<title>Reference: BitBake</title>
<para>
- BitBake is a program written in Python that interprets the metadata
- that makes up Poky. At some point, people wonder what actually happens
- when you type <command>bitbake poky-image-sato</command>. This section
- aims to give an overview of what happens behind the scenes from a
- BitBake perspective.
+ BitBake is a program written in Python that interprets the metadata that makes up Poky.
+ At some point, people wonder what actually happens when you enter:
+ <literallayout class='monospaced'>
+ $ bitbake poky-image-sato
+ </literallayout>
</para>
-
+
<para>
- It is worth noting that BitBake aims to be a generic "task" executor
- capable of handling complex dependency relationships. As such it has no
- real knowledge of what the tasks it is executing actually do. It just
- considers a list of tasks with dependencies and handles metadata
- consisting of variables in a certain format which get passed to the
- tasks.
+ This appendix provides an overview of what happens behind the scenes from BitBake's perspective.
</para>
+ <note><para>
+ BitBake strives to be a generic "task" executor that is capable of handling complex dependency relationships.
+ As such, it has no real knowledge of what the tasks being executed actually do.
+ BitBake just considers a list of tasks with dependencies and handles metadata
+ that consists of variables in a certain format that get passed to the tasks.
+ </para></note>
+
<section id='ref-bitbake-parsing'>
<title>Parsing</title>
<para>
The first thing BitBake does is work out its configuration by
looking for a file called <filename>bitbake.conf</filename>.
- BitBake searches through the <varname>BBPATH</varname> environment
+ BitBake examines the <varname>BBPATH</varname> environment
variable looking for a <filename class="directory">conf/</filename>
- directory containing a <filename>bitbake.conf</filename> file and
- adds the first <filename>bitbake.conf</filename> file found in
+ directory that contains a <filename>bitbake.conf</filename> file.
+ BitBake adds the first <filename>bitbake.conf</filename> file found in
<varname>BBPATH</varname> (similar to the PATH environment variable).
For Poky, <filename>bitbake.conf</filename> is found in <filename
class="directory">meta/conf/</filename>.
files to include from a <filename class="directory">conf/</filename>
directory below the directories listed in <varname>BBPATH</varname>.
In general the most important configuration file from a user's perspective
- is <filename>local.conf</filename>, which contains a users customized
- settings for Poky. Other notable configuration files are the distribution
+ is <filename>local.conf</filename>, which contains a user's customized
+ settings for Poky.
+ Other notable configuration files are the distribution
configuration file (set by the <glossterm><link linkend='var-DISTRO'>
DISTRO</link></glossterm> variable) and the machine configuration file
(set by the <glossterm><link linkend='var-MACHINE'>MACHINE</link>
- </glossterm> variable). The <glossterm><link linkend='var-DISTRO'>
- DISTRO</link></glossterm> and <glossterm><link linkend='var-MACHINE'>
- MACHINE</link></glossterm> environment variables are both usually set in
- the <filename>local.conf</filename> file. Valid distribution
+ </glossterm> variable).
+ The DISTRO and MACHINE environment variables are both usually set in
+ the <filename>local.conf</filename> file.
+ Valid distribution
configuration files are available in the <filename class="directory">
meta/conf/distro/</filename> directory and valid machine configuration
files in the <filename class="directory">meta/conf/machine/</filename>
- directory. Within the <filename class="directory">
- meta/conf/machine/include/</filename> directory are various <filename>
- tune-*.inc</filename> configuration files which provide common
- "tuning" settings specific to and shared between particular
- architectures and machines.
+ directory.
+ Within the <filename class="directory">meta/conf/machine/include/</filename>
+ directory are various <filename>tune-*.inc</filename> configuration files that provide common
+ "tuning" settings specific to and shared between particular architectures and machines.
</para>
<para>
- After the parsing of the configuration files some standard classes
- are included. In particular, <filename>base.bbclass</filename> is
- always included, as will any other classes
- specified in the configuration using the <glossterm><link
- linkend='var-INHERIT'>INHERIT</link></glossterm>
- variable. Class files are searched for in a classes subdirectory
+ After the parsing of the configuration files some standard classes are included.
+ The <filename>base.bbclass</filename> file is always included.
+ Other classes that are specified in the configuration using the
+ <glossterm><link linkend='var-INHERIT'>INHERIT</link></glossterm>
+ variable are also inculded.
+ Class files are searched for in a classes subdirectory
under the paths in <varname>BBPATH</varname> in the same way as
configuration files.
</para>
variable <glossterm><link linkend='var-BBFILES'>BBFILES</link></glossterm>
is set, usually in
<filename>local.conf</filename>, and defines the list of places to search for
- <filename class="extension">.bb</filename> files. By
- default this specifies the <filename class="directory">meta/packages/
+ <filename class="extension">.bb</filename> files.
+ By default this specifies the <filename class="directory">meta/packages/
</filename> directory within Poky, but other directories such as
<filename class="directory">meta-extras/</filename> can be included
- too. Adding extra content to
- <glossterm><link linkend='var-BBFILES'>BBFILES</link></glossterm> is best
- acheived through the use of BitBake
+ too.
+ Adding extra content to BBFILES is best acheived through the use of BitBake
<link linkend='usingpoky-changes-layers'>"layers"</link>.
</para>
<para>
- BitBake parses each <filename class="extension">.bb</filename> file in
- <glossterm><link linkend='var-BBFILES'>BBFILES</link></glossterm> and
- stores the values of various variables. In summary, for each
- <filename class="extension">.bb</filename>
+ BitBake parses each <filename class="extension">.bb</filename> file in BBFILES and
+ stores the values of various variables.
+ In summary, for each <filename class="extension">.bb</filename>
file the configuration + base class of variables are set, followed
by the data in the <filename class="extension">.bb</filename> file
itself, followed by any inherit commands that
