549 lines
18 KiB
ReStructuredText
549 lines
18 KiB
ReStructuredText
Writing kernel-doc comments
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===========================
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The Linux kernel source files may contain structured documentation
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comments in the kernel-doc format to describe the functions, types
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and design of the code. It is easier to keep documentation up-to-date
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when it is embedded in source files.
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.. note:: The kernel-doc format is deceptively similar to javadoc,
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gtk-doc or Doxygen, yet distinctively different, for historical
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reasons. The kernel source contains tens of thousands of kernel-doc
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comments. Please stick to the style described here.
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.. note:: kernel-doc does not cover Rust code: please see
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Documentation/rust/general-information.rst instead.
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The kernel-doc structure is extracted from the comments, and proper
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`Sphinx C Domain`_ function and type descriptions with anchors are
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generated from them. The descriptions are filtered for special kernel-doc
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highlights and cross-references. See below for details.
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.. _Sphinx C Domain: http://www.sphinx-doc.org/en/stable/domains.html
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Every function that is exported to loadable modules using
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``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
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comment. Functions and data structures in header files which are intended
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to be used by modules should also have kernel-doc comments.
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It is good practice to also provide kernel-doc formatted documentation
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for functions externally visible to other kernel files (not marked
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``static``). We also recommend providing kernel-doc formatted
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documentation for private (file ``static``) routines, for consistency of
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kernel source code layout. This is lower priority and at the discretion
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of the maintainer of that kernel source file.
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How to format kernel-doc comments
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---------------------------------
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The opening comment mark ``/**`` is used for kernel-doc comments. The
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``kernel-doc`` tool will extract comments marked this way. The rest of
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the comment is formatted like a normal multi-line comment with a column
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of asterisks on the left side, closing with ``*/`` on a line by itself.
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The function and type kernel-doc comments should be placed just before
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the function or type being described in order to maximise the chance
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that somebody changing the code will also change the documentation. The
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overview kernel-doc comments may be placed anywhere at the top indentation
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level.
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Running the ``kernel-doc`` tool with increased verbosity and without actual
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output generation may be used to verify proper formatting of the
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documentation comments. For example::
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scripts/kernel-doc -v -none drivers/foo/bar.c
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The documentation format is verified by the kernel build when it is
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requested to perform extra gcc checks::
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make W=n
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Function documentation
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----------------------
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The general format of a function and function-like macro kernel-doc comment is::
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/**
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* function_name() - Brief description of function.
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* @arg1: Describe the first argument.
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* @arg2: Describe the second argument.
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* One can provide multiple line descriptions
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* for arguments.
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*
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* A longer description, with more discussion of the function function_name()
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* that might be useful to those using or modifying it. Begins with an
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* empty comment line, and may include additional embedded empty
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* comment lines.
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*
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* The longer description may have multiple paragraphs.
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*
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* Context: Describes whether the function can sleep, what locks it takes,
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* releases, or expects to be held. It can extend over multiple
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* lines.
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* Return: Describe the return value of function_name.
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*
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* The return value description can also have multiple paragraphs, and should
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* be placed at the end of the comment block.
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*/
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The brief description following the function name may span multiple lines, and
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ends with an argument description, a blank comment line, or the end of the
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comment block.
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Function parameters
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~~~~~~~~~~~~~~~~~~~
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Each function argument should be described in order, immediately following
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the short function description. Do not leave a blank line between the
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function description and the arguments, nor between the arguments.
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Each ``@argument:`` description may span multiple lines.
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.. note::
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If the ``@argument`` description has multiple lines, the continuation
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of the description should start at the same column as the previous line::
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* @argument: some long description
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* that continues on next lines
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or::
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* @argument:
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* some long description
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* that continues on next lines
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If a function has a variable number of arguments, its description should
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be written in kernel-doc notation as::
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* @...: description
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Function context
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~~~~~~~~~~~~~~~~
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The context in which a function can be called should be described in a
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section named ``Context``. This should include whether the function
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sleeps or can be called from interrupt context, as well as what locks
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it takes, releases and expects to be held by its caller.
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Examples::
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* Context: Any context.
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* Context: Any context. Takes and releases the RCU lock.
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* Context: Any context. Expects <lock> to be held by caller.
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* Context: Process context. May sleep if @gfp flags permit.
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* Context: Process context. Takes and releases <mutex>.
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* Context: Softirq or process context. Takes and releases <lock>, BH-safe.
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* Context: Interrupt context.
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Return values
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~~~~~~~~~~~~~
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The return value, if any, should be described in a dedicated section
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named ``Return``.
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.. note::
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#) The multi-line descriptive text you provide does *not* recognize
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line breaks, so if you try to format some text nicely, as in::
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* Return:
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* 0 - OK
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* -EINVAL - invalid argument
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* -ENOMEM - out of memory
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this will all run together and produce::
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Return: 0 - OK -EINVAL - invalid argument -ENOMEM - out of memory
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So, in order to produce the desired line breaks, you need to use a
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ReST list, e. g.::
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* Return:
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* * 0 - OK to runtime suspend the device
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* * -EBUSY - Device should not be runtime suspended
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#) If the descriptive text you provide has lines that begin with
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some phrase followed by a colon, each of those phrases will be taken
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as a new section heading, which probably won't produce the desired
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effect.
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Structure, union, and enumeration documentation
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-----------------------------------------------
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The general format of a struct, union, and enum kernel-doc comment is::
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/**
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* struct struct_name - Brief description.
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* @member1: Description of member1.
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* @member2: Description of member2.
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* One can provide multiple line descriptions
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* for members.
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*
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* Description of the structure.
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*/
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You can replace the ``struct`` in the above example with ``union`` or
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``enum`` to describe unions or enums. ``member`` is used to mean struct
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and union member names as well as enumerations in an enum.
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The brief description following the structure name may span multiple
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lines, and ends with a member description, a blank comment line, or the
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end of the comment block.
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Members
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~~~~~~~
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Members of structs, unions and enums should be documented the same way
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as function parameters; they immediately succeed the short description
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and may be multi-line.
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Inside a struct or union description, you can use the ``private:`` and
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``public:`` comment tags. Structure fields that are inside a ``private:``
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area are not listed in the generated output documentation.
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The ``private:`` and ``public:`` tags must begin immediately following a
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``/*`` comment marker. They may optionally include comments between the
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``:`` and the ending ``*/`` marker.
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Example::
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/**
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* struct my_struct - short description
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* @a: first member
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* @b: second member
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* @d: fourth member
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*
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* Longer description
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*/
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struct my_struct {
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int a;
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int b;
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/* private: internal use only */
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int c;
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/* public: the next one is public */
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int d;
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};
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Nested structs/unions
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~~~~~~~~~~~~~~~~~~~~~
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It is possible to document nested structs and unions, like::
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/**
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* struct nested_foobar - a struct with nested unions and structs
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* @memb1: first member of anonymous union/anonymous struct
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* @memb2: second member of anonymous union/anonymous struct
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* @memb3: third member of anonymous union/anonymous struct
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* @memb4: fourth member of anonymous union/anonymous struct
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* @bar: non-anonymous union
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* @bar.st1: struct st1 inside @bar
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* @bar.st2: struct st2 inside @bar
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* @bar.st1.memb1: first member of struct st1 on union bar
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* @bar.st1.memb2: second member of struct st1 on union bar
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* @bar.st2.memb1: first member of struct st2 on union bar
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* @bar.st2.memb2: second member of struct st2 on union bar
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*/
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struct nested_foobar {
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/* Anonymous union/struct*/
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union {
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struct {
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int memb1;
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int memb2;
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};
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struct {
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void *memb3;
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int memb4;
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};
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};
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union {
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struct {
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int memb1;
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int memb2;
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} st1;
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struct {
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void *memb1;
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int memb2;
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} st2;
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} bar;
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};
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.. note::
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#) When documenting nested structs or unions, if the struct/union ``foo``
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is named, the member ``bar`` inside it should be documented as
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``@foo.bar:``
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#) When the nested struct/union is anonymous, the member ``bar`` in it
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should be documented as ``@bar:``
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In-line member documentation comments
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The structure members may also be documented in-line within the definition.
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There are two styles, single-line comments where both the opening ``/**`` and
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closing ``*/`` are on the same line, and multi-line comments where they are each
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on a line of their own, like all other kernel-doc comments::
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/**
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* struct foo - Brief description.
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* @foo: The Foo member.
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*/
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struct foo {
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int foo;
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/**
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* @bar: The Bar member.
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*/
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int bar;
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/**
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* @baz: The Baz member.
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*
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* Here, the member description may contain several paragraphs.
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*/
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int baz;
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union {
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/** @foobar: Single line description. */
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int foobar;
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};
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/** @bar2: Description for struct @bar2 inside @foo */
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struct {
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/**
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* @bar2.barbar: Description for @barbar inside @foo.bar2
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*/
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int barbar;
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} bar2;
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};
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Typedef documentation
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---------------------
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The general format of a typedef kernel-doc comment is::
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/**
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* typedef type_name - Brief description.
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*
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* Description of the type.
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*/
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Typedefs with function prototypes can also be documented::
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/**
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* typedef type_name - Brief description.
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* @arg1: description of arg1
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* @arg2: description of arg2
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*
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* Description of the type.
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*
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* Context: Locking context.
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* Return: Meaning of the return value.
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*/
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typedef void (*type_name)(struct v4l2_ctrl *arg1, void *arg2);
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Highlights and cross-references
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-------------------------------
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The following special patterns are recognized in the kernel-doc comment
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descriptive text and converted to proper reStructuredText markup and `Sphinx C
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Domain`_ references.
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.. attention:: The below are **only** recognized within kernel-doc comments,
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**not** within normal reStructuredText documents.
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``funcname()``
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Function reference.
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``@parameter``
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Name of a function parameter. (No cross-referencing, just formatting.)
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``%CONST``
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Name of a constant. (No cross-referencing, just formatting.)
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````literal````
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A literal block that should be handled as-is. The output will use a
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``monospaced font``.
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Useful if you need to use special characters that would otherwise have some
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meaning either by kernel-doc script or by reStructuredText.
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This is particularly useful if you need to use things like ``%ph`` inside
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a function description.
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``$ENVVAR``
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Name of an environment variable. (No cross-referencing, just formatting.)
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``&struct name``
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Structure reference.
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``&enum name``
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Enum reference.
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``&typedef name``
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Typedef reference.
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``&struct_name->member`` or ``&struct_name.member``
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Structure or union member reference. The cross-reference will be to the struct
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or union definition, not the member directly.
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``&name``
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A generic type reference. Prefer using the full reference described above
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instead. This is mostly for legacy comments.
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Cross-referencing from reStructuredText
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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No additional syntax is needed to cross-reference the functions and types
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defined in the kernel-doc comments from reStructuredText documents.
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Just end function names with ``()`` and write ``struct``, ``union``, ``enum``
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or ``typedef`` before types.
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For example::
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See foo().
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See struct foo.
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See union bar.
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See enum baz.
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See typedef meh.
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However, if you want custom text in the cross-reference link, that can be done
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through the following syntax::
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See :c:func:`my custom link text for function foo <foo>`.
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See :c:type:`my custom link text for struct bar <bar>`.
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For further details, please refer to the `Sphinx C Domain`_ documentation.
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Overview documentation comments
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-------------------------------
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To facilitate having source code and comments close together, you can include
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kernel-doc documentation blocks that are free-form comments instead of being
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kernel-doc for functions, structures, unions, enums, or typedefs. This could be
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used for something like a theory of operation for a driver or library code, for
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example.
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This is done by using a ``DOC:`` section keyword with a section title.
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The general format of an overview or high-level documentation comment is::
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/**
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* DOC: Theory of Operation
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*
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* The whizbang foobar is a dilly of a gizmo. It can do whatever you
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* want it to do, at any time. It reads your mind. Here's how it works.
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*
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* foo bar splat
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*
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* The only drawback to this gizmo is that is can sometimes damage
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* hardware, software, or its subject(s).
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*/
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The title following ``DOC:`` acts as a heading within the source file, but also
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as an identifier for extracting the documentation comment. Thus, the title must
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be unique within the file.
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Including kernel-doc comments
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=============================
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The documentation comments may be included in any of the reStructuredText
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documents using a dedicated kernel-doc Sphinx directive extension.
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The kernel-doc directive is of the format::
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.. kernel-doc:: source
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:option:
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The *source* is the path to a source file, relative to the kernel source
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tree. The following directive options are supported:
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export: *[source-pattern ...]*
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Include documentation for all functions in *source* that have been exported
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using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either in *source* or in any
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of the files specified by *source-pattern*.
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The *source-pattern* is useful when the kernel-doc comments have been placed
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in header files, while ``EXPORT_SYMBOL`` and ``EXPORT_SYMBOL_GPL`` are next to
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the function definitions.
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Examples::
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.. kernel-doc:: lib/bitmap.c
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:export:
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.. kernel-doc:: include/net/mac80211.h
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:export: net/mac80211/*.c
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internal: *[source-pattern ...]*
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Include documentation for all functions and types in *source* that have
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**not** been exported using ``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` either
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in *source* or in any of the files specified by *source-pattern*.
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Example::
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.. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
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:internal:
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identifiers: *[ function/type ...]*
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Include documentation for each *function* and *type* in *source*.
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If no *function* is specified, the documentation for all functions
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and types in the *source* will be included.
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Examples::
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.. kernel-doc:: lib/bitmap.c
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:identifiers: bitmap_parselist bitmap_parselist_user
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.. kernel-doc:: lib/idr.c
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:identifiers:
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no-identifiers: *[ function/type ...]*
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Exclude documentation for each *function* and *type* in *source*.
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Example::
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.. kernel-doc:: lib/bitmap.c
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:no-identifiers: bitmap_parselist
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functions: *[ function/type ...]*
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This is an alias of the 'identifiers' directive and deprecated.
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doc: *title*
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Include documentation for the ``DOC:`` paragraph identified by *title* in
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*source*. Spaces are allowed in *title*; do not quote the *title*. The *title*
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is only used as an identifier for the paragraph, and is not included in the
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output. Please make sure to have an appropriate heading in the enclosing
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reStructuredText document.
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Example::
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.. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
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:doc: High Definition Audio over HDMI and Display Port
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Without options, the kernel-doc directive includes all documentation comments
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from the source file.
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The kernel-doc extension is included in the kernel source tree, at
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``Documentation/sphinx/kerneldoc.py``. Internally, it uses the
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``scripts/kernel-doc`` script to extract the documentation comments from the
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source.
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.. _kernel_doc:
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How to use kernel-doc to generate man pages
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-------------------------------------------
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If you just want to use kernel-doc to generate man pages you can do this
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from the kernel git tree::
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$ scripts/kernel-doc -man \
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$(git grep -l '/\*\*' -- :^Documentation :^tools) \
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| scripts/split-man.pl /tmp/man
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Some older versions of git do not support some of the variants of syntax for
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path exclusion. One of the following commands may work for those versions::
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$ scripts/kernel-doc -man \
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$(git grep -l '/\*\*' -- . ':!Documentation' ':!tools') \
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| scripts/split-man.pl /tmp/man
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$ scripts/kernel-doc -man \
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$(git grep -l '/\*\*' -- . ":(exclude)Documentation" ":(exclude)tools") \
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| scripts/split-man.pl /tmp/man
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