summaryrefslogtreecommitdiff
path: root/Documentation/doc-guide/kernel-doc.rst
blob: 192c36af39e2effe1ae5cc24dcbc658c4494fa31 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
Writing kernel-doc comments
===========================

The Linux kernel source files may contain structured documentation
comments in the kernel-doc format to describe the functions, types
and design of the code. It is easier to keep documentation up-to-date
when it is embedded in source files.

.. note:: The kernel-doc format is deceptively similar to javadoc,
   gtk-doc or Doxygen, yet distinctively different, for historical
   reasons. The kernel source contains tens of thousands of kernel-doc
   comments. Please stick to the style described here.

The kernel-doc structure is extracted from the comments, and proper
`Sphinx C Domain`_ function and type descriptions with anchors are
generated from them. The descriptions are filtered for special kernel-doc
highlights and cross-references. See below for details.

.. _Sphinx C Domain: http://www.sphinx-doc.org/en/stable/domains.html

Every function that is exported to loadable modules using
``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
comment. Functions and data structures in header files which are intended
to be used by modules should also have kernel-doc comments.

It is good practice to also provide kernel-doc formatted documentation
for functions externally visible to other kernel files (not marked
``static``). We also recommend providing kernel-doc formatted
documentation for private (file ``static``) routines, for consistency of
kernel source code layout. This is lower priority and at the discretion
of the maintainer of that kernel source file.

How to format kernel-doc comments
---------------------------------

The opening comment mark ``/**`` is used for kernel-doc comments. The
``kernel-doc`` tool will extract comments marked this way. The rest of
the comment is formatted like a normal multi-line comment with a column
of asterisks on the left side, closing with ``*/`` on a line by itself.

The function and type kernel-doc comments should be placed just before
the function or type being described in order to maximise the chance
that somebody changing the code will also change the documentation. The
overview kernel-doc comments may be placed anywhere at the top indentation
level.

Running the ``kernel-doc`` tool with increased verbosity and without actual
output generation may be used to verify proper formatting of the
documentation comments. For example::

	scripts/kernel-doc -v -none drivers/foo/bar.c

The documentation format is verified by the kernel build when it is
requested to perform extra gcc checks::

	make W=n

Function documentation
----------------------

The general format of a function and function-like macro kernel-doc comment is::

  /**
   * function_name() - Brief description of function.
   * @arg1: Describe the first argument.
   * @arg2: Describe the second argument.
   *        One can provide multiple line descriptions
   *        for arguments.
   *
   * A longer description, with more discussion of the function function_name()
   * that might be useful to those using or modifying it. Begins with an
   * empty comment line, and may include additional embedded empty
   * comment lines.
   *
   * The longer description may have multiple paragraphs.
   *
   * Context: Describes whether the function can sleep, what locks it takes,
   *          releases, or expects to be held. It can extend over multiple
   *          lines.
   * Return: Describe the return value of function_name.
   *
   * The return value description can also have multiple paragraphs, and should
   * be placed at the end of the comment block.
   */

The brief description following the function name may span multiple lines, and
ends with an argument description, a blank comment line, or the end of the
comment block.

Function parameters
~~~~~~~~~~~~~~~~~~~

Each function argument should be described in order, immediately following
the short function description.  Do not leave a blank line between the
function description and the arguments, nor between the arguments.

Each ``@argument:`` description may span multiple lines.

.. note::

   If the ``@argument`` description has multiple lines, the continuation
   of the description should start at the same column as the previous line::

      * @argument: some long description
      *            that continues on next lines

   or::

      * @argument:
      *		some long description
      *		that continues on next lines

If a function has a variable number of arguments, its description should
be written in kernel-doc notation as::

      * @...: description

Function context
~~~~~~~~~~~~~~~~

The context in which a function can be called should be described in a
section named ``Context``. This should include whether the function
sleeps or can be called from interrupt context, as well as what locks
it takes, releases and expects to be held by its caller.

Examples::

  * Context: Any context.
  * Context: Any context. Takes and releases the RCU lock.
  * Context: Any context. Expects <lock> to be held by caller.
  * Context: Process context. May sleep if @gfp flags permit.
  * Context: Process context. Takes and releases <mutex>.
  * Context: Softirq or process context. Takes and releases <lock>, BH-safe.
  * Context: Interrupt context.

Return values
~~~~~~~~~~~~~

The return value, if any, should be described in a dedicated section
named ``Return``.

.. note::

  #) The multi-line descriptive text you provide does *not* recognize
     line breaks, so if you try to format some text nicely, as in::

	* Return:
	* 0 - OK
	* -EINVAL - invalid argument
	* -ENOMEM - out of memory

     this will all run together and produce::

	Return: 0 - OK -EINVAL - invalid argument -ENOMEM - out of memory

     So, in order to produce the desired line breaks, you need to use a
     ReST list, e. g.::

      * Return:
      * * 0		- OK to runtime suspend the device
      * * -EBUSY	- Device should not be runtime suspended

  #) If the descriptive text you provide has lines that begin with
     some phrase followed by a colon, each of those phrases will be taken
     as a new section heading, which probably won't produce the desired
     effect.

Structure, union, and enumeration documentation
-----------------------------------------------

The general format of a struct, union, and enum kernel-doc comment is::

  /**
   * struct struct_name - Brief description.
   * @member1: Description of member1.
   * @member2: Description of member2.
   *           One can provide multiple line descriptions
   *           for members.
   *
   * Description of the structure.
   */

You can replace the ``struct`` in the above example with ``union`` or
``enum``  to describe unions or enums. ``member`` is used to mean struct
and union member names as well as enumerations in an enum.

The brief description following the structure name may span multiple
lines, and ends with a member description, a blank comment line, or the
end of the comment block.

Members
~~~~~~~

Members of structs, unions and enums should be documented the same way
as function parameters; they immediately succeed the short description
and may be multi-line.

Inside a struct or union description, you can use the ``private:`` and
``public:`` comment tags. Structure fields that are inside a ``private:``
area are not listed in the generated output documentation.

The ``private:`` and ``public:`` tags must begin immediately following a
``/*`` comment marker. They may optionally include comments between the
``:`` and the ending ``*/`` marker.

Example::

  /**
   * struct my_struct - short description
   * @a: first member
   * @b: second member
   * @d: fourth member
   *
   * Longer description
   */
  struct my_struct {
      int a;
      int b;
  /* private: internal use only */
      int c;
  /* public: the next one is public */
      int d;
  };

Nested structs/unions
~~~~~~~~~~~~~~~~~~~~~

It is possible to document nested structs and unions, like::

      /**
       * struct nested_foobar - a struct with nested unions and structs
       * @memb1: first member of anonymous union/anonymous struct
       * @memb2: second member of anonymous union/anonymous struct
       * @memb3: third member of anonymous union/anonymous struct
       * @memb4: fourth member of anonymous union/anonymous struct
       * @bar: non-anonymous union
       * @bar.st1: struct st1 inside @bar
       * @bar.st2: struct st2 inside @bar
       * @bar.st1.memb1: first member of struct st1 on union bar
       * @bar.st1.memb2: second member of struct st1 on union bar
       * @bar.st2.memb1: first member of struct st2 on union bar
       * @bar.st2.memb2: second member of struct st2 on union bar
       */
      struct nested_foobar {
        /* Anonymous union/struct*/
        union {
          struct {
            int memb1;
            int memb2;
        }
          struct {
            void *memb3;
            int memb4;
          }
        }
        union {
          struct {
            int memb1;
            int memb2;
          } st1;
          struct {
            void *memb1;
            int memb2;
          } st2;
        } bar;
      };

.. note::

   #) When documenting nested structs or unions, if the struct/union ``foo``
      is named, the member ``bar`` inside it should be documented as
      ``@foo.bar:``
   #) When the nested struct/union is anonymous, the member ``bar`` in it
      should be documented as ``@bar:``

In-line member documentation comments
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The structure members may also be documented in-line within the definition.
There are two styles, single-line comments where both the opening ``/**`` and
closing ``*/`` are on the same line, and multi-line comments where they are each
on a line of their own, like all other kernel-doc comments::

  /**
   * struct foo - Brief description.
   * @foo: The Foo member.
   */
  struct foo {
        int foo;
        /**
         * @bar: The Bar member.
         */
        int bar;
        /**
         * @baz: The Baz member.
         *
         * Here, the member description may contain several paragraphs.
         */
        int baz;
        union {
                /** @foobar: Single line description. */
                int foobar;
        };
        /** @bar2: Description for struct @bar2 inside @foo */
        struct {
                /**
                 * @bar2.barbar: Description for @barbar inside @foo.bar2
                 */
                int barbar;
        } bar2;
  };

Typedef documentation
---------------------

The general format of a typedef kernel-doc comment is::

  /**
   * typedef type_name - Brief description.
   *
   * Description of the type.
   */

Typedefs with function prototypes can also be documented::

  /**
   * typedef type_name - Brief description.
   * @arg1: description of arg1
   * @arg2: description of arg2
   *
   * Description of the type.
   *
   * Context: Locking context.
   * Return: Meaning of the return value.
   */
   typedef void (*type_name)(struct v4l2_ctrl *arg1, void *arg2);

Highlights and cross-references
-------------------------------

The following special patterns are recognized in the kernel-doc comment
descriptive text and converted to proper reStructuredText markup and `Sphinx C
Domain`_ references.

.. attention:: The below are **only** recognized within kernel-doc comments,
	       **not** within normal reStructuredText documents.

``funcname()``
  Function reference.

``@parameter``
  Name of a function parameter. (No cross-referencing, just formatting.)

``%CONST``
  Name of a constant. (No cross-referencing, just formatting.)

````literal````
  A literal block that should be handled as-is. The output will use a
  ``monospaced font``.

  Useful if you need to use special characters that would otherwise have some
  meaning either by kernel-doc script or by reStructuredText.

  This is particularly useful if you need to use things like ``%ph`` inside
  a function description.

``$ENVVAR``
  Name of an environment variable. (No cross-referencing, just formatting.)

``&struct name``
  Structure reference.

``&enum name``
  Enum reference.

``&typedef name``
  Typedef reference.

``&struct_name->member`` or ``&struct_name.member``
  Structure or union member reference. The cross-reference will be to the struct
  or union definition, not the member directly.

``&name``
  A generic type reference. Prefer using the full reference described above
  instead. This is mostly for legacy comments.

Cross-referencing from reStructuredText
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To cross-reference the functions and types defined in the kernel-doc comments
from reStructuredText documents, please use the `Sphinx C Domain`_
references. For example::

  See function :c:func:`foo` and struct/union/enum/typedef :c:type:`bar`.

While the type reference works with just the type name, without the
struct/union/enum/typedef part in front, you may want to use::

  See :c:type:`struct foo <foo>`.
  See :c:type:`union bar <bar>`.
  See :c:type:`enum baz <baz>`.
  See :c:type:`typedef meh <meh>`.

This will produce prettier links, and is in line with how kernel-doc does the
cross-references.

For further details, please refer to the `Sphinx C Domain`_ documentation.

Overview documentation comments
-------------------------------

To facilitate having source code and comments close together, you can include
kernel-doc documentation blocks that are free-form comments instead of being
kernel-doc for functions, structures, unions, enums, or typedefs. This could be
used for something like a theory of operation for a driver or library code, for
example.

This is done by using a ``DOC:`` section keyword with a section title.

The general format of an overview or high-level documentation comment is::

  /**
   * DOC: Theory of Operation
   *
   * The whizbang foobar is a dilly of a gizmo. It can do whatever you
   * want it to do, at any time. It reads your mind. Here's how it works.
   *
   * foo bar splat
   *
   * The only drawback to this gizmo is that is can sometimes damage
   * hardware, software, or its subject(s).
   */

The title following ``DOC:`` acts as a heading within the source file, but also
as an identifier for extracting the documentation comment. Thus, the title must
be unique within the file.

Including kernel-doc comments
=============================

The documentation comments may be included in any of the reStructuredText
documents using a dedicated kernel-doc Sphinx directive extension.

The kernel-doc directive is of the format::

  .. kernel-doc:: source
     :option:

The *source* is the path to a source file, relative to the kernel source
tree. The following directive options are supported:

export: *[source-pattern ...]*
  Include documentation for all functions in *source* that have been exported
  using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either in *source* or in any
  of the files specified by *source-pattern*.

  The *source-pattern* is useful when the kernel-doc comments have been placed
  in header files, while ``EXPORT_SYMBOL`` and ``EXPORT_SYMBOL_GPL`` are next to
  the function definitions.

  Examples::

    .. kernel-doc:: lib/bitmap.c
       :export:

    .. kernel-doc:: include/net/mac80211.h
       :export: net/mac80211/*.c

internal: *[source-pattern ...]*
  Include documentation for all functions and types in *source* that have
  **not** been exported using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either
  in *source* or in any of the files specified by *source-pattern*.

  Example::

    .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
       :internal:

doc: *title*
  Include documentation for the ``DOC:`` paragraph identified by *title* in
  *source*. Spaces are allowed in *title*; do not quote the *title*. The *title*
  is only used as an identifier for the paragraph, and is not included in the
  output. Please make sure to have an appropriate heading in the enclosing
  reStructuredText document.

  Example::

    .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
       :doc: High Definition Audio over HDMI and Display Port

functions: *[ function ...]*
  Include documentation for each *function* in *source*.
  If no *function* is specified, the documentation for all functions
  and types in the *source* will be included.

  Examples::

    .. kernel-doc:: lib/bitmap.c
       :functions: bitmap_parselist bitmap_parselist_user

    .. kernel-doc:: lib/idr.c
       :functions:

Without options, the kernel-doc directive includes all documentation comments
from the source file.

The kernel-doc extension is included in the kernel source tree, at
``Documentation/sphinx/kerneldoc.py``. Internally, it uses the
``scripts/kernel-doc`` script to extract the documentation comments from the
source.

.. _kernel_doc:

How to use kernel-doc to generate man pages
-------------------------------------------

If you just want to use kernel-doc to generate man pages you can do this
from the kernel git tree::

  $ scripts/kernel-doc -man \
    $(git grep -l '/\*\*' -- :^Documentation :^tools) \
    | scripts/split-man.pl /tmp/man

Some older versions of git do not support some of the variants of syntax for
path exclusion.  One of the following commands may work for those versions::

  $ scripts/kernel-doc -man \
    $(git grep -l '/\*\*' -- . ':!Documentation' ':!tools') \
    | scripts/split-man.pl /tmp/man

  $ scripts/kernel-doc -man \
    $(git grep -l '/\*\*' -- . ":(exclude)Documentation" ":(exclude)tools") \
    | scripts/split-man.pl /tmp/man