bitbake: user-manual-metadata.xml: Edits to "Sharing Functionality"
Applied some review edits from Paul to the section. (Bitbake rev: f4dc71a3ff2c7f2ca6093b751883a1244f8d3847) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark
Richard Purdie
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@ -488,15 +488,16 @@
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<title>Sharing Functionality</title>
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<para>
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BitBake allows for metadata sharing through include files and
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class files (<filename>.bbclass</filename>).
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BitBake allows for metadata sharing through include files
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(<filename>.inc</filename>) and class files
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(<filename>.bbclass</filename>).
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For example, suppose you have a piece of common functionality
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such as a task definition that you want to share between
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more than one recipe.
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In this case, creating a <filename>.bbclass</filename>
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file that contains the common functionality and uses the
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<filename>inherit</filename> directive would be a common
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way to share the task.
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file that contains the common functionality and then using
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the <filename>inherit</filename> directive in your recipes to
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inherit the class would be a common way to share the task.
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</para>
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<para>
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@ -504,19 +505,24 @@
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allow you to share functionality between recipes.
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Specifically, the mechanisms include <filename>include</filename>,
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<filename>inherit</filename>, <filename>INHERIT</filename>, and
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<filename>require</filename> statements.
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<filename>require</filename> directives.
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</para>
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<section id='locating-include-and-class-files'>
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<title>Locating Include and Class Files</title>
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<para>
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BitBake uses the <filename>BBPATH</filename> variable
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to locate needed class and configuration files.
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BitBake uses the
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>
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variable to locate needed include and class files.
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The <filename>BBPATH</filename> variable is analogous to
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the environment variable <filename>PATH</filename>.
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Use of <filename>BBPATH</filename> is specific to the build
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environment (e.g. Yocto Project, OpenEmbedded, and so forth).
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</para>
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<para>
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In order for include and class files to be found by BitBake,
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they need to be located in a "classes" subdirectory that can
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be found in <filename>BBPATH</filename>.
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</para>
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</section>
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@ -527,27 +533,36 @@
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When writing a recipe or class file, you can use the
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<filename>inherit</filename> directive to inherit the
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functionality of a class (<filename>.bbclass</filename>).
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BitBake only supports this directive when used within these
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two types of files (i.e. <filename>.bb</filename> and
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<filename>.bbclass</filename> files).
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BitBake only supports this directive when used within recipe
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and class files (i.e. <filename>.bb</filename> and
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<filename>.bbclass</filename>).
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</para>
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<para>
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The <filename>inherit</filename> directive is a rudimentary
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means of specifying what classes of functionality your
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recipe requires.
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recipes require.
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For example, you can easily abstract out the tasks involved in
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building a package that uses Autoconf and Automake and put
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those tasks into a class file that can be used by your package.
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As an example, an <filename>autotools.bbclass</filename> file
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could use the following directive to inherit needed
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site information:
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</para>
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<para>
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As an example, your recipes could use the following directive
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to inherit an <filename>autotools.bbclass</filename> file.
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The class file would contain common functionality for using
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Autotools that could be shared across recipes:
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<literallayout class='monospaced'>
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inherit siteinfo
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inherit autotools
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</literallayout>
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In this case, BitBake would search for the directory
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<filename>classes/siteinfo.bbclass</filename>
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<filename>classes/autotools.bbclass</filename>
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in <filename>BBPATH</filename>.
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<note>
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You can override any values and functions of the
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inherited class within your recipe by doing so
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after the "inherit" statement.
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</note>
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</para>
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</section>
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@ -566,9 +581,9 @@
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<para>
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As an example, suppose you needed a recipe to include some
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self-test files:
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self-test definitions:
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<literallayout class='monospaced'>
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include test_recipe.inc
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include test_defs.inc
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</literallayout>
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<note>
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The <filename>include</filename> directive does not
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@ -598,17 +613,28 @@
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</para>
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<para>
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Similar to how BitBake uses <filename>include</filename>,
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Similar to how BitBake uses
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<link linkend='include-directive'><filename>include</filename></link>,
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if the path specified
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on the require line is a relative path, BitBake locates
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the first file it can find within <filename>BBPATH</filename>.
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</para>
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<para>
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As an example, suppose you needed a recipe to require some
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self-test files:
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As an example, suppose you have two versions of a recipe
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(e.g. <filename>foo_1.2.2.bb</filename> and
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<filename>foo_2.0.0.bb</filename>) where
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each version contains some identical functionality that could be
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shared.
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You could create an include file named <filename>foo.inc</filename>
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that contains the common definitions needed to build "foo".
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You need to be sure <filename>foo.inc</filename> is located in the
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same directory as your two recipe files as well.
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Once these conditions are set up, you can share the functionality
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using a <filename>require</filename> directive from within each
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recipe:
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<literallayout class='monospaced'>
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require test_recipe.inc
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require foo.inc
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</literallayout>
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</para>
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</section>
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@ -625,12 +651,25 @@
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</para>
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<para>
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Suppose you needed to inherit a multilib global class.
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As an example, suppose you needed to inherit a class
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file called <filename>abc.bbclass</filename> from a
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configuration file as follows:
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<literallayout class='monospaced'>
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INHERIT += "multilib_global"
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INHERIT += "abc"
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</literallayout>
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This configuration directive causes the named class to be inherited
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at the point of the directive during parsing.
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This configuration directive causes the named
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class to be inherited at the point of the directive
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during parsing.
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As with the <filename>inherit</filename> directive, the
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<filename>.bbclass</filename> file must be located in a
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"classes" subdirectory in one of the directories specified
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in <filename>BBPATH</filename>.
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<note>
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Because <filename>.conf</filename> files are parsed
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first during BitBake's execution, using
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<filename>INHERIT</filename> to inherit a class effectively
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inherits the class globally (i.e. for all recipes).
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</note>
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</para>
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</section>
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</section>
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