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(From yocto-docs rev: a9a3248b12b85f3637ebe5eddd4b1a29268d5598) Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
525 lines
28 KiB
XML
525 lines
28 KiB
XML
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"
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[<!ENTITY % poky SYSTEM "../poky.ent"> %poky; ] >
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<chapter id='ref-terms'>
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<title>Yocto Project Terms</title>
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<para>
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Following is a list of terms and definitions users new to the Yocto
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Project development environment might find helpful.
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While some of these terms are universal, the list includes them
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just in case:
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<itemizedlist>
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<listitem><para>
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<emphasis>Append Files:</emphasis>
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Files that append build information to a recipe file.
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Append files are known as BitBake append files and
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<filename>.bbappend</filename> files.
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The OpenEmbedded build system expects every append file to have
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a corresponding recipe (<filename>.bb</filename>) file.
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Furthermore, the append file and corresponding recipe file
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must use the same root filename.
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The filenames can differ only in the file type suffix used
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(e.g.
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<filename>formfactor_0.0.bb</filename> and
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<filename>formfactor_0.0.bbappend</filename>).</para>
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<para>Information in append files extends or overrides the
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information in the similarly-named recipe file.
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For an example of an append file in use, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#using-bbappend-files'>Using .bbappend Files in Your Layer</ulink>"
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section in the Yocto Project Development Tasks Manual.</para>
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<para>When you name an append file, you can use the
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"<filename>%</filename>" wildcard character to allow for
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matching recipe names.
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For example, suppose you have an append file named as follows:
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<literallayout class='monospaced'>
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busybox_1.21.%.bbappend
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</literallayout>
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That append file would match any
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<filename>busybox_1.21.</filename><replaceable>x</replaceable><filename>.bb</filename>
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version of the recipe.
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So, the append file would match any of the following recipe names:
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<literallayout class='monospaced'>
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busybox_1.21.1.bb
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busybox_1.21.2.bb
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busybox_1.21.3.bb
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busybox_1.21.10.bb
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busybox_1.21.25.bb
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</literallayout>
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<note><title>Important</title>
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The use of the "<filename>%</filename>" character
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is limited in that it only works directly in front of the
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<filename>.bbappend</filename> portion of the append file's
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name.
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You cannot use the wildcard character in any other
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location of the name.
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</note>
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</para></listitem>
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<listitem><para id='bitbake-term'>
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<emphasis>BitBake:</emphasis>
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The task executor and scheduler used by the OpenEmbedded build
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system to build images.
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For more information on BitBake, see the
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<ulink url='&YOCTO_DOCS_BB_URL;'>BitBake User Manual</ulink>.
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</para></listitem>
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<listitem><para id='board-support-package-bsp-term'>
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<emphasis>Board Support Package (BSP):</emphasis>
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A group of drivers, definitions, and other components that
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provide support for a specific hardware configuration.
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For more information on BSPs, see the
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<ulink url='&YOCTO_DOCS_BSP_URL;'>Yocto Project Board Support Package (BSP) Developer's Guide</ulink>.
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</para></listitem>
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<listitem>
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<para id='build-directory'>
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<emphasis>Build Directory:</emphasis>
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This term refers to the area used by the OpenEmbedded build
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system for builds.
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The area is created when you <filename>source</filename> the
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setup environment script that is found in the Source Directory
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(i.e. <link linkend='structure-core-script'><filename>&OE_INIT_FILE;</filename></link>).
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The
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<link linkend='var-TOPDIR'><filename>TOPDIR</filename></link>
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variable points to the Build Directory.</para>
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<para>You have a lot of flexibility when creating the Build
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Directory.
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Following are some examples that show how to create the
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directory.
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The examples assume your
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<link linkend='source-directory'>Source Directory</link> is
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named <filename>poky</filename>:
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<itemizedlist>
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<listitem><para>Create the Build Directory inside your
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Source Directory and let the name of the Build
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Directory default to <filename>build</filename>:
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<literallayout class='monospaced'>
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$ cd $HOME/poky
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$ source &OE_INIT_FILE;
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</literallayout>
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</para></listitem>
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<listitem><para>Create the Build Directory inside your
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home directory and specifically name it
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<filename>test-builds</filename>:
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<literallayout class='monospaced'>
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$ cd $HOME
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$ source poky/&OE_INIT_FILE; test-builds
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</literallayout>
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</para></listitem>
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<listitem><para>
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Provide a directory path and specifically name the
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Build Directory.
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Any intermediate folders in the pathname must exist.
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This next example creates a Build Directory named
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<filename>YP-&POKYVERSION;</filename>
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in your home directory within the existing
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directory <filename>mybuilds</filename>:
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<literallayout class='monospaced'>
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$ cd $HOME
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$ source $HOME/poky/&OE_INIT_FILE; $HOME/mybuilds/YP-&POKYVERSION;
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</literallayout>
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</para></listitem>
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</itemizedlist>
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<note>
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By default, the Build Directory contains
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<link linkend='var-TMPDIR'><filename>TMPDIR</filename></link>,
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which is a temporary directory the build system uses for
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its work.
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<filename>TMPDIR</filename> cannot be under NFS.
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Thus, by default, the Build Directory cannot be under NFS.
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However, if you need the Build Directory to be under NFS,
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you can set this up by setting <filename>TMPDIR</filename>
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in your <filename>local.conf</filename> file
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to use a local drive.
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Doing so effectively separates <filename>TMPDIR</filename>
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from <filename>TOPDIR</filename>, which is the Build
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Directory.
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</note>
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</para></listitem>
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<listitem><para id='hardware-build-system-term'>
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<emphasis>Build Host:</emphasis>
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The system used to build images in a Yocto Project
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Development environment.
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The build system is sometimes referred to as the
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<firstterm>development host</firstterm>.
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</para></listitem>
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<listitem><para>
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<emphasis>Classes:</emphasis>
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Files that provide for logic encapsulation and inheritance so
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that commonly used patterns can be defined once and then
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easily used in multiple recipes.
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For reference information on the Yocto Project classes, see the
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"<link linkend='ref-classes'>Classes</link>" chapter.
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Class files end with the <filename>.bbclass</filename>
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filename extension.
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</para></listitem>
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<listitem><para>
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<emphasis>Configuration File:</emphasis>
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Files that hold global definitions of variables,
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user-defined variables, and hardware configuration
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information.
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These files tell the OpenEmbedded build system what to
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build and what to put into the image to support a
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particular platform.</para>
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<para>Configuration files end with a <filename>.conf</filename>
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filename extension.
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The <filename>conf/local.conf</filename> configuration file in
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the
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<link linkend='build-directory'>Build Directory</link>
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contains user-defined variables that affect every build.
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The <filename>meta-poky/conf/distro/poky.conf</filename>
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configuration file defines Yocto "distro" configuration
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variables used only when building with this policy.
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Machine configuration files, which
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are located throughout the
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<link linkend='source-directory'>Source Directory</link>, define
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variables for specific hardware and are only used when building
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for that target (e.g. the
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<filename>machine/beaglebone.conf</filename> configuration
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file defines variables for the Texas Instruments ARM Cortex-A8
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development board).
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</para></listitem>
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<listitem><para id='term-container-layer'>
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<emphasis>Container Layer:</emphasis>
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Layers that hold other layers.
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An example of a container layer is OpenEmbedded's
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<ulink url='https://github.com/openembedded/meta-openembedded'><filename>meta-openembedded</filename></ulink>
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layer.
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The <filename>meta-openembedded</filename> layer contains
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many <filename>meta-*</filename> layers.
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</para></listitem>
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<listitem><para id='cross-development-toolchain'>
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<emphasis>Cross-Development Toolchain:</emphasis>
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In general, a cross-development toolchain is a collection of
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software development tools and utilities that run on one
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architecture and allow you to develop software for a
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different, or targeted, architecture.
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These toolchains contain cross-compilers, linkers, and
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debuggers that are specific to the target architecture.</para>
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<para>The Yocto Project supports two different cross-development
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toolchains:
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<itemizedlist>
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<listitem><para>
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A toolchain only used by and within
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BitBake when building an image for a target
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architecture.
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</para></listitem>
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<listitem><para>A relocatable toolchain used outside of
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BitBake by developers when developing applications
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that will run on a targeted device.
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</para></listitem>
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</itemizedlist></para>
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<para>Creation of these toolchains is simple and automated.
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For information on toolchain concepts as they apply to the
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Yocto Project, see the
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"<ulink url='&YOCTO_DOCS_OM_URL;#cross-development-toolchain-generation'>Cross-Development Toolchain Generation</ulink>"
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section in the Yocto Project Overview and Concepts Manual.
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You can also find more information on using the
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relocatable toolchain in the
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<ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink>
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manual.
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</para></listitem>
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<listitem><para>
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<emphasis>Extensible Software Development Kit (eSDK):</emphasis>
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A custom SDK for application developers.
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This eSDK allows developers to incorporate their library
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and programming changes back into the image to make
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their code available to other application developers.</para>
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<para>For information on the eSDK, see the
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<ulink url='&YOCTO_DOCS_SDK_URL;'>Yocto Project Application Development and the Extensible Software Development Kit (eSDK)</ulink>
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manual.
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</para></listitem>
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<listitem><para>
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<emphasis>Image:</emphasis>
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An image is an artifact of the BitBake build process given
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a collection of recipes and related Metadata.
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Images are the binary output that run on specific hardware or
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QEMU and are used for specific use-cases.
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For a list of the supported image types that the Yocto Project
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provides, see the
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"<link linkend='ref-images'>Images</link>"
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chapter.
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</para></listitem>
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<listitem><para>
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<emphasis>Layer:</emphasis>
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A collection of related recipes.
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Layers allow you to consolidate related metadata to
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customize your build.
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Layers also isolate information used when building
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for multiple architectures.
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Layers are hierarchical in their ability to override
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previous specifications.
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You can include any number of available layers from the
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Yocto Project and customize the build by adding your
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layers after them.
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You can search the Layer Index for layers used within
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Yocto Project.</para>
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<para>For introductory information on layers, see the
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"<ulink url='&YOCTO_DOCS_OM_URL;#the-yocto-project-layer-model'>The Yocto Project Layer Model</ulink>"
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section in the Yocto Project Overview and Concepts Manual.
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For more detailed information on layers, see the
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"<ulink url='&YOCTO_DOCS_DEV_URL;#understanding-and-creating-layers'>Understanding and Creating Layers</ulink>"
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section in the Yocto Project Development Tasks Manual.
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For a discussion specifically on BSP Layers, see the
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"<ulink url='&YOCTO_DOCS_BSP_URL;#bsp-layers'>BSP Layers</ulink>"
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section in the Yocto Project Board Support Packages (BSP)
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Developer's Guide.
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</para></listitem>
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<listitem><para id='metadata'>
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<emphasis>Metadata:</emphasis>
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A key element of the Yocto Project is the Metadata that
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is used to construct a Linux distribution and is contained
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in the files that the
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<link linkend='build-system-term'>OpenEmbedded build system</link>
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parses when building an image.
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In general, Metadata includes recipes, configuration
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files, and other information that refers to the build
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instructions themselves, as well as the data used to
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control what things get built and the effects of the
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build.
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Metadata also includes commands and data used to
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indicate what versions of software are used, from
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where they are obtained, and changes or additions to the
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software itself (patches or auxiliary files) that
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are used to fix bugs or customize the software for use
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in a particular situation.
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OpenEmbedded-Core is an important set of validated
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metadata.</para>
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<para>In the context of the kernel ("kernel Metadata"), the
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term refers to the kernel config fragments and features
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contained in the
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<ulink url='&YOCTO_GIT_URL;/cgit/cgit.cgi/yocto-kernel-cache'><filename>yocto-kernel-cache</filename></ulink>
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Git repository.
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</para></listitem>
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<listitem><para id='oe-core'>
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<emphasis>OpenEmbedded-Core (OE-Core):</emphasis>
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OE-Core is metadata comprised of foundational recipes,
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classes, and associated files that are meant to be
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common among many different OpenEmbedded-derived systems,
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including the Yocto Project.
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OE-Core is a curated subset of an original repository
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developed by the OpenEmbedded community that has been
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pared down into a smaller, core set of continuously
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validated recipes.
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The result is a tightly controlled and an quality-assured
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core set of recipes.</para>
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<para>You can see the Metadata in the
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<filename>meta</filename> directory of the Yocto Project
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<ulink url='http://git.yoctoproject.org/cgit/cgit.cgi'>Source Repositories</ulink>.
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</para></listitem>
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<listitem><para id='build-system-term'>
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<emphasis>OpenEmbedded Build System:</emphasis>
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The build system specific to the Yocto Project.
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The OpenEmbedded build system is based on another project known
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as "Poky", which uses
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<link linkend='bitbake-term'>BitBake</link> as the task
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executor.
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Throughout the Yocto Project documentation set, the
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OpenEmbedded build system is sometimes referred to simply
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as "the build system".
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If other build systems, such as a host or target build system
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are referenced, the documentation clearly states the
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difference.
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<note>
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For some historical information about Poky, see the
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<link linkend='poky'>Poky</link> term.
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</note>
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</para></listitem>
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<listitem><para>
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<emphasis>Package:</emphasis>
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In the context of the Yocto Project, this term refers to a
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recipe's packaged output produced by BitBake (i.e. a
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"baked recipe").
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A package is generally the compiled binaries produced from the
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recipe's sources.
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You "bake" something by running it through BitBake.</para>
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<para>It is worth noting that the term "package" can,
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in general, have subtle meanings.
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For example, the packages referred to in the
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"<link linkend='required-packages-for-the-build-host'>Required Packages for the Build Host</link>"
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section are compiled binaries that, when installed, add
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functionality to your Linux distribution.</para>
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<para>Another point worth noting is that historically within
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the Yocto Project, recipes were referred to as packages - thus,
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the existence of several BitBake variables that are seemingly
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mis-named,
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(e.g. <link linkend='var-PR'><filename>PR</filename></link>,
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<link linkend='var-PV'><filename>PV</filename></link>, and
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<link linkend='var-PE'><filename>PE</filename></link>).
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</para></listitem>
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<listitem><para>
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<emphasis>Package Groups:</emphasis>
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Arbitrary groups of software Recipes.
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You use package groups to hold recipes that, when built,
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usually accomplish a single task.
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For example, a package group could contain the recipes for a
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company’s proprietary or value-add software.
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Or, the package group could contain the recipes that enable
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graphics.
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A package group is really just another recipe.
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Because package group files are recipes, they end with the
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<filename>.bb</filename> filename extension.
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</para></listitem>
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<listitem><para id='poky'>
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<emphasis>Poky:</emphasis>
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Poky, which is pronounced <emphasis>Pock</emphasis>-ee,
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is a reference embedded distribution and a reference
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test configuration.
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Poky provides the following:
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<itemizedlist>
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<listitem><para>
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A base-level functional distro used to illustrate
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how to customize a distribution.
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</para></listitem>
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<listitem><para>
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A means by which to test the Yocto Project
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components (i.e. Poky is used to validate
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the Yocto Project).
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</para></listitem>
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<listitem><para>
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A vehicle through which you can download
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the Yocto Project.
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</para></listitem>
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</itemizedlist>
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Poky is not a product level distro.
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Rather, it is a good starting point for customization.
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<note>
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Poky began as an open-source
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project initially developed by OpenedHand.
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OpenedHand developed Poky from the existing
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OpenEmbedded build system to create a commercially
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supportable build system for embedded Linux.
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After Intel Corporation acquired OpenedHand, the
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poky project became the basis for the Yocto Project's
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build system.
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</note>
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</para></listitem>
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<listitem><para>
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<emphasis>Recipe:</emphasis>
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A set of instructions for building packages.
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A recipe describes where you get source code, which patches
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to apply, how to configure the source, how to compile it and so on.
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Recipes also describe dependencies for libraries or for other
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recipes.
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Recipes represent the logical unit of execution, the software
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to build, the images to build, and use the
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<filename>.bb</filename> file extension.
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</para></listitem>
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<listitem><para id='reference-kit-term'>
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<emphasis>Reference Kit:</emphasis>
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A working example of a system, which includes a
|
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<link linkend='board-support-package-bsp-term'>BSP</link>
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as well as a
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<link linkend='hardware-build-system-term'>build host</link>
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||
and other components, that can work on specific hardware.
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</para></listitem>
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<listitem>
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<para id='source-directory'>
|
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<emphasis>Source Directory:</emphasis>
|
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This term refers to the directory structure created as a result
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of creating a local copy of the <filename>poky</filename> Git
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repository <filename>git://git.yoctoproject.org/poky</filename>
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or expanding a released <filename>poky</filename> tarball.
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<note>
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Creating a local copy of the <filename>poky</filename>
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Git repository is the recommended method for setting up
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your Source Directory.
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</note>
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Sometimes you might hear the term "poky directory" used to refer
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to this directory structure.
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<note>
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The OpenEmbedded build system does not support file or
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directory names that contain spaces.
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Be sure that the Source Directory you use does not contain
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these types of names.
|
||
</note></para>
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|
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<para>The Source Directory contains BitBake, Documentation,
|
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Metadata and other files that all support the Yocto Project.
|
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Consequently, you must have the Source Directory in place on
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your development system in order to do any development using
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||
the Yocto Project.</para>
|
||
|
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<para>When you create a local copy of the Git repository, you
|
||
can name the repository anything you like.
|
||
Throughout much of the documentation, "poky"
|
||
is used as the name of the top-level folder of the local copy of
|
||
the poky Git repository.
|
||
So, for example, cloning the <filename>poky</filename> Git
|
||
repository results in a local Git repository whose top-level
|
||
folder is also named "poky".</para>
|
||
|
||
<para>While it is not recommended that you use tarball expansion
|
||
to set up the Source Directory, if you do, the top-level
|
||
directory name of the Source Directory is derived from the
|
||
Yocto Project release tarball.
|
||
For example, downloading and unpacking
|
||
<filename>&YOCTO_POKY_TARBALL;</filename> results in a
|
||
Source Directory whose root folder is named
|
||
<filename>&YOCTO_POKY;</filename>.</para>
|
||
|
||
<para>It is important to understand the differences between the
|
||
Source Directory created by unpacking a released tarball as
|
||
compared to cloning
|
||
<filename>git://git.yoctoproject.org/poky</filename>.
|
||
When you unpack a tarball, you have an exact copy of the files
|
||
based on the time of release - a fixed release point.
|
||
Any changes you make to your local files in the Source Directory
|
||
are on top of the release and will remain local only.
|
||
On the other hand, when you clone the <filename>poky</filename>
|
||
Git repository, you have an active development repository with
|
||
access to the upstream repository's branches and tags.
|
||
In this case, any local changes you make to the local
|
||
Source Directory can be later applied to active development
|
||
branches of the upstream <filename>poky</filename> Git
|
||
repository.</para>
|
||
|
||
<para>For more information on concepts related to Git
|
||
repositories, branches, and tags, see the
|
||
"<ulink url='&YOCTO_DOCS_OM_URL;#repositories-tags-and-branches'>Repositories, Tags, and Branches</ulink>"
|
||
section in the Yocto Project Overview and Concepts Manual.
|
||
</para></listitem>
|
||
<listitem><para><emphasis>Task:</emphasis>
|
||
A unit of execution for BitBake (e.g.
|
||
<link linkend='ref-tasks-compile'><filename>do_compile</filename></link>,
|
||
<link linkend='ref-tasks-fetch'><filename>do_fetch</filename></link>,
|
||
<link linkend='ref-tasks-patch'><filename>do_patch</filename></link>,
|
||
and so forth).
|
||
</para></listitem>
|
||
<listitem><para id='toaster-term'><emphasis>Toaster:</emphasis>
|
||
A web interface to the Yocto Project's
|
||
<link linkend='build-system-term'>OpenEmbedded Build System</link>.
|
||
The interface enables you to configure and run your builds.
|
||
Information about builds is collected and stored in a database.
|
||
For information on Toaster, see the
|
||
<ulink url='&YOCTO_DOCS_TOAST_URL;'>Toaster User Manual</ulink>.
|
||
</para></listitem>
|
||
<listitem><para>
|
||
<emphasis>Upstream:</emphasis>
|
||
A reference to source code or repositories
|
||
that are not local to the development system but located in a
|
||
master area that is controlled by the maintainer of the source
|
||
code.
|
||
For example, in order for a developer to work on a particular
|
||
piece of code, they need to first get a copy of it from an
|
||
"upstream" source.
|
||
</para></listitem>
|
||
</itemizedlist>
|
||
</para>
|
||
|
||
</chapter>
|
||
<!--
|
||
vim: expandtab tw=80 ts=4
|
||
-->
|