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bitbake: user-manual-metadata.xml: Rewrite of the "Functions" section.

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Re-organized this around the 3 types of functions that we seem
to be show-casing here.  The original organization was not very
good.

(Bitbake rev: 77ef63e5c4a9ea633a1be0f9f90366e0ecf555fa)

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
2014-02-05 16:29:54 -06:00
committed by Richard Purdie
parent d022ec3ff5
commit faaca84d6e
1 changed files with 85 additions and 59 deletions
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bitbake/doc/user-manual/user-manual-metadata.xml
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@@ -677,73 +677,81 @@
<section id='functions'> <section id='functions'>
<title>Functions</title> <title>Functions</title>
<note>
This is only supported in <filename>.bb</filename>
and <filename>.bbclass</filename> files.
</note>
<para> <para>
As with most languages, functions are the building blocks As with most languages, functions are the building blocks
that define operations. that define operations.
Bitbake supports shell and Python functions. BitBake supports three types of functions:
An example shell function definition is: <itemizedlist>
<literallayout class='monospaced'> <listitem><para><emphasis>Shell Functions:</emphasis>
Functions written in a shell language and
executed by the shell.
</para></listitem>
<listitem><para><emphasis>BitBake Functions:</emphasis>
Functions written in Python but executed by BitBake using
<filename>bb.build.exec_func()</filename>.
</para></listitem>
<listitem><para><emphasis>Python Functions:</emphasis>
Functions written in Python and executed by Python.
</para></listitem>
</itemizedlist>
Regardless of the type of function, you can only
define them in class (<filename>.bbclass</filename>)
and recipe (<filename>.bb</filename>) files.
</para>
<section id='shell-functions'>
<title>Shell Functions</title>
<para>
These functions are written using a shell language and
executed by the shell.
Here is an example shell function definition:
<literallayout class='monospaced'>
some_function () { some_function () {
echo "Hello World" echo "Hello World"
} }
</literallayout> </literallayout>
An example Python function definition is: When you create these types of functions in your recipe
<literallayout class='monospaced'> or class files, you need to follow the shell programming
rules.
</para>
</section>
<section id='bitbake-functions'>
<title>BitBake Functions</title>
<para>
These functions are written in Python and are executed using
<filename>bb.build.exec_func()</filename>.
</para>
<para>
An example BitBake function is:
<literallayout class='monospaced'>
python some_python_function () { python some_python_function () {
d.setVar("TEXT", "Hello World") d.setVar("TEXT", "Hello World")
print d.getVar("TEXT", True) print d.getVar("TEXT", True)
} }
</literallayout> </literallayout>
In python functions, the "bb" and "os" modules are already Because the Python "bb" and "os" modules are already
imported, there is no need to import those modules. imported, you do not need to import these modules.
The datastore, "d" is also a global variable and always Also in these types of functions, the datastore ("d")
available to these functions automatically. is a global variable and is always automatically
</para> available.
</para>
</section>
<para> <section id='python-functions'>
Bitbake will execute functions of this form using <title>Python Functions</title>
the <filename>bb.build.exec_func()</filename>, which can also be
called from Python functions to execute other functions,
either shell or Python based.
Shell functions can only execute other shell functions.
</para>
<para> <para>
There is also a second way to declare python functions with These functions are written in Python but are executed by
parameters which takes the form: Python.
<literallayout class='monospaced'> Examples of Python functions are utility functions
def some_python_function(arg1, arg2): that you intend to call from in-line Python or
print arg1 + " " + arg2 from within other Python functions.
</literallayout> Here is an example:
The difference is that the second form takes parameters, <literallayout class='monospaced'>
the datastore is not available automatically
and must be passed as a parameter and these functions are
not called with the <filename>exec_func()</filename> but are
executed with direct Python function calls.
The "bb" and "os" modules are still automatically available
and there is no need to import them.
</para>
</section>
<section id='defining-pure-python-functions'>
<title>Defining Pure Python functions</title>
<note>
This is only supported in <filename>.bb</filename>
and <filename>.bbclass</filename> files.
</note>
<para>
For utility functions that you intend to call from
in-line Python or other Python functions, BitBake allows
you to define these as pure Python functions.
Here is an example:
<literallayout class='monospaced'>
def get_depends(d): def get_depends(d):
if d.getVar('SOMECONDITION', True): if d.getVar('SOMECONDITION', True):
return "dependencywithcond" return "dependencywithcond"
@@ -751,10 +759,28 @@
return "dependency" return "dependency"
SOMECONDITION = "1" SOMECONDITION = "1"
DEPENDS = "${@get_depends(d)}" DEPENDS = "${@get_depends(d)}"
</literallayout> </literallayout>
This would result in <filename>DEPENDS</filename> This would result in <filename>DEPENDS</filename>
containing <filename>dependencywithcond</filename>. containing <filename>dependencywithcond</filename>.
</para> </para>
<para>
Here are some things to know about Python functions:
<itemizedlist>
<listitem><para>Python functions take parameters.
</para></listitem>
<listitem><para>The BitBake datastore is not
automatically available.
Consequently, you must pass it in as a
parameter to the function.
</para></listitem>
<listitem><para>The "bb" and "os" Python modules are
automatically available.
You do not need to import them.
</para></listitem>
</itemizedlist>
</para>
</section>
</section> </section>
<section id='tasks'> <section id='tasks'>