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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
46kernel-doc comments can be either "*/" or "**/".
47
48Kernel-doc comments should be placed just before the function
49or data structure being described.
50
51Example kernel-doc function comment:
52
53/**
54 * foobar() - short function description of foobar
55 * @arg1: Describe the first argument to foobar.
56 * @arg2: Describe the second argument to foobar.
57 * One can provide multiple line descriptions
58 * for arguments.
59 *
60 * A longer description, with more discussion of the function foobar()
61 * that might be useful to those using or modifying it. Begins with
62 * empty comment line, and may include additional embedded empty
63 * comment lines.
64 *
65 * The longer description can have multiple paragraphs.
66 **/
67
68The first line, with the short description, must be on a single line.
69
70The @argument descriptions must begin on the very next line following
71this opening short function description line, with no intervening
72empty comment lines.
73
74Example kernel-doc data structure comment.
75
76/**
77 * struct blah - the basic blah structure
78 * @mem1: describe the first member of struct blah
79 * @mem2: describe the second member of struct blah,
80 * perhaps with more lines and words.
81 *
82 * Longer description of this structure.
83 **/
84
85The kernel-doc function comments describe each parameter to the
86function, in order, with the @name lines.
87
88The kernel-doc data structure comments describe each structure member
89in the data structure, with the @name lines.
90
91The longer description formatting is "reflowed", losing your line
92breaks. So presenting carefully formatted lists within these
93descriptions won't work so well; derived documentation will lose
94the formatting.
95
96See the section below "How to add extractable documentation to your
97source files" for more details and notes on how to format kernel-doc
98comments.
99
100Components of the kernel-doc system
101-----------------------------------
102
Linus Torvalds1da177e2005-04-16 15:20:36 -0700103Many places in the source tree have extractable documentation in the
104form of block comments above functions. The components of this system
105are:
106
107- scripts/kernel-doc
108
109 This is a perl script that hunts for the block comments and can mark
110 them up directly into DocBook, man, text, and HTML. (No, not
111 texinfo.)
112
113- Documentation/DocBook/*.tmpl
114
115 These are SGML template files, which are normal SGML files with
116 special place-holders for where the extracted documentation should
117 go.
118
Randy Dunlapc6120932006-11-02 22:07:01 -0800119- scripts/basic/docproc.c
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120
121 This is a program for converting SGML template files into SGML
122 files. When a file is referenced it is searched for symbols
123 exported (EXPORT_SYMBOL), to be able to distinguish between internal
124 and external functions.
125 It invokes kernel-doc, giving it the list of functions that
126 are to be documented.
127 Additionally it is used to scan the SGML template files to locate
128 all the files referenced herein. This is used to generate dependency
129 information as used by make.
130
131- Makefile
132
133 The targets 'sgmldocs', 'psdocs', 'pdfdocs', and 'htmldocs' are used
134 to build DocBook files, PostScript files, PDF files, and html files
135 in Documentation/DocBook.
136
137- Documentation/DocBook/Makefile
138
139 This is where C files are associated with SGML templates.
140
141
142How to extract the documentation
143--------------------------------
144
145If you just want to read the ready-made books on the various
146subsystems (see Documentation/DocBook/*.tmpl), just type 'make
Randy Dunlapd28bee02006-02-01 03:06:57 -0800147psdocs', or 'make pdfdocs', or 'make htmldocs', depending on your
148preference. If you would rather read a different format, you can type
149'make sgmldocs' and then use DocBook tools to convert
150Documentation/DocBook/*.sgml to a format of your choice (for example,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151'db2html ...' if 'make htmldocs' was not defined).
152
153If you want to see man pages instead, you can do this:
154
155$ cd linux
156$ scripts/kernel-doc -man $(find -name '*.c') | split-man.pl /tmp/man
157$ scripts/kernel-doc -man $(find -name '*.h') | split-man.pl /tmp/man
158
159Here is split-man.pl:
160
161-->
162#!/usr/bin/perl
163
164if ($#ARGV < 0) {
165 die "where do I put the results?\n";
166}
167
168mkdir $ARGV[0],0777;
169$state = 0;
170while (<STDIN>) {
171 if (/^\.TH \"[^\"]*\" 4 \"([^\"]*)\"/) {
172 if ($state == 1) { close OUT }
173 $state = 1;
174 $fn = "$ARGV[0]/$1.4";
175 print STDERR "Creating $fn\n";
176 open OUT, ">$fn" or die "can't open $fn: $!\n";
177 print OUT $_;
178 } elsif ($state != 0) {
179 print OUT $_;
180 }
181}
182
183close OUT;
184<--
185
186If you just want to view the documentation for one function in one
187file, you can do this:
188
189$ scripts/kernel-doc -man -function fn file | nroff -man | less
190
191or this:
192
193$ scripts/kernel-doc -text -function fn file
194
195
196How to add extractable documentation to your source files
197---------------------------------------------------------
198
199The format of the block comment is like this:
200
201/**
202 * function_name(:)? (- short description)?
Randy Dunlap891dcd22007-02-10 01:45:53 -0800203(* @parameterx(space)*: (description of parameter x)?)*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700204(* a blank line)?
205 * (Description:)? (Description of function)?
206 * (section header: (section description)? )*
207(*)?*/
208
Robert P. J. Day262086c2007-02-10 01:45:58 -0800209The short function description ***cannot be multiline***, but the other
210descriptions can be (and they can contain blank lines). If you continue
211that initial short description onto a second line, that second line will
212appear further down at the beginning of the description section, which is
213almost certainly not what you had in mind.
214
215Avoid putting a spurious blank line after the function name, or else the
216description will be repeated!
Linus Torvalds1da177e2005-04-16 15:20:36 -0700217
218All descriptive text is further processed, scanning for the following special
219patterns, which are highlighted appropriately.
220
221'funcname()' - function
222'$ENVVAR' - environment variable
223'&struct_name' - name of a structure (up to two words including 'struct')
224'@parameter' - name of a parameter
225'%CONST' - name of a constant.
226
Robert P. J. Day262086c2007-02-10 01:45:58 -0800227NOTE 1: The multi-line descriptive text you provide does *not* recognize
228line breaks, so if you try to format some text nicely, as in:
229
230 Return codes
231 0 - cool
232 1 - invalid arg
233 2 - out of memory
234
235this will all run together and produce:
236
237 Return codes 0 - cool 1 - invalid arg 2 - out of memory
238
239NOTE 2: If the descriptive text you provide has lines that begin with
240some phrase followed by a colon, each of those phrases will be taken as
241a new section heading, which means you should similarly try to avoid text
242like:
243
244 Return codes:
245 0: cool
246 1: invalid arg
247 2: out of memory
248
249every line of which would start a new section. Again, probably not
250what you were after.
251
Linus Torvalds1da177e2005-04-16 15:20:36 -0700252Take a look around the source tree for examples.
253
254
Randy Dunlapd28bee02006-02-01 03:06:57 -0800255kernel-doc for structs, unions, enums, and typedefs
256---------------------------------------------------
257
258Beside functions you can also write documentation for structs, unions,
259enums and typedefs. Instead of the function name you must write the name
260of the declaration; the struct/union/enum/typedef must always precede
261the name. Nesting of declarations is not supported.
262Use the argument mechanism to document members or constants.
263
264Inside a struct description, you can use the "private:" and "public:"
265comment tags. Structure fields that are inside a "private:" area
266are not listed in the generated output documentation.
267
268Example:
269
270/**
271 * struct my_struct - short description
272 * @a: first member
273 * @b: second member
274 *
275 * Longer description
276 */
277struct my_struct {
278 int a;
279 int b;
280/* private: */
281 int c;
282};
283
284
Linus Torvalds1da177e2005-04-16 15:20:36 -0700285How to make new SGML template files
286-----------------------------------
287
288SGML template files (*.tmpl) are like normal SGML files, except that
289they can contain escape sequences where extracted documentation should
290be inserted.
291
292!E<filename> is replaced by the documentation, in <filename>, for
293functions that are exported using EXPORT_SYMBOL: the function list is
294collected from files listed in Documentation/DocBook/Makefile.
295
296!I<filename> is replaced by the documentation for functions that are
297_not_ exported using EXPORT_SYMBOL.
298
299!D<filename> is used to name additional files to search for functions
300exported using EXPORT_SYMBOL.
301
302!F<filename> <function [functions...]> is replaced by the
303documentation, in <filename>, for the functions listed.
304
305
306Tim.
307*/ <twaugh@redhat.com>