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Based on kernel version 3.13. Page generated on 2014-01-20 22:03 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	 * Return: Describe the return value of foobar.
69	 */
70	
71	The short description following the subject can span multiple lines
72	and ends with an @argument description, an empty line or the end of
73	the comment block.
74	
75	The @argument descriptions must begin on the very next line following
76	this opening short function description line, with no intervening
77	empty comment lines.
78	
79	If a function parameter is "..." (varargs), it should be listed in
80	kernel-doc notation as:
81	 * @...: description
82	
83	The return value, if any, should be described in a dedicated section
84	named "Return".
85	
86	Example kernel-doc data structure comment.
87	
88	/**
89	 * struct blah - the basic blah structure
90	 * @mem1:	describe the first member of struct blah
91	 * @mem2:	describe the second member of struct blah,
92	 *		perhaps with more lines and words.
93	 *
94	 * Longer description of this structure.
95	 */
96	
97	The kernel-doc function comments describe each parameter to the
98	function, in order, with the @name lines.
99	
100	The kernel-doc data structure comments describe each structure member
101	in the data structure, with the @name lines.
102	
103	The longer description formatting is "reflowed", losing your line
104	breaks.  So presenting carefully formatted lists within these
105	descriptions won't work so well; derived documentation will lose
106	the formatting.
107	
108	See the section below "How to add extractable documentation to your
109	source files" for more details and notes on how to format kernel-doc
110	comments.
111	
112	Components of the kernel-doc system
113	-----------------------------------
114	
115	Many places in the source tree have extractable documentation in the
116	form of block comments above functions.  The components of this system
117	are:
118	
119	- scripts/kernel-doc
120	
121	  This is a perl script that hunts for the block comments and can mark
122	  them up directly into DocBook, man, text, and HTML. (No, not
123	  texinfo.)
124	
125	- Documentation/DocBook/*.tmpl
126	
127	  These are SGML template files, which are normal SGML files with
128	  special place-holders for where the extracted documentation should
129	  go.
130	
131	- scripts/basic/docproc.c
132	
133	  This is a program for converting SGML template files into SGML
134	  files. When a file is referenced it is searched for symbols
135	  exported (EXPORT_SYMBOL), to be able to distinguish between internal
136	  and external functions.
137	  It invokes kernel-doc, giving it the list of functions that
138	  are to be documented.
139	  Additionally it is used to scan the SGML template files to locate
140	  all the files referenced herein. This is used to generate dependency
141	  information as used by make.
142	
143	- Makefile
144	
145	  The targets 'xmldocs', 'psdocs', 'pdfdocs', and 'htmldocs' are used
146	  to build XML DocBook files, PostScript files, PDF files, and html files
147	  in Documentation/DocBook. The older target 'sgmldocs' is equivalent
148	  to 'xmldocs'.
149	
150	- Documentation/DocBook/Makefile
151	
152	  This is where C files are associated with SGML templates.
153	
154	
155	How to extract the documentation
156	--------------------------------
157	
158	If you just want to read the ready-made books on the various
159	subsystems (see Documentation/DocBook/*.tmpl), just type 'make
160	psdocs', or 'make pdfdocs', or 'make htmldocs', depending on your
161	preference.  If you would rather read a different format, you can type
162	'make xmldocs' and then use DocBook tools to convert
163	Documentation/DocBook/*.xml to a format of your choice (for example,
164	'db2html ...' if 'make htmldocs' was not defined).
165	
166	If you want to see man pages instead, you can do this:
167	
168	$ cd linux
169	$ scripts/kernel-doc -man $(find -name '*.c') | split-man.pl /tmp/man
170	$ scripts/kernel-doc -man $(find -name '*.h') | split-man.pl /tmp/man
171	
172	Here is split-man.pl:
173	
174	-->
175	#!/usr/bin/perl
176	
177	if ($#ARGV < 0) {
178	   die "where do I put the results?\n";
179	}
180	
181	mkdir $ARGV[0],0777;
182	$state = 0;
183	while (<STDIN>) {
184	    if (/^\.TH \"[^\"]*\" 9 \"([^\"]*)\"/) {
185		if ($state == 1) { close OUT }
186		$state = 1;
187		$fn = "$ARGV[0]/$1.9";
188		print STDERR "Creating $fn\n";
189		open OUT, ">$fn" or die "can't open $fn: $!\n";
190		print OUT $_;
191	    } elsif ($state != 0) {
192		print OUT $_;
193	    }
194	}
195	
196	close OUT;
197	<--
198	
199	If you just want to view the documentation for one function in one
200	file, you can do this:
201	
202	$ scripts/kernel-doc -man -function fn file | nroff -man | less
203	
204	or this:
205	
206	$ scripts/kernel-doc -text -function fn file
207	
208	
209	How to add extractable documentation to your source files
210	---------------------------------------------------------
211	
212	The format of the block comment is like this:
213	
214	/**
215	 * function_name(:)? (- short description)?
216	(* @parameterx(space)*: (description of parameter x)?)*
217	(* a blank line)?
218	 * (Description:)? (Description of function)?
219	 * (section header: (section description)? )*
220	(*)?*/
221	
222	All "description" text can span multiple lines, although the
223	function_name & its short description are traditionally on a single line.
224	Description text may also contain blank lines (i.e., lines that contain
225	only a "*").
226	
227	"section header:" names must be unique per function (or struct,
228	union, typedef, enum).
229	
230	Use the section header "Return" for sections describing the return value
231	of a function.
232	
233	Avoid putting a spurious blank line after the function name, or else the
234	description will be repeated!
235	
236	All descriptive text is further processed, scanning for the following special
237	patterns, which are highlighted appropriately.
238	
239	'funcname()' - function
240	'$ENVVAR' - environment variable
241	'&struct_name' - name of a structure (up to two words including 'struct')
242	'@parameter' - name of a parameter
243	'%CONST' - name of a constant.
244	
245	NOTE 1:  The multi-line descriptive text you provide does *not* recognize
246	line breaks, so if you try to format some text nicely, as in:
247	
248	  Return:
249	    0 - cool
250	    1 - invalid arg
251	    2 - out of memory
252	
253	this will all run together and produce:
254	
255	  Return: 0 - cool 1 - invalid arg 2 - out of memory
256	
257	NOTE 2:  If the descriptive text you provide has lines that begin with
258	some phrase followed by a colon, each of those phrases will be taken as
259	a new section heading, which means you should similarly try to avoid text
260	like:
261	
262	  Return:
263	    0: cool
264	    1: invalid arg
265	    2: out of memory
266	
267	every line of which would start a new section.  Again, probably not
268	what you were after.
269	
270	Take a look around the source tree for examples.
271	
272	
273	kernel-doc for structs, unions, enums, and typedefs
274	---------------------------------------------------
275	
276	Beside functions you can also write documentation for structs, unions,
277	enums and typedefs. Instead of the function name you must write the name
278	of the declaration;  the struct/union/enum/typedef must always precede
279	the name. Nesting of declarations is not supported.
280	Use the argument mechanism to document members or constants.
281	
282	Inside a struct description, you can use the "private:" and "public:"
283	comment tags.  Structure fields that are inside a "private:" area
284	are not listed in the generated output documentation.  The "private:"
285	and "public:" tags must begin immediately following a "/*" comment
286	marker.  They may optionally include comments between the ":" and the
287	ending "*/" marker.
288	
289	Example:
290	
291	/**
292	 * struct my_struct - short description
293	 * @a: first member
294	 * @b: second member
295	 *
296	 * Longer description
297	 */
298	struct my_struct {
299	    int a;
300	    int b;
301	/* private: internal use only */
302	    int c;
303	};
304	
305	
306	Including documentation blocks in source files
307	----------------------------------------------
308	
309	To facilitate having source code and comments close together, you can
310	include kernel-doc documentation blocks that are free-form comments
311	instead of being kernel-doc for functions, structures, unions,
312	enums, or typedefs.  This could be used for something like a
313	theory of operation for a driver or library code, for example.
314	
315	This is done by using a DOC: section keyword with a section title.  E.g.:
316	
317	/**
318	 * DOC: Theory of Operation
319	 *
320	 * The whizbang foobar is a dilly of a gizmo.  It can do whatever you
321	 * want it to do, at any time.  It reads your mind.  Here's how it works.
322	 *
323	 * foo bar splat
324	 *
325	 * The only drawback to this gizmo is that is can sometimes damage
326	 * hardware, software, or its subject(s).
327	 */
328	
329	DOC: sections are used in SGML templates files as indicated below.
330	
331	
332	How to make new SGML template files
333	-----------------------------------
334	
335	SGML template files (*.tmpl) are like normal SGML files, except that
336	they can contain escape sequences where extracted documentation should
337	be inserted.
338	
339	!E<filename> is replaced by the documentation, in <filename>, for
340	functions that are exported using EXPORT_SYMBOL: the function list is
341	collected from files listed in Documentation/DocBook/Makefile.
342	
343	!I<filename> is replaced by the documentation for functions that are
344	_not_ exported using EXPORT_SYMBOL.
345	
346	!D<filename> is used to name additional files to search for functions
347	exported using EXPORT_SYMBOL.
348	
349	!F<filename> <function [functions...]> is replaced by the
350	documentation, in <filename>, for the functions listed.
351	
352	!P<filename> <section title> is replaced by the contents of the DOC:
353	section titled <section title> from <filename>.
354	Spaces are allowed in <section title>; do not quote the <section title>.
355	
356	!C<filename> is replaced by nothing, but makes the tools check that
357	all DOC: sections and documented functions, symbols, etc. are used.
358	This makes sense to use when you use !F/!P only and want to verify
359	that all documentation is included.
360	
361	Tim.
362	*/ <twaugh@redhat.com>
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