kernel-dev: Added new "Adding Recipe-Space Kernel Features" section.
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>
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Scott Rifenbark
Richard Purdie
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@ -1032,6 +1032,128 @@
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</para>
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</section>
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</section>
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<section id='adding-recipe-space-kernel-features'>
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<title>Adding Recipe-Space Kernel Features</title>
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<para>
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You can add kernel features in the
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<link linkend='recipe-space-metadata'>recipe-space</link> by
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using the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_FEATURES'><filename>KERNEL_FEATURES</filename></ulink>
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variable along with specifying the <filename>.scc</filename> file
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path on the
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<ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
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statement.
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When you add features using this method, the OpenEmbedded build
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system checks to be sure the features are present.
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If the features are not present, the build stops.
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Kernel features are the last elements processed for configuring
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and patching the kernel.
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Therefore, adding features in this manner is a way
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to enforce that specific features are present, and enabled,
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without needing to do a full audit of any other layer's additions
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to the <filename>SRC_URI</filename> statement.
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</para>
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<para>
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You add a kernel feature by providing the feature as part of the
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<filename>KERNEL_FEATURES</filename> variable and by providing the
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path to the feature's <filename>.scc</filename> file, which is
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relative to the root of the kernel Metadata.
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The OpenEmbedded build system searches all forms of kernel
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Metadata on the <filename>SRC_URI</filename> statement regardless
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of whether the Metadata is in the "kernel-cache", system kernel
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Metadata, or a recipe-space Metadata.
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See the
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"<link linkend='kernel-metadata-location'>Kernel Metadata Location</link>"
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section for additional information.
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</para>
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<para>
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When you specify the feature's <filename>.scc</filename> file
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on the <filename>SRC_URI</filename> statement, the OpenEmbedded
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build system adds the directory of that
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<filename>.scc</filename> file, and all its subdirectories,
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to the kernel feature search path.
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Because subdirectories are searched, you can reference a single
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<filename>.scc</filename> file in the
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<filename>SRC_URI</filename> statement to reference multiple kernel
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features.
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</para>
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<para>
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Consider the following example that adds the "test.scc" feature
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to the build.
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<orderedlist>
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<listitem><para>
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Create a <filename>.scc</filename> file and locate it
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just as you would any other patch file,
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<filename>.cfg</filename> file, or fetcher item
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you specify in the <filename>SRC_URI</filename>
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statement.
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<note><title>Notes</title>
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<itemizedlist>
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<listitem><para>
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The directory you use for the
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<filename>.scc</filename> must be added to the
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fetcher search directory just as you would,
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for example, if you were adding a
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<filename>.patch</filename> file.
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</para></listitem>
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<listitem><para>
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You can create additional
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<filename>.scc</filename> files beneath the
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directory that contains the file you are
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adding.
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All subdirectories are searched during the
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build as potential feature directories.
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</para></listitem>
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</itemizedlist>
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</note>
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Continuing with the example, suppose the "test.scc"
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feature you are adding has a
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<filename>test.scc</filename> file in the following
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directory:
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<literallayout class='monospaced'>
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<replaceable>my_recipe</replaceable>
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+-linux-yocto
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+-test.cfg
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+-test.scc
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</literallayout>
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In this example, the <filename>linux-yocto</filename>
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directory has both the feature
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<filename>test.scc</filename> file and a similarly
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named configuration fragment file
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<filename>test.cfg</filename>.
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</para></listitem>
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<listitem><para>
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Add the <filename>.scc</filename> file to the
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recipe's <filename>SRC_URI</filename> statement:
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<literallayout class='monospaced'>
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SRC_URI_append = " file://test.scc"
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</literallayout>
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The leading space before the path is important as the
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path is appended to the existing path.
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</para></listitem>
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<listitem><para>
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Specify the feature as a kernel feature:
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<literallayout class='monospaced'>
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KERNEL_FEATURES_append = " test.scc"
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</literallayout>
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The OpenEmbedded build system processes the kernel feature
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when it builds the kernel.
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<note>
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If other features are contained below "test.scc",
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then their directories are relative to the directory
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containing the <filename>test.scc</filename> file.
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</note>
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</para></listitem>
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</orderedlist>
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</para>
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</section>
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</chapter>
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<!--
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vim: expandtab tw=80 ts=4
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