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documentation/poky-ref-manual/ref-classes.xml: Scrubbed for Poky 

I changed the "Poky" references to "the Yocto Project" and performed
general edits where necessary.

(From yocto-docs rev: a7ef3e7d5c792bde5231b9302e614cb7b5db81b7)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2011-08-19 12:01:54 -07:00 committed by Richard Purdie
parent 32a860851c
commit 95ef8d7a2e
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documentation/poky-ref-manual/ref-classes.xml
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@ -6,21 +6,21 @@
<para>
Class files are used to abstract common functionality and share it amongst multiple
<filename>.bb</filename> files. Any metadata usually found in a
<filename>.bb</filename> file can also be placed in a class
file. Class files are identified by the extension
<filename>.bbclass</filename> and are usually placed
<filename>.bb</filename> files.
Any metadata usually found in a <filename>.bb</filename> file can also be placed in a class
file.
Class files are identified by the extension <filename>.bbclass</filename> and are usually placed
in a <filename>classes/</filename> directory beneath the
<filename>meta*/</filename> directory or the directory pointed
by BUILDDIR (e.g. <filename>build/</filename>)in the same way as
<filename>.conf</filename> files in the <filename
class="directory">conf</filename> directory. Class files are searched for
in BBPATH in the same was as <filename>.conf</filename> files too.
<filename>meta*/</filename> directory found in the Yocto Project file's area
Class files can also be pointed to by BUILDDIR (e.g. <filename>build/</filename>)in the same way as
<filename>.conf</filename> files in the <filename>conf</filename> directory.
Class files are searched for in <filename>BBPATH</filename>
using the same method by which <filename>.conf</filename> files are searched.
</para>
<para>
In most cases inheriting the class is enough to enable its features, although
for some classes you may need to set variables and/or override some of the
for some classes you might need to set variables or override some of the
default behaviour.
</para>
@ -29,13 +29,14 @@
<para>
The base class is special in that every <filename>.bb</filename>
file inherits it automatically. It contains definitions of standard basic
file inherits it automatically.
This class contains definitions for standard basic
tasks such as fetching, unpacking, configuring (empty by default), compiling
(runs any Makefile present), installing (empty by default) and packaging
(empty by default). These are often overridden or extended by other classes
such as <filename>autotools.bbclass</filename> or
<filename>package.bbclass</filename>. The class also contains some commonly
used functions such as <filename>oe_runmake</filename>.
(runs any <filename>Makefile</filename> present), installing (empty by default) and packaging
(empty by default).
These classes are often overridden or extended by other classes
such as <filename>autotools.bbclass</filename> or <filename>package.bbclass</filename>.
The class also contains some commonly used functions such as <filename>oe_runmake</filename>.
</para>
</section>
@ -43,84 +44,71 @@
<title>Autotooled Packages - <filename>autotools.bbclass</filename></title>
<para>
Autotools (autoconf, automake, libtool) bring standardization.
Autotools (<filename>autoconf</filename>, <filename>automake</filename>,
and <filename>libtool</filename>) bring standardization.
This class defines a set of tasks (configure, compile etc.) that
work for all autotooled packages.
work for all Autotooled packages.
It should usually be enough to define a few standard variables as documented in the
<link linkend='usingpoky-extend-addpkg-autotools'>simple autotools
example</link> section and then simply "inherit autotools".
This class can also work with software that emulates autotools.
<link linkend='usingpoky-extend-addpkg-autotools'>Autotooled Package</link> section
and then simply <filename>inherit autotools</filename>.
This class can also work with software that emulates Autotools.
</para>
<para>
It's useful to have some idea of how the tasks defined by this class work
and what they do behind the scenes.
<itemizedlist>
<listitem><para><filename>do_configure</filename> &dash; regenerates the
configure script (using <filename>autoreconf</filename>) and then launches it
with a standard set of arguments used during cross-compilation.
You can pass additional parameters to <filename>configure</filename> through the
<filename><link linkend='var-EXTRA_OECONF'>EXTRA_OECONF</link></filename> variable.
</para></listitem>
<listitem><para><filename>do_compile</filename> &dash; runs <filename>make</filename> with
arguments that specify the compiler and linker.
You can pass additional arguments through
the <filename><link linkend='var-EXTRA_OEMAKE'>EXTRA_OEMAKE</link></filename> variable.
</para></listitem>
<listitem><para><filename>do_install</filename> &dash; runs <filename>make install</filename>
and passes a DESTDIR option, which takes its value from the standard
<filename><link linkend='var-DESTDIR'>DESTDIR</link></filename> variable.
</para></listitem>
</itemizedlist>
</para>
<itemizedlist>
<listitem>
<para>
<filename>do_configure</filename> &dash; regenerates the configure script (using autoreconf)
and then launches it with a standard set of arguments used during
cross-compilation.
You can pass additional parameters to
<filename>configure</filename> through the
<glossterm><link linkend='var-EXTRA_OECONF'>EXTRA_OECONF</link></glossterm> variable.
</para>
</listitem>
<listitem>
<para>
<filename>do_compile</filename> &dash; runs <filename>make</filename> with
arguments that specify the compiler and linker.
You can pass additional arguments through
the <glossterm><link linkend='var-EXTRA_OEMAKE'>EXTRA_OEMAKE</link>
</glossterm> variable.
</para>
</listitem>
<listitem>
<para>
<filename>do_install</filename> &dash; runs <filename>make install</filename>
and passes a <filename>DESTDIR</filename>
option, which takes its value from the standard
<glossterm><link linkend='var-DESTDIR'>DESTDIR</link></glossterm> variable.
</para>
</listitem>
</itemizedlist>
</section>
<section id='ref-classes-update-alternatives'>
<title>Alternatives - <filename>update-alternatives.bbclass</filename></title>
<para>
Several programs can fulfill the same or similar function and
be installed with the same name.
For example, the <filename>ar</filename>
command is available from the "busybox", "binutils" and "elfutils" packages.
Several programs can fulfill the same or similar function and be installed with the same name.
For example, the <filename>ar</filename> command is available from the
<filename>busybox</filename>, <filename>binutils</filename> and
<filename>elfutils</filename> packages.
The <filename>update-alternatives.bbclass</filename> class handles renaming the
binaries so that multiple packages can be installed without conflicts.
The <filename>ar</filename> command still works regardless of which packages are installed
or subsequently removed.
The class renames the conflicting binary in each package
and symlinks the highest priority binary during installation or removal
of packages.
The class renames the conflicting binary in each package and symlinks the highest
priority binary during installation or removal of packages.
</para>
<para>
Four variables control this class:
<itemizedlist>
<listitem><para><filename>ALTERNATIVE_NAME</filename> &dash; The name of the
binary that is replaced (<filename>ar</filename> in this example).</para></listitem>
<listitem><para><filename>ALTERNATIVE_LINK</filename> &dash; The path to
the resulting binary (<filename>/bin/ar</filename> in this example).</para></listitem>
<listitem><para><filename>ALTERNATIVE_PATH</filename> &dash; The path to the
real binary (<filename>/usr/bin/ar.binutils</filename> in this example).</para></listitem>
<listitem><para><filename>ALTERNATIVE_PRIORITY</filename> &dash; The priority of
the binary.
The version with the most features should have the highest priority.</para></listitem>
</itemizedlist>
</para>
<itemizedlist>
<listitem><para><filename>ALTERNATIVE_NAME</filename> &dash; The name of the
binary that is replaced (<filename>ar</filename> in this example).</para></listitem>
<listitem><para><filename>ALTERNATIVE_LINK</filename> &dash; The path to
the resulting binary (<filename>/bin/ar</filename> in this example).</para></listitem>
<listitem><para><filename>ALTERNATIVE_PATH</filename> &dash; The path to the
real binary (<filename>/usr/bin/ar.binutils</filename> in this example).</para></listitem>
<listitem><para><filename>ALTERNATIVE_PRIORITY</filename> &dash; The priority of
the binary.
The version with the most features should have the highest priority.</para></listitem>
</itemizedlist>
<para>
Currently, only one binary per package is supported.
Currently, the Yocto Project supports only one binary per package.
</para>
</section>
@ -128,14 +116,15 @@
<title>Initscripts - <filename>update-rc.d.bbclass</filename></title>
<para>
This class uses update-rc.d to safely install an initscript on behalf of
the package. Details such as making sure the initscript is stopped before
a package is removed and started when the package is installed are taken
care of. Three variables control this class,
<link linkend='var-INITSCRIPT_PACKAGES'>INITSCRIPT_PACKAGES</link>,
<link linkend='var-INITSCRIPT_NAME'>INITSCRIPT_NAME</link> and
<link linkend='var-INITSCRIPT_PARAMS'>INITSCRIPT_PARAMS</link>. See the
links for details.
This class uses <filename>update-rc.d</filename> to safely install an
initialization script on behalf of the package.
The Yocto Project takes care of details such as making sure the script is stopped before
a package is removed and started when the package is installed.
Three variables control this class:
<filename><link linkend='var-INITSCRIPT_PACKAGES'>INITSCRIPT_PACKAGES</link></filename>,
<filename><link linkend='var-INITSCRIPT_NAME'>INITSCRIPT_NAME</link></filename> and
<filename><link linkend='var-INITSCRIPT_PARAMS'>INITSCRIPT_PARAMS</link></filename>.
See the variable links for details.
</para>
</section>
@ -143,17 +132,17 @@
<title>Binary config scripts - <filename>binconfig.bbclass</filename></title>
<para>
Before pkg-config had become widespread, libraries shipped shell
Before <filename>pkg-config</filename> had become widespread, libraries shipped shell
scripts to give information about the libraries and include paths needed
to build software (usually named 'LIBNAME-config'). This class assists
any recipe using such scripts.
to build software (usually named <filename>LIBNAME-config</filename>).
This class assists any recipe using such scripts.
</para>
<para>
During staging Bitbake installs such scripts into the <filename
class="directory">sysroots/</filename> directory. It also changes all
paths to point into the <filename>sysroots/</filename>
directory so all builds which use the script will use the correct
During staging, Bitbake installs such scripts into the
<filename>sysroots/</filename> directory.
BitBake also changes all paths to point into the <filename>sysroots/</filename>
directory so all builds that use the script will use the correct
directories for the cross compiling layout.
</para>
</section>
@ -163,8 +152,8 @@
<para>
This class renames packages so that they follow the Debian naming
policy, i.e. 'glibc' becomes 'libc6' and 'glibc-devel' becomes
'libc6-dev'.
policy (i.e. <filename>glibc</filename> becomes <filename>libc6</filename>
and <filename>glibc-devel</filename> becomes <filename>libc6-dev</filename>.
</para>
</section>
@ -172,15 +161,15 @@
<title>Pkg-config - <filename>pkgconfig.bbclass</filename></title>
<para>
Pkg-config brought standardisation and this class aims to make its
integration smooth for all libraries which make use of it.
<filename>pkg-config</filename> brought standardization and this class aims to make its
integration smooth for all libraries that make use of it.
</para>
<para>
During staging Bitbake installs pkg-config data into the <filename
class="directory">sysroots/</filename> directory. By making use of
sysroot functionality within pkgconfig this class no longer has to
manipulate the files.
During staging, Bitbake installs <filename>pkg-config</filename> data into the
<filename>sysroots/</filename> directory.
By making use of sysroot functionality within <filename>pkg-config</filename>,
this class no longer has to manipulate the files.
</para>
</section>
@ -188,126 +177,131 @@
<title>Distribution of sources - <filename>src_distribute_local.bbclass</filename></title>
<para>
Many software licenses require providing the sources for compiled
binaries. To simplify this process two classes were created:
Many software licenses require that source files be provided along with the binaries.
To simplify this process, two classes were created:
<filename>src_distribute.bbclass</filename> and
<filename>src_distribute_local.bbclass</filename>.
</para>
<para>
Result of their work are <filename>tmp/deploy/source/</filename>
subdirs with sources sorted by <glossterm><link linkend='var-LICENSE'>LICENSE</link>
</glossterm> field. If recipe lists few licenses (or has entries like "Bitstream Vera") source archive is put in each
license dir.
The results of these classes are <filename>tmp/deploy/source/</filename>
subdirs with sources sorted by
<filename><link linkend='var-LICENSE'>LICENSE</link></filename> field.
If recipes list few licenses (or have entries like "Bitstream Vera"),
the source archive is placed in each license directory.
</para>
<para>
Src_distribute_local class has three modes of operating:
This class operates using three modes:
<itemizedlist>
<listitem><para><emphasis>copy:</emphasis> Copies the files to the
distribute directory.</para></listitem>
<listitem><para><emphasis>symlink:</emphasis> Symlinks the files to the
distribute directory.</para></listitem>
<listitem><para><emphasis>move+symlink:</emphasis> Moves the files into
the distribute directory and then symlinks them back.</para></listitem>
</itemizedlist>
</para>
<itemizedlist>
<listitem><para>copy - copies the files to the distribute dir</para></listitem>
<listitem><para>symlink - symlinks the files to the distribute dir</para></listitem>
<listitem><para>move+symlink - moves the files into distribute dir, and symlinks them back</para></listitem>
</itemizedlist>
</section>
<section id='ref-classes-perl'>
<title>Perl modules - <filename>cpan.bbclass</filename></title>
<para>
Recipes for Perl modules are simple - usually needs only
pointing to source archive and inheriting of proper bbclass.
Building is split into two methods dependly on method used by
module authors.
Recipes for Perl modules are simple.
These recipes usually only need to point to the source's archive and then inherit the
proper <filename>.bbclass</filename> file.
Building is split into two methods dependling on which method the module authors used.
</para>
<para>
Modules which use old Makefile.PL based build system require
using of <filename>cpan.bbclass</filename> in their recipes.
Modules that use old <filename>Makefile.PL</filename>-based build system require
<filename>cpan.bbclass</filename> in their recipes.
</para>
<para>
Modules which use Build.PL based build system require
using of <filename>cpan_build.bbclass</filename> in their recipes.
Modules that use <filename>Build.PL</filename>-based build system require
using <filename>cpan_build.bbclass</filename> in their recipes.
</para>
</section>
<section id='ref-classes-distutils'>
<title>Python extensions - <filename>distutils.bbclass</filename></title>
<para>
Recipes for Python extensions are simple - they usually only
require pointing to the source archive and inheriting the proper
bbclasses.
Building is split into two methods depending on the build method
used by the module authors.
Recipes for Python extensions are simple.
These recipes usually only need to point to the source's archive and then inherit
the proper <filename>.bbclass</filename> file.
Building is split into two methods dependling on which method the module authors used.
</para>
<para>
Extensions which use autotools based build system require use
of autotools and distutils-base bbclasses in their recipes.
Extensions that use an Autotools-based build system require Autotools and
<filename>distutils</filename>-based <filename>.bbclasse</filename> files in their recipes.
</para>
<para>
Extensions which use distutils build system require use
of <filename>distutils.bbclass</filename> in their recipes.
Extensions that use <filename>distutils</filename>-based build systems require
<filename>distutils.bbclass</filename> in their recipes.
</para>
</section>
<section id='ref-classes-devshell'>
<title>Developer Shell - <filename>devshell.bbclass</filename></title>
<para>
This class adds the devshell task. Its usually up to distribution policy
to include this class (Poky does). See the <link
linkend='platdev-appdev-devshell'>developing with 'devshell' section</link>
This class adds the <filename>devshell</filename> task.
Distribution policy dictates whether to include this class as the Yocto Project does.
See the <link
linkend='platdev-appdev-devshell'>Development Within a Development Shell</link> section
for more information about using devshell.
</para>
</section>
<section id='ref-classes-package'>
<title>Packaging - <filename>package*.bbclass</filename></title>
<para>
The packaging classes add support for generating packages from a builds
output. The core generic functionality is in
<filename>package.bbclass</filename>, code specific to particular package
types is contained in various sub classes such as
<filename>package_deb.bbclass</filename>, <filename>package_ipk.bbclass</filename>
and <filename>package_rpm.bbclass</filename>. Most users will
want one or more of these classes and this is controlled by the <glossterm>
<link linkend='var-PACKAGE_CLASSES'>PACKAGE_CLASSES</link></glossterm>
variable. The first class listed in this variable will be used for image
generation. Since images are generated from packages a packaging class is
The packaging classes add support for generating packages from a build's
output.
The core generic functionality is in <filename>package.bbclass</filename>.
The code specific
to particular package types is contained in various sub-classes such as
<filename>package_deb.bbclass</filename>, <filename>package_ipk.bbclass</filename>,
and <filename>package_rpm.bbclass</filename>.
Most users will want one or more of these classes.
You can control the list of resulting package formats by using the
<filename><link linkend='var-PACKAGE_CLASSES'>PACKAGE_CLASSES</link></filename>
variable.
The first class listed in this variable is be used for image generation.
Since images are generated from packages, a packaging class is
needed to enable image generation.
</para>
</section>
<section id='ref-classes-kernel'>
<title>Building kernels - <filename>kernel.bbclass</filename></title>
<para>
This class handles building of Linux kernels and the class contains code to know how to build both 2.4 and 2.6 kernel trees. All needed headers are
staged into <glossterm><link
linkend='var-STAGING_KERNEL_DIR'>STAGING_KERNEL_DIR</link></glossterm>
directory to allow building of out-of-tree modules using <filename>module.bbclass</filename>.
This class handles building Linux kernels.
The class contains code to build all kernel trees.
All needed headers are staged into the
<filename><link linkend='var-STAGING_KERNEL_DIR'>STAGING_KERNEL_DIR</link></filename>
directory to allow out-of-tree module builds using <filename>module.bbclass</filename>.
</para>
<para>
This means that each kernel module built is packaged separately and inter-module dependencies are
created by parsing the <filename>modinfo</filename> output. If all modules are
required then installing the "kernel-modules" package will install all
packages with modules and various other kernel packages such as "kernel-vmlinux".
This means that each built kernel module is packaged separately and inter-module
dependencies are created by parsing the <filename>modinfo</filename> output.
If all modules are required, then installing the <filename>kernel-modules</filename>
package installs all packages with modules and various other kernel packages
such as <filename>kernel-vmlinux</filename>.
</para>
<para>
Various other classes are used by the kernel and module classes internally including
<filename>kernel-arch.bbclass</filename>, <filename>module_strip.bbclass</filename>,
<filename>module-base.bbclass</filename> and <filename>linux-kernel-base.bbclass</filename>.
<filename>module-base.bbclass</filename>, and <filename>linux-kernel-base.bbclass</filename>.
</para>
</section>
@ -315,18 +309,20 @@
<title>Creating images - <filename>image.bbclass</filename> and <filename>rootfs*.bbclass</filename></title>
<para>
Those classes add support for creating images in many formats. First the
rootfs is created from packages by one of the <filename>rootfs_*.bbclass</filename>
files (depending on package format used) and then image is created.
These classes add support for creating images in several formats.
First, the root filesystem is created from packages using
one of the <filename>rootfs_*.bbclass</filename>
files (depending on the package format used) and then the image is created.
</para>
The <glossterm><link
linkend='var-IMAGE_FSTYPES'>IMAGE_FSTYPES</link></glossterm>
variable controls which types of image to generate.
The list of packages to install into the image is controlled by the
<glossterm><link
linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></glossterm>
variable.
<para>
The <filename><link linkend='var-IMAGE_FSTYPES'>IMAGE_FSTYPES</link></filename>
variable controls the types of images to generate.
</para>
<para>
The <filename><link linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></filename>
variable controls the list of packages to install into the image.
</para>
</section>
@ -334,11 +330,12 @@
<title>Host System sanity checks - <filename>sanity.bbclass</filename></title>
<para>
This class checks prerequisite software is present to
notify the users of potential problems that will affect their build. It
also performs basic checks of the user configuration from local.conf to
prevent common mistakes resulting in build failures. It's usually up to
distribution policy whether to include this class (Poky does).
This class checks to see if prerequisite software is present so that
users can be notified of potential problems that might affect their build.
The class also performs basic user configuration checks from
the <filename>local.conf</filename> configuration file to
prevent common mistakes that cause build failures.
Distribution policy usually whether to include this class as the Yocto Project does.
</para>
</section>
@ -346,11 +343,11 @@
<title>Generated output quality assurance checks - <filename>insane.bbclass</filename></title>
<para>
This class adds a step to package generation which sanity checks the
packages generated by Poky. There are an ever increasing range of checks
it performs, checking for common problems which break builds/packages/images,
see the bbclass file for more information. It's usually up to distribution
policy whether to include this class (Poky does).
This class adds a step to the package generation process that sanity checks the
packages generated by the Yocto Project.
An ever-increasing range of checks are performed that check for
common problems that break builds.
Distribution policy usually dictates whether to include this class as the Yocto Project does.
</para>
</section>
@ -358,23 +355,28 @@
<title>Autotools configuration data cache - <filename>siteinfo.bbclass</filename></title>
<para>
Autotools can require tests which have to execute on the target hardware.
Since this isn't possible in general when cross compiling, siteinfo is
Autotools can require tests that must execute on the target hardware.
Since this is not possible in general when cross compiling, site information is
used to provide cached test results so these tests can be skipped over but
the correct values used. The <link linkend='structure-meta-site'>meta/site directory</link>
contains test results sorted into different categories like architecture, endianess and
the libc used. Siteinfo provides a list of files containing data relevant to
the current build in the <glossterm><link linkend='var-CONFIG_SITE'>CONFIG_SITE
</link></glossterm> variable which autotools will automatically pick up.
still make the correct values available.
The <filename><link linkend='structure-meta-site'>meta/site directory</link></filename>
contains test results sorted into different categories such as architecture, endianess, and
the libc used.
Site information provides a list of files containing data relevant to
the current build in the
<filename><link linkend='var-CONFIG_SITE'>CONFIG_SITE</link></filename> variable
that Autotools automatically picks up.
</para>
<para>
The class also provides variables like <glossterm><link
linkend='var-SITEINFO_ENDIANESS'>SITEINFO_ENDIANESS</link></glossterm>
and <glossterm><link linkend='var-SITEINFO_BITS'>SITEINFO_BITS</link>
</glossterm> which can be used elsewhere in the metadata.
The class also provides variables like
<filename><link linkend='var-SITEINFO_ENDIANESS'>SITEINFO_ENDIANESS</link></filename>
and <filename><link linkend='var-SITEINFO_BITS'>SITEINFO_BITS</link></filename>
that can be used elsewhere in the metadata.
</para>
<para>
This class is included from <filename>base.bbclass</filename> and is hence always active.
Because this class is included from <filename>base.bbclass</filename>, it is always active.
</para>
</section>
@ -382,8 +384,12 @@
<title>Other Classes</title>
<para>
Only the most useful/important classes are covered here but there are
others, see the <filename>meta/classes</filename> directory for the rest.
Thus far, this appendix has discussed only the most useful and important
classes.
However, other classes exist within the <filename>meta/classes</filename> directory
in the Yocto Project file's directory structure.
You can examine the <filename>.bbclass</filename> files directly for more
information.
</para>
</section>