dev-manual: Read-through edits to "Understanding and Creating Layers".
Some minor edits applied. (From yocto-docs rev: 1897997ad3ef3ada76de77c7fb886fb624dcdfdb) Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark
Richard Purdie
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@ -64,8 +64,8 @@
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the string <filename>meta-</filename>.
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<note>
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It is not a requirement that a layer name begin with the
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prefix <filename>meta-</filename>, but it's a commonly accepted
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standard in the Yocto Project community.
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prefix <filename>meta-</filename>, but it is a commonly
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accepted standard in the Yocto Project community.
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</note>
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For example, when you set up the Source Directory structure,
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you will see several layers:
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@ -194,8 +194,8 @@
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variable then assigns a priority to the layer.
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Applying priorities is useful in situations
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where the same package might appear in multiple
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layers and allows you to choose what layer
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should take precedence.</para></listitem>
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layers and allows you to choose the layer
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that takes precedence.</para></listitem>
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<listitem><para>The
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<filename><ulink url='&YOCTO_DOCS_REF_URL;#var-LAYERVERSION'>LAYERVERSION</ulink></filename>
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variable optionally specifies the version of a
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@ -206,16 +206,17 @@
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variable, which expands to the directory of the current
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layer.</para>
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<para>Through the use of the <filename>BBPATH</filename>
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variable, BitBake locates <filename>.bbclass</filename>
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files, configuration files, and files that are included
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variable, BitBake locates class files
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(<filename>.bbclass</filename>),
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configuration files, and files that are included
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with <filename>include</filename> and
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<filename>require</filename> statements.
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For these cases, BitBake uses the first file that
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matches the name found in <filename>BBPATH</filename>.
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This is similar to the way the <filename>PATH</filename>
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variable is used for binaries.
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We recommend, therefore, that you use unique
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<filename>.bbclass</filename> and configuration
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It is recommended, therefore, that you use unique
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class and configuration
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filenames in your custom layer.</para></listitem>
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<listitem><para><emphasis>Add Content:</emphasis> Depending
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on the type of layer, add the content.
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@ -253,7 +254,8 @@
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configuration.
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In other words, do not copy an entire recipe into your
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layer and then modify it.
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Rather, use <filename>.bbappend</filename> files to override
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Rather, use an append file (<filename>.bbappend</filename>)
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to override
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only those parts of the original recipe you need to modify.
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</para>
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</section>
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@ -263,7 +265,8 @@
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<para>
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Avoid duplicating include files.
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Use <filename>.bbappend</filename> files for each recipe
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Use append files (<filename>.bbappend</filename>)
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for each recipe
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that uses an include file.
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Or, if you are introducing a new recipe that requires
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the included file, use the path relative to the original
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@ -285,7 +288,7 @@
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However, OpenEmbedded's layer <filename>meta-oe</filename>
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does.
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Consequently, <filename>meta-oe</filename> uses
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<filename>.bbappend</filename> files to modify the
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append files to modify the
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<filename>QT_SQL_DRIVER_FLAGS</filename> variable to
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enable the appropriate plug-ins.
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This variable was added to the <filename>qt4.inc</filename>
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@ -392,7 +395,7 @@
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as shown above, put it in
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<filename>meta-one/recipes-core/base-files/base-files/one/</filename>.
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Not only does this make sure the file is used
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only when building for machine "one" but the
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only when building for machine "one", but the
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build process locates the file more quickly.</para>
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<para>In summary, you need to place all files
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referenced from <filename>SRC_URI</filename>
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@ -526,12 +529,12 @@
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"meta" layer at
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<filename>meta/recipes-bsp/formfactor</filename>:
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<literallayout class='monospaced'>
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DESCRIPTION = "Device formfactor information"
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SUMMARY = "Device formfactor information"
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SECTION = "base"
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LICENSE = "MIT"
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LIC_FILES_CHKSUM = "file://${COREBASE}/LICENSE;md5=4d92cd373abda3937c2bc47fbc49d690 \
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file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
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PR = "r41"
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file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"
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PR = "r44"
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SRC_URI = "file://config file://machconfig"
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S = "${WORKDIR}"
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@ -540,12 +543,12 @@
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INHIBIT_DEFAULT_DEPS = "1"
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do_install() {
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# Only install file if it has a contents
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# Only install file if it has a contents
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install -d ${D}${sysconfdir}/formfactor/
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install -m 0644 ${S}/config ${D}${sysconfdir}/formfactor/
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if [ -s "${S}/machconfig" ]; then
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install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
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fi
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if [ -s "${S}/machconfig" ]; then
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install -m 0644 ${S}/machconfig ${D}${sysconfdir}/formfactor/
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fi
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}
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</literallayout>
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In the main recipe, note the
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@ -596,16 +599,22 @@
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<filename>THISDIR</filename>.
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The trailing colon character is important as it ensures that
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items in the list remain colon-separated.
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<note><para>BitBake automatically defines the
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<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
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be searched prior to other paths in the final list.</para>
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<para>Also, not all append files add extra files.
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Many append files simply exist to add build options
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(e.g. <filename>systemd</filename>).
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For these cases, it is not necessary to use the
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"_prepend" part of the statement.</para>
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<note>
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<para>
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BitBake automatically defines the
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<filename>THISDIR</filename> variable.
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You should never set this variable yourself.
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Using "_prepend" ensures your path will
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be searched prior to other paths in the final list.
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</para>
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<para>
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Also, not all append files add extra files.
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Many append files simply exist to add build options
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(e.g. <filename>systemd</filename>).
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For these cases, it is not necessary to use the
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"_prepend" part of the statement.
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</para>
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</note>
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</para>
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</section>
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