docs: get rid of kernel-doc-nano-HOWTO.txt

	- directory with info on the Linux ISDN support, and supported cards.

kbuild/

	- directory with info about the kernel build process.

kernel-doc-nano-HOWTO.txt

	- outdated info about kernel-doc documentation.

kdump/

	- directory with mini HowTo on getting the crash dump code to work.

doc-guide/

NOTE: this document is outdated and will eventually be removed.  See

Documentation/doc-guide/ for current information.

kernel-doc nano-HOWTO

=====================

How to format kernel-doc comments

---------------------------------

In order to provide embedded, 'C' friendly, easy to maintain,

but consistent and extractable documentation of the functions and

data structures in the Linux kernel, the Linux kernel has adopted

a consistent style for documenting functions and their parameters,

and structures and their members.

The format for this documentation is called the kernel-doc format.

It is documented in this Documentation/kernel-doc-nano-HOWTO.txt file.

This style embeds the documentation within the source files, using

a few simple conventions.  The scripts/kernel-doc perl script, the

Documentation/sphinx/kerneldoc.py Sphinx extension and other tools understand

these conventions, and are used to extract this embedded documentation

into various documents.

In order to provide good documentation of kernel functions and data

structures, please use the following conventions to format your

kernel-doc comments in Linux kernel source.

We definitely need kernel-doc formatted documentation for functions

that are exported to loadable modules using EXPORT_SYMBOL.

We also look to 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.  But this is lower priority and at the

discretion of the MAINTAINER of that kernel source file.

Data structures visible in kernel include files should also be

documented using kernel-doc formatted comments.

The opening comment mark "/**" is reserved for kernel-doc comments.

Only comments so marked will be considered by the kernel-doc scripts,

and any comment so marked must be in kernel-doc format.  Do not use

"/**" to be begin a comment block unless the comment block contains

kernel-doc formatted comments.  The closing comment marker for

kernel-doc comments can be either "*/" or "**/", but "*/" is

preferred in the Linux kernel tree.

Kernel-doc comments should be placed just before the function

or data structure being described.

Example kernel-doc function comment:

/**

 * foobar() - short function description of foobar

 * @arg1:	Describe the first argument to foobar.

 * @arg2:	Describe the second argument to foobar.

 *		One can provide multiple line descriptions

 *		for arguments.

 *

 * A longer description, with more discussion of the function foobar()

 * that might be useful to those using or modifying it.  Begins with

 * empty comment line, and may include additional embedded empty

 * comment lines.

 *

 * The longer description can have multiple paragraphs.

 *

 * Return: Describe the return value of foobar.

 */

The short description following the subject can span multiple lines

and ends with an @argument description, an empty line or the end of

the comment block.

The @argument descriptions must begin on the very next line following

this opening short function description line, with no intervening

empty comment lines.

If a function parameter is "..." (varargs), it should be listed in

kernel-doc notation as:

 * @...: description

The return value, if any, should be described in a dedicated section

named "Return".

Example kernel-doc data structure comment.

/**

 * struct blah - the basic blah structure

 * @mem1:	describe the first member of struct blah

 * @mem2:	describe the second member of struct blah,

 *		perhaps with more lines and words.

 *

 * Longer description of this structure.

 */

The kernel-doc function comments describe each parameter to the

function, in order, with the @name lines.

The kernel-doc data structure comments describe each structure member

in the data structure, with the @name lines.

The longer description formatting is "reflowed", losing your line

breaks.  So presenting carefully formatted lists within these

descriptions won't work so well; derived documentation will lose

the formatting.

See the section below "How to add extractable documentation to your

source files" for more details and notes on how to format kernel-doc

comments.

Components of the kernel-doc system

-----------------------------------

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, ReST, man, text, and HTML. (No, not

  texinfo.)

- scripts/docproc.c

  This is a program for converting SGML template files into SGML

  files. When a file is referenced it is searched for symbols

  exported (EXPORT_SYMBOL), to be able to distinguish between internal

  and external functions.

  It invokes kernel-doc, giving it the list of functions that

  are to be documented.

  Additionally it is used to scan the SGML template files to locate

  all the files referenced herein. This is used to generate dependency

  information as used by make.

- Makefile

  The targets 'xmldocs', 'latexdocs', 'pdfdocs', 'epubdocs'and 'htmldocs'

  are used to build XML DocBook files, LaTeX files, PDF files,

  ePub files and html files in Documentation/.

How to extract the documentation

--------------------------------

If you just want to read the ready-made books on the various

subsystems, just type 'make epubdocs', or 'make pdfdocs', or 'make htmldocs',

depending on your preference.  If you would rather read a different format,

you can type 'make xmldocs' and then use DocBook tools to convert

Documentation/output/*.xml to a format of your choice (for example,

'db2html ...' if 'make htmldocs' was not defined).

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 \"[^\"]*\" 9 \"([^\"]*)\"/) {

	if ($state == 1) { close OUT }

	$state = 1;

	$fn = "$ARGV[0]/$1.9";

	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(space)*: (description of parameter x)?)*

(* a blank line)?

 * (Description:)? (Description of function)?

 * (section header: (section description)? )*

(*)?*/

All "description" text can span multiple lines, although the

function_name & its short description are traditionally on a single line.

Description text may also contain blank lines (i.e., lines that contain

only a "*").

"section header:" names must be unique per function (or struct,

union, typedef, enum).

Use the section header "Return" for sections describing the return value

of a function.

Avoid putting a spurious blank line after the function name, or else the

description will be repeated!

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.

NOTE 1:  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 - cool

    1 - invalid arg

    2 - out of memory

this will all run together and produce:

  Return: 0 - cool 1 - invalid arg 2 - out of memory

NOTE 2:  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 means you should similarly try to avoid text

like:

  Return:

    0: cool

    1: invalid arg

    2: out of memory

every line of which would start a new section.  Again, probably not

what you were after.

Take a look around the source tree for examples.

kernel-doc for structs, unions, enums, and typedefs

---------------------------------------------------

Beside functions you can also write documentation for structs, unions,

enums and typedefs. Instead of the function name you must write the name

of the declaration;  the struct/union/enum/typedef must always precede

the name. Nesting of declarations is not supported.

Use the argument mechanism to document members or constants.

Inside a struct 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

 *

 * Longer description

 */

struct my_struct {

    int a;

    int b;

/* private: internal use only */

    int c;

};

Including documentation blocks in source files

----------------------------------------------

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.  E.g.:

/**

 * 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).

 */

DOC: sections are used in ReST files.

Tim.

*/ <twaugh@redhat.com>

and print formatted documentation to standard output.

The documentation comments are identified by "/**" opening comment mark. See

Documentation/kernel-doc-nano-HOWTO.txt for the documentation comment syntax.

Documentation/doc-guide/kernel-doc.rst for the documentation comment syntax.

Output format selection (mutually exclusive):

  -docbook		Output DocBook format.