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bitbake: user-manual-metadata.xml: Added new section on mapping functions.

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Fixes [YOCTO #5472]
Fixes [YOCTO #1973]

Created a new section called "Automatically Mapping Functions
Within the Context of a Class".  This section addresses the
EXPORT_FUNCTIONS "operator", which was the last of the adjustments
to the variables bug against the BB manual (1973).  The related
bug (5472) is a general bug against enhancing the BB manual, which
this change caps off.

The section here was reviewed and approved by Richard Purdie.

(Bitbake rev: cec33d4fdc05db3a41e978f3a1ab977730c443eb)

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
2014-04-02 12:26:02 +00:00
committed by Richard Purdie
parent 3e528d3e4b
commit a5775abb19
1 changed files with 76 additions and 0 deletions
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76
bitbake/doc/user-manual/user-manual-metadata.xml
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@@ -792,6 +792,82 @@
</itemizedlist>
</para>
</section>
<section id='automatically-mapping-functions-within-the-context-of-a-class'>
<title>Automatically Mapping Functions Within the Context of a Class</title>
<para>
Through coding techniques and the use of
<filename>EXPORT_FUNCTIONS</filename>, BitBake supports
automatic mapping for functions within the context of
a class.
</para>
<para>
To understand the benefits of this feature, consider the basic scenario
where a class defines a function and your recipe inherits the class.
In this basic scenario, your recipe has access to the function in the
class by way of inheritance and can freely call and use the function
as defined in the class.
However, if you need to have a modified version of that function
in your recipe you are limited to using either your modified version
of the function or using "prepend_" or "_append" operators to add
code to be executed before or after the original function in the
class.
Your recipe cannot use both versions of the fucntion.
</para>
<para>
Function mapping allows you to access both your custom function
function that is defined in the recipe and the original function that
is defined in the class.
You have this access all from within your recipe.
To accomplish this, you need some things in place:
<itemizedlist>
<listitem><para>
The class needs to define the function as follows:
<literallayout class='monospaced'>
&lt;classname&gt;_&lt;functionname&gt;
</literallayout>
For example, if you have a class file
<filename>bar.bbclass</filename> and a function named
<filename>do_foo</filename>, the class must define the function
as follows:
<literallayout class='monospaced'>
bar_do_foo
</literallayout>
</para></listitem>
<listitem><para>
The class needs to contain the <filename>EXPORT_FUNCTIONS</filename>
statement as follows:
<literallayout class='monospaced'>
EXPORT_FUNCTIONS &lt;functionname&gt;
</literallayout>
For example, continuing with the same example, the
statement in the <filename>bar.bbclass</filename> would be
as follows:
<literallayout class='monospaced'>
EXPORT_FUNCTIONS do_foo
</literallayout>
</para></listitem>
<listitem><para>
You need to call the function appropriately from within your
recipe.
Continuing with the same example,
your recipe would call the <filename>do_foo</filename> function
from the recipe by referring to it as
<filename>bar_do_foo</filename>.
To call your modified version of the function as defined in your
recipe, call it as <filename>do_foo</filename>.
</para></listitem>
</itemizedlist>
With these conditions met, your single recipe
can freely choose between the original function
as defined in the class file and the modified function in your recipe.
If you do not set up these conditions, you are limited to using one function
or the other.
</para>
</section>
</section>
<section id='tasks'>