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

<chapter id='sdk-extensible'>

<title>Using the Extensible SDK</title>

<para>
    This chapter describes the extensible SDK and how to use it.
    The extensible SDK makes it easy to add new applications and libraries
    to an image, modify the source for an existing component, test
    changes on the target hardware, and ease integration into the rest of the
    <ulink url='&YOCTO_DOCS_DEV_URL;#build-system-term'>OpenEmbedded build system</ulink>.
</para>

<para>
    Information in this chapter covers features that are not part of the
    standard SDK.
    In other words, the chapter presents information unique to the
    extensible SDK only.
    For information on how to use the standard SDK, see the
    "<link linkend='sdk-using-the-standard-sdk'>Using the Standard SDK</link>"
    chapter.
</para>

<section id='sdk-setting-up-to-use-the-extensible-sdk'>
    <title>Setting Up to Use the Extensible SDK</title>

    <para>
        Getting set up to use the extensible SDK is identical to getting set
        up to use the standard SDK.
        You still need to locate and run the installer and then run the
        environment setup script.
        See the
        "<link linkend='sdk-installing-the-sdk'>Installing the SDK</link>"
        and the
        "<link linkend='sdk-running-the-sdk-environment-setup-script'>Running the SDK Environment Setup Script</link>"
        sections for general information.
        The following items highlight the only differences between getting
        set up to use the extensible SDK as compared to the standard SDK:
        <itemizedlist>
            <listitem><para><emphasis>Default Installation Directory:</emphasis>
                By default, the extensible SDK installs into the
                <filename>poky_sdk</filename> folder of your home directory.
                As with the standard SDK, you can choose to install the
                extensible SDK in any location when you run the installer.
                However, unlike the standard SDK, the location you choose needs
                to be writable for whichever users need to use the SDK,
                since files will need to be written under that directory during
                the normal course of operation.
                </para></listitem>
            <listitem><para><emphasis>Build Tools and Build System:</emphasis>
                The extensible SDK installer performs additional tasks as
                compared to the standard SDK installer.
                The extensible SDK installer extracts build tools specific
                to the SDK and the installer also prepares the internal build
                system within the SDK.
                Here is example output for running the extensible SDK
                installer:
                <literallayout class='monospaced'>
     $ ./poky-glibc-x86_64-core-image-minimal-core2-64-toolchain-ext-2.1+snapshot.sh
     Poky (Yocto Project Reference Distro) Extensible SDK installer version 2.1+snapshot
     ===================================================================================
     Enter target directory for SDK (default: ~/poky_sdk):
     You are about to install the SDK to "/home/scottrif/poky_sdk". Proceed[Y/n]? Y
     Extracting SDK......................................................................done
     Setting it up...
     Extracting buildtools...
     Preparing build system...
     done
     SDK has been successfully set up and is ready to be used.
     Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
      $ . /home/scottrif/poky_sdk/environment-setup-core2-64-poky-linux
                </literallayout>
                </para></listitem>
        </itemizedlist>
    </para>

    <para>
        After installing the SDK, you need to run the SDK environment setup
        script.
        Here is the output:
        <literallayout class='monospaced'>
     $ source environment-setup-core2-64-poky-linux
     SDK environment now set up; additionally you may now run devtool to perform development tasks.
     Run devtool --help for further details.
        </literallayout>
        Once you run the environment setup script, you have
        <filename>devtool</filename> available.
    </para>
</section>

<section id='using-devtool-in-your-sdk-workflow'>
    <title>Using <filename>devtool</filename> in Your SDK Workflow</title>

    <para>
        The cornerstone of the extensible SDK is a command-line tool
        called <filename>devtool</filename>.
        This tool provides a number of features that help
        you build, test and package software within the extensible SDK, and
        optionally integrate it into an image built by the OpenEmbedded build
        system.
    </para>

    <para>
        The <filename>devtool</filename> command line is organized similarly
        to
        <ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink> in that it has a
        number of sub-commands for each function.
        You can run <filename>devtool --help</filename> to see all the
        commands.
    </para>

    <para>
        Two <filename>devtool</filename> subcommands that provide
        entry-points into development are:
        <itemizedlist>
            <listitem><para><emphasis><filename>devtool add</filename></emphasis>:
                Assists in adding new software to be built.
                </para></listitem>
            <listitem><para><emphasis><filename>devtool modify</filename></emphasis>:
                Sets up an environment to enable you to modify the source of
                an existing component.
                </para></listitem>
        </itemizedlist>
        As with the OpenEmbedded build system, "recipes" represent software
        packages within <filename>devtool</filename>.
        When you use <filename>devtool add</filename>, a recipe is
        automatically created.
        When you use <filename>devtool modify</filename>, the specified
        existing recipe is used in order to determine where to get the source
        code and how to patch it.
        In both cases, an environment is set up so that when you build the
        recipe a source tree that is under your control is used in order to
        allow you to make changes to the source as desired.
        By default, both new recipes and the source go into a "workspace"
        directory under the SDK.
    </para>

    <para>
        The remainder of this section presents the
        <filename>devtool add</filename> and
        <filename>devtool modify</filename> workflows.
    </para>

    <section id='sdk-use-devtool-to-add-an-application'>
        <title>Use <filename>devtool add</filename> to Add an Application</title>

        <para>
            The <filename>devtool add</filename> command generates
            a new recipe based on existing source code.
            This command takes advantage of the
            <ulink url='&YOCTO_DOCS_DEV_URL;#devtool-the-workspace-layer-structure'>workspace</ulink>
            layer that many <filename>devtool</filename> commands
            use.
            The command is flexible enough to allow you to extract source
            code into both the workspace or a separate local Git repository
            and to use existing code that does not need to be extracted.
        </para>

        <para>
            Depending on your particular scenario, the arguments and options
            you use with <filename>devtool add</filename> form different
            combinations.
            The following diagram shows common development flows
            you would use with the <filename>devtool add</filename>
            command:
        </para>

        <para>
            <imagedata fileref="figures/sdk-devtool-add-flow.png" align="center" />
        </para>

        <para>
            <orderedlist>
                <listitem><para><emphasis>Generating the New Recipe</emphasis>:
                    The top part of the flow shows three scenarios by which
                    you could use <filename>devtool add</filename> to
                    generate a recipe based on existing source code.</para>

                    <para>In a shared development environment, it is
                    typical where other developers are responsible for
                    various areas of source code.
                    As a developer, you are probably interested in using
                    that source code as part of your development using
                    the Yocto Project.
                    All you need is access to the code, a recipe, and a
                    controlled area in which to do your work.</para>

                    <para>Within the diagram, three possible scenarios
                    feed into the <filename>devtool add</filename> workflow:
                    <itemizedlist>
                        <listitem><para><emphasis>Left</emphasis>:
                            The left scenario represents a common situation
                            where the source code does not exist locally
                            and needs to be extracted.
                            In this situation, you just let it get
                            extracted to the default workspace - you do not
                            want it in some specific location outside of the
                            workspace.
                            Thus, everything you need will be located in the
                            workspace:
                            <literallayout class='monospaced'>
     $ devtool add <replaceable>recipe fetchuri</replaceable>
                            </literallayout>
                            With this command, <filename>devtool</filename>
                            creates a recipe and an append file in the
                            workspace as well as extracts the upstream
                            source files into a local Git repository also
                            within the <filename>sources</filename> folder.
                            </para></listitem>
                        <listitem><para><emphasis>Middle</emphasis>:
                            The middle scenario also represents a situation where
                            the source code does not exist locally.
                            In this case, the code is again upstream
                            and needs to be extracted to some
                            local area - this time outside of the default
                            workspace.
                            As always, if required <filename>devtool</filename> creates
                            a Git repository locally during the extraction.
                            Furthermore, the first positional argument
                            <replaceable>srctree</replaceable> in this case
                            identifies where the
                            <filename>devtool add</filename> command
                            will locate the extracted code outside of the
                            workspace:
                            <literallayout class='monospaced'>
     $ devtool add <replaceable>recipe srctree fetchuri</replaceable>
                            </literallayout>
                            In summary, the source code is pulled from
                            <replaceable>fetchuri</replaceable> and extracted
                            into the location defined by
                            <replaceable>srctree</replaceable> as a local
                            Git repository.</para>

                            <para>Within workspace, <filename>devtool</filename>
                            creates both the recipe and an append file
                            for the recipe.
                            </para></listitem>
                        <listitem><para><emphasis>Right</emphasis>:
                            The right scenario represents a situation
                            where the source tree (srctree) has been
                            previously prepared outside of the
                            <filename>devtool</filename> workspace.
                            </para>

                            <para>The following command names the recipe
                            and identifies where the existing source tree
                            is located:
                            <literallayout class='monospaced'>
     $ devtool add <replaceable>recipe srctree</replaceable>
                            </literallayout>
                            The command examines the source code and creates
                            a recipe for it placing the recipe into the
                            workspace.</para>

                            <para>Because the extracted source code already exists,
                            <filename>devtool</filename> does not try to
                            relocate it into the workspace - just the new
                            the recipe is placed in the workspace.</para>

                            <para>Aside from a recipe folder, the command
                            also creates an append folder and places an initial
                            <filename>*.bbappend</filename> within.
                            </para></listitem>
                    </itemizedlist>
                    </para></listitem>
                <listitem><para><emphasis>Edit the Recipe</emphasis>:
                    At this point, you can use <filename>devtool edit-recipe</filename>
                    to open up the editor as defined by the
                    <filename>$EDITOR</filename> environment variable
                    and modify the file:
                    <literallayout class='monospaced'>
     $ devtool edit-recipe <replaceable>recipe</replaceable>
                    </literallayout>
                    From within the editor, you can make modifications to the
                    recipe that take affect when you build it later.
                    </para></listitem>
                <listitem><para><emphasis>Build the Recipe or Rebuild the Image</emphasis>:
                    At this point in the flow, the next step you
                    take depends on what you are going to do with
                    the new code.</para>
                    <para>If you need to take the build output and eventually
                    move it to the target hardware, you would use
                    <filename>devtool build</filename>:
                    <literallayout class='monospaced'>
     $ devtool build <replaceable>recipe</replaceable>
                    </literallayout></para>
                    <para>On the other hand, if you want an image to
                    contain the recipe's packages for immediate deployment
                    onto a device (e.g. for testing purposes), you can use
                    the <filename>devtool build-image</filename> command:
                    <literallayout class='monospaced'>
     $ devtool build-image <replaceable>image</replaceable>
                    </literallayout>
                    </para></listitem>
                <listitem><para><emphasis>Deploy the Build Output</emphasis>:
                    When you use the <filename>devtool build</filename>
                    command to build out your recipe, you probably want to
                    see if the resulting build output works as expected on target
                    hardware.
                    <note>
                        This step assumes you have a previously built
                        image that is already either running in QEMU or
                        running on actual hardware.
                        Also, it is assumed that for deployment of the image
                        to the target, SSH is installed in the image and if
                        the image is running on real hardware that you have
                        network access to and from your development machine.
                    </note>
                    You can deploy your build output to that target hardware by
                    using the <filename>devtool deploy-target</filename> command:
                    <literallayout class='monospaced'>
     $ devtool deploy-target <replaceable>recipe target</replaceable>
                    </literallayout>
                    The <replaceable>target</replaceable> is a live target machine
                    running as an SSH server.</para>

                    <para>You can, of course, also deploy the image you build
                    using the <filename>devtool build-image</filename> command
                    to actual hardware.
                    However, <filename>devtool</filename> does not provide a
                    specific command that allows you to do this.
                    </para></listitem>
                <listitem><para><emphasis>Optionally Update the Recipe With Patch Files</emphasis>:
                    Once you are satisfied with the recipe, if you have made
                    any changes to the source tree that you want to have
                    applied by the recipe, you need to generate patches
                    from those changes.
                    You do this before moving the recipe
                    to its final layer and cleaning up the workspace area
                    <filename>devtool</filename> uses.
                    This optional step is especially relevant if you are
                    using or adding third-party software.</para>
                    <para>To convert commits created using Git to patch files,
                    use the <filename>devtool update-recipe</filename> command.
                    <note>
                        Any changes you want to turn into patches must be
                        committed to the Git repository in the source tree.
                    </note>
                    <literallayout class='monospaced'>
     $ devtool update-recipe <replaceable>recipe</replaceable>
                    </literallayout>
                    </para></listitem>
                <listitem><para><emphasis>Move the Recipe to its Permanent Layer</emphasis>:
                    Before cleaning up the workspace, you need to move the
                    final recipe to its permanent layer.
                    You must do this before using the
                    <filename>devtool reset</filename> command if you want to
                    retain the recipe.
                    </para></listitem>
                <listitem><para><emphasis>Reset the Recipe</emphasis>:
                    As a final step, you can restore the state such that
                    standard layers and the upstream source is used to build
                    the recipe rather than data in the workspace.
                    To reset the recipe, use the <filename>devtool reset</filename>
                    command:
                    <literallayout class='monospaced'>
     $ devtool reset <replaceable>recipe</replaceable>
                    </literallayout>
                    </para></listitem>
            </orderedlist>
        </para>
    </section>

    <section id='sdk-devtool-use-devtool-modify-to-modify-the-source-of-an-existing-component'>
        <title>Use <filename>devtool modify</filename> to Modify the Source of an Existing Component</title>

        <para>
            The <filename>devtool modify</filename> command prepares the
            way to work on existing code that already has a recipe in
            place.
            The command is flexible enough to allow you to extract code,
            specify the existing recipe, and keep track of and gather any
            patch files from other developers that are
            associated with the code.
        </para>

        <para>
            Depending on your particular scenario, the arguments and options
            you use with <filename>devtool modify</filename> form different
            combinations.
            The following diagram shows common development flows
            you would use with the <filename>devtool modify</filename>
            command:
        </para>

        <para>
            <imagedata fileref="figures/sdk-devtool-modify-flow.png" align="center" />
        </para>

        <para>
            <orderedlist>
                <listitem><para><emphasis>Preparing to Modify the Code</emphasis>:
                    The top part of the flow shows three scenarios by which
                    you could use <filename>devtool modify</filename> to
                    prepare to work on source files.
                    Each scenario assumes the following:
                    <itemizedlist>
                        <listitem><para>The recipe exists in some layer external
                            to the <filename>devtool</filename> workspace.
                            </para></listitem>
                        <listitem><para>The source files exist upstream in an
                            un-extracted state or locally in a previously
                            extracted state.
                            </para></listitem>
                    </itemizedlist>
                    The typical situation is where another developer has
                    created some layer for use with the Yocto Project and
                    their recipe already resides in that layer.
                    Furthermore, their source code is readily available
                    either upstream or locally.
                    <itemizedlist>
                        <listitem><para><emphasis>Left</emphasis>:
                            The left scenario represents a common situation
                            where the source code does not exist locally
                            and needs to be extracted.
                            In this situation, the source is extracted
                            into the default workspace location.
                            The recipe, in this scenario, is in its own
                            layer outside the workspace
                            (i.e.
                            <filename>meta-</filename><replaceable>layername</replaceable>).
                            </para>

                            <para>The following command identifies the recipe
                            and by default extracts the source files:
                            <literallayout class='monospaced'>
     $ devtool modify <replaceable>recipe</replaceable>
                            </literallayout>
                            Once <filename>devtool</filename>locates the recipe,
                            it uses the
                            <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                            variable to locate the source code and
                            any local patch files from other developers are
                            located.
                            <note>
                                You cannot provide an URL for
                                <replaceable>srctree</replaceable> when using the
                                <filename>devtool modify</filename> command.
                            </note>
                            With this scenario, however, since no
                            <replaceable>srctree</replaceable> argument exists, the
                            <filename>devtool modify</filename> command by default
                            extracts the source files to a Git structure.
                            Furthermore, the location for the extracted source is the
                            default area within the workspace.
                            The result is that the command sets up both the source
                            code and an append file within the workspace with the
                            recipe remaining in its original location.
                            </para></listitem>
                        <listitem><para><emphasis>Middle</emphasis>:
                            The middle scenario represents a situation where
                            the source code also does not exist locally.
                            In this case, the code is again upstream
                            and needs to be extracted to some
                            local area as a Git repository.
                            The recipe, in this scenario, is again in its own
                            layer outside the workspace.</para>

                            <para>The following command tells
                            <filename>devtool</filename> what recipe with
                            which to work and, in this case, identifies a local
                            area for the extracted source files that is outside
                            of the default workspace:
                            <literallayout class='monospaced'>
     $ devtool modify <replaceable>recipe srctree</replaceable>
                            </literallayout>
                            As with all extractions, the command uses
                            the recipe's <filename>SRC_URI</filename> to locate the
                            source files.
                            Once the files are located, the command by default
                            extracts them.
                            Providing the <replaceable>srctree</replaceable>
                            argument instructs <filename>devtool</filename> where
                            place the extracted source.</para>

                            <para>Within workspace, <filename>devtool</filename>
                            creates an append file for the recipe.
                            The recipe remains in its original location but
                            the source files are extracted to the location you
                            provided with <replaceable>srctree</replaceable>.
                            </para></listitem>
                        <listitem><para><emphasis>Right</emphasis>:
                            The right scenario represents a situation
                            where the source tree
                            (<replaceable>srctree</replaceable>) exists as a
                            previously extracted Git structure outside of
                            the <filename>devtool</filename> workspace.
                            In this example, the recipe also exists
                            elsewhere in its own layer.
                            </para>

                            <para>The following command tells
                            <filename>devtool</filename> the recipe
                            with which to work, uses the "-n" option to indicate
                            source does not need to be extracted, and uses
                            <replaceable>srctree</replaceable> to point to the
                            previously extracted source files:
                            <literallayout class='monospaced'>
     $ devtool modify -n <replaceable>recipe srctree</replaceable>
                            </literallayout>
                            </para>

                            <para>Once the command finishes, it creates only
                            an append file for the recipe in the workspace.
                            The recipe and the source code remain in their
                            original locations.
                            </para></listitem>
                        </itemizedlist>
                    </para></listitem>
                <listitem><para><emphasis>Edit the Source</emphasis>:
                    Once you have used the <filename>devtool modify</filename>
                    command, you are free to make changes to the source
                    files.
                    You can use any editor you like to make and save
                    your source code modifications.
                    </para></listitem>
                <listitem><para><emphasis>Build the Recipe</emphasis>:
                    Once you have updated the source files, you can build
                    the recipe.
                    </para></listitem>
                <listitem><para><emphasis>Deploy the Build Output</emphasis>:
                    When you use the <filename>devtool build</filename>
                    command to build out your recipe, you probably want to see
                    if the resulting build output works as expected on target
                    hardware.
                    <note>
                        This step assumes you have a previously built
                        image that is already either running in QEMU or
                        running on actual hardware.
                        Also, it is assumed that for deployment of the image
                        to the target, SSH is installed in the image and if
                        the image is running on real hardware that you have
                        network access to and from your development machine.
                    </note>
                    You can deploy your build output to that target hardware by
                    using the <filename>devtool deploy-target</filename> command:
                    <literallayout class='monospaced'>
     $ devtool deploy-target <replaceable>recipe target</replaceable>
                    </literallayout>
                    The <replaceable>target</replaceable> is a live target machine
                    running as an SSH server.</para>

                    <para>You can, of course, also deploy the image you build
                    using the <filename>devtool build-image</filename> command
                    to actual hardware.
                    However, <filename>devtool</filename> does not provide a
                    specific command that allows you to do this.
                    </para></listitem>
                <listitem><para><emphasis>Optionally Create Patch Files for Your Changes</emphasis>:
                    After you have debugged your changes, you can
                    use <filename>devtool update-recipe</filename> to
                    generate patch files for all the commits you have
                    made.
                    <note>
                        Patch files are generated only for changes
                        you have committed.
                    </note>
                    <literallayout class='monospaced'>
     $ devtool update-recipe <replaceable>recipe</replaceable>
                    </literallayout>
                    By default, the
                    <filename>devtool update-recipe</filename> command
                    creates the patch files in a folder named the same
                    as the recipe beneath the folder in which the recipe
                    resides, and updates the recipe's
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                    statement to point to the generated patch files.
                    <note>
                        You can use the
                        "--append <replaceable>LAYERDIR</replaceable>"
                        option to cause the command to create append files
                        in a specific layer rather than the default
                        recipe layer.
                    </note>
                    </para></listitem>
                <listitem><para><emphasis>Restore the Workspace</emphasis>:
                    The <filename>devtool reset</filename> restores the
                    state so that standard layers and upstream sources are
                    used to build the recipe rather than what is in the
                    workspace.
                    <literallayout class='monospaced'>
     $ devtool reset <replaceable>recipe</replaceable>
                    </literallayout>
                    </para></listitem>
            </orderedlist>
        </para>
    </section>
</section>

<section id='sdk-a-closer-look-at-devtool-add'>
    <title>A Closer Look at <filename>devtool add</filename></title>

    <para>
        The <filename>devtool add</filename> command automatically creates a
        recipe based on the source tree with which you provide it.
        Currently, the command has support for the following:
        <itemizedlist>
            <listitem><para>
                Autotools (<filename>autoconf</filename> and
                <filename>automake</filename>)
                </para></listitem>
            <listitem><para>
                CMake
                </para></listitem>
            <listitem><para>
                Scons
                </para></listitem>
            <listitem><para>
                <filename>qmake</filename>
                </para></listitem>
            <listitem><para>
                Plain <filename>Makefile</filename>
                </para></listitem>
            <listitem><para>
                Out-of-tree kernel module
                </para></listitem>
            <listitem><para>
                Binary package (i.e. "-b" option)
                </para></listitem>
            <listitem><para>
                Node.js module through
                <filename>npm</filename>
                </para></listitem>
            <listitem><para>
                Python modules that use <filename>setuptools</filename>
                or <filename>distutils</filename>
                </para></listitem>
        </itemizedlist>
    </para>

    <para>
        Apart from binary packages, the determination of how a source tree
        should be treated is automatic based on the files present within
        that source tree.
        For example, if a <filename>CMakeLists.txt</filename> file is found,
        then the source tree is assumed to be using
        CMake and is treated accordingly.
        <note>
            In most cases, you need to edit the automatically generated
            recipe in order to make it build properly.
            Typically, you would go through several edit and build cycles
            until you can build the recipe.
            Once the recipe can be built, you could use possible further
            iterations to test the recipe on the target device.
        </note>
    </para>

    <para>
        The remainder of this section covers specifics regarding how parts
        of the recipe are generated.
    </para>

    <section id='sdk-name-and-version'>
        <title>Name and Version</title>

        <para>
            If you do not specify a name and version on the command
            line, <filename>devtool add</filename> attempts to determine
            the name and version of the software being built from
            various metadata within the source tree.
            Furthermore, the command sets the name of the created recipe
            file accordingly.
            If the name or version cannot be determined, the
            <filename>devtool add</filename> command prints an error and
            you must re-run the command with both the name and version
            or just the name or version specified.
        </para>

        <para>
            Sometimes the name or version determined from the source tree
            might be incorrect.
            For such a case, you must reset the recipe:
            <literallayout class='monospaced'>
     $ devtool reset -n <replaceable>recipename</replaceable>
            </literallayout>
            After running the <filename>devtool reset</filename> command,
            you need to run <filename>devtool add</filename> again and
            provide the name or the version.
        </para>
    </section>

    <section id='sdk-dependency-detection-and-mapping'>
        <title>Dependency Detection and Mapping</title>

        <para>
            The <filename>devtool add</filename> command attempts to
            detect build-time dependencies and map them to other recipes
            in the system.
            During this mapping, the command fills in the names of those
            recipes in the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
            value within the recipe.
            If a dependency cannot be mapped, then a comment is placed in
            the recipe indicating such.
            The inability to map a dependency might be caused because the
            naming is not recognized or because the dependency simply is
            not available.
            For cases where the dependency is not available, you must use
            the <filename>devtool add</filename> command to add an
            additional recipe to satisfy the dependency and then come
            back to the first recipe and add its name to
            <filename>DEPENDS</filename>.
        </para>

        <para>
            If you need to add runtime dependencies, you can do so by
            adding the following to your recipe:
            <literallayout class='monospaced'>
     RDEPENDS_${PN} += "dependency1 dependency2 ..."
            </literallayout>
            <note>
                The <filename>devtool add</filename> command often cannot
                distinguish between mandatory and optional dependencies.
                Consequently, some of the detected dependencies might
                in fact be optional.
                When in doubt, consult the documentation or the configure
                script for the software the recipe is building for further
                details.
                In some cases, you might find you can substitute the
                dependency for an option to disable the associated
                functionality passed to the configure script.
            </note>
        </para>
    </section>

    <section id='sdk-license-detection'>
        <title>License Detection</title>

        <para>
            The <filename>devtool add</filename> command attempts to
            determine if the software you are adding is able to be
            distributed under a common open-source license and sets the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
            value accordingly.
            You should double-check this value against the documentation
            or source files for the software you are building and update
            that <filename>LICENSE</filename> value if necessary.
        </para>

        <para>
            The <filename>devtool add</filename> command also sets the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink>
            value to point to all files that appear to be license-related.
            However, license statements often appear in comments at the top
            of source files or within documentation.
            Consequently, you might need to amend the
            <filename>LIC_FILES_CHKSUM</filename> variable to point to one
            or more of those comments if present.
            Setting <filename>LIC_FILES_CHKSUM</filename> is particularly
            important for third-party software.
            The mechanism attempts to ensure correct licensing should you
            upgrade the recipe to a newer upstream version in future.
            Any change in licensing is detected and you receive an error
            prompting you to check the license text again.
        </para>

        <para>
            If the <filename>devtool add</filename> command cannot
            determine licensing information, the
            <filename>LICENSE</filename> value is set to "CLOSED" and the
            <filename>LIC_FILES_CHKSUM</filename> vaule remains unset.
            This behavior allows you to continue with development but is
            unlikely to be correct in all cases.
            Consequently, you should check the documentation or source
            files for the software you are building to determine the actual
            license.
        </para>
    </section>

    <section id='sdk-adding-makefile-only-software'>
        <title>Adding Makefile-Only Software</title>

        <para>
            The use of <filename>make</filename> by itself is very common
            in both proprietary and open source software.
            Unfortunately, Makefiles are often not written with
            cross-compilation in mind.
            Thus, <filename>devtool add</filename> often cannot do very
            much to ensure that these Makefiles build correctly.
            It is very common, for example, to explicitly call
            <filename>gcc</filename> instead of using the
            <filename>CC</filename> variable.
            Usually, in a cross-compilation environment,
            <filename>gcc</filename> is the compiler for the build host
            and the cross-compiler is named something similar to
            <filename>arm-poky-linux-gnueabi-gcc</filename> and might
            require some arguments (e.g. to point to the associated sysroot
            for the target machine).
        </para>

        <para>
            When writing a recipe for Makefile-only software, keep the
            following in mind:
            <itemizedlist>
                <listitem><para>
                    You probably need to patch the Makefile to use
                    variables instead of hardcoding tools within the
                    toolchain such as <filename>gcc</filename> and
                    <filename>g++</filename>.
                    </para></listitem>
                <listitem><para>
                    The environment in which <filename>make</filename> runs
                    is set up with various standard variables for
                    compilation (e.g. <filename>CC</filename>,
                    <filename>CXX</filename>, and so forth) in a similar
                    manner to the environment set up by the SDK's
                    environment setup script.
                    One easy way to see these variables is to run the
                    <filename>devtool build</filename> command on the
                    recipe and then look in
                    <filename>oe-logs/run.do_compile</filename>.
                    Towards the top of this file you will see a list of
                    environment variables that are being set.
                    You can take advantage of these variables within the
                    Makefile.
                    </para></listitem>
                <listitem><para>
                    If the Makefile sets a default for a variable using "=",
                    that default overrides the value set in the environment,
                    which is usually not desirable.
                    In this situation, you can either patch the Makefile
                    so it sets the default using the "?=" operator, or
                    you can alternatively force the value on the
                    <filename>make</filename> command line.
                    To force the value on the command line, add the
                    variable setting to
                    <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'><filename>EXTRA_OEMAKE</filename></ulink>
                    within the recipe as follows:
                    <literallayout class='monospaced'>
     EXTRA_OEMAKE += "'CC=${CC}' 'CXX=${CXX}'"
                    </literallayout>
                    In the above example, single quotes are used around the
                    variable settings as the values are likely to contain
                    spaces because required default options are passed to
                    the compiler.
                    </para></listitem>
                <listitem><para>
                    Hardcoding paths inside Makefiles is often problematic
                    in a cross-compilation environment.
                    This is particularly true because those hardcoded paths
                    often point to locations on the build host and thus
                    will either be read-only or will introduce
                    contamination into the cross-compilation by virtue of
                    being specific to the build host rather than the target.
                    Patching the Makefile to use prefix variables or other
                    path variables is usually the way to handle this.
                    </para></listitem>
                <listitem><para>
                    Sometimes a Makefile runs target-specific commands such
                    as <filename>ldconfig</filename>.
                    For such cases, you might be able to simply apply
                    patches that remove these commands from the Makefile.
                    </para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id='sdk-adding-native-tools'>
        <title>Adding Native Tools</title>

        <para>
            Often, you need to build additional tools that run on the
            build host system as opposed to the target.
            You should indicate this using one of the following methods
            when you run <filename>devtool add</filename>:
            <itemizedlist>
                <listitem><para>
                    Specify the name of the recipe such that it ends
                    with "-native".
                    Specifying the name like this produces a recipe that
                    only builds for the build host.
                    </para></listitem>
                <listitem><para>
                    Specify the "&dash;&dash;also-native" option with the
                    <filename>devtool add</filename> command.
                    Specifying this option creates a recipe file that still
                    builds for the target but also creates a variant with
                    a "-native" suffix that builds for the build host.
                    </para></listitem>
            </itemizedlist>
            <note>
                If you need to add a tool that is shipped as part of a
                source tree that builds code for the target, you can
                typically accomplish this by building the native and target
                parts separately rather than within the same compilation
                process.
                Realize though that with the "&dash;&dash;also-native" option, you
                can add the tool using just one recipe file.
            </note>
        </para>
    </section>

    <section id='sdk-adding-node-js-modules'>
        <title>Adding Node.js Modules</title>

        <para>
            You can use the <filename>devtool add</filename> command in the
            following form to add Node.js modules:
            <literallayout class='monospaced'>
     $ devtool add "npm://registry.npmjs.org;name=forever;version=0.15.1"
            </literallayout>
            The name and version parameters are mandatory.
            Lockdown and shrinkwrap files are generated and pointed to by
            the recipe in order to freeze the version that is fetched for
            the dependencies according to the first time.
            This also saves checksums that are verified on future fetches.
            Together, these behaviors ensure the reproducibility and
            integrity of the build.
            <note><title>Notes</title>
                <itemizedlist>
                    <listitem><para>
                        You must use quotes around the URL.
                        The <filename>devtool add</filename> does not require
                        the quotes, but the shell considers ";" as a splitter
                        between multiple commands.
                        Thus, without the quotes,
                        <filename>devtool add</filename> does not receive the
                        other parts, which results in several "command not
                        found" errors.
                        </para></listitem>
                    <listitem><para>
                        In order to support adding
                        Node.js modules, a
                        <filename>nodejs</filename> recipe must be part of your
                        SDK in order to provide Node.js
                        itself.
                        </para></listitem>
                </itemizedlist>
            </note>
        </para>
    </section>
</section>

<section id='sdk-working-with-recipes'>
    <title>Working With Recipes</title>

    <para>
        When building a recipe with <filename>devtool build</filename> the
        typical build progression is as follows:
        <orderedlist>
            <listitem><para>
                Fetch the source
                </para></listitem>
            <listitem><para>
                Unpack the source
                </para></listitem>
            <listitem><para>
                Configure the source
                </para></listitem>
            <listitem><para>
                Compiling the source
                </para></listitem>
            <listitem><para>
                Install the build output
                </para></listitem>
            <listitem><para>
                Package the installed output
                </para></listitem>
        </orderedlist>
        For recipes in the workspace, fetching and unpacking is disabled
        as the source tree has already been prepared and is persistent.
        Each of these build steps is defined as a function, usually with a
        "do_" prefix.
        These functions are typically shell scripts but can instead be written
        in Python.
    </para>

    <para>
        If you look at the contents of a recipe, you will see that the
        recipe does not include complete instructions for building the
        software.
        Instead, common functionality is encapsulated in classes inherited
        with the <filename>inherit</filename> directive, leaving the recipe
        to describe just the things that are specific to the software to be
        built.
        A <ulink url='ref-classes-base'><filename>base</filename></ulink>
        class exists that is implicitly inherited by all recipes and provides
        the functionality that most typical recipes need.
    </para>

    <para>
        The remainder of this section presents information useful when
        working with recipes.
    </para>

    <section id='sdk-finding-logs-and-work-files'>
        <title>Finding Logs and Work Files</title>

        <para>
            When you are debugging a recipe that you previously created using
            <filename>devtool add</filename> or whose source you are modifying
            by using the <filename>devtool modify</filename> command, after
            the first run of <filename>devtool build</filename>, you will
            find some symbolic links created within the source tree:
            <filename>oe-logs</filename>, which points to the directory in
            which log files and run scripts for each build step are created
            and <filename>oe-workdir</filename>, which points to the temporary
            work area for the recipe.
            You can use these links to get more information on what is
            happening at each build step.
        </para>

        <para>
            These locations under <filename>oe-workdir</filename> are
            particularly useful:
            <itemizedlist>
                <listitem><para><filename>image/</filename>:
                    Contains all of the files installed at the
                    <ulink url='&YOCTO_DOCS_REF_URL;ref-tasks-install'><filename>do_install</filename></ulink>
                    stage.
                    Within a recipe, this directory is referred to by the
                    expression
                    <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>.
                    </para></listitem>
                <listitem><para><filename>sysroot-destdir/</filename>:
                    Contains a subset of files installed within
                    <filename>do_install</filename> that have been put into the
                    shared sysroot.
                    For more information, see the
                    "<link linkend='sdk-sharing-files-between-recipes'>Sharing Files Between Recipes</link>"
                    section.
                    </para></listitem>
                <listitem><para><filename>packages-split/</filename>:
                    Contains subdirectories for each package produced by the
                    recipe.
                    For more information, see the
                    "<link linkend='sdk-packaging'>Packaging</link>" section.
                    </para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id='sdk-setting-configure-arguments'>
        <title>Setting Configure Arguments</title>

        <para>
            If the software your recipe is building uses GNU autoconf,
            then a fixed set of arguments is passed to it to enable
            cross-compilation plus any extras specified by
            <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink>
            set within the recipe.
            If you wish to pass additional options, add them to
            <filename>EXTRA_OECONF</filename>.
            Other supported build tools have similar variables
            (e.g.
            <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECMAKE'><filename>EXTRA_OECMAKE</filename></ulink>
            for CMake,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OESCONS'><filename>EXTRA_OESCONS</filename></ulink>
            for Scons, and so forth).
            If you need to pass anything on the <filename>make</filename>
            command line, you can use <filename>EXTRA_OEMAKE</filename> to do
            so.
        </para>

        <para>
            You can use the <filename>devtool configure-help</filename> command
            to help you set the arguments listed in the previous paragraph.
            The command determines the exact options being passed, and shows
            them to you along with any custom arguments specified through
            <filename>EXTRA_OECONF</filename>.
            If applicable, the command also shows you the output of the
            configure script's "&dash;&dash;help" option as a reference.
        </para>
    </section>

    <section id='sdk-sharing-files-between-recipes'>
        <title>Sharing Files Between Recipes</title>

        <para>
            Recipes often need to use files provided by other recipes on
            the build host.
            For example, an application linking to a common library needs
            access to the library itself and its associated headers.
            The way this access is accomplished within the extensible SDK is
            through the sysroot.
            One sysroot exists per "machine" for which the SDK is being built.
            In practical terms, this means a sysroot exists for the target
            machine, and a sysroot exists for the build host.
        </para>

        <para>
            Recipes should never write files directly into the sysroot.
            Instead, files should be installed into standard locations
            during the
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
            task within the
            <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink><filename>}</filename>
            directory.
            A subset of these files automatically go into the sysroot.
            The reason for this limitation is that almost all files that go
            into the sysroot are cataloged in manifests in order to ensure
            they can be removed later when a recipe is modified or removed.
            Thus, the sysroot is able to remain free from stale files.
        </para>
    </section>

    <section id='sdk-packaging'>
        <title>Packaging</title>

        <para>
            Packaging is not always particularly relevant within the
            extensible SDK.
            However, if you examine how build output gets into the final image
            on the target device, it is important to understand packaging
            because the contents of the image are expressed in terms of
            packages and not recipes.
        </para>

        <para>
            During the
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>
            task, files installed during the
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>
            task are split into one main package, which is almost always named
            the same as the recipe, and several other packages.
            This separation is done because not all of those installed files
            are always useful in every image.
            For example, you probably do not need any of the documentation
            installed in a production image.
            Consequently, for each recipe the documentation files are separated
            into a <filename>-doc</filename> package.
            Recipes that package software that has optional modules or
            plugins might do additional package splitting as well.
        </para>

        <para>
            After building a recipe you can see where files have gone by
            looking in the <filename>oe-workdir/packages-split</filename>
            directory, which contains a subdirectory for each package.
            Apart from some advanced cases, 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 controls splitting.
            The <filename>PACKAGES</filename> variable lists all of the
            packages to be produced, while the <filename>FILES</filename>
            variable specifies which files to include in each package,
            using an override to specify the package.
            For example, <filename>FILES_${PN}</filename> specifies the files
            to go into the main package (i.e. the main package is named the
            same as the recipe and
            <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink><filename>}</filename>
            evaluates to the recipe name).
            The order of the <filename>PACKAGES</filename> value is significant.
            For each installed file, the first package whose
            <filename>FILES</filename> value matches the file is the package
            into which the file goes.
            Defaults exist for both the <filename>PACKAGES</filename> and
            <filename>FILES</filename> variables.
            Consequently, you might find you do not even need to set these
            variables in your recipe unless the software the recipe is
            building installs files into non-standard locations.
        </para>
    </section>
</section>

<section id='sdk-restoring-the-target-device-to-its-original-state'>
    <title>Restoring the Target Device to its Original State</title>

    <para>
        If you use the <filename>devtool deploy-target</filename>
        command to write a recipe's build output to the target, and
        you are working on an existing component of the system, then you
        might find yourself in a situation where you need to restore the
        original files that existed prior to running the
        <filename>devtool deploy-target</filename> command.
        Because the <filename>devtool deploy-target</filename> command
        backs up any files it overwrites, you can use the
        <filename>devtool undeploy-target</filename> to restore those files
        and remove any other files the recipe deployed.
        Consider the following example:
        <literallayout class='monospaced'>
     $ devtool undeploy-target lighttpd root@192.168.7.2
        </literallayout>
        If you have deployed multiple applications, you can remove them
        all at once thus restoring the target device back to its
        original state:
        <literallayout class='monospaced'>
     $ devtool undeploy-target -a root@192.168.7.2
        </literallayout>
        Information about files deployed to the target as well as any
        backed up files are stored on the target itself.
        This storage of course requires some additional space
        on the target machine.
        <note>
            The <filename>devtool deploy-target</filename> and
            <filename>devtool undeploy-target</filename> command do not
            currently interact with any package management system on the
            target device (e.g. RPM or OPKG).
            Consequently, you should not intermingle operations
            <filename>devtool deploy-target</filename> and the package
            manager operations on the target device.
            Doing so could result in a conflicting set of files.
        </note>
    </para>
</section>

<section id='sdk-installing-additional-items-into-the-extensible-sdk'>
    <title>Installing Additional Items Into the Extensible SDK</title>

    <para>
        The extensible SDK typically only comes with a small number of tools
        and libraries out of the box.
        If you have a minimal SDK, then it starts mostly empty and is
        populated on-demand.
        However, sometimes you will need to explicitly install extra items
        into the SDK.
        If you need these extra items, you can first search for the items
        using the <filename>devtool search</filename> command.
        For example, suppose you need to link to libGL but you are not sure
        which recipe provides it.
        You can use the following command to find out:
        <literallayout class='monospaced'>
     $ devtool search libGL
     mesa                  A free implementation of the OpenGL API
        </literallayout>
        Once you know the recipe (i.e. <filename>mesa</filename> in this
        example), you can install it:
        <literallayout class='monospaced'>
     $ devtool sdk-install mesa
        </literallayout>
        By default, the <filename>devtool sdk-install</filename> assumes the
        item is available in pre-built form from your SDK provider.
        If the item is not available and it is acceptable to build the item
        from source, you can add the "-s" option as follows:
        <literallayout class='monospaced'>
     $ devtool sdk-install -s mesa
        </literallayout>
        It is important to remember that building the item from source takes
        significantly longer than installing the pre-built artifact.
        Also, if no recipe exists for the item you want to add to the SDK, you
        must instead add it using the <filename>devtool add</filename> command.
    </para>
</section>

<section id='sdk-updating-the-extensible-sdk'>
     <title>Updating the Extensible SDK</title>

     <para>
         If you are working with an extensible SDK that gets occasionally
         updated (e.g. typically when that SDK has been provided to you by
         another party), then you will need to manually pull down those
         updates to your installed SDK.
     </para>

     <para>
         To update your installed SDK, run the following:
         <literallayout class='monospaced'>
     $ devtool sdk-update
         </literallayout>
         The previous command assumes your SDK provider has set the default
         update URL for you.
         If that URL has not been set, you need to specify it yourself as
         follows:
         <literallayout class='monospaced'>
     $ devtool sdk-update <replaceable>path_to_update_directory</replaceable>
         </literallayout>
         <note>
             The URL needs to point specifically to a published SDK and not an
             SDK installer that you would download and install.
         </note>
    </para>
</section>

<section id='sdk-creating-a-derivative-sdk-with-additional-components'>
    <title>Creating a Derivative SDK With Additional Components</title>

    <para>
        You might need to produce an SDK that contains your own custom
        libraries for sending to a third party (e.g., if you are a vendor with
        customers needing to build their own software for the target platform).
        If that is the case, then you can produce a derivative SDK based on
        the currently installed SDK fairly easily.
        Use these steps:
        <orderedlist>
            <listitem><para>If necessary, install an extensible SDK that
                you want to use as a base for your derivative SDK.
                </para></listitem>
            <listitem><para>Source the environment script for the SDK.
                </para></listitem>
            <listitem><para>Add the extra libraries or other components
                you want by using the <filename>devtool add</filename>
                command.
                </para></listitem>
            <listitem><para>Run the <filename>devtool build-sdk</filename>
                command.
                </para></listitem>
        </orderedlist>
        The above procedure takes the recipes added to the workspace and
        constructs a new SDK installer containing those recipes and the
        resulting binary artifacts.
        The recipes go into their own separate layer in the constructed
        derivative SDK, leaving the workspace clean and ready for users
        to add their own recipes.
    </para>
</section>

</chapter>
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