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Linus Torvalds1da177e2005-04-16 15:20:36 -07001kernel-doc nano-HOWTO
2=====================
3
Paul Jackson0842b242008-06-05 22:46:45 -07004How to format kernel-doc comments
5---------------------------------
6
7In order to provide embedded, 'C' friendly, easy to maintain,
8but consistent and extractable documentation of the functions and
9data structures in the Linux kernel, the Linux kernel has adopted
10a consistent style for documenting functions and their parameters,
11and structures and their members.
12
13The format for this documentation is called the kernel-doc format.
14It is documented in this Documentation/kernel-doc-nano-HOWTO.txt file.
15
16This style embeds the documentation within the source files, using
17a few simple conventions. The scripts/kernel-doc perl script, some
18SGML templates in Documentation/DocBook, and other tools understand
19these conventions, and are used to extract this embedded documentation
20into various documents.
21
22In order to provide good documentation of kernel functions and data
23structures, please use the following conventions to format your
24kernel-doc comments in Linux kernel source.
25
26We definitely need kernel-doc formatted documentation for functions
27that are exported to loadable modules using EXPORT_SYMBOL.
28
29We also look to provide kernel-doc formatted documentation for
30functions externally visible to other kernel files (not marked
31"static").
32
33We also recommend providing kernel-doc formatted documentation
34for private (file "static") routines, for consistency of kernel
35source code layout. But this is lower priority and at the
36discretion of the MAINTAINER of that kernel source file.
37
38Data structures visible in kernel include files should also be
39documented using kernel-doc formatted comments.
40
41The opening comment mark "/**" is reserved for kernel-doc comments.
42Only comments so marked will be considered by the kernel-doc scripts,
43and 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
45kernel-doc formatted comments. The closing comment marker for
Randy Dunlapf40b45a2009-02-11 13:04:31 -080046kernel-doc comments can be either "*/" or "**/", but "*/" is
47preferred in the Linux kernel tree.
Paul Jackson0842b242008-06-05 22:46:45 -070048
49Kernel-doc comments should be placed just before the function
50or data structure being described.
51
52Example 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.
Randy Dunlapf40b45a2009-02-11 13:04:31 -080067 */
Paul Jackson0842b242008-06-05 22:46:45 -070068
Johannes Weiner64231332009-09-17 19:26:53 -070069The short description following the subject can span multiple lines
70and ends with an @argument description, an empty line or the end of
71the comment block.
Paul Jackson0842b242008-06-05 22:46:45 -070072
73The @argument descriptions must begin on the very next line following
74this opening short function description line, with no intervening
75empty comment lines.
76
Randy Dunlapd78dd072009-01-06 14:42:40 -080077If a function parameter is "..." (varargs), it should be listed in
78kernel-doc notation as:
79 * @...: description
80
81
Paul Jackson0842b242008-06-05 22:46:45 -070082Example 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.
Randy Dunlapf40b45a2009-02-11 13:04:31 -080091 */
Paul Jackson0842b242008-06-05 22:46:45 -070092
93The kernel-doc function comments describe each parameter to the
94function, in order, with the @name lines.
95
96The kernel-doc data structure comments describe each structure member
97in the data structure, with the @name lines.
98
99The longer description formatting is "reflowed", losing your line
100breaks. So presenting carefully formatted lists within these
101descriptions won't work so well; derived documentation will lose
102the formatting.
103
104See the section below "How to add extractable documentation to your
105source files" for more details and notes on how to format kernel-doc
106comments.
107
108Components of the kernel-doc system
109-----------------------------------
110
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111Many places in the source tree have extractable documentation in the
112form of block comments above functions. The components of this system
113are:
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
Randy Dunlapc6120932006-11-02 22:07:01 -0800127- scripts/basic/docproc.c
Linus Torvalds1da177e2005-04-16 15:20:36 -0700128
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
150How to extract the documentation
151--------------------------------
152
153If you just want to read the ready-made books on the various
154subsystems (see Documentation/DocBook/*.tmpl), just type 'make
Randy Dunlapd28bee02006-02-01 03:06:57 -0800155psdocs', or 'make pdfdocs', or 'make htmldocs', depending on your
156preference. If you would rather read a different format, you can type
157'make sgmldocs' and then use DocBook tools to convert
158Documentation/DocBook/*.sgml to a format of your choice (for example,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700159'db2html ...' if 'make htmldocs' was not defined).
160
161If 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 $(find -name '*.h') | split-man.pl /tmp/man
166
167Here is split-man.pl:
168
169-->
170#!/usr/bin/perl
171
172if ($#ARGV < 0) {
173 die "where do I put the results?\n";
174}
175
176mkdir $ARGV[0],0777;
177$state = 0;
178while (<STDIN>) {
Kevin Diggs65eb3dc2008-08-26 10:26:54 +0200179 if (/^\.TH \"[^\"]*\" 9 \"([^\"]*)\"/) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700180 if ($state == 1) { close OUT }
181 $state = 1;
Kevin Diggs65eb3dc2008-08-26 10:26:54 +0200182 $fn = "$ARGV[0]/$1.9";
Linus Torvalds1da177e2005-04-16 15:20:36 -0700183 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 $_;
188 }
189}
190
191close OUT;
192<--
193
194If you just want to view the documentation for one function in one
195file, you can do this:
196
197$ scripts/kernel-doc -man -function fn file | nroff -man | less
198
199or this:
200
201$ scripts/kernel-doc -text -function fn file
202
203
204How to add extractable documentation to your source files
205---------------------------------------------------------
206
207The format of the block comment is like this:
208
209/**
210 * function_name(:)? (- short description)?
Randy Dunlap891dcd22007-02-10 01:45:53 -0800211(* @parameterx(space)*: (description of parameter x)?)*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700212(* a blank line)?
213 * (Description:)? (Description of function)?
214 * (section header: (section description)? )*
215(*)?*/
216
Robert P. J. Day262086c2007-02-10 01:45:58 -0800217The short function description ***cannot be multiline***, but the other
218descriptions can be (and they can contain blank lines). If you continue
219that initial short description onto a second line, that second line will
220appear further down at the beginning of the description section, which is
221almost certainly not what you had in mind.
222
223Avoid putting a spurious blank line after the function name, or else the
224description will be repeated!
Linus Torvalds1da177e2005-04-16 15:20:36 -0700225
226All descriptive text is further processed, scanning for the following special
227patterns, 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
Robert P. J. Day262086c2007-02-10 01:45:58 -0800235NOTE 1: The multi-line descriptive text you provide does *not* recognize
236line breaks, so if you try to format some text nicely, as in:
237
238 Return codes
239 0 - cool
240 1 - invalid arg
241 2 - out of memory
242
243this will all run together and produce:
244
245 Return codes 0 - cool 1 - invalid arg 2 - out of memory
246
247NOTE 2: If the descriptive text you provide has lines that begin with
248some phrase followed by a colon, each of those phrases will be taken as
249a new section heading, which means you should similarly try to avoid text
250like:
251
252 Return codes:
253 0: cool
254 1: invalid arg
255 2: out of memory
256
257every line of which would start a new section. Again, probably not
258what you were after.
259
Linus Torvalds1da177e2005-04-16 15:20:36 -0700260Take a look around the source tree for examples.
261
262
Randy Dunlapd28bee02006-02-01 03:06:57 -0800263kernel-doc for structs, unions, enums, and typedefs
264---------------------------------------------------
265
266Beside functions you can also write documentation for structs, unions,
267enums and typedefs. Instead of the function name you must write the name
268of the declaration; the struct/union/enum/typedef must always precede
269the name. Nesting of declarations is not supported.
270Use the argument mechanism to document members or constants.
271
272Inside a struct description, you can use the "private:" and "public:"
273comment tags. Structure fields that are inside a "private:" area
Randy Dunlap52dc5ae2009-04-30 15:08:53 -0700274are not listed in the generated output documentation. The "private:"
275and "public:" tags must begin immediately following a "/*" comment
276marker. They may optionally include comments between the ":" and the
277ending "*/" marker.
Randy Dunlapd28bee02006-02-01 03:06:57 -0800278
279Example:
280
281/**
282 * struct my_struct - short description
283 * @a: first member
284 * @b: second member
285 *
286 * Longer description
287 */
288struct my_struct {
289 int a;
290 int b;
Randy Dunlap52dc5ae2009-04-30 15:08:53 -0700291/* private: internal use only */
Randy Dunlapd28bee02006-02-01 03:06:57 -0800292 int c;
293};
294
295
Randy Dunlap28f4d752009-01-06 14:42:43 -0800296Including documentation blocks in source files
297----------------------------------------------
298
299To facilitate having source code and comments close together, you can
300include kernel-doc documentation blocks that are free-form comments
301instead of being kernel-doc for functions, structures, unions,
302enums, or typedefs. This could be used for something like a
303theory of operation for a driver or library code, for example.
304
305This 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
319DOC: sections are used in SGML templates files as indicated below.
320
321
Linus Torvalds1da177e2005-04-16 15:20:36 -0700322How to make new SGML template files
323-----------------------------------
324
325SGML template files (*.tmpl) are like normal SGML files, except that
326they can contain escape sequences where extracted documentation should
327be inserted.
328
329!E<filename> is replaced by the documentation, in <filename>, for
330functions that are exported using EXPORT_SYMBOL: the function list is
331collected from files listed in Documentation/DocBook/Makefile.
332
333!I<filename> is replaced by the documentation for functions that are
334_not_ exported using EXPORT_SYMBOL.
335
336!D<filename> is used to name additional files to search for functions
337exported using EXPORT_SYMBOL.
338
339!F<filename> <function [functions...]> is replaced by the
340documentation, in <filename>, for the functions listed.
341
Randy Dunlap28f4d752009-01-06 14:42:43 -0800342!P<filename> <section title> is replaced by the contents of the DOC:
343section titled <section title> from <filename>.
344Spaces are allowed in <section title>; do not quote the <section title>.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700345
346Tim.
347*/ <twaugh@redhat.com>