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overview-manual, mega-manual: Updates to layers discussion for build flow
The "Metadata, Machine Configuratrion, and Policy Configuration" section discusses the three types of layers fed into the OpenEmbedded build system workflow figure. I updated the figures and text supporting this discussion. The figure had to be moved to the mega-manual/figures folder also. (From yocto-docs rev: 39dd671333f7b3df616920aab08e01c926deca1c) Signed-off-by: Scott Rifenbark <srifenbark@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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@@ -580,64 +580,92 @@
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This section takes a closer look at the layers the build system
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uses to further control the build.
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These layers provide Metadata for the software, machine, and
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policy.
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policies.
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</para>
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<para>
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In general, three types of layer input exist:
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In general, three types of layer input exists.
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You can see them below the "User Configuration" box in the
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<link linkend='general-workflow-figure'>general workflow figure</link>:
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<itemizedlist>
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<listitem><para>
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<emphasis>Policy Configuration:</emphasis>
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Distribution Layers provide top-level or general
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policies for the image or SDK being built.
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For example, this layer would dictate whether BitBake
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produces RPM or IPK packages.
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<emphasis>Metadata (<filename>.bb</filename> + Patches):</emphasis>
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Software layers containing user-supplied recipe files,
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patches, and append files.
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A good example of a software layer might be the
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<ulink url='https://github.com/meta-qt5/meta-qt5'><filename>meta-qt5</filename></ulink>
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layer from the
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<ulink url='http://layers.openembedded.org/layerindex/branch/master/layers/'>OpenEmbedded Layer Index</ulink>.
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This layer is for version 5.0 of the popular
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<ulink url='https://wiki.qt.io/About_Qt'>Qt</ulink>
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cross-platform application development framework for
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desktop, embedded and mobile.
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</para></listitem>
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<listitem><para>
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<emphasis>Machine Configuration:</emphasis>
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Board Support Package (BSP) layers provide machine
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<emphasis>Machine BSP Configuration:</emphasis>
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Board Support Package (BSP) layers (i.e. "BSP Layer"
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in the following figure) providing machine-specific
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configurations.
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This type of information is specific to a particular
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target architecture.
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A good example of a BSP layer from the
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<link linkend='gs-reference-distribution-poky'>Poky Reference Distribution</link>
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is the
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<ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-yocto-bsp'><filename>meta-yocto-bsp</filename></ulink>
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layer.
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</para></listitem>
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<listitem><para>
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<emphasis>Metadata:</emphasis>
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Software layers contain user-supplied recipe files,
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patches, and append files.
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<emphasis>Policy Configuration:</emphasis>
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Distribution Layers (i.e. "Distro Layer" in the
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following figure) providing top-level or general
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policies for the images or SDKs being built for a
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particular distribution.
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For example, in the Poky Reference Distribution the
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distro layer is the
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<ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-poky'><filename>meta-poky</filename></ulink>
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layer.
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Within the distro layer is a
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<filename>conf/distro</filename> directory that
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contains distro configuration files (e.g.
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<ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-poky/conf/distro/poky.conf'><filename>poky.conf</filename></ulink>
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that contain many policy configurations for the
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Poky distribution.
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</para></listitem>
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</itemizedlist>
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</para>
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<para>
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The following figure shows an expanded representation of the
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Metadata, Machine Configuration, and Policy Configuration input
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(layers) boxes of the
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The following figure shows an expanded representation of
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these three layers from the
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<link linkend='general-workflow-figure'>general workflow figure</link>:
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</para>
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<para>
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<imagedata fileref="figures/layer-input.png" align="center" width="8in" depth="7.5in" />
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<imagedata fileref="figures/layer-input.png" align="center" width="816px" depth="1056px" scalefit="1" />
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</para>
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<para>
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In general, all layers have a similar structure.
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They all contain a licensing file
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(e.g. <filename>COPYING</filename>) if the layer is to be
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(e.g. <filename>COPYING.MIT</filename>) if the layer is to be
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distributed, a <filename>README</filename> file as good
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practice and especially if the layer is to be distributed, a
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configuration directory, and recipe directories.
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You can learn about the general structure for layers used with
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the Yocto Project in the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#creating-your-own-layer'>Creating Your Own Layer</ulink>"
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section in the Yocto Project Development Tasks Manual.
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For a general discussion on layers and the many layers from
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which you can draw, see the
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"<link linkend='overview-layers'>Layers</link>" and
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"<link linkend='the-yocto-project-layer-model'>The Yocto Project Layer Model</link>"
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sections both earlier in this manual.
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</para>
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<para>
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The Yocto Project has many layers that can be used.
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You can see a web-interface listing of them on the
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If you explored the previous links, you discovered some
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areas where many layers that work with the Yocto Project
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exist.
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The
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<ulink url="http://git.yoctoproject.org/">Source Repositories</ulink>
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page.
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The layers appear at the bottom categorized under
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"Yocto Metadata Layers."
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These layers are fundamentally a subset of the
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<ulink url="http://layers.openembedded.org/layerindex/layers/">OpenEmbedded Layer Index</ulink>,
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which lists all layers provided by the OpenEmbedded community.
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also shows layers categorized under "Yocto Metadata Layers."
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<note>
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Layers exist in the Yocto Project Source Repositories that
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cannot be found in the OpenEmbedded Layer Index.
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@@ -652,12 +680,6 @@
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should be using as part of the build.
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</para>
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<para>
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For more information on layers, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
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section in the Yocto Project Development Tasks Manual.
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</para>
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<section id="distro-layer">
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<title>Distro Layer</title>
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@@ -704,6 +726,16 @@
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to add distribution-specific configuration,
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initialization scripts, custom image recipes,
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and so forth.
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Examples of <filename>recipes-*</filename>
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directories are <filename>recipes-core</filename>
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and <filename>recipes-extra</filename>.
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Hierarchy and contents within a
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<filename>recipes-*</filename> directory can vary.
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Generally, these directories contain recipe files
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(<filename>*.bb</filename>), recipe append files
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(<filename>*.bbappend</filename>), directories
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that are distro-specific for configuration files,
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and so forth.
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</para></listitem>
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</itemizedlist>
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</para>
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@@ -713,7 +745,8 @@
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<title>BSP Layer</title>
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<para>
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The BSP Layer provides machine configurations.
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The BSP Layer provides machine configurations that
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target specific hardware.
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Everything in this layer is specific to the machine for
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which you are building the image or the SDK.
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A common structure or form is defined for BSP layers.
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@@ -738,8 +771,8 @@
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The remainder of the layer is dedicated to specific recipes
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by function: <filename>recipes-bsp</filename>,
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<filename>recipes-core</filename>,
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<filename>recipes-graphics</filename>, and
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<filename>recipes-kernel</filename>.
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<filename>recipes-graphics</filename>,
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<filename>recipes-kernel</filename>, and so forth.
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Metadata can exist for multiple formfactors, graphics
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support systems, and so forth.
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<note>
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@@ -762,8 +795,8 @@
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</para>
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<para>
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This layer contains any new recipes that your project
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needs in the form of recipe files.
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This layer contains any recipes, append files, and
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patches, that your project needs.
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</para>
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</section>
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</section>
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