path: root/documentation/ref-manual/ref-classes.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<chapter id='ref-classes'>
<title>Classes</title>

<para>
    Class files are used to abstract common functionality and share it amongst
    multiple recipe (<filename>.bb</filename>) files.
    To use a class file, you simply make sure the recipe inherits the class.
    In most cases, when a recipe inherits a class it is enough to enable its
    features.
    There are cases, however, where in the recipe you might need to set
    variables or override some default behavior.
</para>

<para>
    Any <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> usually
    found in a recipe 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 found in the
    <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
    Class files can also be pointed to by
    <link linkend='var-BUILDDIR'><filename>BUILDDIR</filename></link>
    (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
    <link linkend='var-BBPATH'><filename>BBPATH</filename></link>
    using the same method by which <filename>.conf</filename> files are
    searched.
</para>

<para>
    This chapter discusses only the most useful and important classes.
    Other classes do exist within the <filename>meta/classes</filename>
    directory in the
    <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
    You can reference the <filename>.bbclass</filename> files directly
    for more information.
</para>

<section id='ref-classes-allarch'>
    <title><filename>allarch.bbclass</filename></title>

    <para>
        The all architecture (<filename>allarch</filename>) class is inherited
        by recipes that do not produce architecture-specific output.
        The class disables functionality that is normally needed for recipes
        that produce executable binaries (such as building the cross-compiler
        and a C library as pre-requisites, and splitting out of debug symbols
        during packaging).
    </para>

    <para>
        By default, all recipes inherit the
        <link linkend='ref-classes-base'><filename>base</filename></link> and
        <link linkend='ref-classes-package'><filename>package</filename></link>
        classes, which enable functionality
        needed for recipes that produce executable output.
        If your recipe, for example, only produces packages that contain
        configuration files, media files, or scripts (e.g. Python and Perl),
        then it should inherit the <filename>allarch</filename> class.
    </para>
</section>

<section id='ref-classes-base'>
    <title>The base Class - <filename>base.bbclass</filename></title>

    <para>
        The base class is special in that every <filename>.bb</filename>
        file inherits it automatically.
        This class contains definitions for standard basic
        tasks such as fetching, unpacking, configuring (empty by default), compiling
        (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>

<section id='ref-classes-autotools'>
    <title>Autotooled Packages - <filename>autotools.bbclass</filename></title>

    <para>
        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.
        It should usually be enough to define a few standard variables
        and then simply <filename>inherit autotools</filename>.
        This class can also work with software that emulates Autotools.
        For more information, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#usingpoky-extend-addpkg-autotools'>Autotooled Package</ulink>"
        section in the Yocto Project Development Manual.
    </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 in
                <filename>${</filename><link linkend='var-D'><filename>D</filename></link><filename>}</filename>
                as <filename>DESTDIR</filename>.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-update-alternatives'>
    <title>Alternatives - <filename>update-alternatives.bbclass</filename></title>

    <para>
        This class helps the alternatives system when multiple sources provide
        the same command.
        This situation occurs when several programs that have the same or
        similar function are 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.
    </para>

    <para>
        To use this class, you need to define a number of variables:
        <itemizedlist>
            <listitem><para><link linkend='var-ALTERNATIVE'><filename>ALTERNATIVE</filename></link>
                </para></listitem>
            <listitem><para><link linkend='var-ALTERNATIVE_LINK_NAME'><filename>ALTERNATIVE_LINK_NAME</filename></link>
                </para></listitem>
            <listitem><para><link linkend='var-ALTERNATIVE_TARGET'><filename>ALTERNATIVE_TARGET</filename></link>
                </para></listitem>
            <listitem><para><link linkend='var-ALTERNATIVE_PRIORITY'><filename>ALTERNATIVE_PRIORITY</filename></link>
                </para></listitem>
        </itemizedlist>
        These variables list alternative commands needed by a package,
        provide pathnames for links, default links for targets, and
        so forth.
        For details on how to use this class, see the comments in the
        <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta/classes/update-alternatives.bbclass'><filename>update-alternatives.bbclass</filename></ulink>.
    </para>

    <note>
        You can use the <filename>update-alternatives</filename> command
        directly in your recipes.
        However, this class simplifies things in most cases.
    </note>
</section>

<section id='ref-classes-update-rc.d'>
    <title>Initscripts - <filename>update-rc.d.bbclass</filename></title>

    <para>
        This class uses <filename>update-rc.d</filename> to safely install an
        initialization script on behalf of the package.
        The OpenEmbedded build system 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>

<section id='ref-classes-binconfig'>
    <title><filename>binconfig.bbclass</filename></title>

    <para>
        This class helps to correct paths in shell scripts.
    </para>

    <para>
        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
        <filename>LIBNAME-config</filename>).
        This class assists any recipe using such scripts.
    </para>

    <para>
        During staging, the OpenEmbedded build system installs such scripts
        into the <filename>sysroots/</filename> directory.
        Inheriting this class results in all paths in these scripts being
        changed to point into the <filename>sysroots/</filename> directory so
        that all builds that use the script use the correct directories
        for the cross compiling layout.
        See the
        <link linkend='var-BINCONFIG_GLOB'><filename>BINCONFIG_GLOB</filename></link>
        variable for more information.
    </para>
</section>

<section id='ref-classes-bin-package'>
    <title><filename>bin_package.bbclass</filename></title>

    <para>
        The binary package (<filename>bin_package</filename>) class is a
        helper class for recipes that extract the contents of a binary package
        (e.g. an RPM) and install those contents rather than building the
        binary from source.
        The binary package is extracted and new packages in the configured
        output package format are created.
        <note>
            For RPMs and other packages that do not contain a subdirectory,
            you should specify a "subdir" parameter.
            Here is an example where <filename>${BP}</filename> matches the
            subdirectory expected by the default value of
            <link linkend='var-S'><filename>S</filename></link>:
            <literallayout class='monospaced'>
     SRC_URI = "http://example.com/downloads/somepackage.rpm;subdir=${BP}"
            </literallayout>
        </note>
    </para>
</section>

<section id='ref-classes-blacklist'>
    <title><filename>blacklist.bbclass</filename></title>

    <para>
        The blacklist (<filename>blacklist</filename>) class prevents
        the OpenEmbedded build system from building specific recipes
        (blacklists them).
        To use this class, inherit the class globally and set
        <filename>PNBLACKLIST</filename> for each recipe you wish to blacklist.
        Specify the <link linkend='var-PN'><filename>PN</filename></link>
        value as a variable flag (varflag) and provide a reason, which is
        reported, if the package is requested to be built as the value.
        For example, if you want to blacklist a recipe called "exoticware",
        you add the following to your <filename>local.conf</filename>
        or distribution configuration:
        <literallayout class='monospaced'>
     INHERIT += "blacklist"
     PNBLACKLIST[exoticware] = "Not supported by our organization."
        </literallayout>
    </para>
</section>

<section id='ref-classes-boot-directdisk'>
    <title><filename>boot-directdisk.bbclass</filename></title>

    <para>
        The boot direct disk (<filename>boot-directdisk</filename>) class
        creates an image that can be placed directly onto a hard disk using
        <filename>dd</filename> and then booted.
        The image uses SYSLINUX.
    </para>

    <para>
        The end result is a 512 boot sector populated with a
        Master Boot Record (MBR) and partition table followed by an MSDOS
        FAT16 partition containing SYSLINUX and a Linux kernel completed by
        the <filename>ext2</filename> and <filename>ext3</filename>
        root filesystems.
    </para>
</section>

<section id='ref-classes-bootimg'>
    <title><filename>bootimg.bbclass</filename></title>

    <para>
        The boot image (<filename>bootimg</filename> class creates a bootable
        image using SYSLINUX, your kernel and an optional initial RAM disk
        (<filename>initrd</filename>).
    </para>

    <para>
        When you use this class, two things happen:
        <itemizedlist>
            <listitem><para>
                A <filename>.hddimg</filename> file is created.
                This file which is an MSDOS filesystem that contains SYSLINUX,
                a kernel, an <filename>initrd</filename>, and a root filesystem
                image.
                All three of these can be written to hard drives directly and
                also booted on a USB flash disks using <filename>dd</filename>.
                </para></listitem>
            <listitem><para>
                A CD <filename>.iso</filename> image is created.
                When this file is booted, the <filename>initrd</filename>
                boots and processes the label selected in SYSLINUX.
                Actions based on the label are then performed (e.g. installing
                to a hard drive).</para></listitem>
        </itemizedlist>
    </para>

    <para>
        The <filename>bootimg</filename> class supports the
        <link linkend='var-INITRD'><filename>INITRD</filename></link>,
        <link linkend='var-NOISO'><filename>NOISO</filename></link>,
        <link linkend='var-NOHDD'><filename>NOHDD</filename></link>, and
        <link linkend='var-ROOTFS'><filename>ROOTFS</filename></link>
        variables.
    </para>
</section>

<section id='ref-classes-bugzilla'>
    <title><filename>bugzilla.bbclass</filename></title>

    <para>
        The Bugzilla (<filename>bugzilla</filename>) class, if enabled in
        your instance of Bugzilla, automatically files bug reports to that
        enabled instance in response to build failures.
        This class uses Bugzilla's XML-RPC interface.
    </para>
</section>

<section id='ref-classes-buildhistory'>
    <title><filename>buildhistory.bbclass</filename></title>

    <para>
        The Build History (<filename>buildhistory</filename>) class records a
        history of build output metadata, which can be used to detect possible
        regressions as well as used for analysis of the build output.
        For more information on using Build History, see the
        "<link linkend='maintaining-build-output-quality'>Maintaining Build Output Quality</link>"
        section.
    </para>
</section>

<section id='ref-classes-buildstats'>
    <title><filename>buildstats.bbclass</filename></title>

    <para>
        The Build Stats (<filename>buildstats</filename>) class records
        performance statistics about each task executed during the build
        (e.g. elapsed time, CPU usage, and I/O usage).
    </para>

    <para>
        When you use this class, the output goes into the
        <link linkend='var-BUILDSTATS_BASE'><filename>BUILDSTATS_BASE</filename></link>
        directory, which defaults to <filename>${TMPDIR}/buildstats/</filename>.
        You can analyze the elapsed time using
        <filename>scripts/pybootchartgui/pybootchartgui.py</filename>, which
        produces a cascading chart of the entire build process and can be
        useful for highlighting bottlenecks.
    </para>

    <para>
        To enable this class, use the
        <link linkend='var-USER_CLASSES'><filename>USER_CLASSES</filename></link>
        variable from your <filename>local.conf</filename> file.
        The <filename>meta-yocto/conf/local.conf.sample</filename> file
        in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
        enables this class by default.
    </para>
</section>

<section id='ref-classes-chrpath'>
    <title><filename>chrpath.bbclass</filename></title>

    <para>
        The change runtime search path (<filename>chrpath</filename>) class
        is a wrapper around the "chrpath" utility, which is used during the
        build process for <filename>nativesdk</filename> recipes to change
        <filename>RPATH</filename> records within binaries in order to make
        them relocatable.
    </para>
</section>

<section id='ref-classes-ccache'>
    <title><filename>ccache.bbclass</filename></title>

    <para>
        The C/C++ Compiler Cache (<filename>ccache</filename>) class enables
        this cache for the build.
        This class is used to give a minor performance boost during the build.
        However, using the class can lead to unexpected side-effects.
        Thus, it is recommended that you do not use this class.
        See <ulink url='http://ccache.samba.org/'></ulink> for information on
        the C/C++ Compiler Cache.
    </para>
</section>

<section id='ref-classes-clutter'>
    <title><filename>clutter.bbclass</filename></title>

    <para>
        The Clutter (<filename>clutter</filename>) class consolidates the
        major and minor version naming and other common items used by Clutter
        and related recipes.
    </para>
</section>

<section id='ref-classes-cmake'>
    <title><filename>cmake.bbclass</filename></title>

    <para>
        The CMake build system (<filename>cmake</filename>) class allows for
        recipes that need to build software using the CMake build system.
        You can use the
        <link linkend='var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></link>
        variable to specify additional configuration options to be passed on
        the <filename>cmake</filename> command line.
    </para>
</section>

<section id='ref-classes-cml1'>
    <title><filename>cml1.bbclass</filename></title>

    <para>
        The <filename>cml1</filename> class provides basic support for the
        Linux kernel style build configuration system.
    </para>
</section>

<section id='ref-classes-copyleft_compliance'>
    <title><filename>copyleft_compliance.bbclass</filename></title>

    <para>
        The Copyleft Compliance (<filename>copyleft_compliance</filename>) class
        preserves source code for the purposes of license compliance.
        This class is an alternative to the <filename>archive*</filename>
        classes and is still used by some users even though it has been
        deprecated in favor of the
        <link linkend='ref-classes-archiver'><filename>archive*</filename></link>
        classes.
    </para>
</section>

<section id='ref-classes-core-image'>
    <title><filename>core-image.bbclass</filename></title>

    <para>
        The Core Image (<filename>core-image</filename>) class
        provides common definitions for the
        <filename>core-image-*</filename> image recipes, such as support for
        additional
        <link linkend='var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></link>.
    </para>
</section>

<section id='ref-classes-cross'>
    <title><filename>cross.bbclass</filename></title>

    <para>
        The cross-compilation (<filename>cross</filename>) class
        provides support for cross-compilation tools.
    </para>
</section>

<section id='ref-classes-cross-canadian'>
    <title><filename>cross-canadian.bbclass</filename></title>

    <para>
        The Canadian Cross (<filename>cross-canadian</filename>) class
        provides support for Canadian Cross compilation tools for SDKs.
        See the
        "<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>"
        section for more discussion on these cross-compilation tools.
    </para>
</section>

<section id='ref-classes-crosssdk'>
    <title><filename>crosssdk.bbclass</filename></title>

    <para>
        The Cross SDK (<filename>crosssdk</filename>) class
        provides support for cross-compilation tools used for building
        SDKs.
        See the
        "<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>"
        section for more discussion on these cross-compilation tools.
    </para>
</section>

<section id='ref-classes-deploy'>
    <title><filename>deploy.bbclass</filename></title>

    <para>
        The Deploy (<filename>deploy</filename>) class handles deploying files
        to the
        <link linkend='var-DEPLOY_DIR_IMAGE'><filename>DEPLOY_DIR_IMAGE</filename></link>
        directory.
        The main function of this class is to allow the deploy step to be
        accelerated by shared state.
        Recipes that inherit this class should define their own
        <filename>do_deploy</filename> function to copy the files to be
        deployed to
        <link linkend='var-DEPLOY_DIR'><filename>DEPLOYDIR</filename></link>,
        and use <filename>addtask</filename> to add the task at the appropriate
        place, which is usually after <filename>do_compile</filename> or
        <filename>do_install</filename>.
    </para>
</section>

<section id='ref-classes-distrodata'>
    <title><filename>distrodata.bbclass</filename></title>

    <para>
        The Distribution Data (<filename>distrodata</filename>) class
        provides for automatic checking for upstream recipe updates.
    </para>
</section>

<section id='ref-classes-distro_features_check'>
    <title><filename>distro_features_check.bbclass</filename></title>

    <para>
        The Distribution Features Check (<filename>distro_features_check</filename>) class
        allows individual recipes to check for required and conflicting
        <link linkend='var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></link>.
    </para>

    <para>
        This class provides support for the
        <link linkend='var-REQUIRED_DISTRO_FEATURES'><filename>REQUIRED_DISTRO_FEATURES</filename></link>
        and
        <link linkend='var-CONFLICT_DISTRO_FEATURES'><filename>CONFLICT_DISTRO_FEATURES</filename></link>
        variables.
        If any conditions specified in the recipe using the above variables are
        not met, the recipe will be skipped.
    </para>
</section>

<section id='ref-classes-extrausers'>
    <title><filename>extrausers.bbclass</filename></title>

    <para>
        The extra users (<filename>extrausers</filename>) class allows
        additional user and group configuration to be applied at the image
        level.
        Inheriting this class either globally or from an image recipe allows
        additional user and group operations to be performed using the
        <link linkend='var-EXTRA_USERS_PARAMS'><filename>EXTRA_USERS_PARAMS</filename></link>
        variable.
        <note>
            The user and group operations added using the
            <filename>extrausers</filename> class are not tied to a specific
            recipe but can be performed across the image as a whole.
            See the
            <link linkend='ref-classes-useradd'><filename>useradd</filename></link>
            class for information on how to add user and group configuration
            to a specific recipe.
        </note>
    </para>

    <para>
        Here is an example that uses this class in an image recipe:
        <literallayout class='monospaced'>
     inherit extrausers
     EXTRA_USERS_PARAMS = "\
         useradd -p '' tester; \
         groupadd developers; \
         userdel nobody; \
         groupdel -g video; \
         groupmod -g 1020 developers; \
         usermod -s /bin/sh tester; \
         "
        </literallayout>
    </para>
</section>

<section id='ref-classes-fontcache'>
    <title><filename>fontcache.bbclass</filename></title>

    <para>
        The font cache (<filename>fontcache</filename>) class generates the
        proper post-installation and post-remove (postinst and postrm)
        scriptlets for font packages.
        These scriptlets call <filename>fc-cache</filename> (part of
        <filename>Fontconfig</filename>) to add the fonts to the font
        information cache.
        Since the cache files are architecture-specific,
        <filename>fc-cache</filename> runs using QEMU if the postinst
        scriptlets need to be run on the build host during image creation.
    </para>

    <para>
        If the fonts being installed are in packages other than the main
        package, set
        <link linkend='var-FONT_PACKAGES'><filename>FONT_PACKAGES</filename></link>
        to include the packages containing the fonts.
    </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. <filename>eglibc</filename> becomes <filename>libc6</filename>
        and <filename>eglibc-devel</filename> becomes <filename>libc6-dev</filename>.)
    </para>
</section>

<section id='ref-classes-gconf'>
    <title><filename>gconf.bbclass</filename></title>

    <para>
        The GConf (<filename>gconf</filename>) class provides common
        functionality for recipes that need to install GConf schemas.
        The schemas will be put into a separate package
        (<filename>${</filename><link linkend='var-PN'><filename>PN</filename></link><filename>}-gconf</filename>)
        that is created automatically when this class is inherited.
        This package uses the appropriate post-installation and post-remove
        (postinst/postrm) scriptlets to register and unregister the schemas
        in the target image.
    </para>
</section>

<section id='ref-classes-gettext'>
    <title><filename>gettext.bbclass</filename></title>

    <para>
        The GText (<filename>gettext</filename>) class provides support for
        building software that uses the GNU <filename>gettext</filename>
        internationalization and localization system.
        All recipes building software that use
        <filename>gettext</filename> should inherit this class.
    </para>
</section>

<section id='ref-classes-gnome'>
    <title><filename>gnome.bbclass</filename></title>

    <para>
        The GNOME (<filename>gnome</filename>) class supports recipes that
        build software from the GNOME stack.
        This class inherits the
        <link linkend='ref-classes-gnomebase'><filename>gnomebase</filename></link>,
        <link linkend='ref-classes-gtk-icon-cache'><filename>gtk-icon-cache</filename></link>,
        <link linkend='ref-classes-gconf'><filename>gconf</filename></link> and
        <link linkend='ref-classes-mime'><filename>mime</filename></link> classes.
        The class also disables GLib Object System (Gobject) introspection
        where applicable.
    </para>
</section>

<section id='ref-classes-gnomebase'>
    <title><filename>gnomebase.bbclass</filename></title>

    <para>
        The GNOME base (<filename>gnomebase</filename>) class is the base
        class for recipes that build software from the GNOME stack.
    </para>
</section>

<section id='ref-classes-grub-efi'>
    <title><filename>grub-efi.bbclass</filename></title>

    <para>
        The GRUB Extensible Firmware Interface (<filename>grub-efi</filename>)
        class provides <filename>grub-efi</filename>-specific functions for
        building bootable images.
    </para>

    <para>
        This class supports several variables:
        <itemizedlist>
            <listitem><para>
                <link linkend='var-INITRD'><filename>INITRD</filename></link>:
                Indicates a filesystem image to use as an initrd (optional).
                </para></listitem>
            <listitem><para>
                <link linkend='var-ROOTFS'><filename>ROOTFS</filename></link>:
                Indicates a filesystem image to include as the root filesystem
                (optional).</para></listitem>
            <listitem><para>
                <link linkend='var-GRUB_GFXSERIAL'><filename>GRUB_GFXSERIAL</filename></link>:
                Set this to "1" to have graphics and serial in the boot menu.
                </para></listitem>
            <listitem><para>
                <link linkend='var-LABELS'><filename>LABELS</filename></link>:
                A list of targets for the automatic configuration.
                </para></listitem>
            <listitem><para>
                <link linkend='var-APPEND'><filename>APPEND</filename></link>:
                An override list of append strings for each
                <filename>LABEL</filename>.
                </para></listitem>
            <listitem><para>
                <link linkend='var-GRUB_OPTS'><filename>GRUB_OPTS</filename></link>:
                Additional options to add to the configuration (optional).
                Options are delimited using semi-colon characters
                (<filename>;</filename>).</para></listitem>
            <listitem><para>
                <link linkend='var-GRUB_TIMEOUT'><filename>GRUB_TIMEOUT</filename></link>:
                Timeout before executing the default <filename>LABEL</filename>
                (optional).
                </para></listitem>
       </itemizedlist>
   </para>
</section>

<section id='ref-classes-gsettings'>
    <title><filename>gsettings.bbclass</filename></title>

    <para>
        The GSettings (<filename>gsettings</filename>) class
        provides common functionality for recipes that need to install
        GSettings (glib) schemas.
        The schemas are assumed to be part of the main package.
        Appropriate post-installation and post-remove (postinst/postrm)
        scriptlets are added to register and unregister the schemas in the
        target image.
    </para>
</section>

<section id='ref-classes-gtk-doc'>
    <title><filename>gtk-doc.bbclass</filename></title>

    <para>
        The GIMP Toolkit Documentation (<filename>gtk-doc</filename>) class
        is a helper class to pull in the appropriate
        <filename>gtk-doc</filename> dependencies and disable
        <filename>gtk-doc</filename>.
    </para>
</section>

<section id='ref-classes-gtk-icon-cache'>
    <title><filename>gtk-icon-cache.bbclass</filename></title>

    <para>
        The GIMP Toolkit icon cache (<filename>gtk-icon-cache</filename>) class
        Generates the proper post-install and post-remove (postinst/postrm)
        scriptlets for packages that use GTK+ and install icons.
        These scriptlets call <filename>gtk-update-icon-cache</filename> to add
        the fonts to GTK+'s icon cache.
        Since the cache files are architecture-specific,
        <filename>gtk-update-icon-cache</filename> is run using QEMU if the
        postinst scriptlets need to be run on the build host during image
        creation.
    </para>
</section>

<section id='ref-classes-gtk-immodules-cache'>
    <title><filename>gtk-immodules-cache.bbclass</filename></title>

    <para>
        The GIMP Toolkit input method modules
        (<filename>gtk-immodules-cache</filename>) class
        generates the proper post-install and post-remove (postinst/postrm)
        scriptlets for packages that install GTK+ input method modules for
        virtual keyboards.
        These scriptlets call <filename>gtk-update-icon-cache</filename> to add
        the input method modules to the cache.
        Since the cache files are architecture-specific,
        <filename>gtk-update-icon-cache</filename> is run using QEMU if the
        postinst scriptlets need to be run on the build host during image
        creation.
    </para>

    <para>
        If the input method modules being installed are in packages other than
        the main package, set
        <link linkend='var-GTKIMMODULES_PACKAGES'><filename>GTKIMMODULES_PACKAGES</filename></link>
        to include the packages containing the modules.
    </para>
</section>

<section id='ref-classes-gzipnative'>
    <title><filename>gzipnative.bbclass</filename></title>

    <para>
        The <filename>gzip</filename> native (<filename>gzipnative</filename>)
        class enables the use of native versions of <filename>gzip</filename>
        and <filename>pigz</filename> rather than the system versions.
    </para>
</section>

<section id='ref-classes-icecc'>
    <title><filename>icecc.bbclass</filename></title>

    <para>
        The Icecream distributed compile support (<filename>icecc</filename>)
        class stages directories with symlinks from
        <filename>gcc</filename> and <filename>g++</filename> to
        <filename>icecc</filename>, for both native and cross compilers.
        Depending on each configure or compile, the OpenEmbedded build system
        adds the directories at the head of the <filename>PATH</filename> list
        and then sets
        <link linkend='var-ICECC_CXX'><filename>ICECC_CXX</filename></link>
        and
        <link linkend='var-ICECC_CC'><filename>ICEC_CC</filename></link>.
    </para>

    <para>
        For the cross compiler, the class creates a <filename>tar.gz</filename>
        file that contains the Yocto Project toolchain and sets
        <link linkend='var-ICECC_VERSION'><filename>ICECC_VERSION</filename></link>
        accordingly.
    </para>

    <para>
        The class handles all three different compile stages
        (i.e native ,cross-kernel and target) and creates the necessary
        environment <filename>tar.gz</filename> file to be used by the remote
        machines.
        The class also supports SDK generation.
    </para>

    <para>
        If <link linkend='var-ICECC_PATH'><filename>ICECC_PATH</filename></link>
        is not set in your <filename>local.conf</filename> file, then the
        class tries to locate it using <filename>which</filename>.

        If
        <link linkend='var-ICECC_ENV_EXEC'><filename>ICECC_ENV_EXEC</filename></link>
        is set in your <filename>local.conf</filename> file, the variable should
        point to the <filename>icecc-create-env</filename> script provided by
        the user.
        If you do not point to a user-provided script, the build system
        uses the default script provided by the recipe
        <filename>icecc-create-env.bb</filename>.
        <note>
            This script is a modified version and not the one that comes with
            <filename>icecc</filename>.
        </note>
    </para>

    <para>
        If you do not want the Icecream distributed compile support to apply
        to specific packages or classes, you can effectively "blacklist" them
        by listing the packages and classes using the
        <link linkend='var-ICECC_USER_PACKAGE_BL'><filename>ICECC_USER_PACKAGE_BL</filename></link>
        and
        <link linkend='var-ICECC_USER_CLASS_BL'><filename>ICECC_USER_CLASS_BL</filename></link>,
        variables, respectively, in your <filename>local.conf</filename> file.
        Doing so causes the OpenEmbedded build system to handle these
        compilations locally.
    </para>

    <para>
        Additionally, you can list packages using the
        <link linkend='var-ICECC_USER_PACKAGE_WL'><filename>ICECC_USER_PACKAGE_WL</filename></link>
        variable in your <filename>local.conf</filename> file to force
        <filename>icecc</filename> to be enabled for packages using an empty
        <link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>
        variable.
    </para>
</section>

<section id='ref-classes-mime'>
    <title><filename>mime.bbclass</filename></title>

    <para>
        The GNOME (<filename>mime</filename>) class
    </para>
</section>

<section id='ref-classes-pkgconfig'>
    <title>Pkg-config - <filename>pkgconfig.bbclass</filename></title>

    <para>
        <filename>pkg-config</filename> provides a standard way to get
        header and library information.
        This class aims to smooth integration of
        <filename>pkg-config</filename> into libraries that use it.
    </para>

    <para>
        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>

<section id='ref-classes-archiver'>
    <title>Archiving Sources - <filename>archive*.bbclass</filename></title>

    <para>
        Many software licenses require that source code and other materials be
        released with the binaries.
        To help with that task, the following classes are provided:
        <itemizedlist>
            <listitem><filename>archive-original-sources.bbclass</filename></listitem>
            <listitem><filename>archive-patched-sources.bbclass</filename></listitem>
            <listitem><filename>archive-configured-sources.bbclass</filename></listitem>
            <listitem><filename>archiver.bbclass</filename></listitem>
        </itemizedlist>
    </para>

    <para>
        For more details on the source archiver, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Product's Lifecycle</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

<section id='ref-classes-perl'>
    <title>Perl Modules - <filename>cpan.bbclass</filename></title>

    <para>
        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 depending on which method the module authors used.
        <itemizedlist>
            <listitem><para>Modules that use old
                <filename>Makefile.PL</filename>-based build system require
                <filename>cpan.bbclass</filename> in their recipes.
                </para></listitem>
            <listitem><para>Modules that use
                <filename>Build.PL</filename>-based build system require
                using <filename>cpan_build.bbclass</filename> in their recipes.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-distutils'>
    <title>Python Extensions - <filename>distutils.bbclass</filename></title>

    <para>
        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 depending on which method the module authors used.
        <itemizedlist>
            <listitem><para>Extensions that use an Autotools-based build system
                require Autotools and
                <filename>distutils</filename>-based
                <filename>.bbclasse</filename> files in their recipes.
                </para></listitem>
            <listitem><para>Extensions that use
                <filename>distutils</filename>-based build systems require
                <filename>distutils.bbclass</filename> in their recipes.
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-devshell'>
    <title>Developer Shell - <filename>devshell.bbclass</filename></title>

    <para>
        This class adds the <filename>devshell</filename> task.
        Distribution policy dictates whether to include this class.
        See the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#platdev-appdev-devshell'>Using a Development Shell</ulink>" section
        in the Yocto Project Development Manual for more information about using <filename>devshell</filename>.
    </para>
</section>

<section id='ref-classes-packagegroup'>
    <title>Package Groups - <filename>packagegroup.bbclass</filename></title>

    <para>
        This class sets default values appropriate for package group recipes (e.g.
        <filename><link linkend='var-PACKAGES'>PACKAGES</link></filename>,
        <filename><link linkend='var-PACKAGE_ARCH'>PACKAGE_ARCH</link></filename>,
        <filename><link linkend='var-ALLOW_EMPTY'>ALLOW_EMPTY</link></filename>,
        and so forth).
        It is highly recommended that all package group recipes inherit this class.
    </para>
    <para>
        For information on how to use this class, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#usingpoky-extend-customimage-customtasks'>Customizing Images Using Custom Package Groups</ulink>"
        section in the Yocto Project Development Manual.
    </para>
    <para>
        Previously, this class was named <filename>task.bbclass</filename>.
    </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 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.
    </para>

    <para>
        You can control the list of resulting package formats by using the
        <filename><link linkend='var-PACKAGE_CLASSES'>PACKAGE_CLASSES</link></filename>
        variable defined in the <filename>local.conf</filename> configuration file,
        which is located in the <filename>conf</filename> folder of the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        When defining the variable, you can specify one or more package types.
        Since images are generated from packages, a packaging class is
        needed to enable image generation.
        The first class listed in this variable is used for image generation.
    </para>

    <para>
        If you take the optional step to set up a repository (package feed)
        on the development host that can be used by Smart, you can
        install packages from the feed while you are running the image
        on the target (i.e. runtime installation of packages).
        For more information, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#using-runtime-package-management'>Using Runtime Package Management</ulink>"
         section in the Yocto Project Development Manual.
    </para>

    <para>
        The package class you choose can affect build-time performance and has space
        ramifications.
        In general, building a package with IPK takes about thirty percent less
        time as compared to using RPM to build the same or similar package.
        This comparison takes into account a complete build of the package with
        all dependencies previously built.
        The reason for this discrepancy is because the RPM package manager
        creates and processes more
        <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> than the
        IPK package manager.
        Consequently, you might consider setting <filename>PACKAGE_CLASSES</filename>
        to "package_ipk" if you are building smaller systems.
    </para>

    <para>
        Before making your decision on package manager, however, you should
        consider some further things about using RPM:
        <itemizedlist>
            <listitem><para>
                RPM starts to provide more abilities than IPK due to
                the fact that it processes more metadata.
                For example, this information includes individual file types,
                file checksum generation and evaluation on install, sparse file
                support, conflict detection and resolution for Multilib systems,
                ACID style upgrade, and repackaging abilities for rollbacks.
                </para></listitem>
            <listitem><para>
                For smaller systems, the extra space used for the Berkley
                Database and the amount of metadata when using RPM can affect
                your ability to perform on-device upgrades.
                </para></listitem>
        </itemizedlist>
    </para>

    <para>
        You can find additional information on the effects of the package
        class at these two Yocto Project mailing list links:
        <itemizedlist>
            <listitem><para><ulink url='&YOCTO_LISTS_URL;/pipermail/poky/2011-May/006362.html'>
                https://lists.yoctoproject.org/pipermail/poky/2011-May/006362.html</ulink></para></listitem>
            <listitem><para><ulink url='&YOCTO_LISTS_URL;/pipermail/poky/2011-May/006363.html'>
                https://lists.yoctoproject.org/pipermail/poky/2011-May/006363.html</ulink></para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-kernel'>
    <title>Building Kernels - <filename>kernel.bbclass</filename></title>

    <para>
        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 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>.
    </para>
</section>

<section id='ref-classes-image'>
    <title>Creating Images - <filename>image.bbclass</filename> and <filename>rootfs*.bbclass</filename></title>

    <para>
        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.
        <itemizedlist>
            <listitem><para>The
                <filename><link linkend='var-IMAGE_FSTYPES'>IMAGE_FSTYPES</link></filename>
                variable controls the types of images to generate.
                </para></listitem>
            <listitem><para>The
                <filename><link linkend='var-IMAGE_INSTALL'>IMAGE_INSTALL</link></filename>
                variable controls the list of packages to install into the
                image.</para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-sanity'>
    <title>Host System Sanity Checks - <filename>sanity.bbclass</filename></title>

    <para>
        This class checks to see if prerequisite software is present on the host system
        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 determines whether to include this class.
    </para>
</section>

<section id='ref-classes-insane'>
<title><filename>insane.bbclass</filename></title>

    <para>
        This class adds a step to the package generation process so that
        output quality assurance checks are generated by the OpenEmbedded
        build system.
        A range of checks are performed that check the build's output
        for common problems that show up during runtime.
        Distribution policy usually dictates whether to include this class.
    </para>

    <para>
        You can configure the sanity checks so that specific test failures
        either raise a warning or an error message.
        Typically, failures for new tests generate a warning.
        Subsequent failures for the same test would then generate an error
        message once the metadata is in a known and good condition.
    </para>

    <para>
        Use the
        <link linkend='var-WARN_QA'><filename>WARN_QA</filename></link> and
        <link linkend='var-ERROR_QA'><filename>ERROR_QA</filename></link>
         variables to control the behavior of
        these checks at the global level (i.e. in your custom distro
        configuration).
        However, to skip one or more checks in recipes, you should use
        <link linkend='var-INSANE_SKIP'><filename>INSANE_SKIP</filename></link>.
        For example, to skip the check for symbolic link
        <filename>.so</filename> files in the main package of a recipe,
        add the following to the recipe.
        You need to realize that the package name override, in this example
        <filename>${PN}</filename>, must be used:
        <literallayout class='monospaced'>
     INSANE_SKIP_${PN} += "dev-so"
        </literallayout>
        Please keep in mind that the QA checks exist in order to detect real
        or potential problems in the packaged output.
        So exercise caution when disabling these checks.
    </para>

    <para>
        The following list shows the tests you can list with the
        <filename>WARN_QA</filename> and <filename>ERROR_QA</filename>
        variables:
        <itemizedlist>
            <listitem><para><emphasis><filename>ldflags:</filename></emphasis>
                Ensures that the binaries were linked with the
                <filename>LDFLAGS</filename> options provided by the build system.
                If this test fails, check that the <filename>LDFLAGS</filename> variable
                is being passed to the linker command.</para></listitem>
            <listitem><para><emphasis><filename>useless-rpaths:</filename></emphasis>
                Checks for dynamic library load paths (rpaths) in the binaries that
                by default on a standard system are searched by the linker (e.g.
                <filename>/lib</filename> and <filename>/usr/lib</filename>).
                While these paths will not cause any breakage, they do waste space and
                are unnecessary.</para></listitem>
            <listitem><para><emphasis><filename>rpaths:</filename></emphasis>
                Checks for rpaths in the binaries that contain build system paths such
                as <filename>TMPDIR</filename>.
                If this test fails, bad <filename>-rpath</filename> options are being
                passed to the linker commands and your binaries have potential security
                issues.</para></listitem>
            <listitem><para><emphasis><filename>dev-so:</filename></emphasis>
                Checks that the <filename>.so</filename> symbolic links are in the
                <filename>-dev</filename> package and not in any of the other packages.
                In general, these symlinks are only useful for development purposes.
                Thus, the <filename>-dev</filename> package is the correct location for
                them.
                Some very rare cases do exist for dynamically loaded modules where
                these symlinks are needed instead in the main package.
                </para></listitem>
            <listitem><para><emphasis><filename>debug-files:</filename></emphasis>
                Checks for <filename>.debug</filename> directories in anything but the
                <filename>-dbg</filename> package.
                The debug files should all be in the <filename>-dbg</filename> package.
                Thus, anything packaged elsewhere is incorrect packaging.</para></listitem>
            <listitem><para><emphasis><filename>arch:</filename></emphasis>
                Checks the Executable and Linkable Format (ELF) type, bit size, and endianness
                of any binaries to ensure they match the target architecture.
                This test fails if any binaries don't match the type since there would be an
                incompatibility.
                Sometimes software, like bootloaders, might need to bypass this check.
                </para></listitem>
            <listitem><para><emphasis><filename>debug-deps:</filename></emphasis>
                Checks that <filename>-dbg</filename> packages only depend on other
                <filename>-dbg</filename> packages and not on any other types of packages,
                which would cause a packaging bug.</para></listitem>
            <listitem><para><emphasis><filename>dev-deps:</filename></emphasis>
                Checks that <filename>-dev</filename> packages only depend on other
                <filename>-dev</filename> packages and not on any other types of packages,
                which would be a packaging bug.</para></listitem>
            <listitem><para><emphasis><filename>pkgconfig:</filename></emphasis>
                Checks <filename>.pc</filename> files for any
                <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>/<link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>
                paths.
                Any <filename>.pc</filename> file containing these paths is incorrect
                since <filename>pkg-config</filename> itself adds the correct sysroot prefix
                when the files are accessed.</para></listitem>
            <listitem><para><emphasis><filename>textrel:</filename></emphasis>
                Checks for ELF binaries that contain relocations in their
                <filename>.text</filename> sections, which can result in a
                performance impact at runtime.</para></listitem>
            <listitem><para><emphasis><filename>pkgvarcheck:</filename></emphasis>
                Checks through the variables
                <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>,
                <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>,
                <link linkend='var-RSUGGESTS'><filename>RSUGGESTS</filename></link>,
                <link linkend='var-RCONFLICTS'><filename>RCONFLICTS</filename></link>,
                <link linkend='var-RPROVIDES'><filename>RPROVIDES</filename></link>,
                <link linkend='var-RREPLACES'><filename>RREPLACES</filename></link>,
                <link linkend='var-FILES'><filename>FILES</filename></link>,
                <link linkend='var-ALLOW_EMPTY'><filename>ALLOW_EMPTY</filename></link>,
                <filename>pkg_preinst</filename>,
                <filename>pkg_postinst</filename>,
                <filename>pkg_prerm</filename>
                and <filename>pkg_postrm</filename>, and reports if there are
                variable sets that are not package-specific.
                Using these variables without a package suffix is bad practice,
                and might unnecessarily complicate dependencies of other packages
                within the same recipe or have other unintended consequences.
                </para></listitem>
            <listitem><para><emphasis><filename>xorg-driver-abi:</filename></emphasis>
                Checks that all packages containing Xorg drivers have ABI
                dependencies.
                The <filename>xserver-xorg</filename> recipe provides driver
                ABI names.
                All drivers should depend on the ABI versions that they have
                been built against.
                Driver recipes that include
                <filename>xorg-driver-input.inc</filename>
                or <filename>xorg-driver-video.inc</filename> will
                automatically get these versions.
                Consequently, you should only need to explicitly add
                dependencies to binary driver recipes.
                </para></listitem>
            <listitem><para><emphasis><filename>libexec:</filename></emphasis>
                Checks if a package contains files in
                <filename>/usr/libexec</filename>.
                This check is not performed if the
                <filename>libexecdir</filename> variable has been set
                explicitly to <filename>/usr/libexec</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>staticdev:</filename></emphasis>
                Checks for static library files (<filename>*.a</filename>) in
                non-<filename>staticdev</filename> packages.
                </para></listitem>
            <listitem><para><emphasis><filename>la:</filename></emphasis>
                Checks <filename>.la</filename> files for any <filename>TMPDIR</filename>
                paths.
                Any <filename>.la</filename> file containing these paths is incorrect since
                <filename>libtool</filename> adds the correct sysroot prefix when using the
                files automatically itself.</para></listitem>
            <listitem><para><emphasis><filename>desktop:</filename></emphasis>
                Runs the <filename>desktop-file-validate</filename> program
                against any <filename>.desktop</filename> files to validate
                their contents against the specification for
                <filename>.desktop</filename> files.</para></listitem>
            <listitem><para><emphasis><filename>already-stripped:</filename></emphasis>
                Checks that produced binaries have not already been
                stripped prior to the build system extracting debug symbols.
                It is common for upstream software projects to default to
                stripping debug symbols for output binaries.
                In order for debugging to work on the target using
                <filename>-dbg</filename> packages, this stripping must be
                disabled.
                </para></listitem>
            <listitem><para><emphasis><filename>split-strip:</filename></emphasis>
                Reports that splitting or stripping debug symbols from binaries
                has failed.
                </para></listitem>
            <listitem><para><emphasis><filename>arch:</filename></emphasis>
                Checks to ensure the architecture, bit size, and endianness
                of all output binaries matches that of the target.
                This test can detect when the wrong compiler or compiler options
                have been used.
                </para></listitem>
            <listitem><para><emphasis><filename>installed-vs-shipped:</filename></emphasis>
                Reports when files have been installed within
                <filename>do_install</filename> but have not been included in
                any package by way of the
                <link linkend='var-FILES'><filename>FILES</filename></link>
                variable.
                Files that do not appear in any package cannot be present in
                an image later on in the build process.
                Ideally, all installed files should be packaged or not
                installed at all.
                These files can be deleted at the end of
                <filename>do_install</filename> if the files are not
                needed in any package.
                </para></listitem>
            <listitem><para><emphasis><filename>dep-cmp:</filename></emphasis>
                Checks for invalid version comparison statements in runtime
                dependency relationships between packages (i.e. in
                <link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link>,
                <link linkend='var-RRECOMMENDS'><filename>RRECOMMENDS</filename></link>,
                <link linkend='var-RSUGGESTS'><filename>RSUGGESTS</filename></link>,
                <link linkend='var-RPROVIDES'><filename>RPROVIDES</filename></link>,
                <link linkend='var-RREPLACES'><filename>RREPLACES</filename></link>,
                and
                <link linkend='var-RCONFLICTS'><filename>RCONFLICTS</filename></link>
                variable values).
                Any invalid comparisons might trigger failures or undesirable
                behavior when passed to the package manager.
                </para></listitem>
            <listitem><para><emphasis><filename>files-invalid:</filename></emphasis>
                Checks for
                <link linkend='var-FILES'><filename>FILES</filename></link>
                variable values that contain "//", which is invalid.
                </para></listitem>
            <listitem><para><emphasis><filename>incompatible-license:</filename></emphasis>
                Report when packages are excluded from being created due to
                being marked with a license that is in
                <link linkend='var-INCOMPATIBLE_LICENSE'><filename>INCOMPATIBLE_LICENSE</filename></link>.
                </para></listitem>
            <listitem><para><emphasis><filename>compile-host-path:</filename></emphasis>
                Checks the <filename>do_compile</filename> log for indications
                that paths to locations on the build host were used.
                Using such paths might result in host contamination of the
                build output.
                </para></listitem>
            <listitem><para><emphasis><filename>install-host-path:</filename></emphasis>
                Checks the <filename>do_install</filename> log for indications
                that paths to locations on the build host were used.
                Using such paths might result in host contamination of the
                build output.
                </para></listitem>
            <listitem><para><emphasis><filename>libdir:</filename></emphasis>
                Checks for libraries being installed into incorrect
                (possibly hardcoded) installation paths.
                For example, this test will catch recipes that install
                <filename>/lib/bar.so</filename> when
                <filename>${base_libdir}</filename> is "lib32".
                Another example is when recipes install
                <filename>/usr/lib64/foo.so</filename> when
                <filename>${libdir}</filename> is "/usr/lib".
                </para></listitem>
            <listitem><para><emphasis><filename>packages-list:</filename></emphasis>
                Checks for the same package being listed multiple times through
                the <link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>
                variable value.
                Installing the package in this manner can cause errors during
                packaging.
                </para></listitem>
            <listitem><para><emphasis><filename>perm-config:</filename></emphasis>
                Reports lines in <filename>fs-perms.txt</filename> that have
                an invalid format.
                </para></listitem>
            <listitem><para><emphasis><filename>perm-line:</filename></emphasis>
                Reports lines in <filename>fs-perms.txt</filename> that have
                an invalid format.
                </para></listitem>
            <listitem><para><emphasis><filename>perm-link:</filename></emphasis>
                Reports lines in <filename>fs-perms.txt</filename> that
                specify 'link' where the specified target already exists.
                </para></listitem>
            <listitem><para><emphasis><filename>pkgname:</filename></emphasis>
                Checks that all packages in
                <link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>
                have names that do not contain invalid characters (i.e.
                characters other than 0-9, a-z, ., +, and -).
                </para></listitem>
            <listitem><para><emphasis><filename>pn-overrides:</filename></emphasis>
                Checks that a recipe does not have a name
                (<link linkend='var-PN'><filename>PN</filename></link>) value
                that appears in
                <link linkend='var-OVERRIDES'><filename>OVERRIDES</filename></link>.
                If a recipe is named such that its <filename>PN</filename>
                value matches something already in
                <filename>OVERRIDES</filename> (e.g. <filename>PN</filename>
                happens to be the same as
                <link linkend='var-MACHINE'><filename>MACHINE</filename></link>
                or
                <link linkend='var-DISTRO'><filename>DISTRO</filename></link>),
                it can have unexpected consequences.
                For example, assignments such as
                <filename>FILES_${PN} = "xyz"</filename> effectively turn into
                <filename>FILES = "xyz"</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>unsafe-references-in-binaries:</filename></emphasis>
                Reports when a binary installed in
                <filename>${base_libdir}</filename>,
                <filename>${base_bindir}</filename>, or
                <filename>${base_sbindir}</filename>, depends on another
                binary installed under <filename>${exec_prefix}</filename>.
                This dependency is a concern if you want the system to remain
                basically operable if <filename>/usr</filename> is mounted
                separately and is not mounted.
                <note>
                    Defaults for binaries installed in
                    <filename>${base_libdir}</filename>,
                    <filename>${base_bindir}</filename>, and
                    <filename>${base_sbindir}</filename> are
                    <filename>/lib</filename>, <filename>/bin</filename>, and
                    <filename>/sbin</filename>, respectively.
                    The default for a binary installed
                    under <filename>${exec_prefix}</filename> is
                    <filename>/usr</filename>.
                </note>
                </para></listitem>
            <listitem><para><emphasis><filename>unsafe-references-in-scripts:</filename></emphasis>
                Reports when a script file installed in
                <filename>${base_libdir}</filename>,
                <filename>${base_bindir}</filename>, or
                <filename>${base_sbindir}</filename>, depends on files
                installed under <filename>${exec_prefix}</filename>.
                This dependency is a concern if you want the system to remain
                basically operable if <filename>/usr</filename> is mounted
                separately and is not mounted.
                <note>
                    Defaults for binaries installed in
                    <filename>${base_libdir}</filename>,
                    <filename>${base_bindir}</filename>, and
                    <filename>${base_sbindir}</filename> are
                    <filename>/lib</filename>, <filename>/bin</filename>, and
                    <filename>/sbin</filename>, respectively.
                    The default for a binary installed
                    under <filename>${exec_prefix}</filename> is
                    <filename>/usr</filename>.
                </note>
                </para></listitem>
            <listitem><para><emphasis><filename>var-undefined:</filename></emphasis>
                Reports when variables fundamental to packaging (i.e.
                <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>,
                <link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>,
                <link linkend='var-D'><filename>D</filename></link>,
                <link linkend='var-PN'><filename>PN</filename></link>, and
                <link linkend='var-PKGD'><filename>PKGD</filename></link>) are
                undefined during <filename>do_package</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>pkgv-undefined:</filename></emphasis>
                Checks to see if the <filename>PKGV</filename> variable
                is undefined during <filename>do_package</filename>.
                </para></listitem>
            <listitem><para><emphasis><filename>buildpaths:</filename></emphasis>
                Checks for paths to locations on the build host inside the
                output files.
                Currently, this test triggers too many false positives and
                thus is not normally enabled.
                </para></listitem>
            <listitem><para><emphasis><filename>perms:</filename></emphasis>
                Currently, this check is unused but reserved.
                </para></listitem>
            <listitem><para><emphasis><filename>version-going-backwards:</filename></emphasis>
                If Build History is enabled, reports when a package
                being written out has a lower version than the previously
                written package under the same name.
                If you are placing output packages into a feed and
                upgrading packages on a target system using that feed, the
                version of a package going backwards can result in the target
                system not correctly upgrading to the "new" version of the
                package.
                <note>
                    If you are not using runtime package management on your
                    target system, then you do not need to worry about
                    this situation.
                </note>
                </para></listitem>
        </itemizedlist>
    </para>
</section>

<section id='ref-classes-rm-work'>
    <title>Removing Work Files During the Build - <filename>rm_work.bbclass</filename></title>

    <para>
        The OpenEmbedded build system can use a substantial amount of disk
        space during the build process.
        A portion of this space is the work files under the
        <filename>${TMPDIR}/work</filename> directory for each recipe.
        Once the build system generates the packages for a recipe, the work
        files for that recipe are no longer needed.
        However, by default, the build system preserves these files
        for inspection and possible debugging purposes.
        If you would rather have these files deleted to save disk space
        as the build progresses, you can enable <filename>rm_work</filename>
        by adding the following to your <filename>local.conf</filename> file,
        which is found in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
        <literallayout class='monospaced'>
    INHERIT += "rm_work"
        </literallayout>
        If you are modifying and building source code out of the work directory
        for a recipe, enabling <filename>rm_work</filename> will potentially
        result in your changes to the source being lost.
        To exclude some recipes from having their work directories deleted by
        <filename>rm_work</filename>, you can add the names of the recipe or
        recipes you are working on to the <filename>RM_WORK_EXCLUDE</filename>
        variable, which can also be set in your <filename>local.conf</filename>
        file.
        Here is an example:
        <literallayout class='monospaced'>
    RM_WORK_EXCLUDE += "busybox eglibc"
        </literallayout>
    </para>
</section>


<section id='ref-classes-siteinfo'>
    <title>Autotools Configuration Data Cache - <filename>siteinfo.bbclass</filename></title>

    <para>
        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
        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, endianness, and
        the <filename>libc</filename> 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
        <filename><link linkend='var-SITEINFO_ENDIANNESS'>SITEINFO_ENDIANNESS</link></filename>
        and <filename><link linkend='var-SITEINFO_BITS'>SITEINFO_BITS</link></filename>
        that can be used elsewhere in the metadata.
    </para>

    <para>
        Because this class is included from <filename>base.bbclass</filename>, it is always active.
    </para>
</section>

<section id='ref-classes-useradd'>
    <title>Adding Users - <filename>useradd.bbclass</filename></title>

    <para>
        If you have packages that install files that are owned by custom users or groups,
        you can use this class to specify those packages and associate the users and groups
        with those packages.
        The <filename>meta-skeleton/recipes-skeleton/useradd/useradd-example.bb</filename>
        recipe in the <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>
        provides a simple example that shows how to add three
        users and groups to two packages.
        See the <filename>useradd-example.bb</filename> for more information on how to
        use this class.
    </para>
</section>

<section id='ref-classes-externalsrc'>
    <title><filename>externalsrc.bbclass</filename></title>

    <para>
        You can use this class to build software from source code that is
        external to the OpenEmbedded build system.
        Building software from an external source tree means that the build
        system's normal fetch, unpack, and patch process is not used.
    </para>

    <para>
        By default, the OpenEmbedded build system uses the
        <link linkend='var-S'><filename>S</filename></link> and
        <link linkend='var-B'><filename>B</filename></link> variables to
        locate unpacked recipe source code and to build it, respectively.
        When your recipe inherits <filename>externalsrc.bbclass</filename>,
        you use the
        <link linkend='var-EXTERNALSRC'><filename>EXTERNALSRC</filename></link>
        and
        <link linkend='var-EXTERNALSRC_BUILD'><filename>EXTERNALSRC_BUILD</filename></link>
        variables to ultimately define <filename>S</filename> and
        <filename>B</filename>.
    </para>

    <para>
        By default, this class expects the source code to support recipe builds
        that use the <link linkend='var-B'><filename>B</filename></link>
        variable to point to the directory in which the OpenEmbedded build
        system places the generated objects built from the recipes.
        By default, the <filename>B</filename> directory is set to the
        following, which is separate from the source directory
        (<filename>S</filename>):
        <literallayout class='monospaced'>
     ${WORKDIR}/${BPN}/{PV}/
        </literallayout>
        See the glossary entries for the
        <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>,
        <link linkend='var-BPN'><filename>BPN</filename></link>,
        <link linkend='var-PV'><filename>PV</filename></link>,
    </para>

    <para>
        For more information on
        <filename>externalsrc.bbclass</filename>, see the comments in
        <filename>meta/classes/externalsrc.bbclass</filename> in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        For information on how to use <filename>externalsrc.bbclass</filename>,
        see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#building-software-from-an-external-source'>Building Software from an External Source</ulink>"
        section in the Yocto Project Development Manual.
    </para>
</section>

<section id='ref-classes-testimage'>
    <title><filename>testimage.bbclass</filename></title>

    <para>
        You can use this class to enable running a series of automated tests
        for images.
        The class handles loading the tests and starting the image.
        <note>
            Currently, there is only support for running these tests
            under QEMU.
        </note>
    </para>

    <para>
        To use the class, you need to perform steps to set up the
        environment.
        The tests are commands that run on the target system over
        <filename>ssh</filename>.
        they are written in Python and make use of the
        <filename>unittest</filename> module.
    </para>

    <para>
        For information on how to enable, run, and create new tests, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#performing-automated-runtime-testing'>Performing Automated Runtime Testing</ulink>"
        section.
    </para>
</section>

<section id='ref-classes-others'>
    <title>Other Classes</title>

    <para>
        Thus far, this chapter has discussed only the most useful and important
        classes.
        However, other classes exist within the <filename>meta/classes</filename> directory
        in the <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        You can examine the <filename>.bbclass</filename> files directly for more
        information.
    </para>
</section>

<!-- Undocumented classes are:
        allarch.bbclass
        bin_package.bbclass
        blacklist.bbclass
        bootimg.bbclass
        boot-directdisk.bbclass
        bugzilla.bbclass
        buildhistory.bbclass
        buildstats.bbclass
        ccache.bbclass
        chrpath.bbclass
        clutter.bbclass
        cmake.bbclass
        cml1.bbclass
        copyleft_compliance.bbclass
        core-image.bbclass
        cross.bbclass
        cross-canadian.bbclass
        crosssdk.bbclass
        deploy.bbclass
        distrodata.bbclass
        distro_features_check.bbclass
        dummy.bbclass
        extrausers.bbclass
        fontcache.bbclass
        gconf.bbclass
        gettext.bbclass
        gnomebase.bbclass
        gnome.bbclass
        grub-efi.bbclass
        gsettings.bbclass
        gtk-doc.bbclass
        gtk-icon-cache.bbclass
        gtk-immodules-cache.bbclass
        gzipnative.bbclass
        icecc.bbclass
        image-empty.bbclass
        image-live.bbclass
        image-vmdk.bbclass
        image-mklibs.bbclass
        image-prelink.bbclass
        image-swab.bbclass
        image_types.bbclass
        image_types_uboot.bbclass
        insserv.bbclass
        kernel-arch.bbclass
        kernel-module-split.bbclass
        kernel-yocto.bbclass
        lib_package.bbclass
        linux-kernel-base.bbclass
        license.bbclass
        logging.bbclass
        meta.bbclass
        metadata_scm.bbclass
        migrate_localcount.bbclass
        mime.bbclass
        mirrors.bbclass
        multilib*.bbclass
        native.bbclass
        nativesdk.bbclass
        oelint.bbclass
        own-mirrors.bbclass
        packagedata.bbclass
        packageinfo.bbclass
        patch.bbclass
        perlnative.bbclass
        pixbufcache.bbclass
        pkg_distribute.bbclass
        pkg_metainfo.bbclass
        populate_sdk*.bbclass
        prexport.bbclass
        primport.bbclass
        prserv.bbclass
        ptest.bbclass
        python-dir.bbclass
        pythonnative.bbclass
        qemu.bbclass
        qmake*.bbclass
        qt4*.bbclass
        recipe_sanity.bbclass
        relocatable.bbclass
        scons.bbclass
        sdl.bbclass
        setuptools.bbclass
        sip.bbclass
        siteconfig.bbclass
        sourcepkg.bbclass
        spdx.bbclass
        sstate.bbclass
        staging.bbclass
        syslinux.bbclass
        systemd.bbclass
        terminal.bbclass
        tinderclient.bbclass
        toolchain-scripts.bbclass
        typecheck.bbclass
        uboot-config.bbclass
        utility-tasks.bbclass
        utils.bbclass
        vala.bbclass
        waf.bbclass
-->


</chapter>
<!--
vim: expandtab tw=80 ts=4
-->