path: root/usermanual/chapters/usage.xml

<?xml version="1.0" encoding="UTF-8"?>
<chapter id="chapter_using_bitbake_and_oe">
  <title>Using bitbake and OE</title>

  <section id="usage_introduction" xreflabel="introduction">
    <title>Introduction</title>

    <para>If your reading this manual you probably already have some idea of
    what OpenEmbedded is all about, which is taking a lot of software and
    creating something that you can run on another device. Its all about
    downloading some source code, compiling it, creating packages (like .deb
    or .rpm) and/or creating boot images that can written to flash on the
    device. The complexities of cross-compiling and the variety of devices to
    be supported lead to a lot more complexity in on OpenEmbedded based
    distribution than you'd find in a typical desktop distribution (which
    doesn't get cross-compiled).</para>

    <para>A major part of OpenEmbedded deals with compiling source code for
    various projects. For each project OpenEmbedded has to:</para>

    <orderedlist>
      <listitem>
        <para>Download the source code, and any supporting files (such as
        initscripts);</para>
      </listitem>

      <listitem>
        <para>Extract the source code and apply any patches that might be
        wanted;</para>
      </listitem>

      <listitem>
        <para>Configure the software if needed (such as is done by running the
        configure script);</para>
      </listitem>

      <listitem>
        <para>Compile everything;</para>
      </listitem>

      <listitem>
        <para>Package up all the files into some package format, like .deb or
        .rpm or .ipk, ready for installation.</para>
      </listitem>
    </orderedlist>

    <para>As mentioned this is made for more complex than normal due
    to:</para>

    <orderedlist>
      <listitem>
        <para>Cross-compiling: cross-compiling is difficult, and lots of
        software has no support for cross-compiling. All packages included in
        OE are cross-compiled;</para>
      </listitem>

      <listitem>
        <para>Due to cross-compiling the executable's that are created cannot
        normally be run, so any software that tries to run things as part of
        it's build process need to have changes made to handle this some other
        way</para>
      </listitem>
    </orderedlist>

    <para>Of course there's a lot more to OE then just compiling packages
    though. Just some of the things that OE can handle:</para>

    <itemizedlist>
      <listitem>
        <para>Support for glibc and uclibc;</para>
      </listitem>

      <listitem>
        <para>Support for building for multiple targets;</para>
      </listitem>

      <listitem>
        <para>Dependencies - automatically building anything that is required
        for the package your really want;</para>
      </listitem>

      <listitem>
        <para>Creation of flash and disk images for booting directly on the
        target device;</para>
      </listitem>

      <listitem>
        <para>Support for various packaging formats;</para>
      </listitem>

      <listitem>
        <para>Automatically creating all of the cross-compiling tools you'll
        need;</para>
      </listitem>

      <listitem>
        <para>Support for "native" packages that are built for the host
        computer and not for the target;</para>
      </listitem>
    </itemizedlist>

    <para>This chapter assumes you have master the Getting Start guides to
    OpenEmbedded (see the OpenEmbedded web site for details), and therefore
    have an appropriately configured setup and have managed to build the
    cross-compilers for your target. This section talks you through some of
    the background on what is happening with the aim of helping you understand
    how to debug and develop within OpenEmbedded.</para>
  </section>

  <section id="usage_workspace" xreflabel="workspace">
    <title>Work space</title>

    <para>Let's start out by taking a look at a typically working area OE.
    Note that this isn't exactly what you'll see - there are a lot of options that
    can effect exactly how things are done, but it gives us a pretty good idea
    of whats going on. What we are looking at here is the tmp directory (as
    specified by TMPDIR in your local.conf):<screen>%&gt; find tmp -maxdepth 2 -type d 
tmp
tmp/stamps
tmp/cross
tmp/cross/bin
tmp/cross/libexec
tmp/cross/lib  
tmp/cross/share
tmp/cross/sh4-linux
tmp/cache
tmp/cache/titan
tmp/work
tmp/work/busybox-1.2.1-r13
tmp/work/libice-1_1.0.3-r0 
tmp/work/arpwatch-2.1a15-r2
...
tmp/rootfs
tmp/rootfs/bin
tmp/rootfs/usr
tmp/rootfs/media
tmp/rootfs/dev  
tmp/rootfs/var  
tmp/rootfs/lib  
tmp/rootfs/sbin 
tmp/rootfs/mnt  
tmp/rootfs/boot 
tmp/rootfs/sys  
tmp/rootfs/proc 
tmp/rootfs/etc  
tmp/rootfs/home 
tmp/rootfs/tmp  
tmp/staging     
tmp/staging/man 
tmp/staging/x86_64-linux
tmp/staging/pkgdata
tmp/staging/pkgmaps
tmp/staging/var
tmp/staging/sh4-linux
tmp/staging/local
tmp/staging/etc  
tmp/deploy
tmp/deploy/addons
tmp/deploy/ipk   
tmp/deploy/sources
tmp/deploy/images</screen></para>

    <para>The various top level directories under tmp include:</para>

    <variablelist>
      <varlistentry>
        <term>stamps</term>

        <listitem>
          <para>Nothing of interest to users in here. These time stamps are
          used by bitbake to keep track of what tasks it has completed and
          what tasks it still has outstanding. This is how it knows that
          certain actions have been completed and it doesn't need to do them
          again.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>cross</term>

        <listitem>
          <para>Contains the cross-compiler toolchain. That is the gcc and
          binutils that run on the host system but produce output for the
          target system.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>cache</term>

        <listitem>
          <para>Nothing of interest to users in here. This contains the
          bitbake parse cache and is used to avoid the need to parse all of
          the recipes each time bitbake is run. This makes bitbake a lot
          faster on the 2nd and subsequent runs.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>work</term>

        <listitem>
          <para>The work directory. This is the directory in which all
          packages are built - this is where the source code is extract,
          patches applied, software configure, compiled, installed and
          package. This is where you'll spend most of you time looking when
          working in OE.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>rootfs</term>

        <listitem>
          <para>The generated root filesystem image for your target device.
          This is the contents of the root filesystem (NOTE: fakeroot means it
          doesn't have the correct device special nodes and permissions to use
          directly).</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>staging</term>

        <listitem>
          <para>Contains the staging area, which is used to stored natively
          compiled tools and and libraries and headers for the target that are
          required for building other software.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>deploy</term>

        <listitem>
          <para>Contains the final output from OE. This includes the
          installation packages (typically .ipkg packages) and flash and/or
          disk images. This is where you go to get the final product.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para></para>

    <section id="usage_workdir" xreflabel="work directory">
      <title>work directory</title>

      <para>The working directory is where all files are extracted and
      everything is configured, compiled and packaged. In other words this is
      where all the action happens. Each bitbake recipe will produce a
      corresponding directory in the working area, with the name containing
      the recipe name, version and the release number (as defined by the PR
      variable in the recipe).</para>

      <para>In the following example we show some of the directories that are
      created and in this case they are created directly in the work
      directory:<screen>~%&gt; find tmp/work -maxdepth 1 -type d | head -4
tmp/work
tmp/work/busybox-1.2.1-r13
tmp/work/libice-1_1.0.3-r0
tmp/work/arpwatch-2.1a15-r2</screen>Depending on your distribution settings
      you may have an additional subdirectory present:<screen>~%&gt; find tmp/work -maxdepth 2 -type d | head -4
tmp/work
tmp/work/sh4-linux
tmp/work/sh4-linux/busybox-1.2.1-r13
tmp/work/sh4-linux/libice-1_1.0.3-r0
tmp/work/sh4-linux/arpwatch-2.1a15-r2</screen></para>

      <para>where are additional directory corresponding to the target
      architecture and OS has been inserted. This is added by the use of the
      <emphasis>multimachine</emphasis> feature which is used to allow builds
      for multiple targets within the one work directory (which in turn
      enables the sharing of native functionality and a reduction in the time
      taken to build for multiple machines). We'll assume multimachine is not
      being used for the rest of this chapter, just remember to add the extra
      directory if your distribution is using it.</para>

      <para>Using lzo 1.08 as an example we'll examine the working directory
      and see what it contain for a typical recipe:<screen>%&gt; find tmp/work/lzo-1.08-r14 -maxdepth 1
tmp/work/lzo-1.08-r14
tmp/work/lzo-1.08-r14/temp
tmp/work/lzo-1.08-r14/lzo-1.08
tmp/work/lzo-1.08-r14/install
tmp/work/lzo-1.08-r14/image</screen></para>

      <para>The directory, <emphasis
      role="bold">tmp/work/lzo-1.08-r14</emphasis>, is know as the working
      directory for the recipe is held in the <emphasis
      role="bold">WORKDIR</emphasis> variable in bitbake. You'll sometimes see
      recipes refer directly to <emphasis role="bold">WORKDIR</emphasis> and
      if so this is the directory they are referring to. The <emphasis
      role="bold">1.08</emphasis> is the version of lzo and the <emphasis
      role="bold">r14</emphasis> is the release number, as defined by the
      <emphasis role="bold">PR</emphasis> variable in the recipe.</para>

      <para>Under <emphasis role="bold">WORKDIR</emphasis> there are four
      directories:</para>

      <variablelist>
        <varlistentry>
          <term>temp</term>

          <listitem>
            <para>The temp directories contains logs and in some cases scripts
            that actually implement specific tasks.</para>

            <para>You can look at the logs in this directory to get more
            information into what happened (or didn't happen). This is usually
            the first thing to look at when things are going wrong and these
            usually need to be included when reporting bugs.</para>

            <para>The scripts can be used to see what a particular task, such
            as configure or compile, is trying to do.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>lzo-1.08</term>

          <listitem>
            <para>This is the unpacked source code directory, which was
            created when the lzo source code was extracted in this directory.
            The name and format of this directory is therefore dependent on
            the actual source code packaging. Within recipes this directory is
            referred to as <emphasis role="bold">S</emphasis> and is usually
            expected to be named like this, that is
            <emphasis>&lt;name&gt;-&lt;version&gt;</emphasis>. If the source
            code extracts to somewhere else you would need to manually specify
            the value of <emphasis role="bold">S</emphasis> in your
            recipe.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>install</term>

          <listitem>
            <para>The installation directory (or destination directory) is
            where the software needs to be installed into in order to be
            packaged. This directory is referred to as <emphasis
            role="bold">D</emphasis> in recipes. So instead of installing into
            <emphasis role="bold">/usr/bin</emphasis> and <emphasis
            role="bold">/usr/lib</emphasis> for example you would need to
            install into <emphasis role="bold">${D}/usr/bin</emphasis> and
            <emphasis role="bold">${D}/usr/lib</emphasis> in order for the
            packaging system to work.</para>
          </listitem>
        </varlistentry>

        <varlistentry>
          <term>image</term>

          <listitem>
            <para>The image directory is used to split the installed files
            into separate packages. One subdirectory is created per package to
            be generated and the files and moved from the install directory
            (<emphasis role="bold">D</emphasis>) over to this directory as
            each packaging instruction is processed. Typically there will be
            separate documentation (<emphasis>-doc</emphasis>), debugging
            (<emphasis>-dbg</emphasis>) and development
            (<emphasis>-dev</emphasis>) packages automatically created.</para>
          </listitem>
        </varlistentry>
      </variablelist>

      <para>The various variables that can be used in a recipe are described
      in detail in the recipes chapter of this manual.</para>

      <para>What can you do with this information? How about checking out what
      happened during the configuration of lzo:<screen>~%&gt; less tmp/work/lzo-1.08-r14/temp/log.do_configure.*
...
checking whether ccache sh4-linux-gcc -ml -m4 suffers the -fschedule-insns bug... unknown
checking whether ccache sh4-linux-gcc -ml -m4 suffers the -fstrength-reduce bug... unknown
checking whether ccache sh4-linux-gcc -ml -m4 accepts -fstrict-aliasing... yes
checking the alignment of the assembler... 0
checking whether to build assembler versions... no
configure: creating ./config.status
config.status: creating Makefile
config.status: creating examples/Makefile
config.status: creating include/Makefile
config.status: creating ltest/Makefile
config.status: creating minilzo/Makefile
config.status: creating src/Makefile
config.status: creating tests/Makefile
config.status: creating config.h
config.status: executing depfiles commands</screen></para>

      <para>Or perhaps you want to see which files were included in each of
      the generated packages:<screen>~%&gt; find tmp/work/lzo-1.08-r14/install                
tmp/work/lzo-1.08-r14/install
tmp/work/lzo-1.08-r14/install/lzo-doc
tmp/work/lzo-1.08-r14/install/lzo-dbg
tmp/work/lzo-1.08-r14/install/lzo-dbg/usr
tmp/work/lzo-1.08-r14/install/lzo-dbg/usr/lib
tmp/work/lzo-1.08-r14/install/lzo-dbg/usr/lib/.debug
tmp/work/lzo-1.08-r14/install/lzo-dbg/usr/lib/.debug/liblzo.so.1.0.0
tmp/work/lzo-1.08-r14/install/lzo-dev
tmp/work/lzo-1.08-r14/install/lzo-dev/usr
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo2a.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1y.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1b.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1f.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzoconf.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1x.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo16bit.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1a.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1z.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzoutil.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/include/lzo1c.h
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/lib
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/lib/liblzo.a
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/lib/liblzo.so
tmp/work/lzo-1.08-r14/install/lzo-dev/usr/lib/liblzo.la
tmp/work/lzo-1.08-r14/install/lzo.shlibdeps
tmp/work/lzo-1.08-r14/install/lzo-locale
tmp/work/lzo-1.08-r14/install/lzo
tmp/work/lzo-1.08-r14/install/lzo/usr
tmp/work/lzo-1.08-r14/install/lzo/usr/lib
tmp/work/lzo-1.08-r14/install/lzo/usr/lib/liblzo.so.1
tmp/work/lzo-1.08-r14/install/lzo/usr/lib/liblzo.so.1.0.0</screen></para>
    </section>
  </section>

  <section id="usage_tasks" xreflabel="tasks">
    <title>Tasks</title>

    <para>When you build a software package you generally perform a number of
    steps or tasks. These would include things like "download the source
    code", "unpack the source code", "run the configure script", "build the
    software", "install the software" etc. OpenEmbedded builds software in a
    similar way - by performing a set of tasks. Understanding these tasks is
    critical to understanding how things get done in OpenEmbedded.</para>

    <para></para>

    <para>The following is a list of the most commonly seen tasks:</para>

    <variablelist>
      <varlistentry>
        <term>fetch</term>

        <listitem>
          <para>The fetch task is responsible for fetching any source code
          that is required. This means things such as downloading files and
          checking out from svn or git repositories for example.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>unpack</term>

        <listitem>
          <para>The unpack task is responsible for extracting files from
          archives, such as .tar.gz, into the working area and copying any
          additional files into the working area.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>patch</term>

        <listitem>
          <para>The patch task is responsible for applying any patches to the
          unpacked source code</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>configure</term>

        <listitem>
          <para>The configure task takes care of the configuration of the
          package. Running a configure script ("./configure &lt;options&gt;")
          is probably the form of configuration that is most recognised but
          it's not the only configuration system that exists.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>compile</term>

        <listitem>
          <para>The compile task actually compiles the software. This could be
          as simple as running "make".</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>populate_staging (stage)</term>

        <listitem>
          <para>The populate_staging task (stage is an alternate, easier to
          type name, that can be used to refer to this task) is responsible
          for making available libraries and headers (if any) that may be
          required by other packages to build. For example if you compile zlib
          then it's headers and the library need to be made available for
          other applications to include and link against.</para>

          <para>NOTE that this is different to the install (and packaging)
          related tasks in that this is making available things for use during
          build on the development host while the installed files are being
          made available for use on the target device.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term></term>

        <listitem>
          <para></para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>install</term>

        <listitem>
          <para>The install task is responsible for actually installing the
          software. Now this needs to install the software into the
          destination directory (${D}) but once package the destination
          directory will be removed from all the files. In other words if you
          install something into ${D}/bin then it will end up in the /bin
          directory in the package and therefore on the target.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>package</term>

        <listitem>
          <para>The package task takes the installed files and splits them
          into separate directories under the ${WORKDIR}/install directory,
          one per package. It moves the files for the destination directory,
          ${D}, that they were installed in into the appropriate packages
          subdirectory. Usually there will be a main package a separate
          documentation (-doc), development (-dev) and debugging packages
          (-dbg) for example.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>package_write</term>

        <listitem>
          <para>The package_write task is responsible for taking each packages
          subdirectory and creating any actual installation package, such as
          .ipk, .deb or .rpm.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term></term>

        <listitem>
          <para></para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para></para>

    <para>Note that these are not the only possible set of tasks. There are
    various methods available to insert additional tasks in between existing
    tasks if needed. As an example the insane.bbclass, which performs various
    QA checks, does these checks by inserting a new task, qa_configure,
    between the configure and compile tasks to check on the result of
    configuration and another new tasks, qa_staging, between populate_staging
    and build to validate the files that have been staged.</para>

    <para></para>

    <para>You can see a list of all the tasks available for a specific recipe
    by explicitly calling bitbake on the recipe and asking it for a list of
    tasks:</para>

    <para><screen>~%&gt; bitbake -b packages/perl/perl_5.8.8.bb -c listtasks
NOTE: package perl-5.8.8: started
NOTE: package perl-5.8.8-r11: task do_listtasks: started
do_fetchall
do_listtasks
do_rebuild
do_compile
do_build
do_populate_staging
do_mrproper
do_fetch
do_configure
do_clean
do_package
do_unpack
do_install
do_package_write
do_distribute_sources
do_showdata
do_qa_configure
do_qa_staging
do_patch
NOTE: package perl-5.8.8-r11: task do_listtasks: completed
NOTE: package perl-5.8.8: completed
~%&gt; </screen></para>

    <para>Note that <emphasis>do_</emphasis> prefixed to the tasks - the
    <emphasis>do_&lt;task&gt;</emphasis> is the name of the method that
    implements the required functionality for
    <emphasis>&lt;task&gt;</emphasis>, so the above is actually listing the
    methods that implement the available tasks. It's sometimes a but confusing
    but just remember that the do_ is the method name (with a definition
    usually found in the of the .bbclass files in the classes
    directory.)</para>
  </section>

  <section id="usage_workwithsinglepackage"
           xreflabel="working with a single package">
    <title>Working with a single package</title>

    <para>When working on fixing and/or creating a single recipe you can ask
    bitbake to deal directly with a single .bb file only. The <emphasis>-b
    &lt;bb-file&gt;</emphasis> option asks bitbake to only process the named
    file. Note that this ignores any dependencies that are in the recipe, so
    these must have already been handled.</para>

    <para>A typically example of this is to clean and then rebuild a package
    with some debugging information:</para>

    <para><screen>%&gt; bitbake -b &lt;bb-file&gt; -c clean
%&gt; bitbake -b &lt;bb-file&gt; -D</screen></para>

    <para>The various options to bitbake that are useful here are:</para>

    <variablelist>
      <varlistentry>
        <term>-b &lt;bb-file&gt;</term>

        <listitem>
          <para>Specify which recipe to process;</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>-c &lt;action&gt;</term>

        <listitem>
          <para>Specify which action to perform, typically the name of one of
          the tasks supported by the recipe;</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>-D</term>

        <listitem>
          <para>Display debugging information, use two <emphasis
          role="bold">-D</emphasis>'s for additional debugging.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>-f</term>

        <listitem>
          <para>Force an operation. This is useful in getting bitbake to
          perform some operation it normally wouldn't do. For example, if you
          try and compile twice in a row then bitbake will not do anything on
          the second attempt since it has already performed the compile task.
          By adding <emphasis role="bold">-f</emphasis> it will force it to
          perform the action regardless of if it thinks it's been done
          previously.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para>The most common actions (used with -c) are:</para>

    <variablelist>
      <varlistentry>
        <term>fetch</term>

        <listitem>
          <para>Try to download all of the required source files, but don't do
          anything else with them.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>unpack</term>

        <listitem>
          <para>Unpack the source file but don't apply the patches yet.
          Sometimes you may want to look at the extracted, but not patched
          source code and that's what just unpacking will give you (some
          time's handy to get diffs generated against the original
          source).</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>patch</term>

        <listitem>
          <para>Apply any patches.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>configure</term>

        <listitem>
          <para>Performs and configuration that is required for the
          software.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>compile</term>

        <listitem>
          <para>Perform the actual compilation steps of the software.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>stage</term>

        <listitem>
          <para>If any files, such as header and libraries, will be required
          by other packages then they need to be installed into the staging
          area and that's what this task takes care of.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>install</term>

        <listitem>
          <para>Install the software in preparation for packaging.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>package</term>

        <listitem>
          <para>Package the software. Remember that this moves the files from
          the installation directory, D, into the packing install area. So to
          re-package you also need to re-install first.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term>clean</term>

        <listitem>
          <para>Delete the entire directory for this version of the software.
          Usually done to allow a test build with no chance of old files or
          changes being left behind.</para>
        </listitem>
      </varlistentry>
    </variablelist>

    <para>Note that each of the actions that corresponds to task's will run
    any preceding tasks that have not yet been performed. So starting with
    compile will also perform the fetch, unpack, patch and configure
    actions.</para>

    <para>A typically development session might involve editing files in the
    working directory and recompiling until it all works:<screen>[... test ...]
%&gt; bitbake -b packages/testapp/testapp_4.3.bb -c compile -D

[... save a copy of main.c and make some changes ...]
%&gt; vi tmp/work/testapp-4.3-r0/main.c
%&gt; bitbake -b packages/testapp/testapp_4.3.bb -c compile -D -f

[... create a patch and add it to the recipe ...]
%&gt; vi packages/testapp/testapp_4.3.bb

[... test from clean ...]
%&gt; bitbake -b packages/testapp/testapp_4.3.bb -c clean
%&gt; bitbake -b packages/testapp/testapp_4.3.bb

[... NOTE: How to create the patch is not covered at this point ...]</screen></para>

    <para>Here's another example showing how you might go about fixing up the
    packaging in your recipe:<screen>%&gt; bitbake -b packages/testapp/testapp_4.3.bb -c install -f
%&gt; bitbake -b packages/testapp/testapp_4.3.bb -c stage -f
%&gt; find tmp/work/testapp_4.3/install
...
%&gt; vi packages/testapp/testapp_4.3.bb</screen>At this stage you play with
    the <emphasis role="bold">PACKAGE_</emphasis> and <emphasis
    role="bold">FILES_</emphasis> variables and then repeat the above
    sequence.</para>

    <para>Note how we install and then stage. This is one of those things
    where understanding the tasks helps a lot! Remember that stage moves the
    files from where they were installed (${D}) into the various
    subdirectories (under <emphasis role="bold">${WORKDIR}/instal</emphasis>l)
    for each package. So if you try and run a stage task without a prior
    install there won't be any files there to stage! Note also that the stage
    tasks clears all the subdirectories in <emphasis
    role="bold">${WORKDIR}/install</emphasis> so you won't get any left over
    files. But beware, the install task doesn't clear <emphasis
    role="bold">${D}</emphasis> directory, so any left over files from a
    previous packing attempt will be left behind (which is ok if all you care
    about it staging).</para>
  </section>

  <section id="usage_interactive_bitbake" xreflabel="interactive bitbake">
    <title>Interactive bitbake</title>

    <para>To interactively test things use:<screen>%&gt; bitbake -i</screen>this
    will open the bitbake shell. From here there are a lot of commands
    available (try help).</para>

    <para>First thing you will want to do is parse all of the recipes (recent
    bitbake version do this automatically when needed, so you don't need to
    manually do this anymore):<screen>BB&gt;&gt; parse</screen>You can now
    build a specific recipe:<screen>BB&gt;&gt; build net-snmp</screen>If it
    fails you may want to clean the build before trying again:<screen>BB&gt;&gt; clean net-snmp</screen>If
    you update the recipe by editing the .bb file (to fix some issues) then
    you will want to clean the package, reparse the modified recipe, and the
    build again:<screen>BB&gt;&gt; clean net-snmp
BB&gt;&gt; reparse net-snmp
BB&gt;&gt; build net-snmp</screen>Note that you can use wildcards in the
    bitbake shell as well:<screen>BB&gt;&gt; build t*</screen></para>

    <para></para>
  </section>

  <section id="usage_devshell" xreflabel="devshell">
    <title>Devshell</title>

    <para>[To be done]</para>
  </section>

  <section id="usage_patches" xreflabel="patching">
    <title>Patching and patch management</title>

    <para>[To be done]</para>
  </section>
</chapter>