forked from brl/citadel
933 lines
44 KiB
XML
933 lines
44 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="bitbake-user-manual-execution">
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<title>Execution</title>
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<para>
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The primary purpose for running BitBake is to produce some kind
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of output such as a single installable package, a kernel, a software
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development kit, or even a full, board-specific bootable Linux image,
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complete with bootloader, kernel, and root filesystem.
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Of course, you can execute the <filename>bitbake</filename>
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command with options that cause it to execute single tasks,
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compile single recipe files, capture or clear data, or simply
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return information about the execution environment.
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</para>
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<para>
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This chapter describes BitBake's execution process from start
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to finish when you use it to create an image.
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The execution process is launched using the following command
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form:
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<literallayout class='monospaced'>
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$ bitbake <replaceable>target</replaceable>
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</literallayout>
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For information on the BitBake command and its options,
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see
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"<link linkend='bitbake-user-manual-command'>The BitBake Command</link>"
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section.
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<note>
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<para>
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Prior to executing BitBake, you should take advantage of available
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parallel thread execution on your build host by setting the
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<link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>
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variable in your project's <filename>local.conf</filename>
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configuration file.
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</para>
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<para>
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A common method to determine this value for your build host is to run
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the following:
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<literallayout class='monospaced'>
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$ grep processor /proc/cpuinfo
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</literallayout>
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This command returns the number of processors, which takes into
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account hyper-threading.
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Thus, a quad-core build host with hyper-threading most likely
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shows eight processors, which is the value you would then assign to
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<filename>BB_NUMBER_THREADS</filename>.
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</para>
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<para>
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A possibly simpler solution is that some Linux distributions
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(e.g. Debian and Ubuntu) provide the <filename>ncpus</filename> command.
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</para>
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</note>
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</para>
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<section id='parsing-the-base-configuration-metadata'>
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<title>Parsing the Base Configuration Metadata</title>
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<para>
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The first thing BitBake does is parse base configuration
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metadata.
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Base configuration metadata consists of your project's
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<filename>bblayers.conf</filename> file to determine what
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layers BitBake needs to recognize, all necessary
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<filename>layer.conf</filename> files (one from each layer),
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and <filename>bitbake.conf</filename>.
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The data itself is of various types:
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<itemizedlist>
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<listitem><para><emphasis>Recipes:</emphasis>
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Details about particular pieces of software.
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</para></listitem>
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<listitem><para><emphasis>Class Data:</emphasis>
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An abstraction of common build information
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(e.g. how to build a Linux kernel).
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</para></listitem>
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<listitem><para><emphasis>Configuration Data:</emphasis>
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Machine-specific settings, policy decisions,
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and so forth.
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Configuration data acts as the glue to bind everything
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together.</para></listitem>
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</itemizedlist>
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</para>
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<para>
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The <filename>layer.conf</filename> files are used to
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construct key variables such as
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>
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and
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<link linkend='var-BBFILES'><filename>BBFILES</filename></link>.
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<filename>BBPATH</filename> is used to search for
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configuration and class files under the
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<filename>conf</filename> and <filename>classes</filename>
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directories, respectively.
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<filename>BBFILES</filename> is used to locate both recipe
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and recipe append files
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(<filename>.bb</filename> and <filename>.bbappend</filename>).
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If there is no <filename>bblayers.conf</filename> file,
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it is assumed the user has set the <filename>BBPATH</filename>
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and <filename>BBFILES</filename> directly in the environment.
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</para>
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<para>
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Next, the <filename>bitbake.conf</filename> file is located
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using the <filename>BBPATH</filename> variable that was
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just constructed.
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The <filename>bitbake.conf</filename> file may also include other
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configuration files using the
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<filename>include</filename> or
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<filename>require</filename> directives.
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</para>
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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>
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<link linkend='var-BB_ENV_WHITELIST'><filename>BB_ENV_WHITELIST</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_ENV_EXTRAWHITE'><filename>BB_ENV_EXTRAWHITE</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_PRESERVE_ENV'><filename>BB_PRESERVE_ENV</filename></link>
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</para></listitem>
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<listitem><para>
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<link linkend='var-BB_ORIGENV'><filename>BB_ORIGENV</filename></link>
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</para></listitem>
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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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</itemizedlist>
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The first four variables in this list relate to how BitBake treats shell
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environment variables during task execution.
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By default, BitBake cleans the environment variables and provides tight
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control over the shell execution environment.
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However, through the use of these first four variables, you can
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apply your control regarding the
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environment variables allowed to be used by BitBake in the shell
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during execution of tasks.
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See the
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"<link linkend='passing-information-into-the-build-task-environment'>Passing Information Into the Build Task Environment</link>"
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section and the information about these variables in the
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variable glossary for more information on how they work and
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on how to use them.
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</para>
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<para>
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The base configuration metadata is global
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and therefore affects all recipes and tasks that are executed.
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</para>
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<para>
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BitBake first searches 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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Recall that if BitBake cannot find a <filename>bblayers.conf</filename>
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file, then it is assumed the user has set the <filename>BBPATH</filename>
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and <filename>BBFILES</filename> variables directly in the environment.
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</para>
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<para>
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For each directory (layer) in this list, a <filename>conf/layer.conf</filename>
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file is located 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 automatically set up
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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.
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</para>
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<para>
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BitBake then expects to find the <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 such as files specific to the architecture,
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the machine, the local environment, and so forth.
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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 BitBake <filename>.conf</filename> files.
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Some variables directly influence BitBake's behavior.
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These variables might have been set from the environment
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depending on the environment variables previously
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mentioned or set in the configuration files.
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The
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"<link linkend='ref-variables-glos'>Variables Glossary</link>"
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chapter presents a full list of variables.
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</para>
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<para>
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After parsing configuration files, BitBake uses its rudimentary
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inheritance mechanism, which is through class files, to inherit
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some standard classes.
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BitBake parses a class when the inherit directive responsible
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for getting that class is encountered.
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</para>
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<para>
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The <filename>base.bbclass</filename> file 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
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<filename>classes</filename> 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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A good way to get an idea of the configuration files and
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the class files used in your execution environment is to
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run the following BitBake command:
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<literallayout class='monospaced'>
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$ bitbake -e > mybb.log
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</literallayout>
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Examining the top of the <filename>mybb.log</filename>
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shows you the many configuration files and class files
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used in your execution environment.
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</para>
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<note>
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<para>
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You need to be aware of how BitBake parses curly braces.
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If a recipe uses a closing curly brace within the function and
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the character has no leading spaces, BitBake produces a parsing
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error.
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If you use a pair of curly braces in a shell function, the
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closing curly brace must not be located at the start of the line
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without leading spaces.
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</para>
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<para>
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Here is an example that causes BitBake to produce a parsing
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error:
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<literallayout class='monospaced'>
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fakeroot create_shar() {
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cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
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usage()
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{
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echo "test"
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###### The following "}" at the start of the line causes a parsing error ######
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}
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EOF
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}
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</literallayout>
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Writing the recipe this way avoids the error:
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<literallayout class='monospaced'>
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fakeroot create_shar() {
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cat << "EOF" > ${SDK_DEPLOY}/${TOOLCHAIN_OUTPUTNAME}.sh
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usage()
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{
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echo "test"
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######The following "}" with a leading space at the start of the line avoids the error ######
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}
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EOF
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}
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</literallayout>
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</para>
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</note>
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</section>
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<section id='locating-and-parsing-recipes'>
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<title>Locating and Parsing Recipes</title>
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<para>
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During the configuration phase, BitBake will have set
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<link linkend='var-BBFILES'><filename>BBFILES</filename></link>.
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BitBake now uses it to construct a list of recipes to parse,
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along with any append files (<filename>.bbappend</filename>)
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to apply.
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<filename>BBFILES</filename> is a space-separated list of
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available files and supports wildcards.
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An example would be:
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<literallayout class='monospaced'>
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BBFILES = "/path/to/bbfiles/*.bb /path/to/appends/*.bbappend"
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</literallayout>
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BitBake parses each recipe and append file located
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with <filename>BBFILES</filename> and stores the values of
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various variables into the datastore.
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<note>
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Append files are applied in the order they are encountered in
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<filename>BBFILES</filename>.
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</note>
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For each file, a fresh copy of the base configuration is
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made, then the recipe is parsed line by line.
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Any inherit statements cause BitBake to find and
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then parse class files (<filename>.bbclass</filename>)
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using
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<link linkend='var-BBPATH'><filename>BBPATH</filename></link>
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as the search path.
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Finally, BitBake parses in order any append files found in
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<filename>BBFILES</filename>.
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</para>
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<para>
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One common convention is to use the recipe filename to define
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pieces of metadata.
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For example, in <filename>bitbake.conf</filename> the recipe
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name and version are used to set the variables
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<link linkend='var-PN'><filename>PN</filename></link> and
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<link linkend='var-PV'><filename>PV</filename></link>:
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<literallayout class='monospaced'>
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PN = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[0] or 'defaultpkgname'}"
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PV = "${@bb.parse.BBHandler.vars_from_file(d.getVar('FILE', False),d)[1] or '1.0'}"
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</literallayout>
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In this example, a recipe called "something_1.2.3.bb" would set
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<filename>PN</filename> to "something" and
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<filename>PV</filename> to "1.2.3".
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</para>
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<para>
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By the time parsing is complete for a recipe, BitBake
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has a list of tasks that the recipe defines and a set of
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data consisting of keys and values as well as
|
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dependency information about the tasks.
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</para>
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<para>
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BitBake does not need all of this information.
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It only needs a small subset of the information to make
|
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decisions about the recipe.
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Consequently, BitBake caches the values in which it is
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interested and does not store the rest of the information.
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Experience has shown it is faster to re-parse the metadata than to
|
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try and write it out to the disk and then reload it.
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|
</para>
|
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|
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<para>
|
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Where possible, subsequent BitBake commands reuse this cache of
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recipe information.
|
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The validity of this cache is determined by first computing a
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checksum of the base configuration data (see
|
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|
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<link linkend='var-BB_HASHCONFIG_WHITELIST'><filename>BB_HASHCONFIG_WHITELIST</filename></link>)
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and then checking if the checksum matches.
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If that checksum matches what is in the cache and the recipe
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and class files have not changed, Bitbake is able to use
|
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the cache.
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BitBake then reloads the cached information about the recipe
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instead of reparsing it from scratch.
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</para>
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<para>
|
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Recipe file collections exist to allow the user to
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have multiple repositories of
|
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<filename>.bb</filename> files that contain the same
|
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exact package.
|
||
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For example, one could easily use them to make one's
|
||
|
|
own local copy of an upstream repository, but with
|
||
|
|
custom modifications that one does not want upstream.
|
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|
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Here is an example:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
BBFILES = "/stuff/openembedded/*/*.bb /stuff/openembedded.modified/*/*.bb"
|
||
|
|
BBFILE_COLLECTIONS = "upstream local"
|
||
|
|
BBFILE_PATTERN_upstream = "^/stuff/openembedded/"
|
||
|
|
BBFILE_PATTERN_local = "^/stuff/openembedded.modified/"
|
||
|
|
BBFILE_PRIORITY_upstream = "5"
|
||
|
|
BBFILE_PRIORITY_local = "10"
|
||
|
|
</literallayout>
|
||
|
|
<note>
|
||
|
|
The layers mechanism is now the preferred method of collecting
|
||
|
|
code.
|
||
|
|
While the collections code remains, its main use is to set layer
|
||
|
|
priorities and to deal with overlap (conflicts) between layers.
|
||
|
|
</note>
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='bb-bitbake-providers'>
|
||
|
|
<title>Providers</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Assuming BitBake has been instructed to execute a target
|
||
|
|
and that all the recipe files have been parsed, BitBake
|
||
|
|
starts to figure out how to build the target.
|
||
|
|
BitBake looks through the <filename>PROVIDES</filename> list
|
||
|
|
for each of the recipes.
|
||
|
|
A <filename>PROVIDES</filename> list is the list of names by which
|
||
|
|
the recipe can be known.
|
||
|
|
Each recipe's <filename>PROVIDES</filename> list is created
|
||
|
|
implicitly through the recipe's
|
||
|
|
<link linkend='var-PN'><filename>PN</filename></link> variable
|
||
|
|
and explicitly through the recipe's
|
||
|
|
<link linkend='var-PROVIDES'><filename>PROVIDES</filename></link>
|
||
|
|
variable, which is optional.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
When a recipe uses <filename>PROVIDES</filename>, that recipe's
|
||
|
|
functionality can be found under an alternative name or names other
|
||
|
|
than the implicit <filename>PN</filename> name.
|
||
|
|
As an example, suppose a recipe named <filename>keyboard_1.0.bb</filename>
|
||
|
|
contained the following:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
PROVIDES += "fullkeyboard"
|
||
|
|
</literallayout>
|
||
|
|
The <filename>PROVIDES</filename> list for this recipe becomes
|
||
|
|
"keyboard", which is implicit, and "fullkeyboard", which is explicit.
|
||
|
|
Consequently, the functionality found in
|
||
|
|
<filename>keyboard_1.0.bb</filename> can be found under two
|
||
|
|
different names.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='bb-bitbake-preferences'>
|
||
|
|
<title>Preferences</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The <filename>PROVIDES</filename> list is only part of the solution
|
||
|
|
for figuring out a target's recipes.
|
||
|
|
Because targets might have multiple providers, BitBake needs
|
||
|
|
to prioritize providers by determining provider preferences.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
A common example in which a target has multiple providers
|
||
|
|
is "virtual/kernel", which is on the
|
||
|
|
<filename>PROVIDES</filename> list for each kernel recipe.
|
||
|
|
Each machine often selects the best kernel provider by using a
|
||
|
|
line similar to the following in the machine configuration file:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
|
||
|
|
</literallayout>
|
||
|
|
The default
|
||
|
|
<link linkend='var-PREFERRED_PROVIDER'><filename>PREFERRED_PROVIDER</filename></link>
|
||
|
|
is the provider with the same name as the target.
|
||
|
|
Bitbake iterates through each target it needs to build and
|
||
|
|
resolves them and their dependencies using this process.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Understanding how providers are chosen is made complicated by the fact
|
||
|
|
that multiple versions might exist for a given provider.
|
||
|
|
BitBake defaults to the highest version of a provider.
|
||
|
|
Version comparisons are made using the same method as Debian.
|
||
|
|
You can use the
|
||
|
|
<link linkend='var-PREFERRED_VERSION'><filename>PREFERRED_VERSION</filename></link>
|
||
|
|
variable to specify a particular version.
|
||
|
|
You can influence the order by using the
|
||
|
|
<link linkend='var-DEFAULT_PREFERENCE'><filename>DEFAULT_PREFERENCE</filename></link>
|
||
|
|
variable.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
By default, files have a preference of "0".
|
||
|
|
Setting <filename>DEFAULT_PREFERENCE</filename> to "-1" makes the
|
||
|
|
recipe unlikely to be used unless it is explicitly referenced.
|
||
|
|
Setting <filename>DEFAULT_PREFERENCE</filename> to "1" makes it
|
||
|
|
likely the recipe is used.
|
||
|
|
<filename>PREFERRED_VERSION</filename> overrides any
|
||
|
|
<filename>DEFAULT_PREFERENCE</filename> setting.
|
||
|
|
<filename>DEFAULT_PREFERENCE</filename> is often used to mark newer
|
||
|
|
and more experimental recipe versions until they have undergone
|
||
|
|
sufficient testing to be considered stable.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
When there are multiple “versions” of a given recipe,
|
||
|
|
BitBake defaults to selecting the most recent
|
||
|
|
version, unless otherwise specified.
|
||
|
|
If the recipe in question has a
|
||
|
|
<link linkend='var-DEFAULT_PREFERENCE'><filename>DEFAULT_PREFERENCE</filename></link>
|
||
|
|
set lower than the other recipes (default is 0), then
|
||
|
|
it will not be selected.
|
||
|
|
This allows the person or persons maintaining
|
||
|
|
the repository of recipe files to specify
|
||
|
|
their preference for the default selected version.
|
||
|
|
Additionally, the user can specify their preferred version.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
If the first recipe is named <filename>a_1.1.bb</filename>, then the
|
||
|
|
<link linkend='var-PN'><filename>PN</filename></link> variable
|
||
|
|
will be set to “a”, and the
|
||
|
|
<link linkend='var-PV'><filename>PV</filename></link>
|
||
|
|
variable will be set to 1.1.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Thus, if a recipe named <filename>a_1.2.bb</filename> exists, BitBake
|
||
|
|
will choose 1.2 by default.
|
||
|
|
However, if you define the following variable in a
|
||
|
|
<filename>.conf</filename> file that BitBake parses, you
|
||
|
|
can change that preference:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
PREFERRED_VERSION_a = "1.1"
|
||
|
|
</literallayout>
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<note>
|
||
|
|
<para>
|
||
|
|
It is common for a recipe to provide two versions -- a stable,
|
||
|
|
numbered (and preferred) version, and a version that is
|
||
|
|
automatically checked out from a source code repository that
|
||
|
|
is considered more "bleeding edge" but can be selected only
|
||
|
|
explicitly.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
For example, in the OpenEmbedded codebase, there is a standard,
|
||
|
|
versioned recipe file for BusyBox,
|
||
|
|
<filename>busybox_1.22.1.bb</filename>,
|
||
|
|
but there is also a Git-based version,
|
||
|
|
<filename>busybox_git.bb</filename>, which explicitly contains the line
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
DEFAULT_PREFERENCE = "-1"
|
||
|
|
</literallayout>
|
||
|
|
to ensure that the numbered, stable version is always preferred
|
||
|
|
unless the developer selects otherwise.
|
||
|
|
</para>
|
||
|
|
</note>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='bb-bitbake-dependencies'>
|
||
|
|
<title>Dependencies</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Each target BitBake builds consists of multiple tasks such as
|
||
|
|
<filename>fetch</filename>, <filename>unpack</filename>,
|
||
|
|
<filename>patch</filename>, <filename>configure</filename>,
|
||
|
|
and <filename>compile</filename>.
|
||
|
|
For best performance on multi-core systems, BitBake considers each
|
||
|
|
task as an independent
|
||
|
|
entity with its own set of dependencies.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Dependencies are defined through several variables.
|
||
|
|
You can find information about variables BitBake uses in
|
||
|
|
the <link linkend='ref-variables-glos'>Variables Glossary</link>
|
||
|
|
near the end of this manual.
|
||
|
|
At a basic level, it is sufficient to know that BitBake uses the
|
||
|
|
<link linkend='var-DEPENDS'><filename>DEPENDS</filename></link> and
|
||
|
|
<link linkend='var-RDEPENDS'><filename>RDEPENDS</filename></link> variables when
|
||
|
|
calculating dependencies.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
For more information on how BitBake handles dependencies, see the
|
||
|
|
"<link linkend='dependencies'>Dependencies</link>" section.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='ref-bitbake-tasklist'>
|
||
|
|
<title>The Task List</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Based on the generated list of providers and the dependency information,
|
||
|
|
BitBake can now calculate exactly what tasks it needs to run and in what
|
||
|
|
order it needs to run them.
|
||
|
|
The
|
||
|
|
"<link linkend='executing-tasks'>Executing Tasks</link>" section has more
|
||
|
|
information on how BitBake chooses which task to execute next.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The build now starts with BitBake forking off threads up to the limit set in the
|
||
|
|
<link linkend='var-BB_NUMBER_THREADS'><filename>BB_NUMBER_THREADS</filename></link>
|
||
|
|
variable.
|
||
|
|
BitBake continues to fork threads as long as there are tasks ready to run,
|
||
|
|
those tasks have all their dependencies met, and the thread threshold has not been
|
||
|
|
exceeded.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
It is worth noting that you can greatly speed up the build time by properly setting
|
||
|
|
the <filename>BB_NUMBER_THREADS</filename> variable.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
As each task completes, a timestamp is written to the directory specified by the
|
||
|
|
<link linkend='var-STAMP'><filename>STAMP</filename></link> variable.
|
||
|
|
On subsequent runs, BitBake looks in the build directory within
|
||
|
|
<filename>tmp/stamps</filename> and does not rerun
|
||
|
|
tasks that are already completed unless a timestamp is found to be invalid.
|
||
|
|
Currently, invalid timestamps are only considered on a per
|
||
|
|
recipe file basis.
|
||
|
|
So, for example, if the configure stamp has a timestamp greater than the
|
||
|
|
compile timestamp for a given target, then the compile task would rerun.
|
||
|
|
Running the compile task again, however, has no effect on other providers
|
||
|
|
that depend on that target.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The exact format of the stamps is partly configurable.
|
||
|
|
In modern versions of BitBake, a hash is appended to the
|
||
|
|
stamp so that if the configuration changes, the stamp becomes
|
||
|
|
invalid and the task is automatically rerun.
|
||
|
|
This hash, or signature used, is governed by the signature policy
|
||
|
|
that is configured (see the
|
||
|
|
"<link linkend='checksums'>Checksums (Signatures)</link>"
|
||
|
|
section for information).
|
||
|
|
It is also possible to append extra metadata to the stamp using
|
||
|
|
the <filename>[stamp-extra-info]</filename> task flag.
|
||
|
|
For example, OpenEmbedded uses this flag to make some tasks machine-specific.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<note>
|
||
|
|
Some tasks are marked as "nostamp" tasks.
|
||
|
|
No timestamp file is created when these tasks are run.
|
||
|
|
Consequently, "nostamp" tasks are always rerun.
|
||
|
|
</note>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
For more information on tasks, see the
|
||
|
|
"<link linkend='tasks'>Tasks</link>" section.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='executing-tasks'>
|
||
|
|
<title>Executing Tasks</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Tasks can be either a shell task or a Python task.
|
||
|
|
For shell tasks, BitBake writes a shell script to
|
||
|
|
<filename>${</filename><link linkend='var-T'><filename>T</filename></link><filename>}/run.do_taskname.pid</filename>
|
||
|
|
and then executes the script.
|
||
|
|
The generated shell script contains all the exported variables,
|
||
|
|
and the shell functions with all variables expanded.
|
||
|
|
Output from the shell script goes to the file
|
||
|
|
<filename>${T}/log.do_taskname.pid</filename>.
|
||
|
|
Looking at the expanded shell functions in the run file and
|
||
|
|
the output in the log files is a useful debugging technique.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
For Python tasks, BitBake executes the task internally and logs
|
||
|
|
information to the controlling terminal.
|
||
|
|
Future versions of BitBake will write the functions to files
|
||
|
|
similar to the way shell tasks are handled.
|
||
|
|
Logging will be handled in a way similar to shell tasks as well.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The order in which BitBake runs the tasks is controlled by its
|
||
|
|
task scheduler.
|
||
|
|
It is possible to configure the scheduler and define custom
|
||
|
|
implementations for specific use cases.
|
||
|
|
For more information, see these variables that control the
|
||
|
|
behavior:
|
||
|
|
<itemizedlist>
|
||
|
|
<listitem><para>
|
||
|
|
<link linkend='var-BB_SCHEDULER'><filename>BB_SCHEDULER</filename></link>
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para>
|
||
|
|
<link linkend='var-BB_SCHEDULERS'><filename>BB_SCHEDULERS</filename></link>
|
||
|
|
</para></listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
It is possible to have functions run before and after a task's main
|
||
|
|
function.
|
||
|
|
This is done using the <filename>[prefuncs]</filename>
|
||
|
|
and <filename>[postfuncs]</filename> flags of the task
|
||
|
|
that lists the functions to run.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='checksums'>
|
||
|
|
<title>Checksums (Signatures)</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
A checksum is a unique signature of a task's inputs.
|
||
|
|
The signature of a task can be used to determine if a task
|
||
|
|
needs to be run.
|
||
|
|
Because it is a change in a task's inputs that triggers running
|
||
|
|
the task, BitBake needs to detect all the inputs to a given task.
|
||
|
|
For shell tasks, this turns out to be fairly easy because
|
||
|
|
BitBake 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, some things should not be included in
|
||
|
|
the checksum.
|
||
|
|
First, there is the actual specific build path of a given task -
|
||
|
|
the working directory.
|
||
|
|
It does not matter if the working directory changes because it should not
|
||
|
|
affect the output for target packages.
|
||
|
|
The simplistic approach for excluding the working directory is to set
|
||
|
|
it to some fixed value and create the checksum for the "run" script.
|
||
|
|
BitBake goes one step better and uses the
|
||
|
|
<link linkend='var-BB_HASHBASE_WHITELIST'><filename>BB_HASHBASE_WHITELIST</filename></link>
|
||
|
|
variable to define a list of variables that should never be included
|
||
|
|
when generating the signatures.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Another problem results from the "run" scripts containing functions that
|
||
|
|
might or might not get called.
|
||
|
|
The incremental build solution contains code that figures out dependencies
|
||
|
|
between shell functions.
|
||
|
|
This code is used to prune the "run" scripts down to the minimum set,
|
||
|
|
thereby alleviating this problem and making the "run" scripts much more
|
||
|
|
readable as a bonus.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
So far we have solutions for shell scripts.
|
||
|
|
What about Python tasks?
|
||
|
|
The same approach applies even though these tasks are more difficult.
|
||
|
|
The process needs to figure out what variables a Python function accesses
|
||
|
|
and what functions it calls.
|
||
|
|
Again, the incremental build solution contains code that first figures out
|
||
|
|
the variable and function dependencies, and then creates a checksum for the data
|
||
|
|
used as the input to the task.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Like the working directory case, situations exist where dependencies
|
||
|
|
should be ignored.
|
||
|
|
For these cases, you can instruct the build process to ignore a dependency
|
||
|
|
by using a line like the following:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
PACKAGE_ARCHS[vardepsexclude] = "MACHINE"
|
||
|
|
</literallayout>
|
||
|
|
This example ensures that the <filename>PACKAGE_ARCHS</filename> variable does not
|
||
|
|
depend on the value of <filename>MACHINE</filename>, even if it does reference it.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Equally, there are cases where we need to add dependencies BitBake
|
||
|
|
is not able to find.
|
||
|
|
You can accomplish this by using a line like the following:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
PACKAGE_ARCHS[vardeps] = "MACHINE"
|
||
|
|
</literallayout>
|
||
|
|
This example explicitly adds the <filename>MACHINE</filename> variable as a
|
||
|
|
dependency for <filename>PACKAGE_ARCHS</filename>.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Consider a case with in-line Python, for example, where BitBake is not
|
||
|
|
able to figure out dependencies.
|
||
|
|
When running in debug mode (i.e. using <filename>-DDD</filename>), BitBake
|
||
|
|
produces output when it discovers something for which it cannot figure out
|
||
|
|
dependencies.
|
||
|
|
</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 build directory.
|
||
|
|
The checksum (or signature) for a particular task needs to add the hashes
|
||
|
|
of all the tasks on which the particular task depends.
|
||
|
|
Choosing which dependencies to add is a policy decision.
|
||
|
|
However, the effect is to generate a master checksum that combines the basehash
|
||
|
|
and the hashes of the task's dependencies.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
At the code level, there are a variety of ways both the basehash and the
|
||
|
|
dependent task hashes can be influenced.
|
||
|
|
Within the BitBake configuration file, we can give BitBake some extra information
|
||
|
|
to help it construct the basehash.
|
||
|
|
The following statement effectively results in a list of global variable
|
||
|
|
dependency excludes - variables never included in any checksum.
|
||
|
|
This example uses variables from OpenEmbedded to help illustrate
|
||
|
|
the concept:
|
||
|
|
<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 the work directory, which is part of
|
||
|
|
<filename>TMPDIR</filename>.
|
||
|
|
</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 OpenEmbedded Core
|
||
|
|
uses: "OEBasic" and "OEBasicHash".
|
||
|
|
By default, there is a dummy "noop" signature handler enabled in BitBake.
|
||
|
|
This means that behavior is unchanged from previous versions.
|
||
|
|
<filename>OE-Core</filename> uses the "OEBasicHash" signature handler by default
|
||
|
|
through this setting in the <filename>bitbake.conf</filename> file:
|
||
|
|
<literallayout class='monospaced'>
|
||
|
|
BB_SIGNATURE_HANDLER ?= "OEBasicHash"
|
||
|
|
</literallayout>
|
||
|
|
The "OEBasicHash" <filename>BB_SIGNATURE_HANDLER</filename> is the same as the
|
||
|
|
"OEBasic" version but adds the task hash to the stamp files.
|
||
|
|
This results in any metadata change that changes the task hash, automatically
|
||
|
|
causing the task to be run again.
|
||
|
|
This removes the need to bump
|
||
|
|
<link linkend='var-PR'><filename>PR</filename></link>
|
||
|
|
values, and changes to metadata automatically ripple across the build.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
It is also worth noting that the end result of these signature generators is to
|
||
|
|
make some dependency and hash information available to the build.
|
||
|
|
This information includes:
|
||
|
|
<itemizedlist>
|
||
|
|
<listitem><para><filename>BB_BASEHASH_task-</filename><replaceable>taskname</replaceable>:
|
||
|
|
The base hashes for each task in the recipe.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>BB_BASEHASH_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
|
||
|
|
The base hashes for each dependent task.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>BBHASHDEPS_</filename><replaceable>filename</replaceable><filename>:</filename><replaceable>taskname</replaceable>:
|
||
|
|
The task dependencies for each task.
|
||
|
|
</para></listitem>
|
||
|
|
<listitem><para><filename>BB_TASKHASH</filename>:
|
||
|
|
The hash of the currently running task.
|
||
|
|
</para></listitem>
|
||
|
|
</itemizedlist>
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
It is worth noting that BitBake's "-S" option lets you
|
||
|
|
debug Bitbake's processing of signatures.
|
||
|
|
The options passed to -S allow different debugging modes
|
||
|
|
to be used, either using BitBake's own debug functions
|
||
|
|
or possibly those defined in the metadata/signature handler
|
||
|
|
itself.
|
||
|
|
The simplest parameter to pass is "none", which causes a
|
||
|
|
set of signature information to be written out into
|
||
|
|
<filename>STAMPS_DIR</filename>
|
||
|
|
corresponding to the targets specified.
|
||
|
|
The other currently available parameter is "printdiff",
|
||
|
|
which causes BitBake to try to establish the closest
|
||
|
|
signature match it can (e.g. in the sstate cache) and then
|
||
|
|
run <filename>bitbake-diffsigs</filename> over the matches
|
||
|
|
to determine the stamps and delta where these two
|
||
|
|
stamp trees diverge.
|
||
|
|
<note>
|
||
|
|
It is likely that future versions of BitBake will
|
||
|
|
provide other signature handlers triggered through
|
||
|
|
additional "-S" parameters.
|
||
|
|
</note>
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
You can find more information on checksum metadata in the
|
||
|
|
"<link linkend='task-checksums-and-setscene'>Task Checksums and Setscene</link>"
|
||
|
|
section.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
|
||
|
|
<section id='setscene'>
|
||
|
|
<title>Setscene</title>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
The setscene process enables BitBake to handle "pre-built" artifacts.
|
||
|
|
The ability to handle and reuse these artifacts allows BitBake
|
||
|
|
the luxury of not having to build something from scratch every time.
|
||
|
|
Instead, BitBake can use, when possible, existing build artifacts.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
BitBake needs to have reliable data indicating whether or not an
|
||
|
|
artifact is compatible.
|
||
|
|
Signatures, described in the previous section, provide an ideal
|
||
|
|
way of representing whether an artifact is compatible.
|
||
|
|
If a signature is the same, an object can be reused.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
If an object can be reused, the problem then becomes how to
|
||
|
|
replace a given task or set of tasks with the pre-built artifact.
|
||
|
|
BitBake solves the problem with the "setscene" process.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
When BitBake is asked to build a given target, before building anything,
|
||
|
|
it first asks whether cached information is available for any of the
|
||
|
|
targets it's building, or any of the intermediate targets.
|
||
|
|
If cached information is available, BitBake uses this information instead of
|
||
|
|
running the main tasks.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
BitBake first calls the function defined by the
|
||
|
|
<link linkend='var-BB_HASHCHECK_FUNCTION'><filename>BB_HASHCHECK_FUNCTION</filename></link>
|
||
|
|
variable with a list of tasks and corresponding
|
||
|
|
hashes it wants to build.
|
||
|
|
This function is designed to be fast and returns a list
|
||
|
|
of the tasks for which it believes in can obtain artifacts.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Next, for each of the tasks that were returned as possibilities,
|
||
|
|
BitBake executes a setscene version of the task that the possible
|
||
|
|
artifact covers.
|
||
|
|
Setscene versions of a task have the string "_setscene" appended to the
|
||
|
|
task name.
|
||
|
|
So, for example, the task with the name <filename>xxx</filename> has
|
||
|
|
a setscene task named <filename>xxx_setscene</filename>.
|
||
|
|
The setscene version of the task executes and provides the necessary
|
||
|
|
artifacts returning either success or failure.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
As previously mentioned, an artifact can cover more than one task.
|
||
|
|
For example, it is pointless to obtain a compiler if you
|
||
|
|
already have the compiled binary.
|
||
|
|
To handle this, BitBake calls the
|
||
|
|
<link linkend='var-BB_SETSCENE_DEPVALID'><filename>BB_SETSCENE_DEPVALID</filename></link>
|
||
|
|
function for each successful setscene task to know whether or not it needs
|
||
|
|
to obtain the dependencies of that task.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
Finally, after all the setscene tasks have executed, BitBake calls the
|
||
|
|
function listed in
|
||
|
|
<link linkend='var-BB_SETSCENE_VERIFY_FUNCTION2'><filename>BB_SETSCENE_VERIFY_FUNCTION2</filename></link>
|
||
|
|
with the list of tasks BitBake thinks has been "covered".
|
||
|
|
The metadata can then ensure that this list is correct and can
|
||
|
|
inform BitBake that it wants specific tasks to be run regardless
|
||
|
|
of the setscene result.
|
||
|
|
</para>
|
||
|
|
|
||
|
|
<para>
|
||
|
|
You can find more information on setscene metadata in the
|
||
|
|
"<link linkend='task-checksums-and-setscene'>Task Checksums and Setscene</link>"
|
||
|
|
section.
|
||
|
|
</para>
|
||
|
|
</section>
|
||
|
|
</chapter>
|