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+<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
+[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
+
+<chapter id='closer-look'>
+<title>A Closer Look at the Yocto Project Development Environment</title>
+
+ <para>
+ This chapter takes a more detailed look at the Yocto Project
+ development environment.
+ The following diagram represents the development environment at a
+ high level.
+ The remainder of this chapter expands on the fundamental input, output,
+ process, and
+ <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>) blocks
+ in the Yocto Project development environment.
+ </para>
+
+ <para id='general-yocto-environment-figure'>
+ <imagedata fileref="figures/yocto-environment-ref.png" align="center" width="8in" depth="4.25in" />
+ </para>
+
+ <para>
+ The generalized Yocto Project Development Environment consists of
+ several functional areas:
+ <itemizedlist>
+ <listitem><para><emphasis>User Configuration:</emphasis>
+ Metadata you can use to control the build process.
+ </para></listitem>
+ <listitem><para><emphasis>Metadata Layers:</emphasis>
+ Various layers that provide software, machine, and
+ distro Metadata.</para></listitem>
+ <listitem><para><emphasis>Source Files:</emphasis>
+ Upstream releases, local projects, and SCMs.</para></listitem>
+ <listitem><para><emphasis>Build System:</emphasis>
+ Processes under the control of
+ <ulink url='&YOCTO_DOCS_DEV_URL;#bitbake-term'>BitBake</ulink>.
+ This block expands on how BitBake fetches source, applies
+ patches, completes compilation, analyzes output for package
+ generation, creates and tests packages, generates images, and
+ generates cross-development tools.</para></listitem>
+ <listitem><para><emphasis>Package Feeds:</emphasis>
+ Directories containing output packages (RPM, DEB or IPK),
+ which are subsequently used in the construction of an image or
+ SDK, produced by the build system.
+ These feeds can also be copied and shared using a web server or
+ other means to facilitate extending or updating existing
+ images on devices at runtime if runtime package management is
+ enabled.</para></listitem>
+ <listitem><para><emphasis>Images:</emphasis>
+ Images produced by the development process.
+ </para></listitem>
+ <listitem><para><emphasis>Application Development SDK:</emphasis>
+ Cross-development tools that are produced along with an image
+ or separately with BitBake.</para></listitem>
+ </itemizedlist>
+ </para>
+
+ <section id="user-configuration">
+ <title>User Configuration</title>
+
+ <para>
+ User configuration helps define the build.
+ Through user configuration, you can tell BitBake the
+ target architecture for which you are building the image,
+ where to store downloaded source, and other build properties.
+ </para>
+
+ <para>
+ The following figure shows an expanded representation of the
+ "User Configuration" box of the
+ <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>:
+ </para>
+
+ <para>
+ <imagedata fileref="figures/user-configuration.png" align="center" width="5.5in" depth="3.5in" />
+ </para>
+
+ <para>
+ BitBake needs some basic configuration files in order to complete
+ a build.
+ These files are <filename>*.conf</filename> files.
+ The minimally necessary ones reside as example files in the
+ <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
+ For simplicity, this section refers to the Source Directory as
+ the "Poky Directory."
+ </para>
+
+ <para>
+ When you clone the <filename>poky</filename> Git repository or you
+ download and unpack a Yocto Project release, you can set up the
+ Source Directory to be named anything you want.
+ For this discussion, the cloned repository uses the default
+ name <filename>poky</filename>.
+ <note>
+ The Poky repository is primarily an aggregation of existing
+ repositories.
+ It is not a canonical upstream source.
+ </note>
+ </para>
+
+ <para>
+ The <filename>meta-yocto</filename> layer inside Poky contains
+ a <filename>conf</filename> directory that has example
+ configuration files.
+ These example files are used as a basis for creating actual
+ configuration files when you source the build environment
+ script
+ (i.e.
+ <link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>
+ or
+ <link linkend='structure-memres-core-script'><filename>oe-init-build-env-memres</filename></link>).
+ </para>
+
+ <para>
+ Sourcing the build environment script creates a
+ <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>
+ if one does not already exist.
+ BitBake uses the Build Directory for all its work during builds.
+ The Build Directory has a <filename>conf</filename> directory that
+ contains default versions of your <filename>local.conf</filename>
+ and <filename>bblayers.conf</filename> configuration files.
+ These default configuration files are created only if versions
+ do not already exist in the Build Directory at the time you
+ source the build environment setup script.
+ </para>
+
+ <para>
+ Because the Poky repository is fundamentally an aggregation of
+ existing repositories, some users might be familiar with running
+ the <filename>&OE_INIT_FILE;</filename> or
+ <filename>oe-init-build-env-memres</filename> script in the context
+ of separate OpenEmbedded-Core and BitBake repositories rather than a
+ single Poky repository.
+ This discussion assumes the script is executed from within a cloned
+ or unpacked version of Poky.
+ </para>
+
+ <para>
+ Depending on where the script is sourced, different sub-scripts
+ are called to set up the Build Directory (Yocto or OpenEmbedded).
+ Specifically, the script
+ <filename>scripts/oe-setup-builddir</filename> inside the
+ poky directory sets up the Build Directory and seeds the directory
+ (if necessary) with configuration files appropriate for the
+ Yocto Project development environment.
+ <note>
+ The <filename>scripts/oe-setup-builddir</filename> script
+ uses the <filename>$TEMPLATECONF</filename> variable to
+ determine which sample configuration files to locate.
+ </note>
+ </para>
+
+ <para>
+ The <filename>local.conf</filename> file provides many
+ basic variables that define a build environment.
+ Here is a list of a few.
+ To see the default configurations in a <filename>local.conf</filename>
+ file created by the build environment script, see the
+ <filename>local.conf.sample</filename> in the
+ <filename>meta-yocto</filename> layer:
+ <itemizedlist>
+ <listitem><para><emphasis>Parallelism Options:</emphasis>
+ Controlled by the
+ <link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>,
+ <link linkend='var-PARALLEL_MAKE'><filename>PARALLEL_MAKE</filename></link>,
+ and
+ <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_NUMBER_PARSE_THREADS'><filename>BB_NUMBER_PARSE_THREADS</filename></ulink>
+ variables.</para></listitem>
+ <listitem><para><emphasis>Target Machine Selection:</emphasis>
+ Controlled by the
+ <link linkend='var-MACHINE'><filename>MACHINE</filename></link>
+ variable.</para></listitem>
+ <listitem><para><emphasis>Download Directory:</emphasis>
+ Controlled by the
+ <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
+ variable.</para></listitem>
+ <listitem><para><emphasis>Shared State Directory:</emphasis>
+ Controlled by the
+ <link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link>
+ variable.</para></listitem>
+ <listitem><para><emphasis>Build Output:</emphasis>
+ Controlled by the
+ <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>
+ variable.</para></listitem>
+ </itemizedlist>
+ <note>
+ Configurations set in the <filename>conf/local.conf</filename>
+ file can also be set in the
+ <filename>conf/site.conf</filename> and
+ <filename>conf/auto.conf</filename> configuration files.
+ </note>
+ </para>
+
+ <para>
+ The <filename>bblayers.conf</filename> file tells BitBake what
+ layers you want considered during the build.
+ By default, the layers listed in this file include layers
+ minimally needed by the build system.
+ However, you must manually add any custom layers you have created.
+ You can find more information on working with the
+ <filename>bblayers.conf</filename> file in the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#enabling-your-layer'>Enabling Your Layer</ulink>"
+ section in the Yocto Project Development Manual.
+ </para>
+
+ <para>
+ The files <filename>site.conf</filename> and
+ <filename>auto.conf</filename> are not created by the environment
+ initialization script.
+ If you want these configuration files, you must create them
+ yourself:
+ <itemizedlist>
+ <listitem><para><emphasis><filename>site.conf</filename>:</emphasis>
+ You can use the <filename>conf/site.conf</filename>
+ configuration file to configure multiple build directories.
+ For example, suppose you had several build environments and
+ they shared some common features.
+ You can set these default build properties here.
+ A good example is perhaps the packaging format to use
+ through the
+ <link linkend='var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></link>
+ variable.</para>
+ <para>One useful scenario for using the
+ <filename>conf/site.conf</filename> file is to extend your
+ <link linkend='var-BBPATH'><filename>BBPATH</filename></link>
+ variable to include the path to a
+ <filename>conf/site.conf</filename>.
+ Then, when BitBake looks for Metadata using
+ <filename>BBPATH</filename>, it finds the
+ <filename>conf/site.conf</filename> file and applies your
+ common configurations found in the file.
+ To override configurations in a particular build directory,
+ alter the similar configurations within that build
+ directory's <filename>conf/local.conf</filename> file.
+ </para></listitem>
+ <listitem><para><emphasis><filename>auto.conf</filename>:</emphasis>
+ This file is not hand-created.
+ Rather, the file is usually created and written to by
+ an autobuilder.
+ The settings put into the file are typically the same as
+ you would find in the <filename>conf/local.conf</filename>
+ or the <filename>conf/site.conf</filename> files.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ You can edit all configuration files to further define
+ any particular build environment.
+ This process is represented by the "User Configuration Edits"
+ box in the figure.
+ </para>
+
+ <para>
+ When you launch your build with the
+ <filename>bitbake <replaceable>target</replaceable></filename> command, BitBake
+ sorts out the configurations to ultimately define your build
+ environment.
+ </para>
+ </section>
+
+ <section id="metadata-machine-configuration-and-policy-configuration">
+ <title>Metadata, Machine Configuration, and Policy Configuration</title>
+
+ <para>
+ The previous section described the user configurations that
+ define BitBake's global behavior.
+ This section takes a closer look at the layers the build system
+ uses to further control the build.
+ These layers provide Metadata for the software, machine, and
+ policy.
+ </para>
+
+ <para>
+ In general, three types of layer input exist:
+ <itemizedlist>
+ <listitem><para><emphasis>Policy Configuration:</emphasis>
+ Distribution Layers provide top-level or general
+ policies for the image or SDK being built.
+ For example, this layer would dictate whether BitBake
+ produces RPM or IPK packages.</para></listitem>
+ <listitem><para><emphasis>Machine Configuration:</emphasis>
+ Board Support Package (BSP) layers provide machine
+ configurations.
+ This type of information is specific to a particular
+ target architecture.</para></listitem>
+ <listitem><para><emphasis>Metadata:</emphasis>
+ Software layers contain user-supplied recipe files,
+ patches, and append files.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ The following figure shows an expanded representation of the
+ Metadata, Machine Configuration, and Policy Configuration input
+ (layers) boxes of the
+ <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>:
+ </para>
+
+ <para>
+ <imagedata fileref="figures/layer-input.png" align="center" width="8in" depth="7.5in" />
+ </para>
+
+ <para>
+ In general, all layers have a similar structure.
+ They all contain a licensing file
+ (e.g. <filename>COPYING</filename>) if the layer is to be
+ distributed, a <filename>README</filename> file as good practice
+ and especially if the layer is to be distributed, a
+ configuration directory, and recipe directories.
+ </para>
+
+ <para>
+ The Yocto Project has many layers that can be used.
+ You can see a web-interface listing of them on the
+ <ulink url="http://git.yoctoproject.org/">Source Repositories</ulink>
+ page.
+ The layers are shown at the bottom categorized under
+ "Yocto Metadata Layers."
+ These layers are fundamentally a subset of the
+ <ulink url="http://layers.openembedded.org/layerindex/layers/">OpenEmbedded Metadata Index</ulink>,
+ which lists all layers provided by the OpenEmbedded community.
+ <note>
+ Layers exist in the Yocto Project Source Repositories that
+ cannot be found in the OpenEmbedded Metadata Index.
+ These layers are either deprecated or experimental in nature.
+ </note>
+ </para>
+
+ <para>
+ BitBake uses the <filename>conf/bblayers.conf</filename> file,
+ which is part of the user configuration, to find what layers it
+ should be using as part of the build.
+ </para>
+
+ <para>
+ For more information on layers, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
+ section in the Yocto Project Development Manual.
+ </para>
+
+ <section id="distro-layer">
+ <title>Distro Layer</title>
+
+ <para>
+ The distribution layer provides policy configurations for your
+ distribution.
+ Best practices dictate that you isolate these types of
+ configurations into their own layer.
+ Settings you provide in
+ <filename>conf/distro/<replaceable>distro</replaceable>.conf</filename> override
+ similar
+ settings that BitBake finds in your
+ <filename>conf/local.conf</filename> file in the Build
+ Directory.
+ </para>
+
+ <para>
+ The following list provides some explanation and references
+ for what you typically find in the distribution layer:
+ <itemizedlist>
+ <listitem><para><emphasis>classes:</emphasis>
+ Class files (<filename>.bbclass</filename>) hold
+ common functionality that can be shared among
+ recipes in the distribution.
+ When your recipes inherit a class, they take on the
+ settings and functions for that class.
+ You can read more about class files in the
+ "<link linkend='ref-classes'>Classes</link>" section.
+ </para></listitem>
+ <listitem><para><emphasis>conf:</emphasis>
+ This area holds configuration files for the
+ layer (<filename>conf/layer.conf</filename>),
+ the distribution
+ (<filename>conf/distro/<replaceable>distro</replaceable>.conf</filename>),
+ and any distribution-wide include files.
+ </para></listitem>
+ <listitem><para><emphasis>recipes-*:</emphasis>
+ Recipes and append files that affect common
+ functionality across the distribution.
+ This area could include recipes and append files
+ to add distribution-specific configuration,
+ initialization scripts, custom image recipes,
+ and so forth.</para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id="bsp-layer">
+ <title>BSP Layer</title>
+
+ <para>
+ The BSP Layer provides machine configurations.
+ Everything in this layer is specific to the machine for which
+ you are building the image or the SDK.
+ A common structure or form is defined for BSP layers.
+ You can learn more about this structure in the
+ <ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
+ <note>
+ In order for a BSP layer to be considered compliant with the
+ Yocto Project, it must meet some structural requirements.
+ </note>
+ </para>
+
+ <para>
+ The BSP Layer's configuration directory contains
+ configuration files for the machine
+ (<filename>conf/machine/<replaceable>machine</replaceable>.conf</filename>) and,
+ of course, the layer (<filename>conf/layer.conf</filename>).
+ </para>
+
+ <para>
+ The remainder of the layer is dedicated to specific recipes
+ by function: <filename>recipes-bsp</filename>,
+ <filename>recipes-core</filename>,
+ <filename>recipes-graphics</filename>, and
+ <filename>recipes-kernel</filename>.
+ Metadata can exist for multiple formfactors, graphics
+ support systems, and so forth.
+ <note>
+ While the figure shows several <filename>recipes-*</filename>
+ directories, not all these directories appear in all
+ BSP layers.
+ </note>
+ </para>
+ </section>
+
+ <section id="software-layer">
+ <title>Software Layer</title>
+
+ <para>
+ The software layer provides the Metadata for additional
+ software packages used during the build.
+ This layer does not include Metadata that is specific to the
+ distribution or the machine, which are found in their
+ respective layers.
+ </para>
+
+ <para>
+ This layer contains any new recipes that your project needs
+ in the form of recipe files.
+ </para>
+ </section>
+ </section>
+
+ <section id="sources-dev-environment">
+ <title>Sources</title>
+
+ <para>
+ In order for the OpenEmbedded build system to create an image or
+ any target, it must be able to access source files.
+ The
+ <link linkend='general-yocto-environment-figure'>general Yocto Project Development Environment figure</link>
+ represents source files using the "Upstream Project Releases",
+ "Local Projects", and "SCMs (optional)" boxes.
+ The figure represents mirrors, which also play a role in locating
+ source files, with the "Source Mirror(s)" box.
+ </para>
+
+ <para>
+ The method by which source files are ultimately organized is
+ a function of the project.
+ For example, for released software, projects tend to use tarballs
+ or other archived files that can capture the state of a release
+ guaranteeing that it is statically represented.
+ On the other hand, for a project that is more dynamic or
+ experimental in nature, a project might keep source files in a
+ repository controlled by a Source Control Manager (SCM) such as
+ Git.
+ Pulling source from a repository allows you to control
+ the point in the repository (the revision) from which you want to
+ build software.
+ Finally, a combination of the two might exist, which would give the
+ consumer a choice when deciding where to get source files.
+ </para>
+
+ <para>
+ BitBake uses the
+ <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
+ variable to point to source files regardless of their location.
+ Each recipe must have a <filename>SRC_URI</filename> variable
+ that points to the source.
+ </para>
+
+ <para>
+ Another area that plays a significant role in where source files
+ come from is pointed to by the
+ <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
+ variable.
+ This area is a cache that can hold previously downloaded source.
+ You can also instruct the OpenEmbedded build system to create
+ tarballs from Git repositories, which is not the default behavior,
+ and store them in the <filename>DL_DIR</filename> by using the
+ <link linkend='var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></link>
+ variable.
+ </para>
+
+ <para>
+ 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</filename></link>
+ class to include that 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</filename> class, 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
+ <link linkend='ref-tasks-fetch'><filename>do_fetch</filename></link>
+ 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>
+
+ <note>
+ For information on how to have the OpenEmbedded build system
+ generate tarballs for Git repositories and place them in the
+ <link linkend='var-DL_DIR'><filename>DL_DIR</filename></link>
+ directory, see the
+ <link linkend='var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></link>
+ variable.
+ </note>
+
+ <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.
+ The OpenEmbedded build system provides classes to generate
+ different package types, and you specify which classes to enable
+ through 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</filename></link>
+ class.
+ </para>
+
+ <para>
+ The package feed area resides in the Build Directory.
+ The directory the build system uses to temporarily store packages
+ is determined by a combination of variables and the particular
+ package manager in use.
+ See the "Package Feeds" box in the illustration and note the
+ information to the right of that area.
+ In particular, the following defines where package files are
+ kept:
+ <itemizedlist>
+ <listitem><para><link linkend='var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></link>:
+ Defined as <filename>tmp/deploy</filename> in the Build
+ Directory.
+ </para></listitem>
+ <listitem><para><filename>DEPLOY_DIR_*</filename>:
+ Depending on the package manager used, the package type
+ sub-folder.
+ Given RPM, IPK, or DEB packaging and tarball creation, the
+ <link linkend='var-DEPLOY_DIR_RPM'><filename>DEPLOY_DIR_RPM</filename></link>,
+ <link linkend='var-DEPLOY_DIR_IPK'><filename>DEPLOY_DIR_IPK</filename></link>,
+ <link linkend='var-DEPLOY_DIR_DEB'><filename>DEPLOY_DIR_DEB</filename></link>,
+ or
+ <link linkend='var-DEPLOY_DIR_TAR'><filename>DEPLOY_DIR_TAR</filename></link>,
+ variables are used, respectively.
+ </para></listitem>
+ <listitem><para><link linkend='var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></link>:
+ Defines architecture-specific sub-folders.
+ For example, packages could exist for the i586 or qemux86
+ architectures.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ BitBake uses the <filename>do_package_write_*</filename> tasks to
+ generate packages and place them into the package holding area (e.g.
+ <filename>do_package_write_ipk</filename> for IPK packages).
+ See the
+ "<link linkend='ref-tasks-package_write_deb'><filename>do_package_write_deb</filename></link>",
+ "<link linkend='ref-tasks-package_write_ipk'><filename>do_package_write_ipk</filename></link>",
+ "<link linkend='ref-tasks-package_write_rpm'><filename>do_package_write_rpm</filename></link>",
+ and
+ "<link linkend='ref-tasks-package_write_tar'><filename>do_package_write_tar</filename></link>"
+ sections for additional information.
+ As an example, consider a scenario where an IPK packaging manager
+ is being used and package architecture support for both i586
+ and qemux86 exist.
+ Packages for the i586 architecture are placed in
+ <filename>build/tmp/deploy/ipk/i586</filename>, while packages for
+ the qemux86 architecture are placed in
+ <filename>build/tmp/deploy/ipk/qemux86</filename>.
+ </para>
+ </section>
+
+ <section id='bitbake-dev-environment'>
+ <title>BitBake</title>
+
+ <para>
+ The OpenEmbedded build system uses
+ <ulink url='&YOCTO_DOCS_DEV_URL;#bitbake-term'>BitBake</ulink>
+ 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>
+
+ <para>
+ Separate documentation exists for the BitBake tool.
+ See the
+ <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual'>BitBake User Manual</ulink>
+ for reference material on BitBake.
+ </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
+ <link linkend='ref-tasks-fetch'><filename>do_fetch</filename></link>
+ and
+ <link linkend='ref-tasks-unpack'><filename>do_unpack</filename></link>
+ tasks fetch the source files and unpack them into the work
+ directory.
+ <note>
+ For every local file (e.g. <filename>file://</filename>)
+ that is part of a recipe's
+ <link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
+ statement, the OpenEmbedded build system takes a checksum
+ of the file for the recipe and inserts the checksum into
+ the signature for the <filename>do_fetch</filename>.
+ If any local file has been modified, the
+ <filename>do_fetch</filename> task and all tasks that
+ depend on it are re-executed.
+ </note>
+ 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 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 that 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> -
+ The base directory where the OpenEmbedded build system
+ performs all its work during the build.
+ </para></listitem>
+ <listitem><para><link linkend='var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></link> -
+ The architecture of the built package or packages.
+ </para></listitem>
+ <listitem><para><link linkend='var-TARGET_OS'><filename>TARGET_OS</filename></link> -
+ The operating system of the target device.
+ </para></listitem>
+ <listitem><para><link linkend='var-PN'><filename>PN</filename></link> -
+ The name of the built package.
+ </para></listitem>
+ <listitem><para><link linkend='var-PV'><filename>PV</filename></link> -
+ The version of the recipe used to build the package.
+ </para></listitem>
+ <listitem><para><link linkend='var-PR'><filename>PR</filename></link> -
+ The revision of the recipe used to build the package.
+ </para></listitem>
+ <listitem><para><link linkend='var-WORKDIR'><filename>WORKDIR</filename></link> -
+ The location within <filename>TMPDIR</filename> where
+ a specific package is built.
+ </para></listitem>
+ <listitem><para><link linkend='var-S'><filename>S</filename></link> -
+ Contains the unpacked source files for a given recipe.
+ </para></listitem>
+ </itemizedlist>
+ </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
+ <link linkend='ref-tasks-patch'><filename>do_patch</filename></link>
+ 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
+ <link linkend='ref-tasks-configure'><filename>do_configure</filename></link>
+ task are specific
+ to source code configuration for the source code
+ being built by the recipe.</para>
+
+ <para>If you are using the
+ <link linkend='ref-classes-autotools'><filename>autotools</filename></link>
+ class,
+ 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> file.
+ </para></listitem>
+ <listitem><para><emphasis><filename>do_compile</filename>:</emphasis>
+ Once a configuration task has been satisfied, BitBake
+ compiles the source using the
+ <link linkend='ref-tasks-compile'><filename>do_compile</filename></link>
+ 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 is, by
+ default, 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
+ <link linkend='ref-tasks-install'><filename>do_install</filename></link>
+ 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
+ <link linkend='ref-tasks-package'><filename>do_package</filename></link>
+ and
+ <link linkend='ref-tasks-packagedata'><filename>do_packagedata</filename></link>
+ 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> -
+ The destination directory for packages before they are
+ split.
+ </para></listitem>
+ <listitem><para><link linkend='var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></link> -
+ A shared, global-state directory that holds data
+ generated during the packaging process.
+ </para></listitem>
+ <listitem><para><link linkend='var-PKGDESTWORK'><filename>PKGDESTWORK</filename></link> -
+ A temporary work area used by the
+ <filename>do_package</filename> task.
+ </para></listitem>
+ <listitem><para><link linkend='var-PKGDEST'><filename>PKGDEST</filename></link> -
+ The parent directory for packages after they have
+ been split.
+ </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 the
+ <link linkend='ref-classes-package'><filename>package</filename></link>
+ class.
+ </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
+ <link linkend='ref-tasks-rootfs'><filename>do_rootfs</filename></link>
+ 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 is
+ read-only.
+ </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>
+ Along with writing out the root filesystem image, the
+ <filename>do_rootfs</filename> task creates a manifest file
+ (<filename>.manifest</filename>) in the same directory as
+ the root filesystem image that lists out, line-by-line, the
+ installed packages.
+ This manifest file is useful for the
+ <link linkend='ref-classes-testimage'><filename>testimage</filename></link>
+ class, for example, to determine whether or not to run
+ specific tests.
+ See the
+ <link linkend='var-IMAGE_MANIFEST'><filename>IMAGE_MANIFEST</filename></link>
+ variable for additional information.
+ </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.
+ For information on advantages gained when building a
+ cross-development toolchain using the
+ <link linkend='ref-tasks-populate_sdk'><filename>do_populate_sdk</filename></link>
+ task, see the
+ "<ulink url='&YOCTO_DOCS_ADT_URL;#optionally-building-a-toolchain-installer'>Optionally Building a Toolchain Installer</ulink>"
+ section in the Yocto Project Application Developer's Guide.
+ </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 filesystem 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,
+ see 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>tmp/deploy/images/<replaceable>machine</replaceable>/</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 appropriate directory containing images for
+ the current configuration.
+ <itemizedlist>
+ <listitem><para><filename><replaceable>kernel-image</replaceable></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/<replaceable>machine</replaceable></filename>
+ directory can contain multiple image files for the
+ machine.</para></listitem>
+ <listitem><para><filename><replaceable>root-filesystem-image</replaceable></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/<replaceable>machine</replaceable></filename>
+ directory can contain multiple root filesystems for the
+ machine.</para></listitem>
+ <listitem><para><filename><replaceable>kernel-modules</replaceable></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/<replaceable>machine</replaceable></filename>
+ directory can contain multiple kernel module tarballs
+ for the machine.</para></listitem>
+ <listitem><para><filename><replaceable>bootloaders</replaceable></filename>:
+ Bootloaders supporting the image, if applicable to the
+ target machine.
+ The <filename>deploy/images/<replaceable>machine</replaceable></filename>
+ directory can contain multiple bootloaders for the
+ machine.</para></listitem>
+ <listitem><para><filename><replaceable>symlinks</replaceable></filename>:
+ The <filename>deploy/images/<replaceable>machine</replaceable></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 <replaceable>imagename</replaceable></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>
+ <listitem><para><link linkend='var-SDKPATH'><filename>SDKPATH</filename></link>:
+ Defines the default SDK installation path offered by the
+ installation script.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+</chapter>
+<!--
+vim: expandtab tw=80 ts=4
+-->