<!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=' overview-manual-concepts'> <title>Yocto Project Concepts</title> <para> This chapter provides explanations for Yocto Project concepts that go beyond the surface of "how-to" information and reference (or look-up) material. Concepts such as components, the <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> workflow, cross-development toolchains, shared state cache, and so forth are explained. </para> <section id='yocto-project-components'> <title>Yocto Project Components</title> <para> The <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink> task executor together with various types of configuration files form the <ulink url='&YOCTO_DOCS_REF_URL;#oe-core'>OpenEmbedded-Core</ulink>. 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 Tasks 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='openembedded-build-system-build-concepts'>OpenEmbedded Build System Concepts</link>" section. </para> <section id='usingpoky-components-bitbake'> <title>BitBake</title> <para> BitBake is the tool at the heart of the <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> and is responsible for parsing the <ulink url='&YOCTO_DOCS_REF_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"). 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='overview-components-recipes'> <title>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='overview-components-classes'> <title>Classes</title> <para> Class files (<filename>.bbclass</filename>) contain information that is useful to share between recipes files. An example is the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink> class, which contains common settings for any application that Autotools uses. The "<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes'>Classes</ulink>" chapter in the Yocto Project Reference Manual provides details about classes and how to use them. </para> </section> <section id='overview-components-configurations'> <title>Configurations</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>conf/local.conf</filename>, which is found in the <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>. </para> </section> </section> <section id='overview-layers'> <title>Layers</title> <para> Layers are repositories that contain related metadata (i.e. sets of instructions) that tell the OpenEmbedded build system how to build a target. Yocto Project's <link linkend='the-yocto-project-layer-model'>layer model</link> facilitates collaboration, sharing, customization, and reuse within the Yocto Project development environment. Layers logically separate information for your project. For example, you can use a layer to hold all the configurations for a particular piece of hardware. Isolating hardware-specific configurations allows you to share other metadata by using a different layer where that metadata might be common across several pieces of hardware. </para> <para> Many layers exist that work in the Yocto Project development environment. The <ulink url='https://caffelli-staging.yoctoproject.org/software-overview/layers/'>Yocto Project Curated Layer Index</ulink> and <ulink url='http://layers.openembedded.org/layerindex/branch/master/layers/'>OpenEmbedded Layer Index</ulink> both contain layers from which you can use or leverage. </para> <para> By convention, layers in the Yocto Project follow a specific form. Conforming to a known structure allows BitBake to make assumptions during builds on where to find types of metadata. You can find procedures and learn about tools (i.e. <filename>bitbake-layers</filename>) for creating layers suitable for the Yocto Project in the "<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>" section of the Yocto Project Development Tasks Manual. </para> </section> <section id="openembedded-build-system-build-concepts"> <title>OpenEmbedded Build System Concepts</title> <para> This section takes a more detailed look inside the build process used by the <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink>, which is the build system specific to the Yocto Project. At the heart of the build system is BitBake, the task executor. </para> <para> The following diagram represents the high-level workflow of a build. The remainder of this section expands on the fundamental input, output, process, and metadata logical blocks that make up the workflow. </para> <para id='general-workflow-figure'> <imagedata fileref="figures/YP-flow-diagram.png" format="PNG" align='center' width="8in"/> </para> <para> In general, the build's workflow 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_REF_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 Software Development Kit (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 workflow. </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-workflow-figure'>general workflow figure</link>: </para> <para> <imagedata fileref="figures/user-configuration.png" align="center" width="8in" depth="4.5in" /> </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 <filename>build/conf</filename> directory of the <ulink url='&YOCTO_DOCS_REF_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 <ulink url='&YOCTO_DOCS_REF_URL;#poky'>Poky</ulink> 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-poky</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 <ulink url='&YOCTO_DOCS_REF_URL;#structure-core-script'><filename>&OE_INIT_FILE;</filename></ulink>, which is the build environment script. </para> <para> Sourcing the build environment script creates a <ulink url='&YOCTO_DOCS_REF_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> script in the context of separate <ulink url='&YOCTO_DOCS_REF_URL;#oe-core'>OpenEmbedded-Core</ulink> 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 <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-poky/conf/local.conf.sample'><filename>local.conf.sample</filename></ulink> in the <filename>meta-poky</filename> layer: <itemizedlist> <listitem><para> <emphasis>Target Machine Selection:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink> variable. </para></listitem> <listitem><para> <emphasis>Download Directory:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink> variable. </para></listitem> <listitem><para> <emphasis>Shared State Directory:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink> variable. </para></listitem> <listitem><para> <emphasis>Build Output:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink> variable. </para></listitem> <listitem><para> <emphasis>Distribution Policy:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-DISTRO'><filename>DISTRO</filename></ulink> variable. </para></listitem> <listitem><para> <emphasis>Packaging Format:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink> variable. </para></listitem> <listitem><para> <emphasis>SDK Target Architecture:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKMACHINE'><filename>SDKMACHINE</filename></ulink> variable. </para></listitem> <listitem><para> <emphasis>Extra Image Packages:</emphasis> Controlled by the <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_IMAGE_FEATURES'><filename>EXTRA_IMAGE_FEATURES</filename></ulink> 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 Tasks 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 the <filename>site.conf</filename> file, you need to create that yourself. The <filename>auto.conf</filename> file is typically created by an autobuilder: <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 <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink> variable.</para> <para>One useful scenario for using the <filename>conf/site.conf</filename> file is to extend your <ulink url='&YOCTO_DOCS_REF_URL;#var-BBPATH'><filename>BBPATH</filename></ulink> 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> 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. It is important to understand that the <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> reads the configuration files in a specific order: <filename>site.conf</filename>, <filename>auto.conf</filename>, and <filename>local.conf</filename>. And, the build system applies the normal assignment statement rules as described in the "<ulink url='&YOCTO_DOCS_BB_URL;#bitbake-user-manual-metadata'>Syntax and Operators</ulink>" chapter of the BitBake User Manual. Because the files are parsed in a specific order, variable assignments for the same variable could be affected. For example, if the <filename>auto.conf</filename> file and the <filename>local.conf</filename> set <replaceable>variable1</replaceable> to different values, because the build system parses <filename>local.conf</filename> after <filename>auto.conf</filename>, <replaceable>variable1</replaceable> is assigned the value from the <filename>local.conf</filename> file. </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 policies. </para> <para> In general, three types of layer input exists. You can see them below the "User Configuration" box in the <link linkend='general-workflow-figure'>general workflow figure</link>: <itemizedlist> <listitem><para> <emphasis>Metadata (<filename>.bb</filename> + Patches):</emphasis> Software layers containing user-supplied recipe files, patches, and append files. A good example of a software layer might be the <ulink url='https://github.com/meta-qt5/meta-qt5'><filename>meta-qt5</filename></ulink> layer from the <ulink url='http://layers.openembedded.org/layerindex/branch/master/layers/'>OpenEmbedded Layer Index</ulink>. This layer is for version 5.0 of the popular <ulink url='https://wiki.qt.io/About_Qt'>Qt</ulink> cross-platform application development framework for desktop, embedded and mobile. </para></listitem> <listitem><para> <emphasis>Machine BSP Configuration:</emphasis> Board Support Package (BSP) layers (i.e. "BSP Layer" in the following figure) providing machine-specific configurations. This type of information is specific to a particular target architecture. A good example of a BSP layer from the <link linkend='gs-reference-distribution-poky'>Poky Reference Distribution</link> is the <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-yocto-bsp'><filename>meta-yocto-bsp</filename></ulink> layer. </para></listitem> <listitem><para> <emphasis>Policy Configuration:</emphasis> Distribution Layers (i.e. "Distro Layer" in the following figure) providing top-level or general policies for the images or SDKs being built for a particular distribution. For example, in the Poky Reference Distribution the distro layer is the <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-poky'><filename>meta-poky</filename></ulink> layer. Within the distro layer is a <filename>conf/distro</filename> directory that contains distro configuration files (e.g. <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta-poky/conf/distro/poky.conf'><filename>poky.conf</filename></ulink> that contain many policy configurations for the Poky distribution. </para></listitem> </itemizedlist> </para> <para> The following figure shows an expanded representation of these three layers from the <link linkend='general-workflow-figure'>general workflow figure</link>: </para> <para> <imagedata fileref="figures/layer-input.png" align="center" width="8in" depth="8in" /> </para> <para> In general, all layers have a similar structure. They all contain a licensing file (e.g. <filename>COPYING.MIT</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. You can learn about the general structure for layers used with the Yocto Project in the "<ulink url='&YOCTO_DOCS_DEV_URL;#creating-your-own-layer'>Creating Your Own Layer</ulink>" section in the Yocto Project Development Tasks Manual. For a general discussion on layers and the many layers from which you can draw, see the "<link linkend='overview-layers'>Layers</link>" and "<link linkend='the-yocto-project-layer-model'>The Yocto Project Layer Model</link>" sections both earlier in this manual. </para> <para> If you explored the previous links, you discovered some areas where many layers that work with the Yocto Project exist. The <ulink url="http://git.yoctoproject.org/">Source Repositories</ulink> also shows layers categorized under "Yocto Metadata Layers." <note> Layers exist in the Yocto Project Source Repositories that cannot be found in the OpenEmbedded Layer 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> <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 "<ulink url='&YOCTO_DOCS_REF_URL;#ref-classes'>Classes</ulink>" chapter of the Yocto Reference Manual. </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. Examples of <filename>recipes-*</filename> directories are <filename>recipes-core</filename> and <filename>recipes-extra</filename>. Hierarchy and contents within a <filename>recipes-*</filename> directory can vary. Generally, these directories contain recipe files (<filename>*.bb</filename>), recipe append files (<filename>*.bbappend</filename>), directories that are distro-specific for configuration files, and so forth. </para></listitem> </itemizedlist> </para> </section> <section id="bsp-layer"> <title>BSP Layer</title> <para> The BSP Layer provides machine configurations that target specific hardware. 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>, <filename>recipes-kernel</filename>, and so forth. 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 recipes, append files, and patches, that your project needs. </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-workflow-figure'>general workflow 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 Materials" 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></ulink> 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 <link linkend='general-workflow-figure'>general workflow figure</link>: </para> <para> <imagedata fileref="figures/source-input.png" width="6in" depth="6in" align="center" /> </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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-externalsrc'><filename>externalsrc</filename></ulink> 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> </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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink> task inside BitBake uses the <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink> variable and the argument's prefix to determine the correct fetcher module. <note> For information on how to have the OpenEmbedded build system generate tarballs for Git repositories and place them in the <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink> directory, see the <ulink url='&YOCTO_DOCS_REF_URL;#var-BB_GENERATE_MIRROR_TARBALLS'><filename>BB_GENERATE_MIRROR_TARBALLS</filename></ulink> variable. </note> </para> <para> When fetching a repository, BitBake uses the <ulink url='&YOCTO_DOCS_REF_URL;#var-SRCREV'><filename>SRCREV</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-PREMIRRORS'><filename>PREMIRRORS</filename></ulink> and <ulink url='&YOCTO_DOCS_REF_URL;#var-MIRRORS'><filename>MIRRORS</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-DL_DIR'><filename>DL_DIR</filename></ulink> 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_REF_URL;#build-directory'>Build Directory</ulink>. The <link linkend='general-workflow-figure'>general workflow 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink> variable. Before placing the packages into package feeds, the build process validates them with generated output quality assurance checks through the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-insane'><filename>insane</filename></ulink> 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> <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></ulink>: 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR_RPM'><filename>DEPLOY_DIR_RPM</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR_IPK'><filename>DEPLOY_DIR_IPK</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR_DEB'><filename>DEPLOY_DIR_DEB</filename></ulink>, or <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR_TAR'><filename>DEPLOY_DIR_TAR</filename></ulink>, variables are used, respectively. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>: Defines architecture-specific sub-folders. For example, packages could exist for the i586 or qemux86 architectures. </para></listitem> </itemizedlist> </para> <para> BitBake uses the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_deb'><filename>do_package_write_*</filename></ulink> 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 "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_deb'><filename>do_package_write_deb</filename></ulink>", "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_ipk'><filename>do_package_write_ipk</filename></ulink>", "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_rpm'><filename>do_package_write_rpm</filename></ulink>", and "<ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_tar'><filename>do_package_write_tar</filename></ulink>" sections in the Yocto Project Reference Manual 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_REF_URL;#bitbake-term'>BitBake</ulink> to produce images and Software Development Kits (SDKs). You can see from the <link linkend='general-workflow-figure'>general workflow figure</link>, the BitBake area consists of several functional areas. This section takes a closer look at each of those areas. <note> 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. </note> </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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-fetch'><filename>do_fetch</filename></ulink> and <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink> tasks fetch the source files and unpack them into the <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink>. <note> For every local file (e.g. <filename>file://</filename>) that is part of a recipe's <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink> 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> task. 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 Build Directory, which has a defined structure. For additional general information on the Build Directory, see the "<ulink url='&YOCTO_DOCS_REF_URL;#structure-core-build'><filename>build/</filename></ulink>" section in the Yocto Project Reference Manual. </para> <para> Each recipe has an area in the Build Directory where the unpacked source code resides. The <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> variable points to this area for a recipe's unpacked source code. The name of that directory for any given recipe is defined from several different variables. The preceding figure and the following list describe the Build Directory's hierarchy: <itemizedlist> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>: The base directory where the OpenEmbedded build system performs all its work during the build. The default base directory is the <filename>tmp</filename> directory. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCH'><filename>PACKAGE_ARCH</filename></ulink>: The architecture of the built package or packages. Depending on the eventual destination of the package or packages (i.e. machine architecture, <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>build host</ulink>, SDK, or specific machine), <filename>PACKAGE_ARCH</filename> varies. See the variable's description for details. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-TARGET_OS'><filename>TARGET_OS</filename></ulink>: The operating system of the target device. A typical value would be "linux" (e.g. "qemux86-poky-linux"). </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PN'><filename>PN</filename></ulink>: The name of the recipe used to build the package. This variable can have multiple meanings. However, when used in the context of input files, <filename>PN</filename> represents the the name of the recipe. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>: The location where the OpenEmbedded build system builds a recipe (i.e. does the work to create the package). <itemizedlist> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>: The version of the recipe used to build the package. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink>: The revision of the recipe used to build the package. </para></listitem> </itemizedlist> </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink>: Contains the unpacked source files for a given recipe. <itemizedlist> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-BPN'><filename>BPN</filename></ulink>: The name of the recipe used to build the package. The <filename>BPN</filename> variable is a version of the <filename>PN</filename> variable but with common prefixes and suffixes removed. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PV'><filename>PV</filename></ulink>: The version of the recipe used to build the package. </para></listitem> </itemizedlist> </para></listitem> </itemizedlist> <note> In the previous figure, notice that two sample hierarchies exist: one based on package architecture (i.e. <filename>PACKAGE_ARCH</filename>) and one based on a machine (i.e. <filename>MACHINE</filename>). The underlying structures are identical. The differentiator being what the OpenEmbedded build system is using as a build target (e.g. general architecture, a build host, an SDK, or a specific machine). </note> </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="7in" depth="6in" /> </para> <para> The <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink> task uses a recipe's <ulink url='&YOCTO_DOCS_REF_URL;#var-SRC_URI'><filename>SRC_URI</filename></ulink> statements and the <ulink url='&YOCTO_DOCS_REF_URL;#var-FILESPATH'><filename>FILESPATH</filename></ulink> variable to locate applicable patch files. </para> <para> Default processing for patch files assumes the files have either <filename>*.patch</filename> or <filename>*.diff</filename> file types. You can use <filename>SRC_URI</filename> parameters to change the way the build system recognizes patch files. See the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink> task for more information. </para> <para> BitBake finds and applies multiple patches for a single recipe in the order in which it locates the patches. The <filename>FILESPATH</filename> variable defines the default set of directories that the build system uses to search for patch files. Once found, patches are applied to the recipe's source files, which are located in the <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> 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. For more information on how to create patches and how the build system processes patches, see the "<ulink url='&YOCTO_DOCS_DEV_URL;#new-recipe-patching-code'>Patching Code</ulink>" section in the Yocto Project Development Tasks Manual. You can also see the "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-devtool-use-devtool-modify-to-modify-the-source-of-an-existing-component'>Use <filename>devtool modify</filename> to Modify the Source of an Existing Component</ulink>" section in the Yocto Project Application Development and the Extensible Software Development Kit (SDK) manual and the "<ulink url='&YOCTO_DOCS_KERNEL_DEV_URL;#using-traditional-kernel-development-to-patch-the-kernel'>Using Traditional Kernel Development to Patch the Kernel</ulink>" section in the Yocto Project Linux Kernel Development Manual. </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. Once compilation occurs, the files are copied to a holding area in preparation for packaging: <imagedata fileref="figures/configuration-compile-autoreconf.png" align="center" width="7in" depth="5in" /> </para> <para> This step in the build process consists of the following tasks: <itemizedlist> <listitem><para> <emphasis><ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-prepare_recipe_sysroot'><filename>do_prepare_recipe_sysroot</filename></ulink></emphasis>: This task sets up the two sysroots in <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}</filename> (i.e. <filename>recipe-sysroot</filename> and <filename>recipe-sysroot-native</filename>) so that the sysroots contain the contents of the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></ulink> tasks of the recipes on which the recipe containing the tasks depends. A sysroot exists for both the target and for the native binaries, which run on the host system. </para></listitem> <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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-configure'><filename>do_configure</filename></ulink> task are specific to configurations for the source code being built by the recipe.</para> <para>If you are using the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink> class, you can add additional configuration options by using the <ulink url='&YOCTO_DOCS_REF_URL;#var-EXTRA_OECONF'><filename>EXTRA_OECONF</filename></ulink> or <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGECONFIG_CONFARGS'><filename>PACKAGECONFIG_CONFARGS</filename></ulink> variables. For information on how this variable works within that class, see the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-autotools'><filename>autotools</filename></ulink> class <ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/poky/tree/meta/classes/autotools.bbclass'>here</ulink>. </para></listitem> <listitem><para> <emphasis><filename>do_compile</filename></emphasis>: Once a configuration task has been satisfied, BitBake compiles the source using the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-compile'><filename>do_compile</filename></ulink> task. Compilation occurs in the directory pointed to by the <ulink url='&YOCTO_DOCS_REF_URL;#var-B'><filename>B</filename></ulink> variable. Realize that the <filename>B</filename> directory is, by default, the same as the <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> directory. </para></listitem> <listitem><para> <emphasis><filename>do_install</filename></emphasis>: After compilation completes, BitBake executes the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink> task. This task copies files from the <filename>B</filename> directory and places them in a holding area pointed to by the <ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink> variable. Packaging occurs later using files from this holding directory. </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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink> and <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-packagedata'><filename>do_packagedata</filename></ulink> tasks combine to analyze the files found in the <ulink url='&YOCTO_DOCS_REF_URL;#var-D'><filename>D</filename></ulink> 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> <ulink url='&YOCTO_DOCS_REF_URL;#var-PKGD'><filename>PKGD</filename></ulink>: The destination directory for packages before they are split. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></ulink>: A shared, global-state directory that holds data generated during the packaging process. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PKGDESTWORK'><filename>PKGDESTWORK</filename></ulink>: A temporary work area used by the <filename>do_package</filename> task. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PKGDEST'><filename>PKGDEST</filename></ulink>: The parent directory for packages after they have been split. </para></listitem> </itemizedlist> The <ulink url='&YOCTO_DOCS_REF_URL;#var-FILES'><filename>FILES</filename></ulink> variable defines the files that go into each package in <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGES'><filename>PACKAGES</filename></ulink>. If you want details on how this is accomplished, you can look at the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-package'><filename>package</filename></ulink> class. </para> <para> Depending on the type of packages being created (RPM, DEB, or IPK), the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_deb'><filename>do_package_write_*</filename></ulink> 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 several tasks and variables. The <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-rootfs'><filename>do_rootfs</filename></ulink> task creates the root filesystem (file and directory structure) for an image. This task uses several key variables to help create the list of packages to actually install: <itemizedlist> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_INSTALL'><filename>IMAGE_INSTALL</filename></ulink>: Lists out the base set of packages to install from the Package Feeds area. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_EXCLUDE'><filename>PACKAGE_EXCLUDE</filename></ulink>: Specifies packages that should not be installed. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FEATURES'><filename>IMAGE_FEATURES</filename></ulink>: Specifies features to include in the image. Most of these features map to additional packages for installation. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_CLASSES'><filename>PACKAGE_CLASSES</filename></ulink>: Specifies the package backend to use and consequently helps determine where to locate packages within the Package Feeds area. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_LINGUAS'><filename>IMAGE_LINGUAS</filename></ulink>: Determines the language(s) for which additional language support packages are installed. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_INSTALL'><filename>PACKAGE_INSTALL</filename></ulink>: The final list of packages passed to the package manager for installation into the image. </para></listitem> </itemizedlist> </para> <para> With <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_ROOTFS'><filename>IMAGE_ROOTFS</filename></ulink> pointing to the location of the filesystem under construction and the <filename>PACKAGE_INSTALL</filename> variable providing the final list of packages to install, the root file system is created. </para> <para> Package installation is under control of the package manager (e.g. dnf/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. As part of the final stage of package installation, postinstall scripts that are part of the packages are run. Any scripts 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> The final stages of the <filename>do_rootfs</filename> task handle post processing. Post processing includes creation of a manifest file and optimizations. </para> <para> The manifest file (<filename>.manifest</filename>) resides in the same directory as the root filesystem image. This file lists out, line-by-line, the installed packages. The manifest file is useful for the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-testimage*'><filename>testimage</filename></ulink> class, for example, to determine whether or not to run specific tests. See the <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_MANIFEST'><filename>IMAGE_MANIFEST</filename></ulink> variable for additional information. </para> <para> Optimizing processes run across the image include <filename>mklibs</filename>, <filename>prelink</filename>, and any other post-processing commands as defined by the <ulink url='&YOCTO_DOCS_REF_URL;#var-ROOTFS_POSTPROCESS_COMMAND'><filename>ROOTFS_POSTPROCESS_COMMAND</filename></ulink> variable. The <filename>mklibs</filename> process optimizes the size of the libraries, while the <filename>prelink</filename> process optimizes the dynamic linking of shared libraries to reduce start up time of executables. </para> <para> After the root filesystem is built, processing begins on the image through the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-image'><filename>do_image</filename></ulink> task. The build system runs any pre-processing commands as defined by the <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_PREPROCESS_COMMAND'><filename>IMAGE_PREPROCESS_COMMAND</filename></ulink> variable. This variable specifies a list of functions to call before the OpenEmbedded build system creates the final image output files. </para> <para> The OpenEmbedded build system dynamically creates <filename>do_image_*</filename> tasks as needed, based on the image types specified in the <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></ulink> variable. The process turns everything into an image file or a set of image files and can compress the root filesystem image to reduce the overall size of the image. The formats used for the root filesystem depend on the <filename>IMAGE_FSTYPES</filename> variable. Compression depends on whether the formats support compression. </para> <para> As an example, a dynamically created task when creating a particular image <replaceable>type</replaceable> would take the following form: <literallayout class='monospaced'> do_image_<replaceable>type</replaceable> </literallayout> So, if the <replaceable>type</replaceable> as specified by the <filename>IMAGE_FSTYPES</filename> were <filename>ext4</filename>, the dynamically generated task would be as follows: <literallayout class='monospaced'> do_image_ext4 </literallayout> </para> <para> The final task involved in image creation is the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-image-complete'><filename>do_image_complete</filename></ulink> task. This task completes the image by applying any image post processing as defined through the <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_POSTPROCESS_COMMAND'><filename>IMAGE_POSTPROCESS_COMMAND</filename></ulink> variable. The variable specifies a list of functions to call once the OpenEmbedded build system has created the final image output files. <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> </para> </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 for both the standard and extensible SDKs: <imagedata fileref="figures/sdk-generation.png" align="center" /> <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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sdk'><filename>do_populate_sdk</filename></ulink> task, see the "<ulink url='&YOCTO_DOCS_SDK_URL;#sdk-building-an-sdk-installer'>Building an SDK Installer</ulink>" section in the Yocto Project Application Development and the Extensible Software Development Kit (SDK) manual. </note> </para> <para> Like image generation, the SDK script process consists of several stages and depends on many variables. The <filename>do_populate_sdk</filename> and <filename>do_populate_sdk_ext</filename> tasks use 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 helps create the standard SDK and 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKMACHINE'><filename>SDKMACHINE</filename></ulink>. </para> <para> The <filename>do_populate_sdk_ext</filename> task helps create the extensible SDK and handles host and target parts differently than its counter part does for the standard SDK. For the extensible SDK, the task encapsulates the build system, which includes everything needed (host and target) for the SDK. </para> <para> Regardless of the type of SDK being constructed, the tasks perform some cleanup after which a cross-development environment setup script and any needed configuration files are created. The final output is the Cross-development toolchain installation script (<filename>.sh</filename> file), which includes the environment setup script. </para> </section> <section id='stamp-files-and-the-rerunning-of-tasks'> <title>Stamp Files and the Rerunning of Tasks</title> <para> For each task that completes successfully, BitBake writes a stamp file into the <ulink url='&YOCTO_DOCS_REF_URL;#var-STAMPS_DIR'><filename>STAMPS_DIR</filename></ulink> directory. The beginning of the stamp file's filename is determined by the <ulink url='&YOCTO_DOCS_REF_URL;#var-STAMP'><filename>STAMP</filename></ulink> variable, and the end of the name consists of the task's name and current <link linkend='overview-checksums'>input checksum</link>. <note> This naming scheme assumes that <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_SIGNATURE_HANDLER'><filename>BB_SIGNATURE_HANDLER</filename></ulink> is "OEBasicHash", which is almost always the case in current OpenEmbedded. </note> To determine if a task needs to be rerun, BitBake checks if a stamp file with a matching input checksum exists for the task. If such a stamp file exists, the task's output is assumed to exist and still be valid. If the file does not exist, the task is rerun. <note> <para>The stamp mechanism is more general than the shared state (sstate) cache mechanism described in the "<link linkend='setscene-tasks-and-shared-state'>Setscene Tasks and Shared State</link>" section. BitBake avoids rerunning any task that has a valid stamp file, not just tasks that can be accelerated through the sstate cache.</para> <para>However, you should realize that stamp files only serve as a marker that some work has been done and that these files do not record task output. The actual task output would usually be somewhere in <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink> (e.g. in some recipe's <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>.) What the sstate cache mechanism adds is a way to cache task output that can then be shared between build machines.</para> </note> Since <filename>STAMPS_DIR</filename> is usually a subdirectory of <filename>TMPDIR</filename>, removing <filename>TMPDIR</filename> will also remove <filename>STAMPS_DIR</filename>, which means tasks will properly be rerun to repopulate <filename>TMPDIR</filename>. </para> <para> If you want some task to always be considered "out of date", you can mark it with the <ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'><filename>nostamp</filename></ulink> varflag. If some other task depends on such a task, then that task will also always be considered out of date, which might not be what you want. </para> <para> For details on how to view information about a task's signature, see the "<ulink url='&YOCTO_DOCS_DEV_URL;#dev-viewing-task-variable-dependencies'>Viewing Task Variable Dependencies</ulink>" section in the Yocto Project Development Tasks Manual. </para> </section> <section id='setscene-tasks-and-shared-state'> <title>Setscene Tasks and Shared State</title> <para> The description of tasks so far assumes that BitBake needs to build everything and there are no prebuilt objects available. BitBake does support skipping tasks if prebuilt objects are available. These objects are usually made available in the form of a shared state (sstate) cache. <note> For information on variables affecting sstate, see the <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink> and <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_MIRRORS'><filename>SSTATE_MIRRORS</filename></ulink> variables. </note> </para> <para> The idea of a setscene task (i.e <filename>do_</filename><replaceable>taskname</replaceable><filename>_setscene</filename>) is a version of the task where instead of building something, BitBake can skip to the end result and simply place a set of files into specific locations as needed. In some cases, it makes sense to have a setscene task variant (e.g. generating package files in the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_deb'><filename>do_package_write_*</filename></ulink> task). In other cases, it does not make sense, (e.g. a <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-patch'><filename>do_patch</filename></ulink> task or <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-unpack'><filename>do_unpack</filename></ulink> task) since the work involved would be equal to or greater than the underlying task. </para> <para> In the OpenEmbedded build system, the common tasks that have setscene variants are <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>, <filename>do_package_write_*</filename>, <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-deploy'><filename>do_deploy</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-packagedata'><filename>do_packagedata</filename></ulink>, and <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-populate_sysroot'><filename>do_populate_sysroot</filename></ulink>. Notice that these are most of the tasks whose output is an end result. </para> <para> The OpenEmbedded build system has knowledge of the relationship between these tasks and other tasks that precede them. For example, if BitBake runs <filename>do_populate_sysroot_setscene</filename> for something, there is little point in running any of the <filename>do_fetch</filename>, <filename>do_unpack</filename>, <filename>do_patch</filename>, <filename>do_configure</filename>, <filename>do_compile</filename>, and <filename>do_install</filename> tasks. However, if <filename>do_package</filename> needs to be run, BitBake would need to run those other tasks. </para> <para> It becomes more complicated if everything can come from an sstate cache because some objects are simply not required at all. For example, you do not need a compiler or native tools, such as quilt, if there is nothing to compile or patch. If the <filename>do_package_write_*</filename> packages are available from sstate, BitBake does not need the <filename>do_package</filename> task data. </para> <para> To handle all these complexities, BitBake runs in two phases. The first is the "setscene" stage. During this stage, BitBake first checks the sstate cache for any targets it is planning to build. BitBake does a fast check to see if the object exists rather than a complete download. If nothing exists, the second phase, which is the setscene stage, completes and the main build proceeds. </para> <para> If objects are found in the sstate cache, the OpenEmbedded build system works backwards from the end targets specified by the user. For example, if an image is being built, the OpenEmbedded build system first looks for the packages needed for that image and the tools needed to construct an image. If those are available, the compiler is not needed. Thus, the compiler is not even downloaded. If something was found to be unavailable, or the download or setscene task fails, the OpenEmbedded build system then tries to install dependencies, such as the compiler, from the cache. </para> <para> The availability of objects in the sstate cache is handled by the function specified by the <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_HASHCHECK_FUNCTION'><filename>BB_HASHCHECK_FUNCTION</filename></ulink> variable and returns a list of the objects that are available. The function specified by the <ulink url='&YOCTO_DOCS_BB_URL;#var-BB_SETSCENE_DEPVALID'><filename>BB_SETSCENE_DEPVALID</filename></ulink> variable is the function that determines whether a given dependency needs to be followed, and whether for any given relationship the function needs to be passed. The function returns a True or False value. </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-workflow-figure'>general workflow 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 "<ulink url='&YOCTO_DOCS_REF_URL;#ref-images'>Images</ulink>" chapter in the Yocto Project Reference Manual. </para> <para> Images are written out to the <ulink url='&YOCTO_DOCS_REF_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 <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></ulink> variable points to the <filename>deploy</filename> directory, while the <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR_IMAGE'><filename>DEPLOY_DIR_IMAGE</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-KERNEL_IMAGETYPE'><filename>KERNEL_IMAGETYPE</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-IMAGE_FSTYPES'><filename>IMAGE_FSTYPES</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-MODULE_TARBALL_DEPLOY'><filename>MODULE_TARBALL_DEPLOY</filename></ulink> 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-workflow-figure'>general Yocto Project Development Environment figure</link>, the output labeled "Application Development SDK" represents an SDK. The SDK generation process differs depending on whether you build a standard SDK (e.g. <filename>bitbake -c populate_sdk</filename> <replaceable>imagename</replaceable>) or an extensible SDK (e.g. <filename>bitbake -c populate_sdk_ext</filename> <replaceable>imagename</replaceable>). This section is going to take a closer look at this output: <imagedata fileref="figures/sdk.png" align="center" width="9in" depth="7.25in" /> </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 environment setup script is added so that you can initialize the environment before using the tools. </para> <note><title>Notes</title> <itemizedlist> <listitem><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 or building and installing your own SDK installer. </para></listitem> <listitem><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. </para></listitem> <listitem><para> For information on setting up a cross-development environment, see the <ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink> manual. </para></listitem> </itemizedlist> </note> <para> Once built, the SDK installers are written out to the <filename>deploy/sdk</filename> folder inside the <ulink url='&YOCTO_DOCS_REF_URL;#build-directory'>Build Directory</ulink> as shown in the figure at the beginning of this section. Depending on the type of SDK, several variables exist that help configure these files. The following list shows the variables associated with a standard SDK: <itemizedlist> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></ulink>: Points to the <filename>deploy</filename> directory. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKMACHINE'><filename>SDKMACHINE</filename></ulink>: 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> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKIMAGE_FEATURES'><filename>SDKIMAGE_FEATURES</filename></ulink>: Lists the features to include in the "target" part of the SDK. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-TOOLCHAIN_HOST_TASK'><filename>TOOLCHAIN_HOST_TASK</filename></ulink>: 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> <ulink url='&YOCTO_DOCS_REF_URL;#var-TOOLCHAIN_TARGET_TASK'><filename>TOOLCHAIN_TARGET_TASK</filename></ulink>: Lists packages that make up the target part of the SDK (i.e. the part built for the target hardware). </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKPATH'><filename>SDKPATH</filename></ulink>: Defines the default SDK installation path offered by the installation script. </para></listitem> </itemizedlist> This next list, shows the variables associated with an extensible SDK: <itemizedlist> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPLOY_DIR'><filename>DEPLOY_DIR</filename></ulink>: Points to the <filename>deploy</filename> directory. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_EXT_TYPE'><filename>SDK_EXT_TYPE</filename></ulink>: Controls whether or not shared state artifacts are copied into the extensible SDK. By default, all required shared state artifacts are copied into the SDK. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_INCLUDE_PKGDATA'><filename>SDK_INCLUDE_PKGDATA</filename></ulink>: Specifies whether or not packagedata will be included in the extensible SDK for all recipes in the "world" target. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_INCLUDE_TOOLCHAIN'><filename>SDK_INCLUDE_TOOLCHAIN</filename></ulink>: Specifies whether or not the toolchain will be included when building the extensible SDK. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_LOCAL_CONF_WHITELIST'><filename>SDK_LOCAL_CONF_WHITELIST</filename></ulink>: A list of variables allowed through from the build system configuration into the extensible SDK configuration. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_LOCAL_CONF_BLACKLIST'><filename>SDK_LOCAL_CONF_BLACKLIST</filename></ulink>: A list of variables not allowed through from the build system configuration into the extensible SDK configuration. </para></listitem> <listitem><para> <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_INHERIT_BLACKLIST'><filename>SDK_INHERIT_BLACKLIST</filename></ulink>: A list of classes to remove from the <ulink url='&YOCTO_DOCS_REF_URL;#var-INHERIT'><filename>INHERIT</filename></ulink> value globally within the extensible SDK configuration. </para></listitem> </itemizedlist> </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_REF_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_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink> manual. </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 <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink> 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. <note> The extensible SDK does not use <filename>gcc-cross-canadian</filename> since this SDK ships a copy of the OpenEmbedded build system and the sysroot within it contains <filename>gcc-cross</filename>. </note> </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., <filename>gcc-cross-canadian</filename>, <filename>binutils-cross-canadian</filename>, and other <filename>nativesdk-*</filename> tools), which are tools native to the SDK (i.e. native to <ulink url='&YOCTO_DOCS_REF_URL;#var-SDK_ARCH'><filename>SDK_ARCH</filename></ulink>), 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKMACHINE'><filename>SDKMACHINE</filename></ulink>, 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-SDKMACHINE'><filename>SDKMACHINE</filename></ulink>, 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_SDK_URL;#sdk-building-an-sdk-installer'>Building an SDK Installer</ulink>" section in the Yocto Project Application Development and the Extensible Software Development Kit (eSDK) manual. </note> </section> <section id="shared-state-cache"> <title>Shared State Cache</title> <para> By design, the OpenEmbedded build system builds everything from scratch unless <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> 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. <note> The OpenEmbedded build system does not maintain <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> 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;#automatically-incrementing-a-binary-package-revision-number'>Automatically Incrementing a Binary Package Revision Number</ulink>" section in the Yocto Project Development Tasks Manual. </note> </para> <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='concepts-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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink> and <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink> 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='overview-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 <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>. 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. <note> Both native and cross packages run on the <ulink url='&YOCTO_DOCS_REF_URL;#hardware-build-system-term'>build host</ulink>. However, cross packages generate output for the target architecture. </note> 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, solutions for shell scripts exist. 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 situations, 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-PACKAGE_ARCHS'><filename>PACKAGE_ARCHS</filename></ulink> variable does not depend on the value of <ulink url='&YOCTO_DOCS_REF_URL;#var-MACHINE'><filename>MACHINE</filename></ulink>, even if it does reference it. </para> <para> Equally, there are cases where you 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> As an example, consider a case with in-line Python 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_REF_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, a variety of ways exist by which both the basehash and the dependent task hashes can be influenced. Within the BitBake configuration file, you 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink> since that variable is actually constructed as a path within <ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>, 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 <ulink url='&YOCTO_DOCS_REF_URL;#oe-core'>OE-Core</ulink> 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. OE-Core 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_REF_URL;#metadata'>Metadata</ulink> change that changes the task hash, automatically causing the task to be run again. This removes the need to bump <ulink url='&YOCTO_DOCS_REF_URL;#var-PR'><filename>PR</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-sstate'><filename>sstate</filename></ulink> 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> Two types of output exist. One type is just about creating a directory in <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>. A good example is the output of either <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink> or <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink>. 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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-deploy'><filename>do_deploy</filename></ulink> example taken from the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-deploy'><filename>deploy</filename></ulink> class: <literallayout class='monospaced'> DEPLOYDIR = "${WORKDIR}/deploy-${PN}" SSTATETASKS += "do_deploy" do_deploy[sstate-inputdirs] = "${DEPLOYDIR}" do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}" python do_deploy_setscene () { sstate_setscene(d) } addtask do_deploy_setscene do_deploy[dirs] = "${DEPLOYDIR} ${B}" </literallayout> The following list explains the previous example: <itemizedlist> <listitem><para> Adding "do_deploy" to <filename>SSTATETASKS</filename> adds some required sstate-related processing, which is implemented in the <ulink url='&YOCTO_DOCS_REF_URL;#ref-classes-sstate'><filename>sstate</filename></ulink> class, to before and after the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-deploy'><filename>do_deploy</filename></ulink> task. </para></listitem> <listitem><para> The <filename>do_deploy[sstate-inputdirs] = "${DEPLOYDIR}"</filename> declares that <filename>do_deploy</filename> places its output in <filename>${DEPLOYDIR}</filename> when run normally (i.e. when not using the sstate cache). This output becomes the input to the shared state cache. </para></listitem> <listitem><para> The <filename>do_deploy[sstate-outputdirs] = "${DEPLOY_DIR_IMAGE}"</filename> line causes the contents of the shared state cache to be copied to <filename>${DEPLOY_DIR_IMAGE}</filename>. <note> If <filename>do_deploy</filename> is not already in the shared state cache or if its input checksum (signature) has changed from when the output was cached, the task will be run to populate the shared state cache, after which the contents of the shared state cache is copied to <filename>${DEPLOY_DIR_IMAGE}</filename>. If <filename>do_deploy</filename> is in the shared state cache and its signature indicates that the cached output is still valid (i.e. if no relevant task inputs have changed), then the contents of the shared state cache will be copied directly to <filename>${DEPLOY_DIR_IMAGE}</filename> by the <filename>do_deploy_setscene</filename> task instead, skipping the <filename>do_deploy</filename> task. </note> </para></listitem> <listitem><para> The following task definition is glue logic needed to make the previous settings effective: <literallayout class='monospaced'> python do_deploy_setscene () { sstate_setscene(d) } addtask do_deploy_setscene </literallayout> <filename>sstate_setscene()</filename> takes the flags above as input and accelerates the <filename>do_deploy</filename> task through the shared state cache if possible. If the task was accelerated, <filename>sstate_setscene()</filename> returns True. Otherwise, it returns False, and the normal <filename>do_deploy</filename> task runs. For more information, see the "<ulink url='&YOCTO_DOCS_BB_URL;#setscene'>setscene</ulink>" section in the BitBake User Manual. </para></listitem> <listitem><para> The <filename>do_deploy[dirs] = "${DEPLOYDIR} ${B}"</filename> line creates <filename>${DEPLOYDIR}</filename> and <filename>${B}</filename> before the <filename>do_deploy</filename> task runs, and also sets the current working directory of <filename>do_deploy</filename> to <filename>${B}</filename>. For more information, see the "<ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'>Variable Flags</ulink>" section in the BitBake User Manual. <note> In cases where <filename>sstate-inputdirs</filename> and <filename>sstate-outputdirs</filename> would be the same, you can use <filename>sstate-plaindirs</filename>. For example, to preserve the <filename>${PKGD}</filename> and <filename>${PKGDEST}</filename> output from the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink> task, use the following: <literallayout class='monospaced'> do_package[sstate-plaindirs] = "${PKGD} ${PKGDEST}" </literallayout> </note> </para></listitem> <listitem><para> <filename>sstate-inputdirs</filename> and <filename>sstate-outputdirs</filename> can also be used with multiple directories. For example, the following declares <filename>PKGDESTWORK</filename> and <filename>SHLIBWORK</filename> as shared state input directories, which populates the shared state cache, and <filename>PKGDATA_DIR</filename> and <filename>SHLIBSDIR</filename> as the corresponding shared state output directories: <literallayout class='monospaced'> do_package[sstate-inputdirs] = "${PKGDESTWORK} ${SHLIBSWORKDIR}" do_package[sstate-outputdirs] = "${PKGDATA_DIR} ${SHLIBSDIR}" </literallayout> </para></listitem> <listitem><para> These methods also include the ability to take a lockfile when manipulating shared state directory structures, for cases where file additions or removals are sensitive: <literallayout class='monospaced'> do_package[sstate-lockfile] = "${PACKAGELOCK}" </literallayout> </para></listitem> </itemizedlist> </para> <para> Behind the scenes, the shared state code works by looking in <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink> and <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_MIRRORS'><filename>SSTATE_MIRRORS</filename></ulink> for shared state files. Here is an example: <literallayout class='monospaced'> SSTATE_MIRRORS ?= "\ file://.* http://someserver.tld/share/sstate/PATH;downloadfilename=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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_ipk'><filename>do_package_write_ipk</filename></ulink> 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.n </para> </section> <section id='concepts-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='concepts-overview-debugging'> <title>Debugging</title> <para> Seeing what metadata went into creating the input signature of a shared state (sstate) task can be a useful debugging aid. This information is available in signature information (<filename>siginfo</filename>) files in <ulink url='&YOCTO_DOCS_REF_URL;#var-SSTATE_DIR'><filename>SSTATE_DIR</filename></ulink>. For information on how to view and interpret information in <filename>siginfo</filename> files, see the "<ulink url='&YOCTO_DOCS_DEV_URL;#dev-viewing-task-variable-dependencies'>Viewing Task Variable Dependencies</ulink>" section in the Yocto Project Development Tasks Manual. </para> </section> <section id='concepts-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 <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink> 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. <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> </para> </section> </section> </section> <section id='automatically-added-runtime-dependencies'> <title>Automatically Added Runtime Dependencies</title> <para> The OpenEmbedded build system automatically adds common types of runtime dependencies between packages, which means that you do not need to explicitly declare the packages using <ulink url='&YOCTO_DOCS_REF_URL;#var-RDEPENDS'><filename>RDEPENDS</filename></ulink>. Three automatic mechanisms exist (<filename>shlibdeps</filename>, <filename>pcdeps</filename>, and <filename>depchains</filename>) that handle shared libraries, package configuration (pkg-config) modules, and <filename>-dev</filename> and <filename>-dbg</filename> packages, respectively. For other types of runtime dependencies, you must manually declare the dependencies. <itemizedlist> <listitem><para> <filename>shlibdeps</filename>: During the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package'><filename>do_package</filename></ulink> task of each recipe, all shared libraries installed by the recipe are located. For each shared library, the package that contains the shared library is registered as providing the shared library. More specifically, the package is registered as providing the <ulink url='https://en.wikipedia.org/wiki/Soname'>soname</ulink> of the library. The resulting shared-library-to-package mapping is saved globally in <ulink url='&YOCTO_DOCS_REF_URL;#var-PKGDATA_DIR'><filename>PKGDATA_DIR</filename></ulink> by the <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-packagedata'><filename>do_packagedata</filename></ulink> task.</para> <para>Simultaneously, all executables and shared libraries installed by the recipe are inspected to see what shared libraries they link against. For each shared library dependency that is found, <filename>PKGDATA_DIR</filename> is queried to see if some package (likely from a different recipe) contains the shared library. If such a package is found, a runtime dependency is added from the package that depends on the shared library to the package that contains the library.</para> <para>The automatically added runtime dependency also includes a version restriction. This version restriction specifies that at least the current version of the package that provides the shared library must be used, as if "<replaceable>package</replaceable> (>= <replaceable>version</replaceable>)" had been added to <filename>RDEPENDS</filename>. This forces an upgrade of the package containing the shared library when installing the package that depends on the library, if needed.</para> <para>If you want to avoid a package being registered as providing a particular shared library (e.g. because the library is for internal use only), then add the library to <ulink url='&YOCTO_DOCS_REF_URL;#var-PRIVATE_LIBS'><filename>PRIVATE_LIBS</filename></ulink> inside the package's recipe. </para></listitem> <listitem><para> <filename>pcdeps</filename>: During the <filename>do_package</filename> task of each recipe, all pkg-config modules (<filename>*.pc</filename> files) installed by the recipe are located. For each module, the package that contains the module is registered as providing the module. The resulting module-to-package mapping is saved globally in <filename>PKGDATA_DIR</filename> by the <filename>do_packagedata</filename> task.</para> <para>Simultaneously, all pkg-config modules installed by the recipe are inspected to see what other pkg-config modules they depend on. A module is seen as depending on another module if it contains a "Requires:" line that specifies the other module. For each module dependency, <filename>PKGDATA_DIR</filename> is queried to see if some package contains the module. If such a package is found, a runtime dependency is added from the package that depends on the module to the package that contains the module. <note> The <filename>pcdeps</filename> mechanism most often infers dependencies between <filename>-dev</filename> packages. </note> </para></listitem> <listitem><para> <filename>depchains</filename>: If a package <filename>foo</filename> depends on a package <filename>bar</filename>, then <filename>foo-dev</filename> and <filename>foo-dbg</filename> are also made to depend on <filename>bar-dev</filename> and <filename>bar-dbg</filename>, respectively. Taking the <filename>-dev</filename> packages as an example, the <filename>bar-dev</filename> package might provide headers and shared library symlinks needed by <filename>foo-dev</filename>, which shows the need for a dependency between the packages.</para> <para>The dependencies added by <filename>depchains</filename> are in the form of <ulink url='&YOCTO_DOCS_REF_URL;#var-RRECOMMENDS'><filename>RRECOMMENDS</filename></ulink>. <note> By default, <filename>foo-dev</filename> also has an <filename>RDEPENDS</filename>-style dependency on <filename>foo</filename>, because the default value of <filename>RDEPENDS_${PN}-dev</filename> (set in <filename>bitbake.conf</filename>) includes "${PN}". </note></para> <para>To ensure that the dependency chain is never broken, <filename>-dev</filename> and <filename>-dbg</filename> packages are always generated by default, even if the packages turn out to be empty. See the <ulink url='&YOCTO_DOCS_REF_URL;#var-ALLOW_EMPTY'><filename>ALLOW_EMPTY</filename></ulink> variable for more information. </para></listitem> </itemizedlist> </para> <para> The <filename>do_package</filename> task depends on the <filename>do_packagedata</filename> task of each recipe in <ulink url='&YOCTO_DOCS_REF_URL;#var-DEPENDS'><filename>DEPENDS</filename></ulink> through use of a <filename>[</filename><ulink url='&YOCTO_DOCS_BB_URL;#variable-flags'><filename>deptask</filename></ulink><filename>]</filename> declaration, which guarantees that the required shared-library/module-to-package mapping information will be available when needed as long as <filename>DEPENDS</filename> has been correctly set. </para> </section> <section id='fakeroot-and-pseudo'> <title>Fakeroot and Pseudo</title> <para> Some tasks are easier to implement when allowed to perform certain operations that are normally reserved for the root user (e.g. <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-install'><filename>do_install</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-package_write_deb'><filename>do_package_write*</filename></ulink>, <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-rootfs'><filename>do_rootfs</filename></ulink>, and <ulink url='&YOCTO_DOCS_REF_URL;#ref-tasks-image'><filename>do_image*</filename></ulink>). For example, the <filename>do_install</filename> task benefits from being able to set the UID and GID of installed files to arbitrary values. </para> <para> One approach to allowing tasks to perform root-only operations would be to require <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink> to run as root. However, this method is cumbersome and has security issues. The approach that is actually used is to run tasks that benefit from root privileges in a "fake" root environment. Within this environment, the task and its child processes believe that they are running as the root user, and see an internally consistent view of the filesystem. As long as generating the final output (e.g. a package or an image) does not require root privileges, the fact that some earlier steps ran in a fake root environment does not cause problems. </para> <para> The capability to run tasks in a fake root environment is known as "<ulink url='http://man.he.net/man1/fakeroot'>fakeroot</ulink>", which is derived from the BitBake keyword/variable flag that requests a fake root environment for a task. </para> <para> In the <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink>, the program that implements fakeroot is known as Pseudo. Pseudo overrides system calls by using the environment variable <filename>LD_PRELOAD</filename>, which results in the illusion of running as root. To keep track of "fake" file ownership and permissions resulting from operations that require root permissions, Pseudo uses an SQLite 3 database. This database is stored in <filename>${</filename><ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink><filename>}/pseudo/files.db</filename> for individual recipes. Storing the database in a file as opposed to in memory gives persistence between tasks and builds, which is not accomplished using fakeroot. <note><title>Caution</title> If you add your own task that manipulates the same files or directories as a fakeroot task, then that task also needs to run under fakeroot. Otherwise, the task cannot run root-only operations, and cannot see the fake file ownership and permissions set by the other task. You need to also add a dependency on <filename>virtual/fakeroot-native:do_populate_sysroot</filename>, giving the following: <literallayout class='monospaced'> fakeroot do_mytask () { ... } do_mytask[depends] += "virtual/fakeroot-native:do_populate_sysroot" </literallayout> </note> For more information, see the <ulink url='&YOCTO_DOCS_BB_URL;#var-FAKEROOT'><filename>FAKEROOT*</filename></ulink> variables in the BitBake User Manual. You can also reference the "<ulink url='http://www.ibm.com/developerworks/opensource/library/os-aapseudo1/index.html'>Pseudo</ulink>" and "<ulink url='https://github.com/wrpseudo/pseudo/wiki/WhyNotFakeroot'>Why Not Fakeroot?</ulink>" articles for background information on Pseudo. </para> </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_REF_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='https://en.wikipedia.org/wiki/Mesa_(computer_graphics)'>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. <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> </para> </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 <ulink url="&YOCTO_DOCS_REF_URL;#var-DISTRO_FEATURES"><filename>DISTRO_FEATURES</filename></ulink> statement in your <filename>local.conf</filename> file: <literallayout class='monospaced'> DISTRO_FEATURES_append = " wayland" </literallayout> <note> If X11 has been enabled elsewhere, Weston will build Wayland with X11 support </note> </para> </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 <ulink url='&YOCTO_DOCS_REF_URL;#var-CORE_IMAGE_EXTRA_INSTALL'><filename>CORE_IMAGE_EXTRA_INSTALL</filename></ulink> 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="overview-licenses"> <title>Licenses</title> <para> This section describes the mechanism by which the <ulink url='&YOCTO_DOCS_REF_URL;#build-system-term'>OpenEmbedded build system</ulink> 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 Tasks 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-LIC_FILES_CHKSUM'><filename>LIC_FILES_CHKSUM</filename></ulink> 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> <note><title>Notes</title> <itemizedlist> <listitem><para> When using "beginline" and "endline", realize that line numbering begins with one and not zero. Also, the included lines are inclusive (i.e. lines five through and including 29 in the previous example for <filename>licfile1.txt</filename>). </para></listitem> <listitem><para> When a license check fails, the selected license text is included as part of the QA message. Using this output, you can determine the exact start and finish for the needed license text. </para></listitem> </itemizedlist> </note> </para> <para> The build system uses the <ulink url='&YOCTO_DOCS_REF_URL;#var-S'><filename>S</filename></ulink> 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> and isolates lines five through 16 as license text. The second line refers to a file in <ulink url='&YOCTO_DOCS_REF_URL;#var-WORKDIR'><filename>WORKDIR</filename></ulink>. </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. <note><title>Tips</title> <itemizedlist> <listitem><para> If you specify an empty or invalid "md5" parameter, <ulink url='&YOCTO_DOCS_REF_URL;#bitbake-term'>BitBake</ulink> 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. </para></listitem> <listitem><para> If the whole file contains only license text, you do not need to use the "beginline" and "endline" parameters. </para></listitem> </itemizedlist> </note> </para> </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 <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_FLAGS'><filename>LICENSE_FLAGS</filename></ulink> 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 <ulink url='&YOCTO_DOCS_REF_URL;#var-LICENSE_FLAGS_WHITELIST'><filename>LICENSE_FLAGS_WHITELIST</filename></ulink> 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 <filename>LICENSE_FLAGS</filename> strings found in recipes against <filename>LICENSE_FLAGS_WHITELIST</filename> 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 ?= "" </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" 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 <filename>LICENSE_FLAGS</filename> 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 (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 -->