1207 lines
58 KiB
XML
1207 lines
58 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='closer-look'>
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<title>A Closer Look at the Yocto Project Development Environment</title>
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<para>
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This chapter takes a more detailed look at the Yocto Project
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development environment.
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The following diagram represents the development environment at a
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high level.
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The remainder of this chapter expands on the fundamental input, output,
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process, and
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<ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>) blocks
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in the Yocto Project development environment.
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</para>
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<para id='general-yocto-environment-figure'>
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<imagedata fileref="figures/yocto-environment-ref.png" align="center" width="8in" depth="4.25in" />
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</para>
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<para>
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The generalized Yocto Project Development Environment consists of
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several functional areas:
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<itemizedlist>
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<listitem><para><emphasis>User Configuration:</emphasis>
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Metadata you can use to control the build process.
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</para></listitem>
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<listitem><para><emphasis>Metadata Layers:</emphasis>
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Various layers that provide software, machine, and
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distro Metadata.</para></listitem>
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<listitem><para><emphasis>Source Files:</emphasis>
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Upstream releases, local projects, and SCMs.</para></listitem>
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<listitem><para><emphasis>Build System:</emphasis>
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Processes under the control of BitBake.
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This block expands on how BitBake fetches source, applies
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patches, completes compilation, analyzes output for package
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generation, creates and tests packages, generates images, and
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generates cross-development tools.</para></listitem>
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<listitem><para><emphasis>Package Feeds:</emphasis>
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Directories containing output packages (rpm, deb or ipk),
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which are subsequently used in the construction of an image or
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SDK, produced by the build system.
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These feeds can also be copied and shared using a web server or
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other means to facilitate extending or updating existing
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images on devices at runtime if runtime package management is
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enabled.</para></listitem>
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<listitem><para><emphasis>Images:</emphasis>
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Images produced by the development process.
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Where do they go?
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Can you mess with them (i.e. freely delete them or move them?).
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</para></listitem>
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<listitem><para><emphasis>Application Development SDK:</emphasis>
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Cross-development tools that are produced along with an image
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or separately with BitBake.</para></listitem>
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</itemizedlist>
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</para>
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<section id="user-configuration">
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<title>User Configuration</title>
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<para>
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User configuration helps define the build.
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Through user configuration, you can tell BitBake the
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target architecture for which you are building the image,
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where to store downloaded source, and other build properties.
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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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"User Configuration" box of the
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<link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>:
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</para>
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<para>
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<imagedata fileref="figures/user-configuration.png" align="center" width="5.5in" depth="3.5in" />
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</para>
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<para>
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BitBake needs some basic configuration files in order to complete
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a build.
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These files are <filename>*.conf</filename> files.
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The minimally necessary ones reside as example files in the
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<ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
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For simplicity, this section refers to the Source Directory as
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the "Poky Directory."
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</para>
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<para>
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When you clone the <filename>poky</filename> Git repository or you
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download and unpack a Yocto Project release, you can set up the
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Source Directory to be named anything you want.
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For this discussion, the cloned repository uses the default
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name <filename>poky</filename>.
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<note>
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The Poky repository is primarily an aggregation of existing
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repositories.
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It is not a canonical upstream source.
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</note>
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</para>
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<para>
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The <filename>meta-yocto</filename> layer inside Poky contains
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a <filename>conf</filename> directory that has example
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configuration files.
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These example files are used as a basis for creating actual
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configuration files when you source the build environment
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script
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(i.e.
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<link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>
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or
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<link linkend='structure-memres-core-script'><filename>oe-init-build-env-memres</filename></link>).
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</para>
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<para>
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Sourcing the build environment script creates a
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<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>
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if one does not already exist.
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BitBake uses the Build Directory for all its work during builds.
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The Build Directory has a <filename>conf</filename> directory that
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contains default versions of your <filename>local.conf</filename>
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and <filename>bblayers.conf</filename> configuration files.
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These default configuration files are created only if versions
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do not already exist in the Build Directory at the time you
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source the build environment setup script.
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</para>
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<para>
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Because the Poky repository is fundamentally an aggregation of
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existing repositories, some users might be familiar with running
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the <filename>&OE_INIT_FILE;</filename> or
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<filename>oe-init-build-env-memres</filename> script in the context
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of separate OpenEmbedded-Core and BitBake repositories rather than a
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single Poky repository.
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This discussion assumes the script is executed from within a cloned
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or unpacked version of Poky.
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</para>
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<para>
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Depending on where the script is sourced, different sub-scripts
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are called to set up the Build Directory (Yocto or OpenEmbedded).
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Specifically, the script
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<filename>scripts/oe-setup-builddir</filename> inside the
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poky directory sets up the Build Directory and seeds the directory
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(if necessary) with configuration files appropriate for the
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Yocto Project development environment.
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<note>
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The <filename>scripts/oe-setup-builddir</filename> script
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uses the <filename>$TEMPLATECONF</filename> variable to
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determine which sample configuration files to locate.
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</note>
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</para>
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<para>
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The <filename>local.conf</filename> file provides many
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basic variables that define a build environment.
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Here is a list of a few.
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To see the default configurations in a <filename>local.conf</filename>
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file created by the build environment script, see the
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<filename>local.conf.sample</filename> in the
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<filename>meta-yocto</filename> layer:
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<itemizedlist>
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<listitem><para><emphasis>Parallelism Options:</emphasis>
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Controlled by the
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<link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>
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and
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<link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>
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variables.</para></listitem>
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<listitem><para><emphasis>Target Machine Selection:</emphasis>
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Controlled by the
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<link linkend='var-MACHINE'><filename>MACHINE</filename></link>
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variable.</para></listitem>
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<listitem><para><emphasis>Download Directory:</emphasis>
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Controlled by the
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<link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
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variable.</para></listitem>
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<listitem><para><emphasis>Shared State Directory:</emphasis>
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Controlled by the
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<link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link>
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variable.</para></listitem>
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<listitem><para><emphasis>Build Output:</emphasis>
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Controlled by the
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<link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>
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variable.</para></listitem>
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</itemizedlist>
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<note>
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Configurations set in the <filename>conf/local.conf</filename>
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file can also be set in the
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<filename>conf/site.conf</filename> and
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<filename>conf/auto.conf</filename> configuration files.
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</note>
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</para>
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<para>
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The <filename>bblayers.conf</filename> file tells BitBake what
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layers you want considered during the build.
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By default, the layers listed in this file include layers
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minimally needed by the build system.
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However, you must manually add any custom layers you have created.
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You can find more information on working with the
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<filename>bblayers.conf</filename> file in the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#enabling-your-layer'>Enabling Your Layer</ulink>"
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section in the Yocto Project Development Manual.
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</para>
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<para>
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The files <filename>site.conf</filename> and
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<filename>auto.conf</filename> are not created by the environment
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initialization script.
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If you want these configuration files, you must create them
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yourself:
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<itemizedlist>
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<listitem><para><emphasis><filename>site.conf</filename>:</emphasis>
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You can use the <filename>conf/site.conf</filename>
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configuration file to configure multiple build directories.
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For example, suppose you had several build environments and
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they shared some common features.
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You can set these default build properties here.
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A good example is perhaps the level of parallelism you want
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to use through the
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<link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>
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and
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<link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>
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variables.</para>
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<para>One useful scenario for using the
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<filename>conf/site.conf</filename> file is to extend your
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>
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variable to include the path to a
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<filename>conf/site.conf</filename>.
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Then, when BitBake looks for Metadata using
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<filename>BBPATH</filename>, it finds the
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<filename>conf/site.conf</filename> file and applies your
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common configurations found in the file.
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To override configurations in a particular build directory,
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alter the similar configurations within that build
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directory's <filename>conf/local.conf</filename> file.
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</para></listitem>
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<listitem><para><emphasis><filename>auto.conf</filename>:</emphasis>
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This file is not hand-created.
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Rather, the file is usually created and written to by
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an autobuilder.
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The settings put into the file are typically the same as
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you would find in the <filename>conf/local.conf</filename>
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or the <filename>conf/site.conf</filename> files.
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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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You can edit all configuration files to further define
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any particular build environment.
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This process is represented by the "User Configuration Edits"
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box in the figure.
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</para>
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<para>
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When you launch your build with the
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<filename>bitbake <target></filename> command, BitBake
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sorts out the configurations to ultimately define your build
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environment.
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</para>
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</section>
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<section id="metadata-machine-configuration-and-policy-configuration">
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<title>Metadata, Machine Configuration, and Policy Configuration</title>
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<para>
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The previous section described the user configurations that
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define the BitBake's global behavior.
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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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</para>
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<para>
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In general, three types of layer input exist:
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<itemizedlist>
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<listitem><para><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.</para></listitem>
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<listitem><para><emphasis>Machine Configuration:</emphasis>
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Board Support Package (BSP) layers provide machine
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configurations.
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This type of information is specific to a particular
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target architecture.</para></listitem>
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<listitem><para><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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</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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<link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment 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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</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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distributed, a <filename>README</filename> file as good practice
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and especially if the layer is to be distributed, a
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configuration directory, and recipe directories.
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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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<ulink url="http://git.yoctoproject.org/">Source Repositories</ulink>
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page.
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The layers are shown 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 Metadata Index</ulink>,
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which lists all layers provided by the OpenEmbedded community.
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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 Metadata Index.
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These layers are either deprecated or experimental in nature.
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</note>
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</para>
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<para>
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BitBake uses the <filename>conf/bblayers.conf</filename> file,
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which is part of the user configuration, to find what layers it
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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 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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<para>
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The distribution layer provides policy configurations for your
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distribution.
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Best practices dictate that you isolate these types of
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configurations into their own layer.
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Settings you provide in
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<filename>conf/<distro>.conf</filename> override similar
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settings that BitBake finds in your
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<filename>conf/local.conf</filename> file in the Build
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Directory.
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</para>
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<para>
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The following list provides some explanation and references
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for what you typically find in the distribution layer:
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<itemizedlist>
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<listitem><para><emphasis>classes:</emphasis>
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Class files (<filename>.bbclass</filename>) holds
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common functionality that can be shared among
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recipes in the distribution.
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When your recipes inherit a class, they take on the
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settings and functions for that class.
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You can read more about class files in the
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"<link linkend='ref-classes'>Classes</link>" section.
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</para></listitem>
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<listitem><para><emphasis>conf:</emphasis>
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This area holds configuration files for the
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layer (<filename>conf/layer.conf</filename>),
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the distribution
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(<filename>conf/distro/<distro>.conf</filename>),
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and any distribution-wide include files.
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</para></listitem>
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<listitem><para><emphasis>recipes-*:</emphasis>
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Recipes and append files that affect common
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functionality across the distribution.
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This area could include recipes and append files to
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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.</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id="bsp-layer">
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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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Everything in this layer is specific to the machine for which
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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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You can learn more about this structure in the
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<ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
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<note>
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In order for a BSP layer to be considered compliant with the
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Yocto Project, it must meet some structural requirements.
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</note>
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</para>
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<para>
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The BSP Layer's configuration directory contains
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configuration files for the machine
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(<filename>conf/machine/<machine>.conf</filename>) and,
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of course, the layer (<filename>conf/layer.conf</filename>).
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</para>
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<para>
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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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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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While the figure shows several <filename>recipe-*</filename>
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directories, not all these directories appear in all
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BSP layers.
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</note>
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</para>
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</section>
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<section id="software-layer">
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<title>Software Layer</title>
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<para>
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The software layer provides the Metadata for additional
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software packages used during the build.
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This layer does not include Metadata that is specific to the
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distribution or the machine, which are found in their
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respective layers.
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</para>
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<para>
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This layer contains any new recipes that your project needs
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in the form of recipe files.
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</para>
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</section>
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</section>
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<section id="sources-dev-environment">
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<title>Sources</title>
|
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|
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<para>
|
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In order for the OpenEmbedded build system to create an image or
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any target, it must be able to access source files.
|
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The
|
|
<link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>
|
|
represents source files using the "Upstream Project Releases",
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"Local Projects", and "SCMs (optional)" boxes.
|
|
The figure represents mirrors, which also play a role in locating
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source files, with the "Source Mirror(s)" box.
|
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</para>
|
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<para>
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The method by which source files are ultimately organized is
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a function of the project.
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For example, for released software, projects tend to use tarballs
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or other archived files that can capture the state of a release
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guaranteeing that it is statically represented.
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On the other hand, for a project that is more dynamic or
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experimental in nature, a project might keep source files in a
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repository controlled by a Source Control Manager (SCM) such as
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Git.
|
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Pulling source from a repository allows you to control
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the point in the repository (the revision) from which you want to
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build software.
|
|
Finally, a combination of the two might exist, which would give the
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consumer a choice when deciding where to get source files.
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</para>
|
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<para>
|
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BitBake uses the
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<link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
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variable to point to source files regardless of their location.
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Each recipe must have a <filename>SRC_URI</filename> variable
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that points to the source.
|
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</para>
|
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<para>
|
|
Another area that plays a significant role in where source files
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comes from is pointed to by the
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<link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
|
|
variable.
|
|
This area is a cache that can hold previously downloaded source.
|
|
Judicious use of a <filename>DL_DIR</filename> directory can
|
|
save the build system a trip across the Internet when looking
|
|
for files.
|
|
A good method for using a download directory is to have
|
|
<filename>DL_DIR</filename> point to an area outside of your
|
|
Build Directory.
|
|
Doing so allows you to safely delete the Build Directory
|
|
if needed without fear of removing any downloaded source file.
|
|
</para>
|
|
|
|
<para>
|
|
The remainder of this section provides a deeper look into the
|
|
source files and the mirrors.
|
|
Here is a more detailed look at the source file area of the
|
|
base figure:
|
|
<imagedata fileref="figures/source-input.png" align="center" width="7in" depth="7.5in" />
|
|
</para>
|
|
|
|
<section id='upstream-project-releases'>
|
|
<title>Upstream Project Releases</title>
|
|
|
|
<para>
|
|
Upstream project releases exist anywhere in the form of an
|
|
archived file (e.g. tarball or zip file).
|
|
These files correspond to individual recipes.
|
|
For example, the figure uses specific releases each for
|
|
BusyBox, Qt, and Dbus.
|
|
An archive file can be for any released product that can be
|
|
built using a recipe.
|
|
</para>
|
|
</section>
|
|
|
|
<section id='local-projects'>
|
|
<title>Local Projects</title>
|
|
|
|
<para>
|
|
Local projects are custom bits of software the user provides.
|
|
These bits reside somewhere local to a project - perhaps
|
|
a directory into which the user checks in items (e.g.
|
|
a local directory containing a development source tree
|
|
used by the group).
|
|
</para>
|
|
|
|
<para>
|
|
The canonical method through which to include a local project
|
|
is to use the
|
|
<link linkend='ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></link>
|
|
class to include local project.
|
|
You use either the <filename>local.conf</filename> or a
|
|
recipe's append file to override or set the
|
|
recipe to point to the local directory on your disk to pull
|
|
in the whole source tree.
|
|
</para>
|
|
|
|
<para>
|
|
For information on how to use the
|
|
<filename>externalsrc.bbclass</filename>, see the
|
|
"<link linkend='ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></link>"
|
|
section.
|
|
</para>
|
|
</section>
|
|
|
|
<section id='scms'>
|
|
<title>Source Control Managers (Optional)</title>
|
|
|
|
<para>
|
|
Another place the build system can get source files from is
|
|
through an SCM such as Git or Subversion.
|
|
In this case, a repository is cloned or checked out.
|
|
The <filename>do_fetch</filename> task inside BitBake uses
|
|
the <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
|
|
variable and the argument's prefix to determine the correct
|
|
fetcher module.
|
|
</para>
|
|
|
|
<para>
|
|
When fetching a repository, BitBake uses the
|
|
<link linkend='var-SRCREV'><filename>SRCREV</filename></link>
|
|
variable to determine the specific revision from which to
|
|
build.
|
|
</para>
|
|
</section>
|
|
|
|
<section id='source-mirrors'>
|
|
<title>Source Mirror(s)</title>
|
|
|
|
<para>
|
|
Two kinds of mirrors exist: pre-mirrors and regular mirrors.
|
|
The <link linkend='var-PREMIRRORS'><filename>PREMIRRORS</filename></link>
|
|
and
|
|
<link linkend='var-MIRRORS'><filename>MIRRORS</filename></link>
|
|
variables point to these, respectively.
|
|
BitBake checks pre-mirrors before looking upstream for any
|
|
source files.
|
|
Pre-mirrors are appropriate when you have a shared directory
|
|
that is not a directory defined by the
|
|
<link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
|
|
variable.
|
|
A Pre-mirror typically points to a shared directory that is
|
|
local to your organization.
|
|
</para>
|
|
|
|
<para>
|
|
Regular mirrors can be any site across the Internet that is
|
|
used as an alternative location for source code should the
|
|
primary site not be functioning for some reason or another.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id="package-feeds-dev-environment">
|
|
<title>Package Feeds</title>
|
|
|
|
<para>
|
|
When the OpenEmbedded build system generates an image or an SDK,
|
|
it gets the packages from a package feed area located in the
|
|
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
|
|
The
|
|
<link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>
|
|
shows this package feeds area in the upper-right corner.
|
|
</para>
|
|
|
|
<para>
|
|
This section looks a little closer into the package feeds area used
|
|
by the build system.
|
|
Here is a more detailed look at the area:
|
|
<imagedata fileref="figures/package-feeds.png" align="center" width="7in" depth="6in" />
|
|
</para>
|
|
|
|
<para>
|
|
Package feeds are an intermediary step in the build process.
|
|
BitBake generates packages whose type is defined by the
|
|
<link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link>
|
|
variable.
|
|
Before placing the packages into package feeds,
|
|
the build process validates them with generated output quality
|
|
assurance checks through the
|
|
<link linkend='ref-classes-insane'><filename>insane.bbclass</filename></link>
|
|
class.
|
|
</para>
|
|
|
|
<para>
|
|
The package feed area resides in
|
|
<filename>tmp/deploy</filename> of the Build Directory.
|
|
Folders are created that correspond to the package type
|
|
(IPK, DEB, or RPM) created.
|
|
Further organization is derived through the value of the
|
|
<link linkend='var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></link>
|
|
variable for each package.
|
|
For example, packages can exist for the i586 or qemux86
|
|
architectures.
|
|
The package files themselves reside within the appropriate
|
|
architecture folder.
|
|
</para>
|
|
|
|
<para>
|
|
BitBake uses the <filename>do_package_write_*</filename> task to
|
|
place generated packages into the package holding area (e.g.
|
|
<filename>do_package_write_ipk</filename> for IPK packages).
|
|
</para>
|
|
</section>
|
|
|
|
<section id='bitbake-dev-environment'>
|
|
<title>BitBake</title>
|
|
|
|
<para>
|
|
The OpenEmbedded build system uses BitBake to produce images.
|
|
You can see from the
|
|
<link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>,
|
|
the BitBake area consists of several functional areas.
|
|
This section takes a closer look at each of those areas.
|
|
</para>
|
|
|
|
<section id='source-fetching-dev-environment'>
|
|
<title>Source Fetching</title>
|
|
|
|
<para>
|
|
The first stages of building a recipe are to fetch and unpack
|
|
the source code:
|
|
<imagedata fileref="figures/source-fetching.png" align="center" width="6.5in" depth="5in" />
|
|
</para>
|
|
|
|
<para>
|
|
The <filename>do_fetch</filename> and
|
|
<filename>do_unpack</filename> tasks fetch the source files
|
|
and unpack them into a working directory.
|
|
By default, everything is accomplished in the
|
|
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>,
|
|
which has a defined structure.
|
|
For additional general information on the Build Directory,
|
|
see the
|
|
"<link linkend='structure-core-build'><filename>build/</filename></link>"
|
|
section.
|
|
</para>
|
|
|
|
<para>
|
|
Unpacked source source files are pointed to by the
|
|
<link linkend='var-S'><filename>S</filename></link> variable.
|
|
Each recipe has an area in the Build Directory where the
|
|
unpacked source code resides.
|
|
The name of directory for any given recipe is defined from
|
|
several different variables.
|
|
You can see the variables that define these directories
|
|
by looking at the figure:
|
|
<itemizedlist>
|
|
<listitem><para><link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-TARGET_OS'><filename>TARGET_OS</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-PN'><filename>PN</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-PV'><filename>PV</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-PR'><filename>PR</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-S'><filename>S</filename></link>
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
Briefly, the <filename>S</filename> directory contains the
|
|
unpacked source files for a recipe.
|
|
The <filename>WORKDIR</filename> directory is where all the
|
|
building goes on for a given recipe.
|
|
</para>
|
|
</section>
|
|
|
|
<section id='patching-dev-environment'>
|
|
<title>Patching</title>
|
|
|
|
<para>
|
|
Once source code is fetched and unpacked, BitBake locates
|
|
patch files and applies them to the source files:
|
|
<imagedata fileref="figures/patching.png" align="center" width="6in" depth="5in" />
|
|
</para>
|
|
|
|
<para>
|
|
The <filename>do_patch</filename> task processes recipes by
|
|
using the
|
|
<link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
|
|
variable to locate applicable patch files, which by default
|
|
are <filename>*.patch</filename> or
|
|
<filename>*.diff</filename> files, or any file if
|
|
"apply=yes" is specified for the file in
|
|
<filename>SRC_URI</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
BitBake finds and applies multiple patches for a single recipe
|
|
in the order in which it finds the patches.
|
|
Patches are applied to the recipe's source files located in the
|
|
<link linkend='var-S'><filename>S</filename></link> directory.
|
|
</para>
|
|
|
|
<para>
|
|
For more information on how the source directories are
|
|
created, see the
|
|
"<link linkend='source-fetching-dev-environment'>Source Fetching</link>"
|
|
section.
|
|
</para>
|
|
</section>
|
|
|
|
<section id='configuration-and-compilation-dev-environment'>
|
|
<title>Configuration and Compilation</title>
|
|
|
|
<para>
|
|
After source code is patched, BitBake executes tasks that
|
|
configure and compile the source code:
|
|
<imagedata fileref="figures/configuration-compile-autoreconf.png" align="center" width="7in" depth="5in" />
|
|
</para>
|
|
|
|
<para>
|
|
This step in the build process consists of three tasks:
|
|
<itemizedlist>
|
|
<listitem><para><emphasis><filename>do_configure</filename>:</emphasis>
|
|
This task configures the source by enabling and
|
|
disabling any build-time and configuration options for
|
|
the software being built.
|
|
Configurations can come from the recipe itself as well
|
|
as from an inherited class.
|
|
Additionally, the software itself might configure itself
|
|
depending on the target for which it is being built.
|
|
</para>
|
|
|
|
<para>The configurations handled by the
|
|
<filename>do_configure</filename> task are specific
|
|
to source code configuration for the source code
|
|
being built by the recipe.</para>
|
|
|
|
<para>If you are using
|
|
<link linkend='ref-classes-autotools'><filename>autotools.bbclass</filename></link>,
|
|
you can add additional configuration options by using
|
|
the <link linkend='var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></link>
|
|
variable.
|
|
For information on how this variable works within
|
|
that class, see the
|
|
<filename>meta/classes/autotools.bbclass</filename>.
|
|
</para></listitem>
|
|
<listitem><para><emphasis><filename>do_compile</filename>:</emphasis>
|
|
Once a configuration task has been satisfied, BitBake
|
|
compiles the source using the
|
|
<filename>do_compile</filename> task.
|
|
Compilation occurs in the directory pointed to by the
|
|
<link linkend='var-B'><filename>B</filename></link>
|
|
variable.
|
|
Realize that the <filename>B</filename> directory, by
|
|
default, is the same as the
|
|
<link linkend='var-S'><filename>S</filename></link>
|
|
directory.</para></listitem>
|
|
<listitem><para><emphasis><filename>do_install</filename>:</emphasis>
|
|
Once compilation is done, BitBake executes the
|
|
<filename>do_install</filename> task.
|
|
This task copies files from the <filename>B</filename>
|
|
directory and places them in a holding area pointed to
|
|
by the
|
|
<link linkend='var-D'><filename>D</filename></link>
|
|
variable.</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='package-splitting-dev-environment'>
|
|
<title>Package Splitting</title>
|
|
|
|
<para>
|
|
After source code is configured and compiled, the
|
|
OpenEmbedded build system analyzes
|
|
the results and splits the output into packages:
|
|
<imagedata fileref="figures/analysis-for-package-splitting.png" align="center" width="7in" depth="7in" />
|
|
</para>
|
|
|
|
<para>
|
|
The <filename>do_package</filename> and
|
|
<filename>do_packagedata</filename> tasks combine to analyze
|
|
the files found in the
|
|
<link linkend='var-D'><filename>D</filename></link> directory
|
|
and split them into subsets based on available packages and
|
|
files.
|
|
The analyzing process involves the following as well as other
|
|
items: splitting out debugging symbols,
|
|
looking at shared library dependencies between packages,
|
|
and looking at package relationships.
|
|
The <filename>do_packagedata</filename> task creates package
|
|
metadata based on the analysis such that the
|
|
OpenEmbedded build system can generate the final packages.
|
|
Working, staged, and intermediate results of the analysis
|
|
and package splitting process use these areas:
|
|
<itemizedlist>
|
|
<listitem><para><link linkend='var-PKGD'><filename>PKGD</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-PKGDESTWORK'><filename>PKGDESTWORK</filename></link>
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-PKGDEST'><filename>PKGDEST</filename></link>
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
The <link linkend='var-FILES'><filename>FILES</filename></link>
|
|
variable defines the files that go into each package in
|
|
<link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>.
|
|
If you want details on how this is accomplished, you can
|
|
look at
|
|
<link linkend='ref-classes-package'><filename>package.bbclass</filename></link>.
|
|
</para>
|
|
|
|
<para>
|
|
Depending on the type of packages being created (RPM, DEB, or
|
|
IPK), the <filename>do_package_write_*</filename> task
|
|
creates the actual packages and places them in the
|
|
Package Feed area, which is
|
|
<filename>${TMPDIR}/deploy</filename>.
|
|
You can see the
|
|
"<link linkend='package-feeds-dev-environment'>Package Feeds</link>"
|
|
section for more detail on that part of the build process.
|
|
<note>
|
|
Support for creating feeds directly from the
|
|
<filename>deploy/*</filename> directories does not exist.
|
|
Creating such feeds usually requires some kind of feed
|
|
maintenance mechanism that would upload the new packages
|
|
into an official package feed (e.g. the
|
|
Ångström distribution).
|
|
This functionality is highly distribution-specific
|
|
and thus is not provided out of the box.
|
|
</note>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='image-generation-dev-environment'>
|
|
<title>Image Generation</title>
|
|
|
|
<para>
|
|
Once packages are split and stored in the Package Feeds area,
|
|
the OpenEmbedded build system uses BitBake to generate the
|
|
root filesystem image:
|
|
<imagedata fileref="figures/image-generation.png" align="center" width="6in" depth="7in" />
|
|
</para>
|
|
|
|
<para>
|
|
The image generation process consists of several stages and
|
|
depends on many variables.
|
|
The <filename>do_rootfs</filename> task uses these key variables
|
|
to help create the list of packages to actually install:
|
|
<itemizedlist>
|
|
<listitem><para><link linkend='var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></link>:
|
|
Lists out the base set of packages to install from
|
|
the Package Feeds area.</para></listitem>
|
|
<listitem><para><link linkend='var-PACKAGE_EXCLUDE'><filename>PACKAGE_EXCLUDE</filename></link>:
|
|
Specifies packages that should not be installed.
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></link>:
|
|
Specifies features to include in the image.
|
|
Most of these features map to additional packages for
|
|
installation.</para></listitem>
|
|
<listitem><para><link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link>:
|
|
Specifies the package backend to use and consequently
|
|
helps determine where to locate packages within the
|
|
Package Feeds area.</para></listitem>
|
|
<listitem><para><link linkend='var-IMAGE_LINGUAS'><filename>IMAGE_LINGUAS</filename></link>:
|
|
Determines the language(s) for which additional
|
|
language support packages are installed.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
Package installation is under control of the package manager
|
|
(e.g. smart/rpm, opkg, or apt/dpkg) regardless of whether or
|
|
not package management is enabled for the target.
|
|
At the end of the process, if package management is not
|
|
enabled for the target, the package manager's data files
|
|
are deleted from the root filesystem.
|
|
</para>
|
|
|
|
<para>
|
|
During image generation, the build system attempts to run
|
|
all post installation scripts.
|
|
Any that fail to run on the build host are run on the
|
|
target when the target system is first booted.
|
|
If you are using a
|
|
<ulink url='&YOCTO_DOCS_DEV_URL;#creating-a-read-only-root-filesystem'>read-only root filesystem</ulink>,
|
|
all the post installation scripts must succeed during the
|
|
package installation phase since the root filesystem cannot be
|
|
written into.
|
|
</para>
|
|
|
|
<para>
|
|
During Optimization, optimizing processes are run across
|
|
the image.
|
|
These processes include <filename>mklibs</filename> and
|
|
<filename>prelink</filename>.
|
|
The <filename>mklibs</filename> process optimizes the size
|
|
of the libraries.
|
|
A <filename>prelink</filename> process optimizes the dynamic
|
|
linking of shared libraries to reduce start up time of
|
|
executables.
|
|
</para>
|
|
|
|
<para>
|
|
Part of the image generation process includes compressing the
|
|
root filesystem image.
|
|
Compression is accomplished through several optimization
|
|
routines designed to reduce the overall size of the image.
|
|
</para>
|
|
|
|
<para>
|
|
After the root filesystem has been constructed, the image
|
|
generation process turns everything into an image file or
|
|
a set of image files.
|
|
The formats used for the root filesystem depend on the
|
|
<link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link>
|
|
variable.
|
|
</para>
|
|
|
|
<note>
|
|
The entire image generation process is run under Pseudo.
|
|
Running under Pseudo ensures that the files in the root
|
|
filesystem have correct ownership.
|
|
</note>
|
|
</section>
|
|
|
|
<section id='sdk-generation-dev-environment'>
|
|
<title>SDK Generation</title>
|
|
|
|
<para>
|
|
The OpenEmbedded build system uses BitBake to generate the
|
|
Software Development Kit (SDK) installer script:
|
|
<imagedata fileref="figures/sdk-generation.png" align="center" width="6in" depth="7in" />
|
|
</para>
|
|
|
|
<note>
|
|
For more information on the cross-development toolchain
|
|
generation, see the
|
|
"<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>"
|
|
section.
|
|
</note>
|
|
|
|
<para>
|
|
Like image generation, the SDK script process consists of
|
|
several stages and depends on many variables.
|
|
The <filename>do_populate_sdk</filename> task uses these
|
|
key variables to help create the list of packages to actually
|
|
install.
|
|
For information on the variables listed in the figure, see the
|
|
"<link linkend='sdk-dev-environment'>Application Development SDK</link>"
|
|
section.
|
|
</para>
|
|
|
|
<para>
|
|
The <filename>do_populate_sdk</filename> task handles two
|
|
parts: a target part and a host part.
|
|
The target part is the part built for the target hardware and
|
|
includes libraries and headers.
|
|
The host part is the part of the SDK that runs on the
|
|
<link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>.
|
|
</para>
|
|
|
|
<para>
|
|
Once both parts are constructed, the
|
|
<filename>do_populate_sdk</filename> task performs some cleanup
|
|
on both parts.
|
|
After the cleanup, the task creates a cross-development
|
|
environment setup script and any configuration files that
|
|
might be needed.
|
|
</para>
|
|
|
|
<para>
|
|
The final output of the task is the Cross-development
|
|
toolchain installation script (<filename>.sh</filename> file),
|
|
which includes the environment setup script.
|
|
</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section id='images-dev-environment'>
|
|
<title>Images</title>
|
|
|
|
<para>
|
|
The images produced by the OpenEmbedded build system
|
|
are compressed forms of the
|
|
root filesystems that are ready to boot on a target device.
|
|
You can see from the
|
|
<link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>
|
|
that BitBake output in part consists of images.
|
|
This section is going to look more closely at this output:
|
|
<imagedata fileref="figures/images.png" align="center" width="5.5in" depth="5.5in" />
|
|
</para>
|
|
|
|
<para>
|
|
For a list of example images that the Yocto Project provides,
|
|
the
|
|
"<link linkend='ref-images'>Images</link>" chapter.
|
|
</para>
|
|
|
|
<para>
|
|
Images are written out to the
|
|
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>
|
|
inside the <filename>deploy/images/<machine>/</filename>
|
|
folder as shown in the figure.
|
|
This folder contains any files expected to be loaded on the
|
|
target device.
|
|
The
|
|
<link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>
|
|
variable points to the <filename>deploy</filename> directory,
|
|
while the
|
|
<link linkend='var-DEPLOY_DIR_IMAGE'><filename>DEPLOY_DIR_IMAGE</filename></link>
|
|
variable points to the machine-specific directory.
|
|
<itemizedlist>
|
|
<listitem><para><filename><kernel-image></filename>:
|
|
A kernel binary file.
|
|
The <link linkend='var-KERNEL_IMAGETYPE'><filename>KERNEL_IMAGETYPE</filename></link>
|
|
variable setting determines the naming scheme for the
|
|
kernel image file.
|
|
Depending on that variable, the file could begin with
|
|
a variety of naming strings.
|
|
The <filename>deploy/images/<machine></filename>
|
|
directory can contain multiple image files for the
|
|
machine.</para></listitem>
|
|
<listitem><para><filename><root-filesystem-image></filename>:
|
|
Root filesystems for the target device (e.g.
|
|
<filename>*.ext3</filename> or <filename>*.bz2</filename>
|
|
files).
|
|
The <link linkend='var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></link>
|
|
variable setting determines the root filesystem image
|
|
type.
|
|
The <filename>deploy/images/<machine></filename>
|
|
directory can contain multiple root filesystems for the
|
|
machine.</para></listitem>
|
|
<listitem><para><filename><kernel-modules></filename>:
|
|
Tarballs that contain all the modules built for the kernel.
|
|
Kernel module tarballs exist for legacy purposes and
|
|
can be suppressed by setting the
|
|
<link linkend='var-MODULE_TARBALL_DEPLOY'><filename>MODULE_TARBALL_DEPLOY</filename></link>
|
|
variable to "0".
|
|
The <filename>deploy/images/<machine></filename>
|
|
directory can contain multiple kernel module tarballs
|
|
for the machine.</para></listitem>
|
|
<listitem><para><filename><bootloaders></filename>:
|
|
Bootloaders supporting the image, if applicable to the
|
|
target machine.
|
|
The <filename>deploy/images/<machine></filename>
|
|
directory can contain multiple bootloaders for the
|
|
machine.</para></listitem>
|
|
<listitem><para><filename><symlinks></filename>:
|
|
The <filename>deploy/images/<machine></filename>
|
|
folder contains
|
|
a symbolic link that points to the most recently built file
|
|
for each machine.
|
|
These links might be useful for external scripts that
|
|
need to obtain the latest version of each file.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</section>
|
|
|
|
<section id='sdk-dev-environment'>
|
|
<title>Application Development SDK</title>
|
|
|
|
<para>
|
|
In the
|
|
<link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>,
|
|
the output labeled "Application Development SDK" represents an
|
|
SDK.
|
|
This section is going to take a closer look at this output:
|
|
<imagedata fileref="figures/sdk.png" align="center" width="5in" depth="4in" />
|
|
</para>
|
|
|
|
<para>
|
|
The specific form of this output is a self-extracting
|
|
SDK installer (<filename>*.sh</filename>) that, when run,
|
|
installs the SDK, which consists of a cross-development
|
|
toolchain, a set of libraries and headers, and an SDK
|
|
environment setup script.
|
|
Running this installer essentially sets up your
|
|
cross-development environment.
|
|
You can think of the cross-toolchain as the "host"
|
|
part because it runs on the SDK machine.
|
|
You can think of the libraries and headers as the "target"
|
|
part because they are built for the target hardware.
|
|
The setup script is added so that you can initialize the
|
|
environment before using the tools.
|
|
</para>
|
|
|
|
<note>
|
|
<para>
|
|
The Yocto Project supports several methods by which you can
|
|
set up this cross-development environment.
|
|
These methods include downloading pre-built SDK installers,
|
|
building and installing your own SDK installer, or running
|
|
an Application Development Toolkit (ADT) installer to
|
|
install not just cross-development toolchains
|
|
but also additional tools to help in this type of
|
|
development.
|
|
</para>
|
|
|
|
<para>
|
|
For background information on cross-development toolchains
|
|
in the Yocto Project development environment, see the
|
|
"<link linkend='cross-development-toolchain-generation'>Cross-Development Toolchain Generation</link>"
|
|
section.
|
|
For information on setting up a cross-development
|
|
environment, see the
|
|
"<ulink url='&YOCTO_DOCS_ADT_URL;#installing-the-adt'>Installing the ADT and Toolchains</ulink>"
|
|
section in the Yocto Project Application Developer's Guide.
|
|
</para>
|
|
</note>
|
|
|
|
<para>
|
|
Once built, the SDK installers are written out to the
|
|
<filename>deploy/sdk</filename> folder inside the
|
|
<ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>
|
|
as shown in the figure at the beginning of this section.
|
|
Several variables exist that help configure these files:
|
|
<itemizedlist>
|
|
<listitem><para><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>:
|
|
Points to the <filename>deploy</filename>
|
|
directory.</para></listitem>
|
|
<listitem><para><link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>:
|
|
Specifies the architecture of the machine
|
|
on which the cross-development tools are run to
|
|
create packages for the target hardware.
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-SDKIMAGE_FEATURES'><filename>SDKIMAGE_FEATURES</filename></link>:
|
|
Lists the features to include in the "target" part
|
|
of the SDK.
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-TOOLCHAIN_HOST_TASK'><filename>TOOLCHAIN_HOST_TASK</filename></link>:
|
|
Lists packages that make up the host
|
|
part of the SDK (i.e. the part that runs on
|
|
the <filename>SDKMACHINE</filename>).
|
|
When you use
|
|
<filename>bitbake -c populate_sdk <imagename></filename>
|
|
to create the SDK, a set of default packages
|
|
apply.
|
|
This variable allows you to add more packages.
|
|
</para></listitem>
|
|
<listitem><para><link linkend='var-TOOLCHAIN_TARGET_TASK'><filename>TOOLCHAIN_TARGET_TASK</filename></link>:
|
|
Lists packages that make up the target part
|
|
of the SDK (i.e. the part built for the
|
|
target hardware).
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|
|
<!--
|
|
vim: expandtab tw=80 ts=4
|
|
-->
|