path: root/documentation/dev-manual/dev-manual-common-tasks.xml

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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<chapter id='extendpoky'>

<title>Common Tasks</title>
    <para>
        This chapter describes fundamental procedures such as creating layers,
        adding new software packages, extending or customizing images,
        porting work to new hardware (adding a new machine), and so forth.
        You will find the procedures documented here occur often in the
        develop cycle using the Yocto Project.
    </para>

    <section id="understanding-and-creating-layers">
        <title>Understanding and Creating Layers</title>

        <para>
            The OpenEmbedded build system supports organizing
            <link linkend='metadata'>Metadata</link> into multiple layers.
            Layers allow you to isolate different types of customizations from
            each other.
            You might find it tempting to keep everything in one layer when
            working on a single project.
            However, the more modular you organize your Metadata, the easier
            it is to cope with future changes.
        </para>

        <para>
            To illustrate how layers are used to keep things modular, consider
            machine customizations.
            These types of customizations typically reside in a special layer,
            rather than a general layer, called a Board Specific Package (BSP)
            Layer.
            Furthermore, the machine customizations should be isolated from
            recipes and Metadata that support a new GUI environment,
            for example.
            This situation gives you a couple of layers: one for the machine
            configurations, and one for the GUI environment.
            It is important to understand, however, that the BSP layer can
            still make machine-specific additions to recipes within the GUI
            environment layer without polluting the GUI layer itself
            with those machine-specific changes.
            You can accomplish this through a recipe that is a BitBake append
            (<filename>.bbappend</filename>) file, which is described later
            in this section.
        </para>

        <para>
        </para>

        <section id='yocto-project-layers'>
            <title>Layers</title>

            <para>
                The <link linkend='source-directory'>Source Directory</link>
                contains both general layers and BSP
                layers right out of the box.
                You can easily identify layers that ship with a
                Yocto Project release in the Source Directory by their
                folder names.
                Folders that are layers begin with the string
                <filename>meta</filename>.
                <note>
                    It is not a requirement that a layer begins with the
                    string <filename>meta</filename>.
                </note>
                For example, when you set up the Source Directory structure,
                you will see several layers:
                <filename>meta</filename>, <filename>meta-hob</filename>,
                <filename>meta-skeleton</filename>,
                <filename>meta-yocto</filename>, and
                <filename>meta-yocto-bsp</filename>.
                Each of these folders is a layer.
            </para>

            <para>
                Furthermore, if you set up a local copy of the
                <filename>meta-intel</filename> Git repository
                and then explore the folder of that general layer,
                you will discover many BSP layers inside.
                For more information on BSP layers, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide.
            </para>
        </section>

        <section id='creating-your-own-layer'>
            <title>Creating Your Own Layer</title>

            <para>
                It is very easy to create your own layers to use with the
                OpenEmbedded build system.
                The Yocto Project ships with scripts that speed up creating
                general layers and BSP layers.
                This section describes the steps you perform by hand to create
                a layer so that you can better understand them.
                For information about the layer-creation scripts, see the
                "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
                section in the Yocto Project Board Support Package (BSP)
                Developer's Guide and the
                "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                section further down in this manual.
            </para>

            <para>
                Follow these general steps to create your layer:
                <orderedlist>
                    <listitem><para><emphasis>Check Existing Layers:</emphasis>
                        Before creating a new layer, you should be sure someone
                        has not already created a layer containing the Metadata
                        you need.
                        You can see the
                        <ulink url='http://layers.openembedded.org/layerindex/layers/'><filename>OpenEmbedded Metadata Index</filename></ulink>
                        for a list of layers from the OpenEmbedded community
                        that can be used in the Yocto Project.
                        </para></listitem>
                    <listitem><para><emphasis>Create a Directory:</emphasis>
                        Create the directory for your layer.
                        While not strictly required, prepend the name of the
                        folder with the string <filename>meta-</filename>.
                        For example:
                        <literallayout class='monospaced'>
     meta-mylayer
     meta-GUI_xyz
     meta-mymachine
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Create a Layer Configuration
                       File:</emphasis>
                       Inside your new layer folder, you need to create a
                       <filename>conf/layer.conf</filename> file.
                       It is easiest to take an existing layer configuration
                       file and copy that to your layer's
                       <filename>conf</filename> directory and then modify the
                       file as needed.</para>
                       <para>The
                       <filename>meta-yocto-bsp/conf/layer.conf</filename> file
                       demonstrates the required syntax:
                       <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

     # We have recipes-* directories, add to BBFILES
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "yoctobsp"
     BBFILE_PATTERN_yoctobsp = "^${LAYERDIR}/"
     BBFILE_PRIORITY_yoctobsp = "5"
                        </literallayout></para>
                        <para>Here is an explanation of the example:
                        <itemizedlist>
                            <listitem><para>The configuration and
                                classes directory is appended to
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink>.
                                <note>
                                    All non-distro layers, which include all BSP
                                    layers, are expected to append the layer
                                    directory to the
                                    <filename>BBPATH</filename>.
                                    On the other hand, distro layers, such as
                                    <filename>meta-yocto</filename>, can choose
                                    to enforce their own precedence over
                                    <filename>BBPATH</filename>.
                                    For an example of that syntax, see the
                                    <filename>layer.conf</filename> file for
                                    the <filename>meta-yocto</filename> layer.
                                </note></para></listitem>
                            <listitem><para>The recipes for the layers are
                                appended to
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILES'>BBFILES</ulink></filename>.
                                </para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_COLLECTIONS'>BBFILE_COLLECTIONS</ulink></filename>
                                variable is then appended with the layer name.
                                </para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PATTERN'>BBFILE_PATTERN</ulink></filename>
                                variable is set to a regular expression and is
                                used to match files from
                                <filename>BBFILES</filename> into a particular
                                layer.
                                In this case,
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
                                is used to make <filename>BBFILE_PATTERN</filename> match within the
                                layer's path.</para></listitem>
                            <listitem><para>The
                                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'>BBFILE_PRIORITY</ulink></filename>
                                variable then assigns a priority to the layer.
                                Applying priorities is useful in situations
                                where the same package might appear in multiple
                                layers and allows you to choose what layer
                                should take precedence.</para></listitem>
                        </itemizedlist></para>
                        <para>Note the use of the
                        <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERDIR'>LAYERDIR</ulink></filename>
                        variable, which expands to the directory of the current
                        layer.</para>
                        <para>Through the use of the <filename>BBPATH</filename>
                        variable, BitBake locates <filename>.bbclass</filename>
                        files, configuration files, and files that are included
                        with <filename>include</filename> and
                        <filename>require</filename> statements.
                        For these cases, BitBake uses the first file that
                        matches the name found in <filename>BBPATH</filename>.
                        This is similar to the way the <filename>PATH</filename>
                        variable is used for binaries.
                        We recommend, therefore, that you use unique
                        <filename>.bbclass</filename> and configuration
                        filenames in your custom layer.</para></listitem>
                    <listitem><para><emphasis>Add Content:</emphasis> Depending
                        on the type of layer, add the content.
                        If the layer adds support for a machine, add the machine
                        configuration in a <filename>conf/machine/</filename>
                        file within the layer.
                        If the layer adds distro policy, add the distro
                        configuration in a <filename>conf/distro/</filename>
                        file with the layer.
                        If the layer introduces new recipes, put the recipes
                        you need in <filename>recipes-*</filename>
                        subdirectories within the layer.
                        <note>In order to be compliant with the Yocto Project,
                            a layer must contain a
                            <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-filelayout-readme'>README file.</ulink>
                            </note></para></listitem>
                </orderedlist>
            </para>

            <para>
                To create layers that are easier to maintain, you should
                consider the following:
                <itemizedlist>
                    <listitem><para>Avoid "overlaying" entire recipes from
                        other layers in your configuration.
                        In other words, do not copy an entire recipe into your
                        layer and then modify it.
                        Use <filename>.bbappend</filename> files to override the
                        parts of the recipe you need to modify.
                        </para></listitem>
                    <listitem><para>Avoid duplicating include files.
                        Use <filename>.bbappend</filename> files for each recipe
                        that uses an include file.
                        Or, if you are introducing a new recipe that requires
                        the included file, use the path relative to the original
                        layer directory to refer to the file.
                        For example, use
                        <filename>require recipes-core/somepackage/somefile.inc</filename>
                        instead of <filename>require somefile.inc</filename>.
                        If you're finding you have to overlay the include file,
                        it could indicate a deficiency in the include file in
                        the layer to which it originally belongs.
                        If this is the case, you need to address that deficiency
                        instead of overlaying the include file.
                        For example, consider how Qt 4 database support plug-ins
                        are configured.
                        The Source Directory does not have MySQL or PostgreSQL,
                        however OpenEmbedded's layer
                        <filename>meta-oe</filename> does.
                        Consequently, <filename>meta-oe</filename> uses
                        <filename>.bbappend</filename> files to modify the
                        <filename>QT_SQL_DRIVER_FLAGS</filename> variable to
                        enable the appropriate plugins.
                        This variable was added to the
                        <filename>qt4.inc</filename> include file in the Source
                        Directory specifically to allow the
                        <filename>meta-oe</filename> layer to be able to control
                        which plugins are built.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                We also recommend the following:
                <itemizedlist>
                    <listitem><para>Store custom layers in a Git repository
                        that uses the
                        <filename>meta-&lt;layer_name&gt;</filename> format.
                        </para></listitem>
                    <listitem><para>Clone the repository alongside other
                        <filename>meta</filename> directories in the
                        <link linkend='source-directory'>Source Directory</link>.
                        </para></listitem>
                 </itemizedlist>
                 Following these recommendations keeps your Source Directory and
                 its configuration entirely inside the Yocto Project's core
                 base.
            </para>
        </section>

        <section id='enabling-your-layer'>
            <title>Enabling Your Layer</title>

            <para>
                Before the OpenEmbedded build system can use your new layer,
                you need to enable it.
                To enable your layer, simply add your layer's path to the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'>BBLAYERS</ulink></filename>
                variable in your <filename>conf/bblayers.conf</filename> file,
                which is found in the
                <link linkend='build-directory'>Build Directory</link>.
                The following example shows how to enable a layer named
                <filename>meta-mylayer</filename>:
                <literallayout class='monospaced'>
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       "
                </literallayout>
            </para>

            <para>
                BitBake parses each <filename>conf/layer.conf</filename> file
                as specified in the <filename>BBLAYERS</filename> variable
                within the <filename>conf/bblayers.conf</filename> file.
                During the processing of each
                <filename>conf/layer.conf</filename> file, BitBake adds the
                recipes, classes and configurations contained within the
                particular layer to the source directory.
            </para>
        </section>

        <section id='using-bbappend-files'>
            <title>Using .bbappend Files</title>

            <para>
                Recipes used to append Metadata to other recipes are called
                BitBake append files.
                BitBake append files use the <filename>.bbappend</filename> file
                type suffix, while the corresponding recipes to which Metadata
                is being appended use the <filename>.bb</filename> file type
                suffix.
            </para>

            <para>
                A <filename>.bbappend</filename> file allows your layer to make
                additions or changes to the content of another layer's recipe
                without having to copy the other recipe into your layer.
                Your <filename>.bbappend</filename> file resides in your layer,
                while the main <filename>.bb</filename> recipe file to
                which you are appending Metadata resides in a different layer.
            </para>

            <para>
                Append files must have the same root names as their corresponding
                recipes.
                For example, the append file
                <filename>someapp_&DISTRO;.bbappend</filename> must apply to
                <filename>someapp_&DISTRO;.bb</filename>.
                This means the original recipe and append file names are version
                number-specific.
                If the corresponding recipe is renamed to update to a newer
                version, the corresponding <filename>.bbappend</filename> file must
                be renamed as well.
                During the build process, BitBake displays an error on starting
                if it detects a <filename>.bbappend</filename> file that does
                not have a corresponding recipe with a matching name.
                See the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_DANGLINGAPPENDS_WARNONLY'><filename>BB_DANGLINGAPPENDS_WARNONLY</filename></ulink>
                variable for information on how to handle this error.
            </para>

            <para>
                Being able to append information to an existing recipe not only
                avoids duplication, but also automatically applies recipe
                changes in a different layer to your layer.
                If you were copying recipes, you would have to manually merge
                changes as they occur.
            </para>

            <para>
                As an example, consider the main formfactor recipe and a
                corresponding formfactor append file both from the
                <link linkend='source-directory'>Source Directory</link>.
                Here is the main formfactor recipe, which is named
                <filename>formfactor_0.0.bb</filename> and located in the
                "meta" layer at
                <filename>meta/recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     DESCRIPTION = "Device formfactor information"
     SECTION = "base"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=3f40d7994397109285ec7b81fdeb3b58 \
                         file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
     PR = "r21"

     SRC_URI = "file://config file://machconfig"
     S = "${WORKDIR}"

     PACKAGE_ARCH = "${MACHINE_ARCH}"
     INHIBIT_DEFAULT_DEPS = "1"

     do_install() {
     	# Only install file if it has a contents
             install -d ${D}${sysconfdir}/formfactor/
             install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
     	if [ -s "${S}/machconfig" ]; then
     	        install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
     	fi
     }          </literallayout>
                In the main recipe, note the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                variable, which tells the OpenEmbedded build system where to
                find files during the build.
            </para>

            <para>
                Following is the append file, which is named
                <filename>formfactor_0.0.bbappend</filename> and is from the
                Crown Bay BSP Layer named
                <filename>meta-intel/meta-crownbay</filename>.
                The file is in <filename>recipes-bsp/formfactor</filename>:
                <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     PRINC := "${@int(PRINC) + 2}"
                </literallayout>
            </para>

            <para>
                By default, the build system uses the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink>
                variable to locate files.
                This append file extends the locations by setting the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                variable.
                Setting this variable in the <filename>.bbappend</filename>
                file is the most reliable and recommended method for adding
                directories to the search path used by the build system
                to find files.
            </para>

            <para>
                The statement in this example extends the directories to include
                <filename>${THISDIR}/${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>,
                which resolves to a directory named
                <filename>formfactor</filename> in the same directory
                in which the append file resides (i.e.
                <filename>meta-intel/meta-crownbay/recipes-bsp/formfactor/formfactor</filename>.
                This implies that you must have the supporting directory
                structure set up that will contain any files or patches you
                will be including from the layer.
            </para>

            <para>
                Using the immediate expansion assignment operator
                <filename>:=</filename> is important because of the reference to
                <filename>THISDIR</filename>.
                The trailing colon character is important as it ensures that
                items in the list remain colon-separated.
                <note><para>BitBake automatically defines the
                    <filename>THISDIR</filename> variable.
                    You should never set this variable yourself.
                    Using <filename>_prepend</filename> ensures your path will
                    be searched prior to other paths in the final list.</para>
                    <para>Also, not all append files add extra files.
                    Many append files simply exist to add build options
                    (e.g. <filename>systemd</filename>).
                    For these cases, it is not necessary to use the
                    "_prepend" part of the statement.</para>
                </note>
            </para>
        </section>

        <section id='prioritizing-your-layer'>
            <title>Prioritizing Your Layer</title>

            <para>
                Each layer is assigned a priority value.
                Priority values control which layer takes precedence if there
                are recipe files with the same name in multiple layers.
                For these cases, the recipe file from the layer with a higher
                priority number takes precedence.
                Priority values also affect the order in which multiple
                <filename>.bbappend</filename> files for the same recipe are
                applied.
                You can either specify the priority manually, or allow the
                build system to calculate it based on the layer's dependencies.
            </para>

            <para>
                To specify the layer's priority manually, use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></ulink>
                variable.
                For example:
                <literallayout class='monospaced'>
     BBFILE_PRIORITY_mylayer = "1"
                </literallayout>
            </para>

            <note>
                <para>It is possible for a recipe with a lower version number
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>
                in a layer that has a higher priority to take precedence.</para>
                <para>Also, the layer priority does not currently affect the
                precedence order of <filename>.conf</filename>
                or <filename>.bbclass</filename> files.
                Future versions of BitBake might address this.</para>
            </note>
        </section>

        <section id='managing-layers'>
            <title>Managing Layers</title>

            <para>
                You can use the BitBake layer management tool to provide a view
                into the structure of recipes across a multi-layer project.
                Being able to generate output that reports on configured layers
                with their paths and priorities and on
                <filename>.bbappend</filename> files and their applicable
                recipes can help to reveal potential problems.
            </para>

            <para>
                Use the following form when running the layer management tool.
                <literallayout class='monospaced'>
     $ bitbake-layers &lt;command&gt; [arguments]
                </literallayout>
                The following list describes the available commands:
                <itemizedlist>
                    <listitem><para><filename><emphasis>help:</emphasis></filename>
                        Displays general help or help on a specified command.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-layers:</emphasis></filename>
                        Shows the current configured layers.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-recipes:</emphasis></filename>
                        Lists available recipes and the layers that provide them.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-overlayed:</emphasis></filename>
                        Lists overlayed recipes.
                        A recipe is overlayed when a recipe with the same name
                        exists in another layer that has a higher layer
                        priority.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-appends:</emphasis></filename>
                        Lists <filename>.bbappend</filename> files and the
                        recipe files to which they apply.
                        </para></listitem>
                    <listitem><para><filename><emphasis>show-cross-depends:</emphasis></filename>
                        Lists dependency relationships between recipes that
                        cross layer boundaries.
                        </para></listitem>
                    <listitem><para><filename><emphasis>flatten:</emphasis></filename>
                        Flattens the layer configuration into a separate output
                        directory.
                        Flattening your layer configuration builds a "flattened"
                        directory that contains the contents of all layers,
                        with any overlayed recipes removed and any
                        <filename>.bbappend</filename> files appended to the
                        corresponding recipes.
                        You might have to perform some manual cleanup of the
                        flattened layer as follows:
                        <itemizedlist>
                            <listitem><para>Non-recipe files (such as patches)
                                are overwritten.
                                The flatten command shows a warning for these
                                files.
                                </para></listitem>
                            <listitem><para>Anything beyond the normal layer
                                setup has been added to the
                                <filename>layer.conf</filename> file.
                                Only the lowest priority layer's
                                <filename>layer.conf</filename> is used.
                                </para></listitem>
                            <listitem><para>Overridden and appended items from
                                <filename>.bbappend</filename> files need to be
                                cleaned up.
                                The contents of each
                                <filename>.bbappend</filename> end up in the
                                flattened recipe.
                                However, if there are appended or changed
                                variable values, you need to tidy these up
                                yourself.
                                Consider the following example.
                                Here, the <filename>bitbake-layers</filename>
                                command adds the line
                                <filename>#### bbappended ...</filename> so that
                                you know where the following lines originate:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "A useful utility"
     ...
     EXTRA_OECONF = "--enable-something"
     ...

     #### bbappended from meta-anotherlayer ####

     DESCRIPTION = "Customized utility"
     EXTRA_OECONF += "--enable-somethingelse"
                                </literallayout>
                                Ideally, you would tidy up these utilities as
                                follows:
                                <literallayout class='monospaced'>
     ...
     DESCRIPTION = "Customized utility"
     ...
     EXTRA_OECONF = "--enable-something --enable-somethingelse"
     ...
                                </literallayout></para></listitem>
                        </itemizedlist></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='creating-a-general-layer-using-the-yocto-layer-script'>
            <title>Creating a General Layer Using the yocto-layer Script</title>

            <para>
                The <filename>yocto-layer</filename> script simplifies
                creating a new general layer.
                <note>
                    For information on BSP layers, see the
                    "<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
                    section in the Yocto Project Board Specific (BSP)
                    Developer's Guide.
                </note>
                The default mode of the script's operation is to prompt you for
                information needed to generate the layer:
                <itemizedlist>
                    <listitem><para>The layer priority
                        </para></listitem>
                    <listitem><para>Whether or not to create a sample recipe.
                        </para></listitem>
                    <listitem><para>Whether or not to create a sample
                        append file.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Use the <filename>yocto-layer create</filename> sub-command
                to create a new general layer.
                In its simplest form, you can create a layer as follows:
                <literallayout class='monospaced'>
     $ yocto-layer create mylayer
                </literallayout>
                The previous example creates a layer named
                <filename>meta-mylayer</filename> in the current directory.
            </para>

            <para>
                As the <filename>yocto-layer create</filename> command runs,
                default values for the prompts appear in brackets.
                Pressing enter without supplying anything for the prompts
                or pressing enter and providing an invalid response causes the
                script to accept the default value.
                Once the script completes, the new layer
                is created in the current working directory.
                The script names the layer by prepending
                <filename>meta-</filename> to the name you provide.
            </para>

            <para>
                Minimally, the script creates the following within the layer:
                <itemizedlist>
                    <listitem><para><emphasis>The <filename>conf</filename>
                        directory:</emphasis>
                        This directory contains the layers
                        <filename>.conf</filename>.
                        The root name for the file is the same as the root name
                        your provided for the layer.
                        </para></listitem>
                    <listitem><para><emphasis>The
                        <filename>COPYING.MIT</filename>:</emphasis>
                        The copyright and use notice for the software.
                        </para></listitem>
                    <listitem><para><emphasis>The <filename>README</filename>
                        file:</emphasis>
                        A file describing the contents of your new layer.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                If you choose to generate a sample recipe file, the script
                prompts you for the name for the recipe and then creates it
                in <filename>&lt;layer&gt;/recipes-example/example/</filename>.
                in a directory named <filename>recipes-example</filename>.
                The script creates a <filename>.bb</filename> file and a
                directory, which contains a sample
                <filename>helloworld.c</filename> source file and along with
                a sample patch file.
                If you do not provide a recipe name, the script uses
                "example".
            </para>

            <para>
                If you choose to generate a sample append file, the script
                prompts you for the name for the file and then creates it
                in <filename>&lt;layer&gt;/recipes-example-bbappend/example-bbappend/</filename>.
                The script creates a <filename>.bbappend</filename> file and a
                directory, which contains a sample patch file.
                If you do not provide a recipe name, the script uses
                "example".
                The script also prompts you for the version of the append file.
                The version should match the recipe to which the append file
                is associated.
            </para>

            <para>
                The easiest way to see how the <filename>yocto-layer</filename>
                script works is to experiment with the script.
                You can also read the usage information by entering the
                following:
                <literallayout class='monospaced'>
     $ yocto-layer help
                </literallayout>
            </para>

            <para>
                Once you create your general layer, you must add it to your
                <filename>bblayers.conf</filename> file.
                Here is an example:
                <literallayout class='monospaced'>
     BBLAYERS = ?" \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        /usr/local/src/yocto/meta-yocto-bsp \
        /usr/local/src/yocto/meta-mylayer \
        "

     BBLAYERS_NON_REMOVABLE ?= " \
        /usr/local/src/yocto/meta \
        /usr/local/src/yocto/meta-yocto \
        "
                </literallayout>
                Adding the layer to this file enables the build system to
                locate the layer during the build.
                </para>
        </section>
    </section>

    <section id='usingpoky-extend-customimage'>
        <title>Customizing Images</title>

        <para>
            You can customize images to satisfy particular requirements.
            This section describes several methods and provides guidelines for each.
        </para>

        <section id='usingpoky-extend-customimage-custombb'>
            <title>Customizing Images Using Custom .bb Files</title>

            <para>
                One way to get additional software into an image is to create a custom image.
                The following example shows the form for the two lines you need:
                <literallayout class='monospaced'>
     IMAGE_INSTALL = "packagegroup-core-x11-base package1 package2"

     inherit core-image
                </literallayout>
            </para>

            <para>
                By creating a custom image, a developer has total control
                over the contents of the image.
                It is important to use the correct names of packages in the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable.
                You must use the OpenEmbedded notation and not the Debian notation for the names
                (e.g. <filename>eglibc-dev</filename> instead of <filename>libc6-dev</filename>).
            </para>

            <para>
                The other method for creating a custom image is to base it on an existing image.
                For example, if you want to create an image based on <filename>core-image-sato</filename>
                but add the additional package <filename>strace</filename> to the image,
                copy the <filename>meta/recipes-sato/images/core-image-sato.bb</filename> to a
                new <filename>.bb</filename> and add the following line to the end of the copy:
                <literallayout class='monospaced'>
     IMAGE_INSTALL += "strace"
                </literallayout>
            </para>
        </section>

        <section id='usingpoky-extend-customimage-customtasks'>
            <title>Customizing Images Using Custom Package Groups</title>

            <para>
                For complex custom images, the best approach is to create a custom package group recipe
                that is used to build the image or images.
                A good example of a package group recipe is
                <filename>meta/recipes-core/packagegroups/packagegroup-core-boot.bb</filename>.
                The
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename>
                variable lists the package group packages you wish to produce. <filename>inherit packagegroup</filename>
                sets appropriate default values and automatically adds <filename>-dev</filename>
                and <filename>-dbg</filename> complementary
                packages for every package specified in <filename>PACKAGES</filename>.
                Note that the inherit line should be towards
                the top of the recipe, certainly before you set <filename>PACKAGES</filename>.
                For each package you specify in <filename>PACKAGES</filename>, you can use
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'>RDEPENDS</ulink></filename>
                and
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'>RRECOMMENDS</ulink></filename>
                entries to provide a list of packages the parent task package should contain.
                Following is an example:
                <literallayout class='monospaced'>
     DESCRIPTION = "My Custom Package Groups"

     inherit packagegroup

     PACKAGES = "\
         packagegroup-custom-apps \
         packagegroup-custom-tools \
         "

     RDEPENDS_packagegroup-custom-apps = "\
         dropbear \
         portmap \
         psplash"

     RDEPENDS_packagegroup-custom-tools = "\
         oprofile \
         oprofileui-server \
         lttng-control \
         lttng-viewer"

     RRECOMMENDS_packagegroup-custom-tools = "\
         kernel-module-oprofile"
                </literallayout>
            </para>

            <para>
                In the previous example, two package group packages are created with their dependencies and their
                recommended package dependencies listed: <filename>packagegroup-custom-apps</filename>, and
                <filename>packagegroup-custom-tools</filename>.
                To build an image using these package group packages, you need to add
                <filename>packagegroup-custom-apps</filename> and/or
                <filename>packagegroup-custom-tools</filename> to
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>.
                For other forms of image dependencies see the other areas of this section.
            </para>
        </section>

        <section id='usingpoky-extend-customimage-imagefeatures'>
            <title>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and
                <filename>EXTRA_IMAGE_FEATURES</filename></title>

            <para>
                You might want to customize your image by enabling or
                disabling high-level image features by using the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
                variables.
                Although the functions for both variables are nearly equivalent,
                best practices dictate using <filename>IMAGE_FEATURES</filename>
                from within a recipe and using
                <filename>EXTRA_IMAGE_FEATURES</filename> from within
                your <filename>local.conf</filename> file, which is found in the
                <link linkend='build-directory'>Build Directory</link>.
            </para>

            <para>
                To understand how these features work, the best reference is
                <filename>meta/classes/core-image.bbclass</filename>.
                In summary, the file looks at the contents of the
                <filename>IMAGE_FEATURES</filename> variable and then maps
                those contents into a set of package groups.
                Based on this information, the build system automatically
                adds the appropriate packages to the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>
                variable.
                Effectively, you are enabling extra features by extending the
                class or creating a custom class for use with specialized image
                <filename>.bb</filename> files.
            </para>

            <para>
                Use the <filename>EXTRA_IMAGE_FEATURES</filename> variable
                from within your local configuration file.
                Using a separate area from which to enable features with
                this variable helps you avoid overwriting the features in the
                image recipe that are enabled with
                <filename>IMAGE_FEATURES</filename>.
                The value of <filename>EXTRA_IMAGE_FEATURES</filename> is added
                to <filename>IMAGE_FEATURES</filename> within
                <filename>meta/conf/bitbake.conf</filename>.
            </para>

            <para>
                To illustrate how you can use these variables to modify your
                image, consider an example that selects the SSH server.
                The Yocto Project ships with two SSH servers you can use
                with your images: Dropbear and OpenSSH.
                Dropbear is a minimal SSH server appropriate for
                resource-constrained environments, while OpenSSH is a
                well-known standard SSH server implementation.
                By default, the <filename>core-image-sato</filename> image
                is configured to use Dropbear.
                The <filename>core-image-basic</filename> and
                <filename>core-image-lsb</filename> images both
                include OpenSSH.
                The <filename>core-image-minimal</filename> image does not
                contain an SSH server.
            </para>

            <para>
                You can customize your image and change these defaults.
                Edit the <filename>IMAGE_FEATURES</filename> variable
                in your recipe or use the
                <filename>EXTRA_IMAGE_FEATURES</filename> in your
                <filename>local.conf</filename> file so that it configures the
                image you are working with to include
                <filename>ssh-server-dropbear</filename> or
                <filename>ssh-server-openssh</filename>.
            </para>

            <note>
                See the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>"
                section in the Yocto Project Reference Manual for a complete
                list of image features that ship with the Yocto Project.
            </note>
        </section>

        <section id='usingpoky-extend-customimage-localconf'>
            <title>Customizing Images Using <filename>local.conf</filename></title>

            <para>
                It is possible to customize image contents by using variables from your
                local configuration in your <filename>conf/local.conf</filename> file.
                Because it is limited to local use, this method generally only allows you to
                add packages and is not as flexible as creating your own customized image.
                When you add packages using local variables this way, you need to realize that
                these variable changes affect all images at the same time and might not be
                what you require.
            </para>

            <para>
                The simplest way to add extra packages to all images is by using the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'>IMAGE_INSTALL</ulink></filename>
                variable with the <filename>_append</filename> operator:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append = " strace"
                </literallayout>
                Use of the syntax is important.
                Specifically, the space between the quote and the package name, which is
                <filename>strace</filename> in this example.
                This space is required since the <filename>_append</filename>
                operator does not add the space.
            </para>

            <para>
                Furthermore, you must use <filename>_append</filename> instead of the <filename>+=</filename>
                operator if you want to avoid ordering issues.
                The reason for this is because doing so unconditionally appends to the variable and
                avoids ordering problems due to the variable being set in image recipes and
                <filename>.bbclass</filename> files with operators like <filename>?=</filename>.
                Using <filename>_append</filename> ensures the operation takes affect.
            </para>

            <para>
                As shown in its simplest use, <filename>IMAGE_INSTALL_append</filename> affects
                all images.
                It is possible to extend the syntax so that the variable applies to a specific image only.
                Here is an example:
                <literallayout class='monospaced'>
     IMAGE_INSTALL_append_pn-core-image-minimal = " strace"
                </literallayout>
                This example adds <filename>strace</filename> to <filename>core-image-minimal</filename>
                only.
            </para>

            <para>
                You can add packages using a similar approach through the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'>CORE_IMAGE_EXTRA_INSTALL</ulink></filename>
                variable.
                If you use this variable, only <filename>core-image-*</filename> images are affected.
            </para>
        </section>
    </section>

    <section id='usingpoky-extend-addpkg'>
        <title>Writing a Recipe to Add a Package to Your Image</title>

        <para>
            Recipes add packages to your image.
            Writing a recipe means creating a <filename>.bb</filename> file that sets some
            variables.
            For information on variables that are useful for recipes and for information about recipe naming
            issues, see the
            "<ulink url='&YOCTO_DOCS_REF_URL;#ref-varlocality-recipe-required'>Required</ulink>"
            section of the Yocto Project Reference Manual.
        </para>

        <para>
            Before writing a recipe from scratch, it is often useful to check
            whether someone else has written one already.
            OpenEmbedded is a good place to look as it has a wider scope and range of packages.
            Because the Yocto Project aims to be compatible with OpenEmbedded, most recipes
            you find there should work for you.
        </para>

        <para>
            For new packages, the simplest way to add a recipe is to base it on a similar
            pre-existing recipe.
            The sections that follow provide some examples that show how to add standard
            types of packages.
        </para>

        <note>
            <para>When writing shell functions, you need to be aware of BitBake's
            curly brace parsing.
            If a recipe uses a closing curly brace within the function and
            the character has no leading spaces, BitBake produces a parsing
            error.
            If you use a pair of curly brace in a shell function, the
            closing curly brace must not be located at the start of the line
            without leading spaces.</para>
            <para>Here is an example that causes BitBake to produce a parsing
            error:
            <literallayout class='monospaced'>
     fakeroot create_shar() {
         cat &lt;&lt; "EOF" &gt; ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
     usage()
     {
       echo "test"
       ###### The following "}" at the start of the line causes a parsing error ######
     }
     EOF
     }
            </literallayout>
            Writing the recipe this way avoids the error:
            <literallayout class='monospaced'>
     fakeroot create_shar() {
         cat &lt;&lt; "EOF" &gt; ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
     usage()
     {
       echo "test"
       ######The following "}" with a leading space at the start of the line avoids the error ######
      }
     EOF
     }
            </literallayout></para>
        </note>

        <section id='usingpoky-extend-addpkg-singlec'>
            <title>Single .c File Package (Hello World!)</title>

            <para>
                Building an application from a single file that is stored locally (e.g. under
                <filename>files/</filename>) requires a recipe that has the file listed in
                the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>
                variable.
                Additionally, you need to manually write the <filename>do_compile</filename> and
                <filename>do_install</filename> tasks.
                The <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename>
                variable defines the
                directory containing the source code, which is set to
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'>
                WORKDIR</ulink></filename> in this case - the directory BitBake uses for the build.
                <literallayout class='monospaced'>
     DESCRIPTION = "Simple helloworld application"
     SECTION = "examples"
     LICENSE = "MIT"
     LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
     PR = "r0"

     SRC_URI = "file://helloworld.c"

     S = "${WORKDIR}"

     do_compile() {
     	${CC} helloworld.c -o helloworld
     }

     do_install() {
     	install -d ${D}${bindir}
     	install -m 0755 helloworld ${D}${bindir}
     }
                </literallayout>
            </para>

            <para>
                By default, the <filename>helloworld</filename>, <filename>helloworld-dbg</filename>,
                and <filename>helloworld-dev</filename> packages are built.
                For information on how to customize the packaging process, see the
                "<link linkend='splitting-an-application-into-multiple-packages'>Splitting an Application
                into Multiple Packages</link>" section.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-autotools'>
            <title>Autotooled Package</title>
            <para>
                Applications that use Autotools such as <filename>autoconf</filename> and
                <filename>automake</filename> require a recipe that has a source archive listed in
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename> and
                also inherits Autotools, which instructs BitBake to use the
                <filename>autotools.bbclass</filename> file, which contains the definitions of all the steps
                needed to build an Autotool-based application.
                The result of the build is automatically packaged.
                And, if the application uses NLS for localization, packages with local information are
                generated (one package per language).
                Following is one example: (<filename>hello_2.3.bb</filename>)
                <literallayout class='monospaced'>
     DESCRIPTION = "GNU Helloworld application"
     SECTION = "examples"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=751419260aa954499f7abaabaa882bbe"
     PR = "r0"

     SRC_URI = "${GNU_MIRROR}/hello/hello-${PV}.tar.gz"

     inherit autotools gettext
                 </literallayout>
            </para>

            <para>
                The variable
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</ulink></filename>
                is used to track source license changes as described in the
                "<ulink url='&YOCTO_DOCS_REF_URL;#usingpoky-configuring-LIC_FILES_CHKSUM'>Tracking License Changes</ulink>" section.
                You can quickly create Autotool-based recipes in a manner similar to the previous example.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-makefile'>
            <title>Makefile-Based Package</title>

            <para>
                Applications that use GNU <filename>make</filename> also require a recipe that has
                the source archive listed in
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                You do not need to add a <filename>do_compile</filename> step since by default BitBake
                starts the <filename>make</filename> command to compile the application.
                If you need additional <filename>make</filename> options, you should store them in the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'>EXTRA_OEMAKE</ulink></filename>
                variable.
                BitBake passes these options into the <filename>make</filename> GNU invocation.
                Note that a <filename>do_install</filename> task is still required.
                Otherwise, BitBake runs an empty <filename>do_install</filename> task by default.
            </para>

            <para>
                Some applications might require extra parameters to be passed to the compiler.
                For example, the application might need an additional header path.
                You can accomplish this by adding to the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink></filename> variable.
                The following example shows this:
                <literallayout class='monospaced'>
     CFLAGS_prepend = "-I ${S}/include "
                </literallayout>
            </para>

            <para>
            In the following example, <filename>mtd-utils</filename> is a makefile-based package:
                <literallayout class='monospaced'>
     DESCRIPTION = "Tools for managing memory technology devices."
     SECTION = "base"
     DEPENDS = "zlib lzo e2fsprogs util-linux"
     HOMEPAGE = "http://www.linux-mtd.infradead.org/"
     LICENSE = "GPLv2+"
     LIC_FILES_CHKSUM = "file://COPYING;md5=0636e73ff0215e8d672dc4c32c317bb3 \
                    file://include/common.h;beginline=1;endline=17;md5=ba05b07912a44ea2bf81ce409380049c"

     SRC_URI = "git://git.infradead.org/mtd-utils.git;protocol=git;tag=995cfe51b0a3cf32f381c140bf72b21bf91cef1b \
	     	file://add-exclusion-to-mkfs-jffs2-git-2.patch"

     S = "${WORKDIR}/git/"

     PR = "r1"

     EXTRA_OEMAKE = "'CC=${CC}' 'RANLIB=${RANLIB}' 'AR=${AR}' \
        'CFLAGS=${CFLAGS} -I${S}/include -DWITHOUT_XATTR' 'BUILDDIR=${S}'"

     do_install () {
	     oe_runmake install DESTDIR=${D} SBINDIR=${sbindir} MANDIR=${mandir} \
            INCLUDEDIR=${includedir}
	     install -d ${D}${includedir}/mtd/
	     for f in ${S}/include/mtd/*.h; do
	     	install -m 0644 $f ${D}${includedir}/mtd/
	     done
     }

     PARALLEL_MAKE = ""

     BBCLASSEXTEND = "native"
                </literallayout>
            </para>

            <para>
                If your sources are available as a tarball instead of a Git repository, you
                will need to provide the URL to the tarball as well as an
                <filename>md5</filename> or <filename>sha256</filename> sum of
                the download.
                Here is an example:
                <literallayout class='monospaced'>
     SRC_URI="ftp://ftp.infradead.org/pub/mtd-utils/mtd-utils-1.4.9.tar.bz2"
     SRC_URI[md5sum]="82b8e714b90674896570968f70ca778b"
                </literallayout>
                You can generate the <filename>md5</filename> or <filename>sha256</filename> sums
                by using the <filename>md5sum</filename> or <filename>sha256sum</filename> commands
                with the target file as the only argument.
                Here is an example:
                <literallayout class='monospaced'>
     $ md5sum mtd-utils-1.4.9.tar.bz2
     82b8e714b90674896570968f70ca778b mtd-utils-1.4.9.tar.bz2
                </literallayout>
            </para>
        </section>

        <section id='splitting-an-application-into-multiple-packages'>
            <title>Splitting an Application into Multiple Packages</title>

            <para>
                You can use the variables
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'>PACKAGES</ulink></filename> and
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'>FILES</ulink></filename>
                to split an application into multiple packages.
            </para>

            <para>
                Following is an example that uses the <filename>libXpm</filename> recipe.
                By default, this recipe generates a single package that contains the library along
                with a few binaries.
                You can modify the recipe to split the binaries into separate packages:
                <literallayout class='monospaced'>
     require xorg-lib-common.inc

     DESCRIPTION = "X11 Pixmap library"
     LICENSE = "X-BSD"
     LIC_FILES_CHKSUM = "file://COPYING;md5=3e07763d16963c3af12db271a31abaa5"
     DEPENDS += "libxext libsm libxt"
     PR = "r3"
     PE = "1"

     XORG_PN = "libXpm"

     PACKAGES =+ "sxpm cxpm"
     FILES_cxpm = "${bindir}/cxpm"
     FILES_sxpm = "${bindir}/sxpm"
                </literallayout>
            </para>

            <para>
                In the previous example, we want to ship the <filename>sxpm</filename>
                and <filename>cxpm</filename> binaries in separate packages.
                Since <filename>bindir</filename> would be packaged into the main
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
                package by default, we prepend the <filename>PACKAGES</filename>
                variable so additional package names are added to the start of list.
                This results in the extra <filename>FILES_*</filename>
                variables then containing information that define which files and
                directories go into which packages.
                Files included by earlier packages are skipped by latter packages.
                Thus, the main <filename>PN</filename> package
                does not include the above listed files.
            </para>
        </section>

        <section id='usingpoky-extend-addpkg-postinstalls'>
            <title>Post-Installation Scripts</title>

            <para>
                To add a post-installation script to a package, add a
                <filename>pkg_postinst_PACKAGENAME()</filename> function to the
                <filename>.bb</filename> file and use
                <filename>PACKAGENAME</filename> as the name of the package you want to attach to the
                <filename>postinst</filename> script.
                Normally,
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'>PN</ulink></filename>
                can be used, which automatically expands to <filename>PACKAGENAME</filename>.
                A post-installation function has the following structure:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     # Commands to carry out
     }
                </literallayout>
            </para>

            <para>
                The script defined in the post-installation function is called when the
                root filesystem is created.
                If the script succeeds, the package is marked as installed.
                If the script fails, the package is marked as unpacked and the script is
                executed when the image boots again.
            </para>

            <para>
                Sometimes it is necessary for the execution of a post-installation
                script to be delayed until the first boot.
                For example, the script might need to be executed on the device itself.
                To delay script execution until boot time, use the following structure in the
                post-installation script:
                <literallayout class='monospaced'>
     pkg_postinst_PACKAGENAME () {
     #!/bin/sh -e
     if [ x"$D" = "x" ]; then
          # Actions to carry out on the device go here
     else
          exit 1
     fi
     }
                </literallayout>
            </para>

            <para>
                The previous example delays execution until the image boots again because the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'>D</ulink></filename>
                variable points
                to the directory containing the image when the root filesystem is created at build time but
                is unset when executed on the first boot.
            </para>
        </section>
    </section>

    <section id="platdev-newmachine">
        <title>Adding a New Machine</title>

        <para>
            Adding a new machine to the Yocto Project is a straightforward process.
            This section provides information that gives you an idea of the changes you must make.
            The information covers adding machines similar to those the Yocto Project already supports.
            Although well within the capabilities of the Yocto Project, adding a totally new architecture
            might require
            changes to <filename>gcc/eglibc</filename> and to the site information, which is
            beyond the scope of this manual.
        </para>

        <para>
            For a complete example that shows how to add a new machine,
            see the
            "<ulink url='&YOCTO_DOCS_BSP_URL;#creating-a-new-bsp-layer-using-the-yocto-bsp-script'>Creating a New BSP Layer Using the yocto-bsp Script</ulink>"
            in the Yocto Project Board Support Package (BSP) Developer's Guide.
        </para>

        <section id="platdev-newmachine-conffile">
            <title>Adding the Machine Configuration File</title>

            <para>
                To add a machine configuration, you need to add a <filename>.conf</filename> file
                with details of the device being added to the <filename>conf/machine/</filename> file.
                The name of the file determines the name the OpenEmbedded build system
                uses to reference the new machine.
            </para>

            <para>
                The most important variables to set in this file are as follows:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_ARCH'>
                        TARGET_ARCH</ulink></filename> (e.g. "arm")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PREFERRED_PROVIDER'>
                        PREFERRED_PROVIDER</ulink></filename>_virtual/kernel (see below)</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE_FEATURES'>
                        MACHINE_FEATURES</ulink></filename> (e.g. "apm screen wifi")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You might also need these variables:
                <itemizedlist>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SERIAL_CONSOLE'>
                        SERIAL_CONSOLE</ulink></filename> (e.g. "115200 ttyS0")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'>
                        KERNEL_IMAGETYPE</ulink></filename> (e.g. "zImage")</para></listitem>
                    <listitem><para><filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'>
                        IMAGE_FSTYPES</ulink></filename> (e.g. "tar.gz jffs2")</para></listitem>
                </itemizedlist>
            </para>

            <para>
                You can find full details on these variables in the reference section.
                You can leverage many existing machine <filename>.conf</filename> files from
                <filename>meta/conf/machine/</filename>.
            </para>
        </section>

        <section id="platdev-newmachine-kernel">
            <title>Adding a Kernel for the Machine</title>

            <para>
                The OpenEmbedded build system needs to be able to build a kernel for the machine.
                You need to either create a new kernel recipe for this machine, or extend an
                existing recipe.
                You can find several kernel examples in the
                Source Directory at <filename>meta/recipes-kernel/linux</filename>
                that you can use as references.
            </para>

            <para>
                If you are creating a new recipe, normal recipe-writing rules apply for setting
                up a
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'>SRC_URI</ulink></filename>.
                Thus, you need to specify any necessary patches and set
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-S'>S</ulink></filename> to point at the source code.
                You need to create a <filename>configure</filename> task that configures the
                unpacked kernel with a defconfig.
                You can do this by using a <filename>make defconfig</filename> command or,
                more commonly, by copying in a suitable <filename>defconfig</filename> file and and then running
                <filename>make oldconfig</filename>.
                By making use of <filename>inherit kernel</filename> and potentially some of the
                <filename>linux-*.inc</filename> files, most other functionality is
                centralized and the the defaults of the class normally work well.
            </para>

            <para>
                If you are extending an existing kernel, it is usually a matter of adding a
                suitable defconfig file.
                The file needs to be added into a location similar to defconfig files
                used for other machines in a given kernel.
                A possible way to do this is by listing the file in the
                <filename>SRC_URI</filename> and adding the machine to the expression in
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-COMPATIBLE_MACHINE'>COMPATIBLE_MACHINE</ulink></filename>:
                <literallayout class='monospaced'>
     COMPATIBLE_MACHINE = '(qemux86|qemumips)'
                </literallayout>
            </para>
        </section>

        <section id="platdev-newmachine-formfactor">
            <title>Adding a Formfactor Configuration File</title>

            <para>
                A formfactor configuration file provides information about the
                target hardware for which the image is being built and information that
                the build system cannot obtain from other sources such as the kernel.
                Some examples of information contained in a formfactor configuration file include
                framebuffer orientation, whether or not the system has a keyboard,
                the positioning of the keyboard in relation to the screen, and
                the screen resolution.
            </para>

            <para>
                The build system uses reasonable defaults in most cases.
                However, if customization is
                necessary, you need to create a <filename>machconfig</filename> file
                in the <filename>meta/recipes-bsp/formfactor/files</filename>
                directory.
                This directory contains directories for specific machines such as
                <filename>qemuarm</filename> and <filename>qemux86</filename>.
                For information about the settings available and the defaults, see the
                <filename>meta/recipes-bsp/formfactor/files/config</filename> file found in the
                same area.
            </para>

            <para>
                Following is an example for qemuarm:
                <literallayout class='monospaced'>
     HAVE_TOUCHSCREEN=1
     HAVE_KEYBOARD=1

     DISPLAY_CAN_ROTATE=0
     DISPLAY_ORIENTATION=0
     #DISPLAY_WIDTH_PIXELS=640
     #DISPLAY_HEIGHT_PIXELS=480
     #DISPLAY_BPP=16
     DISPLAY_DPI=150
     DISPLAY_SUBPIXEL_ORDER=vrgb
                </literallayout>
            </para>
        </section>
    </section>

    <section id="platdev-working-with-libraries">
        <title>Working With Libraries</title>

        <para>
            Libraries are an integral part of your system.
            This section describes some common practices you might find
            helpful when working with libraries to build your system:
            <itemizedlist>
                <listitem><para><link linkend='including-static-library-files'>How to include static library files</link>
                    </para></listitem>
                <listitem><para><link linkend='combining-multiple-versions-library-files-into-one-image'>How to use the Multilib feature to combine multiple versions of library files into a single image</link>
                    </para></listitem>
                <listitem><para><link linkend='installing-multiple-versions-of-the-same-library'>How to install multiple versions of the same library in parallel on the same system</link>
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='including-static-library-files'>
            <title>Including Static Library Files</title>

            <para>
                If you are building a library and the library offers static linking, you can control
                which static library files (<filename>*.a</filename> files) get included in the
                built library.
            </para>

            <para>
                The <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES_*</filename></ulink>
                variables in the
                <filename>meta/conf/bitbake.conf</filename> configuration file define how files installed
                by the <filename>do_install</filename> task are packaged.
                By default, the <filename>PACKAGES</filename> variable contains
                <filename>${PN}-staticdev</filename>, which includes all static library files.
                <note>
                    Some previously released versions of the Yocto Project
                    defined the static library files through
                    <filename>${PN}-dev</filename>.
                </note>
                Following, is part of the BitBake configuration file.
                You can see where the static library files are defined:
                <literallayout class='monospaced'>
     PACKAGES = "${PN}-dbg ${PN} ${PN}-doc ${PN}-dev ${PN}-staticdev ${PN}-locale"
     PACKAGES_DYNAMIC = "${PN}-locale-*"
     FILES = ""

     FILES_${PN} = "${bindir}/* ${sbindir}/* ${libexecdir}/* ${libdir}/lib*${SOLIBS} \
                 ${sysconfdir} ${sharedstatedir} ${localstatedir} \
                 ${base_bindir}/* ${base_sbindir}/* \
                 ${base_libdir}/*${SOLIBS} \
                 ${datadir}/${BPN} ${libdir}/${BPN}/* \
                 ${datadir}/pixmaps ${datadir}/applications \
                 ${datadir}/idl ${datadir}/omf ${datadir}/sounds \
                 ${libdir}/bonobo/servers"

     FILES_${PN}-doc = "${docdir} ${mandir} ${infodir} ${datadir}/gtk-doc \
                 ${datadir}/gnome/help"
     SECTION_${PN}-doc = "doc"

     FILES_${PN}-dev = "${includedir} ${libdir}/lib*${SOLIBSDEV} ${libdir}/*.la \
                     ${libdir}/*.o ${libdir}/pkgconfig ${datadir}/pkgconfig \
                     ${datadir}/aclocal ${base_libdir}/*.o"
     SECTION_${PN}-dev = "devel"
     ALLOW_EMPTY_${PN}-dev = "1"
     RDEPENDS_${PN}-dev = "${PN} (= ${EXTENDPKGV})"

     FILES_${PN}-staticdev = "${libdir}/*.a ${base_libdir}/*.a"
     SECTION_${PN}-staticdev = "devel"
     RDEPENDS_${PN}-staticdev = "${PN}-dev (= ${EXTENDPKGV})"
                </literallayout>
            </para>
        </section>

        <section id="combining-multiple-versions-library-files-into-one-image">
            <title>Combining Multiple Versions of Library Files into One Image</title>

            <para>
                The build system offers the ability to build libraries with different
                target optimizations or architecture formats and combine these together
                into one system image.
                You can link different binaries in the image
                against the different libraries as needed for specific use cases.
                This feature is called "Multilib."
            </para>

            <para>
                An example would be where you have most of a system compiled in 32-bit
                mode using 32-bit libraries, but you have something large, like a database
                engine, that needs to be a 64-bit application and uses 64-bit libraries.
                Multilib allows you to get the best of both 32-bit and 64-bit libraries.
            </para>

            <para>
                While the Multilib feature is most commonly used for 32 and 64-bit differences,
                the approach the build system uses facilitates different target optimizations.
                You could compile some binaries to use one set of libraries and other binaries
                to use other different sets of libraries.
                The libraries could differ in architecture, compiler options, or other
                optimizations.
            </para>

            <para>
                This section overviews the Multilib process only.
                For more details on how to implement Multilib, see the
                <ulink url='&YOCTO_WIKI_URL;/wiki/Multilib'>Multilib</ulink> wiki
                page.
            </para>

            <para>
                Aside from this wiki page, several examples exist in the
                <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/tree/meta-skeleton'><filename>meta-skeleton</filename></ulink>
                layer found in the
               <link linkend='source-directory'>Source Directory</link>:
                <itemizedlist>
                    <listitem><para><filename>conf/multilib-example.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>conf/multilib-example2.conf</filename>
                        configuration file</para></listitem>
                    <listitem><para><filename>recipes-multilib/images/core-image-multilib-example.bb</filename>
                        recipe</para></listitem>
                </itemizedlist>
            </para>

            <section id='preparing-to-use-multilib'>
                <title>Preparing to Use Multilib</title>

                <para>
                    User-specific requirements drive the Multilib feature.
                    Consequently, there is no one "out-of-the-box" configuration that likely
                    exists to meet your needs.
                </para>

                <para>
                    In order to enable Multilib, you first need to ensure your recipe is
                    extended to support multiple libraries.
                    Many standard recipes are already extended and support multiple libraries.
                    You can check in the <filename>meta/conf/multilib.conf</filename>
                    configuration file in the
                    <link linkend='source-directory'>Source Directory</link> to see how this is
                    done using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
                    variable.
                    Eventually, all recipes will be covered and this list will be unneeded.
                </para>

                <para>
                    For the most part, the Multilib class extension works automatically to
                    extend the package name from <filename>${PN}</filename> to
                    <filename>${MLPREFIX}${PN}</filename>, where <filename>MLPREFIX</filename>
                    is the particular multilib (e.g. "lib32-" or "lib64-").
                    Standard variables such as
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RPROVIDES'><filename>RPROVIDES</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>,
                    and <filename>PACKAGES_DYNAMIC</filename> are automatically extended by the system.
                    If you are extending any manual code in the recipe, you can use the
                    <filename>${MLPREFIX}</filename> variable to ensure those names are extended
                    correctly.
                    This automatic extension code resides in <filename>multilib.bbclass</filename>.
                </para>
            </section>

            <section id='using-multilib'>
                <title>Using Multilib</title>

                <para>
                    After you have set up the recipes, you need to define the actual
                    combination of multiple libraries you want to build.
                    You accomplish this through your <filename>local.conf</filename>
                    configuration file in the
                    <link linkend='build-directory'>Build Directory</link>.
                    An example configuration would be as follows:
                    <literallayout class='monospaced'>
     MACHINE = "qemux86-64"
     require conf/multilib.conf
     MULTILIBS = "multilib:lib32"
     DEFAULTTUNE_virtclass-multilib-lib32 = "x86"
     IMAGE_INSTALL = "lib32-connman"
                    </literallayout>
                    This example enables an
                    additional library named <filename>lib32</filename> alongside the
                    normal target packages.
                    When combining these "lib32" alternatives, the example uses "x86" for tuning.
                    For information on this particular tuning, see
                    <filename>meta/conf/machine/include/ia32/arch-ia32.inc</filename>.
                </para>

                <para>
                    The example then includes <filename>lib32-connman</filename>
                    in all the images, which illustrates one method of including a
                    multiple library dependency.
                    You can use a normal image build to include this dependency,
                    for example:
                    <literallayout class='monospaced'>
     $ bitbake core-image-sato
                    </literallayout>
                    You can also build Multilib packages specifically with a command like this:
                    <literallayout class='monospaced'>
     $  bitbake lib32-connman
                    </literallayout>
                </para>
            </section>

            <section id='additional-implementation-details'>
                <title>Additional Implementation Details</title>

                <para>
                    Different packaging systems have different levels of native Multilib
                    support.
                    For the RPM Package Management System, the following implementation details
                    exist:
                    <itemizedlist>
                        <listitem><para>A unique architecture is defined for the Multilib packages,
                            along with creating a unique deploy folder under
                            <filename>tmp/deploy/rpm</filename> in the
                            <link linkend='build-directory'>Build Directory</link>.
                            For example, consider <filename>lib32</filename> in a
                            <filename>qemux86-64</filename> image.
                            The possible architectures in the system are "all", "qemux86_64",
                            "lib32_qemux86_64", and "lib32_x86".</para></listitem>
                        <listitem><para>The <filename>${MLPREFIX}</filename> variable is stripped from
                            <filename>${PN}</filename> during RPM packaging.
                            The naming for a normal RPM package and a Multilib RPM package in a
                            <filename>qemux86-64</filename> system resolves to something similar to
                            <filename>bash-4.1-r2.x86_64.rpm</filename> and
                            <filename>bash-4.1.r2.lib32_x86.rpm</filename>, respectively.
                            </para></listitem>
                        <listitem><para>When installing a Multilib image, the RPM backend first
                            installs the base image and then installs the Multilib libraries.
                            </para></listitem>
                        <listitem><para>The build system relies on RPM to resolve the identical files in the
                            two (or more) Multilib packages.</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    For the IPK Package Management System, the following implementation details exist:
                    <itemizedlist>
                        <listitem><para>The <filename>${MLPREFIX}</filename> is not stripped from
                            <filename>${PN}</filename> during IPK packaging.
                            The naming for a normal RPM package and a Multilib IPK package in a
                            <filename>qemux86-64</filename> system resolves to something like
                            <filename>bash_4.1-r2.x86_64.ipk</filename> and
                            <filename>lib32-bash_4.1-rw_x86.ipk</filename>, respectively.
                            </para></listitem>
                        <listitem><para>The IPK deploy folder is not modified with
                            <filename>${MLPREFIX}</filename> because packages with and without
                            the Multilib feature can exist in the same folder due to the
                            <filename>${PN}</filename> differences.</para></listitem>
                        <listitem><para>IPK defines a sanity check for Multilib installation
                            using certain rules for file comparison, overridden, etc.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>

        <section id='installing-multiple-versions-of-the-same-library'>
            <title>Installing Multiple Versions of the Same Library</title>

            <para>
                Situations can exist where you need to install and use
                multiple versions of the same library on the same system
                at the same time.
                These situations almost always exist when a library API
                changes and you have multiple pieces of software that
                depend on the separate versions of the library.
                To accommodate these situations, you can install multiple
                versions of the same library in parallel on the same system.
            </para>

            <para>
                The process is straight forward as long as the libraries use
                proper versioning.
                With properly versioned libraries, all you need to do to
                individually specify the libraries is create separate,
                appropriately named recipes where the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink> part of the
                name includes a portion that differentiates each library version
                (e.g.the major part of the version number).
                Thus, instead of having a single recipe that loads one version
                of a library (e.g. <filename>clutter</filename>), you provide
                multiple recipes that result in different versions
                of the libraries you want.
                As an example, the following two recipes would allow the
                two separate versions of the <filename>clutter</filename>
                library to co-exist on the same system:
                <literallayout class='monospaced'>
     clutter-1.6_1.6.20.bb
     clutter-1.8_1.8.4.bb
                </literallayout>
                Additionally, if you have other recipes that depend on a given
                library, you need to use the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                variable to create the dependency.
                Continuing with the same example, if you want to have a recipe
                depend on the 1.8 version of the <filename>clutter</filename>
                library, use the following in your recipe:
                <literallayout class='monospaced'>
     DEPENDS = "clutter-1.8"
                </literallayout>
            </para>
        </section>
    </section>

    <section id='configuring-the-kernel'>
        <title>Configuring the Kernel</title>

        <para>
            Configuring the Yocto Project kernel consists of making sure the <filename>.config</filename>
            file has all the right information in it for the image you are building.
            You can use the <filename>menuconfig</filename> tool and configuration fragments to
            make sure your <filename>.config</filename> file is just how you need it.
            This section describes how to use <filename>menuconfig</filename>, create and use
            configuration fragments, and how to interactively tweak your <filename>.config</filename>
            file to create the leanest kernel configuration file possible.
        </para>

        <para>
            For more information on kernel configuration, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#changing-the-configuration'>Changing the Configuration</ulink>"
            section in the Yocto Project Linux Kernel Development Manual.
        </para>

        <section id='using-menuconfig'>
            <title>Using&nbsp;&nbsp;<filename>menuconfig</filename></title>

            <para>
                The easiest way to define kernel configurations is to set them through the
                <filename>menuconfig</filename> tool.
                This tool provides an interactive method with which
                to set kernel configurations.
                For general information on <filename>menuconfig</filename>, see
                <ulink url='http://en.wikipedia.org/wiki/Menuconfig'></ulink>.
            </para>

            <para>
                To use the <filename>menuconfig</filename> tool in the Yocto Project development
                environment, you must build the tool using BitBake.
                Thus, the environment must be set up using the
                <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                script found in the
                <link linkend='build-directory'>Build Directory</link>.
                The following commands build and invoke <filename>menuconfig</filename> assuming the
                <link linkend='source-directory'>Source Directory</link>
                top-level folder is <filename>~/poky</filename>:
                <literallayout class='monospaced'>
     $ cd ~/poky
     $ source oe-init-build-env
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
                Once <filename>menuconfig</filename> comes up, its standard interface allows you to
                interactively examine and configure all the kernel configuration parameters.
                After making your changes, simply exit the tool and save your changes to
                create an updated version of the <filename>.config</filename> configuration file.
            </para>

            <para>
                Consider an example that configures the <filename>linux-yocto-3.4</filename>
                kernel.
                The OpenEmbedded build system recognizes this kernel as
                <filename>linux-yocto</filename>.
                Thus, the following commands from the shell in which you previously sourced the
                environment initialization script cleans the shared state cache and the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>
                directory and then builds and launches <filename>menuconfig</filename>:
                <literallayout class='monospaced'>
     $ bitbake linux-yocto -c menuconfig
                </literallayout>
            </para>

            <para>
                Once <filename>menuconfig</filename> launches, use the interface
                to navigate through the selections to find the configuration settings in
                which you are interested.
                For example, consider the <filename>CONFIG_SMP</filename> configuration setting.
                You can find it at <filename>Processor Type and Features</filename> under
                the configuration selection <filename>Symmetric Multi-processing Support</filename>.
                After highlighting the selection, use the arrow keys to select or deselect
                the setting.
                When you are finished with all your selections, exit out and save them.
            </para>

            <para>
                Saving the selections updates the <filename>.config</filename> configuration file.
                This is the file that the OpenEmbedded build system uses to configure the
                kernel during the build.
                You can find and examine this file in the Build Directory in
                <filename>tmp/work/</filename>.
                The actual <filename>.config</filename> is located in the area where the
                specific kernel is built.
                For example, if you were building a Linux Yocto kernel based on the
                Linux 3.4 kernel and you were building a QEMU image targeted for
                <filename>x86</filename> architecture, the
                <filename>.config</filename> file would be located here:
                <literallayout class='monospaced'>
     ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-3.4.11+git1+84f...
        ...656ed30-r1/linux-qemux86-standard-build
                </literallayout>
                <note>
                    The previous example directory is artificially split and many of the characters
                    in the actual filename are omitted in order to make it more readable.
                    Also, depending on the kernel you are using, the exact pathname
                    for <filename>linux-yocto-3.4...</filename> might differ.
                </note>
            </para>

            <para>
                Within the <filename>.config</filename> file, you can see the kernel settings.
                For example, the following entry shows that symmetric multi-processor support
                is not set:
                <literallayout class='monospaced'>
     # CONFIG_SMP is not set
                </literallayout>
            </para>

            <para>
                A good method to isolate changed configurations is to use a combination of the
                <filename>menuconfig</filename> tool and simple shell commands.
                Before changing configurations with <filename>menuconfig</filename>, copy the
                existing <filename>.config</filename> and rename it to something else,
                use <filename>menuconfig</filename> to make
                as many changes an you want and save them, then compare the renamed configuration
                file against the newly created file.
                You can use the resulting differences as your base to create configuration fragments
                to permanently save in your kernel layer.
                <note>
                    Be sure to make a copy of the <filename>.config</filename> and don't just
                    rename it.
                    The build system needs an existing <filename>.config</filename>
                    from which to work.
                </note>
            </para>
        </section>

        <section id='creating-config-fragments'>
            <title>Creating Configuration Fragments</title>

            <para>
                Configuration fragments are simply kernel options that appear in a file
                placed where the OpenEmbedded build system can find and apply them.
                Syntactically, the configuration statement is identical to what would appear
                in the <filename>.config</filename> file, which is in the
                <link linkend='build-directory'>Build Directory</link> in
                <filename>tmp/work/&lt;arch&gt;-poky-linux/linux-yocto-&lt;release-specific-string&gt;/linux-&lt;arch&gt;-&lt;build-type&gt;</filename>.
            </para>

            <para>
                It is simple to create a configuration fragment.
                For example, issuing the following from the shell creates a configuration fragment
                file named <filename>my_smp.cfg</filename> that enables multi-processor support
                within the kernel:
                <literallayout class='monospaced'>
     $ echo "CONFIG_SMP=y" >> my_smp.cfg
                </literallayout>
                <note>
                    All configuration files must use the <filename>.cfg</filename> extension in order
                    for the OpenEmbedded build system to recognize them as a configuration fragment.
                </note>
            </para>

            <para>
                Where do you put your configuration files?
                You can place these configuration files in the same area pointed to by
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
                The OpenEmbedded build system will pick up the configuration and add it to the
                kernel's configuration.
                For example, suppose you had a set of configuration options in a file called
                <filename>myconfig.cfg</filename>.
                If you put that file inside a directory named <filename>/linux-yocto</filename>
                that resides in the same directory as the kernel's append file and then add
                a <filename>SRC_URI</filename> statement such as the following to the kernel's append file,
                those configuration options will be picked up and applied when the kernel is built.
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg"
                </literallayout>
            </para>

            <para>
                As mentioned earlier, you can group related configurations into multiple files and
                name them all in the <filename>SRC_URI</filename> statement as well.
                For example, you could group separate configurations specifically for Ethernet and graphics
                into their own files and add those by using a <filename>SRC_URI</filename> statement like the
                following in your append file:
                <literallayout class='monospaced'>
     SRC_URI += "file://myconfig.cfg \
            file://eth.cfg \
            file://gfx.cfg"
                </literallayout>
            </para>
        </section>

        <section id='fine-tuning-the-kernel-configuration-file'>
            <title>Fine-Tuning the Kernel Configuration File</title>

            <para>
                You can make sure the <filename>.config</filename> file is as lean or efficient as
                possible by reading the output of the kernel configuration fragment audit,
                noting any issues, making changes to correct the issues, and then repeating.
            </para>

            <para>
                As part of the kernel build process, the
                <filename>kernel_configcheck</filename> task runs.
                This task validates the kernel configuration by checking the final
                <filename>.config</filename> file against the input files.
                During the check, the task produces warning messages for the following
                issues:
                <itemizedlist>
                    <listitem><para>Requested options that did not make the final
                        <filename>.config</filename> file.</para></listitem>
                    <listitem><para>Configuration items that appear twice in the same
                        configuration fragment.</para></listitem>
                    <listitem><para>Configuration items tagged as "required" were overridden.
                        </para></listitem>
                    <listitem><para>A board overrides a non-board specific option.</para></listitem>
                    <listitem><para>Listed options not valid for the kernel being processed.
                        In other words, the option does not appear anywhere.</para></listitem>
                </itemizedlist>
                <note>
                    The <filename>kernel_configcheck</filename> task can also optionally report
                    if an option is overridden during processing.
                </note>
            </para>

            <para>
                For each output warning, a message points to the file
                that contains a list of the options and a pointer to the config
                fragment that defines them.
                Collectively, the files are the key to streamlining the configuration.
            </para>

            <para>
                To streamline the configuration, do the following:
                <orderedlist>
                    <listitem><para>Start with a full configuration that you know
                        works - it builds and boots successfully.
                        This configuration file will be your baseline.</para></listitem>
                    <listitem><para>Separately run the <filename>configme</filename> and
                        <filename>kernel_configcheck</filename> tasks.</para></listitem>
                    <listitem><para>Take the resulting list of files from the
                        <filename>kernel_configcheck</filename> task warnings and do the following:
                        <itemizedlist>
                            <listitem><para>Drop values that are redefined in the fragment but do not
                                change the final <filename>.config</filename> file.</para></listitem>
                            <listitem><para>Analyze and potentially drop values from the
                                <filename>.config</filename> file that override required
                                configurations.</para></listitem>
                            <listitem><para>Analyze and potentially remove non-board specific options.
                                </para></listitem>
                            <listitem><para>Remove repeated and invalid options.</para></listitem>
                        </itemizedlist></para></listitem>
                    <listitem><para>After you have worked through the output of the kernel configuration
                        audit, you can re-run the <filename>configme</filename>
                        and <filename>kernel_configcheck</filename> tasks to see the results of your
                        changes.
                        If you have more issues, you can deal with them as described in the
                        previous step.</para></listitem>
                </orderedlist>
            </para>

            <para>
                Iteratively working through steps two through four eventually yields
                a minimal, streamlined configuration file.
                Once you have the best <filename>.config</filename>, you can build the Linux
                Yocto kernel.
            </para>
        </section>
    </section>

    <section id="patching-the-kernel">
        <title>Patching the Kernel</title>

        <para>
            Patching the kernel involves changing or adding configurations to an existing kernel,
            changing or adding recipes to the kernel that are needed to support specific hardware features,
            or even altering the source code itself.
            <note>
                You can use the <filename>yocto-kernel</filename> script
                found in the <link linkend='source-directory'>Source Directory</link>
                under <filename>scripts</filename> to manage kernel patches and configuration.
                See the "<ulink url='&YOCTO_DOCS_BSP_URL;#managing-kernel-patches-and-config-items-with-yocto-kernel'>Managing kernel Patches and Config Items with yocto-kernel</ulink>"
                section in the Yocto Project Board Support Packages (BSP) Developer's Guide for
                more information.</note>
        </para>

        <para>
            This example creates a simple patch by adding some QEMU emulator console
            output at boot time through <filename>printk</filename> statements in the kernel's
            <filename>calibrate.c</filename> source code file.
            Applying the patch and booting the modified image causes the added
            messages to appear on the emulator's console.
        </para>

        <para>
            The example assumes a clean build exists for the <filename>qemux86</filename>
            machine in a Source Directory named <filename>poky</filename>.
            Furthermore, the <link linkend='build-directory'>Build Directory</link> is
            <filename>build</filename> and is located in <filename>poky</filename> and
            the kernel is based on the Linux 3.4 kernel.
            For general information on how to configure the most efficient build, see the
            "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>" section
            in the Yocto Project Quick Start.
        </para>

        <para>
            Also, for more information on patching the kernel, see the
            "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#applying-patches'>Applying Patches</ulink>"
            section in the Yocto Project Linux Kernel Development Manual.
        </para>

        <section id='create-a-layer-for-your-changes'>
            <title>Create a Layer for your Changes</title>

            <para>
                The first step is to create a layer so you can isolate your changes:
                <literallayout class='monospaced'>
     $cd ~/poky
     $mkdir meta-mylayer
                </literallayout>
                Creating a directory that follows the Yocto Project layer naming
                conventions sets up the layer for your changes.
                The layer is where you place your configuration files, append
                files, and patch files.
                To learn more about creating a layer and filling it with the
                files you need, see the "<link linkend='understanding-and-creating-layers'>Understanding
                and Creating Layers</link>" section.
            </para>
        </section>

        <section id='finding-the-kernel-source-code'>
            <title>Finding the Kernel Source Code</title>

            <para>
                Each time you build a kernel image, the kernel source code is fetched
                and unpacked into the following directory:
                <literallayout class='monospaced'>
     ${S}/linux
                </literallayout>
                See the "<link linkend='finding-the-temporary-source-code'>Finding the Temporary Source Code</link>"
                section and the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> variable
                for more information about where source is kept during a build.
            </para>

            <para>
                For this example, we are going to patch the
                <filename>init/calibrate.c</filename> file
                by adding some simple console <filename>printk</filename> statements that we can
                see when we boot the image using QEMU.
            </para>
        </section>

        <section id='creating-the-patch'>
            <title>Creating the Patch</title>

            <para>
                Two methods exist by which you can create the patch:
                <link linkend='using-a-git-workflow'>Git workflow</link> and
                <link linkend='using-a-quilt-workflow'>Quilt workflow</link>.
                For kernel patches, the Git workflow is more appropriate.
                This section assumes the Git workflow and shows the steps specific to
                this example.
                <orderedlist>
                    <listitem><para><emphasis>Change the working directory</emphasis>:
                        Change to where the kernel source code is before making
                        your edits to the <filename>calibrate.c</filename> file:
                        <literallayout class='monospaced'>
     $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
                        </literallayout>
                        Because you are working in an established Git repository,
                        you must be in this directory in order to commit your changes
                        and create the patch file.
                        <note>The <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink> and
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> variables
                            represent the version and revision for the
                            <filename>linux-yocto</filename> recipe.
                            The <filename>PV</filename> variable includes the Git meta and machine
                            hashes, which make the directory name longer than you might
                            expect.
                        </note></para></listitem>
                    <listitem><para><emphasis>Edit the source file</emphasis>:
                        Edit the <filename>init/calibrate.c</filename> file to have the
                        following changes:
                        <literallayout class='monospaced'>
     void __cpuinit calibrate_delay(void)
     {
         unsigned long lpj;
         static bool printed;
         int this_cpu = smp_processor_id();

         printk("*************************************\n");
         printk("*                                   *\n");
         printk("*        HELLO YOCTO KERNEL         *\n");
         printk("*                                   *\n");
         printk("*************************************\n");

     	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
               .
               .
               .
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Stage and commit your changes</emphasis>:
                        These Git commands display the modified file, stage it, and then
                        commit the file:
                        <literallayout class='monospaced'>
     $ git status
     $ git add init/calibrate.c
     $ git commit -m "calibrate: Add printk example"
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Generate the patch file</emphasis>:
                        This Git command creates the a patch file named
                        <filename>0001-calibrate-Add-printk-example.patch</filename>
                        in the current directory.
                        <literallayout class='monospaced'>
     $ git format-patch -1
                        </literallayout>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='set-up-your-layer-for-the-build'>
            <title>Set Up Your Layer for the Build</title>

            <para>These steps get your layer set up for the build:
                <orderedlist>
                    <listitem><para><emphasis>Create additional structure</emphasis>:
                        Create the additional layer structure:
                        <literallayout class='monospaced'>
     $ cd ~/poky/meta-mylayer
     $ mkdir conf
     $ mkdir recipes-kernel
     $ mkdir recipes-kernel/linux
     $ mkdir recipes-kernel/linux/linux-yocto
                         </literallayout>
                         The <filename>conf</filename> directory holds your configuration files, while the
                         <filename>recipes-kernel</filename> directory holds your append file and
                         your patch file.</para></listitem>
                    <listitem><para><emphasis>Create the layer configuration file</emphasis>:
                        Move to the <filename>meta-mylayer/conf</filename> directory and create
                        the <filename>layer.conf</filename> file as follows:
                        <literallayout class='monospaced'>
     # We have a conf and classes directory, add to BBPATH
     BBPATH .= ":${LAYERDIR}"

     # We have recipes-* directories, add to BBFILES
     BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
                 ${LAYERDIR}/recipes-*/*/*.bbappend"

     BBFILE_COLLECTIONS += "mylayer"
     BBFILE_PATTERN_mylayer = "^${LAYERDIR}/"
     BBFILE_PRIORITY_mylayer = "5"
                         </literallayout>
                         Notice <filename>mylayer</filename> as part of the last three
                         statements.</para></listitem>
                    <listitem><para><emphasis>Create the kernel recipe append file</emphasis>:
                        Move to the <filename>meta-mylayer/recipes-kernel/linux</filename> directory and create
                        the <filename>linux-yocto_3.4.bbappend</filename> file as follows:
                        <literallayout class='monospaced'>
     FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

     SRC_URI += "file://0001-calibrate-Add-printk-example.patch"

     PRINC := "${@int(PRINC) + 1}"
                        </literallayout>
                        The <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESEXTRAPATHS'><filename>FILESEXTRAPATHS</filename></ulink>
                        and <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                        statements enable the OpenEmbedded build system to find the patch file.
                        For more information on using append files, see the
                        "<link linkend='using-bbappend-files'>Using .bbappend Files</link>"
                        section.
                        </para></listitem>
                    <listitem><para><emphasis>Put the patch file in your layer</emphasis>:
                        Move the <filename>0001-calibrate-Add-printk-example.patch</filename> file to
                        the <filename>meta-mylayer/recipes-kernel/linux/linux-yocto</filename>
                        directory.</para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='set-up-for-the-build'>
            <title>Set Up for the Build</title>

            <para>
                Do the following to make sure the build parameters are set up for the example.
                Once you set up these build parameters, they do not have to change unless you
                change the target architecture of the machine you are building:
                <itemizedlist>
                    <listitem><para><emphasis>Build for the correct target architecture:</emphasis> Your
                        selected <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>
                        definition within the <filename>local.conf</filename> file in the
                        <link linkend='build-directory'>Build Directory</link>
                        specifies the target architecture used when building the Linux kernel.
                        By default, <filename>MACHINE</filename> is set to
                        <filename>qemux86</filename>, which specifies a 32-bit
                        <trademark class='registered'>Intel</trademark> Architecture
                        target machine suitable for the QEMU emulator.</para></listitem>
                    <listitem><para><emphasis>Identify your <filename>meta-mylayer</filename>
                        layer:</emphasis> The
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-BBLAYERS'><filename>BBLAYERS</filename></ulink>
                        variable in the
                        <filename>bblayers.conf</filename> file found in the
                        <filename>poky/build/conf</filename> directory needs to have the path to your local
                        <filename>meta-mylayer</filename> layer.
                        By default, the <filename>BBLAYERS</filename> variable contains paths to
                        <filename>meta</filename>, <filename>meta-yocto</filename>, and
                        <filename>meta-yocto-bsp</filename> in the
                        <filename>poky</filename> Git repository.
                        Add the path to your <filename>meta-mylayer</filename> location:
                        <literallayout class='monospaced'>
     BBLAYERS ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       $HOME/poky/meta-yocto-bsp \
       $HOME/poky/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       $HOME/poky/meta \
       $HOME/poky/meta-yocto \
       "
                        </literallayout></para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='build-the-modified-qemu-kernel-image'>
            <title>Build the Modified QEMU Kernel Image</title>

            <para>
                The following steps build your modified kernel image:
                <orderedlist>
                    <listitem><para><emphasis>Be sure your build environment is initialized</emphasis>:
                        Your environment should be set up since you previously sourced
                        the
                        <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>
                        script.
                        If it is not, source the script again from <filename>poky</filename>.
                        <literallayout class='monospaced'>
     $ cd ~/poky
     $ source &OE_INIT_FILE;
                        </literallayout>
                        </para></listitem>
                    <listitem><para><emphasis>Clean up</emphasis>:
                        Be sure to clean the shared state out by running the
                        <filename>cleansstate</filename> BitBake task as follows from your Build Directory:
                        <literallayout class='monospaced'>
     $ bitbake -c cleansstate linux-yocto
                        </literallayout></para>
                        <para><note>Never remove any files by hand from the <filename>tmp/deploy</filename>
                        directory inside the
                        <link linkend='build-directory'>Build Directory</link>.
                        Always use the various BitBake clean tasks to clear out previous
                        build artifacts.
                        </note></para></listitem>
                    <listitem><para><emphasis>Build the image</emphasis>:
                        Next, build the kernel image using this command:
                        <literallayout class='monospaced'>
     $ bitbake -k linux-yocto
                        </literallayout></para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='boot-the-image-and-verify-your-changes'>
            <title>Boot the Image and Verify Your Changes</title>

            <para>
                These steps boot the image and allow you to see the changes
                <orderedlist>
                    <listitem><para><emphasis>Boot the image</emphasis>:
                        Boot the modified image in the QEMU emulator
                        using this command:
                        <literallayout class='monospaced'>
     $ runqemu qemux86
                        </literallayout></para></listitem>
                    <listitem><para><emphasis>Verify the changes</emphasis>:
                        Log into the machine using <filename>root</filename> with no password and then
                        use the following shell command to scroll through the console's boot output.
                        <literallayout class='monospaced'>
     # dmesg | less
                        </literallayout>
                        You should see the results of your <filename>printk</filename> statements
                        as part of the output.</para></listitem>
                </orderedlist>
            </para>
        </section>
    </section>

    <section id='creating-your-own-distribution'>
        <title>Creating Your Own Distribution</title>

        <para>
            When you build an image using the Yocto Project and
            do not alter any distribution
            <link linkend='metadata'>Metadata</link>, you are creating a
            Poky distribution.
            If you wish to gain more control over package alternative
            selections, compile-time options, and other low-level
            configurations, you can create your own distribution.
        </para>

        <para>
            To create your own distribution, the basic steps consist of
            creating your own distribution layer, creating your own
            distribution configuration file, and then adding any needed
            code and Metadata to the layer.
            The following steps provide some more detail:
            <itemizedlist>
                <listitem><para><emphasis>Create a layer for your new distro:</emphasis>
                    Create your distribution layer so that you can keep your
                    Metadata and code for the distribution separate.
                    It is strongly recommended that you create and use your own
                    layer for configuration and code.
                    Using your own layer as compared to just placing
                    configurations in a <filename>local.conf</filename>
                    configuration file makes it easier to reproduce the same
                    build configuration when using multiple build machines.
                    See the
                    "<link linkend='creating-a-general-layer-using-the-yocto-layer-script'>Creating a General Layer Using the yocto-layer Script</link>"
                    section for information on how to quickly set up a layer.
                    </para></listitem>
                <listitem><para><emphasis>Create the distribution configuration file:</emphasis>
                    The distribution configuration file needs to be created in
                    the <filename>conf/distro</filename> directory of your
                    layer.
                    You need to name it using your distribution name
                    (e.g. <filename>mydistro.conf</filename>).</para>
                    <para>You can split out parts of your configuration file
                    into include files and then "require" them from within
                    your distribution configuration file.
                    Be sure to place the include files in the
                    <filename>conf/distro/include</filename> directory of
                    your layer.
                    A common example usage of include files would be to
                    separate out the selection of desired version and revisions
                    for individual recipes.
</para>
                    <para>Your configuration file needs to set the following
                    required variables:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_NAME'><filename>DISTRO_NAME</filename></ulink> [required]
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_VERSION'><filename>DISTRO_VERSION</filename></ulink> [required]
                    </literallayout>
                    These following variables are optional and you typically
                    set them from the distribution configuration file:
                    <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink> [optional]
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RDEPENDS'><filename>DISTRO_EXTRA_RDEPENDS</filename></ulink> [optional]
     <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_EXTRA_RRECOMMENDS'><filename>DISTRO_EXTRA_RRECOMMENDS</filename></ulink> [optional]
     <ulink url='&YOCTO_DOCS_REF_URL;#var-TCLIBC'><filename>TCLIBC</filename></ulink> [optional]
                    </literallayout>
                    <tip>
                        If you want to base your distribution configuration file
                        on the very basic configuration from OE-Core, you
                        can use
                        <filename>conf/distro/defaultsetup.conf</filename> as
                        a reference and just include variables that differ
                        as compared to <filename>defaultsetup.conf</filename>.
                        Alternatively, you can create a distribution
                        configuration file from scratch using the
                        <filename>defaultsetup.conf</filename> file
                        or configuration files from other distributions
                        such as Poky or Angstrom as references.
                    </tip></para></listitem>
                <listitem><para><emphasis>Provide miscellaneous variables:</emphasis>
                    Be sure to define any other variables for which you want to
                    create a default or enforce as part of the distribution
                    configuration.
                    You can include nearly any variable from the
                    <filename>local.conf</filename> file.
                    The variables you use are not limited to the list in the
                    previous bulleted item.</para></listitem>
                <listitem><para><emphasis>Point to Your distribution configuration file:</emphasis>
                    In your <filename>local.conf</filename> file in the
                    <link linkend='build-directory'>Build Directory</link>,
                    set your
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                    variable to point to your distribution's configuration file.
                    For example, if your distribution's configuration file is
                    named <filename>mydistro.conf</filename>, then you point
                    to it as follows:
                    <literallayout class='monospaced'>
     DISTRO = "mydistro"
                    </literallayout></para></listitem>
                <listitem><para><emphasis>Add more to the layer if necessary:</emphasis>
                    Use your layer to hold other information needed for the
                    distribution:
                    <itemizedlist>
                        <listitem><para>Add recipes for installing
                            distro-specific configuration files that are not
                            already installed by another recipe.
                            If you have distro-specific configuration files
                            that are included by an existing recipe, you should
                            add a <filename>.bbappend</filename> for those.
                            For general information on how to add recipes to
                            your layer, see the "<link linkend='creating-your-own-layer'>Creating Your Own Layer</link>"
                            section.</para></listitem>
                        <listitem><para>Add any image recipes that are specific
                            to your distribution.</para></listitem>
                        <listitem><para>Add a <filename>psplash</filename>
                            append file for a branded splash screen.
                            For information on append files, see the
                            "<link linkend='using-bbappend-files'>Using .bbappend Files</link>"
                            section.</para></listitem>
                        <listitem><para>Add any other append files to make
                            custom changes that are specific to individual
                            recipes.</para></listitem>
                    </itemizedlist></para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id='building-a-tiny-system'>
        <title>Building a Tiny System</title>

        <para>
            Very small distributions have some significant advantages such
            as requiring less on-die or in-package memory (cheaper), better
            performance through efficient cache usage, lower power requirements
            due to less memory, faster boot times, and reduced development
            overhead.
            Some real-world examples where a very small distribution gives
            you distinct advantages are digital cameras, medical devices,
            and small headless systems.
        </para>

        <para>
            This section presents information that shows you how you can
            trim your distribution to even smaller sizes than the
            <filename>poky-tiny</filename> distribution, which is around
            5 Mbytes, that can be built out-of-the-box using the Yocto Project.
        </para>

        <section id='tiny-system-overview'>
            <title>Overview</title>

            <para>
                The following list presents the overall steps you need to
                consider and perform to create distributions with smaller
                root filesystems, faster boot times, maintain your critical
                functionality, and avoid initial RAM disks:
                <itemizedlist>
                    <listitem><para>Determine your goals and guiding
                        principles.</para></listitem>
                    <listitem><para>Understand what gives your image size.
                        </para></listitem>
                    <listitem><para>Reduce the size of the root filesystem.
                        </para></listitem>
                    <listitem><para>Reduce the size of the kernel.
                        </para></listitem>
                    <listitem><para>Eliminate packaging requirements.
                        </para></listitem>
                    <listitem><para>Look for other ways to minimize size.
                        </para></listitem>
                    <listitem><para>Iterate on the process.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='goals-and-guiding-principles'>
            <title>Goals and Guiding Principles</title>

            <para>
                Before you can reach your destination, you need to know
                where you are going.
                Here is an example list that you can use as a guide when
                creating very small distributions:
                <itemizedlist>
                    <listitem><para>Determine how much space you need
                        (e.g. a kernel that is 1 Mbyte or less and
                        a root filesystem that is 3 Mbytes or less).
                        </para></listitem>
                    <listitem><para>Find the areas that are currently
                        taking 90% of the space and concentrate on reducing
                        those areas.
                        </para></listitem>
                    <listitem><para>Do not create any difficult "hacks"
                        to achieve your goals.</para></listitem>
                    <listitem><para>Leverage the device-specific
                        options.</para></listitem>
                    <listitem><para>Work in a separate layer so that you
                        keep changes isolated.
                        For information on how to create layers, see
                        the "<link linkend='understanding-and-creating-layers'>Understanding and Creating Layers</link>" section.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='understand-what-gives-your-image-size'>
            <title>Understand What Gives Your Image Size</title>

            <para>
                It is easiest to have something to start with when creating
                your own distribution.
                You can use the Yocto Project out-of-the-box to create the
                <filename>poky-tiny</filename> distribution.
                Ultimately, you will want to make changes in your own
                distribution that are likely modeled after
                <filename>poky-tiny</filename>.
                <note>
                    To use <filename>poky-tiny</filename> in your build,
                    set the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink>
                    variable in your
                    <filename>local.conf</filename> file to "poky-tiny"
                    as described in the
                    "<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
                    section.
                </note>
            </para>

            <para>
                Understanding some memory concepts will help you reduce the
                system size.
                Memory consists of static, dynamic, and temporary memory.
                Static memory is the TEXT (code), DATA (initialized data
                in the code), and BSS (uninitialized data) sections.
                Dynamic memory contains memory that is allocated at runtime,
                stacks, hash tables, and so forth.
                Temporary memory is recovered after the boot process.
                This memory consists of memory used for decompressing
                the kernel and for the <filename>__init__</filename>
                functions.
            </para>

            <para>
                To help you see where you currently are with kernel and root
                filesystem sizes, you can use two tools found in the
                <link linkend='source-directory'>Source Directory</link> in
                the <filename>scripts</filename> directory:
                <itemizedlist>
                    <listitem><para><filename>ksize.py</filename>: Reports
                        component sizes for the kernel build objects.
                        </para></listitem>
                    <listitem><para><filename>dirsize.py</filename>: Reports
                        component sizes for the root filesystem.</para></listitem>
                </itemizedlist>
                This next tool and command helps you organize configuration
                fragments and view file dependencies in a human-readable form:
                <itemizedlist>
                    <listitem><para><filename>merge_config.sh</filename>:
                        Helps you manage configuration files and fragments
                        within the kernel.
                        With this tool, you can merge individual configuration
                        fragments together.
                        The tool allows you to make overrides and warns you
                        of any missing configuration options.
                        The tool is ideal for allowing you to iterate on
                        configurations, create minimal configurations, and
                        create configuration files for different machines
                        without having to duplicate your process.</para>
                        <para>The <filename>merge_config.sh</filename> script is
                        part of the Linux Yocto kernel Git repository in the
                        <filename>scripts/kconfig</filename> directory.</para>
                        <para>For more information on configuration fragments,
                        see the
                        "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#generating-configuration-files'>Generating Configuration Files</ulink>"
                        section of the Yocto Project Linux Kernel Development
                        Manual and the "<link linkend='creating-config-fragments'>Creating Configuration Fragments</link>"
                        section, which is in this manual.</para></listitem>
                    <listitem><para><filename>bitbake -u depexp -g &lt;bitbake_target&gt;</filename>:
                        Using the BitBake command with these options brings up
                        a Dependency Explorer from which you can view file
                        dependencies.
                        Understanding these dependencies allows you to make
                        informed decisions when cutting out various pieces of the
                        kernel and root filesystem.</para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='trim-the-root-filesystem'>
            <title>Trim the Root Filesystem</title>

            <para>
                The root filesystem is made up of packages for booting,
                libraries, and applications.
                To change things, you can configure how the packaging happens,
                which changes the way you build them.
                You can also tweak the filesystem itself or select a different
                filesystem.
            </para>

            <para>
                First, find out what is hogging your root filesystem by running the
                <filename>dirsize.py</filename> script from your root directory:
                <literallayout class='monospaced'>
     $ cd &lt;root-directory-of-image&gt;
     $ dirsize.py 100000 > dirsize-100k.log
     $ cat dirsize-100k.log
                </literallayout>
                You can apply a filter to the script to ignore files under
                a certain size.
                This example filters out anything below 100 Kbytes.
                The sizes reported by the tool are uncompressed and thus,
                will be smaller by a relatively constant factor in a
                compressed root filesystem.
                When you examine your log file, you can focus on areas of the
                root filesystem that take up large amounts of memory.
            </para>

            <para>
                You need to be sure that what you eliminate does not cripple
                the functionality you need.
                One way to see how packages relate to each other is by using
                the Dependency Explorer UI with the BitBake command:
                <literallayout class='monospaced'>
     $ cd &lt;image-directory&gt;
     $ bitbake -u depexp -g &lt;image&gt;
                </literallayout>
                Use the interface to select potential packages you wish to
                eliminate and see their dependency relationships.
            </para>

            <para>
                When deciding how to reduce the size, get rid of packages that
                result in minimal impact on the feature set.
                For example, you might not need a VGA display.
                Or, you might be able to get by with <filename>devtmpfs</filename>
                and <filename>mdev</filename> instead of
                <filename>udev</filename>.
            </para>

            <para>
                Use the <filename>local.conf</filename> file to make changes.
                For example, to eliminate <filename>udev</filename> and
                <filename>glib</filename>, set the following in the
                local configuration file:
                <literallayout class='monospaced'>
     VIRTUAL-RUNTIME_dev_manager = ""
                </literallayout>
            </para>

            <para>
                Finally, you should consider exactly the type of root
                filesystem you need to meet your needs while also reducing
                its size.
                For example, consider <filename>cramfs</filename>,
                <filename>squashfs</filename>, <filename>ubifs</filename>,
                <filename>ext2</filename>, or an <filename>initramfs</filename>
                using <filename>initramfs</filename>.
                Be aware that <filename>ext3</filename> requires a 1 Mbyte
                journal.
                If you are okay with running read-only you do not need this
                journal.
            </para>

            <note>
                After each round of elimination, you need to rebuild your
                system and then use the tools to see the effects of your
                reductions.
            </note>


        </section>

        <section id='trim-the-kernel'>
            <title>Trim the Kernel</title>

            <para>
                The kernel is built by including policies for hardware-independent
                aspects.
                What subsystems do you enable?
                For what architecture are you building?
                Which drivers do you build by default.
                <note>You can modify the kernel source if you want to help
                    with boot time.
                </note>
            </para>

            <para>
                Run the <filename>ksize.py</filename> script from the top-level
                Linux build directory to get an idea of what is making up
                the kernel:
                <literallayout class='monospaced'>
     $ cd &lt;top-level-linux-build-directory&gt;
     $ ksize.py > ksize.log
     $ cat ksize.log
                </literallayout>
                When you examine the log, you will see how much space is
                taken up with the built-in <filename>.o</filename> files for
                drivers, networking, core kernel files, filesystem, sound,
                and so forth.
                The sizes reported by the tool are uncompressed and thus,
                will be smaller by a relatively constant factor in a compressed
                kernel image.
                Look to reduce the areas that are large and taking up around
                the "90% rule."
            </para>

            <para>
                To examine, or drill down, into any particular area, use the
                <filename>-d</filename> option with the script:
                <literallayout class='monospaced'>
     $ ksize.py -d > ksize.log
                </literallayout>
                Using this option breaks out the individual file information
                for each area of the kernel (e.g. drivers, networking, and
                so forth).
            </para>

            <para>
                Use your log file to see what you can eliminate from the kernel
                based on features you can let go.
                For example, if you are not going to need sound, you do not
                need any drivers that support sound.
            </para>

            <para>
                After figuring out what to eliminate, you need to reconfigure
                the kernel to reflect those changes during the next build.
                You could run <filename>menuconfig</filename> and make all your
                changes at once.
                However, that makes it difficult to see the effects of your
                individual eliminations and also makes it difficult to replicate
                the changes for perhaps another target device.
                A better method is to start with no configurations using
                <filename>allnoconfig</filename>, create configuration
                fragments for individual changes, and then manage the
                fragments into a single configuration file using
                <filename>merge_config.sh</filename>.
                The tool makes it easy for you to iterate using the
                configuration change and build cycle.
            </para>

            <para>
                Each time you make configuration changes, you need to rebuild
                the kernel and check to see what impact your changes had on
                the overall size.
            </para>
        </section>

        <section id='remove-package-management-requirements'>
            <title>Remove Package Management Requirements</title>

            <para>
                Packaging requirements add size to the image.
                One way to reduce the size of the image is to remove all the
                packaging requirements from the image.
                This reduction includes both removing the package manager
                and its unique dependencies as well as removing the package
                management data itself.
            </para>

            <para>
                To eliminate all the packaging requirements for an image,
                follow these steps:
                <orderedlist>
                    <listitem><para>Put the following line in your main
                        recipe for the image to remove package management
                        data files:
                        <literallayout class='monospaced'>
     ROOTFS_POSTPROCESS_COMMAND += "remove_packaging_data_files ;
                        </literallayout>
                        For example, the recipe for the
                        <filename>core-image-minimal</filename> image contains
                        this line.
                        You can also add the line to the
                        <filename>local.conf</filename> configuration file.
                        </para></listitem>
                    <listitem><para>Be sure that "package-management" is not
                        part of your
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                        statement for the image.
                        When you remove this feature, you are removing the
                        package manager as well as its dependencies
                        from the root filesystem.
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='look-for-other-ways-to-minimize-size'>
            <title>Look for Other Ways to Minimize Size</title>

            <para>
                Depending on your particular circumstances, other areas that you
                can trim likely exist.
                The key to finding these areas is through tools and methods
                described here combined with experimentation and iteration.
                Here are a couple of areas to experiment with:
                <itemizedlist>
                    <listitem><para><filename>eglibc</filename>:
                        In general, follow this process:
                        <orderedlist>
                            <listitem><para>Remove <filename>eglibc</filename>
                                features from
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                                that you think you do not need.</para></listitem>
                            <listitem><para>Build your distribution.
                                </para></listitem>
                            <listitem><para>If the build fails due to missing
                                symbols in a package, determine if you can
                                reconfigure the package to not need those
                                features.
                                For example, change the configuration to not
                                support wide character support as is done for
                                <filename>ncurses</filename>.
                                Or, if support for those characters is needed,
                                determine what <filename>eglibc</filename>
                                features provide the support and restore the
                                configuration.
                                </para></listitem>
                            <listitem><para>Rebuild and repeat the process.
                                </para></listitem>
                        </orderedlist></para></listitem>
                    <listitem><para><filename>busybox</filename>:
                        For BusyBox, use a process similar as described for
                        <filename>eglibc</filename>.
                        A difference is you will need to boot the resulting
                        system to see if you are able to do everything you
                        expect from the running system.
                        You need to be sure to integrate configuration fragments
                        into Busybox because BusyBox handles its own core
                        features and then allows you to add configuration
                        fragments on top.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='iterate-on-the-process'>
            <title>Iterate on the Process</title>

            <para>
                If you have not reached your goals on system size, you need
                to iterate on the process.
                The process is the same.
                Use the tools and see just what is taking up 90% of the root
                filesystem and the kernel.
                Decide what you can eliminate without limiting your device
                beyond what you need.
            </para>

            <para>
                Depending on your system, a good place to look might be
                Busybox, which provides a stripped down
                version of Unix tools in a single, executable file.
                You might be able to drop virtual terminal services or perhaps
                ipv6.
            </para>
        </section>
    </section>

    <section id='working-with-packages'>
        <title>Working with Packages</title>

        <para>
            This section describes a few tasks that involve packages:
            <itemizedlist>
                <listitem><para>Incrementing a package revision number
                    </para></listitem>
                <listitem><para>Handling a package name alias
                    </para></listitem>
                <listitem><para>Handling optional module packaging
                    </para></listitem>
                <listitem><para>Setting up Runtime Package Management
                    </para></listitem>
                <listitem><para>Setting up and running package test
                    (ptest)
                    </para></listitem>
            </itemizedlist>
        </para>

        <section id='incrementing-a-package-revision-number'>
            <title>Incrementing a Package Revision Number</title>

            <para>
                If a committed change results in changing the package output,
                then the value of the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                variable needs to be increased (or "bumped").
                Increasing <filename>PR</filename> occurs one of two ways:
                <itemizedlist>
                    <listitem><para>Automatically using a Package Revision
                        Service (PR Service).</para></listitem>
                    <listitem><para>Manually incrementing the
                        <filename>PR</filename> variable.</para></listitem>
                </itemizedlist>
            </para>

            <para>
                Given that one of the challenges any build system and its
                users face is how to maintain a package feed that is compatible
                with existing package manager applications such as
                RPM, APT, and OPKG, using an automated system is much
                preferred over a manual system.
                In either system, the main requirement is that version
                numbering increases in a linear fashion and that a number of
                version components exist that support that linear progression.
            </para>

            <para>
                The following two sections provide information on the PR Service
                and on manual <filename>PR</filename> bumping.
            </para>

            <section id='working-with-a-pr-service'>
                <title>Working With a PR Service</title>

                <para>
                    As mentioned, attempting to maintain revision numbers in the
                    <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>
                    is error prone, inaccurate and causes problems for people
                    submitting recipes.
                    Conversely, the PR Service automatically generates
                    increasing numbers, particularly the revision field,
                    which removes the human element.
                    <note>
                        For additional information on using a PR Service, you
                        can see the
                        <ulink url='&YOCTO_WIKI_URL;/wiki/PR_Service'>PR Service</ulink>
                        wiki page.
                    </note>
                </para>

                <para>
                    The Yocto Project uses variables in order of
                    decreasing priority to facilitate revision numbering (i.e.
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PE'><filename>PE</filename></ulink>,
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>, and
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                    for epoch, version and revision, respectively).
                    The values are highly dependent on the policies and
                    procedures of a given distribution and package feed.
                </para>

                <para>
                    Because the OpenEmbedded build system uses
                    "<ulink url='&YOCTO_DOCS_REF_URL;#checksums'>signatures</ulink>",
                    which are unique to a given build, the build system
                    knows when to rebuild packages.
                    All the inputs into a given task are represented by a
                    signature, which can trigger a rebuild when different.
                    Thus, the build system itself does not rely on the
                    <filename>PR</filename> numbers to trigger a rebuild.
                    The signatures, however, can be used to generate
                    <filename>PR</filename> values.
                </para>

                <para>
                    The PR Service works with both
                    <filename>OEBasic</filename> and
                    <filename>OEBasicHash</filename> generators.
                    The value of <filename>PR</filename> bumps when the
                    checksum changes and the different generator mechanisms
                    change signatures under different circumstances.
                </para>

                <para>
                    As implemented, the build system includes values from
                    the PR Service into the <filename>PR</filename> field as
                    an addition using the form "<filename>.x</filename>" so
                    <filename>r0</filename> becomes <filename>r0.1</filename>,
                    <filename>r0.2</filename> and so forth.
                    This scheme allows existing <filename>PR</filename> values
                    to be used for whatever reasons, which include manual
                    <filename>PR</filename> bumps should it be necessary.
                </para>

                <para>
                    By default, the PR Service is not enabled or running.
                    Thus, the packages generated are just "self consistent".
                    The build system adds and removes packages and
                    there are no guarantees about upgrade paths but images
                    will be consistent and correct with the latest changes.
                </para>

                <para>
                    The simplest form for a PR Service is for it to exist
                    for a single host development system that builds the
                    package feed (building system).
                    For this scenario, you can enable the PR Service by adding
                    the following to your <filename>local.conf</filename>
                    file in the
                    <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
                    <literallayout class='monospaced'>
     PRSERV_HOST = "localhost:0"
                    </literallayout>
                    Once the service is started, packages will automatically
                    get increasing <filename>PR</filename> values and
                    BitBake will take care of starting and stopping the server.
                </para>

                <para>
                    If you have a more complex setup where multiple host
                    development systems work against a common, shared package
                    feed, you have a single PR Service running and it is
                    connected to each building system.
                    For this scenario, you need to start the PR Service using
                    the <filename>bitbake-prserv</filename> command:
                    <literallayout class='monospaced'>
     bitbake-prserv &dash;&dash;host &lt;ip&gt; &dash;&dash;port &lt;port&gt; &dash;&dash;start
                    </literallayout>
                    In addition to hand-starting the service, you need to
                    update the <filename>local.conf</filename> file of each
                    building system as described earlier so each system
                    points to the server and port.
                </para>

                <para>
                    It is also recommended you use Build History, which adds
                    some sanity checks to package versions, in conjunction with
                    the server that is running the PR Service.
                    To enable build history, add the following to each building
                    system's <filename>local.conf</filename> file:
                    <literallayout class='monospaced'>
     # It is recommended to activate "buildhistory" for testing the PR service
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
                    </literallayout>
                    For information on Build History, see the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#maintaining-build-output-quality'>Maintaining Build Output Quality</ulink>"
                    section in the Yocto Project Reference Manual.
                </para>

                <note>
                    <para>The OpenEmbedded build system does not maintain
                    <filename>PR</filename> information as part of the
                    shared state (sstate) packages.
                    If you maintain an sstate feed, its expected that either
                    all your building systems that contribute to the sstate
                    feed use a shared PR Service, or you do not run a PR
                    Service on any of your building systems.
                    Having some systems use a PR Service while others do
                    not leads to obvious problems.</para>
                    <para>For more information on shared state, see the
                    "<ulink url='&YOCTO_DOCS_REF_URL;#shared-state-cache'>Shared State Cache</ulink>"
                    section in the Yocto Project Reference Manual.</para>
                </note>
            </section>

            <section id='manually-bumping-pr'>
                <title>Manually Bumping PR</title>

                <para>
                    The alternative to setting up a PR Service is to manually
                    bump the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>
                    variable.
                </para>

                <para>
                    If a committed change results in changing the package output,
                    then the value of the PR variable needs to be increased
                    (or "bumped") as part of that commit.
                    For new recipes you should add the <filename>PR</filename>
                    variable and set its initial value equal to "r0", which is the default.
                    Even though the default value is "r0", the practice of adding it to a new recipe makes
                    it harder to forget to bump the variable when you make changes
                    to the recipe in future.
                </para>

                <para>
                    If you are sharing a common <filename>.inc</filename> file with multiple recipes,
                    you can also use the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-INC_PR'>INC_PR</ulink></filename>
                    variable to ensure that
                    the recipes sharing the <filename>.inc</filename> file are rebuilt when the
                    <filename>.inc</filename> file itself is changed.
                    The <filename>.inc</filename> file must set <filename>INC_PR</filename>
                    (initially to "r0"), and all recipes referring to it should set <filename>PR</filename>
                    to "$(INC_PR).0" initially, incrementing the last number when the recipe is changed.
                    If the <filename>.inc</filename> file is changed then its
                    <filename>INC_PR</filename> should be incremented.
                </para>

                <para>
                    When upgrading the version of a package, assuming the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PV'>PV</ulink></filename>
                    changes, the <filename>PR</filename> variable should be
                    reset to "r0" (or "$(INC_PR).0" if you are using
                    <filename>INC_PR</filename>).
                </para>

                <para>
                    Usually, version increases occur only to packages.
                    However, if for some reason <filename>PV</filename> changes but does not
                    increase, you can increase the
                    <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PE'>PE</ulink></filename>
                    variable (Package Epoch).
                    The <filename>PE</filename> variable defaults to "0".
                </para>

                <para>
                    Version numbering strives to follow the
                    <ulink url='http://www.debian.org/doc/debian-policy/ch-controlfields.html'>
                    Debian Version Field Policy Guidelines</ulink>.
                    These guidelines define how versions are compared and what "increasing" a version means.
                </para>
            </section>
        </section>

        <section id="usingpoky-configuring-DISTRO_PN_ALIAS">
            <title>Handling a Package Name Alias</title>
            <para>
                Sometimes a package name you are using might exist under an alias or as a similarly named
                package in a different distribution.
                The OpenEmbedded build system implements a <filename>distro_check</filename>
                task that automatically connects to major distributions
                and checks for these situations.
                If the package exists under a different name in a different distribution, you get a
                <filename>distro_check</filename> mismatch.
                You can resolve this problem by defining a per-distro recipe name alias using the
                <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_PN_ALIAS'>DISTRO_PN_ALIAS</ulink></filename>
                variable.
            </para>

            <para>
                Following is an example that shows how you specify the <filename>DISTRO_PN_ALIAS</filename>
                variable:
                <literallayout class='monospaced'>
     DISTRO_PN_ALIAS_pn-PACKAGENAME = "distro1=package_name_alias1 \
                                       distro2=package_name_alias2 \
                                       distro3=package_name_alias3 \
                                       ..."
                </literallayout>
            </para>

            <para>
                If you have more than one distribution alias, separate them with a space.
                Note that the build system currently automatically checks the
                Fedora, OpenSUSE, Debian, Ubuntu,
                and Mandriva distributions for source package recipes without having to specify them
                using the <filename>DISTRO_PN_ALIAS</filename> variable.
                For example, the following command generates a report that lists the Linux distributions
                that include the sources for each of the recipes.
                <literallayout class='monospaced'>
     $ bitbake world -f -c distro_check
                </literallayout>
                The results are stored in the <filename>build/tmp/log/distro_check-${DATETIME}.results</filename>
                file found in the
                <link linkend='source-directory'>Source Directory</link>.
            </para>
        </section>

        <section id='handling-optional-module-packaging'>
            <title>Handling Optional Module Packaging</title>

            <para>
                Many pieces of software split functionality into optional
                modules (or plugins) and the plugins that are built
                might depend on configuration options.
                To avoid having to duplicate the logic that determines what
                modules are available in your recipe or to avoid having
                to package each module by hand, the OpenEmbedded build system
                provides functionality to handle module packaging dynamically.
            </para>

            <para>
                To handle optional module packaging, you need to do two things:
                <itemizedlist>
                    <listitem><para>Ensure the module packaging is actually
                        done</para></listitem>
                    <listitem><para>Ensure that any dependencies on optional
                        modules from other recipes are satisfied by your recipe
                        </para></listitem>
                </itemizedlist>
            </para>

            <section id='making-sure-the-packaging-is-done'>
                <title>Making Sure the Packaging is Done</title>

                <para>
                    To ensure the module packaging actually gets done, you use
                    the <filename>do_split_packages</filename> function within
                    the <filename>populate_packages</filename> Python function
                    in your recipe.
                    The <filename>do_split_packages</filename> function
                    searches for a pattern of files or directories under a
                    specified path and creates a package for each one it finds
                    by appending to the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>
                    variable and setting the appropriate values for
                    <filename>FILES_packagename</filename>,
                    <filename>RDEPENDS_packagename</filename>,
                    <filename>DESCRIPTION_packagename</filename>, and so forth.
                    Here is an example from the <filename>lighttpd</filename>
                    recipe:
                    <literallayout class='monospaced'>
     python populate_packages_prepend () {
         lighttpd_libdir = d.expand('${libdir}')
         do_split_packages(d, lighttpd_libdir, '^mod_(.*)\.so$',
                          'lighttpd-module-%s', 'Lighttpd module for %s',
                           extra_depends='')
     }
                    </literallayout>
                    The previous example specifies a number of things in the
                    call to <filename>do_split_packages</filename>.
                    <itemizedlist>
                        <listitem><para>A directory within the files installed
                            by your recipe through <filename>do_install</filename>
                            in which to search.</para></listitem>
                        <listitem><para>A regular expression to match module
                            files in that directory.
                            In the example, note the parentheses () that mark
                            the part of the expression from which the module
                            name should be derived.</para></listitem>
                        <listitem><para>A pattern to use for the package names.
                            </para></listitem>
                        <listitem><para>A description for each package.
                            </para></listitem>
                        <listitem><para>An empty string for
                            <filename>extra_depends</filename>, which disables
                            the default dependency on the main
                            <filename>lighttpd</filename> package.
                            Thus, if a file in <filename>${libdir}</filename>
                            called <filename>mod_alias.so</filename> is found,
                            a package called <filename>lighttpd-module-alias</filename>
                            is created for it and the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DESCRIPTION'><filename>DESCRIPTION</filename></ulink>
                            is set to "Lighttpd module for alias".</para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    Often, packaging modules is as simple as the previous
                    example.
                    However, more advanced options exist that you can use
                    within <filename>do_split_packages</filename> to modify its
                    behavior.
                    And, if you need to, you can add more logic by specifying
                    a hook function that is called for each package.
                    It is also perfectly acceptable to call
                    <filename>do_split_packages</filename> multiple times if
                    you have more than one set of modules to package.
                </para>

                <para>
                    For more examples that show how to use
                    <filename>do_split_packages</filename>, see the
                    <filename>connman.inc</filename> file in the
                    <filename>meta/recipes-connectivity/connman/</filename>
                    directory of the <filename>poky</filename>
                    <link linkend='yocto-project-repositories'>source repository</link>.
                    You can also find examples in
                    <filename>meta/classes/kernel.bbclass</filename>.
                 </para>

                 <para>
                     Following is a reference that shows
                     <filename>do_split_packages</filename> mandatory and
                     optional arguments:
                     <literallayout class='monospaced'>
     Mandatory arguments

     root
        The path in which to search
     file_regex
        Regular expression to match searched files.
        Use parentheses () to mark the part of this
        expression that should be used to derive the
        module name (to be substituted where %s is
        used in other function arguments as noted below)
     output_pattern
        Pattern to use for the package names. Must
        include %s.
     description
        Description to set for each package. Must
        include %s.

     Optional arguments

     postinst
        Postinstall script to use for all packages
        (as a string)
     recursive
        True to perform a recursive search - default
        False
     hook
        A hook function to be called for every match.
        The function will be called with the following
        arguments (in the order listed):

        f
           Full path to the file/directory match
        pkg
           The package name
        file_regex
           As above
        output_pattern
           As above
        modulename
           The module name derived using file_regex

     extra_depends
        Extra runtime dependencies (RDEPENDS) to be
        set for all packages. The default value of None
        causes a dependency on the main package
        (${PN}) - if you do not want this, pass empty
        string '' for this parameter.
     aux_files_pattern
        Extra item(s) to be added to FILES for each
        package. Can be a single string item or a list
        of strings for multiple items. Must include %s.
     postrm
        postrm script to use for all packages (as a
        string)
     allow_dirs
        True to allow directories to be matched -
        default False
     prepend
        If True, prepend created packages to PACKAGES
        instead of the default False which appends them
     match_path
        match file_regex on the whole relative path to
        the root rather than just the file name
     aux_files_pattern_verbatim
        Extra item(s) to be added to FILES for each
        package, using the actual derived module name
        rather than converting it to something legal
        for a package name. Can be a single string item
        or a list of strings for multiple items. Must
        include %s.
     allow_links
        True to allow symlinks to be matched - default
        False
                     </literallayout>
                 </para>
            </section>

            <section id='satisfying-dependencies'>
                <title>Satisfying Dependencies</title>

                <para>
                    The second part for handling optional module packaging
                    is to ensure that any dependencies on optional modules
                    from other recipes are satisfied by your recipe.
                    You can be sure these dependencies are satisfied by
                    using the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES_DYNAMIC'><filename>PACKAGES_DYNAMIC</filename></ulink> variable.
                    Here is an example that continues with the
                    <filename>lighttpd</filename> recipe shown earlier:
                    <literallayout class='monospaced'>
     PACKAGES_DYNAMIC = "lighttpd-module-.*"
                    </literallayout>
                    The name specified in the regular expression can of
                    course be anything.
                    In this example, it is <filename>lighttpd-module-</filename>
                    and is specified as the prefix to ensure that any
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                    and <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>
                    on a package name starting with the prefix are satisfied
                    during build time.
                    If you are using <filename>do_split_packages</filename>
                    as described in the previous section, the value you put in
                    <filename>PACKAGES_DYNAMIC</filename> should correspond to
                    the name pattern specified in the call to
                    <filename>do_split_packages</filename>.
                </para>
            </section>
        </section>

        <section id='setting-up-runtime-package-management'>
            <title>Setting Up Runtime Package Management</title>

            <para>
                For RPM, IPK, and DEB package formats, it is possible to set
                up a repository that is a host-based
                package feed from which you can install packages on the
                target system during runtime.
                Doing so is optional and depends on the following:
                <itemizedlist>
                    <listitem><para>
                        You take specific steps to set up the feed.
                        </para></listitem>
                    <listitem><para>
                        When you build your image, you select to use the
                        appropriate package manager by setting the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>
                        variable.
                        </para></listitem>
                    <listitem><para>
                        You have a web server, such as Apache 2,
                        installed and configured on the development host.
                        </para></listitem>
                    <listitem><para>
                        You have <filename>createrepo</filename> installed on
                        the development host.
                        </para></listitem>
                    <listitem><para>
                        You enable package management on the target by
                        listing "package-management" in the
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                        variable.
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Following are the steps to set up the optional repository.
                This examples assumes you are using RPM and the Apache 2
                server:
                <orderedlist>
                    <listitem><para>
                        Add the directory to your Apache configuration, which
                        you can find at
                        <filename>/etc/httpd/conf/httpd.conf</filename>.
                        Use commands similar to these on the development system.
                        These example commands assume a top-level
                        <link linkend='source-directory'>Source Directory</link>
                        named <filename>poky</filename> in your home directory:
                        <literallayout class='monospaced'>
     &lt;VirtualHost *:80&gt;
       ....
         Alias /rpm ~/poky/build/tmp/deploy/rpm
         &lt;Directory "~/poky/build/tmp/deploy/rpm"&gt;
           Options +Indexes
         &lt;/Directory&gt;
     &lt;/VirtualHost&gt;
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Reload the Apache configuration as follows.
                        For all commands, be sure you have root privileges.
                        </para>
                        <para>
                        If your development system is using Fedora or
                        CentOS, use the following:
                        <literallayout class='monospaced'>
     service httpd reload
                        </literallayout>
                        For Ubuntu, use the following:
                        <literallayout class='monospaced'>
     /etc/init.d/apache2 reload
                        </literallayout>
                        For OpenSUSE, use the following:
                        <literallayout class='monospaced'>
     /etc/init.d/apache2 reload
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Change your working directory to
                        <filename>tmp/deploy/rpm</filename> in the
                        <link linkend='build-directory'>Build Directory</link>.
                        </para></listitem>
                    <listitem><para>
                        Create the repository data on the host using
                        this command:
                        <literallayout class='monospaced'>
     createrepo .
                        </literallayout>
                        </para>
                        <para>
                            <note>
                                If you're updating, add
                                <filename>&dash;&dash;update</filename> to save some time.
                            </note>
                        </para></listitem>
                    <listitem><para>
                        If you are using Security-Enhanced Linux (SELinux),
                        you need to label the files as being accessible
                        through Apache.
                        Use the following command from the development host:
                        <literallayout class='monospaced'>
     chcon -R -h -t httpd_sys_content_t .
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        On the target machine, add the repository to Smart.
                        For <filename>somealias</filename>, provide a local
                        alias for the repository:
                        <literallayout class='monospaced'>
     smart channel &dash;&dash;add &lt;somealias&gt; type=rpm-md baseurl=http://server.name/rpm
                        </literallayout>
                        </para></listitem>
                    <listitem><para>
                        Also from the target machine, fetch the repository
                        information using this command:
                        <literallayout class='monospaced'>
     smart update
                        </literallayout>
                        </para></listitem>
                </orderedlist>
            </para>

            <para>
                After taking these steps and making sure that the other
                requirements mentioned at the beginning of the section are met,
                reboot the target device to take advantage of runtime package
                installations.
            </para>

            <para>
                If your packages are IPK, you can install packages onto an
                existing running system by first sharing the
                <filename>tmp/deploy/ipk/</filename> directory
                through a web server and then by changing
                <filename>/etc/opkg/base-feeds.conf</filename>
                to point at the shared server.
                Following is an example:
                <literallayout class='monospaced'>
     $ src/gz all http://www.mysite.com/somedir/deploy/ipk/all
     $ src/gz armv7a http://www.mysite.com/somedir/deploy/ipk/armv7a
     $ src/gz beagleboard http://www.mysite.com/somedir/deploy/ipk/beagleboard
                </literallayout>
            </para>
        </section>

        <section id='testing-packages-with-ptest'>
            <title>Testing Packages With ptest</title>

            <para>
                A Package Test (ptest) runs tests against packages built
                by the OpenEmbedded build system on the target machine.
                A ptest contains at least two items: the actual test, and
                a shell script (<filename>run-ptest</filename>) that starts
                the test.
                The shell script that starts the test must not contain
                the actual test, the script only starts it.
                On the other hand, the test can be anything from a simple
                shell script that runs a binary and checks the output to
                an elaborate system of test binaries and data files.
            </para>

            <para>
                The test generates output in the format used by
                Automake:
                <literallayout class='monospaced'>
     &lt;result&gt;: &lt;testname&gt;
                </literallayout>
                where the result can be <filename>PASS</filename>,
                <filename>FAIL</filename>, or <filename>SKIP</filename>,
                and the testname can be any identifying string.
            </para>

            <note>
                With this release of the Yocto Project, three recipes exist
                that are "ptest-enabled": <filename>bash</filename>,
                <filename>glib-2.0</filename>, and
                <filename>dbus</filename>.
                These three recipes are Autotool-enabled.
            </note>

            <section id='adding-ptest-to-your-build'>
                <title>Adding ptest to Your Build</title>

                <para>
                    To add package testing to your build, add the
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES'><filename>DISTRO_FEATURES</filename></ulink>
                    and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>
                    variables to your <filename>local.conf</filename> file,
                    which is found in the
                    <link linkend='build-directory'>Build Directory</link>:
                    <literallayout class='monospaced'>
     EXTRA_IMAGE_FEATURES += "ptest"
     DISTRO_FEATURES_append = " ptest-pkgs"
                    </literallayout>
                    Once your build is complete, the ptest files are installed
                    into the <filename>/usr/lib/&lt;package&gt;/ptest</filename>
                    directory within the image, where
                    <filename>&lt;package&gt;</filename> is the name of the
                    package.
                </para>
            </section>

            <section id='running-ptest'>
                <title>Running ptest</title>

                <para>
                    The <filename>ptest-runner</filename> package installs a
                    shell script that loops through all installed ptest test
                    suites and runs them in sequence.
                    Consequently, you might want to add this package to
                    your image.
                </para>
            </section>

            <section id='getting-your-package-ready'>
                <title>Getting Your Package Ready</title>

                <para>
                    In order to enable a recipe to run installed ptests
                    on target hardware,
                    you need to prepare the recipes that build the packages
                    you want to test.
                    Here is what you have to do for each recipe:
                    <itemizedlist>
                        <listitem><para><emphasis>Be sure the recipe
                            inherits ptest:</emphasis>
                            Include the following line in each recipe:
                            <literallayout class='monospaced'>
     inherit ptest
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Create <filename>run-ptest</filename>:</emphasis>
                            This script starts your test.
                            Locate the script where you will refer to it
                            using
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>.
                            Here is an example that starts a test for
                            <filename>dbus</filename>:
                            <literallayout class='monospaced'>
     #!/bin/sh
     cd test
     make -k runtest-TESTS
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Ensure dependencies are
                            met:</emphasis>
                            If the test adds build or runtime dependencies
                            that normally do not exist for the package
                            (such as requiring "make" to run the test suite),
                            use the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                            and
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>
                            variables in your recipe in order for the package
                            to meet the dependencies.
                            Here is an example where the package has a runtime
                            dependency on "make":
                            <literallayout class='monospaced'>
     RDEPENDS_${PN}-ptest += "make"
                            </literallayout>
                            </para></listitem>
                        <listitem><para><emphasis>Add a function to build the
                            test suite:</emphasis>
                            Not many packages support cross-compilation of
                            their test suites.
                            Consequently, you usually need to add a
                            cross-compilation function to the package.
                            </para>
                            <para>Many packages based on Automake compile and
                            run the test suite by using a single command
                            such as <filename>make check</filename>.
                            However, the native <filename>make check</filename>
                            builds and runs on the same computer, while
                            cross-compiling requires that the package is built
                            on the host but executed on the target.
                            The built version of Automake that ships with the
                            Yocto Project includes a patch that separates
                            building and execution.
                            Consequently, packages that use the unaltered,
                            patched version of <filename>make check</filename>
                            automatically cross-compiles.</para>
                            <para>However, you still must add a
                            <filename>do_compile_ptest</filename> function to
                            build the test suite.
                            Add a function similar to the following to your
                            recipe:
                            <literallayout class='monospaced'>
     do_compile_ptest() {
        oe_runmake buildtest-TESTS
     }
                            </literallayout>
                            </para></listitem>
                       <listitem><para><emphasis>Ensure special configurations
                            are set:</emphasis>
                            If the package requires special configurations
                            prior to compiling the test code, you must
                            insert a <filename>do_configure_ptest</filename>
                            function into the recipe.
                            </para></listitem>
                       <listitem><para><emphasis>Install the test
                            suite:</emphasis>
                            The <filename>ptest.bbclass</filename> class
                            automatically copies the file
                            <filename>run-ptest</filename> to the target and
                            then runs make <filename>install-ptest</filename>
                            to run the tests.
                            If this is not enough, you need to create a
                            <filename>do_install_ptest</filename> function and
                            make sure it gets called after the
                            "make install-ptest" completes.
                            </para></listitem>
                    </itemizedlist>
                </para>
            </section>
        </section>
    </section>

    <section id="building-software-from-an-external-source">
        <title>Building Software from an External Source</title>

        <para>
            By default, the OpenEmbedded build system does its work from within the
            <link linkend='build-directory'>Build Directory</link>.
            The build process involves fetching the source files, unpacking them, and then patching them
            if necessary before the build takes place.
        </para>

        <para>
            Situations exist where you might want to build software from source files that are external to
            and thus outside of the <link linkend='source-directory'>Source Directory</link>.
            For example, suppose you have a project that includes a new BSP with a heavily customized
            kernel, a very minimal image, and some new user-space recipes.
            And, you want to minimize exposing the build system to the
            development team so that they can focus on their project and maintain everyone's workflow
            as much as possible.
            In this case, you want a kernel source directory on the development machine where the
            development occurs.
            You want the recipe's
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
            variable to point to the external directory and use it as is, not copy it.
        </para>

        <para>
            To build from software that comes from an external source, all you need to do is
            change your recipe so that it inherits the
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></ulink>
            class and then sets the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>
            variable to point to your external source code.
            Here are the statements to put in your recipe:
            <literallayout class='monospaced'>
     inherit externalsrc
     S = "/some/path/to/your/package/source"
            </literallayout>
        </para>

        <para>
            It is important to know that the <filename>externalsrc.bbclass</filename> assumes that the
            source directory <filename>S</filename> and the Build Directory
            <ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink>
            are different even though these directories are the same by default.
            This assumption is important because it supports building different variants of the recipe
            by using the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
            variable.
            You could allow the Build Directory to be the same as the source directory but you would
            not be able to build more than one variant of the recipe.
            Consequently, if you are building multiple variants of the recipe, you need to establish a
            Build Directory that is different than the Source Directory.
        </para>
    </section>

    <section id="selecting-an-initialization-manager">
        <title>Selecting an Initialization Manager</title>

        <para>
            By default, the Yocto Project uses
            <filename>SysVinit</filename> as the initialization manager.
            However, support also exists for <filename>systemd</filename>,
            which is a full replacement for <filename>init</filename> with
            parallel starting of services, reduced shell overhead and other
            features that are used by many distributions.
        </para>

        <para>
            If you want to use <filename>sysvinit</filename>, you do
            not have to do anything.
            But, if you want to use <filename>systemd</filename>, you must
            take some steps as described in the following sections.
        </para>

<!--
        <note>
            It is recommended that you create your own distribution configuration
            file to hold these settings instead of using your
            <filename>local.conf</filename> file.
            For information on creating your own distribution, see the
            "<link linkend='creating-your-own-distribution'>Creating Your Own Distribution</link>"
            section.
        </note>
-->

        <section id='using-systemd-exclusively'>
            <title>Using systemd Exclusively</title>

            <para>
                Set the following variables in your distribution configuration
                file as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                </literallayout>
                You can also prevent the <filename>sysvinit</filename>
                distribution feature from
                being automatically enabled as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_BACKFILL_CONSIDERED = "sysvinit"
                </literallayout>
                Doing so removes any redundant <filename>sysvinit</filename>
                scripts.
            </para>

            <para>
                For information on the backfill variable, see
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES_BACKFILL_CONSIDERED'><filename>DISTRO_FEATURES_BACKFILL_CONSIDERED</filename></ulink>
                in the Yocto Project Reference Manual.
            </para>
        </section>

        <section id='using-systemd-for-the-main-image-and-using-sysvinit-for-the-rescue-image'>
            <title>Using systemd for the Main Image and Using SysVinit for the Rescue Image</title>

            <para>
                Set the following variables in your distribution configuration
                file as follows:
                <literallayout class='monospaced'>
     DISTRO_FEATURES_append = " systemd"
     VIRTUAL-RUNTIME_init_manager = "systemd"
                </literallayout>
                Doing so causes your main image to use the
                <filename>packagegroup-core-boot.bb</filename> recipe and
                <filename>systemd</filename>.
                The rescue/minimal image cannot use this package group.
                However, it can install <filename>sysvinit</filename>
                and the appropriate packages will have support for both
                <filename>systemd</filename> and <filename>sysvinit</filename>.
            </para>
        </section>
    </section>

    <section id='excluding-recipes-from-the-build'>
        <title>Excluding Recipes From the Build</title>

        <para>
            You might find that there are groups of recipes or append files
            that you want to filter out of the build process.
            Usually, this is not necessary.
            However, on rare occasions where you might want to use a
            layer but exclude parts that are causing problems, such
            as introducing a different version of a recipe, you can
            use
            <ulink url='&YOCTO_DOCS_REF_URL;#var-BBMASK'><filename>BBMASK</filename></ulink>
            to exclude the recipe.
        </para>

        <para>
            It is possible to filter or mask out <filename>.bb</filename> and
            <filename>.bbappend</filename> files.
            You can do this by providing an expression with the
            <filename>BBMASK</filename> variable.
            Here is an example:
            <literallayout class='monospaced'>
     BBMASK = "/meta-mymachine/recipes-maybe/"
            </literallayout>
            Here, all <filename>.bb</filename> and
            <filename>.bbappend</filename> files in the directory that match
            the expression are ignored during the build process.
        </para>

        <note>
            The value you provide is passed to Python's regular expression
            compiler.
            The expression is compared against the full paths to the files.
            For complete syntax information, see Python's documentation at
            <ulink url='http://docs.python.org/release/2.3/lib/re-syntax.html'></ulink>.
        </note>
    </section>

    <section id="platdev-appdev-srcrev">
        <title>Using an External SCM</title>

        <para>
            If you're working on a recipe that pulls from an external Source Code Manager (SCM), it
            is possible to have the OpenEmbedded build system notice new recipe changes added to the
            SCM and then build the resulting package that depends on the new recipes by using the latest
            versions.
            This only works for SCMs from which it is possible to get a sensible revision number for changes.
            Currently, you can do this with Apache Subversion (SVN), Git, and Bazaar (BZR) repositories.
        </para>

        <para>
            To enable this behavior, simply add the following to the <filename>local.conf</filename>
            configuration file found in the
            <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
            <literallayout class='monospaced'>
     SRCREV_pn-&lt;PN&gt; = "${AUTOREV}"
            </literallayout>
            where <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>
            is the name of the recipe for which you want to enable automatic source
            revision updating.
        </para>
    </section>

    <section id='creating-a-read-only-root-filesystem'>
        <title>Creating a Read-Only Root Filesystem</title>

        <para>
            Suppose, for security reasons, you need to disable
            your target device's root filesystem's write permissions
            (i.e. you need a read-only root filesystem).
            Or, perhaps you are running the device's operating system
            from a read-only storage device.
            For either case, you can customize your image for
            that behavior.
        </para>

        <note>
            Supporting a read-only root filesystem requires that the system and
            applications do not try to write to the root filesystem.
            You must configure all parts of the target system to write
            elsewhere, or to gracefully fail in the event of failing to
            write to the root filesystem.
        </note>

        <section id='creating-the-root-filesystem'>
            <title>Creating the Root Filesystem</title>

            <para>
                To create the read-only root filesystem, simply add the
                <filename>read-only-rootfs</filename> feature to your image.
                Using either of the following statements in your
                image recipe or from within the
                <filename>local.conf</filename> file found in the
                <link linkend='build-directory'>Build Directory</link>
                causes the build system to create a read-only root filesystem:
                <literallayout class='monospaced'>
     IMAGE_FEATURES = "read-only-rootfs"
                </literallayout>
                or
                <literallayout class='monospaced'>
     EXTRA_IMAGE_FEATURES = "read-only-rootfs"
                </literallayout>
            </para>

            <para>
                For more information on how to use these variables, see the
                "<link linkend='usingpoky-extend-customimage-imagefeatures'>Customizing Images Using Custom <filename>IMAGE_FEATURES</filename> and <filename>EXTRA_IMAGE_FEATURES</filename></link>"
                section.
                For information on the variables, see
                <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>
                and <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink>.
            </para>
        </section>

        <section id='post-installation-scripts'>
            <title>Post-Installation Scripts</title>

            <para>
                It is very important that you make sure all
                post-Installation (<filename>pkg_postinst</filename>) scripts
                for packages that are installed into the image can be run
                at the time when the root filesystem is created during the
                build on the host system.
                These scripts cannot attempt to run during first-boot on the
                target device.
                With the <filename>read-only-rootfs</filename> feature enabled,
                the build system checks during root filesystem creation to make
                sure all post-installation scripts succeed.
                If any of these scripts still need to be run after the root
                filesystem is created, the build immediately fails.
                These checks during build time ensure that the build fails
                rather than the target device fails later during its
                initial boot operation.
            </para>

            <para>
                Most of the common post-installation scripts generated by the
                build system for the out-of-the-box Yocto Project are engineered
                so that they can run during root filesystem creation
                (e.g. post-installation scripts for caching fonts).
                However, if you create and add custom scripts, you need
                to be sure they can be run during file system creation.
            </para>

            <para>
                Here are some common problems that prevent
                post-installation scripts from running during root filesystem
                creation:
                <itemizedlist>
                    <listitem><para><emphasis>Not using $D in front of absolute paths:</emphasis>
                        The build system defines
                        <filename>$</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink>
                        at root filesystem creation time, and
                        it is blank when run on the target device.
                        This implies two purposes for <filename>$D</filename>:
                        ensuring paths are valid in both the host and target
                        environments, and checking to determine which
                        environment is being used as a method for taking
                        appropriate actions.
                        </para></listitem>
                    <listitem><para><emphasis>Attempting to run processes that are
                        specific to or dependent on the target
                        architecture:</emphasis>
                        You can work around these attempts by using native
                        tools to accomplish the same tasks, or
                        by alternatively running the processes under QEMU,
                        which has the <filename>qemu_run_binary</filename>
                        function.
                        For more information, see the
                        <filename>meta/classes/qemu.bbclass</filename>
                        class in the
                        <link linkend='source-directory'>Source Directory</link>.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

        <section id='areas-with-write-access'>
            <title>Areas With Write Access</title>

            <para>
                With the <filename>read-only-rootfs</filename> feature enabled,
                any attempt by the target to write to the root filesystem at
                runtime fails.
                Consequently, you must make sure that you configure processes
                and applications that attempt these types of writes do so
                to directories with write access (e.g.
                <filename>/tmp</filename> or <filename>/var/run</filename>).
            </para>
        </section>
    </section>

    <section id="platdev-gdb-remotedebug">
        <title>Debugging With the GNU Project Debugger (GDB) Remotely</title>

        <para>
            GDB allows you to examine running programs, which in turn helps you to understand and fix problems.
            It also allows you to perform post-mortem style analysis of program crashes.
            GDB is available as a package within the Yocto Project and is
            installed in SDK images by default.
            See the "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter
            in the Yocto Project Reference Manual for a description of these images.
            You can find information on GDB at <ulink url="http://sourceware.org/gdb/"/>.
        </para>

        <tip>
            For best results, install <filename>-dbg</filename> packages for
            the applications you are going to debug.
            Doing so makes extra debug symbols available that give you more
            meaningful output.
        </tip>

        <para>
            Sometimes, due to memory or disk space constraints, it is not possible
            to use GDB directly on the remote target to debug applications.
            These constraints arise because GDB needs to load the debugging information and the
            binaries of the process being debugged.
            Additionally, GDB needs to perform many computations to locate information such as function
            names, variable names and values, stack traces and so forth - even before starting the
            debugging process.
            These extra computations place more load on the target system and can alter the
            characteristics of the program being debugged.
        </para>

        <para>
            To help get past the previously mentioned constraints, you can use Gdbserver.
            Gdbserver runs on the remote target and does not load any debugging information
            from the debugged process.
            Instead, a GDB instance processes the debugging information that is run on a
            remote computer - the host GDB.
            The host GDB then sends control commands to Gdbserver to make it stop or start the debugged
            program, as well as read or write memory regions of that debugged program.
            All the debugging information loaded and processed as well
            as all the heavy debugging is done by the host GDB.
            Offloading these processes gives the Gdbserver running on the target a chance to remain
            small and fast.
        </para>

        <para>
            Because the host GDB is responsible for loading the debugging information and
            for doing the necessary processing to make actual debugging happen, the
            user has to make sure the host can access the unstripped binaries complete
            with their debugging information and also be sure the target is compiled with no optimizations.
            The host GDB must also have local access to all the libraries used by the
            debugged program.
            Because Gdbserver does not need any local debugging information, the binaries on
            the remote target can remain stripped.
            However, the binaries must also be compiled without optimization
            so they match the host's binaries.
        </para>

        <para>
            To remain consistent with GDB documentation and terminology, the binary being debugged
            on the remote target machine is referred to as the "inferior" binary.
            For documentation on GDB see the
            <ulink url="http://sourceware.org/gdb/documentation/">GDB site</ulink>.
        </para>

        <para>
            The remainder of this section describes the steps you need to take
            to debug using the GNU project debugger.
        </para>

        <section id='platdev-gdb-remotedebug-setup'>
            <title>Set Up the Cross-Development Debugging Environment</title>

            <para>
                Before you can initiate a remote debugging session, you need
                to be sure you have set up the cross-development environment,
                toolchain, and sysroot.
                The "<ulink url='&YOCTO_DOCS_ADT_URL;#adt-prepare'>Preparing for Application Development</ulink>"
                chapter of the Yocto Project Application Developer's Guide
                describes this process.
                Be sure you have read that chapter and have set up
                your environment.
            </para>
        </section>

        <section id="platdev-gdb-remotedebug-launch-gdbserver">
            <title>Launch Gdbserver on the Target</title>

            <para>
                Make sure Gdbserver is installed on the target.
                If it is not, install the package
                <filename>gdbserver</filename>, which needs the
                <filename>libthread-db1</filename> package.
            </para>

            <para>
                Here is an example that when entered from the host
                connects to the target and launches Gdbserver in order to
                "debug" a binary named <filename>helloworld</filename>:
                <literallayout class='monospaced'>
     $ gdbserver localhost:2345 /usr/bin/helloworld
                </literallayout>
                Gdbserver should now be listening on port 2345 for debugging
                commands coming from a remote GDB process that is running on
                the host computer.
                Communication between Gdbserver and the host GDB are done
                using TCP.
                To use other communication protocols, please refer to the
                <ulink url='http://www.gnu.org/software/gdb/'>Gdbserver documentation</ulink>.
            </para>
        </section>

        <section id="platdev-gdb-remotedebug-launch-gdb">
            <title>Launch GDB on the Host Computer</title>

            <para>
                Running GDB on the host computer takes a number of stages, which
                this section describes.
            </para>

            <section id="platdev-gdb-remotedebug-launch-gdb-buildcross">
                <title>Build the Cross-GDB Package</title>
                <para>
                    A suitable GDB cross-binary is required that runs on your
                    host computer but also knows about the the ABI of the
                    remote target.
                    You can get this binary from the
                    <link linkend='cross-development-toolchain'>Cross-Development Toolchain</link>.
                    Here is an example where the toolchain has been installed
                    in the default directory
                    <filename>/opt/poky/&DISTRO;</filename>:
                    <literallayout class='monospaced'>
     /opt/poky/1.4/sysroots/i686-pokysdk-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gdb
                    </literallayout>
                    where <filename>arm</filename> is the target architecture
                    and <filename>linux-gnueabi</filename> is the target ABI.
                </para>

                <para>
                    Alternatively, you can use BitBake to build the
                    <filename>gdb-cross</filename> binary.
                    Here is an example:
                    <literallayout class='monospaced'>
     $ bitbake gdb-cross
                    </literallayout>
                    Once the binary is built, you can find it here:
                    <literallayout class='monospaced'>
     tmp/sysroots/&lt;host-arch&gt;/usr/bin/&lt;target-platform&gt;/&lt;target-abi&gt;-gdb
                    </literallayout>
                </para>
            </section>

            <section id='create-the-gdb-initialization-file'>
                <title>Create the GDB Initialization File and Point to Your Root Filesystem</title>

                <para>
                    Aside from the GDB cross-binary, you also need a GDB
                    initialization file in the same top directory in which
                    your binary resides.
                    When you start GDB on your host development system, GDB
                    finds this initialization file and executes all the
                    commands within.
                    For information on the <filename>.gdbinit</filename>, see
                    "<ulink url='http://sourceware.org/gdb/onlinedocs/gdb/'>Debugging with GDB</ulink>",
                    which is maintained by
                    <ulink url='http://www.sourceware.org'>sourceware.org</ulink>.
                </para>

                <para>
                    You need to add a statement in the
                    <filename>.gdbinit</filename> file that points to your
                    root filesystem.
                    Here is an example that points to the root filesystem for
                    an ARM-based target device:
                    <literallayout class='monospaced'>
     set sysroot /home/jzhang/sysroot_arm
                    </literallayout>
                </para>
            </section>

            <section id="platdev-gdb-remotedebug-launch-gdb-launchhost">
                <title>Launch the Host GDB</title>

                <para>
                    Before launching the host GDB, you need to be sure
                    you have sourced the cross-debugging environment script,
                    which if you installed the root filesystem in the default
                    location is at <filename>/opt/poky/&DISTRO;</filename>
                    and begins with the string "environment-setup".
                    For more information, see the
                    "<ulink url='&YOCTO_DOCS_ADT_URL;#setting-up-the-cross-development-environment'>Setting Up the Cross-Development Environment</ulink>"
                    section in the Yocto Project Application Developer's
                    Guide.
                </para>

                <para>
                    Finally, switch to the directory where the binary resides
                    and run the <filename>cross-gdb</filename> binary.
                    Provide the binary file you are going to debug.
                    For example, the following command continues with the
                    example used in the previous section by loading
                    the <filename>helloworld</filename> binary as well as the
                    debugging information:
                    <literallayout class='monospaced'>
     $ arm-poky-linux-gnuabi-gdb helloworld
                    </literallayout>
                    The commands in your <filename>.gdbinit</filename> execute
                    and the GDB prompt appears.
                </para>
            </section>
        </section>

        <section id='platdev-gdb-connect-to-the-remote-gdb-server'>
            <title>Connect to the Remote GDB Server</title>

            <para>
                From the target, you need to connect to the remote GDB
                server that is running on the host.
                You need to specify the remote host and port.
                Here is the command continuing with the example:
                <literallayout class='monospaced'>
     target remote 192.168.7.2:2345
                </literallayout>
            </para>
        </section>

        <section id="platdev-gdb-remotedebug-launch-gdb-using">
            <title>Use the Debugger</title>

            <para>
                You can now proceed with debugging as normal - as if you were debugging
                on the local machine.
                For example, to instruct GDB to break in the "main" function and then
                continue with execution of the inferior binary use the following commands
                from within GDB:
                <literallayout class='monospaced'>
     (gdb) break main
     (gdb) continue
                </literallayout>
            </para>

            <para>
                For more information about using GDB, see the project's online documentation at
                <ulink url="http://sourceware.org/gdb/download/onlinedocs/"/>.
            </para>
        </section>
    </section>

    <section id="platdev-oprofile">
        <title>Profiling with OProfile</title>

        <para>
            <ulink url="http://oprofile.sourceforge.net/">OProfile</ulink> is a
            statistical profiler well suited for finding performance
            bottlenecks in both user-space software and in the kernel.
            This profiler provides answers to questions like "Which functions does my application spend
            the most time in when doing X?"
            Because the OpenEmbedded build system is well integrated with OProfile, it makes profiling
            applications on target hardware straightforward.
            <note>
                For more information on how to set up and run OProfile, see the
                "<ulink url='&YOCTO_DOCS_PROF_URL;#profile-manual-oprofile'>OProfile</ulink>"
                section in the Yocto Project Profiling and Tracing Manual.
            </note>
        </para>

        <para>
            To use OProfile, you need an image that has OProfile installed.
            The easiest way to do this is with <filename>tools-profile</filename> in the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'>IMAGE_FEATURES</ulink></filename> variable.
            You also need debugging symbols to be available on the system where the analysis
            takes place.
            You can gain access to the symbols by using <filename>dbg-pkgs</filename> in the
            <filename>IMAGE_FEATURES</filename> variable or by
            installing the appropriate <filename>-dbg</filename> packages.
        </para>

        <para>
            For successful call graph analysis, the binaries must preserve the frame
            pointer register and should also be compiled with the
            <filename>-fno-omit-framepointer</filename> flag.
            You can achieve this by setting the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-SELECTED_OPTIMIZATION'>SELECTED_OPTIMIZATION</ulink></filename>
            variable with the following options:
            <literallayout class='monospaced'>
     -fexpensive-optimizations
     -fno-omit-framepointer
     -frename-registers
     -O2
            </literallayout>
            You can also achieve it by setting the
            <filename><ulink url='&YOCTO_DOCS_REF_URL;#var-DEBUG_BUILD'>DEBUG_BUILD</ulink></filename>
            variable to "1" in the <filename>local.conf</filename> configuration file.
            If you use the <filename>DEBUG_BUILD</filename> variable,
            you also add extra debugging information that can make the debug
            packages large.
        </para>

        <section id="platdev-oprofile-target">
            <title>Profiling on the Target</title>

            <para>
                Using OProfile you can perform all the profiling work on the target device.
                A simple OProfile session might look like the following:
            </para>

            <para>
                <literallayout class='monospaced'>
     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
              .
              .
        [do whatever is being profiled]
              .
              .
     # opcontrol --stop
     $ opreport -cl
                </literallayout>
            </para>

            <para>
                In this example, the <filename>reset</filename> command clears any previously profiled data.
                The next command starts OProfile.
                The options used when starting the profiler separate dynamic library data
                within applications, disable kernel profiling, and enable callgraphing up to
                five levels deep.
                <note>
                    To profile the kernel, you would specify the
                    <filename>--vmlinux=/path/to/vmlinux</filename> option.
                    The <filename>vmlinux</filename> file is usually in the source directory in the
                    <filename>/boot/</filename> directory and must match the running kernel.
                </note>
            </para>

            <para>
                After you perform your profiling tasks, the next command stops the profiler.
                After that, you can view results with the <filename>opreport</filename> command with options
                to see the separate library symbols and callgraph information.
            </para>

            <para>
                Callgraphing logs information about time spent in functions and about a function's
                calling function (parent) and called functions (children).
                The higher the callgraphing depth, the more accurate the results.
                However, higher depths also increase the logging overhead.
                Consequently, you should take care when setting the callgraphing depth.
                <note>
                    On ARM, binaries need to have the frame pointer enabled for callgraphing to work.
                    To accomplish this use the <filename>-fno-omit-framepointer</filename> option
                    with <filename>gcc</filename>.
                </note>
            </para>

            <para>
                For more information on using OProfile, see the OProfile
                online documentation at
                <ulink url="http://oprofile.sourceforge.net/docs/"/>.
            </para>
        </section>

        <section id="platdev-oprofile-oprofileui">
            <title>Using OProfileUI</title>

            <para>
                A graphical user interface for OProfile is also available.
                You can download and build this interface from the Yocto Project at
                <ulink url="&YOCTO_GIT_URL;/cgit.cgi/oprofileui/"></ulink>.
                If the "tools-profile" image feature is selected, all necessary binaries
                are installed onto the target device for OProfileUI interaction.
                For a list of image features that ship with the Yocto Project,
                see the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-features-image'>Images</ulink>"
                section in the Yocto Project Reference Manual.
            </para>

            <para>
                Even though the source directory usually includes all needed patches on the target device, you
                might find you need other OProfile patches for recent OProfileUI features.
                If so, see the <ulink url='&YOCTO_GIT_URL;/cgit.cgi/oprofileui/tree/README'>
                OProfileUI README</ulink> for the most recent information.
            </para>

            <section id="platdev-oprofile-oprofileui-online">
                <title>Online Mode</title>

                <para>
                    Using OProfile in online mode assumes a working network connection with the target
                    hardware.
                    With this connection, you just need to run "oprofile-server" on the device.
                    By default, OProfile listens on port 4224.
                    <note>
                        You can change the port using the <filename>--port</filename> command-line
                        option.
                    </note>
                </para>

                <para>
                    The client program is called <filename>oprofile-viewer</filename> and its UI is relatively
                    straightforward.
                    You access key functionality through the buttons on the toolbar, which
                    are duplicated in the menus.
                    Here are the buttons:
                    <itemizedlist>
                        <listitem><para><emphasis>Connect:</emphasis> Connects to the remote host.
                            You can also supply the IP address or hostname.</para></listitem>
                        <listitem><para><emphasis>Disconnect:</emphasis> Disconnects from the target.
                            </para></listitem>
                        <listitem><para><emphasis>Start:</emphasis> Starts profiling on the device.
                            </para></listitem>
                        <listitem><para><emphasis>Stop:</emphasis> Stops profiling on the device and
                            downloads the data to the local host.
                            Stopping the profiler generates the profile and displays it in the viewer.
                            </para></listitem>
                        <listitem><para><emphasis>Download:</emphasis> Downloads the data from the
                            target and generates the profile, which appears in the viewer.</para></listitem>
                        <listitem><para><emphasis>Reset:</emphasis> Resets the sample data on the device.
                            Resetting the data removes sample information collected from previous
                            sampling runs.
                            Be sure you reset the data if you do not want to include old sample information.
                            </para></listitem>
                        <listitem><para><emphasis>Save:</emphasis> Saves the data downloaded from the
                            target to another directory for later examination.</para></listitem>
                        <listitem><para><emphasis>Open:</emphasis> Loads previously saved data.
                            </para></listitem>
                    </itemizedlist>
                </para>

                <para>
                    The client downloads the complete 'profile archive' from
                    the target to the host for processing.
                    This archive is a directory that contains the sample data, the object files,
                    and the debug information for the object files.
                    The archive is then converted using the <filename>oparchconv</filename> script, which is
                    included in this distribution.
                    The script uses <filename>opimport</filename> to convert the archive from
                    the target to something that can be processed on the host.
                </para>

                <para>
                    Downloaded archives reside in the
                    <link linkend='build-directory'>Build Directory</link> in
                    <filename>/tmp</filename> and are cleared up when they are no longer in use.
                </para>

                <para>
                    If you wish to perform kernel profiling, you need to be sure
                    a <filename>vmlinux</filename> file that matches the running kernel is available.
                    In the source directory, that file is usually located in
                    <filename>/boot/vmlinux-KERNELVERSION</filename>, where
                    <filename>KERNEL-version</filename> is the version of the kernel.
                    The OpenEmbedded build system generates separate <filename>vmlinux</filename>
                    packages for each kernel it builds.
                    Thus, it should just be a question of making sure a matching package is
                    installed (e.g. <filename>opkg install kernel-vmlinux</filename>).
                    The files are automatically installed into development and profiling images
                    alongside OProfile.
                    A configuration option exists within the OProfileUI settings page that you can use to
                    enter the location of the <filename>vmlinux</filename> file.
                </para>

                <para>
                    Waiting for debug symbols to transfer from the device can be slow, and it
                    is not always necessary to actually have them on the device for OProfile use.
                    All that is needed is a copy of the filesystem with the debug symbols present
                    on the viewer system.
                    The "<link linkend='platdev-gdb-remotedebug-launch-gdb'>Launch GDB on the Host Computer</link>"
                    section covers how to create such a directory with
                    the <link linkend='source-directory'>Source Directory</link>
                    and how to use the OProfileUI Settings Dialog to specify the location.
                    If you specify the directory, it will be used when the file checksums
                    match those on the system you are profiling.
                </para>
            </section>

            <section id="platdev-oprofile-oprofileui-offline">
                <title>Offline Mode</title>

                <para>
                    If network access to the target is unavailable, you can generate
                    an archive for processing in <filename>oprofile-viewer</filename> as follows:
                    <literallayout class='monospaced'>
     # opcontrol --reset
     # opcontrol --start --separate=lib --no-vmlinux -c 5
            .
            .
     [do whatever is being profiled]
            .
            .
     # opcontrol --stop
     # oparchive -o my_archive
                    </literallayout>
                </para>

                <para>
                    In the above example, <filename>my_archive</filename> is the name of the
                    archive directory where you would like the profile archive to be kept.
                    After the directory is created, you can copy it to another host and load it
                    using <filename>oprofile-viewer</filename> open functionality.
                    If necessary, the archive is converted.
                </para>
            </section>
        </section>
    </section>

    <section id='maintaining-open-source-license-compliance-during-your-products-lifecycle'>
        <title>Maintaining Open Source License Compliance During Your Product's Lifecycle</title>

        <para>
            One of the concerns for a development organization using open source
            software is how to maintain compliance with various open source
            licensing during the lifecycle of the product.
            While this section does not provide legal advice or
            comprehensively cover all scenarios, it does
            present methods that you can use to
            assist you in meeting the compliance requirements during a software
            release.
        </para>

        <para>
            With hundreds of different open source licenses that the Yocto
            Project tracks, it is difficult to know the requirements of each
            and every license.
            However, we can begin to cover the requirements of the major FLOSS licenses, by
            assuming that there are three main areas of concern:
            <itemizedlist>
                <listitem><para>Source code must be provided.</para></listitem>
                <listitem><para>License text for the software must be
                    provided.</para></listitem>
                <listitem><para>Compilation scripts and modifications to the
                    source code must be provided.
                    </para></listitem>
            </itemizedlist>
            There are other requirements beyond the scope of these
            three and the methods described in this section
            (e.g. the mechanism through which source code is distributed).
        </para>

        <para>
            As different organizations have different methods of complying with
            open source licensing, this section is not meant to imply that
            there is only one single way to meet your compliance obligations,
            but rather to describe one method of achieving compliance.
            The remainder of this section describes methods supported to meet the
            previously mentioned three requirements.
            Once you take steps to meet these requirements,
            and prior to releasing images, sources, and the build system,
            you should audit all artifacts to ensure completeness.
            <note>
                The Yocto Project generates a license manifest during
                image creation that is located
                in <filename>${DEPLOY_DIR}/licenses/&lt;image_name-datestamp&gt;</filename>
                to assist with any audits.
            </note>
        </para>

        <section id='providing-the-source-code'>
            <title>Providing the Source Code</title>

            <para>
                Compliance activities should begin before you generate the
                final image.
                The first thing you should look at is the requirement that
                tops the list for most compliance groups - providing
                the source.
                The Yocto Project has a few ways of meeting this
                requirement.
            </para>

            <para>
                One of the easiest ways to meet this requirement is
                to provide the entire
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink>
                used by the build.
                This method, however, has a few issues.
                The most obvious is the size of the directory since it includes
                all sources used in the build and not just the source used in
                the released image.
                It will include toolchain source, and other artifacts, which
                you would not generally release.
                However, the more serious issue for most companies is accidental
                release of proprietary software.
                The Yocto Project provides an archiver class to help avoid
                some of these concerns.
                See the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-archiver'>Archiving Sources - <filename>archive*.bbclass</filename></ulink>"
                section in the Yocto Project Reference Manual for information
                on this class.
            </para>

            <para>
                Before you employ <filename>DL_DIR</filename> or the
                archiver class, you need to decide how you choose to
                provide source.
                The source archiver class can generate tarballs and SRPMs
                and can create them with various levels of compliance in mind.
                One way of doing this (but certainly not the only way) is to
                release just the original source as a tarball.
                You can do this by adding the following to the
                <filename>local.conf</filename> file found in the
                <link linkend='build-directory'>Build Directory</link>:
                <literallayout class='monospaced'>
     ARCHIVER_MODE ?= "original"
     ARCHIVER_CLASS = "${@'archive-${ARCHIVER_MODE}-source' if
     ARCHIVER_MODE != 'none' else ''}"
     INHERIT += "${ARCHIVER_CLASS}"
     SOURCE_ARCHIVE_PACKAGE_TYPE = "tar"
                </literallayout>
                During the creation of your image, the source from all
                recipes that deploy packages to the image is placed within
                subdirectories of
                <filename>DEPLOY_DIR/sources</filename> based on the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                for each recipe.
                Releasing the entire directory enables you to comply with
                requirements concerning providing the unmodified source.
                It is important to note that the size of the directory can
                get large.
            </para>

            <para>
                A way to help mitigate the size issue is to only release
                tarballs for licenses that require the release of
                source.
                Let's assume you are only concerned with GPL code as
                identified with the following:
                <literallayout class='monospaced'>
     $ cd poky/build/tmp/deploy/sources
     $ mkdir ~/gpl_source_release
     $ for dir in */*GPL*; do cp -r $dir ~/gpl_source_release; done
                </literallayout>
                At this point, you could create a tarball from the
                <filename>gpl_source_release</filename> directory and
                provide that to the end user.
                This method would be a step toward achieving compliance
                with section 3a of GPLv2 and with section 6 of GPLv3.
            </para>
        </section>

        <section id='providing-license-text'>
            <title>Providing License Text</title>

            <para>
                One requirement that is often overlooked is inclusion
                of license text.
                This requirement also needs to be dealt with prior to
                generating the final image.
                Some licenses require the license text to accompany
                the binary.
                You can achieve this by adding the following to your
                <filename>local.conf</filename> file:
                <literallayout class='monospaced'>
     COPY_LIC_MANIFEST = "1"
     COPY_LIC_DIRS = "1"
                </literallayout>
                Adding these statements to the configuration file ensures
                that the licenses collected during package generation
                are included on your image.
                As the source archiver has already archived the original
                unmodified source that contains the license files,
                you would have already met the requirements for inclusion
                of the license information with source as defined by the GPL
                and other open source licenses.
            </para>
        </section>

        <section id='providing-compilation-scripts-and-source-code-modifications'>
            <title>Providing Compilation Scripts and Source Code Modifications</title>

            <para>
                At this point, we have addressed all we need to address
                prior to generating the image.
                The next two requirements are addressed during the final
                packaging of the release.
            </para>

            <para>
                By releasing the version of the OpenEmbedded build system
                and the layers used during the build, you will be providing both
                compilation scripts and the source code modifications in one
                step.
            </para>

            <para>
                If the deployment team has a
                <ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP layer</ulink>
                and a distro layer, and those those layers are used to patch,
                compile, package, or modify (in any way) any open source
                software included in your released images, you
                may be required to to release those layers under section 3 of
                GPLv2 or section 1 of GPLv3.
                One way of doing that is with a clean
                checkout of the version of the Yocto Project and layers used
                during your build.
                Here is an example:
                <literallayout class='monospaced'>
     # We built using the &DISTRO_NAME; branch of the poky repo
     $ git clone -b &DISTRO_NAME; git://git.yoctoproject.org/poky
     $ cd poky
     # We built using the release_branch for our layers
     $ git clone -b release_branch git://git.mycompany.com/meta-my-bsp-layer
     $ git clone -b release_branch git://git.mycompany.com/meta-my-software-layer
     # clean up the .git repos
     $ find . -name ".git" -type d -exec rm -rf {} \;
                </literallayout>
                One thing a development organization might want to consider
                for end-user convenience is to modify
                <filename>meta-yocto/conf/bblayers.conf.sample</filename> to
                ensure that when the end user utilizes the released build
                system to build an image, the development organization's
                layers are included in the <filename>bblayers.conf</filename>
                file automatically:
                <literallayout class='monospaced'>
     # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
     # changes incompatibly
     LCONF_VERSION = "6"

     BBPATH = "${TOPDIR}"
     BBFILES ?= ""

     BBLAYERS ?= " \
       ##COREBASE##/meta \
       ##COREBASE##/meta-yocto \
       ##COREBASE##/meta-yocto-bsp \
       ##COREBASE##/meta-mylayer \
       "

     BBLAYERS_NON_REMOVABLE ?= " \
       ##COREBASE##/meta \
       ##COREBASE##/meta-yocto \
       "
                </literallayout>
                Creating and providing an archive of the
                <link linkend='metadata'>Metadata</link> layers
                (recipes, configuration files, and so forth)
                enables you to meet your
                requirements to include the scripts to control compilation
                as well as any modifications to the original source.
            </para>
        </section>
    </section>
</chapter>

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