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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='technical-details'>
+<title>Technical Details</title>
+
+ <para>
+ This chapter provides technical details for various parts of the
+ Yocto Project.
+ Currently, topics include Yocto Project components,
+ cross-toolchain generation, shared state (sstate) cache,
+ x32, Wayland support, and Licenses.
+ </para>
+
+<section id='usingpoky-components'>
+ <title>Yocto Project Components</title>
+
+ <para>
+ The
+ <ulink url='&YOCTO_DOCS_DEV_URL;#bitbake-term'>BitBake</ulink>
+ task executor together with various types of configuration files form
+ the OpenEmbedded Core.
+ This section overviews these components by describing their use and
+ how they interact.
+ </para>
+
+ <para>
+ BitBake handles the parsing and execution of the data files.
+ The data itself is of various types:
+ <itemizedlist>
+ <listitem><para><emphasis>Recipes:</emphasis> Provides details
+ about particular pieces of software.
+ </para></listitem>
+ <listitem><para><emphasis>Class Data:</emphasis> Abstracts
+ common build information (e.g. how to build a Linux kernel).
+ </para></listitem>
+ <listitem><para><emphasis>Configuration Data:</emphasis> Defines
+ machine-specific settings, policy decisions, and so forth.
+ Configuration data acts as the glue to bind everything
+ together.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ BitBake knows how to combine multiple data sources together and refers
+ to each data source as a layer.
+ For information on layers, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and
+ Creating Layers</ulink>" section of the Yocto Project Development Manual.
+ </para>
+
+ <para>
+ Following are some brief details on these core components.
+ For additional information on how these components interact during
+ a build, see the
+ "<link linkend='closer-look'>A Closer Look at the Yocto Project Development Environment</link>"
+ Chapter.
+ </para>
+
+ <section id='usingpoky-components-bitbake'>
+ <title>BitBake</title>
+
+ <para>
+ BitBake is the tool at the heart of the OpenEmbedded build system
+ and is responsible for parsing the
+ <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>,
+ generating a list of tasks from it, and then executing those tasks.
+ </para>
+
+ <para>
+ This section briefly introduces BitBake.
+ If you want more information on BitBake, see the
+ <ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual'>BitBake User Manual</ulink>.
+ </para>
+
+ <para>
+ To see a list of the options BitBake supports, use either of
+ the following commands:
+ <literallayout class='monospaced'>
+ $ bitbake -h
+ $ bitbake --help
+ </literallayout>
+ </para>
+
+ <para>
+ The most common usage for BitBake is <filename>bitbake <replaceable>packagename</replaceable></filename>, where
+ <filename>packagename</filename> is the name of the package you want to build
+ (referred to as the "target" in this manual).
+ The target often equates to the first part of a recipe's filename
+ (e.g. "foo" for a recipe named
+ <filename>foo_1.3.0-r0.bb</filename>).
+ So, to process the <filename>matchbox-desktop_1.2.3.bb</filename> recipe file, you
+ might type the following:
+ <literallayout class='monospaced'>
+ $ bitbake matchbox-desktop
+ </literallayout>
+ Several different versions of <filename>matchbox-desktop</filename> might exist.
+ BitBake chooses the one selected by the distribution configuration.
+ You can get more details about how BitBake chooses between different
+ target versions and providers in the
+ "<ulink url='&YOCTO_DOCS_BB_URL;#bb-bitbake-preferences'>Preferences</ulink>"
+ section of the BitBake User Manual.
+ </para>
+
+ <para>
+ BitBake also tries to execute any dependent tasks first.
+ So for example, before building <filename>matchbox-desktop</filename>, BitBake
+ would build a cross compiler and <filename>glibc</filename> if they had not already
+ been built.
+ </para>
+
+ <para>
+ A useful BitBake option to consider is the <filename>-k</filename> or
+ <filename>--continue</filename> option.
+ This option instructs BitBake to try and continue processing the job
+ as long as possible even after encountering an error.
+ When an error occurs, the target that
+ failed and those that depend on it cannot be remade.
+ However, when you use this option other dependencies can still be
+ processed.
+ </para>
+ </section>
+
+ <section id='usingpoky-components-metadata'>
+ <title>Metadata (Recipes)</title>
+
+ <para>
+ Files that have the <filename>.bb</filename> suffix are "recipes"
+ files.
+ In general, a recipe contains information about a single piece of
+ software.
+ This information includes the location from which to download the
+ unaltered source, any source patches to be applied to that source
+ (if needed), which special configuration options to apply,
+ how to compile the source files, and how to package the compiled
+ output.
+ </para>
+
+ <para>
+ The term "package" is sometimes used to refer to recipes. However,
+ since the word "package" is used for the packaged output from the OpenEmbedded
+ build system (i.e. <filename>.ipk</filename> or <filename>.deb</filename> files),
+ this document avoids using the term "package" when referring to recipes.
+ </para>
+ </section>
+
+ <section id='usingpoky-components-classes'>
+ <title>Classes</title>
+
+ <para>
+ Class files (<filename>.bbclass</filename>) contain information that
+ is useful to share between
+ <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink> files.
+ An example is the
+ <link linkend='ref-classes-autotools'><filename>autotools</filename></link>
+ class, which contains common settings for any application that
+ Autotools uses.
+ The "<link linkend='ref-classes'>Classes</link>" chapter provides
+ details about classes and how to use them.
+ </para>
+ </section>
+
+ <section id='usingpoky-components-configuration'>
+ <title>Configuration</title>
+
+ <para>
+ The configuration files (<filename>.conf</filename>) define various configuration variables
+ that govern the OpenEmbedded build process.
+ These files fall into several areas that define machine configuration options,
+ distribution configuration options, compiler tuning options, general common configuration
+ options, and user configuration options in <filename>local.conf</filename>, which is found
+ in the
+ <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
+ </para>
+ </section>
+</section>
+
+<section id="cross-development-toolchain-generation">
+ <title>Cross-Development Toolchain Generation</title>
+
+ <para>
+ The Yocto Project does most of the work for you when it comes to
+ creating
+ <ulink url='&YOCTO_DOCS_DEV_URL;#cross-development-toolchain'>cross-development toolchains</ulink>.
+ This section provides some technical background on how
+ cross-development toolchains are created and used.
+ For more information on toolchains, you can also see the
+ <ulink url='&YOCTO_DOCS_ADT_URL;'>Yocto Project Application Developer's Guide</ulink>.
+ </para>
+
+ <para>
+ In the Yocto Project development environment, cross-development
+ toolchains are used to build the image and applications that run on the
+ target hardware.
+ With just a few commands, the OpenEmbedded build system creates
+ these necessary toolchains for you.
+ </para>
+
+ <para>
+ The following figure shows a high-level build environment regarding
+ toolchain construction and use.
+ </para>
+
+ <para>
+ <imagedata fileref="figures/cross-development-toolchains.png" width="8in" depth="6in" align="center" />
+ </para>
+
+ <para>
+ Most of the work occurs on the Build Host.
+ This is the machine used to build images and generally work within the
+ the Yocto Project environment.
+ When you run BitBake to create an image, the OpenEmbedded build system
+ uses the host <filename>gcc</filename> compiler to bootstrap a
+ cross-compiler named <filename>gcc-cross</filename>.
+ The <filename>gcc-cross</filename> compiler is what BitBake uses to
+ compile source files when creating the target image.
+ You can think of <filename>gcc-cross</filename> simply as an
+ automatically generated cross-compiler that is used internally within
+ BitBake only.
+ </para>
+
+ <para>
+ The chain of events that occurs when <filename>gcc-cross</filename> is
+ bootstrapped is as follows:
+ <literallayout class='monospaced'>
+ gcc -> binutils-cross -> gcc-cross-initial -> linux-libc-headers -> glibc-initial -> glibc -> gcc-cross -> gcc-runtime
+ </literallayout>
+ <itemizedlist>
+ <listitem><para><filename>gcc</filename>:
+ The build host's GNU Compiler Collection (GCC).
+ </para></listitem>
+ <listitem><para><filename>binutils-cross</filename>:
+ The bare minimum binary utilities needed in order to run
+ the <filename>gcc-cross-initial</filename> phase of the
+ bootstrap operation.
+ </para></listitem>
+ <listitem><para><filename>gcc-cross-initial</filename>:
+ An early stage of the bootstrap process for creating
+ the cross-compiler.
+ This stage builds enough of the <filename>gcc-cross</filename>,
+ the C library, and other pieces needed to finish building the
+ final cross-compiler in later stages.
+ This tool is a "native" package (i.e. it is designed to run on
+ the build host).
+ </para></listitem>
+ <listitem><para><filename>linux-libc-headers</filename>:
+ Headers needed for the cross-compiler.
+ </para></listitem>
+ <listitem><para><filename>glibc-initial</filename>:
+ An initial version of the Embedded GLIBC needed to bootstrap
+ <filename>glibc</filename>.
+ </para></listitem>
+ <listitem><para><filename>gcc-cross</filename>:
+ The final stage of the bootstrap process for the
+ cross-compiler.
+ This stage results in the actual cross-compiler that
+ BitBake uses when it builds an image for a targeted
+ device.
+ <note>
+ If you are replacing this cross compiler toolchain
+ with a custom version, you must replace
+ <filename>gcc-cross</filename>.
+ </note>
+ This tool is also a "native" package (i.e. it is
+ designed to run on the build host).
+ </para></listitem>
+ <listitem><para><filename>gcc-runtime</filename>:
+ Runtime libraries resulting from the toolchain bootstrapping
+ process.
+ This tool produces a binary that consists of the
+ runtime libraries need for the targeted device.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ You can use the OpenEmbedded build system to build an installer for
+ the relocatable SDK used to develop applications.
+ When you run the installer, it installs the toolchain, which contains
+ the development tools (e.g., the
+ <filename>gcc-cross-canadian</filename>),
+ <filename>binutils-cross-canadian</filename>, and other
+ <filename>nativesdk-*</filename> tools you need to cross-compile and
+ test your software.
+ The figure shows the commands you use to easily build out this
+ toolchain.
+ This cross-development toolchain is built to execute on the
+ <link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>,
+ which might or might not be the same
+ machine as the Build Host.
+ <note>
+ If your target architecture is supported by the Yocto Project,
+ you can take advantage of pre-built images that ship with the
+ Yocto Project and already contain cross-development toolchain
+ installers.
+ </note>
+ </para>
+
+ <para>
+ Here is the bootstrap process for the relocatable toolchain:
+ <literallayout class='monospaced'>
+ gcc -> binutils-crosssdk -> gcc-crosssdk-initial -> linux-libc-headers ->
+ glibc-initial -> nativesdk-glibc -> gcc-crosssdk -> gcc-cross-canadian
+ </literallayout>
+ <itemizedlist>
+ <listitem><para><filename>gcc</filename>:
+ The build host's GNU Compiler Collection (GCC).
+ </para></listitem>
+ <listitem><para><filename>binutils-crosssdk</filename>:
+ The bare minimum binary utilities needed in order to run
+ the <filename>gcc-crosssdk-initial</filename> phase of the
+ bootstrap operation.
+ </para></listitem>
+ <listitem><para><filename>gcc-crosssdk-initial</filename>:
+ An early stage of the bootstrap process for creating
+ the cross-compiler.
+ This stage builds enough of the
+ <filename>gcc-crosssdk</filename> and supporting pieces so that
+ the final stage of the bootstrap process can produce the
+ finished cross-compiler.
+ This tool is a "native" binary that runs on the build host.
+ </para></listitem>
+ <listitem><para><filename>linux-libc-headers</filename>:
+ Headers needed for the cross-compiler.
+ </para></listitem>
+ <listitem><para><filename>glibc-initial</filename>:
+ An initial version of the Embedded GLIBC needed to bootstrap
+ <filename>nativesdk-glibc</filename>.
+ </para></listitem>
+ <listitem><para><filename>nativesdk-glibc</filename>:
+ The Embedded GLIBC needed to bootstrap the
+ <filename>gcc-crosssdk</filename>.
+ </para></listitem>
+ <listitem><para><filename>gcc-crosssdk</filename>:
+ The final stage of the bootstrap process for the
+ relocatable cross-compiler.
+ The <filename>gcc-crosssdk</filename> is a transitory compiler
+ and never leaves the build host.
+ Its purpose is to help in the bootstrap process to create the
+ eventual relocatable <filename>gcc-cross-canadian</filename>
+ compiler, which is relocatable.
+ This tool is also a "native" package (i.e. it is
+ designed to run on the build host).
+ </para></listitem>
+ <listitem><para><filename>gcc-cross-canadian</filename>:
+ The final relocatable cross-compiler.
+ When run on the
+ <link linkend='var-SDKMACHINE'><filename>SDKMACHINE</filename></link>,
+ this tool
+ produces executable code that runs on the target device.
+ Only one cross-canadian compiler is produced per architecture
+ since they can be targeted at different processor optimizations
+ using configurations passed to the compiler through the
+ compile commands.
+ This circumvents the need for multiple compilers and thus
+ reduces the size of the toolchains.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+
+ <note>
+ For information on advantages gained when building a
+ cross-development toolchain installer, 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>
+</section>
+
+<section id="shared-state-cache">
+ <title>Shared State Cache</title>
+
+ <para>
+ By design, the OpenEmbedded build system builds everything from scratch unless
+ BitBake can determine that parts do not need to be rebuilt.
+ Fundamentally, building from scratch is attractive as it means all parts are
+ built fresh and there is no possibility of stale data causing problems.
+ When developers hit problems, they typically default back to building from scratch
+ so they know the state of things from the start.
+ </para>
+
+ <para>
+ Building an image from scratch is both an advantage and a disadvantage to the process.
+ As mentioned in the previous paragraph, building from scratch ensures that
+ everything is current and starts from a known state.
+ However, building from scratch also takes much longer as it generally means
+ rebuilding things that do not necessarily need to be rebuilt.
+ </para>
+
+ <para>
+ The Yocto Project implements shared state code that supports incremental builds.
+ The implementation of the shared state code answers the following questions that
+ were fundamental roadblocks within the OpenEmbedded incremental build support system:
+ <itemizedlist>
+ <listitem><para>What pieces of the system have changed and what pieces have
+ not changed?</para></listitem>
+ <listitem><para>How are changed pieces of software removed and replaced?</para></listitem>
+ <listitem><para>How are pre-built components that do not need to be rebuilt from scratch
+ used when they are available?</para></listitem>
+ </itemizedlist>
+ </para>
+
+ <para>
+ For the first question, the build system detects changes in the "inputs" to a given task by
+ creating a checksum (or signature) of the task's inputs.
+ If the checksum changes, the system assumes the inputs have changed and the task needs to be
+ rerun.
+ For the second question, the shared state (sstate) code tracks which tasks add which output
+ to the build process.
+ This means the output from a given task can be removed, upgraded or otherwise manipulated.
+ The third question is partly addressed by the solution for the second question
+ assuming the build system can fetch the sstate objects from remote locations and
+ install them if they are deemed to be valid.
+ </para>
+
+ <note>
+ The OpenEmbedded build system does not maintain
+ <link linkend='var-PR'><filename>PR</filename></link> information
+ as part of the shared state packages.
+ Consequently, considerations exist that affect maintaining shared
+ state feeds.
+ For information on how the OpenEmbedded build system
+ works with packages and can
+ track incrementing <filename>PR</filename> information, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#incrementing-a-package-revision-number'>Incrementing a Package Revision Number</ulink>"
+ section.
+ </note>
+
+ <para>
+ The rest of this section goes into detail about the overall incremental build
+ architecture, the checksums (signatures), shared state, and some tips and tricks.
+ </para>
+
+ <section id='overall-architecture'>
+ <title>Overall Architecture</title>
+
+ <para>
+ When determining what parts of the system need to be built, BitBake
+ works on a per-task basis rather than a per-recipe basis.
+ You might wonder why using a per-task basis is preferred over a per-recipe basis.
+ To help explain, consider having the IPK packaging backend enabled and then switching to DEB.
+ In this case, the
+ <link linkend='ref-tasks-install'><filename>do_install</filename></link>
+ and
+ <link linkend='ref-tasks-package'><filename>do_package</filename></link>
+ task outputs are still valid.
+ However, with a per-recipe approach, the build would not include the
+ <filename>.deb</filename> files.
+ Consequently, you would have to invalidate the whole build and rerun it.
+ Rerunning everything is not the best solution.
+ Also, in this case, the core must be "taught" much about specific tasks.
+ This methodology does not scale well and does not allow users to easily add new tasks
+ in layers or as external recipes without touching the packaged-staging core.
+ </para>
+ </section>
+
+ <section id='checksums'>
+ <title>Checksums (Signatures)</title>
+
+ <para>
+ The shared state code uses a checksum, which is a unique signature of a task's
+ inputs, to determine if a task needs to be run again.
+ Because it is a change in a task's inputs that triggers a rerun, the process
+ needs to detect all the inputs to a given task.
+ For shell tasks, this turns out to be fairly easy because
+ the build process generates a "run" shell script for each task and
+ it is possible to create a checksum that gives you a good idea of when
+ the task's data changes.
+ </para>
+
+ <para>
+ To complicate the problem, there are things that should not be included in
+ the checksum.
+ First, there is the actual specific build path of a given task -
+ the <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>.
+ It does not matter if the work directory changes because it should not
+ affect the output for target packages.
+ Also, the build process has the objective of making native or cross packages relocatable.
+ The checksum therefore needs to exclude <filename>WORKDIR</filename>.
+ The simplistic approach for excluding the work directory is to set
+ <filename>WORKDIR</filename> to some fixed value and create the checksum
+ for the "run" script.
+ </para>
+
+ <para>
+ Another problem results from the "run" scripts containing functions that
+ might or might not get called.
+ The incremental build solution contains code that figures out dependencies
+ between shell functions.
+ This code is used to prune the "run" scripts down to the minimum set,
+ thereby alleviating this problem and making the "run" scripts much more
+ readable as a bonus.
+ </para>
+
+ <para>
+ So far we have solutions for shell scripts.
+ What about Python tasks?
+ The same approach applies even though these tasks are more difficult.
+ The process needs to figure out what variables a Python function accesses
+ and what functions it calls.
+ Again, the incremental build solution contains code that first figures out
+ the variable and function dependencies, and then creates a checksum for the data
+ used as the input to the task.
+ </para>
+
+ <para>
+ Like the <filename>WORKDIR</filename> case, situations exist where dependencies
+ should be ignored.
+ For these cases, you can instruct the build process to ignore a dependency
+ by using a line like the following:
+ <literallayout class='monospaced'>
+ PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
+ </literallayout>
+ This example ensures that the
+ <link linkend='var-PACKAGE_ARCHS'><filename>PACKAGE_ARCHS</filename></link>
+ variable does not
+ depend on the value of
+ <link linkend='var-MACHINE'><filename>MACHINE</filename></link>,
+ even if it does reference it.
+ </para>
+
+ <para>
+ Equally, there are cases where we need to add dependencies BitBake is not able to find.
+ You can accomplish this by using a line like the following:
+ <literallayout class='monospaced'>
+ PACKAGE_ARCHS[vardeps] = "MACHINE"
+ </literallayout>
+ This example explicitly adds the <filename>MACHINE</filename> variable as a
+ dependency for <filename>PACKAGE_ARCHS</filename>.
+ </para>
+
+ <para>
+ Consider a case with in-line Python, for example, where BitBake is not
+ able to figure out dependencies.
+ When running in debug mode (i.e. using <filename>-DDD</filename>), BitBake
+ produces output when it discovers something for which it cannot figure out
+ dependencies.
+ The Yocto Project team has currently not managed to cover those dependencies
+ in detail and is aware of the need to fix this situation.
+ </para>
+
+ <para>
+ Thus far, this section has limited discussion to the direct inputs into a task.
+ Information based on direct inputs is referred to as the "basehash" in the
+ code.
+ However, there is still the question of a task's indirect inputs - the
+ things that were already built and present in the
+ <ulink url='&YOCTO_DOCS_DEV_URL;#build-directory'>Build Directory</ulink>.
+ The checksum (or signature) for a particular task needs to add the hashes
+ of all the tasks on which the particular task depends.
+ Choosing which dependencies to add is a policy decision.
+ However, the effect is to generate a master checksum that combines the basehash
+ and the hashes of the task's dependencies.
+ </para>
+
+ <para>
+ At the code level, there are a variety of ways both the basehash and the
+ dependent task hashes can be influenced.
+ Within the BitBake configuration file, we can give BitBake some extra information
+ to help it construct the basehash.
+ The following statement effectively results in a list of global variable
+ dependency excludes - variables never included in any checksum:
+ <literallayout class='monospaced'>
+ BB_HASHBASE_WHITELIST ?= "TMPDIR FILE PATH PWD BB_TASKHASH BBPATH DL_DIR \
+ SSTATE_DIR THISDIR FILESEXTRAPATHS FILE_DIRNAME HOME LOGNAME SHELL TERM \
+ USER FILESPATH STAGING_DIR_HOST STAGING_DIR_TARGET COREBASE PRSERV_HOST \
+ PRSERV_DUMPDIR PRSERV_DUMPFILE PRSERV_LOCKDOWN PARALLEL_MAKE \
+ CCACHE_DIR EXTERNAL_TOOLCHAIN CCACHE CCACHE_DISABLE LICENSE_PATH SDKPKGSUFFIX"
+ </literallayout>
+ The previous example excludes
+ <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>
+ since that variable is actually constructed as a path within
+ <link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>, which is on
+ the whitelist.
+ </para>
+
+ <para>
+ The rules for deciding which hashes of dependent tasks to include through
+ dependency chains are more complex and are generally accomplished with a
+ Python function.
+ The code in <filename>meta/lib/oe/sstatesig.py</filename> shows two examples
+ of this and also illustrates how you can insert your own policy into the system
+ if so desired.
+ This file defines the two basic signature generators <filename>OE-Core</filename>
+ uses: "OEBasic" and "OEBasicHash".
+ By default, there is a dummy "noop" signature handler enabled in BitBake.
+ This means that behavior is unchanged from previous versions.
+ <filename>OE-Core</filename> uses the "OEBasicHash" signature handler by default
+ through this setting in the <filename>bitbake.conf</filename> file:
+ <literallayout class='monospaced'>
+ BB_SIGNATURE_HANDLER ?= "OEBasicHash"
+ </literallayout>
+ The "OEBasicHash" <filename>BB_SIGNATURE_HANDLER</filename> is the same as the
+ "OEBasic" version but adds the task hash to the stamp files.
+ This results in any
+ <ulink url='&YOCTO_DOCS_DEV_URL;#metadata'>Metadata</ulink>
+ change that changes the task hash, automatically
+ causing the task to be run again.
+ This removes the need to bump <link linkend='var-PR'><filename>PR</filename></link>
+ values, and changes to Metadata automatically ripple across the build.
+ </para>
+
+ <para>
+ It is also worth noting that the end result of these signature generators is to
+ make some dependency and hash information available to the build.
+ This information includes:
+ <itemizedlist>
+ <listitem><para><filename>BB_BASEHASH_task-</filename><replaceable>taskname</replaceable>:
+ The base hashes for each task in the recipe.
+ </para></listitem>
+ <listitem><para><filename>BB_BASEHASH_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
+ The base hashes for each dependent task.
+ </para></listitem>
+ <listitem><para><filename>BBHASHDEPS_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
+ The task dependencies for each task.
+ </para></listitem>
+ <listitem><para><filename>BB_TASKHASH</filename>:
+ The hash of the currently running task.
+ </para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='shared-state'>
+ <title>Shared State</title>
+
+ <para>
+ Checksums and dependencies, as discussed in the previous section, solve half the
+ problem of supporting a shared state.
+ The other part of the problem is being able to use checksum information during the build
+ and being able to reuse or rebuild specific components.
+ </para>
+
+ <para>
+ The
+ <link linkend='ref-classes-sstate'><filename>sstate</filename></link>
+ class is a relatively generic implementation of how to "capture"
+ a snapshot of a given task.
+ The idea is that the build process does not care about the source of a task's output.
+ Output could be freshly built or it could be downloaded and unpacked from
+ somewhere - the build process does not need to worry about its origin.
+ </para>
+
+ <para>
+ There are two types of output, one is just about creating a directory
+ in <link linkend='var-WORKDIR'><filename>WORKDIR</filename></link>.
+ A good example is the output of either
+ <link linkend='ref-tasks-install'><filename>do_install</filename></link>
+ or
+ <link linkend='ref-tasks-package'><filename>do_package</filename></link>.
+ The other type of output occurs when a set of data is merged into a shared directory
+ tree such as the sysroot.
+ </para>
+
+ <para>
+ The Yocto Project team has tried to keep the details of the
+ implementation hidden in <filename>sstate</filename> class.
+ From a user's perspective, adding shared state wrapping to a task
+ is as simple as this
+ <link linkend='ref-tasks-deploy'><filename>do_deploy</filename></link>
+ example taken from the
+ <link linkend='ref-classes-deploy'><filename>deploy</filename></link>
+ class:
+ <literallayout class='monospaced'>
+ DEPLOYDIR = "${WORKDIR}/deploy-${PN}"
+ SSTATETASKS += "do_deploy"
+ do_deploy[sstate-name] = "deploy"
+ do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"
+ do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"
+
+ python do_deploy_setscene () {
+ sstate_setscene(d)
+ }
+ addtask do_deploy_setscene
+ do_deploy[dirs] = "${DEPLOYDIR} ${B}"
+ </literallayout>
+ In this example, we add some extra flags to the task, a name field ("deploy"), an
+ input directory where the task sends data, and the output
+ directory where the data from the task should eventually be copied.
+ We also add a <filename>_setscene</filename> variant of the task and add the task
+ name to the <filename>SSTATETASKS</filename> list.
+ </para>
+
+ <para>
+ If you have a directory whose contents you need to preserve, you can do this with
+ a line like the following:
+ <literallayout class='monospaced'>
+ do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}"
+ </literallayout>
+ This method, as well as the following example, also works for multiple directories.
+ <literallayout class='monospaced'>
+ do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}"
+ do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}"
+ do_package[sstate-lockfile] = "${PACKAGELOCK}"
+ </literallayout>
+ These methods also include the ability to take a lockfile when manipulating
+ shared state directory structures since some cases are sensitive to file
+ additions or removals.
+ </para>
+
+ <para>
+ Behind the scenes, the shared state code works by looking in
+ <link linkend='var-SSTATE_DIR'><filename>SSTATE_DIR</filename></link> and
+ <link linkend='var-SSTATE_MIRRORS'><filename>SSTATE_MIRRORS</filename></link>
+ for shared state files.
+ Here is an example:
+ <literallayout class='monospaced'>
+ SSTATE_MIRRORS ?= "\
+ file://.* http://someserver.tld/share/sstate/PATH \n \
+ file://.* file:///some/local/dir/sstate/PATH"
+ </literallayout>
+ <note>
+ The shared state directory (<filename>SSTATE_DIR</filename>) is
+ organized into two-character subdirectories, where the subdirectory
+ names are based on the first two characters of the hash.
+ If the shared state directory structure for a mirror has the
+ same structure as <filename>SSTATE_DIR</filename>, you must
+ specify "PATH" as part of the URI to enable the build system
+ to map to the appropriate subdirectory.
+ </note>
+ </para>
+
+ <para>
+ The shared state package validity can be detected just by looking at the
+ filename since the filename contains the task checksum (or signature) as
+ described earlier in this section.
+ If a valid shared state package is found, the build process downloads it
+ and uses it to accelerate the task.
+ </para>
+
+ <para>
+ The build processes use the <filename>*_setscene</filename> tasks
+ for the task acceleration phase.
+ BitBake goes through this phase before the main execution code and tries
+ to accelerate any tasks for which it can find shared state packages.
+ If a shared state package for a task is available, the shared state
+ package is used.
+ This means the task and any tasks on which it is dependent are not
+ executed.
+ </para>
+
+ <para>
+ As a real world example, the aim is when building an IPK-based image,
+ only the
+ <link linkend='ref-tasks-package_write_ipk'><filename>do_package_write_ipk</filename></link>
+ tasks would have their
+ shared state packages fetched and extracted.
+ Since the sysroot is not used, it would never get extracted.
+ This is another reason why a task-based approach is preferred over a
+ recipe-based approach, which would have to install the output from every task.
+ </para>
+ </section>
+
+ <section id='tips-and-tricks'>
+ <title>Tips and Tricks</title>
+
+ <para>
+ The code in the build system that supports incremental builds is not
+ simple code.
+ This section presents some tips and tricks that help you work around
+ issues related to shared state code.
+ </para>
+
+ <section id='debugging'>
+ <title>Debugging</title>
+
+ <para>
+ When things go wrong, debugging needs to be straightforward.
+ Because of this, the Yocto Project includes strong debugging
+ tools:
+ <itemizedlist>
+ <listitem><para>Whenever a shared state package is written out, so is a
+ corresponding <filename>.siginfo</filename> file.
+ This practice results in a pickled Python database of all
+ the metadata that went into creating the hash for a given shared state
+ package.</para></listitem>
+ <listitem><para>If you run BitBake with the <filename>--dump-signatures</filename>
+ (or <filename>-S</filename>) option, BitBake dumps out
+ <filename>.siginfo</filename> files in
+ the stamp directory for every task it would have executed instead of
+ building the specified target package.</para></listitem>
+ <listitem><para>There is a <filename>bitbake-diffsigs</filename> command that
+ can process <filename>.siginfo</filename> files.
+ If you specify one of these files, BitBake dumps out the dependency
+ information in the file.
+ If you specify two files, BitBake compares the two files and dumps out
+ the differences between the two.
+ This more easily helps answer the question of "What
+ changed between X and Y?"</para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='invalidating-shared-state'>
+ <title>Invalidating Shared State</title>
+
+ <para>
+ The OpenEmbedded build system uses checksums and shared state
+ cache to avoid unnecessarily rebuilding tasks.
+ Collectively, this scheme is known as "shared state code."
+ </para>
+
+ <para>
+ As with all schemes, this one has some drawbacks.
+ It is possible that you could make implicit changes to your
+ code that the checksum calculations do not take into
+ account.
+ These implicit changes affect a task's output but do not trigger
+ the shared state code into rebuilding a recipe.
+ Consider an example during which a tool changes its output.
+ Assume that the output of <filename>rpmdeps</filename> changes.
+ The result of the change should be that all the
+ <filename>package</filename> and
+ <filename>package_write_rpm</filename> shared state cache
+ items become invalid.
+ However, because the change to the output is
+ external to the code and therefore implicit,
+ the associated shared state cache items do not become
+ invalidated.
+ In this case, the build process uses the cached items rather
+ than running the task again.
+ Obviously, these types of implicit changes can cause problems.
+ </para>
+
+ <para>
+ To avoid these problems during the build, you need to
+ understand the effects of any changes you make.
+ Realize that changes you make directly to a function
+ are automatically factored into the checksum calculation.
+ Thus, these explicit changes invalidate the associated area of
+ shared state cache.
+ However, you need to be aware of any implicit changes that
+ are not obvious changes to the code and could affect the output
+ of a given task.
+ </para>
+
+ <para>
+ When you identify an implicit change, you can easily take steps
+ to invalidate the cache and force the tasks to run.
+ The steps you can take are as simple as changing a function's
+ comments in the source code.
+ For example, to invalidate package shared state files, change
+ the comment statements of
+ <link linkend='ref-tasks-package'><filename>do_package</filename></link>
+ or the comments of one of the functions it calls.
+ Even though the change is purely cosmetic, it causes the
+ checksum to be recalculated and forces the OpenEmbedded build
+ system to run the task again.
+ </para>
+
+ <note>
+ For an example of a commit that makes a cosmetic change to
+ invalidate shared state, see this
+ <ulink url='&YOCTO_GIT_URL;/cgit.cgi/poky/commit/meta/classes/package.bbclass?id=737f8bbb4f27b4837047cb9b4fbfe01dfde36d54'>commit</ulink>.
+ </note>
+ </section>
+ </section>
+</section>
+
+<section id='x32'>
+ <title>x32</title>
+
+ <para>
+ x32 is a processor-specific Application Binary Interface (psABI) for x86_64.
+ An ABI defines the calling conventions between functions in a processing environment.
+ The interface determines what registers are used and what the sizes are for various C data types.
+ </para>
+
+ <para>
+ Some processing environments prefer using 32-bit applications even when running
+ on Intel 64-bit platforms.
+ Consider the i386 psABI, which is a very old 32-bit ABI for Intel 64-bit platforms.
+ The i386 psABI does not provide efficient use and access of the Intel 64-bit processor resources,
+ leaving the system underutilized.
+ Now consider the x86_64 psABI.
+ This ABI is newer and uses 64-bits for data sizes and program pointers.
+ The extra bits increase the footprint size of the programs, libraries,
+ and also increases the memory and file system size requirements.
+ Executing under the x32 psABI enables user programs to utilize CPU and system resources
+ more efficiently while keeping the memory footprint of the applications low.
+ Extra bits are used for registers but not for addressing mechanisms.
+ </para>
+
+ <section id='support'>
+ <title>Support</title>
+
+ <para>
+ This Yocto Project release supports the final specifications of x32
+ psABI.
+ Support for x32 psABI exists as follows:
+ <itemizedlist>
+ <listitem><para>You can create packages and images in x32 psABI format on x86_64 architecture targets.
+ </para></listitem>
+ <listitem><para>You can successfully build many recipes with the x32 toolchain.</para></listitem>
+ <listitem><para>You can create and boot <filename>core-image-minimal</filename> and
+ <filename>core-image-sato</filename> images.</para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='completing-x32'>
+ <title>Completing x32</title>
+
+ <para>
+ Future Plans for the x32 psABI in the Yocto Project include the following:
+ <itemizedlist>
+ <listitem><para>Enhance and fix the few remaining recipes so they
+ work with and support x32 toolchains.</para></listitem>
+ <listitem><para>Enhance RPM Package Manager (RPM) support for x32 binaries.</para></listitem>
+ <listitem><para>Support larger images.</para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id='using-x32-right-now'>
+ <title>Using x32 Right Now</title>
+
+ <para>
+ Follow these steps to use the x32 spABI:
+ <itemizedlist>
+ <listitem><para>Enable the x32 psABI tuning file for <filename>x86_64</filename>
+ machines by editing the <filename>conf/local.conf</filename> like this:
+ <literallayout class='monospaced'>
+ MACHINE = "qemux86-64"
+ DEFAULTTUNE = "x86-64-x32"
+ baselib = "${@d.getVar('BASE_LIB_tune-' + (d.getVar('DEFAULTTUNE', True) \
+ or 'INVALID'), True) or 'lib'}"
+ #MACHINE = "genericx86"
+ #DEFAULTTUNE = "core2-64-x32"
+ </literallayout></para></listitem>
+ <listitem><para>As usual, use BitBake to build an image that supports the x32 psABI.
+ Here is an example:
+ <literallayout class='monospaced'>
+ $ bitbake core-image-sato
+ </literallayout></para></listitem>
+ <listitem><para>As usual, run your image using QEMU:
+ <literallayout class='monospaced'>
+ $ runqemu qemux86-64 core-image-sato
+ </literallayout></para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+</section>
+
+<section id="wayland">
+ <title>Wayland</title>
+
+ <para>
+ <ulink url='http://en.wikipedia.org/wiki/Wayland_(display_server_protocol)'>Wayland</ulink>
+ is a computer display server protocol that
+ provides a method for compositing window managers to communicate
+ directly with applications and video hardware and expects them to
+ communicate with input hardware using other libraries.
+ Using Wayland with supporting targets can result in better control
+ over graphics frame rendering than an application might otherwise
+ achieve.
+ </para>
+
+ <para>
+ The Yocto Project provides the Wayland protocol libraries and the
+ reference
+ <ulink url='http://en.wikipedia.org/wiki/Wayland_(display_server_protocol)#Weston'>Weston</ulink>
+ compositor as part of its release.
+ This section describes what you need to do to implement Wayland and
+ use the compositor when building an image for a supporting target.
+ </para>
+
+ <section id="wayland-support">
+ <title>Support</title>
+
+ <para>
+ The Wayland protocol libraries and the reference Weston compositor
+ ship as integrated packages in the <filename>meta</filename> layer
+ of the
+ <ulink url='&YOCTO_DOCS_DEV_URL;#source-directory'>Source Directory</ulink>.
+ Specifically, you can find the recipes that build both Wayland
+ and Weston at <filename>meta/recipes-graphics/wayland</filename>.
+ </para>
+
+ <para>
+ You can build both the Wayland and Weston packages for use only
+ with targets that accept the
+ <ulink url='http://dri.freedesktop.org/wiki/'>Mesa 3D and Direct Rendering Infrastructure</ulink>,
+ which is also known as Mesa DRI.
+ This implies that you cannot build and use the packages if your
+ target uses, for example, the
+ <trademark class='registered'>Intel</trademark> Embedded Media and
+ Graphics Driver (<trademark class='registered'>Intel</trademark>
+ EMGD) that overrides Mesa DRI.
+ </para>
+
+ <note>
+ Due to lack of EGL support, Weston 1.0.3 will not run directly on
+ the emulated QEMU hardware.
+ However, this version of Weston will run under X emulation without
+ issues.
+ </note>
+ </section>
+
+ <section id="enabling-wayland-in-an-image">
+ <title>Enabling Wayland in an Image</title>
+
+ <para>
+ To enable Wayland, you need to enable it to be built and enable
+ it to be included in the image.
+ </para>
+
+ <section id="enable-building">
+ <title>Building</title>
+
+ <para>
+ To cause Mesa to build the <filename>wayland-egl</filename>
+ platform and Weston to build Wayland with Kernel Mode
+ Setting
+ (<ulink url='https://wiki.archlinux.org/index.php/Kernel_Mode_Setting'>KMS</ulink>)
+ support, include the "wayland" flag in the
+ <link linkend="var-DISTRO_FEATURES"><filename>DISTRO_FEATURES</filename></link>
+ statement in your <filename>local.conf</filename> file:
+ <literallayout class='monospaced'>
+ DISTRO_FEATURES_append = " wayland"
+ </literallayout>
+ </para>
+
+ <note>
+ If X11 has been enabled elsewhere, Weston will build Wayland
+ with X11 support
+ </note>
+ </section>
+
+ <section id="enable-installation-in-an-image">
+ <title>Installing</title>
+
+ <para>
+ To install the Wayland feature into an image, you must
+ include the following
+ <link linkend='var-CORE_IMAGE_EXTRA_INSTALL'><filename>CORE_IMAGE_EXTRA_INSTALL</filename></link>
+ statement in your <filename>local.conf</filename> file:
+ <literallayout class='monospaced'>
+ CORE_IMAGE_EXTRA_INSTALL += "wayland weston"
+ </literallayout>
+ </para>
+ </section>
+ </section>
+
+ <section id="running-weston">
+ <title>Running Weston</title>
+
+ <para>
+ To run Weston inside X11, enabling it as described earlier and
+ building a Sato image is sufficient.
+ If you are running your image under Sato, a Weston Launcher appears
+ in the "Utility" category.
+ </para>
+
+ <para>
+ Alternatively, you can run Weston through the command-line
+ interpretor (CLI), which is better suited for development work.
+ To run Weston under the CLI, you need to do the following after
+ your image is built:
+ <orderedlist>
+ <listitem><para>Run these commands to export
+ <filename>XDG_RUNTIME_DIR</filename>:
+ <literallayout class='monospaced'>
+ mkdir -p /tmp/$USER-weston
+ chmod 0700 /tmp/$USER-weston
+ export XDG_RUNTIME_DIR=/tmp/$USER-weston
+ </literallayout></para></listitem>
+ <listitem><para>Launch Weston in the shell:
+ <literallayout class='monospaced'>
+ weston
+ </literallayout></para></listitem>
+ </orderedlist>
+ </para>
+ </section>
+</section>
+
+<section id="licenses">
+ <title>Licenses</title>
+
+ <para>
+ This section describes the mechanism by which the OpenEmbedded build system
+ tracks changes to licensing text.
+ The section also describes how to enable commercially licensed recipes,
+ which by default are disabled.
+ </para>
+
+ <para>
+ For information that can help you maintain compliance with various open
+ source licensing during the lifecycle of the product, see the
+ "<ulink url='&YOCTO_DOCS_DEV_URL;#maintaining-open-source-license-compliance-during-your-products-lifecycle'>Maintaining Open Source License Compliance During Your Project's Lifecycle</ulink>" section
+ in the Yocto Project Development Manual.
+ </para>
+
+ <section id="usingpoky-configuring-LIC_FILES_CHKSUM">
+ <title>Tracking License Changes</title>
+
+ <para>
+ The license of an upstream project might change in the future.
+ In order to prevent these changes going unnoticed, the
+ <filename><link linkend='var-LIC_FILES_CHKSUM'>LIC_FILES_CHKSUM</link></filename>
+ variable tracks changes to the license text. The checksums are validated at the end of the
+ configure step, and if the checksums do not match, the build will fail.
+ </para>
+
+ <section id="usingpoky-specifying-LIC_FILES_CHKSUM">
+ <title>Specifying the <filename>LIC_FILES_CHKSUM</filename> Variable</title>
+
+ <para>
+ The <filename>LIC_FILES_CHKSUM</filename>
+ variable contains checksums of the license text in the source code for the recipe.
+ Following is an example of how to specify <filename>LIC_FILES_CHKSUM</filename>:
+ <literallayout class='monospaced'>
+ LIC_FILES_CHKSUM = "file://COPYING;md5=xxxx \
+ file://licfile1.txt;beginline=5;endline=29;md5=yyyy \
+ file://licfile2.txt;endline=50;md5=zzzz \
+ ..."
+ </literallayout>
+ </para>
+
+ <para>
+ The build system uses the
+ <filename><link linkend='var-S'>S</link></filename> variable as
+ the default directory when searching files listed in
+ <filename>LIC_FILES_CHKSUM</filename>.
+ The previous example employs the default directory.
+ </para>
+
+ <para>
+ Consider this next example:
+ <literallayout class='monospaced'>
+ LIC_FILES_CHKSUM = "file://src/ls.c;beginline=5;endline=16;\
+ md5=bb14ed3c4cda583abc85401304b5cd4e"
+ LIC_FILES_CHKSUM = "file://${WORKDIR}/license.html;md5=5c94767cedb5d6987c902ac850ded2c6"
+ </literallayout>
+ </para>
+
+ <para>
+ The first line locates a file in
+ <filename>${S}/src/ls.c</filename>.
+ The second line refers to a file in
+ <filename><link linkend='var-WORKDIR'>WORKDIR</link></filename>.
+ </para>
+ <para>
+ Note that <filename>LIC_FILES_CHKSUM</filename> variable is
+ mandatory for all recipes, unless the
+ <filename>LICENSE</filename> variable is set to "CLOSED".
+ </para>
+ </section>
+
+ <section id="usingpoky-LIC_FILES_CHKSUM-explanation-of-syntax">
+ <title>Explanation of Syntax</title>
+ <para>
+ As mentioned in the previous section, the
+ <filename>LIC_FILES_CHKSUM</filename> variable lists all the
+ important files that contain the license text for the source code.
+ It is possible to specify a checksum for an entire file, or a specific section of a
+ file (specified by beginning and ending line numbers with the "beginline" and "endline"
+ parameters, respectively).
+ The latter is useful for source files with a license notice header,
+ README documents, and so forth.
+ If you do not use the "beginline" parameter, then it is assumed that the text begins on the
+ first line of the file.
+ Similarly, if you do not use the "endline" parameter, it is assumed that the license text
+ ends with the last line of the file.
+ </para>
+
+ <para>
+ The "md5" parameter stores the md5 checksum of the license text.
+ If the license text changes in any way as compared to this parameter
+ then a mismatch occurs.
+ This mismatch triggers a build failure and notifies the developer.
+ Notification allows the developer to review and address the license text changes.
+ Also note that if a mismatch occurs during the build, the correct md5
+ checksum is placed in the build log and can be easily copied to the recipe.
+ </para>
+
+ <para>
+ There is no limit to how many files you can specify using the
+ <filename>LIC_FILES_CHKSUM</filename> variable.
+ Generally, however, every project requires a few specifications for license tracking.
+ Many projects have a "COPYING" file that stores the license information for all the source
+ code files.
+ This practice allows you to just track the "COPYING" file as long as it is kept up to date.
+ </para>
+
+ <tip>
+ If you specify an empty or invalid "md5" parameter, BitBake returns an md5 mis-match
+ error and displays the correct "md5" parameter value during the build.
+ The correct parameter is also captured in the build log.
+ </tip>
+
+ <tip>
+ If the whole file contains only license text, you do not need to use the "beginline" and
+ "endline" parameters.
+ </tip>
+ </section>
+ </section>
+
+ <section id="enabling-commercially-licensed-recipes">
+ <title>Enabling Commercially Licensed Recipes</title>
+
+ <para>
+ By default, the OpenEmbedded build system disables
+ components that have commercial or other special licensing
+ requirements.
+ Such requirements are defined on a
+ recipe-by-recipe basis through the
+ <link linkend='var-LICENSE_FLAGS'><filename>LICENSE_FLAGS</filename></link>
+ variable definition in the affected recipe.
+ For instance, the
+ <filename>poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly</filename>
+ recipe contains the following statement:
+ <literallayout class='monospaced'>
+ LICENSE_FLAGS = "commercial"
+ </literallayout>
+ Here is a slightly more complicated example that contains both an
+ explicit recipe name and version (after variable expansion):
+ <literallayout class='monospaced'>
+ LICENSE_FLAGS = "license_${PN}_${PV}"
+ </literallayout>
+ In order for a component restricted by a <filename>LICENSE_FLAGS</filename>
+ definition to be enabled and included in an image, it
+ needs to have a matching entry in the global
+ <link linkend='var-LICENSE_FLAGS_WHITELIST'><filename>LICENSE_FLAGS_WHITELIST</filename></link>
+ variable, which is a variable
+ typically defined in your <filename>local.conf</filename> file.
+ For example, to enable
+ the <filename>poky/meta/recipes-multimedia/gstreamer/gst-plugins-ugly</filename>
+ package, you could add either the string
+ "commercial_gst-plugins-ugly" or the more general string
+ "commercial" to <filename>LICENSE_FLAGS_WHITELIST</filename>.
+ See the
+ "<link linkend='license-flag-matching'>License Flag Matching</link>" section
+ for a full explanation of how <filename>LICENSE_FLAGS</filename> matching works.
+ Here is the example:
+ <literallayout class='monospaced'>
+ LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly"
+ </literallayout>
+ Likewise, to additionally enable the package built from the recipe containing
+ <filename>LICENSE_FLAGS = "license_${PN}_${PV}"</filename>, and assuming
+ that the actual recipe name was <filename>emgd_1.10.bb</filename>,
+ the following string would enable that package as well as
+ the original <filename>gst-plugins-ugly</filename> package:
+ <literallayout class='monospaced'>
+ LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly license_emgd_1.10"
+ </literallayout>
+ As a convenience, you do not need to specify the complete license string
+ in the whitelist for every package.
+ You can use an abbreviated form, which consists
+ of just the first portion or portions of the license string before
+ the initial underscore character or characters.
+ A partial string will match
+ any license that contains the given string as the first
+ portion of its license.
+ For example, the following
+ whitelist string will also match both of the packages
+ previously mentioned as well as any other packages that have
+ licenses starting with "commercial" or "license".
+ <literallayout class='monospaced'>
+ LICENSE_FLAGS_WHITELIST = "commercial license"
+ </literallayout>
+ </para>
+
+ <section id="license-flag-matching">
+ <title>License Flag Matching</title>
+
+ <para>
+ License flag matching allows you to control what recipes the
+ OpenEmbedded build system includes in the build.
+ Fundamentally, the build system attempts to match
+ <link linkend='var-LICENSE_FLAGS'><filename>LICENSE_FLAGS</filename></link>
+ strings found in recipes against
+ <link linkend='var-LICENSE_FLAGS_WHITELIST'><filename>LICENSE_FLAGS_WHITELIST</filename></link>
+ strings found in the whitelist.
+ A match causes the build system to include a recipe in the
+ build, while failure to find a match causes the build system to
+ exclude a recipe.
+ </para>
+
+ <para>
+ In general, license flag matching is simple.
+ However, understanding some concepts will help you
+ correctly and effectively use matching.
+ </para>
+
+ <para>
+ Before a flag
+ defined by a particular recipe is tested against the
+ contents of the whitelist, the expanded string
+ <filename>_${PN}</filename> is appended to the flag.
+ This expansion makes each <filename>LICENSE_FLAGS</filename>
+ value recipe-specific.
+ After expansion, the string is then matched against the
+ whitelist.
+ Thus, specifying
+ <filename>LICENSE_FLAGS = "commercial"</filename>
+ in recipe "foo", for example, results in the string
+ <filename>"commercial_foo"</filename>.
+ And, to create a match, that string must appear in the
+ whitelist.
+ </para>
+
+ <para>
+ Judicious use of the <filename>LICENSE_FLAGS</filename>
+ strings and the contents of the
+ <filename>LICENSE_FLAGS_WHITELIST</filename> variable
+ allows you a lot of flexibility for including or excluding
+ recipes based on licensing.
+ For example, you can broaden the matching capabilities by
+ using license flags string subsets in the whitelist.
+ <note>When using a string subset, be sure to use the part of
+ the expanded string that precedes the appended underscore
+ character (e.g. <filename>usethispart_1.3</filename>,
+ <filename>usethispart_1.4</filename>, and so forth).
+ </note>
+ For example, simply specifying the string "commercial" in
+ the whitelist matches any expanded
+ <filename>LICENSE_FLAGS</filename> definition that starts with
+ the string "commercial" such as "commercial_foo" and
+ "commercial_bar", which are the strings the build system
+ automatically generates for hypothetical recipes named
+ "foo" and "bar" assuming those recipes simply specify the
+ following:
+ <literallayout class='monospaced'>
+ LICENSE_FLAGS = "commercial"
+ </literallayout>
+ Thus, you can choose to exhaustively
+ enumerate each license flag in the whitelist and
+ allow only specific recipes into the image, or
+ you can use a string subset that causes a broader range of
+ matches to allow a range of recipes into the image.
+ </para>
+
+ <para>
+ This scheme works even if the
+ <filename>LICENSE_FLAGS</filename> string already
+ has <filename>_${PN}</filename> appended.
+ For example, the build system turns the license flag
+ "commercial_1.2_foo" into "commercial_1.2_foo_foo" and would
+ match both the general "commercial" and the specific
+ "commercial_1.2_foo" strings found in the whitelist, as
+ expected.
+ </para>
+
+ <para>
+ Here are some other scenarios:
+ <itemizedlist>
+ <listitem><para>You can specify a versioned string in the
+ recipe such as "commercial_foo_1.2" in a "foo" recipe.
+ The build system expands this string to
+ "commercial_foo_1.2_foo".
+ Combine this license flag with a whitelist that has
+ the string "commercial" and you match the flag along
+ with any other flag that starts with the string
+ "commercial".</para></listitem>
+ <listitem><para>Under the same circumstances, you can
+ use "commercial_foo" in the whitelist and the
+ build system not only matches "commercial_foo_1.2" but
+ also matches any license flag with the string
+ "commercial_foo", regardless of the version.
+ </para></listitem>
+ <listitem><para>You can be very specific and use both the
+ package and version parts in the whitelist (e.g.
+ "commercial_foo_1.2") to specifically match a
+ versioned recipe.</para></listitem>
+ </itemizedlist>
+ </para>
+ </section>
+
+ <section id="other-variables-related-to-commercial-licenses">
+ <title>Other Variables Related to Commercial Licenses</title>
+
+ <para>
+ Other helpful variables related to commercial
+ license handling exist and are defined in the
+ <filename>poky/meta/conf/distro/include/default-distrovars.inc</filename> file:
+ <literallayout class='monospaced'>
+ COMMERCIAL_AUDIO_PLUGINS ?= ""
+ COMMERCIAL_VIDEO_PLUGINS ?= ""
+ COMMERCIAL_QT = ""
+ </literallayout>
+ If you want to enable these components, you can do so by making sure you have
+ statements similar to the following
+ in your <filename>local.conf</filename> configuration file:
+ <literallayout class='monospaced'>
+ COMMERCIAL_AUDIO_PLUGINS = "gst-plugins-ugly-mad \
+ gst-plugins-ugly-mpegaudioparse"
+ COMMERCIAL_VIDEO_PLUGINS = "gst-plugins-ugly-mpeg2dec \
+ gst-plugins-ugly-mpegstream gst-plugins-bad-mpegvideoparse"
+ COMMERCIAL_QT ?= "qmmp"
+ LICENSE_FLAGS_WHITELIST = "commercial_gst-plugins-ugly commercial_gst-plugins-bad commercial_qmmp"
+ </literallayout>
+ Of course, you could also create a matching whitelist
+ for those components using the more general "commercial"
+ in the whitelist, but that would also enable all the
+ other packages with
+ <link linkend='var-LICENSE_FLAGS'><filename>LICENSE_FLAGS</filename></link>
+ containing "commercial", which you may or may not want:
+ <literallayout class='monospaced'>
+ LICENSE_FLAGS_WHITELIST = "commercial"
+ </literallayout>
+ </para>
+
+ <para>
+ Specifying audio and video plug-ins as part of the
+ <filename>COMMERCIAL_AUDIO_PLUGINS</filename> and
+ <filename>COMMERCIAL_VIDEO_PLUGINS</filename> statements
+ or commercial Qt components as part of
+ the <filename>COMMERCIAL_QT</filename> statement (along
+ with the enabling <filename>LICENSE_FLAGS_WHITELIST</filename>) includes the
+ plug-ins or components into built images, thus adding
+ support for media formats or components.
+ </para>
+ </section>
+ </section>
+</section>
+</chapter>
+<!--
+vim: expandtab tw=80 ts=4
+-->