Patrick Williams | c124f4f | 2015-09-15 14:41:29 -0500 | [diff] [blame] | 1 | <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" |
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| 4 | |
| 5 | <chapter id='kernel-dev-intro'> |
| 6 | <title>Introduction</title> |
| 7 | |
| 8 | <!-- |
| 9 | <para> |
| 10 | <emphasis>AR - Darren Hart:</emphasis> See if the concepts in these |
| 11 | three bullets are adequately covered in somewhere in this manual: |
| 12 | <itemizedlist> |
| 13 | <listitem><para>Do we convey that our kernel Git repositories |
| 14 | have a clear and continuous history, similar to the way the |
| 15 | kernel Git repositories for <filename>kernel.org</filename> |
| 16 | do. |
| 17 | </para></listitem> |
| 18 | <listitem><para>Does the manual note that Yocto Project delivers |
| 19 | a key set of supported kernel types, where |
| 20 | each type is tailored to meet a specific use (e.g. networking, |
| 21 | consumer, devices, and so forth).</para></listitem> |
| 22 | <listitem><para>Do we convey that the Yocto Project uses a |
| 23 | Git branching strategy that, from a |
| 24 | developer's point of view, results in a linear path from the |
| 25 | baseline kernel.org, through a select group of features and |
| 26 | ends with their BSP-specific commits.</para></listitem> |
| 27 | </itemizedlist> |
| 28 | </para> |
| 29 | --> |
| 30 | |
| 31 | <section id='kernel-dev-overview'> |
| 32 | <title>Overview</title> |
| 33 | |
| 34 | <para> |
| 35 | Regardless of how you intend to make use of the Yocto Project, |
| 36 | chances are you will work with the Linux kernel. |
| 37 | This manual provides background information on the Yocto Linux kernel |
| 38 | <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>, |
| 39 | describes common tasks you can perform using the kernel tools, |
| 40 | and shows you how to use the kernel Metadata needed to work with |
| 41 | the kernel inside the Yocto Project. |
| 42 | </para> |
| 43 | |
| 44 | <para> |
| 45 | Each Yocto Project release has a set of linux-yocto recipes, whose |
| 46 | Git repositories you can view in the Yocto |
| 47 | <ulink url='&YOCTO_GIT_URL;'>Source Repositories</ulink> under |
| 48 | the "Yocto Linux Kernel" heading. |
| 49 | New recipes for the release track the latest upstream developments |
| 50 | and introduce newly-supported platforms. |
| 51 | Previous recipes in the release are refreshed and supported for at |
| 52 | least one additional release. |
| 53 | As they align, these previous releases are updated to include the |
| 54 | latest from the |
| 55 | <ulink url='&YOCTO_HOME_URL;/organization/long-term-support-initiative-ltsi'>Long Term Support Initiative</ulink> |
| 56 | (LTSI) project. |
| 57 | Also included is a linux-yocto development recipe |
| 58 | (<filename>linux-yocto-dev.bb</filename>) should you want to work |
| 59 | with the very latest in upstream Linux kernel development and |
| 60 | kernel Metadata development. |
| 61 | </para> |
| 62 | |
| 63 | <para> |
| 64 | The Yocto Project also provides a powerful set of kernel |
| 65 | tools for managing Linux kernel sources and configuration data. |
| 66 | You can use these tools to make a single configuration change, |
| 67 | apply multiple patches, or work with your own kernel sources. |
| 68 | </para> |
| 69 | |
| 70 | <para> |
| 71 | In particular, the kernel tools allow you to generate configuration |
| 72 | fragments that specify only what you must, and nothing more. |
| 73 | Configuration fragments only need to contain the highest level |
| 74 | visible <filename>CONFIG</filename> options as presented by the Linux |
| 75 | kernel <filename>menuconfig</filename> system. |
| 76 | Contrast this against a complete Linux kernel |
| 77 | <filename>.config</filename>, which includes all the automatically |
| 78 | selected <filename>CONFIG</filename> options. |
| 79 | This efficiency reduces your maintenance effort and allows you |
| 80 | to further separate your configuration in ways that make sense for |
| 81 | your project. |
| 82 | A common split separates policy and hardware. |
| 83 | For example, all your kernels might support |
| 84 | the <filename>proc</filename> and <filename>sys</filename> filesystems, |
| 85 | but only specific boards require sound, USB, or specific drivers. |
| 86 | Specifying these configurations individually allows you to aggregate |
| 87 | them together as needed, but maintains them in only one place. |
| 88 | Similar logic applies to separating source changes. |
| 89 | </para> |
| 90 | |
| 91 | <para> |
| 92 | If you do not maintain your own kernel sources and need to make |
| 93 | only minimal changes to the sources, the released recipes provide a |
| 94 | vetted base upon which to layer your changes. |
| 95 | Doing so allows you to benefit from the continual kernel |
| 96 | integration and testing performed during development of the |
| 97 | Yocto Project. |
| 98 | </para> |
| 99 | |
| 100 | <para> |
| 101 | If, instead, you have a very specific Linux kernel source tree |
| 102 | and are unable to align with one of the official linux-yocto |
| 103 | recipes, an alternative exists by which you can use the Yocto |
| 104 | Project Linux kernel tools with your own kernel sources. |
| 105 | </para> |
| 106 | </section> |
| 107 | |
| 108 | <section id='kernel-dev-other-resources'> |
| 109 | <title>Other Resources</title> |
| 110 | |
| 111 | <para> |
| 112 | The sections that follow provide instructions for completing |
| 113 | specific Linux kernel development tasks. |
| 114 | These instructions assume you are comfortable working with |
| 115 | <ulink url='http://openembedded.org/wiki/Bitbake'>BitBake</ulink> |
| 116 | recipes and basic open-source development tools. |
| 117 | Understanding these concepts will facilitate the process of working |
| 118 | with the kernel recipes. |
| 119 | If you find you need some additional background, please be sure to |
| 120 | review and understand the following documentation: |
| 121 | <itemizedlist> |
| 122 | <listitem><para><ulink url='&YOCTO_DOCS_QS_URL;'>Yocto Project Quick Start</ulink> |
| 123 | </para></listitem> |
| 124 | <listitem><para>The "<ulink url='&YOCTO_DOCS_DEV_URL;#dev-modifying-source-code'>Modifying Source Code</ulink>" |
| 125 | section in the Yocto Project Development Manual |
| 126 | </para></listitem> |
| 127 | <listitem><para>The "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>" section |
| 128 | in the Yocto Project Development Manual</para></listitem> |
| 129 | <listitem><para>The "<ulink url='&YOCTO_DOCS_DEV_URL;#modifying-the-kernel'>Modifying the Kernel</ulink>" section |
| 130 | in the Yocto Project Development Manual.</para></listitem> |
| 131 | </itemizedlist> |
| 132 | </para> |
| 133 | |
| 134 | <para> |
| 135 | Finally, while this document focuses on the manual creation of |
| 136 | recipes, patches, and configuration files, the Yocto Project |
| 137 | Board Support Package (BSP) tools are available to automate |
| 138 | this process with existing content and work well to create the |
| 139 | initial framework and boilerplate code. |
| 140 | For details on these tools, see the |
| 141 | "<ulink url='&YOCTO_DOCS_BSP_URL;#using-the-yocto-projects-bsp-tools'>Using the Yocto Project's BSP Tools</ulink>" |
| 142 | section in the Yocto Project Board Support Package (BSP) Developer's |
| 143 | Guide. |
| 144 | </para> |
| 145 | </section> |
| 146 | </chapter> |
| 147 | <!-- |
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| 149 | --> |