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Based on kernel version 3.3. Page generated on 2012-03-23 21:34 EST.

1	kernel-doc nano-HOWTO
2	=====================
3	
4	How to format kernel-doc comments
5	---------------------------------
6	
7	In order to provide embedded, 'C' friendly, easy to maintain,
8	but consistent and extractable documentation of the functions and
9	data structures in the Linux kernel, the Linux kernel has adopted
10	a consistent style for documenting functions and their parameters,
11	and structures and their members.
12	
13	The format for this documentation is called the kernel-doc format.
14	It is documented in this Documentation/kernel-doc-nano-HOWTO.txt file.
15	
16	This style embeds the documentation within the source files, using
17	a few simple conventions.  The scripts/kernel-doc perl script, some
18	SGML templates in Documentation/DocBook, and other tools understand
19	these conventions, and are used to extract this embedded documentation
20	into various documents.
21	
22	In order to provide good documentation of kernel functions and data
23	structures, please use the following conventions to format your
24	kernel-doc comments in Linux kernel source.
25	
26	We definitely need kernel-doc formatted documentation for functions
27	that are exported to loadable modules using EXPORT_SYMBOL.
28	
29	We also look to provide kernel-doc formatted documentation for
30	functions externally visible to other kernel files (not marked
31	"static").
32	
33	We also recommend providing kernel-doc formatted documentation
34	for private (file "static") routines, for consistency of kernel
35	source code layout.  But this is lower priority and at the
36	discretion of the MAINTAINER of that kernel source file.
37	
38	Data structures visible in kernel include files should also be
39	documented using kernel-doc formatted comments.
40	
41	The opening comment mark "/**" is reserved for kernel-doc comments.
42	Only comments so marked will be considered by the kernel-doc scripts,
43	and any comment so marked must be in kernel-doc format.  Do not use
44	"/**" to be begin a comment block unless the comment block contains
45	kernel-doc formatted comments.  The closing comment marker for
46	kernel-doc comments can be either "*/" or "**/", but "*/" is
47	preferred in the Linux kernel tree.
48	
49	Kernel-doc comments should be placed just before the function
50	or data structure being described.
51	
52	Example kernel-doc function comment:
53	
54	/**
55	 * foobar() - short function description of foobar
56	 * @arg1:	Describe the first argument to foobar.
57	 * @arg2:	Describe the second argument to foobar.
58	 *		One can provide multiple line descriptions
59	 *		for arguments.
60	 *
61	 * A longer description, with more discussion of the function foobar()
62	 * that might be useful to those using or modifying it.  Begins with
63	 * empty comment line, and may include additional embedded empty
64	 * comment lines.
65	 *
66	 * The longer description can have multiple paragraphs.
67	 */
68	
69	The short description following the subject can span multiple lines
70	and ends with an @argument description, an empty line or the end of
71	the comment block.
72	
73	The @argument descriptions must begin on the very next line following
74	this opening short function description line, with no intervening
75	empty comment lines.
76	
77	If a function parameter is "..." (varargs), it should be listed in
78	kernel-doc notation as:
79	 * @...: description
80	
81	
82	Example kernel-doc data structure comment.
83	
84	/**
85	 * struct blah - the basic blah structure
86	 * @mem1:	describe the first member of struct blah
87	 * @mem2:	describe the second member of struct blah,
88	 *		perhaps with more lines and words.
89	 *
90	 * Longer description of this structure.
91	 */
92	
93	The kernel-doc function comments describe each parameter to the
94	function, in order, with the @name lines.
95	
96	The kernel-doc data structure comments describe each structure member
97	in the data structure, with the @name lines.
98	
99	The longer description formatting is "reflowed", losing your line
100	breaks.  So presenting carefully formatted lists within these
101	descriptions won't work so well; derived documentation will lose
102	the formatting.
103	
104	See the section below "How to add extractable documentation to your
105	source files" for more details and notes on how to format kernel-doc
106	comments.
107	
108	Components of the kernel-doc system
109	-----------------------------------
110	
111	Many places in the source tree have extractable documentation in the
112	form of block comments above functions.  The components of this system
113	are:
114	
115	- scripts/kernel-doc
116	
117	  This is a perl script that hunts for the block comments and can mark
118	  them up directly into DocBook, man, text, and HTML. (No, not
119	  texinfo.)
120	
121	- Documentation/DocBook/*.tmpl
122	
123	  These are SGML template files, which are normal SGML files with
124	  special place-holders for where the extracted documentation should
125	  go.
126	
127	- scripts/basic/docproc.c
128	
129	  This is a program for converting SGML template files into SGML
130	  files. When a file is referenced it is searched for symbols
131	  exported (EXPORT_SYMBOL), to be able to distinguish between internal
132	  and external functions.
133	  It invokes kernel-doc, giving it the list of functions that
134	  are to be documented.
135	  Additionally it is used to scan the SGML template files to locate
136	  all the files referenced herein. This is used to generate dependency
137	  information as used by make.
138	
139	- Makefile
140	
141	  The targets 'sgmldocs', 'psdocs', 'pdfdocs', and 'htmldocs' are used
142	  to build DocBook files, PostScript files, PDF files, and html files
143	  in Documentation/DocBook.
144	
145	- Documentation/DocBook/Makefile
146	
147	  This is where C files are associated with SGML templates.
148	
149	
150	How to extract the documentation
151	--------------------------------
152	
153	If you just want to read the ready-made books on the various
154	subsystems (see Documentation/DocBook/*.tmpl), just type 'make
155	psdocs', or 'make pdfdocs', or 'make htmldocs', depending on your
156	preference.  If you would rather read a different format, you can type
157	'make sgmldocs' and then use DocBook tools to convert
158	Documentation/DocBook/*.sgml to a format of your choice (for example,
159	'db2html ...' if 'make htmldocs' was not defined).
160	
161	If you want to see man pages instead, you can do this:
162	
163	$ cd linux
164	$ scripts/kernel-doc -man $(find -name '*.c') | split-man.pl /tmp/man
165	$ scripts/kernel-doc -man $(find -name '*.h') | split-man.pl /tmp/man
166	
167	Here is split-man.pl:
168	
169	-->
170	#!/usr/bin/perl
171	
172	if ($#ARGV < 0) {
173	   die "where do I put the results?\n";
174	}
175	
176	mkdir $ARGV[0],0777;
177	$state = 0;
178	while (<STDIN>) {
179	    if (/^\.TH \"[^\"]*\" 9 \"([^\"]*)\"/) {
180		if ($state == 1) { close OUT }
181		$state = 1;
182		$fn = "$ARGV[0]/$1.9";
183		print STDERR "Creating $fn\n";
184		open OUT, ">$fn" or die "can't open $fn: $!\n";
185		print OUT $_;
186	    } elsif ($state != 0) {
187		print OUT $_;
188	    }
189	}
190	
191	close OUT;
192	<--
193	
194	If you just want to view the documentation for one function in one
195	file, you can do this:
196	
197	$ scripts/kernel-doc -man -function fn file | nroff -man | less
198	
199	or this:
200	
201	$ scripts/kernel-doc -text -function fn file
202	
203	
204	How to add extractable documentation to your source files
205	---------------------------------------------------------
206	
207	The format of the block comment is like this:
208	
209	/**
210	 * function_name(:)? (- short description)?
211	(* @parameterx(space)*: (description of parameter x)?)*
212	(* a blank line)?
213	 * (Description:)? (Description of function)?
214	 * (section header: (section description)? )*
215	(*)?*/
216	
217	All "description" text can span multiple lines, although the
218	function_name & its short description are traditionally on a single line.
219	Description text may also contain blank lines (i.e., lines that contain
220	only a "*").
221	
222	"section header:" names must be unique per function (or struct,
223	union, typedef, enum).
224	
225	Avoid putting a spurious blank line after the function name, or else the
226	description will be repeated!
227	
228	All descriptive text is further processed, scanning for the following special
229	patterns, which are highlighted appropriately.
230	
231	'funcname()' - function
232	'$ENVVAR' - environment variable
233	'&struct_name' - name of a structure (up to two words including 'struct')
234	'@parameter' - name of a parameter
235	'%CONST' - name of a constant.
236	
237	NOTE 1:  The multi-line descriptive text you provide does *not* recognize
238	line breaks, so if you try to format some text nicely, as in:
239	
240	  Return codes
241	    0 - cool
242	    1 - invalid arg
243	    2 - out of memory
244	
245	this will all run together and produce:
246	
247	  Return codes 0 - cool 1 - invalid arg 2 - out of memory
248	
249	NOTE 2:  If the descriptive text you provide has lines that begin with
250	some phrase followed by a colon, each of those phrases will be taken as
251	a new section heading, which means you should similarly try to avoid text
252	like:
253	
254	  Return codes:
255	    0: cool
256	    1: invalid arg
257	    2: out of memory
258	
259	every line of which would start a new section.  Again, probably not
260	what you were after.
261	
262	Take a look around the source tree for examples.
263	
264	
265	kernel-doc for structs, unions, enums, and typedefs
266	---------------------------------------------------
267	
268	Beside functions you can also write documentation for structs, unions,
269	enums and typedefs. Instead of the function name you must write the name
270	of the declaration;  the struct/union/enum/typedef must always precede
271	the name. Nesting of declarations is not supported.
272	Use the argument mechanism to document members or constants.
273	
274	Inside a struct description, you can use the "private:" and "public:"
275	comment tags.  Structure fields that are inside a "private:" area
276	are not listed in the generated output documentation.  The "private:"
277	and "public:" tags must begin immediately following a "/*" comment
278	marker.  They may optionally include comments between the ":" and the
279	ending "*/" marker.
280	
281	Example:
282	
283	/**
284	 * struct my_struct - short description
285	 * @a: first member
286	 * @b: second member
287	 *
288	 * Longer description
289	 */
290	struct my_struct {
291	    int a;
292	    int b;
293	/* private: internal use only */
294	    int c;
295	};
296	
297	
298	Including documentation blocks in source files
299	----------------------------------------------
300	
301	To facilitate having source code and comments close together, you can
302	include kernel-doc documentation blocks that are free-form comments
303	instead of being kernel-doc for functions, structures, unions,
304	enums, or typedefs.  This could be used for something like a
305	theory of operation for a driver or library code, for example.
306	
307	This is done by using a DOC: section keyword with a section title.  E.g.:
308	
309	/**
310	 * DOC: Theory of Operation
311	 *
312	 * The whizbang foobar is a dilly of a gizmo.  It can do whatever you
313	 * want it to do, at any time.  It reads your mind.  Here's how it works.
314	 *
315	 * foo bar splat
316	 *
317	 * The only drawback to this gizmo is that is can sometimes damage
318	 * hardware, software, or its subject(s).
319	 */
320	
321	DOC: sections are used in SGML templates files as indicated below.
322	
323	
324	How to make new SGML template files
325	-----------------------------------
326	
327	SGML template files (*.tmpl) are like normal SGML files, except that
328	they can contain escape sequences where extracted documentation should
329	be inserted.
330	
331	!E<filename> is replaced by the documentation, in <filename>, for
332	functions that are exported using EXPORT_SYMBOL: the function list is
333	collected from files listed in Documentation/DocBook/Makefile.
334	
335	!I<filename> is replaced by the documentation for functions that are
336	_not_ exported using EXPORT_SYMBOL.
337	
338	!D<filename> is used to name additional files to search for functions
339	exported using EXPORT_SYMBOL.
340	
341	!F<filename> <function [functions...]> is replaced by the
342	documentation, in <filename>, for the functions listed.
343	
344	!P<filename> <section title> is replaced by the contents of the DOC:
345	section titled <section title> from <filename>.
346	Spaces are allowed in <section title>; do not quote the <section title>.
347	
348	!C<filename> is replaced by nothing, but makes the tools check that
349	all DOC: sections and documented functions, symbols, etc. are used.
350	This makes sense to use when you use !F/!P only and want to verify
351	that all documentation is included.
352	
353	Tim.
354	*/ <twaugh@redhat.com>
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