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dev-manual: Added section for multi-configuration support 

I added a new section in the "Common Tasks" chapter to support
the fact that BB can now build for multi-configurations.

(From yocto-docs rev: aa21aeb2f3d2f9d5a3a6e7175b7c6f13da5f608e)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Scott Rifenbark 2016-10-19 11:37:17 -07:00 committed by Richard Purdie
parent 5f4b202078
commit 0df906b779
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documentation/dev-manual/dev-manual-common-tasks.xml
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@ -3621,6 +3621,106 @@
</section>
</section>
<section id='platdev-building-targets-with-multiple-configurations'>
<title>Building Targets with Multiple Configurations</title>
<para>
Bitbake also has functionality that allows you to build
multiple targets at the same time, where each target uses
a different configuration.
</para>
<para>
In order to accomplish this, you setup each of the configurations
you need to use in parallel by placing the configuration files in
your current build directory alongside the usual
<filename>local.conf</filename> file.
</para>
<para>
Follow these guidelines to create an environment that supports
multiple configurations:
<itemizedlist>
<listitem><para>
<emphasis>Create Configuration Files</emphasis>:
You need to create a single configuration file for each
configuration for which you want to add support.
These files would contain lines such as the following:
<literallayout class='monospaced'>
MACHINE = "A"
</literallayout>
The files would contain any other variables that can
be set and built in the same directory.
<note>
You can change the
<ulink url='&YOCTO_DOCS_REF_URL;#var-TMPDIR'><filename>TMPDIR</filename></ulink>
to not conflict.
</note></para>
<para>
Furthermore, the configuration file must be located in the
current build directory in a directory named
<filename>multiconfig</filename> under the build's
<filename>conf</filename> directory where
<filename>local.conf</filename> resides.
The reason for this restriction is because the
<filename>BBPATH</filename> variable is not constructed
until the layers are parsed.
Consequently, using the configuration file as a
pre-configuration file is not possible unless it is
located in the current working directory.
</para></listitem>
<listitem><para>
<emphasis>Add the BitBake Multi-Config Variable to you Local Configuration File</emphasis>:
Use the
<filename>BBMULTICONFIG</filename>
variable in your <filename>conf/local.conf</filename>
configuration file to specify each separate configuration.
For example, the following line tells BitBake it should load
<filename>conf/multiconfig/configA.conf</filename>,
<filename>conf/multiconfig/configB.conf</filename>, and
<filename>conf/multiconfig/configC.conf</filename>.
<literallayout class='monospaced'>
BBMULTICONFIG = "configA configB configC"
</literallayout>
</para></listitem>
<listitem><para>
<emphasis>Launch BitBake</emphasis>:
Use the following BitBake command form to launch the
build:
<literallayout class='monospaced'>
$ bitbake [multiconfig:<replaceable>multiconfigname</replaceable>:]<replaceable>target</replaceable> [[[multiconfig:<replaceable>multiconfigname</replaceable>:]<replaceable>target</replaceable>] ... ]
</literallayout>
Following is an example that supports building a minimal
image for configuration A alongside a standard
<filename>core-image-sato</filename>, which takes its
configuration from <filename>local.conf</filename>:
<literallayout class='monospaced'>
$ bitbake multiconfig:configA:core-image-minimal core-image-sato
</literallayout>
</para></listitem>
</itemizedlist>
</para>
<para>
Support for multiple configurations in this current release of
the Yocto Project (&DISTRO_NAME; &DISTRO;) has some known issues:
<itemizedlist>
<listitem><para>
No inter-multi-configuration dependencies exist.
</para></listitem>
<listitem><para>
Shared State (sstate) optimizations do not exist.
Consequently, if the build uses the same object twice
in, for example, two different
<filename>TMPDIR</filename> directories, the build
will either load from an existing sstate cache at the
start or build the object twice.
</para></listitem>
</itemizedlist>
</para>
</section>
<section id="platdev-working-with-libraries">
<title>Working With Libraries</title>