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documentation/kernel-manual/kernel-concepts.xml: New kernel section 

This section is the first attempt at a new, high-level discussion
of Linux Yocto Kernel configuration.  The section is supposed to
introduce the concepts only and leave the "How to" stuff for other
areas of the documentation.  I have thrown this section out to the
Yocto Projects Discussion list for feedback.  It will change.

(From yocto-docs rev: 8d0eabe88e50d1a16fda4b845267c4ee240ce540)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2012-02-07 15:47:22 -06:00 committed by Richard Purdie
parent 3ecda3fb02
commit 70ae82a161
1 changed files with 49 additions and 61 deletions
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documentation/kernel-manual/kernel-concepts.xml
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@ -306,75 +306,63 @@
<section id='kernel-configuration'>
<title>Kernel Configuration</title>
<para>
Kernel configuration, along with kernel features, defines how a kernel image is
built.
Kernel configuration, along with kernel features, defines how a Linux Yocto
kernel image is built.
Through configuration settings, you can customize a Linux Yocto kernel to be
specific to particular hardware.
For example, you can specify sound support or networking support.
This section describes basic concepts behind Kernel configuration within the
Yocto Project.
Yocto Project and references you to other areas for specific configuration
applications.
</para>
<para>
WRITER NOTES:
</para>
<para>
A package consists of tasks and BitBake, in most cases, behaves by fetching, unpacking,
patching, configuring, compiling, installing, packaging, writing, and building.
Configuration is part of the standard BitBake process.
<para>
Explain how <filename>.config</filename> is used when the kernel image is built.
Describe the role of <filename>menuconfig</filename> regarding the
<filename>.config</filename>.
Locate the <filename>.config</filename> for the user.
Not recommended to edit the <filename>.config</filename> file directly.
You can use BitBake to build and invoke the <filename>menuconfig</filename>
tool.
</para>
<para>
Introduce the configuration fragment.
Step through the life of a configuration fragment from idea or need to
change something in the kernel to how it is used when the kernel image is built.
Describe how configuration fragments are created and where they live.
Make sure the syntax of configuration fragments is understood.
</para>
<para>
Talk in general how the user creates a configuration fragment.
Point to example B.2 of the YP Development Manual as a way to use
<filename>menuconfig</filename>.
</para>
<para>
The tool <filename>menuconfig</filename> allows you to choose the features of the
Linux Yocto kernel that will be compiled.
This tool is a convenient method to alter the <filename>.config</filename> file.
You can use a simple interface to scroll through kernel features and disable
and enable configruation variables.
When you save your changes, the contents of the <filename>.config</filename>
are altered.
You can get general information on <filename>menuconfig</filename> at
<ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
</para>
<para>
The Yocto Project employs <filename>menuconfig</filename> by invoking it through
BitBake as follows after making sure the environment setup script has been sourced:
<literallayout class='monospaced'>
Conceptually, Linux Yocto kernel configuration occurs similarly to that needed for any
Linux kernel.
The Linux Yocto kernel build process uses a <filename>.config</filename>, which
is created through the Linux Kernel Coinfiguration (LKC) tool.
You can directly set various configurations in the
<filename>.config</filename> file by using the <filename>menuconfig</filename>
tool as built by BitBake.
You can also affect the configurations in the file by using configuration fragments.
<note>
It is not recommended that you edit the <filename>.config</filename> file directly.
</note>
Here is are some brief descriptions of the ways you can affect the
<filename>.config</filename> file:
<itemizedlist>
<listitem><para><emphasis>The <filename>menuconfig</filename> Tool:</emphasis>
One of many front-ends that allows you to define kernel configurations.
Some others are <filename>make config</filename>,
<filename>make nconfig</filename>, and <filename>make gconfig</filename>.
In the Yocto Project environment, you must use BitBake to build the
<filename>menuconfig</filename> tool before you can use it to define
configurations:
<literallayout class='monospaced'>
$ bitbake linux-yocto -c menuconfig
</literallayout>
You can see how <filename>menuconfig</filename> is used to change a simple
kernel configuration in the
"<ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#changing-the-config-smp-configuration-using-menuconfig'>Changing the&nbsp;&nbsp;<filename>CONFIG_SMP</filename>
Configuration Using&nbsp;&nbsp;<filename>menuconfig</filename></ulink>" section of
The Yocto Project Development Manual.
</para>
<para>
END WRITER NOTES
</literallayout>
After the tool is built, you can interact with it normally.
You can see how <filename>menuconfig</filename> is used to change a simple
kernel configuration in the
"<ulink url='http://www.yoctoproject.org/docs/latest/dev-manual/dev-manual.html#changing-the-config-smp-configuration-using-menuconfig'>Changing the&nbsp;&nbsp;<filename>CONFIG_SMP</filename> Configuration Using&nbsp;&nbsp;<filename>menuconfig</filename></ulink>"
section of The Yocto Project Development Manual.
For general information on <filename>menuconfig</filename>, see
<ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
</para></listitem>
<listitem><para><emphasis>Configuration Fragments:</emphasis> A file with a
list of kernel options just as they would appear syntactically in the
<filename>.config</filename> file.
Configuration fragments are typically logical groupings and are assembled
by the Yocto Project build system to produce input used by the LKC
that ultimately generates the <filename>.config</filename> file.</para>
<para>The
<filename><ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-KERNEL_FEATURES'>KERNEL_FEATURES</ulink></filename>
variable can be used to list configuration fragments.
For further discussion on applying configuration fragments, see the
"<ulink url='http://www.yoctoproject.org/docs/latest/bsp-guide/bsp-guide.html#linux-kernel-configuration'>Linux Kernel Configuration</ulink>"
section in the Yocto Project Board Support Package (BSP) Guide.
</para></listitem>
</itemizedlist>
</para>
</section>