691 lines
33 KiB
XML
691 lines
33 KiB
XML
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<!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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<chapter id="user-manual-execution">
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<title>Execution</title>
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<para>
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Tasks can either be a shell task or a Python task.
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For shell tasks, BitBake writes a shell script to
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<filename>${WORKDIR}/temp/run.do_taskname.pid</filename>
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and then executes the script.
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The generated shell script contains all the exported variables,
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and the shell functions with all variables expanded.
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Output from the shell script goes to the file
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<filename>${WORKDIR}/temp/log.do_taskname.pid</filename>.
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Looking at the expanded shell functions in the run file and
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the output in the log files is a useful debugging technique.
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</para>
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<para>
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For Python tasks, BitBake executes the task internally and logs
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information to the controlling terminal.
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Future versions of BitBake will write the functions to files
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similar to the way shell tasks are handled.
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Logging will be handled in a way similar to shell tasks as well.
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</para>
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<para>
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Once all the tasks have been completed BitBake exits.
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</para>
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<section id='parsing-and-execution'>
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<title>Parsing and Execution</title>
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<section id='parsing-overview'>
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<title>Parsing Overview</title>
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<para>
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BitBake parses configuration files, classes, recipes, and append
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files.
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</para>
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<para>
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The first thing BitBake does is look for the
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<filename>bitbake.conf</filename> file.
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This file resides in the <filename>conf</filename>
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directory, which must be listed in
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>.
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</para>
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<para>
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The <filename>bitbake.conf</filename> file lists other configuration
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files to include from the <filename>conf</filename> directory below the
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directories listed in <filename>BBPATH</filename>.
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In general, the most important of these
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configuration files from a user's perspective
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is <filename>local.conf</filename>, which contains the user's
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customized settings for the build environment.
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</para>
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<para>
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Other notable configuration files are the distribution configuration
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file and the machine configuration file.
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These configuration files are normally identified by
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variables unique to the build systems using BitBake.
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For example, the Yocto Project uses the
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<filename>DISTRO</filename> and <filename>MACHINE</filename>
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variables, respectively.
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</para>
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<para>
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After parsing of the configuration files, some standard classes are
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included.
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The <filename>base.bbclass</filename> file
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is always included.
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Other classes that are specified in the configuration using the
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<link linkend='var-INHERIT'><filename>INHERIT</filename></link>
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variable are also included.
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BitBake searches for class files in a "classes" subdirectory under
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the paths in <filename>BBPATH</filename> in the same way as
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configuration files.
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</para>
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<para>
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After classes are included, the variable
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<filename>BBFILES</filename> is set, usually in
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<filename>local.conf</filename>, and defines the list of
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places to search for recipe and append files.
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Adding extra content to <filename>BBFILES</filename> is best
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achieved through the use of BitBake layers.
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</para>
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<para>
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BitBake parses each recipe and append file located with
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<filename>BBFILES</filename> and stores the values of various
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variables into the datastore.
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In summary, for each recipe and append file pairing, the configuration
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plus the base class of variables are set, followed by the data in the
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recipe file itself, followed by any inherit commands
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that the recipe file might contain.
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</para>
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<para>
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Because parsing recipe and append files is a time consuming
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process, a cache, referred to as the "setscene"
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is kept to speed up subsequent parsing.
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The setscene is invalid if the timestamps of a recipe changes,
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any of the include files change, configuration files change,
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or class files on which the recipe file depends change.
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</para>
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</section>
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<section id='parsing-configuration-files'>
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<title>Configuration files</title>
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<para>
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Prior to parsing configuration files, Bitbake looks
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at certain variables, including:
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<itemizedlist>
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<listitem><para><link linkend='var-BB_ENV_WHITELIST'><filename>BB_ENV_WHITELIST</filename></link></para></listitem>
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<listitem><para><link linkend='var-BB_PRESERVE_ENV'><filename>BB_PRESERVE_ENV</filename></link></para></listitem>
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<listitem><para><link linkend='var-BB_ENV_EXTRAWHITE'><filename>BB_ENV_EXTRAWHITE</filename></link></para></listitem>
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<listitem><para><link linkend='var-BB_ORIGENV'><filename>BB_ORIGENV</filename></link></para></listitem>
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<listitem><para><link linkend='var-PREFERRED_VERSION'><filename>PREFERRED_VERSION</filename></link></para></listitem>
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<listitem><para><link linkend='var-PREFERRED_PROVIDERS'><filename>PREFERRED_PROVIDERS</filename></link></para></listitem>
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</itemizedlist>
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</para>
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<para>
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The first kind of metadata in BitBake is configuration metadata.
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This metadata is global, and therefore affects all packages and
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tasks that are executed.
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</para>
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<para>
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BitBake will first search the current working directory for an
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optional <filename>conf/bblayers.conf</filename> configuration file.
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This file is expected to contain a
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<link linkend='var-BBLAYERS'><filename>BBLAYERS</filename></link>
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variable that is a space delimited list of 'layer' directories.
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For each directory in this list, a <filename>conf/layer.conf</filename>
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file will be searched for and parsed with the
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<link linkend='var-LAYERDIR'><filename>LAYERDIR</filename></link>
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variable being set to the directory where the layer was found.
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The idea is these files will setup
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>
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and other variables correctly for a given build directory automatically
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for the user.
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</para>
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<para>
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BitBake will then expect to find <filename>conf/bitbake.conf</filename>
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file somewhere in the user specified <filename>BBPATH</filename>.
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That configuration file generally has include directives to pull
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in any other metadata (generally files specific to architecture,
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machine, local and so on).
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</para>
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<para>
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Only variable definitions and include directives are allowed
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in <filename>.conf</filename> files.
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The following variables include:
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<itemizedlist>
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<listitem><para>
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<link linkend='var-BITBAKE_UI'><filename>BITBAKE_UI</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BBDEBUG'><filename>BBDEBUG</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-MULTI_PROVIDER_WHITELIST'><filename>MULTI_PROVIDER_WHITELIST</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_NUMBER_PARSE_THREADS'><filename>BB_NUMBER_PARSE_THREADS</filename></link>
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</para></listitem>
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<listitem><para>
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<filename>BBPKGS</filename>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_DEFAULT_TASK'><filename>BB_DEFAULT_TASK</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-TOPDIR'><filename>TOPDIR</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_VERBOSE_LOGS'><filename>BB_VERBOSE_LOGS</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_NICE_LEVEL'><filename>BB_NICE_LEVEL</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BBFILE_COLLECTIONS'><filename>BBFILE_COLLECTIONS</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-ASSUME_PROVIDED'><filename>ASSUME_PROVIDED</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_DANGLINGAPPENDS_WARNONLY'><filename>BB_DANGLINGAPPENDS_WARNONLY</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BBINCLUDED'><filename>BBINCLUDED</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BBFILE_PRIORITY'><filename>BBFILE_PRIORITY</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BUILDNAME'><filename>BUILDNAME</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BBMASK'><filename>BBMASK</filename></link>
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</para></listitem>
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</itemizedlist>
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</para>
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<section id='layers'>
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<title>Layers</title>
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<para>
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Layers allow you to isolate different types of
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customizations from each other.
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While you might find it tempting to keep everything in one layer
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when working on a single project, the more modular you organize
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your metadata, the easier it is to cope with future changes.
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</para>
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<para>
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To illustrate how you can use layers to keep things modular,
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consider machine customizations.
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These types of customizations typically reside in a special layer,
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rather than a general layer, called a Board Specific Package (BSP) Layer.
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Furthermore, the machine customizations should be isolated from
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recipes and metadata that support a new GUI environment, for
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example.
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This situation gives you a couple of layers: one for the machine
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configurations and one for the GUI environment.
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It is important to understand, however, that the BSP layer can still
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make machine-specific additions to recipes within
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the GUI environment layer without polluting the GUI layer itself
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with those machine-specific changes.
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You can accomplish this through a recipe that is a BitBake append
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(<filename>.bbappend</filename>) file.
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</para>
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<para>
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There are certain variables specific to layers:
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<itemizedlist>
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<listitem><para>
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<link linkend='var-LAYERDEPENDS'><filename>LAYERDEPENDS</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-LAYERVERSION'><filename>LAYERVERSION</filename></link>
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</para></listitem>
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</itemizedlist>
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</para>
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</section>
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<section id='schedulers'>
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<title>Schedulers</title>
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<para>
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Variables specific to scheduling functionality exist:
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<itemizedlist>
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<listitem><para>
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<link linkend='var-BB_SCHEDULER'><filename>BB_SCHEDULER</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_SCHEDULERS'><filename>BB_SCHEDULERS</filename></link>
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</para></listitem>
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</itemizedlist>
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</para>
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</section>
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</section>
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<section id='metadata-classes'>
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<title>Classes</title>
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<para>
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BitBake's rudimentary inheritance mechanism is accomplished using
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classes.
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As briefly mentioned in the metadata introduction, BitBake
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parses a class when an inherit directive is encountered, and it
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is located in the <filename>classes</filename> directory
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relative to the directories in
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>.
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</para>
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</section>
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<section id='recipe-bb-files'>
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<title>Recipe (<filename>.bb</filename>) Files</title>
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<para>
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Recipe files, which are files that have the
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<filename>.bb</filename> file extension, are logical units of
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tasks for execution.
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Normally, that logical unit is a package that needs to be
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built.
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</para>
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<para>
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BitBake obeys all inter-recipe dependencies.
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</para>
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<para>
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Recipe files must reside in locations found in the
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<link linkend='var-BBFILES'><filename>BBFILES</filename></link>
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variable.
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</para>
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</section>
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<section id='append-bbappend-files'>
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<title>Append (<filename>.bbappend</filename>) Files</title>
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<para>
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Append files, which are files that have the
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<filename>.bbappend</filename> file extension, add or
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extend build information to an existing
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<link linkend='recipe-bb-files'>recipe file</link>.
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</para>
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<para>
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BitBake expects every append file to have a corresponding recipe 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. <filename>formfactor_0.0.bb</filename> and
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<filename>formfactor_0.0.bbappend</filename>).
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</para>
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<para>
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Information in append files overrides the information in the
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similarly-named recipe file.
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</para>
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</section>
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</section>
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<section id='bitbake-dev-environment'>
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<title>BitBake</title>
|
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|
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<para>
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The OpenEmbedded build system uses BitBake to produce images.
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BitBake consists of several functional areas.
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This section takes a closer look at each of those areas.
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</para>
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<section id='source-fetching-dev-environment'>
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<title>Source Fetching</title>
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<para>
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The first stages of building a recipe are to fetch and unpack
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the source code:
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|
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<imagedata fileref="figures/source-fetching.png" align="center" width="6.5in" depth="5in" />
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</para>
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||
|
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figures/
|
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|
|
<para>
|
||
|
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The <filename>do_fetch</filename> and
|
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|
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<filename>do_unpack</filename> tasks fetch the source files
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and unpack them into the work directory.
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By default, everything is accomplished in the
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|
build directory,
|
||
|
|
which has a defined structure.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Unpacked source files are pointed to by a variable.
|
||
|
|
For example, in the Yocto Project and OpenEmbedded build systems,
|
||
|
|
the <filename>S</filename> variable points to these source files.
|
||
|
|
Each recipe has an area in the Build Directory where the
|
||
|
|
unpacked source code resides.
|
||
|
|
The name of that directory for any given recipe is defined from
|
||
|
|
several different variables.
|
||
|
|
You can see the variables that define these directories
|
||
|
|
by looking at the figure that shows the structure and variables
|
||
|
|
used in the Yocto Project:
|
||
|
|
<itemizedlist>
|
||
|
|
<listitem><para><filename>TMPDIR</filename>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>PACKAGE_ARCH</filename>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>TARGET_OS</filename>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><link linkend='var-PN'><filename>PN</filename></link>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><link linkend='var-PV'><filename>PV</filename></link>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><link linkend='var-PR'><filename>PR</filename></link>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>WORKDIR</filename>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>S</filename>
|
||
|
|
</para></listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Briefly, the <filename>S</filename> directory contains the
|
||
|
|
unpacked source files for a recipe.
|
||
|
|
The <filename>WORKDIR</filename> directory is where all the
|
||
|
|
building goes on for a given recipe.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='patching-dev-environment'>
|
||
|
|
<title>Patching</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Once source code is fetched and unpacked, BitBake locates
|
||
|
|
patch files and applies them to the source files:
|
||
|
|
<imagedata fileref="figures/patching.png" align="center" width="6in" depth="5in" />
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The <filename>do_patch</filename> task processes recipes by
|
||
|
|
using the
|
||
|
|
<link linkend='var-SRC_URI'><filename>SRC_URI</filename></link>
|
||
|
|
variable to locate applicable patch files, which by default
|
||
|
|
are <filename>*.patch</filename> or
|
||
|
|
<filename>*.diff</filename> files, or any file if
|
||
|
|
"apply=yes" is specified for the file in
|
||
|
|
<filename>SRC_URI</filename>.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
BitBake finds and applies multiple patches for a single recipe
|
||
|
|
in the order in which it finds the patches.
|
||
|
|
Patches are applied to the recipe's source files located in the
|
||
|
|
<filename>S</filename> directory.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
For more information on how the source directories are
|
||
|
|
created, see the
|
||
|
|
"<link linkend='source-fetching-dev-environment'>Source Fetching</link>"
|
||
|
|
section.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='configuration-and-compilation-dev-environment'>
|
||
|
|
<title>Configuration and Compilation</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
After source code is patched, BitBake executes tasks that
|
||
|
|
configure and compile the source code:
|
||
|
|
<imagedata fileref="figures/configuration-compile-autoreconf.png" align="center" width="7in" depth="5in" />
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
This step in the build process consists of three tasks:
|
||
|
|
<itemizedlist>
|
||
|
|
<listitem><para><emphasis><filename>do_configure</filename>:</emphasis>
|
||
|
|
This task configures the source by enabling and
|
||
|
|
disabling any build-time and configuration options for
|
||
|
|
the software being built.
|
||
|
|
Configurations can come from the recipe itself as well
|
||
|
|
as from an inherited class.
|
||
|
|
Additionally, the software itself might configure itself
|
||
|
|
depending on the target for which it is being built.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>The configurations handled by the
|
||
|
|
<filename>do_configure</filename> task are specific
|
||
|
|
to source code configuration for the source code
|
||
|
|
being built by the recipe.</para>
|
||
|
|
|
||
|
|
<para>If you are using the Autotools class
|
||
|
|
(<filename>autotools.bbclass</filename>),
|
||
|
|
you can add additional configuration options by using
|
||
|
|
the <filename>EXTRA_OECONF</filename>
|
||
|
|
variable.
|
||
|
|
For information on how this variable works within
|
||
|
|
that class, see the
|
||
|
|
<filename>meta/classes/autotools.bbclass</filename> file.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><emphasis><filename>do_compile</filename>:</emphasis>
|
||
|
|
Once a configuration task has been satisfied, BitBake
|
||
|
|
compiles the source using the
|
||
|
|
<filename>do_compile</filename> task.
|
||
|
|
Compilation occurs in the directory pointed to by the
|
||
|
|
<link linkend='var-B'><filename>B</filename></link>
|
||
|
|
variable.
|
||
|
|
Realize that the <filename>B</filename> directory is, by
|
||
|
|
default, the same as the
|
||
|
|
<filename>S</filename>
|
||
|
|
directory.</para></listitem>
|
||
|
|
<listitem><para><emphasis><filename>do_install</filename>:</emphasis>
|
||
|
|
Once compilation is done, BitBake executes the
|
||
|
|
<filename>do_install</filename> task.
|
||
|
|
This task copies files from the <filename>B</filename>
|
||
|
|
directory and places them in a holding area pointed to
|
||
|
|
by the <filename>D</filename> variable.</para></listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='package-splitting-dev-environment'>
|
||
|
|
<title>Package Splitting</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
After source code is configured and compiled, the
|
||
|
|
OpenEmbedded build system analyzes
|
||
|
|
the results and splits the output into packages:
|
||
|
|
<imagedata fileref="figures/analysis-for-package-splitting.png" align="center" width="7in" depth="7in" />
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The <filename>do_package</filename> and
|
||
|
|
<filename>do_packagedata</filename> tasks combine to analyze
|
||
|
|
the files found in the <filename>D</filename> 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><filename>PKGD</filename>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>PKGDATA_DIR</filename>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>PKGDESTWORK</filename>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>PKGDEST</filename>
|
||
|
|
</para></listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
The <filename>FILES</filename>
|
||
|
|
variable defines the files that go into each package in
|
||
|
|
<link linkend='var-PACKAGES'><filename>PACKAGES</filename></link>.
|
||
|
|
If you want details on how this is accomplished in the Yocto Project
|
||
|
|
for example, you can look at the <filename>package.bbclass</filename>
|
||
|
|
file in a Yocto tree.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Depending on the type of packages being created (RPM, DEB, or
|
||
|
|
IPK), the <filename>do_package_write_*</filename> task
|
||
|
|
creates the actual packages and places them in the
|
||
|
|
Package Feed area, which is
|
||
|
|
<filename>${TMPDIR}/deploy</filename>.
|
||
|
|
<note>
|
||
|
|
Support for creating feeds directly from the
|
||
|
|
<filename>deploy/*</filename> directories does not exist.
|
||
|
|
Creating such feeds usually requires some kind of feed
|
||
|
|
maintenance mechanism that would upload the new packages
|
||
|
|
into an official package feed (e.g. the
|
||
|
|
Ångström distribution).
|
||
|
|
This functionality is highly distribution-specific
|
||
|
|
and thus is not provided out of the box.
|
||
|
|
</note>
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='image-generation-dev-environment'>
|
||
|
|
<title>Image Generation</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Once packages are split and stored in the Package Feeds area,
|
||
|
|
the OpenEmbedded build system uses BitBake to generate the
|
||
|
|
root filesystem image:
|
||
|
|
<imagedata fileref="figures/image-generation.png" align="center" width="6in" depth="7in" />
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The image generation process consists of several stages and
|
||
|
|
depends on many variables.
|
||
|
|
The <filename>do_rootfs</filename> task uses these key variables
|
||
|
|
to help create the list of packages to actually install:
|
||
|
|
<itemizedlist>
|
||
|
|
<listitem><para><filename>IMAGE_INSTALL</filename>:
|
||
|
|
Lists out the base set of packages to install from
|
||
|
|
the Package Feeds area.</para></listitem>
|
||
|
|
<listitem><para><filename>PACKAGE_EXCLUDE</filename>:
|
||
|
|
Specifies packages that should not be installed.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>IMAGE_FEATURES</filename>:
|
||
|
|
Specifies features to include in the image.
|
||
|
|
Most of these features map to additional packages for
|
||
|
|
installation.</para></listitem>
|
||
|
|
<listitem><para><filename>PACKAGE_CLASSES</filename>:
|
||
|
|
Specifies the package backend to use and consequently
|
||
|
|
helps determine where to locate packages within the
|
||
|
|
Package Feeds area.</para></listitem>
|
||
|
|
<listitem><para><filename>IMAGE_LINGUAS</filename>:
|
||
|
|
Determines the language(s) for which additional
|
||
|
|
language support packages are installed.
|
||
|
|
</para></listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Package installation is under control of the package manager
|
||
|
|
(e.g. smart/rpm, opkg, or apt/dpkg) regardless of whether or
|
||
|
|
not package management is enabled for the target.
|
||
|
|
At the end of the process, if package management is not
|
||
|
|
enabled for the target, the package manager's data files
|
||
|
|
are deleted from the root filesystem.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
During image generation, the build system attempts to run
|
||
|
|
all post-installation scripts.
|
||
|
|
Any that fail to run on the build host are run on the
|
||
|
|
target when the target system is first booted.
|
||
|
|
If you are using a
|
||
|
|
read-only root filesystem,
|
||
|
|
all the post installation scripts must succeed during the
|
||
|
|
package installation phase since the root filesystem cannot be
|
||
|
|
written into.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
During Optimization, optimizing processes are run across
|
||
|
|
the image.
|
||
|
|
These processes include <filename>mklibs</filename> and
|
||
|
|
<filename>prelink</filename>.
|
||
|
|
The <filename>mklibs</filename> process optimizes the size
|
||
|
|
of the libraries.
|
||
|
|
A <filename>prelink</filename> process optimizes the dynamic
|
||
|
|
linking of shared libraries to reduce start up time of
|
||
|
|
executables.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Part of the image generation process includes compressing the
|
||
|
|
root filesystem image.
|
||
|
|
Compression is accomplished through several optimization
|
||
|
|
routines designed to reduce the overall size of the image.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
After the root filesystem has been constructed, the image
|
||
|
|
generation process turns everything into an image file or
|
||
|
|
a set of image files.
|
||
|
|
The formats used for the root filesystem depend on the
|
||
|
|
<filename>IMAGE_FSTYPES</filename> variable.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<note>
|
||
|
|
The entire image generation process is run under Pseudo.
|
||
|
|
Running under Pseudo ensures that the files in the root
|
||
|
|
filesystem have correct ownership.
|
||
|
|
</note>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='sdk-generation-dev-environment'>
|
||
|
|
<title>SDK Generation</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The OpenEmbedded build system uses BitBake to generate the
|
||
|
|
Software Development Kit (SDK) installer script:
|
||
|
|
<imagedata fileref="figures/sdk-generation.png" align="center" width="6in" depth="7in" />
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Like image generation, the SDK script process consists of
|
||
|
|
several stages and depends on many variables.
|
||
|
|
The <filename>do_populate_sdk</filename> task uses these
|
||
|
|
key variables to help create the list of packages to actually
|
||
|
|
install.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The <filename>do_populate_sdk</filename> task handles two
|
||
|
|
parts: a target part and a host part.
|
||
|
|
The target part is the part built for the target hardware and
|
||
|
|
includes libraries and headers.
|
||
|
|
The host part is the part of the SDK that runs on the
|
||
|
|
<filename>SDKMACHINE</filename>.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Once both parts are constructed, the
|
||
|
|
<filename>do_populate_sdk</filename> task performs some cleanup
|
||
|
|
on both parts.
|
||
|
|
After the cleanup, the task creates a cross-development
|
||
|
|
environment setup script and any configuration files that
|
||
|
|
might be needed.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The final output of the task is the Cross-development
|
||
|
|
toolchain installation script (<filename>.sh</filename> file),
|
||
|
|
which includes the environment setup script.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
</section>
|
||
|
|
</chapter>
|