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documentation/poky-ref-manual/ref-bitbake.xml: scrubbed for Poky 

I swapped the Yocto Project for Poky throughout.  Some other general
edits were done.  I put in a reference to a spot to learn how to best
set the BB_NUMBER_THREADS variable.

(From yocto-docs rev: 2543a915957014a59e6c49a1cdde270725d47af3)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2011-08-19 10:11:41 -07:00 committed by Richard Purdie
parent 39de08c105
commit 32a860851c
1 changed files with 97 additions and 73 deletions
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170
documentation/poky-ref-manual/ref-bitbake.xml
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@ -6,23 +6,23 @@
<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 enter:
<literallayout class='monospaced'>
BitBake is a program written in Python that interprets the metadata that makes up the Yocto Project.
At some point, developers wonder what actually happens when you enter:
<literallayout class='monospaced'>
$ bitbake core-image-sato
</literallayout>
</literallayout>
</para>
<para>
This appendix provides an overview of what happens behind the scenes from BitBake's perspective.
</para>
<note><para>
<note>
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>
</note>
<section id='ref-bitbake-parsing'>
<title>Parsing</title>
@ -33,61 +33,64 @@
<para>
The first thing BitBake does is look for the <filename>bitbake.conf</filename> file.
Poky keeps this file in <filename>meta/conf/</filename>.
The Yocto Project keeps this file in the Yocto Project file's <filename>meta/conf/</filename>
directory.
BitBake finds it by examining the <filename>BBPATH</filename> environment
variable and looking for the <filename>meta/conf/</filename>
directory.
</para>
<para>
In Poky, <filename>bitbake.conf</filename> lists other configuration
In the Yocto Project, <filename>bitbake.conf</filename> lists other configuration
files to include from a <filename>conf/</filename>
directory below the directories listed in <filename>BBPATH</filename>.
In general the most important configuration file from a user's perspective
In general, the most important configuration file from a user's perspective
is <filename>local.conf</filename>, which contains a user's customized
settings for Poky.
settings for the Yocto Project build environment.
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 DISTRO and MACHINE environment variables are both usually set in
configuration file (set by the
<filename><link linkend='var-DISTRO'>DISTRO</link></filename> variable)
and the machine configuration file
(set by the
<filename><link linkend='var-MACHINE'>MACHINE</link></filename> variable).
The <filename>DISTRO</filename> and <filename>MACHINE</filename> environment
variables are both usually set in
the <filename>local.conf</filename> file.
Valid distribution
configuration files are available in the <filename>
meta/conf/distro/</filename> directory and valid machine configuration
files in the <filename>meta/conf/machine/</filename>
directory.
configuration files are available in the <filename>meta/conf/distro/</filename> directory
and valid machine configuration
files in the <filename>meta/conf/machine/</filename> directory.
Within the <filename>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.
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>
<filename><link linkend='var-INHERIT'>INHERIT</link></filename>
variable are also inculded.
Class files are searched for in a classes subdirectory
Class files are searched for in a <filename>classes</filename> subdirectory
under the paths in <filename>BBPATH</filename> in the same way as
configuration files.
</para>
<para>
After classes are included, the
variable <glossterm><link linkend='var-BBFILES'>BBFILES</link></glossterm>
After classes are included, the variable
<filename><link linkend='var-BBFILES'>BBFILES</link></filename>
is set, usually in
<filename>local.conf</filename>, and defines the list of places to search for
<filename>.bb</filename> files.
By default, the BBFILES variable specifies the <filename>meta/recipes-*/
</filename> directory within Poky.
Adding extra content to BBFILES is best achieved through the use of BitBake
<link linkend='usingpoky-changes-layers'>"layers"</link>.
By default, the <filename>BBFILES</filename> variable specifies the
<filename>meta/recipes-*/</filename> directory within Poky.
Adding extra content to <filename>BBFILES</filename> is best achieved through the use of
BitBake layers as described in the
<link linkend='usingpoky-changes-layers'>BitBake Layers</link> section.
</para>
<para>
BitBake parses each <filename>.bb</filename> file in BBFILES and
BitBake parses each <filename>.bb</filename> file in <filename>BBFILES</filename> and
stores the values of various variables.
In summary, for each <filename>.bb</filename>
file the configuration plus the base class of variables are set, followed
@ -111,13 +114,14 @@
<para>
Once all the <filename>.bb</filename> files have been
parsed, BitBake starts to build the target (core-image-sato in the previous section's
example) and looks for providers of that target.
parsed, BitBake starts to build the target (<filename>core-image-sato</filename>
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 "core-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>.
In the case of <filename>core-image-sato</filename>, it would lead to
<filename>task-base.bb</filename>,
which in turn leads to packages like <filename>Contacts</filename>,
<filename>Dates</filename> and <filename>BusyBox</filename>.
These packages in turn depend on glibc and the toolchain.
</para>
@ -128,12 +132,12 @@
following in the machine configuration file:
</para>
<programlisting>
PREFERRED_PROVIDER_virtual/kernel = "linux-rp"
</programlisting>
<literallayout class='monospaced'>
PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
</literallayout>
<para>
The default <glossterm><link linkend='var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</link></glossterm>
The default <filename><link linkend='var-PREFERRED_PROVIDER'>PREFERRED_PROVIDER</link></filename>
is the provider with the same name as the target.
</para>
@ -142,17 +146,18 @@ PREFERRED_PROVIDER_virtual/kernel = "linux-rp"
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>
You can use the
<filename><link linkend='var-PREFERRED_VERSION'>PREFERRED_VERSION</link></filename>
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>
<filename><link linkend='var-DEFAULT_PREFERENCE'>DEFAULT_PREFERENCE</link></filename>
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
Setting the <filename>DEFAULT_PREFERENCE</filename> to "-1" makes the
package unlikely to be used unless it is explicitly referenced.
Setting the <filename>DEFAULT_PREFERENCE</filename> to "1" makes it likely the package 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 package
versions until they have undergone sufficient testing to be considered stable.
</para>
@ -165,8 +170,10 @@ PREFERRED_PROVIDER_virtual/kernel = "linux-rp"
<title>Dependencies</title>
<para>
Each target BitBake builds consists of multiple tasks such as fetch, unpack, patch, configure,
and compile.
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>
@ -175,12 +182,11 @@ PREFERRED_PROVIDER_virtual/kernel = "linux-rp"
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
At a basic level, it is sufficient to know that BitBake uses the
<filename><link linkend='var-DEPENDS'>DEPENDS</link></filename> and
<filename><link linkend='var-RDEPENDS'>RDEPENDS</link></filename> variables when
calculating dependencies.
</para>
</section>
<section id='ref-bitbake-tasklist'>
@ -191,39 +197,49 @@ PREFERRED_PROVIDER_virtual/kernel = "linux-rp"
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.
<filename><link linkend='var-BB_NUMBER_THREADS'>BB_NUMBER_THREADS</link></filename> 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.
See the
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html#building-image'>
Building an Image</ulink> section in the
<ulink url='http://www.yoctoproject.org/docs/1.1/yocto-project-qs/yocto-project-qs.html'>
Yocto Project Quick Start</ulink> for more information.
</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><link linkend='var-STAMPS'>STAMPS</link></filename> variable (usually
<filename>build/tmp/stamps/*/</filename>).
On subsequent runs, BitBake looks at the STAMPS directory and does not rerun
On subsequent runs, BitBake looks at the <filename>STAMPS</filename> 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>.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.
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>
<note><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.
</para></note>
</note>
</section>
<section id='ref-bitbake-runtask'>
<title>Running a Task</title>
<para>
Tasks can either be a shell task or a python task.
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
@ -268,7 +284,8 @@ Options:
-h, --help show this help message and exit
-b BUILDFILE, --buildfile=BUILDFILE
execute the task against this .bb file, rather than a
package from BBFILES.
package from BBFILES. Does not handle any
dependencies.
-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
@ -276,8 +293,6 @@ 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
@ -285,26 +300,35 @@ Options:
what you are doing). Depending on the base.bbclass a
listtasks tasks is defined and will show available
tasks
-r FILE, --read=FILE read the specified file before bitbake.conf
-r PREFILE, --read=PREFILE
read the specified file before bitbake.conf
-R POSTFILE, --postread=POSTFILE
read the specified file after bitbake.conf
-v, --verbose output more chit-chat to the terminal
-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)
-s, --show-versions show current and preferred versions of all packages
-e, --environment show the global or per-package environment (this is
what used to be bbread)
-g, --graphviz emit the dependency trees of the specified packages in
the dot syntax
-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
-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
-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
-t SERVERTYPE, --servertype=SERVERTYPE
Choose which server to use, none, process or xmlrpc
--revisions-changed Set the exit code depending on whether upstream
floating revisions have changed or not
</screen>
</section>
@ -321,22 +345,22 @@ Options:
<para>
Fetchers are usually triggered by entries in
<glossterm><link linkend='var-SRC_URI'>SRC_URI</link></glossterm>.
<filename><link linkend='var-SRC_URI'>SRC_URI</link></filename>.
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
One useful feature for certain Source Code Manager (SCM) fetchers is the ability to
"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>
This feature works using the <filename><link linkend='var-SRCREV'>SRCREV</link></filename>
variable.
See the
<link linkend='platdev-appdev-srcrev'>Developing within Poky with an External SCM-based Package</link>
section for more information.
<link linkend='platdev-appdev-srcrev'>Development Within Yocto Project for a Package that Uses
an External SCM</link> section for more information.
</para>
</section>