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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
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tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/doc-guide/kernel-doc.rst
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Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+.. title:: Kernel-doc comments
+
+===========================
+Writing kernel-doc comments
+===========================
+
+The Linux kernel source files may contain structured documentation
+comments in the kernel-doc format to describe the functions, types
+and design of the code. It is easier to keep documentation up-to-date
+when it is embedded in source files.
+
+.. note:: The kernel-doc format is deceptively similar to javadoc,
+ 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.
+
+.. note:: kernel-doc does not cover Rust code: please see
+ Documentation/rust/general-information.rst instead.
+
+The kernel-doc structure is extracted from the comments, and proper
+`Sphinx C Domain`_ function and type descriptions with anchors are
+generated from them. The descriptions are filtered for special kernel-doc
+highlights and cross-references. See below for details.
+
+.. _Sphinx C Domain: http://www.sphinx-doc.org/en/stable/domains.html
+
+Every function that is exported to loadable modules using
+``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
+comment. Functions and data structures in header files which are intended
+to be used by modules should also have kernel-doc comments.
+
+It is good practice to also 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. This is lower priority and at the discretion
+of the maintainer of that kernel source file.
+
+How to format kernel-doc comments
+---------------------------------
+
+The opening comment mark ``/**`` is used for kernel-doc comments. The
+``kernel-doc`` tool will extract comments marked this way. The rest of
+the comment is formatted like a normal multi-line comment with a column
+of asterisks on the left side, closing with ``*/`` on a line by itself.
+
+The function and type kernel-doc comments should be placed just before
+the function or type being described in order to maximise the chance
+that somebody changing the code will also change the documentation. The
+overview kernel-doc comments may be placed anywhere at the top indentation
+level.
+
+Running the ``kernel-doc`` tool with increased verbosity and without actual
+output generation may be used to verify proper formatting of the
+documentation comments. For example::
+
+ scripts/kernel-doc -v -none drivers/foo/bar.c
+
+The documentation format is verified by the kernel build when it is
+requested to perform extra gcc checks::
+
+ make W=n
+
+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.
+ *
+ * Context: Describes whether the function can sleep, what locks it takes,
+ * releases, or expects to be held. It can extend over multiple
+ * lines.
+ * Return: Describe the return value of function_name.
+ *
+ * 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.
+
+Function parameters
+~~~~~~~~~~~~~~~~~~~
+
+Each function argument should be described in order, immediately following
+the short function description. Do not leave a blank line between the
+function description and the arguments, nor between the arguments.
+
+Each ``@argument:`` description may span multiple lines.
+
+.. note::
+
+ If the ``@argument`` description has multiple lines, the continuation
+ of the description should start at the same column as the previous line::
+
+ * @argument: some long description
+ * that continues on next lines
+
+ or::
+
+ * @argument:
+ * some long description
+ * that continues on next lines
+
+If a function has a variable number of arguments, its description should
+be written in kernel-doc notation as::
+
+ * @...: description
+
+Function context
+~~~~~~~~~~~~~~~~
+
+The context in which a function can be called should be described in a
+section named ``Context``. This should include whether the function
+sleeps or can be called from interrupt context, as well as what locks
+it takes, releases and expects to be held by its caller.
+
+Examples::
+
+ * Context: Any context.
+ * Context: Any context. Takes and releases the RCU lock.
+ * Context: Any context. Expects <lock> to be held by caller.
+ * Context: Process context. May sleep if @gfp flags permit.
+ * Context: Process context. Takes and releases <mutex>.
+ * Context: Softirq or process context. Takes and releases <lock>, BH-safe.
+ * Context: Interrupt context.
+
+Return values
+~~~~~~~~~~~~~
+
+The return value, if any, should be described in a dedicated section
+named ``Return``.
+
+.. note::
+
+ #) 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
+
+ #) 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 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.
+ * @member1: Description of member1.
+ * @member2: Description of member2.
+ * One can provide multiple line descriptions
+ * for members.
+ *
+ * Description of the structure.
+ */
+
+You can replace the ``struct`` in the above example with ``union`` or
+``enum`` to describe unions or enums. ``member`` 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.
+
+Members
+~~~~~~~
+
+Members of structs, unions and enums should be documented the same way
+as function parameters; they immediately succeed the short description
+and may be multi-line.
+
+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.
+
+Example::
+
+ /**
+ * 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;
+ };
+
+Nested structs/unions
+~~~~~~~~~~~~~~~~~~~~~
+
+It is possible to document nested structs and unions, like::
+
+ /**
+ * struct nested_foobar - a struct with nested unions and structs
+ * @memb1: first member of anonymous union/anonymous struct
+ * @memb2: second member of anonymous union/anonymous struct
+ * @memb3: third member of anonymous union/anonymous struct
+ * @memb4: fourth member of anonymous union/anonymous struct
+ * @bar: non-anonymous union
+ * @bar.st1: struct st1 inside @bar
+ * @bar.st2: struct st2 inside @bar
+ * @bar.st1.memb1: first member of struct st1 on union bar
+ * @bar.st1.memb2: second member of struct st1 on union bar
+ * @bar.st2.memb1: first member of struct st2 on union bar
+ * @bar.st2.memb2: second member of struct st2 on union bar
+ */
+ struct nested_foobar {
+ /* Anonymous union/struct*/
+ union {
+ struct {
+ int memb1;
+ int memb2;
+ };
+ struct {
+ void *memb3;
+ int memb4;
+ };
+ };
+ union {
+ struct {
+ int memb1;
+ int memb2;
+ } st1;
+ struct {
+ void *memb1;
+ int memb2;
+ } st2;
+ } bar;
+ };
+
+.. note::
+
+ #) When documenting nested structs or unions, if the struct/union ``foo``
+ is named, the member ``bar`` inside it should be documented as
+ ``@foo.bar:``
+ #) When the nested struct/union is anonymous, the member ``bar`` in it
+ should be documented as ``@bar:``
+
+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;
+ union {
+ /** @foobar: Single line description. */
+ int foobar;
+ };
+ /** @bar2: Description for struct @bar2 inside @foo */
+ struct {
+ /**
+ * @bar2.barbar: Description for @barbar inside @foo.bar2
+ */
+ int barbar;
+ } bar2;
+ };
+
+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.
+ *
+ * Context: Locking context.
+ * Return: Meaning of the return value.
+ */
+ 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.
+
+.. attention:: The below are **only** recognized within kernel-doc comments,
+ **not** within normal reStructuredText documents.
+
+``funcname()``
+ Function reference.
+
+``@parameter``
+ Name of a function parameter. (No cross-referencing, just formatting.)
+
+``%CONST``
+ Name of a constant. (No cross-referencing, just formatting.)
+
+````literal````
+ 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 or by reStructuredText.
+
+ This is particularly useful if you need to use things like ``%ph`` inside
+ a function description.
+
+``$ENVVAR``
+ 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.
+
+``&name``
+ A generic type reference. Prefer using the full reference described above
+ instead. This is mostly for legacy comments.
+
+Cross-referencing from reStructuredText
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+No additional syntax is needed to cross-reference the functions and types
+defined in the kernel-doc comments from reStructuredText documents.
+Just end function names with ``()`` and write ``struct``, ``union``, ``enum``
+or ``typedef`` before types.
+For example::
+
+ See foo().
+ See struct foo.
+ See union bar.
+ See enum baz.
+ See typedef meh.
+
+However, if you want custom text in the cross-reference link, that can be done
+through the following syntax::
+
+ See :c:func:`my custom link text for function foo <foo>`.
+ See :c:type:`my custom link text for struct bar <bar>`.
+
+For further details, please refer to the `Sphinx C Domain`_ documentation.
+
+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.
+
+=============================
+Including kernel-doc comments
+=============================
+
+The documentation comments may be included in any of the reStructuredText
+documents using a dedicated kernel-doc Sphinx directive extension.
+
+The kernel-doc directive is of the format::
+
+ .. kernel-doc:: source
+ :option:
+
+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.
+
+ Examples::
+
+ .. kernel-doc:: lib/bitmap.c
+ :export:
+
+ .. 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*.
+
+ Example::
+
+ .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
+ :internal:
+
+identifiers: *[ function/type ...]*
+ Include documentation for each *function* and *type* in *source*.
+ If no *function* is specified, the documentation for all functions
+ and types in the *source* will be included.
+
+ Examples::
+
+ .. kernel-doc:: lib/bitmap.c
+ :identifiers: bitmap_parselist bitmap_parselist_user
+
+ .. kernel-doc:: lib/idr.c
+ :identifiers:
+
+no-identifiers: *[ function/type ...]*
+ Exclude documentation for each *function* and *type* in *source*.
+
+ Example::
+
+ .. kernel-doc:: lib/bitmap.c
+ :no-identifiers: bitmap_parselist
+
+functions: *[ function/type ...]*
+ This is an alias of the 'identifiers' directive and deprecated.
+
+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.
+
+ Example::
+
+ .. kernel-doc:: drivers/gpu/drm/i915/intel_audio.c
+ :doc: High Definition Audio over HDMI and Display Port
+
+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/kerneldoc.py``. Internally, it uses the
+``scripts/kernel-doc`` script to extract the documentation comments from the
+source.
+
+.. _kernel_doc:
+
+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 '/\*\*' -- :^Documentation :^tools) \
+ | scripts/split-man.pl /tmp/man
+
+Some older versions of git do not support some of the variants of syntax for
+path exclusion. One of the following commands may work for those versions::
+
+ $ scripts/kernel-doc -man \
+ $(git grep -l '/\*\*' -- . ':!Documentation' ':!tools') \
+ | scripts/split-man.pl /tmp/man
+
+ $ scripts/kernel-doc -man \
+ $(git grep -l '/\*\*' -- . ":(exclude)Documentation" ":(exclude)tools") \
+ | scripts/split-man.pl /tmp/man