Including kernel-doc comments

The Linux kernel source files may contain structured documentation comments, or kernel-doc comments to describe the functions and types and design of the code. The documentation comments may be included to any of the reStructuredText documents using a dedicated kernel-doc Sphinx directive extension.

The kernel-doc directive is of the format:

.. kernel-doc:: source

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.


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

.. 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.


.. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
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 Spaces are allowed in title; do not quote the title.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.


.. 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.


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

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/ Internally, it uses the scripts/kernel-doc script to extract the documentation comments from the source.

Writing kernel-doc comments

In order to provide embedded, “C” friendly, easy to maintain, but consistent and extractable overview, function and type documentation, the Linux kernel has adopted a consistent style for documentation comments. The format for this documentation is called the kernel-doc format, described below. This style embeds the documentation within the source files, using a few simple conventions for adding documentation paragraphs and documenting functions and their parameters, structures and unions and their members, enumerations, and typedefs.


The kernel-doc format is deceptively similar to 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 scripts/kernel-doc script is used by the Sphinx kernel-doc extension in the documentation build to extract this embedded documentation into the various HTML, PDF, and other format 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 the Linux kernel source.

How to format kernel-doc comments

The opening comment mark /** is reserved for kernel-doc comments. Only comments so marked will be considered by the kernel-doc tool. Use it only for comment blocks that contain kernel-doc formatted comments. The usual */ should be used as the closing comment marker. The lines in between should be prefixed by  *  (space star space).

The function and type kernel-doc comments should be placed just before the function or type being described. The overview kernel-doc comments may be freely placed at the top indentation level.

Example kernel-doc function comment:

 * foobar() - Brief description of foobar.
 * @argument1: Description of parameter argument1 of foobar.
 * @argument2: Description of parameter argument2 of foobar.
 * Longer description of foobar.
 * Return: Description of return value of foobar.
int foobar(int argument1, char *argument2)

The format is similar for documentation for structures, enums, paragraphs, etc. See the sections below for specific details of each type.

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

Parameters and member arguments

The kernel-doc function comments describe each parameter to the function and function typedefs or each member of struct/union, in order, with the @argument: descriptions. For each non-private member argument, one @argument definition is needed.

The @argument: descriptions begin on the very next line following the opening brief function description line, with no intervening blank comment lines.

The @argument: descriptions may span multiple lines.


If the @argument description has multiple lines, the continuation of the description should be starting exactly at the same column as the previous line, e. g.:

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


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

If a function or typedef parameter argument is ... (e. g. a variable number of arguments), its description should be listed in kernel-doc notation as:

* @...: description

Private members

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.


 * 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;

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.
 * Return: Describe the return value of foobar.
 * 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.

Return values

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


  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 - 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
  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, with 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.
 * @argument: Description of member member_name.
 * Description of the structure.

On the above, struct is used to mean structs. You can also use union and enum to describe unions and enums. argument 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.

The kernel-doc data structure comments describe each member of the structure, in order, with the member descriptions.

Nested structs/unions

It is possible to document nested structs unions, like:

 * struct nested_foobar - a struct with nested unions and structs
 * @arg1: - first argument of anonymous union/anonymous struct
 * @arg2: - second argument of anonymous union/anonymous struct
 * @arg3: - third argument of anonymous union/anonymous struct
 * @arg4: - fourth argument of anonymous union/anonymous struct
 * @bar.st1.arg1 - first argument of struct st1 on union bar
 * @bar.st1.arg2 - second argument of struct st1 on union bar
 * @bar.st2.arg1 - first argument of struct st2 on union bar
 * @bar.st2.arg2 - second argument of struct st2 on union bar
struct nested_foobar {
  /* Anonymous union/struct*/
  union {
    struct {
      int arg1;
      int arg2;
    struct {
      void *arg3;
      int arg4;
  union {
    struct {
      int arg1;
      int arg2;
    } st1;
    struct {
      void *arg1;
      int arg2;
    } st2;
  } bar;


  1. When documenting nested structs or unions, if the struct/union foo is named, the argument bar inside it should be documented as
  2. When the nested struct/union is anonymous, the argument bar on it should be documented as @bar:

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.
 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.


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

Function reference.
Name of a function parameter. (No cross-referencing, just formatting.)
Name of a constant. (No cross-referencing, just formatting.)

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 of by reStructuredText.

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

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.
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.

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;
      /** @foobar: Single line description. */
      int foobar;

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.


We definitely need kernel-doc formatted documentation for functions that are exported to loadable modules using EXPORT_SYMBOL or EXPORT_SYMBOL_GPL.

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.

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 '/\*\*' |grep -v Documentation/) | ./ /tmp/man

Using the small script below:


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;