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Each branch represents some unique functionality for the BSP or a real-time kernel.
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</para>
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<para>
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The real-time kernel branch has common features for all real-time kernels and contains
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more branches for individual BSP-specific real-time kernels.
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The illustration shows three branches as an example.
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Each branch points the way to specific, unique features for a respective real-time
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kernel as they apply to a given BSP.
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</para>
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<para>
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The resulting tree structure presents a clear path of markers (or branches) to the user
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that for all practical purposes is the kernel needed for any given set of requirements.
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</para>
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</section>
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<section id='branching-and-workflow'>
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<title>Branching Strategy and Workflow</title>
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<para>
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The Yocto Project team creates kernel branches at points where functionality is
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no longer shared and thus, needs to be isolated.
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For example, board-specific incompatibilities would require different functionality
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and would require a branch to separate the features.
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Likewise, for specific kernel features the same branching strategy is used.
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This branching strategy results in a tree that has features organized to be specific
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for particular functionality, single kernel types, or a subset of kernel types.
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This strategy results in not having to store the same feature twice internally in the
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tree.
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Rather we store the unique differences required to apply the feature onto the kernel type
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in question.
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</para>
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<para>
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BSP-specific code additions are handled in a similar manner to kernel-specific additions.
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Some BSPs only make sense given certain kernel types.
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So, for these types, we create branches off the end of that kernel type for all
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of the BSPs that are supported on that kernel type.
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From the perspective of the tools that create the BSP branch, the BSP is really no
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different than a feature.
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Consequently, the same branching strategy applies to BSPs as it does to features.
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So again, rather than store the BSP twice, only the unique differences for the BSP across
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the supported multiple kernels are uniquely stored.
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</para>
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<para>
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While this strategy results in a tree with a significant number of branches, it is
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important to realize that from the customer's point of view, there is a linear
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path that travels from the baseline kernel.org, through a select group of features and
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ends with their BSP-specific commits.
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In other words, the divisions of the kernel are transparent and are not relevant
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to the developer on a day-to-day basis.
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From the customer's perspective, this is the "master" branch.
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They do not need not be aware of the existence of any other branches at all.
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Of course there is value in the existence of these branches
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in the tree, should a person decide to explore them.
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For example, a comparison between two BSPs at either the commit level or at the line-by-line
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code diff level is now a trivial operation.
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</para>
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<para>
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Working with the kernel as a structured tree follows recognized community best practices.
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In particular, the kernel as shipped with the product should be
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considered an 'upstream source' and viewed as a series of
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historical and documented modifications (commits).
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These modifications represent the development and stabilization done
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by the Yocto Project kernel development team.
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</para>
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<para>
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Because commits only change at significant release points in the product life cycle,
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developers can work on a branch created
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from the last relevant commit in the shipped Yocto Project kernel.
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As mentioned previously, the structure is transparent to the user
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because the kernel tree is left in this state after cloning and building the kernel.
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</para>
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</section>
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<section id='source-code-manager-git'>
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<title>Source Code Manager - git</title>
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<para>
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The Source Code Manager (SCM) is git and it is the obvious mechanism for meeting the
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previously mentioned goals.
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Not only is it the SCM for kernel.org but git continues to grow in popularity and
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supports many different work flows, front-ends and management techniques.
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</para>
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<note><para>
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It should be noted that you can use as much, or as little, of what git has to offer
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as is appropriate to your project.
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</para></note>
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</section>
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</section>
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<section id='kernel-tools'>
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<title>Kernel Tools</title>
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<para>
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Since most standard workflows involve moving forward with an existing tree by
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continuing to add and alter the underlying baseline, the tools that manage
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Yocto Project's kernel construction are largely hidden from the developer to
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present a simplified view of the kernel for ease of use.
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</para>
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<para>
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The fundamental properties of the tools that manage and construct the
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kernel are:
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<itemizedlist>
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<listitem><para>the ability to group patches into named, reusable features</para></listitem>
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<listitem><para>to allow top down control of included features</para></listitem>
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<listitem><para>the binding of kernel configuration to kernel patches/features</para></listitem>
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<listitem><para>the presentation of a seamless git repository that blends Yocto Project value with the kernel.org history and development</para></listitem>
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</itemizedlist>
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</para>
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<para>
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The tools that construct a kernel tree will be discussed later in this
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document. The following tools form the foundation of the Yocto Project
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kernel toolkit:
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<itemizedlist>
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<listitem><para>git : distributed revision control system created by Linus Torvalds</para></listitem>
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<listitem><para>guilt: quilt on top of git</para></listitem>
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<listitem><para>*cfg : kernel configuration management and classification</para></listitem>
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<listitem><para>kgit*: Yocto Project kernel tree creation and management tools</para></listitem>
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<listitem><para>scc : series & configuration compiler</para></listitem>
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</itemizedlist>
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</para>
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</section>
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</section>
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<!-- <section id='concepts2'>
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<title>Kernel Concepts</title>
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<itemizedlist>
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<listitem><para>What tools and commands are used with the kernel.</para></listitem>
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<listitem><para>Source Control Manager (SCM).</para></listitem>
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<listitem><para>What are some workflows that you can apply using the kernel.</para></listitem>
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</itemizedlist>
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</section> -->
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<section id='actions'>
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<title>How to get things accomplished with the kernel</title>
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<para>
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This section describes how to accomplish tasks involving the kernel's tree structure.
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The information covers the following:
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<itemizedlist>
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<listitem><para>Tree construction</para></listitem>
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<listitem><para>Build strategies</para></listitem>
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<listitem><para>Series & Configuration Compiler</para></listitem>
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<listitem><para>kgit</para></listitem>
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<listitem><para>Workflow examples</para></listitem>
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<listitem><para>Source Code Manager (SCM)</para></listitem>
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<listitem><para>Board Support Package (BSP) template migration</para></listitem>
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<listitem><para>BSP creation</para></listitem>
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<listitem><para>Patching</para></listitem>
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<listitem><para>Updating BSP patches and configuration</para></listitem>
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<listitem><para>guilt</para></listitem>
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<listitem><para>scc file example</para></listitem>
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<listitem><para>"dirty" string</para></listitem>
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<listitem><para>Transition kernel layer</para></listitem>
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</itemizedlist>
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</para>
|
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<section id='tree-construction'>
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<title>Tree Construction</title>
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<para>
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The Yocto Project kernel repository, as shipped with the product, is created by
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compiling and executing the set of feature descriptions for every BSP/feature
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in the product. Those feature descriptions list all necessary patches,
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configuration, branching, tagging and feature divisions found in the kernel.
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</para>
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<para>
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The files used to describe all the valid features and BSPs in the Yocto Project
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kernel can be found in any clone of the kernel git tree. The directory
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wrs/cfg/kernel-cache/ is a snapshot of all the kernel configuration and
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feature descriptions (.scc) that were used to build the kernel repository.
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It should however be noted, that browsing the snapshot of feature
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descriptions and patches is not an effective way to determine what is in a
|
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particular kernel branch. Using git directly to get insight into the changes
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|
in a branch is more efficient and a more flexible way to inspect changes to
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the kernel. Examples of using git to inspect kernel commits are in the
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following sections.
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</para>
|
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<para>
|
|
As a reminder, it is envisioned that a ground up reconstruction of the
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complete kernel tree is an action only taken by Yocto Project staff during an
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active development cycle. When an end user creates a project, it takes
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advantage of this complete tree in order to efficiently place a git tree
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within their project.
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</para>
|
|
<para>
|
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The general flow of the project specific kernel tree construction is as follows:
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<orderedlist>
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<listitem><para>a top level kernel feature is passed to the kernel build subsystem,
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normally this is a BSP for a particular kernel type.</para></listitem>
|
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<listitem><para>the file that describes the top level feature is located by searching
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system directories:</para>
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<itemizedlist>
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<listitem><para>the kernel-cache under linux/wrs/cfg/kernel-cache</para></listitem>
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<listitem><para>kernel-*-cache directories in layers</para></listitem>
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<listitem><para>configured and default templates</para></listitem>
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</itemizedlist>
|
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<para>In a typical build a feature description of the format:
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<bsp name>-<kernel type>.scc is the target of the search.
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</para></listitem>
|
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|
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<listitem><para>once located, the feature description is compiled into a simple script
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of actions, or an existing equivalent script which was part of the
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shipped kernel is located.</para></listitem>
|
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|
|
<listitem><para>extra features are appended to the top level feature description. Extra
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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
|
|
-->
|