poky/documentation/sdk-manual/sdk-extensible.xml

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<chapter id='sdk-extensible'>

    <title>Using the Extensible SDK</title>

    <para>
        This chapter describes the extensible SDK and how to install it.
        Information covers the pieces of the SDK, how to install it, and
        presents a look at using the <filename>devtool</filename>
        functionality.
        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_REF_URL;#build-system-term'>OpenEmbedded build system</ulink>.
        <note>
            For a side-by-side comparison of main features supported for an
            extensible SDK as compared to a standard SDK, see the
            "<link linkend='sdk-manual-intro'>Introduction</link>"
            section.
        </note>
    </para>

    <para>
        In addition to the functionality available through
        <filename>devtool</filename>, you can alternatively make use of the
        toolchain directly, for example from Makefile and Autotools.
        See the
        "<link linkend='sdk-working-projects'>Using the SDK Toolchain Directly</link>"
        chapter for more information.
    </para>

    <section id='sdk-extensible-sdk-intro'>
        <title>Why use the Extensible SDK and What is in It?</title>

        <para>
            The extensible SDK provides a cross-development toolchain and
            libraries tailored to the contents of a specific image.
            You would use the Extensible SDK if you want a toolchain experience
            supplemented with the powerful set of <filename>devtool</filename>
            commands tailored for the Yocto Project environment.
        </para>

        <para>
            The installed extensible SDK consists of several files and
            directories.
            Basically, it contains an SDK environment setup script, some
            configuration files, an internal build system, and the
            <filename>devtool</filename> functionality.
        </para>
    </section>

    <section id='sdk-installing-the-extensible-sdk'>
        <title>Installing the Extensible SDK</title>

        <para>
            The first thing you need to do is install the SDK on your
            <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>Build Host</ulink>
            by running the <filename>*.sh</filename> installation script.
        </para>

        <para>
            You can download a tarball installer, which includes the
            pre-built toolchain, the <filename>runqemu</filename>
            script, the internal build system, <filename>devtool</filename>,
            and support files from the appropriate
            <ulink url='&YOCTO_TOOLCHAIN_DL_URL;'>toolchain</ulink>
            directory within the Index of Releases.
            Toolchains are available for several 32-bit and 64-bit
            architectures with the <filename>x86_64</filename> directories,
            respectively.
            The toolchains the Yocto Project provides are based off the
            <filename>core-image-sato</filename> and
            <filename>core-image-minimal</filename> images and contain
            libraries appropriate for developing against that image.
        </para>

        <para>
            The names of the tarball installer scripts are such that a
            string representing the host system appears first in the
            filename and then is immediately followed by a string
            representing the target architecture.
            An extensible SDK has the string "-ext" as part of the name.
            Following is the general form:
            <literallayout class='monospaced'>
     poky-glibc-<replaceable>host_system</replaceable>-<replaceable>image_type</replaceable>-<replaceable>arch</replaceable>-toolchain-ext-<replaceable>release_version</replaceable>.sh

     Where:
         <replaceable>host_system</replaceable> is a string representing your development system:

                    i686 or x86_64.

         <replaceable>image_type</replaceable> is the image for which the SDK was built:

                    core-image-sato or core-image-minimal

         <replaceable>arch</replaceable> is a string representing the tuned target architecture:

                    aarch64, armv5e, core2-64, i586, mips32r2, mips64, ppc7400, or cortexa8hf-neon

         <replaceable>release_version</replaceable> is a string representing the release number of the Yocto Project:

                    &DISTRO;, &DISTRO;+snapshot
            </literallayout>
            For example, the following SDK installer is for a 64-bit
            development host system and a i586-tuned target architecture
            based off the SDK for <filename>core-image-sato</filename> and
            using the current &DISTRO; snapshot:
            <literallayout class='monospaced'>
     poky-glibc-x86_64-core-image-sato-i586-toolchain-ext-&DISTRO;.sh
            </literallayout>
            <note>
                As an alternative to downloading an SDK, you can build the
                SDK installer.
                For information on building the installer, see the
                "<link linkend='sdk-building-an-sdk-installer'>Building an SDK Installer</link>"
                section.
            </note>
        </para>

        <para>
            The SDK and toolchains are self-contained and by default are
            installed into the <filename>poky_sdk</filename> folder in your
            home directory.
            You can choose to install the extensible SDK in any location when
            you run the installer.
            However, because files need to be written under that directory
            during the normal course of operation, the location you choose
            for installation must be writable for whichever
            users need to use the SDK.
        </para>

        <para>
            The following command shows how to run the installer given a
            toolchain tarball for a 64-bit x86 development host system and
            a 64-bit x86 target architecture.
            The example assumes the SDK installer is located in
            <filename>~/Downloads/</filename> and has execution rights.
            <note>
                If you do not have write permissions for the directory
                into which you are installing the SDK, the installer
                notifies you and exits.
                For that case, set up the proper permissions in the directory
                and run the installer again.
            </note>
            <literallayout class='monospaced'>
     $ ./Downloads/poky-glibc-x86_64-core-image-minimal-core2-64-toolchain-ext-2.5.sh
     Poky (Yocto Project Reference Distro) Extensible SDK installer version 2.5
     ==========================================================================
     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...
     Parsing recipes: 100% |##################################################################| Time: 0:00:52
     Initialising tasks: 100% |###############################################################| Time: 0:00:00
     Checking sstate mirror object availability: 100% |#######################################| Time: 0:00:00
     Loading cache: 100% |####################################################################| Time: 0:00:00
     Initialising tasks: 100% |###############################################################| Time: 0:00:00
     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>
    </section>

    <section id='sdk-running-the-extensible-sdk-environment-setup-script'>
        <title>Running the Extensible SDK Environment Setup Script</title>

        <para>
            Once you have the SDK installed, you must run the SDK environment
            setup script before you can actually use the SDK.
            This setup script resides in the directory you chose when you
            installed the SDK, which is either the default
            <filename>poky_sdk</filename> directory or the directory you
            chose during installation.
        </para>

        <para>
            Before running the script, be sure it is the one that matches the
            architecture for which you are developing.
            Environment setup scripts begin with the string
            "<filename>environment-setup</filename>" and include as part of
            their name the tuned target architecture.
            As an example, the following commands set the working directory
            to where the SDK was installed and then source the environment
            setup script.
            In this example, the setup script is for an IA-based
            target machine using i586 tuning:
            <literallayout class='monospaced'>
     $ cd /home/scottrif/poky_sdk
     $ 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>
            Running the setup script defines many environment variables needed
            in order to use the SDK (e.g. <filename>PATH</filename>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-CC'><filename>CC</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#var-LD'><filename>LD</filename></ulink>,
            and so forth).
            If you want to see all the environment variables the script
            exports, examine the installation file itself.
        </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.
            <note><title>Tip</title>
                The use of <filename>devtool</filename> is not limited to
                the extensible SDK.
                You can use <filename>devtool</filename> to help you easily
                develop any project whose build output must be part of an
                image built using the build system.
            </note>
        </para>

        <para>
            The <filename>devtool</filename> command line is organized
            similarly to
            <ulink url='&YOCTO_DOCS_OM_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.
            <note>
                See the
                "<ulink url='&YOCTO_DOCS_REF_URL;#ref-devtool-reference'><filename>devtool</filename>&nbsp;Quick Reference</ulink>"
                in the Yocto Project Reference Manual for a
                <filename>devtool</filename> quick reference.
            </note>
        </para>

        <para>
            Three <filename>devtool</filename> subcommands exist that provide
            entry-points into development:
            <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>
                <listitem><para>
                    <emphasis><filename>devtool upgrade</filename></emphasis>:
                    Updates an existing recipe so that you can build it for
                    an updated set of source files.
                    </para></listitem>
            </itemizedlist>
            As with the 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, 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>,
            <filename>devtool modify</filename>, and
            <filename>devtool upgrade</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_REF_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 for other developers to be responsible for
                        various areas of source code.
                        As a developer, you are probably interested in using
                        that source code as part of your development within
                        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 in the figure represents a
                                common situation where the source code does not
                                exist locally and needs to be extracted.
                                In this situation, the source code is extracted
                                to the default workspace - you do not
                                want the files 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>
                                extracts the upstream source files into a local
                                Git repository within the
                                <filename>sources</filename> folder.
                                The command then creates a recipe named
                                <replaceable>recipe</replaceable> and a
                                corresponding append file in the workspace.
                                If you do not provide
                                <replaceable>recipe</replaceable>, the command
                                makes an attempt to determine the recipe name.
                                </para></listitem>
                            <listitem><para>
                                <emphasis>Middle</emphasis>:
                                The middle scenario in the figure 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.
                                <note>
                                    If required, <filename>devtool</filename>
                                    always creates
                                    a Git repository locally during the
                                    extraction.
                                </note>
                                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.
                                You need to specify an empty directory:
                                <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 a
                                recipe named <replaceable>recipe</replaceable>
                                along with an associated append file.
                                </para></listitem>
                            <listitem><para>
                                <emphasis>Right</emphasis>:
                                The right scenario in the figure represents a
                                situation where the
                                <replaceable>srctree</replaceable> has been
                                previously prepared outside of the
                                <filename>devtool</filename> workspace.</para>

                                <para>The following command provides a new
                                recipe name and identifies the existing source
                                tree location:
                                <literallayout class='monospaced'>
     $ devtool add <replaceable>recipe srctree</replaceable>
                                </literallayout>
                                The command examines the source code and
                                creates a recipe named
                                <replaceable>recipe</replaceable> for the code
                                and places the recipe into the workspace.
                                </para>

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

                                <para>Aside from a recipe folder, the command
                                also creates an associated append folder and
                                places an initial
                                <filename>*.bbappend</filename> file within.
                                </para></listitem>
                        </itemizedlist>
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Edit the Recipe</emphasis>:
                        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>:
                        The next step you take depends on what you are going
                        to do with the new code.</para>

                        <para>If you need to eventually move the build output
                        to the target hardware, use the following
                        <filename>devtool</filename> command:
                        <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 from the workspace
                        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 the target hardware.
                        <note>
                            This step assumes you have a previously built
                            image that is already either running in QEMU or
                            is 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,
                            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 to actual hardware by using the
                        <filename>devtool build-image</filename> command.
                        However, <filename>devtool</filename> does not provide
                        a specific command that allows you to deploy the
                        image to actual hardware.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Finish Your Work With the Recipe</emphasis>:
                        The <filename>devtool finish</filename> command creates
                        any patches corresponding to commits in the local
                        Git repository, moves the new recipe to a more permanent
                        layer, and then resets the recipe so that the recipe is
                        built normally rather than from the workspace.
                        <literallayout class='monospaced'>
     $ devtool finish <replaceable>recipe layer</replaceable>
                        </literallayout>
                        <note>
                            Any changes you want to turn into patches must be
                            committed to the Git repository in the source tree.
                        </note></para>

                        <para>As mentioned, the
                        <filename>devtool finish</filename> command moves the
                        final recipe to its permanent layer.
                        </para>

                        <para>As a final process of the
                        <filename>devtool finish</filename> command, the state
                        of the standard layers and the upstream source is
                        restored so that you can build the recipe from those
                        areas rather than the workspace.
                        <note>
                            You can use the <filename>devtool reset</filename>
                            command to put things back should you decide you
                            do not want to proceed with your work.
                            If you do use this command, realize that the source
                            tree is preserved.
                        </note>
                        </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 local recipe in
                place that is used to build the software.
                The command is flexible enough to allow you to extract code
                from an upstream source, 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 for 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 locally in a layer external
                                to the <filename>devtool</filename> workspace.
                                </para></listitem>
                            <listitem><para>
                                The source files exist either 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 a 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 in the figure represents a
                                common situation where the source code does
                                not exist locally and it needs to be extracted
                                from an upstream source.
                                In this situation, the source is extracted
                                into the default <filename>devtool</filename>
                                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, <filename>devtool</filename> uses the
                                recipe's
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                                statements to locate the source code and any
                                local patch files from other developers.</para>

                                <para>With this scenario, no
                                <replaceable>srctree</replaceable> argument
                                exists.
                                Consequently, the default behavior of the
                                <filename>devtool modify</filename> command is
                                to extract the source files pointed to by the
                                <filename>SRC_URI</filename> statements into a
                                local Git structure.
                                Furthermore, the location for the extracted
                                source is the default area within the
                                <filename>devtool</filename> workspace.
                                The result is that the command sets up both
                                the source code and an append file within the
                                workspace while the recipe remains in its
                                original location.</para>

                                <para>Additionally, if you have any non-patch
                                local files (i.e. files referred to with
                                <filename>file://</filename> entries in
                                <filename>SRC_URI</filename> statement excluding
                                <filename>*.patch/</filename> or
                                <filename>*.diff</filename>), these files are
                                copied to an
                                <filename>oe-local-files</filename> folder
                                under the newly created source tree.
                                Copying the files here gives you a convenient
                                area from which you can modify the files.
                                Any changes or additions you make to those
                                files are incorporated into the build the next
                                time you build the software just as are other
                                changes you might have made to the source.
                                </para></listitem>
                            <listitem><para>
                                <emphasis>Middle</emphasis>:
                                The middle scenario in the figure 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 local
                                and in its own layer outside the workspace.
                                </para>

                                <para>The following command tells
                                <filename>devtool</filename> the recipe with
                                which to work and, in this case, identifies a
                                local area for the extracted source files that
                                exists outside of the default
                                <filename>devtool</filename> workspace:
                                <literallayout class='monospaced'>
     $ devtool modify <replaceable>recipe srctree</replaceable>
                                </literallayout>
                                <note>
                                    You cannot provide a URL for
                                    <replaceable>srctree</replaceable> using
                                    the <filename>devtool</filename> command.
                                </note>
                                As with all extractions, the command uses
                                the recipe's <filename>SRC_URI</filename>
                                statements to locate the source files and any
                                associated patch files.
                                Non-patch files are copied to an
                                <filename>oe-local-files</filename> folder
                                under the newly created source tree.</para>

                                <para>Once the files are located, the command
                                by default extracts them into
                                <replaceable>srctree</replaceable>.</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 provide with
                                <replaceable>srctree</replaceable>.
                                </para></listitem>
                            <listitem><para>
                                <emphasis>Right</emphasis>:
                                The right scenario in the figure represents a
                                situation where the source tree
                                (<replaceable>srctree</replaceable>) already
                                exists locally as a previously extracted Git
                                structure outside of the
                                <filename>devtool</filename> workspace.
                                In this example, the recipe also exists
                                elsewhere locally 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>If an <filename>oe-local-files</filename>
                                subdirectory happens to exist and it contains
                                non-patch files, the files are used.
                                However, if the subdirectory does not exist and
                                you run the <filename>devtool finish</filename>
                                command, any non-patch files that might exist
                                next to the recipe are removed because it
                                appears to <filename>devtool</filename> that
                                you have deleted those files.</para>

                                <para>Once the
                                <filename>devtool modify</filename> command
                                finishes, it creates only an append file for
                                the recipe in the <filename>devtool</filename>
                                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 or Rebuild the Image</emphasis>:
                        The next step you take depends on what you are going
                        to do with the new code.</para>

                        <para>If you need to eventually move the build output
                        to the target hardware, use the following
                        <filename>devtool</filename> command:
                        <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 from the workspace
                        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, use other methods to deploy
                        the image you built using the
                        <filename>devtool build-image</filename> command to
                        actual hardware.
                        <filename>devtool</filename> does not provide
                        a specific command to deploy the image to actual
                        hardware.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Finish Your Work With the Recipe</emphasis>:
                        The <filename>devtool finish</filename> command creates
                        any patches corresponding to commits in the local
                        Git repository, updates the recipe to point to them
                        (or creates a <filename>.bbappend</filename> file to do
                        so, depending on the specified destination layer), and
                        then resets the recipe so that the recipe is built
                        normally rather than from the workspace.
                        <literallayout class='monospaced'>
     $ devtool finish <replaceable>recipe layer</replaceable>
                        </literallayout>
                        <note>
                            Any changes you want to turn into patches must be
                            staged and committed within the local Git
                            repository before you use the
                            <filename>devtool finish</filename> command.
                        </note></para>

                        <para>Because there is no need to move the recipe,
                        <filename>devtool finish</filename> either updates the
                        original recipe in the original layer or the command
                        creates a <filename>.bbappend</filename> file in a
                        different layer as provided by
                        <replaceable>layer</replaceable>.
                        Any work you did in the
                        <filename>oe-local-files</filename> directory is
                        preserved in the original files next to the recipe
                        during the <filename>devtool finish</filename>
                        command.</para>

                        <para>As a final process of the
                        <filename>devtool finish</filename> command, the state
                        of the standard layers and the upstream source is
                        restored so that you can build the recipe from those
                        areas rather than from the workspace.
                        <note>
                            You can use the <filename>devtool reset</filename>
                            command to put things back should you decide you
                            do not want to proceed with your work.
                            If you do use this command, realize that the source
                            tree is preserved.
                        </note>
                        </para></listitem>
                </orderedlist>
            </para>
        </section>

        <section id='sdk-devtool-use-devtool-upgrade-to-create-a-version-of-the-recipe-that-supports-a-newer-version-of-the-software'>
            <title>Use <filename>devtool upgrade</filename> to Create a Version of the Recipe that Supports a Newer Version of the Software</title>

            <para>
                The <filename>devtool upgrade</filename> command upgrades
                an existing recipe to that of a more up-to-date version
                found upstream.
                Throughout the life of software, recipes continually undergo
                version upgrades by their upstream publishers.
                You can use the <filename>devtool upgrade</filename>
                workflow to make sure your recipes you are using for builds
                are up-to-date with their upstream counterparts.
                <note>
                    Several methods exist by which you can upgrade recipes -
                    <filename>devtool upgrade</filename> happens to be one.
                    You can read about all the methods by which you can
                    upgrade recipes in the
                    "<ulink url='&YOCTO_DOCS_DEV_URL;#gs-upgrading-recipes'>Upgrading Recipes</ulink>"
                    section of the Yocto Project Development Tasks Manual.
                </note>
            </para>

            <para>
                The <filename>devtool upgrade</filename> command is flexible
                enough to allow you to specify source code revision and
                versioning schemes, extract code into or out of the
                <filename>devtool</filename>
                <ulink url='&YOCTO_DOCS_REF_URL;#devtool-the-workspace-layer-structure'>workspace</ulink>,
                and work with any source file forms that the
                <ulink url='&YOCTO_DOCS_BB_URL;#bb-fetchers'>fetchers</ulink>
                support.
            </para>

            <para>
                The following diagram shows the common development flow
                used with the <filename>devtool upgrade</filename> command:
            </para>

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

            <para>
                <orderedlist>
                    <listitem><para>
                        <emphasis>Initiate the Upgrade</emphasis>:
                        The top part of the flow shows the typical scenario by
                        which you use the <filename>devtool upgrade</filename>
                        command.
                        The following conditions exist:
                        <itemizedlist>
                            <listitem><para>
                                The recipe exists in a local layer external
                                to the <filename>devtool</filename> workspace.
                                </para></listitem>
                            <listitem><para>
                                The source files for the new release
                                exist in the same location pointed to by
                                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                                in the recipe (e.g. a tarball with the new
                                version number in the name, or as a different
                                revision in the upstream Git repository).
                                </para></listitem>
                        </itemizedlist>
                        A common situation is where third-party software has
                        undergone a revision so that it has been upgraded.
                        The recipe you have access to is likely in your own
                        layer.
                        Thus, you need to upgrade the recipe to use the
                        newer version of the software:
                        <literallayout class='monospaced'>
     $ devtool upgrade -V <replaceable>version recipe</replaceable>
                        </literallayout>
                        By default, the <filename>devtool upgrade</filename>
                        command extracts source code into the
                        <filename>sources</filename> directory in the
                        <ulink url='&YOCTO_DOCS_REF_URL;#devtool-the-workspace-layer-structure'>workspace</ulink>.
                        If you want the code extracted to any other location,
                        you need to provide the
                        <replaceable>srctree</replaceable> positional argument
                        with the command as follows:
                        <literallayout class='monospaced'>
     $ devtool upgrade -V <replaceable>version recipe srctree</replaceable>
                        </literallayout>
                        <note>
                            In this example, the "-V" option specifies the new
                            version.
                            If you don't use "-V", the command upgrades the
                            recipe to the latest version.
                        </note>
                        If the source files pointed to by the
                        <filename>SRC_URI</filename> statement in the recipe
                        are in a Git repository, you must provide the "-S"
                        option and specify a revision for the software.</para>

                        <para>Once <filename>devtool</filename> locates the
                        recipe, it uses the <filename>SRC_URI</filename>
                        variable to locate the source code and any local patch
                        files from other developers.
                        The result is that the command sets up the source
                        code, the new version of the recipe, and an append file
                        all within the workspace.</para>

                        <para>Additionally, if you have any non-patch
                        local files (i.e. files referred to with
                        <filename>file://</filename> entries in
                        <filename>SRC_URI</filename> statement excluding
                        <filename>*.patch/</filename> or
                        <filename>*.diff</filename>), these files are
                        copied to an
                        <filename>oe-local-files</filename> folder
                        under the newly created source tree.
                        Copying the files here gives you a convenient
                        area from which you can modify the files.
                        Any changes or additions you make to those
                        files are incorporated into the build the next
                        time you build the software just as are other
                        changes you might have made to the source.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Resolve any Conflicts created by the Upgrade</emphasis>:
                        Conflicts could exist due to the software being
                        upgraded to a new version.
                        Conflicts occur if your recipe specifies some patch
                        files in <filename>SRC_URI</filename> that conflict
                        with changes made in the new version of the software.
                        For such cases, you need to resolve the conflicts
                        by editing the source and following the normal
                        <filename>git rebase</filename> conflict resolution
                        process.</para>

                        <para>Before moving onto the next step, be sure to
                        resolve any such conflicts created through use of a
                        newer or different version of the software.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>Build the Recipe or Rebuild the Image</emphasis>:
                        The next step you take depends on what you are going
                        to do with the new code.</para>

                        <para>If you need to eventually move the build output
                        to the target hardware, use the following
                        <filename>devtool</filename> command:
                        <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 from the workspace
                        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 or <filename>bitbake</filename> to build
                        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>Finish Your Work With the Recipe</emphasis>:
                        The <filename>devtool finish</filename> command creates
                        any patches corresponding to commits in the local
                        Git repository, moves the new recipe to a more
                        permanent layer, and then resets the recipe so that
                        the recipe is built normally rather than from the
                        workspace.</para>

                        <para>Any work you did in the
                        <filename>oe-local-files</filename> directory is
                        preserved in the original files next to the recipe
                        during the <filename>devtool finish</filename>
                        command.</para>

                        <para>
                        If you specify a destination layer that is the same as
                        the original source, then the old version of the
                        recipe and associated files are removed prior to
                        adding the new version.
                        <literallayout class='monospaced'>
     $ devtool finish <replaceable>recipe layer</replaceable>
                        </literallayout>
                        <note>
                            Any changes you want to turn into patches must be
                            committed to the Git repository in the source tree.
                        </note></para>

                        <para>As a final process of the
                        <filename>devtool finish</filename> command, the state
                        of the standard layers and the upstream source is
                        restored so that you can build the recipe from those
                        areas rather than the workspace.
                        <note>
                            You can use the <filename>devtool reset</filename>
                            command to put things back should you decide you
                            do not want to proceed with your work.
                            If you do use this command, realize that the source
                            tree is preserved.
                        </note>
                        </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 you provide with the command.
            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
                    </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 the recipe successfully builds.
                Once the recipe builds, 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> uses various metadata
                within the source tree in an attempt to determine
                the name and version of the software being built.
                Based on what the tool determines, <filename>devtool</filename>
                sets the name of the created recipe file accordingly.
            </para>

            <para>
                If <filename>devtool</filename> cannot determine the name and
                version, the command prints an error.
                For such cases, you must re-run the command and provide
                the name and version, just the name, or just the version as
                part of the command line.
            </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 as part of the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink>
                variable within the recipe.
                If a dependency cannot be mapped, <filename>devtool</filename>
                places a comment in the recipe indicating such.
                The inability to map a dependency can result from naming not
                being 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 that satisfies the dependency.
                Once you add that recipe, you need to update the
                <filename>DEPENDS</filename> variable in the original recipe
                to include the new recipe.
            </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} += "<replaceable>dependency1 dependency2 ...</replaceable>"
                </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 with an option that disables 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.
                If so, the command sets the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE'><filename>LICENSE</filename></ulink>
                value accordingly.
                You should double-check the value added by the command against
                the documentation or source files for the software you are
                building and, if necessary, update that
                <filename>LICENSE</filename> value.
            </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.
                Realize that license statements often appear in comments at
                the top of source files or within the documentation.
                In such cases, the command does not recognize those license
                statements.
                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, <filename>devtool</filename>
                sets the <filename>LICENSE</filename> value to "CLOSED" and
                leaves the <filename>LIC_FILES_CHKSUM</filename> value unset.
                This behavior allows you to continue with development even
                though the settings are unlikely to be correct in all cases.
                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 Make 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
                <ulink url='&YOCTO_DOCS_REF_URL;#var-CC'><filename>CC</filename></ulink>
                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 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 Make 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, a list of environment
                        variables exists 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.
                        For this case, 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>
                        or
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink>
                        within the recipe.
                        Here is an example using <filename>EXTRA_OEMAKE</filename>:
                        <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 because they
                        are 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
                        situation.
                        </para></listitem>
                    <listitem><para>
                        Sometimes a Makefile runs target-specific commands such
                        as <filename>ldconfig</filename>.
                        For such cases, you might be able to 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
                <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>build host</ulink>
                as opposed to the target.
                You should indicate this requirement by 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 two
                different ways to add Node.js modules: 1) Through
                <filename>npm</filename> and, 2) from a repository or local
                source.
            </para>

            <para>
                Use the following form to add Node.js modules through
                <filename>npm</filename>:
                <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.
                            </para></listitem>
                    </itemizedlist>
                </note>
            </para>

            <para>
                As mentioned earlier, you can also add Node.js modules
                directly from a repository or local source tree.
                To add modules this way, use <filename>devtool add</filename>
                in the following form:
                <literallayout class='monospaced'>
     $ devtool add https://github.com/diversario/node-ssdp
                </literallayout>
                In this example, <filename>devtool</filename> fetches the
                specified Git repository, detects the code as Node.js
                code, fetches dependencies using <filename>npm</filename>, and
                sets
                <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink>
                accordingly.
            </para>
        </section>
    </section>

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

        <para>
            When building a recipe using the
            <filename>devtool build</filename> command, the typical build
            progresses 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>
                    Compile 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 (task), usually
            with a "do_" prefix (e.g.
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink>,
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink>,
            and so forth).
            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.
            This technique leaves the recipe to describe just the things that
            are specific to the software being built.
            A
            <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-base'><filename>base</filename></ulink>
            class exists that is implicitly inherited by all recipes and
            provides the functionality that most recipes typically 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>
                After the first run of the <filename>devtool build</filename>
                command, recipes that were previously created using the
                <filename>devtool add</filename> command or whose sources were
                modified using the <filename>devtool modify</filename>
                command contain symbolic links created within the source tree:
                <itemizedlist>
                    <listitem><para>
                        <filename>oe-logs</filename>:
                        This link points to the directory in which log files
                        and run scripts for each build step are created.
                        </para></listitem>
                    <listitem><para>
                        <filename>oe-workdir</filename>:
                        This link points to the temporary work area for the
                        recipe.
                        The following locations under
                        <filename>oe-workdir</filename> are particularly
                        useful:
                            <itemizedlist>
                                <listitem><para>
                                    <filename>image/</filename>:
                                    Contains all of the files installed during
                                    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></listitem>
                </itemizedlist>
                You can use these links to get more information on what is
                happening at each build step.
            </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>
                or
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink>
                set within the recipe.
                If you wish to pass additional options, add them to
                <filename>EXTRA_OECONF</filename> or
                <filename>PACKAGECONFIG_CONFARGS</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> or the
                <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink>
                variables 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> or
                <filename>PACKAGECONFIG_CONFARGS</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
                <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>build host</ulink>.
                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 goes 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 into several other packages.
                This separation exists because not all of those installed files
                are 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 containing optional modules or
                plugins might undergo 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 by
                using an override to specify the package.
                For example, <filename>FILES_${PN}</filename> specifies the
                files to go into the main package (i.e. the main package has
                the same name as the recipe and
                <filename>${</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> command 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 using the "-a" option thus restoring the target device 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> commands do not
                currently interact with any package management system on the
                target device (e.g. RPM or OPKG).
                Consequently, you should not intermingle
                <filename>devtool deploy-target</filename> and 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>
            Out of the box the extensible SDK typically only comes with a small
            number of tools and libraries.
            A minimal SDK starts mostly empty and is populated on-demand.
            Sometimes you must 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 libGL.
            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> command
            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 the item using the
            <filename>devtool add</filename> command.
        </para>
    </section>

    <section id='sdk-applying-updates-to-an-installed-extensible-sdk'>
        <title>Applying Updates to an Installed Extensible SDK</title>

        <para>
            If you are working with an installed extensible SDK that gets
            occasionally updated (e.g. a third-party SDK), then you will need
            to manually "pull down" the updates into the installed SDK.
        </para>

        <para>
            To update your installed SDK, use <filename>devtool</filename> as
            follows:
            <literallayout class='monospaced'>
     $ devtool sdk-update
            </literallayout>
            The previous command assumes your SDK provider has set the default
            update URL for you through the
            <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_UPDATE_URL'><filename>SDK_UPDATE_URL</filename></ulink>
            variable as described in the
            "<link linkend='sdk-providing-updates-to-the-extensible-sdk-after-installation'>Providing Updates to the Extensible SDK After Installation</link>"
            section.
            If the SDK provider has not set that default URL, you need to
            specify it yourself in the command 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 to 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.
            A good example would be if you were a vendor with customers that
            use your SDK to build their own platform-specific software and
            those customers need an SDK that has custom libraries.
            In such a case, you can produce a derivative SDK based on the
            currently installed SDK fairly easily by following 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 previous steps take the recipes added to the workspace and
            construct a new SDK installer that contains those recipes and the
            resulting binary artifacts.
            The recipes go into their own separate layer in the constructed
            derivative SDK, which leaves the workspace clean and ready for
            users to add their own recipes.
        </para>
    </section>
</chapter>
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