kernel-doc nano-HOWTO
=====================

Many places in the source tree have extractable documentation in the
form of block comments above functions.  The components of this system
are:

- scripts/kernel-doc

  This is a perl script that hunts for the block comments and can mark
  them up directly into DocBook, man, text, and HTML. (No, not
  texinfo.)

- Documentation/DocBook/*.tmpl

  These are SGML template files, which are normal SGML files with
  special place-holders for where the extracted documentation should
  go.

- scripts/docproc.c

  This is a program for converting SGML template files into SGML
  files.  It invokes kernel-doc, giving it the list of functions that
  are to be documented.

- scripts/gen-all-syms

  This is a script that lists the EXPORT_SYMBOL symbols in a list of C
  files.

- scripts/docgen

  This script invokes docproc, telling it which functions are to be
  documented (this list comes from gen-all-syms).

- Makefile

  The targets 'sgmldocs', 'psdocs', and 'pdfdocs' are used to build
  DocBook files, PostScript files, and PDF files in
  Documentation/DocBook.

- Documentation/DocBook/Makefile

  This is where C files are associated with SGML templates.


How to extract the documentation
--------------------------------

If you just want to read the ready-made books on the various
subsystems (see Documentation/DocBook/*.tmpl), just type 'make
psdocs', or 'make pdfdocs', depending on your preference.  If you
would rather read a different format, you can type 'make sgmldocs' and
then use DocBook tools to convert Documentation/DocBook/*.sgml to a
format of your choice (for example, 'db2html ...').

If you want to see man pages instead, you can do this:

$ cd linux
$ scripts/kernel-doc -man $(find -name '*.c') | split-man.pl /tmp/man
$ scripts/kernel-doc -man $(find -name '*.h') | split-man.pl /tmp/man

Here is split-man.pl:

-->
#!/usr/bin/perl

if ($#ARGV < 0) {
   die "where do I put the results?\n";
}

mkdir $ARGV[0],0777;
$state = 0;
while (<STDIN>) {
    if (/^\.TH \"[^\"]*\" 4 \"([^\"]*)\"/) {
	if ($state == 1) { close OUT }
	$state = 1;
	$fn = "$ARGV[0]/$1.4";
	print STDERR "Creating $fn\n";
	open OUT, ">$fn" or die "can't open $fn: $!\n";
	print OUT $_;
    } elsif ($state != 0) {
	print OUT $_;
    }
}

close OUT;
<--

If you just want to view the documentation for one function in one
file, you can do this:

$ scripts/kernel-doc -man -function fn file | nroff -man | less

or this:

$ scripts/kernel-doc -text -function fn file


How to add extractable documentation to your source files
---------------------------------------------------------

The format of the block comment is like this:

/**
 * function_name(:)? (- short description)?
(* @parameterx: (description of parameter x)?)*
(* a blank line)?
 * (Description:)? (Description of function)?
 * (section header: (section description)? )*
(*)?*/

The short function description cannot be multiline, but the other
descriptions can be.

All descriptive text is further processed, scanning for the following special
patterns, which are highlighted appropriately.

'funcname()' - function
'$ENVVAR' - environment variable
'&struct_name' - name of a structure (up to two words including 'struct')
'@parameter' - name of a parameter
'%CONST' - name of a constant.

Take a look around the source tree for examples.


How to make new SGML template files
-----------------------------------

SGML template files (*.tmpl) are like normal SGML files, except that
they can contain escape sequences where extracted documentation should
be inserted.

!E<filename> is replaced by the documentation, in <filename>, for
functions that are exported using EXPORT_SYMBOL: the function list is
collected from files listed in Documentation/DocBook/Makefile.

!I<filename> is replaced by the documentation for functions that are
_not_ exported using EXPORT_SYMBOL.

!F<filename> <function [functions...]> is replaced by the
documentation, in <filename>, for the functions listed.


Tim.
*/ <twaugh@redhat.com>

