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<chapter id='usingpoky'>
<title>Using Poky</title>

    <para>
        This section gives an overview of the components that make up Poky 
        following by information about running poky builds and dealing with any
        problems that may arise.
    </para>

<section id='usingpoky-components'>
    <title>Poky Overview</title>

    <para>
        The bitbake task executor together with various types of configuration files form the core of Poky.
        This section overviews the bitbake task executor and the
        configuration files by describing what they are used for and they they interact.
    </para>
    
    <para>  
        Bitbake handles the parsing and execution of the data files. 
        The data itself is of various types:
    <itemizedlist>
        <listitem><para>Recipes:  Provides details about particular pieces of software</para></listitem>
        <listitem><para>Class Data:  An abstraction of common build information (e.g. how to build a 
          Linux kernel).</para></listitem>
        <listitem><para>Configuration Data:  Defines machine-specific settings, policy decisions, etc.
          Configuration data acts a the glue to bind everything together.</para></listitem>
    </itemizedlist>
    </para>

    <para> 
        Bitbake knows how to combine multiple data sources together and refers to each data source
        as a <link linkend='usingpoky-changes-layers'>'layer'</link>.
    </para>

    <para>
        Following are some brief details on these core components.
        For more detailed information on these components see the 
        <link linkend='ref-structure'>'Reference: Directory Structure'</link>
        appendix.
    </para>

    <section id='usingpoky-components-bitbake'>
        <title>Bitbake</title>

        <para>
            Bitbake is the tool at the heart of Poky and is responsible
            for parsing the metadata, generating a list of tasks from it
            and then executing them. To see a list of the options bitbake
            supports look at 'bitbake --help'.
        </para>

        <para>
            The most common usage for bitbake is <filename>bitbake &lt;packagename&gt;</filename>, where
            packagename is the name of the package you want to build (referred to as the 'target'
            in this manual). 
            The target often equates to the first part of a <filename>.bb</filename> filename.
            So, to run the <filename>matchbox-desktop_1.2.3.bb</filename> file, you
            might type the following:
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop
            </literallayout>
            Several different versions of <filename>matchbox-desktop</filename> might exist.
            Bitbake chooses the one selected by the distribution configuration.
            You can get more details about how bitbake chooses between different versions
            and providers in the <link linkend='ref-bitbake-providers'>
            'Preferences and Providers'</link> section.
        </para>
        <para>
            Bitbake also tries to execute any dependent tasks first.
            So for example, before building <filename>matchbox-desktop</filename> bitbake
            would build a cross compiler and glibc if they had not already been built.
        </para>

    </section>

    <section id='usingpoky-components-metadata'>
        <title>Metadata (Recipes)</title>

        <para>
            The <filename>.bb</filename> files are usually referred to as 'recipes'. 
            In general, a recipe contains information about a single piece of software such
            as from where to download the source patches (if any are needed), which special 
            configuration options to apply, how to compile the source files, and how to 
            package the compiled output. 
        </para>

        <para>
            The term 'package' can also be used to describe recipes.
            However, since the same word is used for the packaged output from Poky (i.e. .ipk or .deb
            files), this document avoids it.
        </para>

    </section>

    <section id='usingpoky-components-classes'>
        <title>Classes</title>

        <para>
            Class files (<filename>.bbclass</filename>) contain information that is useful to share
            between metadata files. 
            An example is the autotools class, which contains
            common settings for any application that autotools uses.
            The <link linkend='ref-classes'>Reference: Classes</link> appendix provides details
            about common classes and how to use them.
        </para>
    </section>

    <section id='usingpoky-components-configuration'>
        <title>Configuration</title>

        <para>
            The configuration files (<filename>.conf</filename>) define various configuration variables
            that govern what Poky does. 
            These files are split into several areas that define machine configuration options, 
            distribution configuration options, compiler tuning options, general common configuration
            options and user configuration options (<filename>local.conf</filename>).
        </para>
    </section>

</section>


<section id='usingpoky-build'>
    <title>Running a Build</title>

    <para>
        First the Poky build environment needs to be set up using the following command:
    </para>
    <para>
        <literallayout class='monospaced'>
     $ source poky-init-build-env [build_dir]
        </literallayout>
    </para>
    <para>
        The build_dir is the dir containing all the build's object files. The default 
        build dir is poky-dir/build. A different build_dir can be used for each of the targets. 
        For example, ~/build/x86 for a qemux86 target, and ~/build/arm for a qemuarm target.
        Please refer to <link linkend="structure-core-script">poky-init-build-env</link>
        for more detailed information.
    </para>
    <para>
        Once the Poky build environment is set up, a target can be built using:
    </para>
    <para>
        <literallayout class='monospaced'>
     $ bitbake &lt;target&gt;
        </literallayout>
    </para>
    <para>
        The target is the name of the recipe you want to build. 
        Common targets are the images in <filename>meta/recipes-core/images</filename>),
        <filename>/meta/recipes-sato/images</filename>, etc.
        Or, the target can be the name of a recipe for a specific piece of software such as 
        <application>busybox</application>. 
        For more details about the standard images available, see the 
        <link linkend="ref-images">'Reference: Images'</link> appendix.
    </para>
</section>

<section id='usingpoky-install'>
    <title>Installing and Using the Result</title>

    <para>
        Once an image has been built it often needs to be installed. 
        The images/kernels built by Poky are placed in the 
        <filename class="directory">tmp/deploy/images</filename> directory. 
        Running qemux86 and qemuarm images is described in the
        'Using Pre-Built Binaries and QEMU' section of the Yocto Project Quick Start.
        See <ulink url="http://www.yoctoproject.org//docs/yocto-quick-start/yocto-project-qs.html"/>
        for the guide. 
        For information about how to install these images, see the documentation for your
        particular board/machine.
    </para>

</section>

<section id='usingpoky-debugging'>
    <title>Debugging Build Failures</title>

    <para>
        The exact method for debugging Poky depends on the nature of the 
        problem and on the system's area from which the bug originates. 
        Standard debugging practises such as comparison against the last 
        known working version with examination of the changes and the reapplication of steps 
        to identify the one causing the problem are
        valid for Poky just as they are for any other system. 
        It's impossible to detail every possible potential failure but here are some general
        tips to aid in debugging:
    </para>

    <section id='usingpoky-debugging-taskfailures'>
        <title>Task Failures</title>

        <para>The log file for shell tasks is available in <filename>${WORKDIR}/temp/log.do_taskname.pid</filename>. 
            For example, the "compile" task of busybox 1.01 on the ARM spitz machine might be 
            <filename>tmp/work/armv5te-poky-linux-gnueabi/busybox-1.01/temp/log.do_compile.1234</filename>.
            To see what bitbake runs to generate that log, look at the corresponding 
            <filename>run.do_taskname.pid </filename> file located in the same directory.
        </para>

        <para>
            Presently, the output from python tasks is sent directly to the console.
        </para>
    </section>

    <section id='usingpoky-debugging-taskrunning'>
        <title>Running Specific Tasks</title>

        <para>
            Any given package consists of a set of tasks.  
            In most cases the series is: fetch, unpack, patch, configure,
            compile, install, package, package_write and build. 
            The default task is "build" and any tasks on which it depends build first - hence, 
            the standard bitbake behaviour. 
            Some tasks exist, such as devshell, that are not part of the default build chain.  
            If you wish to run a task that is not part of the default build chain you can use the 
            "-c" option in bitbake as follows:
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devshell
            </literallayout>
        </para>

        <para>
            If you wish to rerun a task use the force option "-f". 
            For example, the following sequence forces recompilation after changing files in the 
            working directory.
        </para>

        <para>
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop
     [make some changes to the source code in the WORKDIR]
     $ bitbake matchbox-desktop -c compile -f
     $ bitbake matchbox-desktop
            </literallayout>
        </para>

        <para>
            This sequence first builds <filename>matchbox-desktop</filename> and then recompiles it.
            The last command reruns all tasks, basically the packaging tasks, after the compile.
            Bitbake recognizes that the "compile" task was rerun and therefore understands that the other
            tasks also need to be run again.
        </para>

        <para>
            You can view a list of tasks in a given package by running the "listtasks" task.
            For example:
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c
            </literallayout>
            The results are in the file <filename>${WORKDIR}/temp/log.do_listtasks</filename>.
        </para>
    </section>

    <section id='usingpoky-debugging-dependencies'>
        <title>Dependency Graphs</title>

        <para>
            Sometimes it can be hard to see why bitbake wants to build some other packages before a given 
            package you've specified.
            The <filename>bitbake -g targetname</filename> command creates the <filename>depends.dot</filename> and
            <filename>task-depends.dot</filename> files in the current directory. 
            These files show the package and task dependencies and are useful for debugging problems.
            You can use the <filename>bitbake -g -u depexp targetname</filename> command to display the results 
            in a more human-readable form.
        </para>
    </section>

    <section id='usingpoky-debugging-bitbake'>
        <title>General Bitbake Problems</title>

        <para>
            You can see debug output from bitbake by using the "-D" option.
            The debug output gives more information about what bitbake
            is doing and the reason behind it. 
            Each "-D" option you use increases the logging level.
            The most common usage is <filename>-DDD</filename>.
        </para>

        <para>
            The output from <filename>bitbake -DDD -v targetname</filename> can reveal why
            bitbake chose a certain version of a package or why bitbake
            picked a certain provider.
            This command could also help you in a situation where you think bitbake did something 
            unexpected.
        </para>
    </section>

    <section id='usingpoky-debugging-buildfile'>
        <title>Building with No Dependencies</title>
        <para>
            If you really want to build a specific <filename>.bb</filename> file, you can use
            the command form <filename>bitbake -b somepath/somefile.bb</filename>. 
            This command form does not check for dependencies so you should use it
            only when you know its dependencies already exist. 
            You can also specify fragments of the filename and bitbake checks for a unique match.
        </para>
    </section>

    <section id='usingpoky-debugging-variables'>
        <title>Variables</title>
        <para>
            The "-e" option dumps the resulting environment for
            either the configuration (no package specified) or for a
            specific package when specified with the "-b" option.
        </para>
    </section>
    
    <section id='usingpoky-debugging-others'>
        <title>Other Tips</title>
        <tip>
        <para>
            When adding new packages it is worth watching for undesireable items making their way
            into compiler command lines.
            For example, you do not want references to local system files like 
            <filename>/usr/lib/</filename> or <filename>/usr/include/</filename>.
        </para>
        </tip>
        <tip>
        <para>
            If you want to remove the psplash boot splashscreen, add "psplash=false"
            to  the kernel command line.
            Doing so prevents psplash from loading thus allowing you to see the console.
            It is also possible to switch out of the splashscreen by 
            switching the virtual console (e.g. Fn+Left or Fn+Right on a Zaurus).
        </para>
        </tip>
    </section>
</section>

</chapter>
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