documentation/dev-manual/dev-manual-common-tasks.xml: Review comments
Applied the review comments from Paul Eggleton for the new section on "Understanding and Using Layers." (From yocto-docs rev: 6bf5854dd355afdbc01c4c4fb94a4062bd9eae20) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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@ -77,7 +77,8 @@
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you need.
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You can see the
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<ulink url='http://www.openembedded.org/wiki/LayerIndex'><filename>LayerIndex</filename></ulink>
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to determine what types of layers already exist in the Yocto Project.</para></listitem>
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for a list of layers from the OpenEmbedded community that can be used in the
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Yocto Project.</para></listitem>
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<listitem><para><emphasis>Create a Directory:</emphasis> Create the directory
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for your layer.
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Traditionally, prepend the name of the folder with the string
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variable is then appended with the layer name.
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The
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<filename><ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-BBFILE_PATTERN'>BBFILE_PATTERN</ulink></filename>
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variable immediately expands with a regular expression used to match files from
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<filename>BBFILES</filename> into a particular layer, in this case by using
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the base pathname.
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variable is set to a regular expression and is used to match files
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from <filename>BBFILES</filename> into a particular layer.
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In this case, immediate expansion of
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<filename><ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-LAYERDIR'>LAYERDIR</ulink></filename>
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sets <filename>BBFILES_PATTERN</filename> to the layer's path.
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The
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<filename><ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-BBFILE_PRIORITY'>BBFILE_PRIORITY</ulink></filename>
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variable then assigns different priorities to the files in different layers.
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variable then assigns a priority to the layer.
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Applying priorities is useful in situations where the same package might appear in multiple
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layers and allows you to choose what layer should take precedence.</para>
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<para>Note the use of the
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@ -127,8 +130,9 @@
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The <filename>LAYERDIR</filename> variable expands to the directory of the current layer and
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requires the immediate expansion operator so that BitBake does not wait to expand the variable
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when it's parsing a different directory.</para>
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<para>BitBake can locate where other <filename>.bbclass</filename> and configuration files
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are applied through the <filename>BBPATH</filename> environment variable.
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<para>BitBake locates included <filename>.bbclass</filename>, configuration,
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and other files using the <filename>include</filename> and <filename>require</filename>
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statements by way of the <filename>BBPATH</filename> environment variable.
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For these cases, BitBake uses the first file with the matching name found in
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<filename>BBPATH</filename>.
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This is similar to the way the <filename>PATH</filename> variable is used for binaries.
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During the processing of each <filename>conf/layer.conf</filename> file, BitBake adds the
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recipes, classes and configurations contained within the particular layer to the Yocto
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Project.
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To create your own layer, independent of the Yocto Project files,
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simply create a directory with a <filename>conf/layer.conf</filename> file and
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add the directory to your <filename>bblayers.conf</filename> file.
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</para>
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</section>
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This means the original recipe and append file names are version number specific.
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If the underlying recipe is renamed to update to a newer version, the
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corresponding <filename>.bbappend</filename> file must be renamed as well.
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During the build process, BitBake displays warnings on starting if it detects a
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During the build process, BitBake displays an error on starting if it detects a
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<filename>.bbappend</filename> file that does not have an underlying recipe
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with the proper name.
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with a matching name.
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</para>
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<para>
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<literallayout class='monospaced'>
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FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
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</literallayout>
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Using the immediate expansion assignment operator <filename>:=</filename> and the trailing colon
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are important so that the resulting list of pathnames is syntactically correct.
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Using the immediate expansion assignment operator <filename>:=</filename> is important because
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of the reference to <filename>THISDIR</filename>.
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The trailing colon character is important as it ensures that items in the list remain
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colon-separated.
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<note>BitBake automatically defines the <filename>THISDIR</filename> variable.
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You should never set this variable yourself.
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Using <filename>_prepend</filename> ensures your path will be searched prior to other
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Use the following form when running the layer management tool.
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<literallayout class='monospaced'>
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$ bitbake-layers <command> [arguments]
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Available commands:
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flatten
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flattens layer configuration into a separate output directory.
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help
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display general help or help on a specified command
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show_appends
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list bbappend files and recipe files they apply to
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show_layers
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show current configured layers
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show_overlayed
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list overlayed recipes (where there is a recipe in another layer that has a higher layer priority)
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help
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display general help or help on a specified command
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</literallayout>
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</para>
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<para>
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The following list describes the available commands:
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<itemizedlist>
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<listitem><para><filename><emphasis>flatten:</emphasis></filename>
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Flattens the layer configuration into a separate output directory.
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Flattening your layer configuration builds a "flattened" directory that contains
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the contents of all layers, with any overlayed recipes removed and any
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recipe append files (<filename>.bbappend</filename>) appended to the corresponding recipes.
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Only the lowest priority layer's <filename>layer.conf</filename> is used.
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</para></listitem>
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<listitem><para>Overridden and appended items from <filename>.bbappend</filename>
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files never need to be cleaned up.</para></listitem>
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files need to be cleaned up.
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For example, the contents of each <filename>.bbappend</filename> end up in the
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flattened recipe.
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However, if there are appended or changed variable values, you need to tidy
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these up yourself.</para></listitem>
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</itemizedlist></para></listitem>
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<listitem><para><filename><emphasis>help:</emphasis></filename>
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Displays general help or help on a specified command.</para></listitem>
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<listitem><para><filename><emphasis>show_appends:</emphasis></filename>
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Lists <filename>.bbappend</filename> files and the recipe files to which
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they apply.</para></listitem>
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<listitem><para><filename><emphasis>show_layers:</emphasis></filename>
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Show the current configured layers.</para></listitem>
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<listitem><para><filename><emphasis>show_overlayed:</emphasis></filename>
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Lists overlayed recipes.
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Overlayed recipes appear in another layer that has a higher layer priority.
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</para></listitem>
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</itemizedlist>
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</para>
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</section>
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