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bitbake: user-manual-metadata: Expand parsing process docuemtnation

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(Bitbake rev: 2596dd2b42c06ef258032356294cc345a6e25fed)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Richard Purdie
2014-01-18 14:32:51 +00:00
parent d6b8f746d4
commit 7b99bc04ac
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bitbake/doc/user-manual/user-manual-metadata.xml
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<para> For the 'deptask', 'rdeptask', 'depends', 'rdepends' and 'recrdeptask' flags please see the dependencies section.</para> <para> For the 'deptask', 'rdeptask', 'depends', 'rdepends' and 'recrdeptask' flags please see the dependencies section.</para>
</section> </section>
<section id='parsing-and-execution'>
<title>Parsing and Execution</title>
<section id='parsing-overview'> <section id='parsing-overview'>
<title>Parsing</title> <title>Parsing Overview</title>
<para>
BitBake parses configuration files, classes, and
<filename>.bb</filename> files.
</para>
<para>
The first thing BitBake does is look for the
<filename>bitbake.conf</filename> file.
This file resides in the within the <filename>conf/</filename>
directory.
BitBake finds it by examining its <filename>BBPATH</filename>
environment variable and looking for the
<filename>conf/</filename> directory.
</para>
<para>
The <filename>bitbake.conf</filename> file lists other configuration
files to include from a <filename>conf/</filename> directory below the
directories listed in <filename>BBPATH</filename>.
In general, the most important configuration file from a user's perspective
is <filename>local.conf</filename>, which contains a user's
customized settings for the build environment.
Other notable configuration files are the distribution configuration
file (set by the <filename>DISTRO</filename> variable) and the machine
configuration file (set by the <filename>MACHINE</filename> variable).
The <filename>DISTRO</filename> and <filename>MACHINE</filename> BitBake
environment variables are both usually set in the
<filename>local.conf file</filename>.
Valid distribution configuration files are available
in the <filename>conf/distro/</filename> directory and valid machine
configuration files in the <filename>meta/conf/machine/</filename>
directory.
Within the <filename>conf/machine/include/</filename> directory are
various <filename>tune-*.inc</filename> configuration files
that provide common "tuning" settings specific to and shared between
particular architectures and machines.
</para>
<para>
After parsing of the configuration files, some standard classes are
included.
The <filename>base.bbclass</filename> file
is always included.
Other classes that are specified in the configuration using the
<filename>INHERIT</filename> variable are also included.
Class files are searched for in a classes subdirectory under
the paths in <filename>BBPATH</filename> in the same way as
configuration files.
</para>
<para>
After classes are included, the variable
<filename>BBFILES</filename> is set, usually in
<filename>local.conf</filename>, and defines the list of
places to search for <filename>.bb</filename> files.
Adding extra content to <filename>BBFILES</filename> is best
achieved through the use of BitBake layers as described in the
Layers section below.
</para>
<para>
BitBake parses each <filename>.bb</filename> file in
<filename>BBFILES</filename> and stores the values of various
variables.
In summary, for each <filename>.bb</filename> file the configuration
plus the base class of variables are set, followed by the data in the
<filename>.bb</filename> file itself, followed by any inherit commands
that <filename>.bb</filename> file might contain.
</para>
<para>
Because parsing <filename>.bb</filename> files is a time consuming
process, a cache is kept to speed up subsequent parsing.
This cache is invalid if the timestamp of the
<filename>.bb</filename> file itself changes, or if the timestamps of
any of the include, configuration files or class files on which
the <filename>.bb</filename> file depends change.
</para>
</section>
<section id='configiguration-files'> <section id='configiguration-files'>
<title>Configuration files</title> <title>Configuration files</title>
<para> <para>
The first kind of metadata in BitBake is configuration metadata. The first kind of metadata in BitBake is configuration metadata.
This metadata is global, and therefore affects all packages and This metadata is global, and therefore affects all packages and