<!DOCTYPE appendix PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <appendix id='ref-classes'> <title>Reference: Classes</title> <para> Class files are used to abstract common functionality and share it amongst multiple <filename class="extension">.bb</filename> files. Any metadata usually found in a <filename class="extension">.bb</filename> file can also be placed in a class file. Class files are identified by the extension <filename class="extension">.bbclass</filename> and are usually placed in a <filename class="directory">classes/</filename> directory beneath the <filename class="directory">meta/</filename> directory or the <filename class="directory">build/</filename> directory in the same way as <filename class="extension">.conf</filename> files in the <filename class="directory">conf</filename> directory. Class files are searched for in BBPATH in the same was as <filename class="extension">.conf</filename> files too. </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 default behaviour. </para> <section id='ref-classes-base'> <title>The base class - <filename>base.bbclass</filename></title> <para> The base class is special in that every <filename class="extension">.bb</filename> file inherits it automatically. It contains definitions of 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 contains some commonly some commonly used functions such as <function>oe_libinstall</function> and <function>oe_runmake</function>. The end of the class file has a list of standard mirrors for software projects for use by the fetcher code. </para> </section> <section id='ref-classes-autotools'> <title>Autotooled Packages - <filename>autotools.bbclass</filename></title> <para> Autotools (autoconf, automake, libtool) brings standardisation and this class aims to define a set of tasks (configure, compile etc.) that will work for all autotooled packages. It should usualy 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. </para> <para> Its useful to have some idea of the tasks this class defines work and what they do behind the scenes. </para> <itemizedlist> <listitem> <para> 'do_configure' regenearates the configure script and then launches it with a standard set of arguments used during cross-compilation. Additional parameters can be passed to <command>configure</command> through the <glossterm><link linkend='var-EXTRA_OECONF'>EXTRA_OECONF</link></glossterm> variable. </para> </listitem> <listitem> <para> 'do_compile' runs <command>make</command> with arguments specifying the compiler and linker. Additional arguments can be passed through the <glossterm><link linkend='var-EXTRA_OEMAKE'>EXTRA_OEMAKE</link> </glossterm> variable. </para> </listitem> <listitem> <para> 'do_install' runs <command>make install</command> passing a DESTDIR option taking its value from the standard <glossterm><link linkend='var-DESTDIR'>DESTDIR</link></glossterm> variable. </para> </listitem> </itemizedlist> <para> By default the class does not stage headers and libraries so the recipe author needs to add their own <function>do_stage()</function> task. For typical recipes the following example code will usually be enough: <programlisting> do_stage() { autotools_stage_all }</programlisting> </para> </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 they can be installed with the same name. For example the <command>ar</command> command is available from the "busybox", "binutils" and "elfutils" packages. This class handles the renaming of the binaries so multiple packages can be installed which would otherwise conflict and yet the <command>ar</command> command still works regardless of which are installed or subsequently removed. It renames the conflicting binary in each package and symlinks the highest priority binary during installation or removal of packages. Four variables control this class: </para> <variablelist> <varlistentry> <term>ALTERNATIVE_NAME</term> <listitem> <para> Name of binary which will be replaced (<command>ar</command> in this example) </para> </listitem> </varlistentry> <varlistentry> <term>ALTERNATIVE_LINK</term> <listitem> <para> Path to resulting binary ("/bin/ar" in this example) </para> </listitem> </varlistentry> <varlistentry> <term>ALTERNATIVE_PATH</term> <listitem> <para> Path to real binary ("/usr/bin/ar.binutils" in this example) </para> </listitem> </varlistentry> <varlistentry> <term>ALTERNATIVE_PRIORITY</term> <listitem> <para> Priority of binary, the version with the most features should have the highest priority </para> </listitem> </varlistentry> </variablelist> </section> <section id='ref-classes-update-rc.d'> <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. </para> </section> <section id='ref-classes-binconfig'> <title>Binary config scripts - <filename>binconfig.bbclass</filename></title> <para> Before pkg-config became 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. </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 class="directory">sysroots/</filename> directory so all builds which use the script will use the correct directories for the cross compiling layout. </para> </section> <section id='ref-classes-debian'> <title>Debian renaming - <filename>debian.bbclass</filename></title> <para> This class renames packages so that they follow the Debian naming policy, i.e. 'glibc' becomes 'libc6' and 'glibc-devel' becomes 'libc6-dev'. </para> </section> <section id='ref-classes-pkgconfig'> <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. </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. </para> </section> <section id='ref-classes-src-distribute'> <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: <filename>src_distribute.bbclass</filename> and <filename>src_distribute_local.bbclass</filename>. </para> <para> Result of their work are <filename class="directory">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. </para> <para> Src_distribute_local class has three modes of operating: </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. </para> <para> Modules which use old Makefile.PL based build system require using of <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. </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. </para> <para> Extensions which use autotools based build system require use of autotools and distutils-base bbclasses in their recipes. </para> <para> Extensions which use distutils build system require use of <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> 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> and <filename>package_ipk.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 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>. </para> <para> The means that each kerel module built is packaged separately and inter-module dependencies are created by parsing the <command>modinfo</command> 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" are also generated. </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>. </para> </section> <section id='ref-classes-image'> <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. 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> </section> <section id='ref-classes-sanity'> <title>Host System sanity checks - <filename>sanity.bbclass</filename></title> <para> This class checks prerequisite software is present to try and identify and notify the user of problems which will affect their build. It also performs basic checks of the users configuration from local.conf to prevent common mistakes and resulting build failures. Its usually up to distribution policy to include this class (Poky does). </para> </section> <section id='ref-classes-insane'> <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 this makes, checking for common problems which break builds/packages/images, see the bbclass file for more information. Its usually up to distribution policy to include this class (Poky does). to soon). </para> </section> <section id='ref-classes-siteinfo'> <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 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. </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. </para> <para> This class is included from <filename>base.bbclass</filename> and is hence always active. </para> </section> <section id='ref-classes-others'> <title>Other Classes</title> <para> Only the most useful/important classes are covered here but there are others, see the <filename class="directory">meta/classes</filename> directory for the rest. </para> </section> <!-- Undocumented classes are: base_srpm.bbclass bootimg.bbclass ccache.inc ccdv.bbclass cml1.bbclass cross.bbclass flow-lossage.bbclass gconf.bbclass gettext.bbclass gnome.bbclass gtk-icon-cache.bbclass icecc.bbclass lib_package.bbclass mozilla.bbclass multimachine.bbclass native.bbclass oelint.bbclass patch.bbclass patcher.bbclass pkg_distribute.bbclass pkg_metainfo.bbclass poky.bbclass rm_work.bbclass rpm_core.bbclass scons.bbclass sdk.bbclass sdl.bbclass sip.bbclass sourcepkg.bbclass srec.bbclass syslinux.bbclass tinderclient.bbclass tmake.bbclass xfce.bbclass xlibs.bbclass --> </appendix> <!-- vim: expandtab tw=80 ts=4 -->