269 lines
13 KiB
XML
269 lines
13 KiB
XML
|
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
|
||
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
|
||
|
|
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
|
||
|
|
|
||
|
|
<chapter id='kernel-dev-intro'>
|
||
|
|
<title>Introduction</title>
|
||
|
|
|
||
|
|
<section id='kernel-dev-overview'>
|
||
|
|
<title>Overview</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Regardless of how you intend to make use of the Yocto Project,
|
||
|
|
chances are you will work with the Linux kernel.
|
||
|
|
This manual describes how to set up your build host to support
|
||
|
|
kernel development, introduces the kernel development process,
|
||
|
|
provides background information on the Yocto Linux kernel
|
||
|
|
<ulink url='&YOCTO_DOCS_REF_URL;#metadata'>Metadata</ulink>,
|
||
|
|
describes common tasks you can perform using the kernel tools,
|
||
|
|
shows you how to use the kernel Metadata needed to work with
|
||
|
|
the kernel inside the Yocto Project, and provides insight into how
|
||
|
|
the Yocto Project team develops and maintains Yocto Linux kernel
|
||
|
|
Git repositories and Metadata.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Each Yocto Project release has a set of Yocto Linux kernel recipes,
|
||
|
|
whose Git repositories you can view in the Yocto
|
||
|
|
<ulink url='&YOCTO_GIT_URL;'>Source Repositories</ulink> under
|
||
|
|
the "Yocto Linux Kernel" heading.
|
||
|
|
New recipes for the release track the latest Linux kernel
|
||
|
|
upstream developments from
|
||
|
|
<ulink url='http://www.kernel.org'></ulink> and introduce
|
||
|
|
newly-supported platforms.
|
||
|
|
Previous recipes in the release are refreshed and supported for at
|
||
|
|
least one additional Yocto Project release.
|
||
|
|
As they align, these previous releases are updated to include the
|
||
|
|
latest from the Long Term Support Initiative (LTSI) project.
|
||
|
|
You can learn more about Yocto Linux kernels and LTSI in the
|
||
|
|
"<link linkend='kernel-big-picture'>Yocto Project Kernel Development and Maintenance</link>"
|
||
|
|
section.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Also included is a Yocto Linux kernel development recipe
|
||
|
|
(<filename>linux-yocto-dev.bb</filename>) should you want to work
|
||
|
|
with the very latest in upstream Yocto Linux kernel development and
|
||
|
|
kernel Metadata development.
|
||
|
|
<note>
|
||
|
|
For more on Yocto Linux kernels, see the
|
||
|
|
"<link linkend='kernel-big-picture'>Yocto Project Kernel Development and Maintenance</link>
|
||
|
|
section.
|
||
|
|
</note>
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The Yocto Project also provides a powerful set of kernel
|
||
|
|
tools for managing Yocto Linux kernel sources and configuration data.
|
||
|
|
You can use these tools to make a single configuration change,
|
||
|
|
apply multiple patches, or work with your own kernel sources.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
In particular, the kernel tools allow you to generate configuration
|
||
|
|
fragments that specify only what you must, and nothing more.
|
||
|
|
Configuration fragments only need to contain the highest level
|
||
|
|
visible <filename>CONFIG</filename> options as presented by the
|
||
|
|
Yocto Linux kernel <filename>menuconfig</filename> system.
|
||
|
|
Contrast this against a complete Yocto Linux kernel
|
||
|
|
<filename>.config</filename> file, which includes all the automatically
|
||
|
|
selected <filename>CONFIG</filename> options.
|
||
|
|
This efficiency reduces your maintenance effort and allows you
|
||
|
|
to further separate your configuration in ways that make sense for
|
||
|
|
your project.
|
||
|
|
A common split separates policy and hardware.
|
||
|
|
For example, all your kernels might support the
|
||
|
|
<filename>proc</filename> and <filename>sys</filename> filesystems,
|
||
|
|
but only specific boards require sound, USB, or specific drivers.
|
||
|
|
Specifying these configurations individually allows you to aggregate
|
||
|
|
them together as needed, but maintains them in only one place.
|
||
|
|
Similar logic applies to separating source changes.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
If you do not maintain your own kernel sources and need to make
|
||
|
|
only minimal changes to the sources, the released recipes provide a
|
||
|
|
vetted base upon which to layer your changes.
|
||
|
|
Doing so allows you to benefit from the continual kernel
|
||
|
|
integration and testing performed during development of the
|
||
|
|
Yocto Project.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
If, instead, you have a very specific Linux kernel source tree
|
||
|
|
and are unable to align with one of the official Yocto Linux kernel
|
||
|
|
recipes, an alternative exists by which you can use the Yocto
|
||
|
|
Project Linux kernel tools with your own kernel sources.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The remainder of this manual provides instructions for completing
|
||
|
|
specific Linux kernel development tasks.
|
||
|
|
These instructions assume you are comfortable working with
|
||
|
|
<ulink url='http://openembedded.org/wiki/Bitbake'>BitBake</ulink>
|
||
|
|
recipes and basic open-source development tools.
|
||
|
|
Understanding these concepts will facilitate the process of working
|
||
|
|
with the kernel recipes.
|
||
|
|
If you find you need some additional background, please be sure to
|
||
|
|
review and understand the following documentation:
|
||
|
|
<itemizedlist>
|
||
|
|
<listitem><para>
|
||
|
|
<ulink url='&YOCTO_DOCS_QS_URL;'>Yocto Project Quick Start</ulink>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
<ulink url='&YOCTO_DOCS_SDK_URL;#using-devtool-in-your-sdk-workflow'><filename>devtool</filename> workflow</ulink>
|
||
|
|
as described in the Yocto Project Application Development and
|
||
|
|
the Extensible Software Development Kit (eSDK) manual.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
The
|
||
|
|
"<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
|
||
|
|
section in the Yocto Project Development Tasks Manual.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
The
|
||
|
|
"<link linkend='kernel-modification-workflow'>Kernel Modification Workflow</link>"
|
||
|
|
section.
|
||
|
|
</para></listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Finally, while this document focuses on the manual creation of
|
||
|
|
recipes, patches, and configuration files, the Yocto Project
|
||
|
|
Board Support Package (BSP) tools are available to automate
|
||
|
|
this process with existing content and work well to create the
|
||
|
|
initial framework and boilerplate code.
|
||
|
|
For details on these tools, see the
|
||
|
|
"<ulink url='&YOCTO_DOCS_BSP_URL;#using-the-yocto-projects-bsp-tools'>Using the Yocto Project's BSP Tools</ulink>"
|
||
|
|
section in the Yocto Project Board Support Package (BSP) Developer's
|
||
|
|
Guide.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='kernel-modification-workflow'>
|
||
|
|
<title>Kernel Modification Workflow</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Kernel modification involves changing the Yocto Project kernel,
|
||
|
|
which could involve changing configuration options as well as adding
|
||
|
|
new kernel recipes.
|
||
|
|
Configuration changes can be added in the form of configuration
|
||
|
|
fragments, while recipe modification comes through the kernel's
|
||
|
|
<filename>recipes-kernel</filename> area in a kernel layer you create.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
This section presents a high-level overview of the Yocto Project
|
||
|
|
kernel modification workflow.
|
||
|
|
The illustration and accompanying list provide general information
|
||
|
|
and references for further information.
|
||
|
|
<imagedata fileref="figures/kernel-dev-flow.png"
|
||
|
|
width="9in" depth="5in" align="center" scalefit="1" />
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
<orderedlist>
|
||
|
|
<listitem><para>
|
||
|
|
<emphasis>Set Up Your Host Development System to Support
|
||
|
|
Development Using the Yocto Project:</emphasis>
|
||
|
|
See the
|
||
|
|
"<ulink url='&YOCTO_DOCS_QS_URL;#yp-resources'>Setting Up to Use the Yocto Project</ulink>"
|
||
|
|
section in the Yocto Project Quick Start for options on how
|
||
|
|
to get a build host ready to use the Yocto Project.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
<emphasis>Set Up Your Host Development System for Kernel Development:</emphasis>
|
||
|
|
It is recommended that you use <filename>devtool</filename>
|
||
|
|
and an extensible SDK for kernel development.
|
||
|
|
Alternatively, you can use traditional kernel development
|
||
|
|
methods with the Yocto Project.
|
||
|
|
Either way, there are steps you need to take to get the
|
||
|
|
development environment ready.</para>
|
||
|
|
|
||
|
|
<para>Using <filename>devtool</filename> and the eSDK requires
|
||
|
|
that you have a clean build of the image and that you are
|
||
|
|
set up with the appropriate eSDK.
|
||
|
|
For more information, see the
|
||
|
|
"<link linkend='getting-ready-to-develop-using-devtool'>Getting Ready to Develop Using <filename>devtool</filename></link>"
|
||
|
|
section.</para>
|
||
|
|
|
||
|
|
<para>Using traditional kernel development requires that you
|
||
|
|
have the kernel source available in an isolated local Git
|
||
|
|
repository.
|
||
|
|
For more information, see the
|
||
|
|
"<link linkend='getting-ready-for-traditional-kernel-development'>Getting Ready for Traditional Kernel Development</link>"
|
||
|
|
section.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
<emphasis>Make Changes to the Kernel Source Code if
|
||
|
|
applicable:</emphasis>
|
||
|
|
Modifying the kernel does not always mean directly
|
||
|
|
changing source files.
|
||
|
|
However, if you have to do this, you make the changes to the
|
||
|
|
files in the eSDK's Build Directory if you are using
|
||
|
|
<filename>devtool</filename>.
|
||
|
|
For more information, see the
|
||
|
|
"<link linkend='using-devtool-to-patch-the-kernel'>Using <filename>devtool</filename> to Patch the Kernel</link>"
|
||
|
|
section.</para>
|
||
|
|
|
||
|
|
<para>If you are using traditional kernel development, you
|
||
|
|
edit the source files in the kernel's local Git repository.
|
||
|
|
For more information, see the
|
||
|
|
"<link linkend='using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</link>"
|
||
|
|
section.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
<emphasis>Make Kernel Configuration Changes if
|
||
|
|
Applicable:</emphasis>
|
||
|
|
If your situation calls for changing the kernel's
|
||
|
|
configuration, you can use
|
||
|
|
<link linkend='using-menuconfig'><filename>menuconfig</filename></link>,
|
||
|
|
which allows you to interactively develop and test the
|
||
|
|
configuration changes you are making to the kernel.
|
||
|
|
Saving changes you make with <filename>menuconfig</filename>
|
||
|
|
updates the kernel's <filename>.config</filename> file.
|
||
|
|
<note><title>Warning</title>
|
||
|
|
Try to resist the temptation to directly edit an
|
||
|
|
existing <filename>.config</filename> file, which is
|
||
|
|
found in the Build Directory among the source code
|
||
|
|
used for the build.
|
||
|
|
Doing so, can produce unexpected results when the
|
||
|
|
OpenEmbedded build system regenerates the configuration
|
||
|
|
file.
|
||
|
|
</note>
|
||
|
|
Once you are satisfied with the configuration
|
||
|
|
changes made using <filename>menuconfig</filename>
|
||
|
|
and you have saved them, you can directly compare the
|
||
|
|
resulting <filename>.config</filename> file against an
|
||
|
|
existing original and gather those changes into a
|
||
|
|
<link linkend='creating-config-fragments'>configuration fragment file</link>
|
||
|
|
to be referenced from within the kernel's
|
||
|
|
<filename>.bbappend</filename> file.</para>
|
||
|
|
|
||
|
|
<para>Additionally, if you are working in a BSP layer
|
||
|
|
and need to modify the BSP's kernel's configuration,
|
||
|
|
you can use the
|
||
|
|
<ulink url='&YOCTO_DOCS_BSP_URL;#managing-kernel-patches-and-config-items-with-yocto-kernel'><filename>yocto-kernel</filename></ulink>
|
||
|
|
script as well as <filename>menuconfig</filename>.
|
||
|
|
The <filename>yocto-kernel</filename> script lets
|
||
|
|
you interactively set up kernel configurations.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
<emphasis>Rebuild the Kernel Image With Your Changes:</emphasis>
|
||
|
|
Rebuilding the kernel image applies your changes.
|
||
|
|
Depending on your target hardware, you can verify your changes
|
||
|
|
on actual hardware or perhaps QEMU.
|
||
|
|
</para></listitem>
|
||
|
|
</orderedlist>
|
||
|
|
The remainder of this developer's guide covers common tasks typically
|
||
|
|
used during kernel development, advanced Metadata usage, and Yocto Linux
|
||
|
|
kernel maintenance concepts.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
</chapter>
|
||
|
|
<!--
|
||
|
|
vim: expandtab tw=80 ts=4
|
||
|
|
-->
|