path: root/documentation/ref-manual/usingpoky.xml

<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >

<chapter id='usingpoky'>
<title>Using the Yocto Project</title>

    <para>
        This chapter describes common usage for the Yocto Project.
        The information is introductory in nature as other manuals in the Yocto Project
        documentation set provide more details on how to use the Yocto Project.
    </para>

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

    <para>
        This section provides a summary of the build process and provides information
        for less obvious aspects of the build process.
        For general information on how to build an image using the OpenEmbedded build
        system, see the
        "<ulink url='&YOCTO_DOCS_QS_URL;#building-image'>Building an Image</ulink>"
        section of the Yocto Project Quick Start.
    </para>

    <section id='build-overview'>
        <title>Build Overview</title>

        <para>
            The first thing you need to do is set up the OpenEmbedded build
            environment by sourcing an environment setup script
            (i.e.
            <link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>
            or
            <link linkend='structure-memres-core-script'><filename>oe-init-build-env-memres</filename></link>).
            Here is an example:
            <literallayout class='monospaced'>
     $ source &OE_INIT_FILE; [<replaceable>build_dir</replaceable>]
            </literallayout>
        </para>

        <para>
            The <replaceable>build_dir</replaceable> argument is optional and specifies the directory the
            OpenEmbedded build system uses for the build -
            the <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
            If you do not specify a Build Directory, it defaults to a directory
            named <filename>build</filename> in your current working directory.
            A common practice is to use a different Build Directory for different targets.
            For example, <filename>~/build/x86</filename> for a <filename>qemux86</filename>
            target, and <filename>~/build/arm</filename> for a <filename>qemuarm</filename> target.
        </para>

        <para>
            Once the build environment is set up, you can build a target using:
            <literallayout class='monospaced'>
     $ bitbake <replaceable>target</replaceable>
            </literallayout>
        </para>

        <para>
            The <replaceable>target</replaceable> 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. all found in the
            <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
            Or, the target can be the name of a recipe for a specific piece of software such as
            BusyBox.
            For more details about the images the OpenEmbedded build system supports, see the
            "<link linkend="ref-images">Images</link>" chapter.
        </para>

        <note>
            Building an image without GNU General Public License Version
            3 (GPLv3), or similarly licensed, components is supported for
            only minimal and base images.
            See the "<link linkend='ref-images'>Images</link>" chapter for more information.
        </note>
    </section>

    <section id='building-an-image-using-gpl-components'>
        <title>Building an Image Using GPL Components</title>

        <para>
            When building an image using GPL components, you need to maintain your original
            settings and not switch back and forth applying different versions of the GNU
            General Public License.
            If you rebuild using different versions of GPL, dependency errors might occur
            due to some components not being rebuilt.
        </para>
    </section>
</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 and kernels built by the OpenEmbedded build system are placed in the
        <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink> in
        <filename class="directory">tmp/deploy/images</filename>.
        For information on how to run pre-built images such as <filename>qemux86</filename>
        and <filename>qemuarm</filename>, see the
        "<ulink url='&YOCTO_DOCS_QS_URL;#using-pre-built'>Using Pre-Built Binaries and QEMU</ulink>"
        section in the Yocto Project Quick Start.
        For information about how to install these images, see the documentation for your
        particular board or machine.
    </para>
</section>

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

    <para>
        The exact method for debugging build failures depends on the nature of
        the problem and on the system's area from which the bug originates.
        Standard debugging practices such as comparison against the last
        known working version with examination of the changes and the
        re-application of steps to identify the one causing the problem are
        valid for the Yocto Project just as they are for any other system.
        Even though it is impossible to detail every possible potential failure,
        this section provides some general tips to aid in debugging.
    </para>

    <para>
        A useful feature for debugging is the error reporting tool.
        Configuring the Yocto Project to use this tool causes the
        OpenEmbedded build system to produce error reporting commands as
        part of the console output.
        You can enter the commands after the build completes
        to log error information
        into a common database, that can help you figure out what might be
        going wrong.
        For information on how to enable and use this feature, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#using-the-error-reporting-tool'>Using the Error Reporting Tool</ulink>"
        section in the Yocto Project Development Manual.
    </para>

    <para>
        For discussions on debugging, see the
        "<ulink url='&YOCTO_DOCS_DEV_URL;#platdev-gdb-remotedebug'>Debugging With the GNU Project Debugger (GDB) Remotely</ulink>"
        and
        "<ulink url='&YOCTO_DOCS_DEV_URL;#adt-eclipse'>Working within Eclipse</ulink>"
        sections in the Yocto Project Development Manual.
    </para>

    <note>
        The remainder of this section presents many examples of the
        <filename>bitbake</filename> command.
        You can learn about BitBake by reading the
        <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual'>BitBake User Manual</ulink>.
    </note>


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

        <para>The log file for shell tasks is available in
            <filename>${WORKDIR}/temp/log.do_<replaceable>taskname</replaceable>.pid</filename>.
            For example, the <filename>do_compile</filename> task for the QEMU minimal image for the x86
            machine (<filename>qemux86</filename>) might be
            <filename>tmp/work/qemux86-poky-linux/core-image-minimal/1.0-r0/temp/log.do_compile.20830</filename>.
            To see what
            <ulink url='&YOCTO_DOCS_DEV_URL;#bitbake-term'>BitBake</ulink>
            runs to generate that log, look at the corresponding
            <filename>run.do_<replaceable>taskname</replaceable>.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.
            The standard BitBake behavior in most cases is:
            <filename>do_fetch</filename>,
            <filename>do_unpack</filename>,
            <filename>do_patch</filename>, <filename>do_configure</filename>,
            <filename>do_compile</filename>, <filename>do_install</filename>,
            <filename>do_package</filename>,
            <filename>do_package_write_*</filename>, and
            <filename>do_build</filename>.
            The default task is <filename>do_build</filename> and any tasks
            on which it depends build first.
            Some tasks, such as <filename>do_devshell</filename>, 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 <filename>-c</filename> option in BitBake.
            Here is an example:
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c devshell
            </literallayout>
        </para>

        <para>
            If you wish to rerun a task, use the <filename>-f</filename> force
            option.
            For example, the following sequence forces recompilation after
            changing files in the work directory.
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop
               .
               .
        <replaceable>make some changes to the source code in the work directory</replaceable>
               .
               .
     $ bitbake matchbox-desktop -c compile -f
     $ bitbake matchbox-desktop
            </literallayout>
        </para>

        <para>
            This sequence first builds and then recompiles
            <filename>matchbox-desktop</filename>.
            The last command reruns all tasks (basically the packaging tasks)
            after the compile.
            BitBake recognizes that the <filename>do_compile</filename>
            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
            <filename>do_listtasks</filename> task as follows:
            <literallayout class='monospaced'>
     $ bitbake matchbox-desktop -c listtasks
            </literallayout>
            The results appear as output to the console and are also 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
            other packages before building a given package you have specified.
            The <filename>bitbake -g <replaceable>targetname</replaceable></filename> command
            creates the <filename>pn-buildlist</filename>,
            <filename>pn-depends.dot</filename>,
            <filename>package-depends.dot</filename>, and
            <filename>task-depends.dot</filename> files in the current
            directory.
            These files show what will be built and the package and task
            dependencies, which are useful for debugging problems.
            You can use the
            <filename>bitbake -g -u depexp <replaceable>targetname</replaceable></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 <filename>-D</filename> option.
            The debug output gives more information about what BitBake
            is doing and the reason behind it.
            Each <filename>-D</filename> option you use increases the logging level.
            The most common usage is <filename>-DDD</filename>.
        </para>

        <para>
            The output from <filename>bitbake -DDD -v</filename> <replaceable>targetname</replaceable> 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='development-host-system-issues'>
        <title>Development Host System Issues</title>

        <para>
            Sometimes issues on the host development system can cause your
            build to fail.
            Following are known, host-specific problems.
            Be sure to always consult the
            <ulink url='&YOCTO_RELEASE_NOTES;'>Release Notes</ulink>
            for a look at all release-related issues.
            <itemizedlist>
                <listitem><para><emphasis><filename>eglibc-initial</filename> fails to build</emphasis>:
                    If your development host system has the unpatched
                    <filename>GNU Make 3.82</filename>,
                    the
                    <link linkend='ref-tasks-install'><filename>do_install</filename></link>
                    task fails for <filename>eglibc-initial</filename> during
                    the build.</para>
                    <para>Typically, every distribution that ships
                    <filename>GNU Make 3.82</filename> as
                    the default already has the patched version.
                    However, some distributions, such as Debian, have
                    <filename>GNU Make 3.82</filename> as an option, which
                    is unpatched.
                    You will see this error on these types of distributions.
                    Switch to <filename>GNU Make 3.81</filename> or patch
                    your <filename>make</filename> to solve the problem.
                    </para></listitem>
            </itemizedlist>
        </para>
    </section>

    <section id='usingpoky-debugging-buildfile'>
        <title>Building with No Dependencies</title>
        <para>
            To build a specific recipe (<filename>.bb</filename> file),
            you can use the following command form:
            <literallayout class='monospaced'>
     $ bitbake -b <replaceable>somepath</replaceable>/<replaceable>somerecipe</replaceable>.bb
            </literallayout>
            This command form does not check for dependencies.
            Consequently, you should use it
            only when you know existing dependencies have been met.
            <note>
                You can also specify fragments of the filename.
                In this case, BitBake checks for a unique match.
            </note>
        </para>
    </section>

    <section id='usingpoky-debugging-variables'>
        <title>Variables</title>
        <para>
            You can use the <filename>-e</filename> BitBake option to
            display the parsing environment for a configuration.
            The following displays the general parsing environment:
            <literallayout class='monospaced'>
     $ bitbake -e
            </literallayout>
            This next example shows the parsing environment for a specific
            recipe:
            <literallayout class='monospaced'>
     $ bitbake -e <replaceable>recipename</replaceable>
            </literallayout>
        </para>
    </section>

    <section id='recipe-logging-mechanisms'>
        <title>Recipe Logging Mechanisms</title>
        <para>
            Best practices exist while writing recipes that both log build progress and
            act on build conditions such as warnings and errors.
            Both Python and Bash language bindings exist for the logging mechanism:
            <itemizedlist>
                <listitem><para><emphasis>Python:</emphasis> For Python functions, BitBake
                    supports several loglevels: <filename>bb.fatal</filename>,
                    <filename>bb.error</filename>, <filename>bb.warn</filename>,
                    <filename>bb.note</filename>, <filename>bb.plain</filename>,
                    and <filename>bb.debug</filename>.</para></listitem>
                <listitem><para><emphasis>Bash:</emphasis> For Bash functions, the same set
                    of loglevels exist and are accessed with a similar syntax:
                    <filename>bbfatal</filename>, <filename>bberror</filename>,
                    <filename>bbwarn</filename>, <filename>bbnote</filename>,
                    <filename>bbplain</filename>, and <filename>bbdebug</filename>.</para></listitem>
            </itemizedlist>
        </para>

        <para>
            For guidance on how logging is handled in both Python and Bash recipes, see the
            <filename>logging.bbclass</filename> file in the
            <filename>meta/classes</filename> folder of the
            <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
        </para>

        <section id='logging-with-python'>
            <title>Logging With Python</title>
            <para>
                When creating recipes using Python and inserting code that handles build logs,
                keep in mind the goal is to have informative logs while keeping the console as
                "silent" as possible.
                Also, if you want status messages in the log, use the "debug" loglevel.
            </para>

            <para>
                Following is an example written in Python.
                The code handles logging for a function that determines the
                number of tasks needed to be run.
                See the
                "<link linkend='ref-tasks-listtasks'><filename>do_listtasks</filename></link>"
                section for additional information:
                <literallayout class='monospaced'>
     python do_listtasks() {
         bb.debug(2, "Starting to figure out the task list")
         if noteworthy_condition:
             bb.note("There are 47 tasks to run")
         bb.debug(2, "Got to point xyz")
         if warning_trigger:
             bb.warn("Detected warning_trigger, this might be a problem later.")
         if recoverable_error:
             bb.error("Hit recoverable_error, you really need to fix this!")
         if fatal_error:
             bb.fatal("fatal_error detected, unable to print the task list")
         bb.plain("The tasks present are abc")
         bb.debug(2, "Finished figuring out the tasklist")
     }
                </literallayout>
            </para>
        </section>

        <section id='logging-with-bash'>
            <title>Logging With Bash</title>
            <para>
                When creating recipes using Bash and inserting code that handles build
                logs, you have the same goals - informative with minimal console output.
                The syntax you use for recipes written in Bash is similar to that of
                recipes written in Python described in the previous section.
            </para>

            <para>
                Following is an example written in Bash.
                The code logs the progress of the <filename>do_my_function</filename> function.
                <literallayout class='monospaced'>
     do_my_function() {
         bbdebug 2 "Running do_my_function"
         if [ exceptional_condition ]; then
             bbnote "Hit exceptional_condition"
         fi
         bbdebug 2  "Got to point xyz"
         if [ warning_trigger ]; then
             bbwarn "Detected warning_trigger, this might cause a problem later."
         fi
         if [ recoverable_error ]; then
             bberror "Hit recoverable_error, correcting"
         fi
         if [ fatal_error ]; then
             bbfatal "fatal_error detected"
         fi
         bbdebug 2 "Completed do_my_function"
     }
                </literallayout>
            </para>
        </section>
    </section>

    <section id='usingpoky-debugging-others'>
        <title>Other Tips</title>

        <para>
            Here are some other tips that you might find useful:
            <itemizedlist>
                <listitem><para>When adding new packages, it is worth watching for
                    undesirable 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></listitem>
                <listitem><para>If you want to remove the <filename>psplash</filename>
                    boot splashscreen,
                    add <filename>psplash=false</filename> to  the kernel command line.
                    Doing so prevents <filename>psplash</filename> from loading
                    and thus allows 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></listitem>
            </itemizedlist>
        </para>
    </section>
</section>

<section id='maintaining-build-output-quality'>
    <title>Maintaining Build Output Quality</title>

    <para>
        Many factors can influence the quality of a build.
        For example, if you upgrade a recipe to use a new version of an upstream software
        package or you experiment with some new configuration options, subtle changes
        can occur that you might not detect until later.
        Consider the case where your recipe is using a newer version of an upstream package.
        In this case, a new version of a piece of software might introduce an optional
        dependency on another library, which is auto-detected.
        If that library has already been built when the software is building,
        the software will link to the built library and that library will be pulled
        into your image along with the new software even if you did not want the
        library.
    </para>

    <para>
        The
        <link linkend='ref-classes-buildhistory'><filename>buildhistory</filename></link>
        class exists to help you maintain
        the quality of your build output.
        You can use the class to highlight unexpected and possibly unwanted
        changes in the build output.
        When you enable build history, it records information about the contents of
        each package and image and then commits that information to a local Git
        repository where you can examine the information.
    </para>

    <para>
        The remainder of this section describes the following:
        <itemizedlist>
           <listitem><para>How you can enable and disable
               build history</para></listitem>
           <listitem><para>How to understand what the build history contains
               </para></listitem>
           <listitem><para>How to limit the information used for build history
               </para></listitem>
           <listitem><para>How to examine the build history from both a
               command-line and web interface</para></listitem>
       </itemizedlist>
    </para>

    <section id='enabling-and-disabling-build-history'>
        <title>Enabling and Disabling Build History</title>

        <para>
            Build history is disabled by default.
            To enable it, add the following <filename>INHERIT</filename>
            statement and set the
            <link linkend='var-BUILDHISTORY_COMMIT'><filename>BUILDHISTORY_COMMIT</filename></link>
            variable to "1" at the end of your
            <filename>conf/local.conf</filename> file found in the
            <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
            <literallayout class='monospaced'>
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "1"
            </literallayout>
            Enabling build history as previously described
            causes the build process to collect build
            output information and commit it to a local
            <ulink url='&YOCTO_DOCS_DEV_URL;#git'>Git</ulink> repository.
            <note>
                Enabling build history increases your build times slightly,
                particularly for images, and increases the amount of disk
                space used during the build.
            </note>
        </para>

        <para>
            You can disable build history by removing the previous statements
            from your <filename>conf/local.conf</filename> file.
        </para>
    </section>

    <section id='understanding-what-the-build-history-contains'>
        <title>Understanding What the Build History Contains</title>

        <para>
            Build history information is kept in
            <filename>${</filename><link linkend='var-TOPDIR'><filename>TOPDIR</filename></link><filename>}/buildhistory</filename>
            in the Build Directory as defined by the
            <link linkend='var-BUILDHISTORY_DIR'><filename>BUILDHISTORY_DIR</filename></link>
            variable.
            The following is an example abbreviated listing:
            <imagedata fileref="figures/buildhistory.png" align="center" width="6in" depth="4in" />
        </para>

        <para>
            At the top level, there is a <filename>metadata-revs</filename> file
            that lists the revisions of the repositories for the layers enabled
            when the build was produced.
            The rest of the data splits into separate
            <filename>packages</filename>, <filename>images</filename> and
            <filename>sdk</filename> directories, the contents of which are
            described below.
        </para>

        <section id='build-history-package-information'>
            <title>Build History Package Information</title>

            <para>
                The history for each package contains a text file that has
                name-value pairs with information about the package.
                For example, <filename>buildhistory/packages/core2-poky-linux/busybox/busybox/latest</filename>
                contains the following:
                <literallayout class='monospaced'>
     PV = 1.19.3
     PR = r3
     RDEPENDS = update-rc.d eglibc (>= 2.13)
     RRECOMMENDS = busybox-syslog busybox-udhcpc
     PKGSIZE = 564701
     FILES = /usr/bin/* /usr/sbin/* /usr/libexec/* /usr/lib/lib*.so.* \
        /etc /com /var /bin/* /sbin/* /lib/*.so.* /usr/share/busybox \
        /usr/lib/busybox/* /usr/share/pixmaps /usr/share/applications \
        /usr/share/idl /usr/share/omf /usr/share/sounds /usr/lib/bonobo/servers
     FILELIST = /etc/busybox.links /etc/init.d/hwclock.sh /bin/busybox /bin/sh
                </literallayout>
                Most of these name-value pairs correspond to variables used
                to produce the package.
                The exceptions are <filename>FILELIST</filename>, which is the
                actual list of files in the package, and
                <filename>PKGSIZE</filename>, which is the total size of files
                in the package in bytes.
            </para>

            <para>
                There is also a file corresponding to the recipe from which the
                package came (e.g.
                <filename>buildhistory/packages/core2-poky-linux/busybox/latest</filename>):
                <literallayout class='monospaced'>
     PV = 1.19.3
     PR = r3
     DEPENDS = virtual/i586-poky-linux-gcc virtual/i586-poky-linux-compilerlibs \
        virtual/libc update-rc.d-native
     PACKAGES = busybox-httpd busybox-udhcpd busybox-udhcpc busybox-syslog \
        busybox-mdev busybox-dbg busybox busybox-doc busybox-dev \
        busybox-staticdev busybox-locale
                </literallayout>
            </para>

            <para>
                Finally, for those recipes fetched from a version control
                system (e.g., Git), a file exists that lists source revisions
                that are specified in the recipe and lists the actual revisions
                used during the build.
                Listed and actual revisions might differ when
                <link linkend='var-SRCREV'><filename>SRCREV</filename></link>
                is set to
                <filename>${<link linkend='var-AUTOREV'>AUTOREV</link>}</filename>.
                Here is an example assuming
                <filename>buildhistory/packages/emenlow-poky-linux/linux-yocto/latest_srcrev</filename>):
                <literallayout class='monospaced'>
     # SRCREV_machine = "b5c37fe6e24eec194bb29d22fdd55d73bcc709bf"
     SRCREV_machine = "b5c37fe6e24eec194bb29d22fdd55d73bcc709bf"
     # SRCREV_emgd = "caea08c988e0f41103bbe18eafca20348f95da02"
     SRCREV_emgd = "caea08c988e0f41103bbe18eafca20348f95da02"
     # SRCREV_meta = "c2ed0f16fdec628242a682897d5d86df4547cf24"
     SRCREV_meta = "c2ed0f16fdec628242a682897d5d86df4547cf24"
                </literallayout>
                You can use the <filename>buildhistory-collect-srcrevs</filename>
                command to collect the stored <filename>SRCREV</filename> values
                from build history and report them in a format suitable for use in
                global configuration (e.g., <filename>local.conf</filename>
                or a distro include file) to override floating
                <filename>AUTOREV</filename> values to a fixed set of revisions.
                Here is some example output from this command:
                <literallayout class='monospaced'>
     # emenlow-poky-linux
     SRCREV_machine_pn-linux-yocto = "b5c37fe6e24eec194bb29d22fdd55d73bcc709bf"
     SRCREV_emgd_pn-linux-yocto = "caea08c988e0f41103bbe18eafca20348f95da02"
     SRCREV_meta_pn-linux-yocto = "c2ed0f16fdec628242a682897d5d86df4547cf24"
     # core2-poky-linux
     SRCREV_pn-kmod = "62081c0f68905b22f375156d4532fd37fa5c8d33"
     SRCREV_pn-blktrace = "d6918c8832793b4205ed3bfede78c2f915c23385"
     SRCREV_pn-opkg = "649"
                </literallayout>
                <note>
                    Here are some notes on using the
                    <filename>buildhistory-collect-srcrevs</filename> command:
                    <itemizedlist>
                        <listitem><para>By default, only values where the
                            <filename>SRCREV</filename> was
                            not hardcoded (usually when <filename>AUTOREV</filename>
                            was used) are reported.
                            Use the <filename>-a</filename> option to see all
                            <filename>SRCREV</filename> values.
                            </para></listitem>
                        <listitem><para>The output statements might not have any effect
                            if overrides are applied elsewhere in the build system
                            configuration.
                            Use the <filename>-f</filename> option to add the
                            <filename>forcevariable</filename> override to each output line
                            if you need to work around this restriction.
                            </para></listitem>
                        <listitem><para>The script does apply special handling when
                            building for multiple machines.
                            However, the script does place a
                            comment before each set of values that specifies
                            which triplet to which they belong as shown above
                            (e.g., <filename>emenlow-poky-linux</filename>).
                            </para></listitem>
                    </itemizedlist>
                </note>
            </para>
        </section>

        <section id='build-history-image-information'>
            <title>Build History Image Information</title>

            <para>
                The files produced for each image are as follows:
                <itemizedlist>
                    <listitem><para><filename>image-files:</filename>
                        A directory containing selected files from the root
                        filesystem.
                        The files are defined by
                        <link linkend='var-BUILDHISTORY_IMAGE_FILES'><filename>BUILDHISTORY_IMAGE_FILES</filename></link>.
                        </para></listitem>
                    <listitem><para><filename>build-id.txt:</filename>
                        Human-readable information about the build configuration
                        and metadata source revisions.
                        This file contains the full build header as printed
                        by BitBake.</para></listitem>
                    <listitem><para><filename>*.dot:</filename>
                        Dependency graphs for the image that are
                        compatible with <filename>graphviz</filename>.
                        </para></listitem>
                    <listitem><para><filename>files-in-image.txt:</filename>
 	                    A list of files in the image with permissions,
                        owner, group, size, and symlink information.
                        </para></listitem>
                    <listitem><para><filename>image-info.txt:</filename>
                        A text file containing name-value pairs with information
                        about the image.
                        See the following listing example for more information.
                        </para></listitem>
                    <listitem><para><filename>installed-package-names.txt:</filename>
                        A list of installed packages by name only.</para></listitem>
                    <listitem><para><filename>installed-package-sizes.txt:</filename>
                        A list of installed packages ordered by size.
                        </para></listitem>
                    <listitem><para><filename>installed-packages.txt:</filename>
                        A list of installed packages with full package
                        filenames.</para></listitem>
                </itemizedlist>
                <note>
                    Installed package information is able to be gathered and
                    produced even if package management is disabled for the final
                    image.
                </note>
            </para>

            <para>
                Here is an example of <filename>image-info.txt</filename>:
                <literallayout class='monospaced'>
     DISTRO = poky
     DISTRO_VERSION = 1.1+snapshot-20120207
     USER_CLASSES = image-mklibs image-prelink
     IMAGE_CLASSES = image_types
     IMAGE_FEATURES = debug-tweaks x11-base apps-x11-core \
        package-management ssh-server-dropbear package-management
     IMAGE_LINGUAS = en-us en-gb
     IMAGE_INSTALL = packagegroup-core-boot packagegroup-base-extended
     BAD_RECOMMENDATIONS =
     ROOTFS_POSTPROCESS_COMMAND = buildhistory_get_image_installed ;   rootfs_update_timestamp ;
     IMAGE_POSTPROCESS_COMMAND = buildhistory_get_imageinfo ;
     IMAGESIZE = 171816
                </literallayout>
                Other than <filename>IMAGESIZE</filename>, which is the
                total size of the files in the image in Kbytes, the
                name-value pairs are variables that may have influenced the
                content of the image.
                This information is often useful when you are trying to determine
                why a change in the package or file listings has occurred.
            </para>
        </section>

        <section id='using-build-history-to-gather-image-information-only'>
            <title>Using Build History to Gather Image Information Only</title>

            <para>
                As you can see, build history produces image information,
                including dependency graphs, so you can see why something
                was pulled into the image.
                If you are just interested in this information and not
                interested in collecting specific package or SDK information,
                you can enable writing only image information without
                any history by adding the following to your
                <filename>conf/local.conf</filename> file found in the
                <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>:
                <literallayout class='monospaced'>
     INHERIT += "buildhistory"
     BUILDHISTORY_COMMIT = "0"
     BUILDHISTORY_FEATURES = "image"
                </literallayout>
                Here, you set the
                <link linkend='var-BUILDHISTORY_FEATURES'><filename>BUILDHISTORY_FEATURES</filename></link>
                variable to use the image feature only.
            </para>
        </section>

        <section id='build-history-sdk-information'>
            <title>Build History SDK Information</title>
            <para>
                Build history collects similar information on the contents
                of SDKs (e.g. <filename>meta-toolchain</filename>
                or <filename>bitbake -c populate_sdk imagename</filename>)
                as compared to information it collects for images.
                The following list shows the files produced for each SDK:
                <itemizedlist>
                    <listitem><para><filename>files-in-sdk.txt:</filename>
                        A list of files in the SDK with permissions,
                        owner, group, size, and symlink information.
                        This list includes both the host and target parts
                        of the SDK.
                        </para></listitem>
                    <listitem><para><filename>sdk-info.txt:</filename>
                        A text file containing name-value pairs with information
                        about the SDK.
                        See the following listing example for more information.
                        </para></listitem>
                    <listitem><para>The following information appears under
                        each of the <filename>host</filename>
                        and <filename>target</filename> directories
                        for the portions of the SDK that run on the host and
                        on the target, respectively:
                        <itemizedlist>
                            <listitem><para><filename>depends.dot:</filename>
                                Dependency graph for the SDK that is
                                compatible with <filename>graphviz</filename>.
                                </para></listitem>
                            <listitem><para><filename>installed-package-names.txt:</filename>
                                A list of installed packages by name only.
                                </para></listitem>
                            <listitem><para><filename>installed-package-sizes.txt:</filename>
                                A list of installed packages ordered by size.
                                </para></listitem>
                            <listitem><para><filename>installed-packages.txt:</filename>
                                A list of installed packages with full package
                                filenames.</para></listitem>
                            </itemizedlist>
                        </para></listitem>
                </itemizedlist>
            </para>

            <para>
                Here is an example of <filename>sdk-info.txt</filename>:
                <literallayout class='monospaced'>
     DISTRO = poky
     DISTRO_VERSION = 1.3+snapshot-20130327
     SDK_NAME = poky-eglibc-i686-arm
     SDK_VERSION = 1.3+snapshot
     SDKMACHINE =
     SDKIMAGE_FEATURES = dev-pkgs dbg-pkgs
     BAD_RECOMMENDATIONS =
     SDKSIZE = 352712
                </literallayout>
                Other than <filename>SDKSIZE</filename>, which is the
                total size of the files in the SDK in Kbytes, the
                name-value pairs are variables that might have influenced the
                content of the SDK.
                This information is often useful when you are trying to
                determine why a change in the package or file listings
                has occurred.
            </para>
        </section>

        <section id='examining-build-history-information'>
            <title>Examining Build History Information</title>

            <para>
                You can examine build history output from the command line or
                from a web interface.
            </para>

            <para>
                To see any changes that have occurred (assuming you have
                <link linkend='var-BUILDHISTORY_COMMIT'><filename>BUILDHISTORY_COMMIT = "1"</filename></link>),
                you can simply
                use any Git command that allows you to view the history of
                a repository.
                Here is one method:
                <literallayout class='monospaced'>
      $ git log -p
                </literallayout>
                You need to realize, however, that this method does show
                changes that are not significant (e.g. a package's size
                changing by a few bytes).
            </para>

            <para>
                A command-line tool called <filename>buildhistory-diff</filename>
                does exist, though, that queries the Git repository and prints just
                the differences that might be significant in human-readable form.
                Here is an example:
                <literallayout class='monospaced'>
     $ ~/poky/poky/scripts/buildhistory-diff . HEAD^
     Changes to images/qemux86_64/eglibc/core-image-minimal (files-in-image.txt):
        /etc/anotherpkg.conf was added
        /sbin/anotherpkg was added
        * (installed-package-names.txt):
        *   anotherpkg was added
     Changes to images/qemux86_64/eglibc/core-image-minimal (installed-package-names.txt):
        anotherpkg was added
     packages/qemux86_64-poky-linux/v86d: PACKAGES: added "v86d-extras"
        * PR changed from "r0" to "r1"
        * PV changed from "0.1.10" to "0.1.12"
     packages/qemux86_64-poky-linux/v86d/v86d: PKGSIZE changed from 110579 to 144381 (+30%)
        * PR changed from "r0" to "r1"
        * PV changed from "0.1.10" to "0.1.12"
                </literallayout>
            </para>

            <para>
                To see changes to the build history using a web interface, follow
                the instruction in the <filename>README</filename> file here.
                <ulink url='http://git.yoctoproject.org/cgit/cgit.cgi/buildhistory-web/'></ulink>.
            </para>

            <para>
                Here is a sample screenshot of the interface:
                <imagedata fileref="figures/buildhistory-web.png" align="center" scalefit="1" width="130%" contentdepth="130%" />
            </para>
        </section>
    </section>
</section>

<section id='speeding-up-the-build'>
    <title>Speeding Up the Build</title>

    <para>
        Build time can be an issue.
        By default, the build system uses three simple controls to try and
        maximize build efficiency:
        <itemizedlist>
            <listitem><para>
                <link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>
                </para></listitem>
            <listitem><para>
                <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_NUMBER_PARSE_THREADS'><filename>BB_NUMBER_PARSE_THREADS</filename></ulink>
                </para></listitem>
            <listitem><para>
                <link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>
                </para></listitem>
        </itemizedlist>
        These three variables all scale to the number of processor cores
        available on the build system.
        This auto-scaling ensures that the build system fundamentally takes
        advantage of potential parallel operations during the build
        based on the build machine's capabilities.
    </para>

    <para>
        If you need to achieve even faster builds than what the build system
        produces by default, you can consider and implement some of the
        following:
        <itemizedlist>
            <listitem><para>
                <filename>BB_NUMBER_THREADS</filename>,
                <filename>BB_NUMBER_PARSE_THREADS</filename>, and
                <filename>PARALLEL_MAKE</filename>:
                As previously mentioned, the build system scales the values
                for these variables.
                However, you can manually override them in your
                <filename>local.conf</filename> file if you are not satisfied
                with the defaults.
                </para></listitem>
            <listitem><para>
                File system type:
                The file system type that the build is being performed on can
                also influence performance.
                Using <filename>ext4</filename> is recommended as compared
                to <filename>ext2</filename> and <filename>ext3</filename>
                due to <filename>ext4</filename> improved features
                such as extents.
                </para></listitem>
            <listitem><para>
                Disabling the updating of access time using
                <filename>noatime</filename>:
                The <filename>noatime</filename> mount option prevents the
                build system from updating file and directory access times.
                </para></listitem>
            <listitem><para>
                Setting a longer commit:
                Using the "commit=" mount option increases the interval
                in seconds between disk cache writes.
                Changing this interval from the five second default to
                something longer increases the risk of data loss but decreases
                the need to write to the disk, thus increasing the build
                performance.
                </para></listitem>
            <listitem><para>
                Choosing the packaging backend:
                Of the available packaging backends, IPK is the fastest.
                Additionally, selecting a singular packaging backend also
                helps.
                </para></listitem>
            <listitem><para>
                Using <filename>/tmp</filename> as a temporary file system:
                While this can help speed up the build, the benefits are
                limited due to the compiler using
                <filename>-pipe</filename>.
                The build system goes to some lengths to avoid
                <filename>sync()</filename> calls into the
                file system on the principle that if there was a significant
                failure, the
                <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>
                contents could easily be rebuilt.
                </para></listitem>
            <listitem><para>
                Inheriting the
                <link linkend='ref-classes-rm-work'><filename>rm_work</filename></link>
                class:
                Inheriting this class has shown to speed up builds due to
                significantly lower amounts of data stored in the data
                cache as well as on disk.
                Inheriting this class also makes cleanup of
                <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>
                faster, at the expense of being easily able to dive into the
                source code.
                File system maintainers have recommended that the fastest way
                to clean up large numbers of files is to reformat partitions
                rather than delete files due to the linear nature of partitions.
                This, of course, assumes you structure the disk partitions and
                file systems in a way that this is practical.
                </para></listitem>
        </itemizedlist>
        Aside from the previous list, you should keep some trade offs in
        mind that can help you speed up the build:
        <itemizedlist>
            <listitem><para>
                Exclude debug symbols and other debug information:
                If you do not need these symbols and other debug information,
                disabling the <filename>*-dbg</filename> package generation
                can speed up the build.
                You can disable this generation by setting the
                <link linkend='var-INHIBIT_PACKAGE_DEBUG_SPLIT'><filename>INHIBIT_PACKAGE_DEBUG_SPLIT</filename></link>
                variable to "1".
                </para></listitem>
            <listitem><para>
                Disable static library generation for recipes derived from
                <filename>autoconf</filename> or <filename>libtool</filename>:
                Following is an example showing how to disable static
                libraries and still provide an override to handle exceptions:
                <literallayout class='monospaced'>
     STATICLIBCONF = "--disable-static"
     STATICLIBCONF_sqlite3-native = ""
     EXTRA_OECONF += "${STATICLIBCONF}"
                </literallayout>
                <note><title>Notes</title>
                    <itemizedlist>
                        <listitem><para>
                            Some recipes need static libraries in order to work
                            correctly (e.g. <filename>pseudo-native</filename>
                            needs <filename>sqlite3-native</filename>).
                            Overrides, as in the previous example, account for
                            these kinds of exceptions.
                            </para></listitem>
                        <listitem><para>
                            Some packages have packaging code that assumes the
                            presence of the static libraries.
                            If so, you might need to exclude them as well.
                            </para></listitem>
                    </itemizedlist>
                </note>
            </para></listitem>
        </itemizedlist>
    </para>
</section>
</chapter>
<!--
vim: expandtab tw=80 ts=4
-->