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<?xml version="1.0"?>
<!--
ex:ts=4:sw=4:sts=4:et
-*- tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*-
-->
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<book>
<bookinfo>
<title>BitBake User Manual</title>
<authorgroup>
<corpauthor>BitBake Team</corpauthor>
</authorgroup>
<copyright>
<year>2004</year>
<holder>Chris Larson</holder>
<holder>Phil Blundell</holder>
</copyright>
<legalnotice>
<para>This work is licensed under the Creative Commons Attribution License. To view a copy of this license, visit <ulink url="http://creativecommons.org/licenses/by/2.0/">http://creativecommons.org/licenses/by/2.0/</ulink> or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.</para>
</legalnotice>
</bookinfo>
<chapter>
<title>Introduction</title>
<section>
<title>Overview</title>
<para>BitBake is, at its simplest, a tool for executing
tasks and managing metadata. As such, its similarities to GNU make and other
build tools are readily apparent. It was inspired by Portage, the package management system used by the Gentoo Linux distribution. BitBake is the basis of the <ulink url="http://www.openembedded.org/">OpenEmbedded</ulink> project, which is being used to build and maintain a number of embedded Linux distributions, including OpenZaurus and Familiar.</para>
</section>
<section>
<title>Background and Goals</title>
<para>Prior to BitBake, no other build tool adequately met
the needs of an aspiring embedded Linux distribution. All of the
buildsystems used by traditional desktop Linux distributions lacked
important functionality, and none of the ad-hoc
<emphasis>buildroot</emphasis> systems, prevalent in the
embedded space, were scalable or maintainable.</para>
<para>Some important goals for BitBake were:
<itemizedlist>
<listitem><para>Handle crosscompilation.</para></listitem>
<listitem><para>Handle interpackage dependencies (build time on target architecture, build time on native architecture, and runtime).</para></listitem>
<listitem><para>Support running any number of tasks within a given package, including, but not limited to, fetching upstream sources, unpacking them, patching them, configuring them, et cetera.</para></listitem>
<listitem><para>Must be linux distribution agnostic (both build and target).</para></listitem>
<listitem><para>Must be architecture agnostic</para></listitem>
<listitem><para>Must support multiple build and target operating systems (including cygwin, the BSDs, etc).</para></listitem>
<listitem><para>Must be able to be self contained, rather than tightly integrated into the build machine's root filesystem.</para></listitem>
<listitem><para>There must be a way to handle conditional metadata (on target architecture, operating system, distribution, machine).</para></listitem>
<listitem><para>It must be easy for the person using the tools to supply their own local metadata and packages to operate against.</para></listitem>
<listitem><para>Must make it easy to collaborate
between multiple projects using BitBake for their
builds.</para></listitem>
<listitem><para>Should provide an inheritance mechanism to
share common metadata between many packages.</para></listitem>
<listitem><para>Et cetera...</para></listitem>
</itemizedlist>
</para>
<para>BitBake satisfies all these and many more. Flexibility and power have always been the priorities. It is highly extensible, supporting embedded Python code and execution of any arbitrary tasks.</para>
</section>
</chapter>
<chapter>
<title>Metadata</title>
<section>
<title>Description</title>
<itemizedlist>
<para>BitBake metadata can be classified into 3 major areas:</para>
<listitem>
<para>Configuration Files</para>
</listitem>
<listitem>
<para>.bb Files</para>
</listitem>
<listitem>
<para>Classes</para>
</listitem>
</itemizedlist>
<para>What follows are a large number of examples of BitBake metadata. Any syntax which isn't supported in any of the aforementioned areas will be documented as such.</para>
<section>
<title>Basic variable setting</title>
<para><screen><varname>VARIABLE</varname> = "value"</screen></para>
<para>In this example, <varname>VARIABLE</varname> is <literal>value</literal>.</para>
</section>
<section>
<title>Variable expansion</title>
<para>BitBake supports variables referencing one another's contents using a syntax which is similar to shell scripting</para>
<para><screen><varname>A</varname> = "aval"
<varname>B</varname> = "pre${A}post"</screen></para>
<para>This results in <varname>A</varname> containing <literal>aval</literal> and <varname>B</varname> containing <literal>preavalpost</literal>.</para>
</section>
<section>
<title>Immediate variable expansion (:=)</title>
<para>:= results in a variable's contents being expanded immediately, rather than when the variable is actually used.</para>
<para><screen><varname>T</varname> = "123"
<varname>A</varname> := "${B} ${A} test ${T}"
<varname>T</varname> = "456"
<varname>B</varname> = "${T} bval"
<varname>C</varname> = "cval"
<varname>C</varname> := "${C}append"</screen></para>
<para>In that example, <varname>A</varname> would contain <literal> test 123</literal>, <varname>B</varname> would contain <literal>456 bval</literal>, and <varname>C</varname> would be <literal>cvalappend</literal>.</para>
</section>
<section>
<title>Appending (+=) and prepending (=+)</title>
<para><screen><varname>B</varname> = "bval"
<varname>B</varname> += "additionaldata"
<varname>C</varname> = "cval"
<varname>C</varname> =+ "test"</screen></para>
<para>In this example, <varname>B</varname> is now <literal>bval additionaldata</literal> and <varname>C</varname> is <literal>test cval</literal>.</para>
</section>
<section>
<title>Conditional metadata set</title>
<para>OVERRIDES is a <quote>:</quote> seperated variable containing each item you want to satisfy conditions. So, if you have a variable which is conditional on <quote>arm</quote>, and <quote>arm</quote> is in OVERRIDES, then the <quote>arm</quote> specific version of the variable is used rather than the non-conditional version. Example:</para>
<para><screen><varname>OVERRIDES</varname> = "architecture:os:machine"
<varname>TEST</varname> = "defaultvalue"
<varname>TEST_os</varname> = "osspecificvalue"
<varname>TEST_condnotinoverrides</varname> = "othercondvalue"</screen></para>
<para>In this example, <varname>TEST</varname> would be <literal>osspecificvalue</literal>, due to the condition <quote>os</quote> being in <varname>OVERRIDES</varname>.</para>
</section>
<section>
<title>Conditional appending</title>
<para>BitBake also supports appending and prepending to variables based on whether something is in OVERRIDES. Example:</para>
<para><screen><varname>DEPENDS</varname> = "glibc ncurses"
<varname>OVERRIDES</varname> = "machine:local"
<varname>DEPENDS_append_machine</varname> = " libmad"</screen></para>
<para>In this example, <varname>DEPENDS</varname> is set to <literal>glibc ncurses libmad</literal>.</para>
</section>
<section>
<title>Inclusion</title>
<para>Next, there is the <literal>include</literal> directive, which causes BitBake to parse in whatever file you specify, and insert it at that location, which is not unlike <command>make</command>. However, if the path specified on the <literal>include</literal> line is a relative path, BitBake will locate the first one it can find within <envar>BBPATH</envar>.</para>
</section>
<section>
<title>Python variable expansion</title>
<para><screen><varname>DATE</varname> = "${@time.strftime('%Y%m%d',time.gmtime())}"</screen></para>
<para>This would result in the <varname>DATE</varname> variable containing today's date.</para>
</section>
<section>
<title>Defining executable metadata</title>
<para><emphasis>NOTE:</emphasis> This is only supported in .bb and .bbclass files.</para>
<para><screen>do_mytask () {
echo "Hello, world!"
}</screen></para>
<para>This is essentially identical to setting a variable, except that this variable happens to be executable shell code.</para>
<para><screen>python do_printdate () {
import time
print time.strftime('%Y%m%d', time.gmtime())
}</screen></para>
<para>This is the similar to the previous, but flags it as python so that BitBake knows it is python code.</para>
</section>
<section>
<title>Defining python functions into the global python namespace</title>
<para><emphasis>NOTE:</emphasis> This is only supported in .bb and .bbclass files.</para>
<para><screen>def get_depends(bb, d):
if bb.data.getVar('SOMECONDITION', d, 1):
return "dependencywithcond"
else:
return "dependency"
<varname>SOMECONDITION</varname> = "1"
<varname>DEPENDS</varname> = "${@get_depends(bb, d)}"</screen></para>
<para>This would result in <varname>DEPENDS</varname> containing <literal>dependencywithcond</literal>.</para>
</section>
<section>
<title>Inheritance</title>
<para><emphasis>NOTE:</emphasis> This is only supported in .bb and .bbclass files.</para>
<para>The <literal>inherit</literal> directive is a means of specifying what classes of functionality your .bb requires. It is a rudamentary form of inheritence. For example, you can easily abstract out the tasks involved in building a package that uses autoconf and automake, and put that into a bbclass for your packages to make use of. A given bbclass is located by searching for classes/filename.oeclass in <envar>BBPATH</envar>, where filename is what you inherited.</para>
</section>
<section>
<title>Tasks</title>
<para><emphasis>NOTE:</emphasis> This is only supported in .bb and .bbclass files.</para>
<para>In BitBake, each step that needs to be run for a given .bb is known as a task. There is a command <literal>addtask</literal> to add new tasks (must be a defined python executable metadata and must start with <quote>do_</quote>) and describe intertask dependencies.</para>
<para><screen>python do_printdate () {
import time
print time.strftime('%Y%m%d', time.gmtime())
}
addtask printdate before do_build</screen></para>
<para>This defines the necessary python function and adds it as a task which is now a dependency of do_build (the default task). If anyone executes the do_build task, that will result in do_printdate being run first.</para>
</section>
<section>
<title>Events</title>
<para><emphasis>NOTE:</emphasis> This is only supported in .bb and .bbclass files.</para>
<para>BitBake also implements a means of registering event handlers. Events are triggered at certain points during operation, such as, the beginning of operation against a given .bb, the start of a given task, task failure, task success, et cetera. The intent was to make it easy to do things like email notifications on build failure.</para>
<para><emphasis>[Insert instructions on how to add event handlers here]</emphasis></para>
</section>
</section>
<section>
<title>Parsing</title>
<section>
<title>Configuration Files</title>
<para>The first of the classifications of metadata in BitBake is configuration metadata. This metadata is global, and therefore affects <emphasis>all</emphasis> packages and tasks which are executed. Currently, BitBake has hardcoded knowledge of a single configuration file. It expects to find 'conf/bitbake.conf' somewhere in the user specified <envar>BBPATH</envar>. That configuration file generally has include directives to pull in any other metadata (generally files specific to architecture, machine, <emphasis>local</emphasis> and so on.</para>
<para>Only variable definitions and include directives are allowed in .conf files.</para>
</section>
<section>
<title>Classes</title>
<para>BitBake classes are our rudamentary inheritence mechanism. As briefly mentioned in the metadata introduction, they're parsed when an <literal>inherit</literal> directive is encountered, and they are located in classes/ relative to the dirs in <envar>BBPATH</envar>.</para>
</section>
<section>
<title>.bb Files</title>
<para>A BitBake (.bb) file is a logical unit of tasks to be executed. Normally this is a package to be built. Inter-.bb dependencies are obeyed. The files themselves are located via the <varname>BBFILES</varname> variable, which is set to a space seperated list of .bb files, and does handle wildcards.</para>
</section>
</section>
</chapter>
<chapter>
<title>Commands</title>
<section>
<title>bbread</title>
<para>bbread is a command for displaying BitBake metadata. When run with no arguments, it has the core parse 'conf/bitbake.conf', as located in BBPATH, and displays that. If you supply a file on the commandline, such as a .bb, then it parses that afterwards, using the aforementioned configuration metadata.</para>
</section>
<section>
<title>bbmake</title>
<programlisting format="linespecific"><literal>usage: bbmake [options] [package ...]
Executes the specified task (default is 'build') for a given set of BitBake files.
It expects that BBFILES is defined, which is a space seperated list of files to
be executed. BBFILES does support wildcards.
Default packages to be executed are all packages in BBFILES.
Default BBFILES are the .bb files in the current directory.
options:
--version show program's version number and exit
-h, --help show this help message and exit
-k, --continue continue as much as possible after an error. While the
target that failed, and those that depend on it, cannot
be remade, the other dependencies of these targets can
be processed all the same.
-f, --force force run of specified cmd, regardless of stamp status
-cCMD, --cmd=CMD Specify task to execute
-rFILE, --read=FILE read the specified file before bitbake.conf
-v, --verbose output more chit-chat to the terminal
-n, --dry-run don't execute, just go through the motions
-p, --parse-only quit after parsing the BB files (developers only)
-d, --disable-psyco disable using the psyco just-in-time compiler (not
recommended)
-s, --show-versions show current and preferred versions of all packages</literal>
</programlisting>
</section>
</chapter>
<appendix>
<title>Reference</title>
<section>
<title>Required Metadata</title>
<para>test</para>
</section>
</appendix>
</book>
|
