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<chapter>
  <title>The BitBake command</title>
  <section>
    <title>Introduction</title>
    <para>bitbake is the primary command in the system. It
    facilitates executing tasks in a single .bb file, or executing
    a given task on a set of multiple .bb files, accounting for
    interdependencies amongst them.</para>
  </section>
  <section>
    <title>Usage and syntax</title>
    <para>
      <screen>
      <prompt>$</prompt>bitbake --help usage: bitbake [options]
      [package ...] Executes the specified task (default is
      'build') for a given set of BitBake files. It expects that
      BBFILES is defined, which is a space separated list of files
      to be executed. BBFILES does support wildcards. Default
      BBFILES are the .bb files in the current directory. options:
      --version show program's version number and exit -h, --help
      show this help message and exit -b BUILDFILE,
      --buildfile=BUILDFILE execute the task against this .bb file,
      rather than a package from BBFILES. -k, --continue continue
      as much as possible after an error. While the target that
      failed, and those that depend on it, cannot be remade, the
      other dependencies of these targets can be processed all the
      same. -f, --force force run of specified cmd, regardless of
      stamp status -i, --interactive drop into the interactive mode
      also called the BitBake shell. -c CMD, --cmd=CMD Specify task
      to execute. Note that this only executes the specified task
      for the providee and the packages it depends on, i.e.
      'compile' does not implicitly call stage for the dependencies
      (IOW: use only if you know what you are doing). Depending on
      the base.bbclass a listtasks task is defined and will show
      available tasks -r FILE, --read=FILE read the specified file
      before bitbake.conf -v, --verbose output more chit-chat to
      the terminal -D, --debug Increase the debug level. You can
      specify this more than once. -n, --dry-run don't execute,
      just go through the motions -p, --parse-only quit after
      parsing the BB files (developers only) -s, --show-versions
      show current and preferred versions of all packages -e,
      --environment show the global or per-package environment
      (this is what used to be bbread) -g, --graphviz emit the
      dependency trees of the specified packages in the dot syntax
      -I IGNORED_DOT_DEPS, --ignore-deps=IGNORED_DOT_DEPS Stop
      processing at the given list of dependencies when generating
      dependency graphs. This can help to make the graph more
      appealing -l DEBUG_DOMAINS, --log-domains=DEBUG_DOMAINS Show
      debug logging for the specified logging domains -P, --profile
      profile the command and print a report</screen>
    </para>
    <para>
      <example>
        <title>Executing a task against a single .bb</title>
        <para>Executing tasks for a single file is relatively
        simple. You specify the file in question, and BitBake
        parses it and executes the specified task (or
        <quote>build</quote>by default). It obeys intertask
        dependencies when doing so.</para>
        <para>
        <quote>clean</quote>task:</para>
        <para>
          <screen>
          <prompt>$</prompt>bitbake -b blah_1.0.bb -c
          clean</screen>
        </para>
        <para>
        <quote>build</quote>task:</para>
        <para>
          <screen>
          <prompt>$</prompt>bitbake -b blah_1.0.bb</screen>
        </para>
      </example>
    </para>
    <para>
      <example>
        <title>Executing tasks against a set of .bb files</title>
        <para>There are a number of additional complexities
        introduced when one wants to manage multiple .bb files.
        Clearly there needs to be a way to tell BitBake what files
        are available, and of those, which we want to execute at
        this time. There also needs to be a way for each .bb to
        express its dependencies, both for build time and runtime.
        There must be a way for the user to express their
        preferences when multiple .bb's provide the same
        functionality, or when there are multiple versions of a
        .bb.</para>
        <para>The next section, Metadata, outlines how to specify
        such things.</para>
        <para>Note that the bitbake command, when not using
        --buildfile, accepts a
        <varname>PROVIDER</varname>, not a filename or anything
        else. By default, a .bb generally PROVIDES its packagename,
        packagename-version, and
        packagename-version-revision.</para>
        <screen>
        <prompt>$</prompt>bitbake blah</screen>
        <screen>
        <prompt>$</prompt>bitbake blah-1.0</screen>
        <screen>
        <prompt>$</prompt>bitbake blah-1.0-r0</screen>
        <screen>
        <prompt>$</prompt>bitbake -c clean blah</screen>
        <screen>
        <prompt>$</prompt>bitbake virtual/whatever</screen>
        <screen>
        <prompt>$</prompt>bitbake -c clean
        virtual/whatever</screen>
      </example>
      <example>
        <title>Generating dependency graphs</title>
        <para>BitBake is able to generate dependency graphs using
        the dot syntax. These graphs can be converted to images
        using the
        <application>dot</application>application from
        <ulink url="http://www.graphviz.org">Graphviz</ulink>. Two
        files will be written into the current working directory,
        <emphasis>depends.dot</emphasis>containing dependency
        information at the package level and
        <emphasis>task-depends.dot</emphasis>containing a breakdown
        of the dependencies at the task level. To stop depending on
        common depends, one can use the
        <prompt>-I depend</prompt>to omit these from the graph.
        This can lead to more readable graphs. This way,
        <varname>DEPENDS</varname>from inherited classes such as
        base.bbclass can be removed from the graph.</para>
        <screen>
        <prompt>$</prompt>bitbake -g blah</screen>
        <screen>
        <prompt>$</prompt>bitbake -g -I virtual/whatever -I bloom
        blah</screen>
      </example>
    </para>
  </section>
  <section>
    <title>Special variables</title>
    <para>Certain variables affect BitBake operation:</para>
    <section>
      <title>
        <varname>BB_NUMBER_THREADS</varname>
      </title>
      <para>The number of threads BitBake should run at once
      (default: 1).</para>
    </section>
  </section>
  <section>
    <title>Metadata</title>
    <para>As you may have seen in the usage information, or in the
    information about .bb files, the
    <varname>BBFILES</varname>variable is how the BitBake tool
    locates its files. This variable is a space separated list of
    files that are available, and supports wildcards.
    <example>
      <title>Setting BBFILES</title>
      <programlisting>
      <varname>BBFILES</varname>=
      "/path/to/bbfiles/*.bb"</programlisting>
    </example></para>
    <para>With regard to dependencies, it expects the .bb to define
    a
    <varname>DEPENDS</varname>variable, which contains a space
    separated list of
    <quote>package names</quote>, which themselves are the
    <varname>PN</varname>variable. The
    <varname>PN</varname>variable is, in general, set to a
    component of the .bb filename by default.</para>
    <example>
      <title>Depending on another .bb</title>
      <para>a.bb:
      <screen>PN = "package-a" DEPENDS +=
      "package-b"</screen></para>
      <para>b.bb:
      <screen>PN = "package-b"</screen></para>
    </example>
    <example>
      <title>Using PROVIDES</title>
      <para>This example shows the usage of the
      <varname>PROVIDES</varname>variable, which allows a given .bb
      to specify what functionality it provides.</para>
      <para>package1.bb:
      <screen>PROVIDES += "virtual/package"</screen></para>
      <para>package2.bb:
      <screen>DEPENDS += "virtual/package"</screen></para>
      <para>package3.bb:
      <screen>PROVIDES += "virtual/package"</screen></para>
      <para>As you can see, we have two different .bb's that
      provide the same functionality (virtual/package). Clearly,
      there needs to be a way for the person running BitBake to
      control which of those providers gets used. There is, indeed,
      such a way.</para>
      <para>The following would go into a .conf file, to select
      package1:
      <screen>PREFERRED_PROVIDER_virtual/package =
      "package1"</screen></para>
    </example>
    <example>
      <title>Specifying version preference</title>
      <para>When there are multiple
      <quote>versions</quote>of a given package, BitBake defaults
      to selecting the most recent version, unless otherwise
      specified. If the .bb in question has a
      <varname>DEFAULT_PREFERENCE</varname>set lower than the other
      .bb's (default is 0), then it will not be selected. This
      allows the person or persons maintaining the repository of
      .bb files to specify their preference for the default
      selected version. In addition, the user can specify their
      preferred version.</para>
      <para>If the first .bb is named
      <filename>a_1.1.bb</filename>, then the
      <varname>PN</varname>variable will be set to
      <quote>a</quote>, and the
      <varname>PV</varname>variable will be set to 1.1.</para>
      <para>If we then have an
      <filename>a_1.2.bb</filename>, BitBake will choose 1.2 by
      default. However, if we define the following variable in a
      .conf that BitBake parses, we can change that.
      <screen>PREFERRED_VERSION_a = "1.1"</screen></para>
    </example>
    <example>
	    <title>Using
      <quote>bbfile collections</quote></title>
      <para>bbfile collections exist to allow the user to have
      multiple repositories of bbfiles that contain the same exact
      package. For example, one could easily use them to make one's
      own local copy of an upstream repository, but with custom
      modifications that one does not want upstream. Usage:</para>
      <screen>BBFILES = "/stuff/openembedded/*/*.bb
      /stuff/openembedded.modified/*/*.bb" BBFILE_COLLECTIONS =
      "upstream local" BBFILE_PATTERN_upstream =
      "^/stuff/openembedded/" BBFILE_PATTERN_local =
      "^/stuff/openembedded.modified/" BBFILE_PRIORITY_upstream =
      "5" BBFILE_PRIORITY_local = "10"</screen>
    </example>
  </section>
</chapter>