xref: /kernel/linux/linux-5.10/Documentation/doc-guide/parse-headers.rst

===========================
Including uAPI header files
===========================

Sometimes, it is useful to include header files and C example codes in
order to describe the userspace API and to generate cross-references
between the code and the documentation. Adding cross-references for
userspace API files has an additional vantage: Sphinx will generate warnings
if a symbol is not found at the documentation. That helps to keep the
uAPI documentation in sync with the Kernel changes.
The :ref:`parse_headers.pl <parse_headers>` provide a way to generate such
cross-references. It has to be called via Makefile, while building the
documentation. Please see ``Documentation/userspace-api/media/Makefile`` for an example
about how to use it inside the Kernel tree.

.. _parse_headers:

parse_headers.pl
^^^^^^^^^^^^^^^^

NAME
****


parse_headers.pl - parse a C file, in order to identify functions, structs,
enums and defines and create cross-references to a Sphinx book.


SYNOPSIS
********


\ **parse_headers.pl**\  [<options>] <C_FILE> <OUT_FILE> [<EXCEPTIONS_FILE>]

Where <options> can be: --debug, --help or --usage.


OPTIONS
*******



\ **--debug**\

 Put the script in verbose mode, useful for debugging.



\ **--usage**\

 Prints a brief help message and exits.



\ **--help**\

 Prints a more detailed help message and exits.


DESCRIPTION
***********


Convert a C header or source file (C_FILE), into a ReStructured Text
included via ..parsed-literal block with cross-references for the
documentation files that describe the API. It accepts an optional
EXCEPTIONS_FILE with describes what elements will be either ignored or
be pointed to a non-default reference.

The output is written at the (OUT_FILE).

It is capable of identifying defines, functions, structs, typedefs,
enums and enum symbols and create cross-references for all of them.
It is also capable of distinguish #define used for specifying a Linux
ioctl.

The EXCEPTIONS_FILE contain two types of statements: \ **ignore**\  or \ **replace**\ .

The syntax for the ignore tag is:


ignore \ **type**\  \ **name**\

The \ **ignore**\  means that it won't generate cross references for a
\ **name**\  symbol of type \ **type**\ .

The syntax for the replace tag is:


replace \ **type**\  \ **name**\  \ **new_value**\

The \ **replace**\  means that it will generate cross references for a
\ **name**\  symbol of type \ **type**\ , but, instead of using the default
replacement rule, it will use \ **new_value**\ .

For both statements, \ **type**\  can be either one of the following:


\ **ioctl**\

 The ignore or replace statement will apply to ioctl definitions like:

 #define	VIDIOC_DBG_S_REGISTER 	 _IOW('V', 79, struct v4l2_dbg_register)



\ **define**\

 The ignore or replace statement will apply to any other #define found
 at C_FILE.



\ **typedef**\

 The ignore or replace statement will apply to typedef statements at C_FILE.



\ **struct**\

 The ignore or replace statement will apply to the name of struct statements
 at C_FILE.



\ **enum**\

 The ignore or replace statement will apply to the name of enum statements
 at C_FILE.



\ **symbol**\

 The ignore or replace statement will apply to the name of enum value
 at C_FILE.

 For replace statements, \ **new_value**\  will automatically use :c:type:
 references for \ **typedef**\ , \ **enum**\  and \ **struct**\  types. It will use :ref:
 for \ **ioctl**\ , \ **define**\  and \ **symbol**\  types. The type of reference can
 also be explicitly defined at the replace statement.



EXAMPLES
********


ignore define _VIDEODEV2_H


Ignore a #define _VIDEODEV2_H at the C_FILE.

ignore symbol PRIVATE


On a struct like:

enum foo { BAR1, BAR2, PRIVATE };

It won't generate cross-references for \ **PRIVATE**\ .

replace symbol BAR1 :c:type:\`foo\`
replace symbol BAR2 :c:type:\`foo\`


On a struct like:

enum foo { BAR1, BAR2, PRIVATE };

It will make the BAR1 and BAR2 enum symbols to cross reference the foo
symbol at the C domain.


BUGS
****


Report bugs to Mauro Carvalho Chehab <mchehab@kernel.org>


COPYRIGHT
*********


Copyright (c) 2016 by Mauro Carvalho Chehab <mchehab+samsung@kernel.org>.

License GPLv2: GNU GPL version 2 <https://gnu.org/licenses/gpl.html>.

This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.