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documentation/poky-ref-manual/ref-bitbake.xml: Completed general edits. 

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
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Scott Rifenbark 2010-12-03 12:23:03 -08:00 committed by Saul Wold
parent be622ae87e
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@ -28,15 +28,15 @@
<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 examines the <varname>BBPATH</varname> environment
variable looking for a <filename class="directory">conf/</filename>
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>.
BitBake parses configuration files, classes, and <filename>.bb</filename> files.
</para>
<para>
The first thing BitBake does is look for the <filename>bitbake.conf</filename> file.
Poky keeps this file in <filename class="directory">meta/conf/</filename>.
BitBake finds it by examining the <varname>BBPATH</varname> environment
variable and looking for the <filename class="directory">meta/conf/</filename>
directory.
</para>
<para>
@ -75,12 +75,12 @@
</para>
<para>
After the parsing of the configuration files is complete, the
After classes are included, the
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/
By default, the BBFILES variable 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.
@ -92,19 +92,19 @@
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
file the configuration plus the 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
<filename class="extension">.bb</filename> file might contain.
</para>
<para>
Parsing <filename class="extension">.bb</filename> files is a time
consuming process, so a cache is kept to speed up subsequent parsing.
Because parsing <filename class="extension">.bb</filename> files is a time
consuming process, a cache is kept to speed up subsequent parsing.
This cache is invalid if the timestamp of the <filename class="extension">.bb</filename>
file itself has changed, or if the timestamps of any of the include,
file itself changes, or if the timestamps of any of the include,
configuration or class files the <filename class="extension">.bb</filename>
file depends on have changed.
file depends on changes.
</para>
</section>
@ -113,58 +113,53 @@
<para>
Once all the <filename class="extension">.bb</filename> files have been
parsed, BitBake will proceed to build "poky-image-sato" (or whatever was
specified on the commandline) and looks for providers of that target.
parsed, BitBake starts to build the target (poky-image-sato in the previous section's
example) and looks for providers of that target.
Once a provider is selected, BitBake resolves all the dependencies for
the target. In the case of "poky-image-sato", it would lead to
<filename>task-base.bb</filename>
which in turn would lead to packages like <application>Contacts</application>,
<application>Dates</application>, <application>BusyBox</application>
and these in turn depend on glibc and the toolchain.
the target.
In the case of "poky-image-sato", it would lead to <filename>task-base.bb</filename>,
which in turn leads to packages like <application>Contacts</application>,
<application>Dates</application> and <application>BusyBox</application>.
These packages in turn depend on glibc and the toolchain.
</para>
<para>
Sometimes a target might have multiple providers and a common example
is "virtual/kernel" that is provided by each kernel package. Each machine
will often elect the best provider of its kernel with a line like the
Sometimes a target might have multiple providers.
An common example is "virtual/kernel", which is provided by each kernel package.
Each machine often elects the best kernel provider by using a line similar to the
following in the machine configuration file:
</para>
<programlisting><glossterm><link linkend='var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</link></glossterm>_virtual/kernel = "linux-rp"</programlisting>
<programlisting>
PREFERRED_PROVIDER_virtual/kernel = "linux-rp"
</programlisting>
<para>
The default <glossterm><link linkend='var-PREFERRED_PROVIDER'>
PREFERRED_PROVIDER</link></glossterm> is the provider with the same name as
the target.
The default <glossterm><link linkend='var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</link></glossterm>
is the provider with the same name as the target.
</para>
<para>
Understanding how providers are chosen is complicated by the fact
multiple versions might be present. BitBake defaults to the highest
version of a provider by default. Version comparisons are made using
the same method as Debian. The <glossterm><link
linkend='var-PREFERRED_VERSION'>PREFERRED_VERSION</link></glossterm>
variable can be used to specify a particular version
(usually in the distro configuration) but the order can
also be influenced by the <glossterm><link
linkend='var-DEFAULT_PREFERENCE'>DEFAULT_PREFERENCE</link></glossterm>
variable. By default files
have a preference of "0". Setting the
<glossterm><link
linkend='var-DEFAULT_PREFERENCE'>DEFAULT_PREFERENCE</link></glossterm> to "-1" will
make a package unlikely to be used unless it was explicitly referenced and
"1" makes it likely the package will be used.
<glossterm><link
linkend='var-PREFERRED_VERSION'>PREFERRED_VERSION</link></glossterm> overrides
any <glossterm><link
linkend='var-DEFAULT_PREFERENCE'>DEFAULT_PREFERENCE</link></glossterm>. <glossterm><link
linkend='var-DEFAULT_PREFERENCE'>DEFAULT_PREFERENCE</link></glossterm>
is often used to mark more
experimental new versions of packages until they've undergone sufficient
testing to be considered stable.
Understanding how providers are chosen is made complicated by the fact
that multiple versions might exist.
BitBake defaults to the highest version of a provider.
Version comparisons are made using the same method as Debian.
You can use the <glossterm><link linkend='var-PREFERRED_VERSION'>PREFERRED_VERSION</link></glossterm>
variable to specify a particular version (usually in the distro configuration).
You can influence the order by using the
<glossterm><link linkend='var-DEFAULT_PREFERENCE'>DEFAULT_PREFERENCE</link></glossterm>
variable.
By default, files have a preference of "0".
Setting the DEFAULT_PREFERENCE to "-1" makes the package unlikely to be used unless it is
explicitly referenced.
Setting the DEFAULT_PREFERENCE to "1" makes it likely the package is used.
PREFERRED_VERSION overrides any DEFAULT_PREFERENCE setting.
DEFAULT_PREFERENCE is often used to mark newer and more experimental package
versions until they have undergone sufficient testing to be considered stable.
</para>
<para>
The end result is that internally, BitBake has now built a list of
providers for each target it needs in order of priority.
In summary, BitBake has created a list of providers, which is prioritized, for each target.
</para>
</section>
@ -172,18 +167,20 @@
<title>Dependencies</title>
<para>
Each target BitBake builds consists of multiple tasks (e.g. fetch,
unpack, patch, configure, compile etc.). For best performance on
multi-core systems, BitBake considers each task as an independent
entity with a set of dependencies. There are many variables that
are used to signify these dependencies and more information can be found
about these in the <ulink url='http://bitbake.berlios.de/manual/'>
BitBake manual</ulink>. At a basic level it is sufficient to know
that BitBake uses the <glossterm><link
linkend='var-DEPENDS'>DEPENDS</link></glossterm> and
<glossterm><link linkend='var-RDEPENDS'>RDEPENDS</link></glossterm> variables when
calculating dependencies and descriptions of these variables are
available through the links.
Each target BitBake builds consists of multiple tasks such as fetch, unpack, patch, configure,
and compile.
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
<ulink url='http://bitbake.berlios.de/manual/'>BitBake manual</ulink>.
At a basic level it is sufficient to know that BitBake uses the
<glossterm><link linkend='var-DEPENDS'>DEPENDS</link></glossterm> and
<glossterm><link linkend='var-RDEPENDS'>RDEPENDS</link></glossterm> variables when
calculating dependencies.
</para>
</section>
@ -193,69 +190,75 @@
<para>
Based on the generated list of providers and the dependency information,
BitBake can now calculate exactly which tasks it needs to run and in what
order. The build now starts with BitBake forking off threads up to
the limit set in the <glossterm><link
linkend='var-BB_NUMBER_THREADS'>BB_NUMBER_THREADS</link></glossterm> variable
as long as there are tasks ready to run, i.e. tasks with all their
dependencies met.
BitBake can now calculate exactly what tasks it needs to run and in what
order it needs to run them.
The build now starts with BitBake forking off threads up to the limit set in the
<glossterm><link linkend='var-BB_NUMBER_THREADS'>BB_NUMBER_THREADS</link></glossterm> variable.
BitBake continues to fork threads as long as there are tasks ready to run,
those taksks have all their dependencies met, and the thread threshold has not been
exceeded.
</para>
<para>
As each task completes, a timestamp is written to the directory
specified by the <glossterm><link
linkend='var-STAMPS'>STAMPS</link></glossterm> variable (usually
<filename class="directory">build/tmp/stamps/*/</filename>). On
subsequent runs, BitBake looks at the <glossterm><link
linkend='var-STAMPS'>STAMPS</link></glossterm>
directory and will not rerun
tasks its already completed unless a timestamp is found to be invalid.
Currently, invalid timestamps are only considered on a per <filename
class="extension">.bb</filename> file basis so if for example the configure stamp has a timestamp greater than the
compile timestamp for a given target the compile task would rerun but this
has no effect on other providers depending on that target. This could
change or become configurable in future versions of BitBake. Some tasks
are marked as "nostamp" tasks which means no timestamp file will be written
and the task will always rerun.
As each task completes, a timestamp is written to the directory specified by the
<glossterm><link linkend='var-STAMPS'>STAMPS</link></glossterm> variable (usually
<filename class="directory">build/tmp/stamps/*/</filename>).
On subsequent runs, BitBake looks at the STAMPS directory 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
<filename class="extension">.bb</filename> 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.
This behavior could change or become configurable in future versions of BitBake.
</para>
<para>Once all the tasks have been completed BitBake exits.</para>
<note><para>
Some tasks are marked as "nostamp" tasks.
No timestamp file is created when these tasks are run.
Consequently, "nostamp" tasks are always rerun.
</para></note>
</section>
<section id='ref-bitbake-runtask'>
<title>Running a Task</title>
<para>
It's worth noting what BitBake does to run a task. A task can either
be a shell task or a python task. For shell tasks, BitBake writes a
shell script to <filename>${WORKDIR}/temp/run.do_taskname.pid</filename>
and then executes the script. The generated
shell script contains all the exported variables, and the shell functions
with all variables expanded. Output from the shell script is
sent to the file <filename>${WORKDIR}/temp/log.do_taskname.pid</filename>.
Looking at the
expanded shell functions in the run file and the output in the log files
Tasks can either be a shell task or a python task.
For shell tasks, BitBake writes a shell script to
<filename>${WORKDIR}/temp/run.do_taskname.pid</filename> and then executes the script.
The generated shell script contains all the exported variables, and the shell functions
with all variables expanded.
Output from the shell script goes to the file <filename>${WORKDIR}/temp/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>
Python functions are executed internally to BitBake itself and
logging goes to the controlling terminal. Future versions of BitBake will
write the functions to files in a similar way to shell functions and
logging will also go to the log files in a similar way.
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 way similar to shell tasks as well.
</para>
<para>
Once all the tasks have been completed BitBake exits.
</para>
</section>
<section id='ref-bitbake-commandline'>
<title>Commandline</title>
<title>BitBake Command Line</title>
<para>
To quote from "bitbake --help":
Following is the bitbake manpage:
</para>
<screen>Usage: bitbake [options] [package ...]
<screen>
$ bitbake --help
Usage: bitbake [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 separated list of files to
@ -275,6 +278,8 @@ Options:
-a, --tryaltconfigs continue with builds by trying to use alternative
providers where possible.
-f, --force force run of specified cmd, regardless of stamp status
-i, --interactive drop into the interactive mode also called the BitBake
shell.
-c CMD, --cmd=CMD Specify task to execute. Note that this only executes
the specified task for the providee and the packages
it depends on, i.e. 'compile' does not implicitly call
@ -287,9 +292,6 @@ Options:
-D, --debug Increase the debug level. You can specify this more
than once.
-n, --dry-run don't execute, just go through the motions
-S, --dump-signatures
don't execute, just dump out the signature
construction information
-p, --parse-only quit after parsing the BB files (developers only)
-d, --disable-psyco disable using the psyco just-in-time compiler (not
recommended)
@ -298,46 +300,45 @@ Options:
what used to be bbread)
-g, --graphviz emit the dependency trees of the specified packages in
the dot syntax
-I EXTRA_ASSUME_PROVIDED, --ignore-deps=EXTRA_ASSUME_PROVIDED
Assume these dependencies don't exist and are already
provided (equivalent to ASSUME_PROVIDED). Useful to
make dependency graphs more appealing
-I IGNORED_DOT_DEPS, --ignore-deps=IGNORED_DOT_DEPS
Stop processing at the given list of dependencies when
generating dependency graphs. This can help to make
the graph more appealing
-l DEBUG_DOMAINS, --log-domains=DEBUG_DOMAINS
Show debug logging for the specified logging domains
-P, --profile profile the command and print a report
-u UI, --ui=UI userinterface to use
--revisions-changed Set the exit code depending on whether upstream
floating revisions have changed or not</screen>
</screen>
</section>
<section id='ref-bitbake-fetchers'>
<title>Fetchers</title>
<para>
As well as the containing the parsing and task/dependency handling
code, BitBake also contains a set of "fetcher" modules which allow
fetching of source code from various types of sources. Example
sources might be from disk with the metadata, from websites, from
remote shell accounts or from SCM systems like cvs/subversion/git.
BitBake also contains a set of "fetcher" modules that allow
retrieval of source code from various types of sources.
For example, BitBake can get source code from a disk with the metadata, from websites,
from remote shell accounts or from Source Code Management (SCM) systems
like <filename>cvs/subversion/git</filename>.
</para>
<para>
The fetchers are usually triggered by entries in
<glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm>. Information about the
options and formats of entries for specific fetchers can be found in the
<ulink url='http://bitbake.berlios.de/manual/'>BitBake manual</ulink>.
Fetchers are usually triggered by entries in
<glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm>.
You can find information about the options and formats of entries for specific
fetchers in the <ulink url='http://bitbake.berlios.de/manual/'>BitBake manual</ulink>.
</para>
<para>
One useful feature for certain SCM fetchers is the ability to
"auto-update" when the upstream SCM changes version. Since this
requires certain functionality from the SCM only certain systems
support it, currently Subversion, Bazaar and to a limited extent, Git. It
works using the <glossterm><link linkend='var-SRCREV'>SRCREV</link>
</glossterm> variable. See the <link linkend='platdev-appdev-srcrev'>
developing with an external SCM based project</link> section for more
information.
"auto-update" when the upstream SCM changes version.
Since this ability requires certain functionality from the SCM, not all
systems support it.
Currently Subversion, Bazaar and to a limited extent, Git support the ability to "auto-update".
This feature works using the <glossterm><link linkend='var-SRCREV'>SRCREV</link></glossterm>
variable.
See the
<link linkend='platdev-appdev-srcrev'>Developing within Poky with an External SCM-based Package</link>
section for more information.
</para>
</section>