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 first line, with the short description, must be on a single line. 70 71The @argument descriptions must begin on the very next line following 72this opening short function description line, with no intervening 73empty comment lines. 74 75If a function parameter is "..." (varargs), it should be listed in 76kernel-doc notation as: 77 * @...: description 78 79 80Example kernel-doc data structure comment. 81 82/** 83 * struct blah - the basic blah structure 84 * @mem1: describe the first member of struct blah 85 * @mem2: describe the second member of struct blah, 86 * perhaps with more lines and words. 87 * 88 * Longer description of this structure. 89 */ 90 91The kernel-doc function comments describe each parameter to the 92function, in order, with the @name lines. 93 94The kernel-doc data structure comments describe each structure member 95in the data structure, with the @name lines. 96 97The longer description formatting is "reflowed", losing your line 98breaks. So presenting carefully formatted lists within these 99descriptions won't work so well; derived documentation will lose 100the formatting. 101 102See the section below "How to add extractable documentation to your 103source files" for more details and notes on how to format kernel-doc 104comments. 105 106Components of the kernel-doc system 107----------------------------------- 108 109Many places in the source tree have extractable documentation in the 110form of block comments above functions. The components of this system 111are: 112 113- scripts/kernel-doc 114 115 This is a perl script that hunts for the block comments and can mark 116 them up directly into DocBook, man, text, and HTML. (No, not 117 texinfo.) 118 119- Documentation/DocBook/*.tmpl 120 121 These are SGML template files, which are normal SGML files with 122 special place-holders for where the extracted documentation should 123 go. 124 125- scripts/basic/docproc.c 126 127 This is a program for converting SGML template files into SGML 128 files. When a file is referenced it is searched for symbols 129 exported (EXPORT_SYMBOL), to be able to distinguish between internal 130 and external functions. 131 It invokes kernel-doc, giving it the list of functions that 132 are to be documented. 133 Additionally it is used to scan the SGML template files to locate 134 all the files referenced herein. This is used to generate dependency 135 information as used by make. 136 137- Makefile 138 139 The targets 'sgmldocs', 'psdocs', 'pdfdocs', and 'htmldocs' are used 140 to build DocBook files, PostScript files, PDF files, and html files 141 in Documentation/DocBook. 142 143- Documentation/DocBook/Makefile 144 145 This is where C files are associated with SGML templates. 146 147 148How to extract the documentation 149-------------------------------- 150 151If you just want to read the ready-made books on the various 152subsystems (see Documentation/DocBook/*.tmpl), just type 'make 153psdocs', or 'make pdfdocs', or 'make htmldocs', depending on your 154preference. If you would rather read a different format, you can type 155'make sgmldocs' and then use DocBook tools to convert 156Documentation/DocBook/*.sgml to a format of your choice (for example, 157'db2html ...' if 'make htmldocs' was not defined). 158 159If you want to see man pages instead, you can do this: 160 161$ cd linux 162$ scripts/kernel-doc -man $(find -name '*.c') | split-man.pl /tmp/man 163$ scripts/kernel-doc -man $(find -name '*.h') | split-man.pl /tmp/man 164 165Here is split-man.pl: 166 167--> 168#!/usr/bin/perl 169 170if ($#ARGV < 0) { 171 die "where do I put the results?\n"; 172} 173 174mkdir $ARGV[0],0777; 175$state = 0; 176while (<STDIN>) { 177 if (/^\.TH \"[^\"]*\" 9 \"([^\"]*)\"/) { 178 if ($state == 1) { close OUT } 179 $state = 1; 180 $fn = "$ARGV[0]/$1.9"; 181 print STDERR "Creating $fn\n"; 182 open OUT, ">$fn" or die "can't open $fn: $!\n"; 183 print OUT $_; 184 } elsif ($state != 0) { 185 print OUT $_; 186 } 187} 188 189close OUT; 190<-- 191 192If you just want to view the documentation for one function in one 193file, you can do this: 194 195$ scripts/kernel-doc -man -function fn file | nroff -man | less 196 197or this: 198 199$ scripts/kernel-doc -text -function fn file 200 201 202How to add extractable documentation to your source files 203--------------------------------------------------------- 204 205The format of the block comment is like this: 206 207/** 208 * function_name(:)? (- short description)? 209(* @parameterx(space)*: (description of parameter x)?)* 210(* a blank line)? 211 * (Description:)? (Description of function)? 212 * (section header: (section description)? )* 213(*)?*/ 214 215The short function description ***cannot be multiline***, but the other 216descriptions can be (and they can contain blank lines). If you continue 217that initial short description onto a second line, that second line will 218appear further down at the beginning of the description section, which is 219almost certainly not what you had in mind. 220 221Avoid putting a spurious blank line after the function name, or else the 222description will be repeated! 223 224All descriptive text is further processed, scanning for the following special 225patterns, which are highlighted appropriately. 226 227'funcname()' - function 228'$ENVVAR' - environment variable 229'&struct_name' - name of a structure (up to two words including 'struct') 230'@parameter' - name of a parameter 231'%CONST' - name of a constant. 232 233NOTE 1: The multi-line descriptive text you provide does *not* recognize 234line breaks, so if you try to format some text nicely, as in: 235 236 Return codes 237 0 - cool 238 1 - invalid arg 239 2 - out of memory 240 241this will all run together and produce: 242 243 Return codes 0 - cool 1 - invalid arg 2 - out of memory 244 245NOTE 2: If the descriptive text you provide has lines that begin with 246some phrase followed by a colon, each of those phrases will be taken as 247a new section heading, which means you should similarly try to avoid text 248like: 249 250 Return codes: 251 0: cool 252 1: invalid arg 253 2: out of memory 254 255every line of which would start a new section. Again, probably not 256what you were after. 257 258Take a look around the source tree for examples. 259 260 261kernel-doc for structs, unions, enums, and typedefs 262--------------------------------------------------- 263 264Beside functions you can also write documentation for structs, unions, 265enums and typedefs. Instead of the function name you must write the name 266of the declaration; the struct/union/enum/typedef must always precede 267the name. Nesting of declarations is not supported. 268Use the argument mechanism to document members or constants. 269 270Inside a struct description, you can use the "private:" and "public:" 271comment tags. Structure fields that are inside a "private:" area 272are not listed in the generated output documentation. 273 274Example: 275 276/** 277 * struct my_struct - short description 278 * @a: first member 279 * @b: second member 280 * 281 * Longer description 282 */ 283struct my_struct { 284 int a; 285 int b; 286/* private: */ 287 int c; 288}; 289 290 291Including documentation blocks in source files 292---------------------------------------------- 293 294To facilitate having source code and comments close together, you can 295include kernel-doc documentation blocks that are free-form comments 296instead of being kernel-doc for functions, structures, unions, 297enums, or typedefs. This could be used for something like a 298theory of operation for a driver or library code, for example. 299 300This is done by using a DOC: section keyword with a section title. E.g.: 301 302/** 303 * DOC: Theory of Operation 304 * 305 * The whizbang foobar is a dilly of a gizmo. It can do whatever you 306 * want it to do, at any time. It reads your mind. Here's how it works. 307 * 308 * foo bar splat 309 * 310 * The only drawback to this gizmo is that is can sometimes damage 311 * hardware, software, or its subject(s). 312 */ 313 314DOC: sections are used in SGML templates files as indicated below. 315 316 317How to make new SGML template files 318----------------------------------- 319 320SGML template files (*.tmpl) are like normal SGML files, except that 321they can contain escape sequences where extracted documentation should 322be inserted. 323 324!E<filename> is replaced by the documentation, in <filename>, for 325functions that are exported using EXPORT_SYMBOL: the function list is 326collected from files listed in Documentation/DocBook/Makefile. 327 328!I<filename> is replaced by the documentation for functions that are 329_not_ exported using EXPORT_SYMBOL. 330 331!D<filename> is used to name additional files to search for functions 332exported using EXPORT_SYMBOL. 333 334!F<filename> <function [functions...]> is replaced by the 335documentation, in <filename>, for the functions listed. 336 337!P<filename> <section title> is replaced by the contents of the DOC: 338section titled <section title> from <filename>. 339Spaces are allowed in <section title>; do not quote the <section title>. 340 341Tim. 342*/ <twaugh@redhat.com> 343