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documentation/dev-manual/dev-manual-common-tasks.xml: New section 

Added a new section on building from an external source tree.
This addition was driven by a need through two community members
whose feedback was picked up by Darren.

Reported-by: Inaky Perez-Gonzales <inaky.perez-gonzales@intel.com>
Reported-by: Mohamed Abbas <mohamed.abbas@intel.com>
(From yocto-docs rev: c9548803f58e5055d6686dbc16c94308296ccf2a)

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 2012-02-28 12:13:06 -06:00 committed by Richard Purdie
parent 6aeeeba08f
commit ad5de9715a
1 changed files with 55 additions and 0 deletions
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@ -1436,6 +1436,61 @@ so that there are some definite steps on how to do this. I need more detail her
</para>
</section>
<section id="building-software-from-an-external-source">
<title>Building Software from an External Source</title>
<para>
By default, the Yocto Project build system does its work from within the
<link linkend='yocto-project-build-directory'>Yocto Project Build Directory</link>.
The build process involves fetching the source files, unpacking them, and then patching them
if necessary before the build takes place.
</para>
<para>
Situations exist where you might want to build software from source files that are external to
and thus outside of the <link linkend='yocto-project-files'>Yocto Project Files</link>.
For example, suppose you have a project that includes a new BSP with a heavily customized
kernel, a very minimal image, and some new user-space recipes.
And, you want to minimize the exposure to the Yocto Project build system to the
development team so that they can focus on their project and maintain everyone's workflow
as much as possible.
In this case, you want a kernel source directory on the development machine where the
development occurs.
You want the recipe's
<ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-SRC_URI'><filename>SRC_URI</filename></ulink>
variable to point to the external directory and use it as is, not copy it.
</para>
<para>
To build from software that comes from an external source, all you need to do is
change your recipe so that it inherits the
<ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#ref-classes-externalsrc'><filename>externalsrc.bbclass</filename></ulink>
class and then sets the
<ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-S'><filename>S</filename></ulink>
variable to point to your external source code.
Here are the statements to put in your recipe:
<literallayout class='monospaced'>
inherit externalsrc
S = "/some/path/to/your/package/source"
</literallayout>
</para>
<para>
It is important to know that the <filename>externalsrc.bbclass</filename> assumes that the
source directory <filename>S</filename> and the build directory
<ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual.html#var-B'><filename>B</filename></ulink>
are different even though by default these directories are the same.
This assumption is important because it supports building different variants of the recipe
by using the
<ulink url='http://www.yoctoproject.org/docs/latest/poky-ref-manual/poky-ref-manual#var-BBCLASSEXTEND'><filename>BBCLASSEXTEND</filename></ulink>
variable.
You could allow the build directory to be the same as the source directory but you would
not be able to build more than one variant of the recipe.
Consequently, if you are building multiple variants of the recipe, you need to establish a
build directory that is different than the source directory.
</para>
</section>
<section id="usingpoky-changes">
<title>Making and Maintaining Changes</title>
<para>