linux/Documentation/kernel-doc-nano-HOWTO.txt
<<
>>
Prefs
   1kernel-doc nano-HOWTO
   2=====================
   3
   4How 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 "**/", but "*/" is
  47preferred in the Linux kernel tree.
  48
  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.
  67 */
  68
  69The 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.
  72
  73The @argument descriptions must begin on the very next line following
  74this opening short function description line, with no intervening
  75empty comment lines.
  76
  77If a function parameter is "..." (varargs), it should be listed in
  78kernel-doc notation as:
  79 * @...: description
  80
  81
  82Example 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.
  91 */
  92
  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
 111Many 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
 127- scripts/basic/docproc.c
 128
 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
 155psdocs', 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,
 159'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>) {
 179    if (/^\.TH \"[^\"]*\" 9 \"([^\"]*)\"/) {
 180        if ($state == 1) { close OUT }
 181        $state = 1;
 182        $fn = "$ARGV[0]/$1.9";
 183        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)?
 211(* @parameterx(space)*: (description of parameter x)?)*
 212(* a blank line)?
 213 * (Description:)? (Description of function)?
 214 * (section header: (section description)? )*
 215(*)?*/
 216
 217All "description" text can span multiple lines, although the
 218function_name & its short description are traditionally on a single line.
 219Description text may also contain blank lines (i.e., lines that contain
 220only a "*").
 221
 222"section header:" names must be unique per function (or struct,
 223union, typedef, enum).
 224
 225Avoid putting a spurious blank line after the function name, or else the
 226description will be repeated!
 227
 228All descriptive text is further processed, scanning for the following special
 229patterns, which are highlighted appropriately.
 230
 231'funcname()' - function
 232'$ENVVAR' - environment variable
 233'&struct_name' - name of a structure (up to two words including 'struct')
 234'@parameter' - name of a parameter
 235'%CONST' - name of a constant.
 236
 237NOTE 1:  The multi-line descriptive text you provide does *not* recognize
 238line breaks, so if you try to format some text nicely, as in:
 239
 240  Return codes
 241    0 - cool
 242    1 - invalid arg
 243    2 - out of memory
 244
 245this will all run together and produce:
 246
 247  Return codes 0 - cool 1 - invalid arg 2 - out of memory
 248
 249NOTE 2:  If the descriptive text you provide has lines that begin with
 250some phrase followed by a colon, each of those phrases will be taken as
 251a new section heading, which means you should similarly try to avoid text
 252like:
 253
 254  Return codes:
 255    0: cool
 256    1: invalid arg
 257    2: out of memory
 258
 259every line of which would start a new section.  Again, probably not
 260what you were after.
 261
 262Take a look around the source tree for examples.
 263
 264
 265kernel-doc for structs, unions, enums, and typedefs
 266---------------------------------------------------
 267
 268Beside functions you can also write documentation for structs, unions,
 269enums and typedefs. Instead of the function name you must write the name
 270of the declaration;  the struct/union/enum/typedef must always precede
 271the name. Nesting of declarations is not supported.
 272Use the argument mechanism to document members or constants.
 273
 274Inside a struct description, you can use the "private:" and "public:"
 275comment tags.  Structure fields that are inside a "private:" area
 276are not listed in the generated output documentation.  The "private:"
 277and "public:" tags must begin immediately following a "/*" comment
 278marker.  They may optionally include comments between the ":" and the
 279ending "*/" marker.
 280
 281Example:
 282
 283/**
 284 * struct my_struct - short description
 285 * @a: first member
 286 * @b: second member
 287 *
 288 * Longer description
 289 */
 290struct my_struct {
 291    int a;
 292    int b;
 293/* private: internal use only */
 294    int c;
 295};
 296
 297
 298Including documentation blocks in source files
 299----------------------------------------------
 300
 301To facilitate having source code and comments close together, you can
 302include kernel-doc documentation blocks that are free-form comments
 303instead of being kernel-doc for functions, structures, unions,
 304enums, or typedefs.  This could be used for something like a
 305theory of operation for a driver or library code, for example.
 306
 307This is done by using a DOC: section keyword with a section title.  E.g.:
 308
 309/**
 310 * DOC: Theory of Operation
 311 *
 312 * The whizbang foobar is a dilly of a gizmo.  It can do whatever you
 313 * want it to do, at any time.  It reads your mind.  Here's how it works.
 314 *
 315 * foo bar splat
 316 *
 317 * The only drawback to this gizmo is that is can sometimes damage
 318 * hardware, software, or its subject(s).
 319 */
 320
 321DOC: sections are used in SGML templates files as indicated below.
 322
 323
 324How to make new SGML template files
 325-----------------------------------
 326
 327SGML template files (*.tmpl) are like normal SGML files, except that
 328they can contain escape sequences where extracted documentation should
 329be inserted.
 330
 331!E<filename> is replaced by the documentation, in <filename>, for
 332functions that are exported using EXPORT_SYMBOL: the function list is
 333collected from files listed in Documentation/DocBook/Makefile.
 334
 335!I<filename> is replaced by the documentation for functions that are
 336_not_ exported using EXPORT_SYMBOL.
 337
 338!D<filename> is used to name additional files to search for functions
 339exported using EXPORT_SYMBOL.
 340
 341!F<filename> <function [functions...]> is replaced by the
 342documentation, in <filename>, for the functions listed.
 343
 344!P<filename> <section title> is replaced by the contents of the DOC:
 345section titled <section title> from <filename>.
 346Spaces are allowed in <section title>; do not quote the <section title>.
 347
 348!C<filename> is replaced by nothing, but makes the tools check that
 349all DOC: sections and documented functions, symbols, etc. are used.
 350This makes sense to use when you use !F/!P only and want to verify
 351that all documentation is included.
 352
 353Tim.
 354*/ <twaugh@redhat.com>
 355
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.