150 lines
7.4 KiB
XML
150 lines
7.4 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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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='kernel-dev-intro'>
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<title>Introduction</title>
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<!--
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<para>
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<emphasis>AR - Darren Hart:</emphasis> See if the concepts in these
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three bullets are adequately covered in somewhere in this manual:
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<itemizedlist>
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<listitem><para>Do we convey that our kernel Git repositories
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have a clear and continuous history, similar to the way the
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kernel Git repositories for <filename>kernel.org</filename>
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do.
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</para></listitem>
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<listitem><para>Does the manual note that Yocto Project delivers
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a key set of supported kernel types, where
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each type is tailored to meet a specific use (e.g. networking,
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consumer, devices, and so forth).</para></listitem>
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<listitem><para>Do we convey that the Yocto Project uses a
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Git branching strategy that, from a
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developer's point of view, results in a linear path from the
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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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-->
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<section id='kernel-dev-overview'>
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<title>Overview</title>
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<para>
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Regardless of how you intend to make use of the Yocto Project,
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chances are you will work with the Linux kernel.
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This manual provides background information on the Yocto Linux kernel
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<ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>,
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describes common tasks you can perform using the kernel tools,
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and shows you how to use the kernel Metadata needed to work with
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the kernel inside the Yocto Project.
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</para>
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<para>
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Each Yocto Project release has a set of linux-yocto recipes, whose
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Git repositories you can view in the Yocto
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<ulink url='&YOCTO_GIT_URL;'>Source Repositories</ulink> under
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the "Yocto Linux Kernel" heading.
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New recipes for the release track the latest upstream developments
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and introduce newly-supported platforms.
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Previous recipes in the release are refreshed and supported for at
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least one additional release.
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As they align, these previous releases are updated to include the
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latest from the
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<ulink url='&YOCTO_HOME_URL;/organization/long-term-support-initiative-ltsi'>Long Term Support Initiative</ulink>
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(LTSI) project.
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Also included is a linux-yocto development recipe
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(<filename>linux-yocto-dev.bb</filename>) should you want to work
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with the very latest in upstream Linux kernel development and
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kernel Metadata development.
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</para>
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<para>
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The Yocto Project also provides a powerful set of kernel
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tools for managing Linux kernel sources and configuration data.
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You can use these tools to make a single configuration change,
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apply multiple patches, or work with your own kernel sources.
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</para>
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<para>
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In particular, the kernel tools allow you to generate configuration
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fragments that specify only what you must, and nothing more.
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Configuration fragments only need to contain the highest level
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visible <filename>CONFIG</filename> options as presented by the Linux
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kernel <filename>menuconfig</filename> system.
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Contrast this against a complete Linux kernel
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<filename>.config</filename>, which includes all the automatically
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selected <filename>CONFIG</filename> options.
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This efficiency reduces your maintenance effort and allows you
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to further separate your configuration in ways that make sense for
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your project.
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A common split separates policy and hardware.
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For example, all your kernels might support
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the <filename>proc</filename> and <filename>sys</filename> filesystems,
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but only specific boards require sound, USB, or specific drivers.
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Specifying these configurations individually allows you to aggregate
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them together as needed, but maintains them in only one place.
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Similar logic applies to separating source changes.
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</para>
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<para>
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If you do not maintain your own kernel sources and need to make
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only minimal changes to the sources, the released recipes provide a
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vetted base upon which to layer your changes.
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Doing so allows you to benefit from the continual kernel
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integration and testing performed during development of the
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Yocto Project.
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</para>
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<para>
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If, instead, you have a very specific Linux kernel source tree
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and are unable to align with one of the official linux-yocto
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recipes, an alternative exists by which you can use the Yocto
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Project Linux kernel tools with your own kernel sources.
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</para>
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</section>
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<section id='kernel-dev-other-resources'>
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<title>Other Resources</title>
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<para>
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The sections that follow provide instructions for completing
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specific Linux kernel development tasks.
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These instructions assume you are comfortable working with
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<ulink url='http://openembedded.org/wiki/Bitbake'>BitBake</ulink>
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recipes and basic open-source development tools.
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Understanding these concepts will facilitate the process of working
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with the kernel recipes.
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If you find you need some additional background, please be sure to
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review and understand the following documentation:
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<itemizedlist>
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<listitem><para><ulink url='&YOCTO_DOCS_QS_URL;'>Yocto Project Quick Start</ulink>
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</para></listitem>
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<listitem><para>The "<ulink url='&YOCTO_DOCS_DEV_URL;#dev-modifying-source-code'>Modifying Source Code</ulink>"
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section in the Yocto Project Development Manual
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</para></listitem>
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<listitem><para>The "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>" section
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in the Yocto Project Development Manual</para></listitem>
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<listitem><para>The "<ulink url='&YOCTO_DOCS_DEV_URL;#modifying-the-kernel'>Modifying the Kernel</ulink>" section
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in the Yocto Project Development Manual.</para></listitem>
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</itemizedlist>
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</para>
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<para>
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Finally, while this document focuses on the manual creation of
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recipes, patches, and configuration files, the Yocto Project
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Board Support Package (BSP) tools are available to automate
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this process with existing content and work well to create the
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initial framework and boilerplate code.
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For details on these tools, see the
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"<ulink url='&YOCTO_DOCS_BSP_URL;#using-the-yocto-projects-bsp-tools'>Using the Yocto Project's BSP Tools</ulink>"
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section in the Yocto Project Board Support Package (BSP) Developer's
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Guide.
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</para>
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</section>
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</chapter>
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<!--
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vim: expandtab tw=80 ts=4
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-->
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