path: root/documentation/sdk-manual/sdk-extensible.xml

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

<chapter id='sdk-extensible'>

    <title>Using the Extensible SDK</title>

    <para>
        This chapter describes the extensible SDK and how to 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, Autotools, and
        <trademark class='trade'>Eclipse</trademark>-based projects.
        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-setting-up-to-use-the-extensible-sdk'>
        <title>Setting Up to Use the Extensible SDK</title>

        <para>
            The first thing you need to do is install the SDK on your host
            development machine 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 directory under
            <ulink url='&YOCTO_TOOLCHAIN_DL_URL;'></ulink>.
            Toolchains are available for 32-bit and 64-bit x86 development
            systems from the <filename>i686</filename> and
            <filename>x86_64</filename> directories, respectively.
            The toolchains the Yocto Project provides are based off the
            <filename>core-image-sato</filename> image and contain
            libraries appropriate for developing against that image.
            Each type of development system supports five or more target
            architectures.
        </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.
            <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.

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

                    i586, x86_64, powerpc, mips, armv7a or armv5te

         <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.
                Another helpful resource for building an installer is the
                <ulink url='https://wiki.yoctoproject.org/wiki/TipsAndTricks/RunningEclipseAgainstBuiltImage'>Cookbook guide to Making an Eclipse Debug Capable Image</ulink>
                wiki page.
                This wiki page focuses on development when using the Eclipse
                IDE.
            </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, the location you choose needs to be writable for whichever
            users need to use the SDK, since files will need to be written
            under that directory during the normal course of operation.
        </para>

        <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>.
            <note>
                If you do not have write permissions for the directory
                into which you are installing the SDK, the installer
                notifies you and exits.
                Be sure you have write permissions in the directory and
                run the installer again.
            </note>
            <literallayout class='monospaced'>
     $ ./poky-glibc-x86_64-core-image-minimal-core2-64-toolchain-ext-&DISTRO;.sh
     Poky (Yocto Project Reference Distro) Extensible SDK installer version &DISTRO;
     ===================================================================================
     Enter target directory for SDK (default: ~/poky_sdk):
     You are about to install the SDK to "/home/scottrif/poky_sdk". Proceed[Y/n]? Y
     Extracting SDK......................................................................done
     Setting it up...
     Extracting buildtools...
     Preparing build system...
     done
     SDK has been successfully set up and is ready to be used.
     Each time you wish to use the SDK in a new shell session, you need to source the environment setup script e.g.
      $ . /home/scottrif/poky_sdk/environment-setup-core2-64-poky-linux
            </literallayout>
        </para>
    </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 it.
            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>
            When you run the setup script, many environment variables are
            defined:
            <literallayout class='monospaced'>
     <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKTARGETSYSROOT'><filename>SDKTARGETSYSROOT</filename></ulink> - The path to the sysroot used for cross-compilation
     <ulink url='&YOCTO_DOCS_REF_URL;#var-PKG_CONFIG_PATH'><filename>PKG_CONFIG_PATH</filename></ulink> - The path to the target pkg-config files
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CONFIG_SITE'><filename>CONFIG_SITE</filename></ulink> - A GNU autoconf site file preconfigured for the target
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CC'><filename>CC</filename></ulink> - The minimal command and arguments to run the C compiler
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CXX'><filename>CXX</filename></ulink> - The minimal command and arguments to run the C++ compiler
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CPP'><filename>CPP</filename></ulink> - The minimal command and arguments to run the C preprocessor
     <ulink url='&YOCTO_DOCS_REF_URL;#var-AS'><filename>AS</filename></ulink> - The minimal command and arguments to run the assembler
     <ulink url='&YOCTO_DOCS_REF_URL;#var-LD'><filename>LD</filename></ulink> - The minimal command and arguments to run the linker
     <ulink url='&YOCTO_DOCS_REF_URL;#var-GDB'><filename>GDB</filename></ulink> - The minimal command and arguments to run the GNU Debugger
     <ulink url='&YOCTO_DOCS_REF_URL;#var-STRIP'><filename>STRIP</filename></ulink> - The minimal command and arguments to run 'strip', which strips symbols
     <ulink url='&YOCTO_DOCS_REF_URL;#var-RANLIB'><filename>RANLIB</filename></ulink> - The minimal command and arguments to run 'ranlib'
     <ulink url='&YOCTO_DOCS_REF_URL;#var-OBJCOPY'><filename>OBJCOPY</filename></ulink> - The minimal command and arguments to run 'objcopy'
     <ulink url='&YOCTO_DOCS_REF_URL;#var-OBJDUMP'><filename>OBJDUMP</filename></ulink> - The minimal command and arguments to run 'objdump'
     <ulink url='&YOCTO_DOCS_REF_URL;#var-AR'><filename>AR</filename></ulink> - The minimal command and arguments to run 'ar'
     <ulink url='&YOCTO_DOCS_REF_URL;#var-NM'><filename>NM</filename></ulink> - The minimal command and arguments to run 'nm'
     <ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_PREFIX'><filename>TARGET_PREFIX</filename></ulink> - The toolchain binary prefix for the target tools
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CROSS_COMPILE'><filename>CROSS_COMPILE</filename></ulink> - The toolchain binary prefix for the target tools
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CONFIGURE_FLAGS'><filename>CONFIGURE_FLAGS</filename></ulink> - The minimal arguments for GNU configure
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'><filename>CFLAGS</filename></ulink> - Suggested C flags
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CXXFLAGS'><filename>CXXFLAGS</filename></ulink> - Suggested C++ flags
     <ulink url='&YOCTO_DOCS_REF_URL;#var-LDFLAGS'><filename>LDFLAGS</filename></ulink> - Suggested linker flags when you use CC to link
     <ulink url='&YOCTO_DOCS_REF_URL;#var-CPPFLAGS'><filename>CPPFLAGS</filename></ulink> - Suggested preprocessor flags
            </literallayout>
        </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 OpenEmbedded 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 that provide
            entry-points into development are:
            <itemizedlist>
                <listitem><para>
                    <emphasis><filename>devtool add</filename></emphasis>:
                    Assists in adding new software to be built.
                    </para></listitem>
                <listitem><para>
                    <emphasis><filename>devtool modify</filename></emphasis>:
                    Sets up an environment to enable you to modify the source of
                    an existing component.
                    </para></listitem>
                <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 OpenEmbedded build system, "recipes" represent software
            packages within <filename>devtool</filename>.
            When you use <filename>devtool add</filename>, a recipe is
            automatically created.
            When you use <filename>devtool modify</filename>, the specified
            existing recipe is used in order to determine where to get the source
            code and how to patch it.
            In both cases, an environment is set up so that when you build the
            recipe a source tree that is under your control is used in order to
            allow you to make changes to the source as desired.
            By default, both new recipes and the source go into a "workspace"
            directory under the SDK.
        </para>

        <para>
            The remainder of this section presents the
            <filename>devtool add</filename>,
            <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 where other developers are responsible for
                        various areas of source code.
                        As a developer, you are probably interested in using
                        that source code as part of your development using
                        the Yocto Project.
                        All you need is access to the code, a recipe, and a
                        controlled area in which to do your work.</para>

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

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

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

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

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

                        <para>You can, of course, also deploy the image you build
                        using the <filename>devtool build-image</filename> command
                        to actual hardware.
                        However, <filename>devtool</filename> does not provide a
                        specific command that allows you to do this.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>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 recipe in
                place.
                The command is flexible enough to allow you to extract code,
                specify the existing recipe, and keep track of and gather any
                patch files from other developers that are
                associated with the code.
            </para>

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

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

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

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

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

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

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

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

                        <para>You can, of course, also deploy the image you build
                        using the <filename>devtool build-image</filename> command
                        to actual hardware.
                        However, <filename>devtool</filename> does not provide a
                        specific command that allows you to do this.
                        </para></listitem>
                    <listitem><para>
                        <emphasis>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
                            committed to the Git repository in the source tree.
                        </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> in a different
                        layer as provided by <replaceable>layer</replaceable>.
                        </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-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 fetchers support.
            </para>

            <para>
                Depending on your particular scenario, the arguments and
                options you use with <filename>devtool upgrade</filename> form
                different combinations.
                The following diagram shows a common development flow
                you would use 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 a typical scenario by
                        which you could use
                        <filename>devtool upgrade</filename>.
                        The following conditions exist:
                        <itemizedlist>
                            <listitem><para>
                                The recipe exists in some layer external
                                to the <filename>devtool</filename> workspace.
                                </para></listitem>
                            <listitem><para>
                                The source files for the new release
                                exist adjacent to 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 are located.
                        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></listitem>
                    <listitem><para><emphasis>
                        Resolve any Conflicts created by the Upgrade</emphasis>:
                        At this point, 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.
                        If this is the case, 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</emphasis>:
                        Once you have your recipe in order, you can build it.
                        You can either use <filename>devtool build</filename>
                        or <filename>bitbake</filename>.
                        Either method produces build output that is stored
                        in
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>.
                        </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.
                        If you specify a destination layer that is the same as
                        the original source, then the old version of the
                        recipe and associated files will be 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 with which you provide it.
            Currently, the command has support for the following:
            <itemizedlist>
                <listitem><para>
                    Autotools (<filename>autoconf</filename> and
                    <filename>automake</filename>)
                    </para></listitem>
                <listitem><para>
                    CMake
                    </para></listitem>
                <listitem><para>
                    Scons
                    </para></listitem>
                <listitem><para>
                    <filename>qmake</filename>
                    </para></listitem>
                <listitem><para>
                    Plain <filename>Makefile</filename>
                    </para></listitem>
                <listitem><para>
                    Out-of-tree kernel module
                    </para></listitem>
                <listitem><para>
                    Binary package (i.e. "-b" option)
                    </para></listitem>
                <listitem><para>
                    Node.js module
                    </para></listitem>
                <listitem><para>
                    Python modules that use <filename>setuptools</filename>
                    or <filename>distutils</filename>
                    </para></listitem>
            </itemizedlist>
        </para>

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

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

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

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

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

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

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

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

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

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

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

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

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

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

            <para>
                When writing a recipe for Makefile-only software, keep the
                following in mind:
                <itemizedlist>
                    <listitem><para>
                        You probably need to patch the Makefile to use
                        variables instead of hardcoding tools within the
                        toolchain such as <filename>gcc</filename> and
                        <filename>g++</filename>.
                        </para></listitem>
                    <listitem><para>
                        The environment in which <filename>make</filename> runs
                        is set up with various standard variables for
                        compilation (e.g. <filename>CC</filename>,
                        <filename>CXX</filename>, and so forth) in a similar
                        manner to the environment set up by the SDK's
                        environment setup script.
                        One easy way to see these variables is to run the
                        <filename>devtool build</filename> command on the
                        recipe and then look in
                        <filename>oe-logs/run.do_compile</filename>.
                        Towards the top of this file you will see a list of
                        environment variables that are being set.
                        You can take advantage of these variables within the
                        Makefile.
                        </para></listitem>
                    <listitem><para>
                        If the Makefile sets a default for a variable using "=",
                        that default overrides the value set in the environment,
                        which is usually not desirable.
                        In this situation, you can either patch the Makefile
                        so it sets the default using the "?=" operator, or
                        you can alternatively force the value on the
                        <filename>make</filename> command line.
                        To force the value on the command line, add the
                        variable setting to
                        <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OEMAKE'><filename>EXTRA_OEMAKE</filename></ulink>
                        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 by virtue of
                        being specific to the build host rather than the target.
                        Patching the Makefile to use prefix variables or other
                        path variables is usually the way to handle this.
                        </para></listitem>
                    <listitem><para>
                        Sometimes a Makefile runs target-specific commands such
                        as <filename>ldconfig</filename>.
                        For such cases, you might be able to simply apply
                        patches that remove these commands from the Makefile.
                        </para></listitem>
                </itemizedlist>
            </para>
        </section>

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

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

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

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

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

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

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

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

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

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

            <para>
                If the software your recipe is building uses GNU autoconf,
                then a fixed set of arguments is passed to it to enable
                cross-compilation plus any extras specified by
                <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink>
                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 build host.
                For example, an application linking to a common library needs
                access to the library itself and its associated headers.
                The way this access is accomplished within the extensible SDK is
                through the sysroot.
                One sysroot exists per "machine" for which the SDK is being built.
                In practical terms, this means a sysroot exists for the target
                machine, and a sysroot exists for the build host.
            </para>

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

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

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

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

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

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

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

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

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

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

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

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

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

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