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documentation: dev-manual - Updates to configuring Kernel section

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Eliminated the section A.2, which had an example of how to use
menuconfig in the kerenl example appendix.  The information is
now merged into the similar section in Chapter 4 "Common
Tasks."  It was decided that the Appendix A examples in the
manual were too detailed for a general development guide.

(From yocto-docs rev: f88ec421b257657f02cc0f132ec2580c17f07cef)

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
2012-10-08 08:49:23 -07:00
committed by Richard Purdie
parent d38325cbca
commit 274095d4c2
2 changed files with 81 additions and 300 deletions
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documentation/dev-manual/dev-manual-common-tasks.xml
+81 -7
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@@ -1352,6 +1352,8 @@
<para>
The easiest way to define kernel configurations is to set them through the
<filename>menuconfig</filename> tool.
This tool provides an interactive method with which
to set kernel configurations.
For general information on <filename>menuconfig</filename>, see
<ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
</para>
@@ -1359,6 +1361,9 @@
<para>
To use the <filename>menuconfig</filename> tool in the Yocto Project development
environment, you must build the tool using BitBake.
Thus, the environment must be set up using the <filename>&OE_INIT_FILE;</filename>
script found in the
<link linkend='build-directory'>Build Directory</link>.
The following commands build and invoke <filename>menuconfig</filename> assuming the
source directory top-level folder is <filename>~/poky</filename>:
<literallayout class='monospaced'>
@@ -1367,17 +1372,86 @@
$ bitbake linux-yocto -c menuconfig
</literallayout>
Once <filename>menuconfig</filename> comes up, its standard interface allows you to
examine and configure all the kernel configuration parameters.
Once you have made your changes, simply exit the tool and save your changes to
interactively examine and configure all the kernel configuration parameters.
After making your changes, simply exit the tool and save your changes to
create an updated version of the <filename>.config</filename> configuration file.
</para>
<para>
For an example that shows how to change a specific kernel option
using <filename>menuconfig</filename>, see the
"<link linkend='changing-the-config-smp-configuration-using-menuconfig'>Changing
the <filename>CONFIG_SMP</filename> Configuration Using <filename>menuconfig</filename></link>"
section.
Consider an example that configures the <filename>linux-yocto-3.4</filename>
kernel.
The OpenEmbedded build system recognizes this kernel as
<filename>linux-yocto</filename>.
Thus, the following commands from the shell in which you previously sourced the
environment initialization script cleans the shared state cache and the
<ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
directory and then builds and launches <filename>menuconfig</filename>:
<literallayout class='monospaced'>
$ bitbake linux-yocto -c menuconfig
</literallayout>
</para>
<para>
Once <filename>menuconfig</filename> launches, you use the interface
to navigate through the selections to find the configuration settings in
which you are interested.
For example, consider the <filename>CONFIG_SMP</filename> configuration setting.
You can find it at <filename>Processor Type and Features</filename> under
the configuration selection <filename>Symmetric Multi-processing Support</filename>.
After highlighting the selection, you can use the arrow keys to select or deselect
the setting.
When you are finished with all your selections, exit out and save them.
</para>
<para>
Saving the selections updates the <filename>.config</filename> configuration file.
This is the file that the OpenEmbedded build system uses to configure the
kernel during the build.
You can find and examine this file in the build directory in
<filename>tmp/work/</filename>.
The actual <filename>.config</filename> is located in the area where the
specific kernel is built.
For example, if you were building a Linux Yocto kernel based on the
Linux 3.4 kernel and you were building a QEMU image targeted for
<filename>x86</filename> architecture, the
<filename>.config</filename> file would be located here:
<literallayout class='monospaced'>
~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.4.11+git1+84f...
...656ed30-r1/linux-qemux86-standard-build
</literallayout>
<note>
The previous example directory is artificially split and many of the characters
in the actual filename are omitted in order to make it more readable.
Also, depending on the kernel you are using, the exact pathname
for <filename>linux-yocto-3.4...</filename> might differ.
</note>
</para>
<para>
Within the <filename>.config</filename> file, you can see the kernel settings.
For example, the following entry shows that symmetric multi-processor support
is not set:
<literallayout class='monospaced'>
# CONFIG_SMP is not set
</literallayout>
</para>
<para>
A good method to isolate changed configurations is to use a combination of the
<filename>menuconfig</filename> tool and simple shell commands.
Before changing configurations with <filename>menuconfig</filename>, copy the
existing <filename>.config</filename> and rename it to something else,
use <filename>menuconfig</filename> to make
as many changes an you want and save them, then compare the renamed configuration
file against the newly created file.
You can use the resulting differences as your base to create configuration fragments
to permanently save in your kernel layer.
<note>
Be sure to make a copy of the <filename>.config</filename> and don't just
rename it.
The build system needs an existing <filename>.config</filename>
from which to work.
</note>
</para>
</section>