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bitbake: user-manual-metadata.xml: Edits to the "Sharing Functionality" section.
Applied some review edits from Paul to the section. (Bitbake rev: 56321b18808f5ed932543d907b9ebcfbf4420233) 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
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Richard Purdie
Richard Purdie
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@@ -484,49 +484,132 @@
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</section>
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</section>
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<section id='inheritance'>
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<title>Inheritance</title>
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<section id='sharing-functionality'>
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<title>Sharing Functionality</title>
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<section id='inheritance-directive'>
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<title>Inheritance Directive</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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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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</para>
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<note>
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This is only supported in <filename>.bb</filename> and
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<filename>.bbclass</filename> files.
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</note>
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<para>
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This section presents the mechanisms BitBake provides to
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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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</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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The inherit directive is a means of specifying what classes
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of functionality your <filename>.bb</filename> requires.
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It is a rudimentary form of inheritance.
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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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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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</section>
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<section id='inherit-directive'>
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<title><filename>inherit</filename> Directive</title>
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<para>
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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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</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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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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that into a bbclass for your packages to make use of.
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A given bbclass is located by searching for classes/filename.bbclass
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in <filename>BBPATH</filename>, where filename is what you inherited.
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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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<literallayout class='monospaced'>
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inherit siteinfo
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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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in <filename>BBPATH</filename>.
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</para>
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</section>
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<section id='inclusion-directive'>
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<title>Inclusion Directive</title>
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<section id='include-directive'>
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<title><filename>include</filename> Directive</title>
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<para>
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BitBake understands the <filename>include</filename>
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directive.
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This directive causes BitBake to parse whatever file you specify,
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and insert it at that location, which is not unlike Make.
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However, if the path specified on the include line is a
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relative path, BitBake will locate the first one it can find
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within <filename>BBPATH</filename>.
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and to insert that file at that location.
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The directive is much like Make except that if the path specified
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on the include 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 include some
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self-test files:
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<literallayout class='monospaced'>
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include test_recipe.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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produce an error when the file cannot be found.
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Consequently, it is recommended that if the file you
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are including is expected to exist, you should use
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<link linkend='require-inclusion'><filename>require</filename></link>
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instead of <filename>include</filename>.
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Doing so makes sure that an error is produced if the
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file cannot be found.
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</note>
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</para>
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</section>
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<section id='requiring-inclusion'>
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<title>Requiring Inclusion</title>
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<section id='require-inclusion'>
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<title><filename>require</filename> Directive</title>
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<para>
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In contrast to the include directive, require will raise a
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ParseError if the file to be included cannot
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BitBake understands the <filename>require</filename>
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directive.
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This directive behaves just like the
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<filename>include</filename> directive with the exception that
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BitBake raises a parsing error if the file to be included cannot
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be found.
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Otherwise it will behave just like the include directive.
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Thus, any file you require is inserted into the file that is
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being parsed at the location of the directive.
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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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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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<literallayout class='monospaced'>
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require test_recipe.inc
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</literallayout>
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</para>
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</section>
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@@ -534,9 +617,20 @@
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<title><filename>INHERIT</filename> Configuration Directive</title>
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<para>
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When creating a configuration file (<filename>.conf</filename>),
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you can use the <filename>INHERIT</filename> directive to
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inherit a class.
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BitBake only supports this directive when used within
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a configuration file.
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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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<literallayout class='monospaced'>
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INHERIT += "multilib_global"
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</literallayout>
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This configuration directive causes the named class to be inherited
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at this point during parsing.
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This variable is only valid in configuration files.
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at the point of the directive during parsing.
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</para>
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</section>
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</section>
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