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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	NOTE: this document is outdated and will eventually be removed.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