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kernel-dev: Added new "Adding Recipe-Space Kernel Features" section.

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Fixes [YOCTO #4047]

I added a new section describing how to add kernel features
from within a kernel recipe through the KERNEL_FEATURES
variable and the SRC_URI statement.

(From yocto-docs rev: d30925c65e3f49b2ba481f1e7f9cac98fe86f6af)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark
2016-03-31 14:42:10 -07:00
committed by Richard Purdie
parent f30bfe990a
commit 23dbf81edd
1 changed files with 122 additions and 0 deletions
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documentation/kernel-dev/kernel-dev-common.xml
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@@ -1032,6 +1032,128 @@
</para> </para>
</section> </section>
</section> </section>
<section id='adding-recipe-space-kernel-features'>
<title>Adding Recipe-Space Kernel Features</title>
<para>
You can add kernel features in the
<link linkend='recipe-space-metadata'>recipe-space</link> by
using the
<ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
variable along with specifying the <filename>.scc</filename> file
path on the
<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
statement.
When you add features using this method, the OpenEmbedded build
system checks to be sure the features are present.
If the features are not present, the build stops.
Kernel features are the last elements processed for configuring
and patching the kernel.
Therefore, adding features in this manner is a way
to enforce that specific features are present, and enabled,
without needing to do a full audit of any other layer's additions
to the <filename>SRC_URI</filename> statement.
</para>
<para>
You add a kernel feature by providing the feature as part of the
<filename>KERNEL_FEATURES</filename> variable and by providing the
path to the feature's <filename>.scc</filename> file, which is
relative to the root of the kernel Metadata.
The OpenEmbedded build system searches all forms of kernel
Metadata on the <filename>SRC_URI</filename> statement regardless
of whether the Metadata is in the "kernel-cache", system kernel
Metadata, or a recipe-space Metadata.
See the
"<link linkend='kernel-metadata-location'>Kernel Metadata Location</link>"
section for additional information.
</para>
<para>
When you specify the feature's <filename>.scc</filename> file
on the <filename>SRC_URI</filename> statement, the OpenEmbedded
build system adds the directory of that
<filename>.scc</filename> file, and all its subdirectories,
to the kernel feature search path.
Because subdirectories are searched, you can reference a single
<filename>.scc</filename> file in the
<filename>SRC_URI</filename> statement to reference multiple kernel
features.
</para>
<para>
Consider the following example that adds the "test.scc" feature
to the build.
<orderedlist>
<listitem><para>
Create a <filename>.scc</filename> file and locate it
just as you would any other patch file,
<filename>.cfg</filename> file, or fetcher item
you specify in the <filename>SRC_URI</filename>
statement.
<note><title>Notes</title>
<itemizedlist>
<listitem><para>
The directory you use for the
<filename>.scc</filename> must be added to the
fetcher search directory just as you would,
for example, if you were adding a
<filename>.patch</filename> file.
</para></listitem>
<listitem><para>
You can create additional
<filename>.scc</filename> files beneath the
directory that contains the file you are
adding.
All subdirectories are searched during the
build as potential feature directories.
</para></listitem>
</itemizedlist>
</note>
Continuing with the example, suppose the "test.scc"
feature you are adding has a
<filename>test.scc</filename> file in the following
directory:
<literallayout class='monospaced'>
<replaceable>my_recipe</replaceable>
|
+-linux-yocto
|
+-test.cfg
+-test.scc
</literallayout>
In this example, the <filename>linux-yocto</filename>
directory has both the feature
<filename>test.scc</filename> file and a similarly
named configuration fragment file
<filename>test.cfg</filename>.
</para></listitem>
<listitem><para>
Add the <filename>.scc</filename> file to the
recipe's <filename>SRC_URI</filename> statement:
<literallayout class='monospaced'>
SRC_URI_append = " file://test.scc"
</literallayout>
The leading space before the path is important as the
path is appended to the existing path.
</para></listitem>
<listitem><para>
Specify the feature as a kernel feature:
<literallayout class='monospaced'>
KERNEL_FEATURES_append = " test.scc"
</literallayout>
The OpenEmbedded build system processes the kernel feature
when it builds the kernel.
<note>
If other features are contained below "test.scc",
then their directories are relative to the directory
containing the <filename>test.scc</filename> file.
</note>
</para></listitem>
</orderedlist>
</para>
</section>
</chapter> </chapter>
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