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1Writing kernel-doc comments
2===========================
3
4The Linux kernel source files may contain structured documentation
5comments in the kernel-doc format to describe the functions, types
6and design of the code. It is easier to keep documentation up-to-date
7when it is embedded in source files.
8
9.. note:: The kernel-doc format is deceptively similar to javadoc,
10 gtk-doc or Doxygen, yet distinctively different, for historical
11 reasons. The kernel source contains tens of thousands of kernel-doc
12 comments. Please stick to the style described here.
13
14The kernel-doc structure is extracted from the comments, and proper
15`Sphinx C Domain`_ function and type descriptions with anchors are
16generated from them. The descriptions are filtered for special kernel-doc
17highlights and cross-references. See below for details.
18
19.. _Sphinx C Domain: http://www.sphinx-doc.org/en/stable/domains.html
20
21Every function that is exported to loadable modules using
22``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
23comment. Functions and data structures in header files which are intended
24to be used by modules should also have kernel-doc comments.
25
26It is good practice to also provide kernel-doc formatted documentation
27for functions externally visible to other kernel files (not marked
28``static``). We also recommend providing kernel-doc formatted
29documentation for private (file ``static``) routines, for consistency of
30kernel source code layout. This is lower priority and at the discretion
31of the maintainer of that kernel source file.
32
33How to format kernel-doc comments
34---------------------------------
35
36The opening comment mark ``/**`` is used for kernel-doc comments. The
37``kernel-doc`` tool will extract comments marked this way. The rest of
38the comment is formatted like a normal multi-line comment with a column
39of asterisks on the left side, closing with ``*/`` on a line by itself.
40
41The function and type kernel-doc comments should be placed just before
42the function or type being described in order to maximise the chance
43that somebody changing the code will also change the documentation. The
44overview kernel-doc comments may be placed anywhere at the top indentation
45level.
46
47Running the ``kernel-doc`` tool with increased verbosity and without actual
48output generation may be used to verify proper formatting of the
49documentation comments. For example::
50
51 scripts/kernel-doc -v -none drivers/foo/bar.c
52
53The documentation format is verified by the kernel build when it is
54requested to perform extra gcc checks::
55
56 make W=n
57
58Function documentation
59----------------------
60
61The general format of a function and function-like macro kernel-doc comment is::
62
63 /**
64 * function_name() - Brief description of function.
65 * @arg1: Describe the first argument.
66 * @arg2: Describe the second argument.
67 * One can provide multiple line descriptions
68 * for arguments.
69 *
70 * A longer description, with more discussion of the function function_name()
71 * that might be useful to those using or modifying it. Begins with an
72 * empty comment line, and may include additional embedded empty
73 * comment lines.
74 *
75 * The longer description may have multiple paragraphs.
76 *
77 * Context: Describes whether the function can sleep, what locks it takes,
78 * releases, or expects to be held. It can extend over multiple
79 * lines.
80 * Return: Describe the return value of function_name.
81 *
82 * The return value description can also have multiple paragraphs, and should
83 * be placed at the end of the comment block.
84 */
85
86The brief description following the function name may span multiple lines, and
87ends with an argument description, a blank comment line, or the end of the
88comment block.
89
90Function parameters
91~~~~~~~~~~~~~~~~~~~
92
93Each function argument should be described in order, immediately following
94the short function description. Do not leave a blank line between the
95function description and the arguments, nor between the arguments.
96
97Each ``@argument:`` description may span multiple lines.
98
99.. note::
100
101 If the ``@argument`` description has multiple lines, the continuation
102 of the description should start at the same column as the previous line::
103
104 * @argument: some long description
105 * that continues on next lines
106
107 or::
108
109 * @argument:
110 * some long description
111 * that continues on next lines
112
113If a function has a variable number of arguments, its description should
114be written in kernel-doc notation as::
115
116 * @...: description
117
118Function context
119~~~~~~~~~~~~~~~~
120
121The context in which a function can be called should be described in a
122section named ``Context``. This should include whether the function
123sleeps or can be called from interrupt context, as well as what locks
124it takes, releases and expects to be held by its caller.
125
126Examples::
127
128 * Context: Any context.
129 * Context: Any context. Takes and releases the RCU lock.
130 * Context: Any context. Expects <lock> to be held by caller.
131 * Context: Process context. May sleep if @gfp flags permit.
132 * Context: Process context. Takes and releases <mutex>.
133 * Context: Softirq or process context. Takes and releases <lock>, BH-safe.
134 * Context: Interrupt context.
135
136Return values
137~~~~~~~~~~~~~
138
139The return value, if any, should be described in a dedicated section
140named ``Return``.
141
142.. note::
143
144 #) The multi-line descriptive text you provide does *not* recognize
145 line breaks, so if you try to format some text nicely, as in::
146
147 * Return:
148 * 0 - OK
149 * -EINVAL - invalid argument
150 * -ENOMEM - out of memory
151
152 this will all run together and produce::
153
154 Return: 0 - OK -EINVAL - invalid argument -ENOMEM - out of memory
155
156 So, in order to produce the desired line breaks, you need to use a
157 ReST list, e. g.::
158
159 * Return:
160 * * 0 - OK to runtime suspend the device
161 * * -EBUSY - Device should not be runtime suspended
162
163 #) If the descriptive text you provide has lines that begin with
164 some phrase followed by a colon, each of those phrases will be taken
165 as a new section heading, which probably won't produce the desired
166 effect.
167
168Structure, union, and enumeration documentation
169-----------------------------------------------
170
171The general format of a struct, union, and enum kernel-doc comment is::
172
173 /**
174 * struct struct_name - Brief description.
175 * @member1: Description of member1.
176 * @member2: Description of member2.
177 * One can provide multiple line descriptions
178 * for members.
179 *
180 * Description of the structure.
181 */
182
183You can replace the ``struct`` in the above example with ``union`` or
184``enum`` to describe unions or enums. ``member`` is used to mean struct
185and union member names as well as enumerations in an enum.
186
187The brief description following the structure name may span multiple
188lines, and ends with a member description, a blank comment line, or the
189end of the comment block.
190
191Members
192~~~~~~~
193
194Members of structs, unions and enums should be documented the same way
195as function parameters; they immediately succeed the short description
196and may be multi-line.
197
198Inside a struct or union description, you can use the ``private:`` and
199``public:`` comment tags. Structure fields that are inside a ``private:``
200area are not listed in the generated output documentation.
201
202The ``private:`` and ``public:`` tags must begin immediately following a
203``/*`` comment marker. They may optionally include comments between the
204``:`` and the ending ``*/`` marker.
205
206Example::
207
208 /**
209 * struct my_struct - short description
210 * @a: first member
211 * @b: second member
212 * @d: fourth member
213 *
214 * Longer description
215 */
216 struct my_struct {
217 int a;
218 int b;
219 /* private: internal use only */
220 int c;
221 /* public: the next one is public */
222 int d;
223 };
224
225Nested structs/unions
226~~~~~~~~~~~~~~~~~~~~~
227
228It is possible to document nested structs and unions, like::
229
230 /**
231 * struct nested_foobar - a struct with nested unions and structs
232 * @memb1: first member of anonymous union/anonymous struct
233 * @memb2: second member of anonymous union/anonymous struct
234 * @memb3: third member of anonymous union/anonymous struct
235 * @memb4: fourth member of anonymous union/anonymous struct
236 * @bar: non-anonymous union
237 * @bar.st1: struct st1 inside @bar
238 * @bar.st2: struct st2 inside @bar
239 * @bar.st1.memb1: first member of struct st1 on union bar
240 * @bar.st1.memb2: second member of struct st1 on union bar
241 * @bar.st2.memb1: first member of struct st2 on union bar
242 * @bar.st2.memb2: second member of struct st2 on union bar
243 */
244 struct nested_foobar {
245 /* Anonymous union/struct*/
246 union {
247 struct {
248 int memb1;
249 int memb2;
250 }
251 struct {
252 void *memb3;
253 int memb4;
254 }
255 }
256 union {
257 struct {
258 int memb1;
259 int memb2;
260 } st1;
261 struct {
262 void *memb1;
263 int memb2;
264 } st2;
265 } bar;
266 };
267
268.. note::
269
270 #) When documenting nested structs or unions, if the struct/union ``foo``
271 is named, the member ``bar`` inside it should be documented as
272 ``@foo.bar:``
273 #) When the nested struct/union is anonymous, the member ``bar`` in it
274 should be documented as ``@bar:``
275
276In-line member documentation comments
277~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
278
279The structure members may also be documented in-line within the definition.
280There are two styles, single-line comments where both the opening ``/**`` and
281closing ``*/`` are on the same line, and multi-line comments where they are each
282on a line of their own, like all other kernel-doc comments::
283
284 /**
285 * struct foo - Brief description.
286 * @foo: The Foo member.
287 */
288 struct foo {
289 int foo;
290 /**
291 * @bar: The Bar member.
292 */
293 int bar;
294 /**
295 * @baz: The Baz member.
296 *
297 * Here, the member description may contain several paragraphs.
298 */
299 int baz;
300 union {
301 /** @foobar: Single line description. */
302 int foobar;
303 };
304 /** @bar2: Description for struct @bar2 inside @foo */
305 struct {
306 /**
307 * @bar2.barbar: Description for @barbar inside @foo.bar2
308 */
309 int barbar;
310 } bar2;
311 };
312
313Typedef documentation
314---------------------
315
316The general format of a typedef kernel-doc comment is::
317
318 /**
319 * typedef type_name - Brief description.
320 *
321 * Description of the type.
322 */
323
324Typedefs with function prototypes can also be documented::
325
326 /**
327 * typedef type_name - Brief description.
328 * @arg1: description of arg1
329 * @arg2: description of arg2
330 *
331 * Description of the type.
332 *
333 * Context: Locking context.
334 * Return: Meaning of the return value.
335 */
336 typedef void (*type_name)(struct v4l2_ctrl *arg1, void *arg2);
337
338Highlights and cross-references
339-------------------------------
340
341The following special patterns are recognized in the kernel-doc comment
342descriptive text and converted to proper reStructuredText markup and `Sphinx C
343Domain`_ references.
344
345.. attention:: The below are **only** recognized within kernel-doc comments,
346 **not** within normal reStructuredText documents.
347
348``funcname()``
349 Function reference.
350
351``@parameter``
352 Name of a function parameter. (No cross-referencing, just formatting.)
353
354``%CONST``
355 Name of a constant. (No cross-referencing, just formatting.)
356
357````literal````
358 A literal block that should be handled as-is. The output will use a
359 ``monospaced font``.
360
361 Useful if you need to use special characters that would otherwise have some
362 meaning either by kernel-doc script or by reStructuredText.
363
364 This is particularly useful if you need to use things like ``%ph`` inside
365 a function description.
366
367``$ENVVAR``
368 Name of an environment variable. (No cross-referencing, just formatting.)
369
370``&struct name``
371 Structure reference.
372
373``&enum name``
374 Enum reference.
375
376``&typedef name``
377 Typedef reference.
378
379``&struct_name->member`` or ``&struct_name.member``
380 Structure or union member reference. The cross-reference will be to the struct
381 or union definition, not the member directly.
382
383``&name``
384 A generic type reference. Prefer using the full reference described above
385 instead. This is mostly for legacy comments.
386
387Cross-referencing from reStructuredText
388~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
389
390To cross-reference the functions and types defined in the kernel-doc comments
391from reStructuredText documents, please use the `Sphinx C Domain`_
392references. For example::
393
394 See function :c:func:`foo` and struct/union/enum/typedef :c:type:`bar`.
395
396While the type reference works with just the type name, without the
397struct/union/enum/typedef part in front, you may want to use::
398
399 See :c:type:`struct foo <foo>`.
400 See :c:type:`union bar <bar>`.
401 See :c:type:`enum baz <baz>`.
402 See :c:type:`typedef meh <meh>`.
403
404This will produce prettier links, and is in line with how kernel-doc does the
405cross-references.
406
407For further details, please refer to the `Sphinx C Domain`_ documentation.
408
409Overview documentation comments
410-------------------------------
411
412To facilitate having source code and comments close together, you can include
413kernel-doc documentation blocks that are free-form comments instead of being
414kernel-doc for functions, structures, unions, enums, or typedefs. This could be
415used for something like a theory of operation for a driver or library code, for
416example.
417
418This is done by using a ``DOC:`` section keyword with a section title.
419
420The general format of an overview or high-level documentation comment is::
421
422 /**
423 * DOC: Theory of Operation
424 *
425 * The whizbang foobar is a dilly of a gizmo. It can do whatever you
426 * want it to do, at any time. It reads your mind. Here's how it works.
427 *
428 * foo bar splat
429 *
430 * The only drawback to this gizmo is that is can sometimes damage
431 * hardware, software, or its subject(s).
432 */
433
434The title following ``DOC:`` acts as a heading within the source file, but also
435as an identifier for extracting the documentation comment. Thus, the title must
436be unique within the file.
437
438Including kernel-doc comments
439=============================
440
441The documentation comments may be included in any of the reStructuredText
442documents using a dedicated kernel-doc Sphinx directive extension.
443
444The kernel-doc directive is of the format::
445
446 .. kernel-doc:: source
447 :option:
448
449The *source* is the path to a source file, relative to the kernel source
450tree. The following directive options are supported:
451
452export: *[source-pattern ...]*
453 Include documentation for all functions in *source* that have been exported
454 using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either in *source* or in any
455 of the files specified by *source-pattern*.
456
457 The *source-pattern* is useful when the kernel-doc comments have been placed
458 in header files, while ``EXPORT_SYMBOL`` and ``EXPORT_SYMBOL_GPL`` are next to
459 the function definitions.
460
461 Examples::
462
463 .. kernel-doc:: lib/bitmap.c
464 :export:
465
466 .. kernel-doc:: include/net/mac80211.h
467 :export: net/mac80211/*.c
468
469internal: *[source-pattern ...]*
470 Include documentation for all functions and types in *source* that have
471 **not** been exported using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either
472 in *source* or in any of the files specified by *source-pattern*.
473
474 Example::
475
476 .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
477 :internal:
478
479identifiers: *[ function/type ...]*
480 Include documentation for each *function* and *type* in *source*.
481 If no *function* is specified, the documentation for all functions
482 and types in the *source* will be included.
483
484 Examples::
485
486 .. kernel-doc:: lib/bitmap.c
487 :identifiers: bitmap_parselist bitmap_parselist_user
488
489 .. kernel-doc:: lib/idr.c
490 :identifiers:
491
492functions: *[ function/type ...]*
493 This is an alias of the 'identifiers' directive and deprecated.
494
495doc: *title*
496 Include documentation for the ``DOC:`` paragraph identified by *title* in
497 *source*. Spaces are allowed in *title*; do not quote the *title*. The *title*
498 is only used as an identifier for the paragraph, and is not included in the
499 output. Please make sure to have an appropriate heading in the enclosing
500 reStructuredText document.
501
502 Example::
503
504 .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
505 :doc: High Definition Audio over HDMI and Display Port
506
507Without options, the kernel-doc directive includes all documentation comments
508from the source file.
509
510The kernel-doc extension is included in the kernel source tree, at
511``Documentation/sphinx/kerneldoc.py``. Internally, it uses the
512``scripts/kernel-doc`` script to extract the documentation comments from the
513source.
514
515.. _kernel_doc:
516
517How to use kernel-doc to generate man pages
518-------------------------------------------
519
520If you just want to use kernel-doc to generate man pages you can do this
521from the kernel git tree::
522
523 $ scripts/kernel-doc -man \
524 $(git grep -l '/\*\*' -- :^Documentation :^tools) \
525 | scripts/split-man.pl /tmp/man
526
527Some older versions of git do not support some of the variants of syntax for
528path exclusion. One of the following commands may work for those versions::
529
530 $ scripts/kernel-doc -man \
531 $(git grep -l '/\*\*' -- . ':!Documentation' ':!tools') \
532 | scripts/split-man.pl /tmp/man
533
534 $ scripts/kernel-doc -man \
535 $(git grep -l '/\*\*' -- . ":(exclude)Documentation" ":(exclude)tools") \
536 | scripts/split-man.pl /tmp/man
1.. title:: Kernel-doc comments
2
3===========================
4Writing kernel-doc comments
5===========================
6
7The Linux kernel source files may contain structured documentation
8comments in the kernel-doc format to describe the functions, types
9and design of the code. It is easier to keep documentation up-to-date
10when it is embedded in source files.
11
12.. note:: The kernel-doc format is deceptively similar to javadoc,
13 gtk-doc or Doxygen, yet distinctively different, for historical
14 reasons. The kernel source contains tens of thousands of kernel-doc
15 comments. Please stick to the style described here.
16
17.. note:: kernel-doc does not cover Rust code: please see
18 Documentation/rust/general-information.rst instead.
19
20The kernel-doc structure is extracted from the comments, and proper
21`Sphinx C Domain`_ function and type descriptions with anchors are
22generated from them. The descriptions are filtered for special kernel-doc
23highlights and cross-references. See below for details.
24
25.. _Sphinx C Domain: http://www.sphinx-doc.org/en/stable/domains.html
26
27Every function that is exported to loadable modules using
28``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
29comment. Functions and data structures in header files which are intended
30to be used by modules should also have kernel-doc comments.
31
32It is good practice to also provide kernel-doc formatted documentation
33for functions externally visible to other kernel files (not marked
34``static``). We also recommend providing kernel-doc formatted
35documentation for private (file ``static``) routines, for consistency of
36kernel source code layout. This is lower priority and at the discretion
37of the maintainer of that kernel source file.
38
39How to format kernel-doc comments
40---------------------------------
41
42The opening comment mark ``/**`` is used for kernel-doc comments. The
43``kernel-doc`` tool will extract comments marked this way. The rest of
44the comment is formatted like a normal multi-line comment with a column
45of asterisks on the left side, closing with ``*/`` on a line by itself.
46
47The function and type kernel-doc comments should be placed just before
48the function or type being described in order to maximise the chance
49that somebody changing the code will also change the documentation. The
50overview kernel-doc comments may be placed anywhere at the top indentation
51level.
52
53Running the ``kernel-doc`` tool with increased verbosity and without actual
54output generation may be used to verify proper formatting of the
55documentation comments. For example::
56
57 scripts/kernel-doc -v -none drivers/foo/bar.c
58
59The documentation format is verified by the kernel build when it is
60requested to perform extra gcc checks::
61
62 make W=n
63
64Function documentation
65----------------------
66
67The general format of a function and function-like macro kernel-doc comment is::
68
69 /**
70 * function_name() - Brief description of function.
71 * @arg1: Describe the first argument.
72 * @arg2: Describe the second argument.
73 * One can provide multiple line descriptions
74 * for arguments.
75 *
76 * A longer description, with more discussion of the function function_name()
77 * that might be useful to those using or modifying it. Begins with an
78 * empty comment line, and may include additional embedded empty
79 * comment lines.
80 *
81 * The longer description may have multiple paragraphs.
82 *
83 * Context: Describes whether the function can sleep, what locks it takes,
84 * releases, or expects to be held. It can extend over multiple
85 * lines.
86 * Return: Describe the return value of function_name.
87 *
88 * The return value description can also have multiple paragraphs, and should
89 * be placed at the end of the comment block.
90 */
91
92The brief description following the function name may span multiple lines, and
93ends with an argument description, a blank comment line, or the end of the
94comment block.
95
96Function parameters
97~~~~~~~~~~~~~~~~~~~
98
99Each function argument should be described in order, immediately following
100the short function description. Do not leave a blank line between the
101function description and the arguments, nor between the arguments.
102
103Each ``@argument:`` description may span multiple lines.
104
105.. note::
106
107 If the ``@argument`` description has multiple lines, the continuation
108 of the description should start at the same column as the previous line::
109
110 * @argument: some long description
111 * that continues on next lines
112
113 or::
114
115 * @argument:
116 * some long description
117 * that continues on next lines
118
119If a function has a variable number of arguments, its description should
120be written in kernel-doc notation as::
121
122 * @...: description
123
124Function context
125~~~~~~~~~~~~~~~~
126
127The context in which a function can be called should be described in a
128section named ``Context``. This should include whether the function
129sleeps or can be called from interrupt context, as well as what locks
130it takes, releases and expects to be held by its caller.
131
132Examples::
133
134 * Context: Any context.
135 * Context: Any context. Takes and releases the RCU lock.
136 * Context: Any context. Expects <lock> to be held by caller.
137 * Context: Process context. May sleep if @gfp flags permit.
138 * Context: Process context. Takes and releases <mutex>.
139 * Context: Softirq or process context. Takes and releases <lock>, BH-safe.
140 * Context: Interrupt context.
141
142Return values
143~~~~~~~~~~~~~
144
145The return value, if any, should be described in a dedicated section
146named ``Return``.
147
148.. note::
149
150 #) The multi-line descriptive text you provide does *not* recognize
151 line breaks, so if you try to format some text nicely, as in::
152
153 * Return:
154 * 0 - OK
155 * -EINVAL - invalid argument
156 * -ENOMEM - out of memory
157
158 this will all run together and produce::
159
160 Return: 0 - OK -EINVAL - invalid argument -ENOMEM - out of memory
161
162 So, in order to produce the desired line breaks, you need to use a
163 ReST list, e. g.::
164
165 * Return:
166 * * 0 - OK to runtime suspend the device
167 * * -EBUSY - Device should not be runtime suspended
168
169 #) If the descriptive text you provide has lines that begin with
170 some phrase followed by a colon, each of those phrases will be taken
171 as a new section heading, which probably won't produce the desired
172 effect.
173
174Structure, union, and enumeration documentation
175-----------------------------------------------
176
177The general format of a struct, union, and enum kernel-doc comment is::
178
179 /**
180 * struct struct_name - Brief description.
181 * @member1: Description of member1.
182 * @member2: Description of member2.
183 * One can provide multiple line descriptions
184 * for members.
185 *
186 * Description of the structure.
187 */
188
189You can replace the ``struct`` in the above example with ``union`` or
190``enum`` to describe unions or enums. ``member`` is used to mean struct
191and union member names as well as enumerations in an enum.
192
193The brief description following the structure name may span multiple
194lines, and ends with a member description, a blank comment line, or the
195end of the comment block.
196
197Members
198~~~~~~~
199
200Members of structs, unions and enums should be documented the same way
201as function parameters; they immediately succeed the short description
202and may be multi-line.
203
204Inside a struct or union description, you can use the ``private:`` and
205``public:`` comment tags. Structure fields that are inside a ``private:``
206area are not listed in the generated output documentation.
207
208The ``private:`` and ``public:`` tags must begin immediately following a
209``/*`` comment marker. They may optionally include comments between the
210``:`` and the ending ``*/`` marker.
211
212Example::
213
214 /**
215 * struct my_struct - short description
216 * @a: first member
217 * @b: second member
218 * @d: fourth member
219 *
220 * Longer description
221 */
222 struct my_struct {
223 int a;
224 int b;
225 /* private: internal use only */
226 int c;
227 /* public: the next one is public */
228 int d;
229 };
230
231Nested structs/unions
232~~~~~~~~~~~~~~~~~~~~~
233
234It is possible to document nested structs and unions, like::
235
236 /**
237 * struct nested_foobar - a struct with nested unions and structs
238 * @memb1: first member of anonymous union/anonymous struct
239 * @memb2: second member of anonymous union/anonymous struct
240 * @memb3: third member of anonymous union/anonymous struct
241 * @memb4: fourth member of anonymous union/anonymous struct
242 * @bar: non-anonymous union
243 * @bar.st1: struct st1 inside @bar
244 * @bar.st2: struct st2 inside @bar
245 * @bar.st1.memb1: first member of struct st1 on union bar
246 * @bar.st1.memb2: second member of struct st1 on union bar
247 * @bar.st2.memb1: first member of struct st2 on union bar
248 * @bar.st2.memb2: second member of struct st2 on union bar
249 */
250 struct nested_foobar {
251 /* Anonymous union/struct*/
252 union {
253 struct {
254 int memb1;
255 int memb2;
256 };
257 struct {
258 void *memb3;
259 int memb4;
260 };
261 };
262 union {
263 struct {
264 int memb1;
265 int memb2;
266 } st1;
267 struct {
268 void *memb1;
269 int memb2;
270 } st2;
271 } bar;
272 };
273
274.. note::
275
276 #) When documenting nested structs or unions, if the struct/union ``foo``
277 is named, the member ``bar`` inside it should be documented as
278 ``@foo.bar:``
279 #) When the nested struct/union is anonymous, the member ``bar`` in it
280 should be documented as ``@bar:``
281
282In-line member documentation comments
283~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
284
285The structure members may also be documented in-line within the definition.
286There are two styles, single-line comments where both the opening ``/**`` and
287closing ``*/`` are on the same line, and multi-line comments where they are each
288on a line of their own, like all other kernel-doc comments::
289
290 /**
291 * struct foo - Brief description.
292 * @foo: The Foo member.
293 */
294 struct foo {
295 int foo;
296 /**
297 * @bar: The Bar member.
298 */
299 int bar;
300 /**
301 * @baz: The Baz member.
302 *
303 * Here, the member description may contain several paragraphs.
304 */
305 int baz;
306 union {
307 /** @foobar: Single line description. */
308 int foobar;
309 };
310 /** @bar2: Description for struct @bar2 inside @foo */
311 struct {
312 /**
313 * @bar2.barbar: Description for @barbar inside @foo.bar2
314 */
315 int barbar;
316 } bar2;
317 };
318
319Typedef documentation
320---------------------
321
322The general format of a typedef kernel-doc comment is::
323
324 /**
325 * typedef type_name - Brief description.
326 *
327 * Description of the type.
328 */
329
330Typedefs with function prototypes can also be documented::
331
332 /**
333 * typedef type_name - Brief description.
334 * @arg1: description of arg1
335 * @arg2: description of arg2
336 *
337 * Description of the type.
338 *
339 * Context: Locking context.
340 * Return: Meaning of the return value.
341 */
342 typedef void (*type_name)(struct v4l2_ctrl *arg1, void *arg2);
343
344Highlights and cross-references
345-------------------------------
346
347The following special patterns are recognized in the kernel-doc comment
348descriptive text and converted to proper reStructuredText markup and `Sphinx C
349Domain`_ references.
350
351.. attention:: The below are **only** recognized within kernel-doc comments,
352 **not** within normal reStructuredText documents.
353
354``funcname()``
355 Function reference.
356
357``@parameter``
358 Name of a function parameter. (No cross-referencing, just formatting.)
359
360``%CONST``
361 Name of a constant. (No cross-referencing, just formatting.)
362
363````literal````
364 A literal block that should be handled as-is. The output will use a
365 ``monospaced font``.
366
367 Useful if you need to use special characters that would otherwise have some
368 meaning either by kernel-doc script or by reStructuredText.
369
370 This is particularly useful if you need to use things like ``%ph`` inside
371 a function description.
372
373``$ENVVAR``
374 Name of an environment variable. (No cross-referencing, just formatting.)
375
376``&struct name``
377 Structure reference.
378
379``&enum name``
380 Enum reference.
381
382``&typedef name``
383 Typedef reference.
384
385``&struct_name->member`` or ``&struct_name.member``
386 Structure or union member reference. The cross-reference will be to the struct
387 or union definition, not the member directly.
388
389``&name``
390 A generic type reference. Prefer using the full reference described above
391 instead. This is mostly for legacy comments.
392
393Cross-referencing from reStructuredText
394~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
395
396No additional syntax is needed to cross-reference the functions and types
397defined in the kernel-doc comments from reStructuredText documents.
398Just end function names with ``()`` and write ``struct``, ``union``, ``enum``
399or ``typedef`` before types.
400For example::
401
402 See foo().
403 See struct foo.
404 See union bar.
405 See enum baz.
406 See typedef meh.
407
408However, if you want custom text in the cross-reference link, that can be done
409through the following syntax::
410
411 See :c:func:`my custom link text for function foo <foo>`.
412 See :c:type:`my custom link text for struct bar <bar>`.
413
414For further details, please refer to the `Sphinx C Domain`_ documentation.
415
416Overview documentation comments
417-------------------------------
418
419To facilitate having source code and comments close together, you can include
420kernel-doc documentation blocks that are free-form comments instead of being
421kernel-doc for functions, structures, unions, enums, or typedefs. This could be
422used for something like a theory of operation for a driver or library code, for
423example.
424
425This is done by using a ``DOC:`` section keyword with a section title.
426
427The general format of an overview or high-level documentation comment is::
428
429 /**
430 * DOC: Theory of Operation
431 *
432 * The whizbang foobar is a dilly of a gizmo. It can do whatever you
433 * want it to do, at any time. It reads your mind. Here's how it works.
434 *
435 * foo bar splat
436 *
437 * The only drawback to this gizmo is that is can sometimes damage
438 * hardware, software, or its subject(s).
439 */
440
441The title following ``DOC:`` acts as a heading within the source file, but also
442as an identifier for extracting the documentation comment. Thus, the title must
443be unique within the file.
444
445=============================
446Including kernel-doc comments
447=============================
448
449The documentation comments may be included in any of the reStructuredText
450documents using a dedicated kernel-doc Sphinx directive extension.
451
452The kernel-doc directive is of the format::
453
454 .. kernel-doc:: source
455 :option:
456
457The *source* is the path to a source file, relative to the kernel source
458tree. The following directive options are supported:
459
460export: *[source-pattern ...]*
461 Include documentation for all functions in *source* that have been exported
462 using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either in *source* or in any
463 of the files specified by *source-pattern*.
464
465 The *source-pattern* is useful when the kernel-doc comments have been placed
466 in header files, while ``EXPORT_SYMBOL`` and ``EXPORT_SYMBOL_GPL`` are next to
467 the function definitions.
468
469 Examples::
470
471 .. kernel-doc:: lib/bitmap.c
472 :export:
473
474 .. kernel-doc:: include/net/mac80211.h
475 :export: net/mac80211/*.c
476
477internal: *[source-pattern ...]*
478 Include documentation for all functions and types in *source* that have
479 **not** been exported using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either
480 in *source* or in any of the files specified by *source-pattern*.
481
482 Example::
483
484 .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
485 :internal:
486
487identifiers: *[ function/type ...]*
488 Include documentation for each *function* and *type* in *source*.
489 If no *function* is specified, the documentation for all functions
490 and types in the *source* will be included.
491
492 Examples::
493
494 .. kernel-doc:: lib/bitmap.c
495 :identifiers: bitmap_parselist bitmap_parselist_user
496
497 .. kernel-doc:: lib/idr.c
498 :identifiers:
499
500no-identifiers: *[ function/type ...]*
501 Exclude documentation for each *function* and *type* in *source*.
502
503 Example::
504
505 .. kernel-doc:: lib/bitmap.c
506 :no-identifiers: bitmap_parselist
507
508functions: *[ function/type ...]*
509 This is an alias of the 'identifiers' directive and deprecated.
510
511doc: *title*
512 Include documentation for the ``DOC:`` paragraph identified by *title* in
513 *source*. Spaces are allowed in *title*; do not quote the *title*. The *title*
514 is only used as an identifier for the paragraph, and is not included in the
515 output. Please make sure to have an appropriate heading in the enclosing
516 reStructuredText document.
517
518 Example::
519
520 .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
521 :doc: High Definition Audio over HDMI and Display Port
522
523Without options, the kernel-doc directive includes all documentation comments
524from the source file.
525
526The kernel-doc extension is included in the kernel source tree, at
527``Documentation/sphinx/kerneldoc.py``. Internally, it uses the
528``scripts/kernel-doc`` script to extract the documentation comments from the
529source.
530
531.. _kernel_doc:
532
533How to use kernel-doc to generate man pages
534-------------------------------------------
535
536If you just want to use kernel-doc to generate man pages you can do this
537from the kernel git tree::
538
539 $ scripts/kernel-doc -man \
540 $(git grep -l '/\*\*' -- :^Documentation :^tools) \
541 | scripts/split-man.pl /tmp/man
542
543Some older versions of git do not support some of the variants of syntax for
544path exclusion. One of the following commands may work for those versions::
545
546 $ scripts/kernel-doc -man \
547 $(git grep -l '/\*\*' -- . ':!Documentation' ':!tools') \
548 | scripts/split-man.pl /tmp/man
549
550 $ scripts/kernel-doc -man \
551 $(git grep -l '/\*\*' -- . ":(exclude)Documentation" ":(exclude)tools") \
552 | scripts/split-man.pl /tmp/man