Documentation/doc-guide/sphinx.rst - linux/kernel/git/dtor/input - Git at Google


            
            .. _sphinxdoc:


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

            
            Using Sphinx for kernel documentation

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


            The Linux kernel uses `Sphinx`_ to generate pretty documentation from

            
            `reStructuredText`_ files under ``Documentation``. To build the documentation in

            
            HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated

            
            documentation is placed in ``Documentation/output``.


            .. _Sphinx: http://www.sphinx-doc.org/

            
            .. _reStructuredText: http://docutils.sourceforge.net/rst.html


            The reStructuredText files may contain directives to include structured

            
            documentation comments, or kernel-doc comments, from source files. Usually these

            
            are used to describe the functions and types and design of the code. The

            
            kernel-doc comments have some special structure and formatting, but beyond that

            
            they are also treated as reStructuredText.


            Finally, there are thousands of plain text documentation files scattered around

            
            ``Documentation``. Some of these will likely be converted to reStructuredText

            
            over time, but the bulk of them will remain in plain text.


            .. _sphinx_install:


            Sphinx Install

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


            The ReST markups currently used by the Documentation/ files are meant to be

            
            built with ``Sphinx`` version 3.4.3 or higher.


            There's a script that checks for the Sphinx requirements. Please see

            
            :ref:`sphinx-pre-install` for further details.


            Most distributions are shipped with Sphinx, but its toolchain is fragile,

            
            and it is not uncommon that upgrading it or some other Python packages

            
            on your machine would cause the documentation build to break.


            A way to avoid that is to use a different version than the one shipped

            
            with your distributions. In order to do so, it is recommended to install

            
            Sphinx inside a virtual environment, using ``virtualenv-3``

            
            or ``virtualenv``, depending on how your distribution packaged Python 3.


            In summary, if you want to install the latest version of Sphinx, you

            
            should do::


                   $ virtualenv sphinx_latest

            
                   $ . sphinx_latest/bin/activate

            
                   (sphinx_latest) $ pip install -r Documentation/sphinx/requirements.txt


            After running ``. sphinx_latest/bin/activate``, the prompt will change,

            
            in order to indicate that you're using the new environment. If you

            
            open a new shell, you need to rerun this command to enter again at

            
            the virtual environment before building the documentation.


            Image output

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


            The kernel documentation build system contains an extension that

            
            handles images in both GraphViz and SVG formats (see :ref:`sphinx_kfigure`).


            For it to work, you need to install both GraphViz and ImageMagick

            
            packages. If those packages are not installed, the build system will

            
            still build the documentation, but won't include any images at the

            
            output.


            PDF and LaTeX builds

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


            Such builds are currently supported only with Sphinx versions 2.4 and higher.


            For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265.


            Depending on the distribution, you may also need to install a series of

            
            ``texlive`` packages that provide the minimal set of functionalities

            
            required for ``XeLaTeX`` to work.


            Math Expressions in HTML

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


            Some ReST pages contain math expressions. Due to the way Sphinx works,

            
            those expressions are written using LaTeX notation.

            
            There are two options for Sphinx to render math expressions in html output.

            
            One is an extension called `imgmath`_ which converts math expressions into

            
            images and embeds them in html pages.

            
            The other is an extension called `mathjax`_ which delegates math rendering

            
            to JavaScript capable web browsers.

            
            The former was the only option for pre-6.1 kernel documentation and it

            
            requires quite a few texlive packages including amsfonts and amsmath among

            
            others.


            Since kernel release 6.1, html pages with math expressions can be built

            
            without installing any texlive packages. See `Choice of Math Renderer`_ for

            
            further info.


            .. _imgmath: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.imgmath

            
            .. _mathjax: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.mathjax


            .. _sphinx-pre-install:


            Checking for Sphinx dependencies

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


            There's a script that automatically checks for Sphinx dependencies. If it can

            
            recognize your distribution, it will also give a hint about the install

            
            command line options for your distro::


            	$ ./tools/docs/sphinx-pre-install

            
            	Checking if the needed tools for Fedora release 26 (Twenty Six) are available

            
            	Warning: better to also install "texlive-luatex85".

            
            	You should run:


            		sudo dnf install -y texlive-luatex85

            
            		/usr/bin/virtualenv sphinx_2.4.4

            
            		. sphinx_2.4.4/bin/activate

            
            		pip install -r Documentation/sphinx/requirements.txt


            	Can't build as 1 mandatory dependency is missing at ./tools/docs/sphinx-pre-install line 468.


            By default, it checks all the requirements for both html and PDF, including

            
            the requirements for images, math expressions and LaTeX build, and assumes

            
            that a virtual Python environment will be used. The ones needed for html

            
            builds are assumed to be mandatory; the others to be optional.


            It supports two optional parameters:


            ``--no-pdf``

            
            	Disable checks for PDF;


            ``--no-virtualenv``

            
            	Use OS packaging for Sphinx instead of Python virtual environment.


            Installing Sphinx Minimal Version

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


            When changing Sphinx build system, it is important to ensure that

            
            the minimal version will still be supported. Nowadays, it is

            
            becoming harder to do that on modern distributions, as it is not

            
            possible to install with Python 3.13 and above.


            Testing with the lowest supported Python version as defined at

            
            Documentation/process/changes.rst can be done by creating

            
            a venv with it with, and install minimal requirements with::


            	/usr/bin/python3.9 -m venv sphinx_min

            
            	. sphinx_min/bin/activate

            
            	pip install -r Documentation/sphinx/min_requirements.txt


            A more comprehensive test can be done by using:


            	tools/docs/test_doc_build.py


            Such script create one Python venv per supported version,

            
            optionally building documentation for a range of Sphinx versions.


            Sphinx Build

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


            The usual way to generate the documentation is to run ``make htmldocs`` or

            
            ``make pdfdocs``. There are also other formats available: see the documentation

            
            section of ``make help``. The generated documentation is placed in

            
            format-specific subdirectories under ``Documentation/output``.


            To generate documentation, Sphinx (``sphinx-build``) must obviously be

            
            installed.  For PDF output you'll also need ``XeLaTeX`` and ``convert(1)``

            
            from ImageMagick (https://www.imagemagick.org).\ [#ink]_ All of these are

            
            widely available and packaged in distributions.


            To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make

            
            variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose

            
            output.


            It is also possible to pass an extra DOCS_CSS overlay file, in order to customize

            
            the html layout, by using the ``DOCS_CSS`` make variable.


            By default, the "Alabaster" theme is used to build the HTML documentation;

            
            this theme is bundled with Sphinx and need not be installed separately.

            
            The Sphinx theme can be overridden by using the ``DOCS_THEME`` make variable.


            .. note::


               Some people might prefer to use the RTD theme for html output.

            
               Depending on the Sphinx version, it should be installed separately,

            
               with ``pip install sphinx_rtd_theme``.


            There is another make variable ``SPHINXDIRS``, which is useful when test

            
            building a subset of documentation.  For example, you can build documents

            
            under ``Documentation/doc-guide`` by running

            
            ``make SPHINXDIRS=doc-guide htmldocs``.

            
            The documentation section of ``make help`` will show you the list of

            
            subdirectories you can specify.


            To remove the generated documentation, run ``make cleandocs``.


            .. [#ink] Having ``inkscape(1)`` from Inkscape (https://inkscape.org)

            
            	  as well would improve the quality of images embedded in PDF

            
            	  documents, especially for kernel releases 5.18 and later.


            Choice of Math Renderer

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


            Since kernel release 6.1, mathjax works as a fallback math renderer for

            
            html output.\ [#sph1_8]_


            Math renderer is chosen depending on available commands as shown below:


            .. table:: Math Renderer Choices for HTML


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

            
                Math renderer Required commands Image format

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

            
                imgmath       latex, dvipng     PNG (raster)

            
                mathjax

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


            The choice can be overridden by setting an environment variable

            
            ``SPHINX_IMGMATH`` as shown below:


            .. table:: Effect of Setting ``SPHINX_IMGMATH``


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

            
                Setting                Renderer

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

            
                ``SPHINX_IMGMATH=yes`` imgmath

            
                ``SPHINX_IMGMATH=no``  mathjax

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


            .. [#sph1_8] Fallback of math renderer requires Sphinx >=1.8.


            Writing Documentation

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


            Adding new documentation can be as simple as:


            1. Add a new ``.rst`` file somewhere under ``Documentation``.

            
            2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.


            .. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html


            This is usually good enough for simple documentation (like the one you're

            
            reading right now), but for larger documents it may be advisable to create a

            
            subdirectory (or use an existing one). For example, the graphics subsystem

            
            documentation is under ``Documentation/gpu``, split to several ``.rst`` files,

            
            and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from

            
            the main index.


            See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do

            
            with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place

            
            to get started with reStructuredText. There are also some `Sphinx specific

            
            markup constructs`_.


            .. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html

            
            .. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html


            Specific guidelines for the kernel documentation

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


            Here are some specific guidelines for the kernel documentation:


            * Please don't go overboard with reStructuredText markup. Keep it

            
              simple. For the most part the documentation should be plain text with

            
              just enough consistency in formatting that it can be converted to

            
              other formats.


            * Please keep the formatting changes minimal when converting existing

            
              documentation to reStructuredText.


            * Also update the content, not just the formatting, when converting

            
              documentation.


            * Please stick to this order of heading adornments:


              1. ``=`` with overline for document title::


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

            
                   Document title

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


              2. ``=`` for chapters::


                   Chapters

            
                   ========


              3. ``-`` for sections::


                   Section

            
                   -------


              4. ``~`` for subsections::


                   Subsection

            
                   ~~~~~~~~~~


              Although RST doesn't mandate a specific order ("Rather than imposing a fixed

            
              number and order of section title adornment styles, the order enforced will be

            
              the order as encountered."), having the higher levels the same overall makes

            
              it easier to follow the documents.


            * For inserting fixed width text blocks (for code examples, use case

            
              examples, etc.), use ``::`` for anything that doesn't really benefit

            
              from syntax highlighting, especially short snippets. Use

            
              ``.. code-block:: <language>`` for longer code blocks that benefit

            
              from highlighting. For a short snippet of code embedded in the text, use \`\`.


            The C domain

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


            The **Sphinx C Domain** (name c) is suited for documentation of C API. E.g. a

            
            function prototype:


            .. code-block:: rst


                .. c:function:: int ioctl( int fd, int request )


            The C domain of the kernel-doc has some additional features. E.g. you can

            
            *rename* the reference name of a function with a common name like ``open`` or

            
            ``ioctl``:


            .. code-block:: rst


                 .. c:function:: int ioctl( int fd, int request )

            
                    :name: VIDIOC_LOG_STATUS


            The func-name (e.g. ioctl) remains in the output but the ref-name changed from

            
            ``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also

            
            changed to ``VIDIOC_LOG_STATUS``.


            Please note that there is no need to use ``c:func:`` to generate cross

            
            references to function documentation.  Due to some Sphinx extension magic,

            
            the documentation build system will automatically turn a reference to

            
            ``function()`` into a cross reference if an index entry for the given

            
            function name exists.  If you see ``c:func:`` use in a kernel document,

            
            please feel free to remove it.


            Tables

            
            ------


            ReStructuredText provides several options for table syntax. Kernel style for

            
            tables is to prefer *simple table* syntax or *grid table* syntax. See the

            
            `reStructuredText user reference for table syntax`_ for more details.


            .. _reStructuredText user reference for table syntax:

            
               https://docutils.sourceforge.io/docs/user/rst/quickref.html#tables


            list tables

            
            ~~~~~~~~~~~


            The list-table formats can be useful for tables that are not easily laid

            
            out in the usual Sphinx ASCII-art formats.  These formats are nearly

            
            impossible for readers of the plain-text documents to understand, though,

            
            and should be avoided in the absence of a strong justification for their

            
            use.


            The ``flat-table`` is a double-stage list similar to the ``list-table`` with

            
            some additional features:


            * column-span: with the role ``cspan`` a cell can be extended through

            
              additional columns


            * row-span: with the role ``rspan`` a cell can be extended through

            
              additional rows


            * auto span rightmost cell of a table row over the missing cells on the right

            
              side of that table-row.  With Option ``:fill-cells:`` this behavior can

            
              changed from *auto span* to *auto fill*, which automatically inserts (empty)

            
              cells instead of spanning the last cell.


            options:


            * ``:header-rows:``   [int] count of header rows

            
            * ``:stub-columns:``  [int] count of stub columns

            
            * ``:widths:``        [[int] [int] ... ] widths of columns

            
            * ``:fill-cells:``    instead of auto-spanning missing cells, insert missing cells


            roles:


            * ``:cspan:`` [int] additional columns (*morecols*)

            
            * ``:rspan:`` [int] additional rows (*morerows*)


            The example below shows how to use this markup.  The first level of the staged

            
            list is the *table-row*. In the *table-row* there is only one markup allowed,

            
            the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` )

            
            and *targets* (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row

            
            <last row>`).


            .. code-block:: rst


               .. flat-table:: table title

            
                  :widths: 2 1 1 3


                  * - head col 1

            
                    - head col 2

            
                    - head col 3

            
                    - head col 4


                  * - row 1

            
                    - field 1.1

            
                    - field 1.2 with autospan


                  * - row 2

            
                    - field 2.1

            
                    - :rspan:`1` :cspan:`1` field 2.2 - 3.3


                  * .. _`last row`:


                    - row 3


            Rendered as:


               .. flat-table:: table title

            
                  :widths: 2 1 1 3


                  * - head col 1

            
                    - head col 2

            
                    - head col 3

            
                    - head col 4


                  * - row 1

            
                    - field 1.1

            
                    - field 1.2 with autospan


                  * - row 2

            
                    - field 2.1

            
                    - :rspan:`1` :cspan:`1` field 2.2 - 3.3


                  * .. _`last row`:


                    - row 3


            Cross-referencing

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


            Cross-referencing from one documentation page to another can be done simply by

            
            writing the path to the document file, no special syntax required. The path can

            
            be either absolute or relative. For absolute paths, start it with

            
            "Documentation/". For example, to cross-reference to this page, all the

            
            following are valid options, depending on the current document's directory (note

            
            that the ``.rst`` extension is required)::


                See Documentation/doc-guide/sphinx.rst. This always works.

            
                Take a look at sphinx.rst, which is at this same directory.

            
                Read ../sphinx.rst, which is one directory above.


            If you want the link to have a different rendered text other than the document's

            
            title, you need to use Sphinx's ``doc`` role. For example::


                See :doc:`my custom link text for document sphinx <sphinx>`.


            For most use cases, the former is preferred, as it is cleaner and more suited

            
            for people reading the source files. If you come across a ``:doc:`` usage that

            
            isn't adding any value, please feel free to convert it to just the document

            
            path.


            For information on cross-referencing to kernel-doc functions or types, see

            
            Documentation/doc-guide/kernel-doc.rst.


            Referencing commits

            
            ~~~~~~~~~~~~~~~~~~~


            References to git commits are automatically hyperlinked given that they are

            
            written in one of these formats::


                commit 72bf4f1767f0

            
                commit 72bf4f1767f0 ("net: do not leave an empty skb in write queue")


            .. _sphinx_kfigure:


            Figures & Images

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


            If you want to add an image, you should use the ``kernel-figure`` and

            
            ``kernel-image`` directives. E.g. to insert a figure with a scalable

            
            image format, use SVG (:ref:`svg_image_example`)::


                .. kernel-figure::  svg_image.svg

            
                   :alt:    simple SVG image


                   SVG image example


            .. _svg_image_example:


            .. kernel-figure::  svg_image.svg

            
               :alt:    simple SVG image


               SVG image example


            The kernel figure (and image) directive supports **DOT** formatted files, see


            * DOT: http://graphviz.org/pdf/dotguide.pdf

            
            * Graphviz: http://www.graphviz.org/content/dot-language


            A simple example (:ref:`hello_dot_file`)::


              .. kernel-figure::  hello.dot

            
                 :alt:    hello world


                 DOT's hello world example


            .. _hello_dot_file:


            .. kernel-figure::  hello.dot

            
               :alt:    hello world


               DOT's hello world example


            Embedded *render* markups (or languages) like Graphviz's **DOT** are provided by the

            
            ``kernel-render`` directives.::


              .. kernel-render:: DOT

            
                 :alt: foobar digraph

            
                 :caption: Embedded **DOT** (Graphviz) code


                 digraph foo {

            
                  "bar" -> "baz";

            
                 }


            How this will be rendered depends on the installed tools. If Graphviz is

            
            installed, you will see a vector image. If not, the raw markup is inserted as

            
            *literal-block* (:ref:`hello_dot_render`).


            .. _hello_dot_render:


            .. kernel-render:: DOT

            
               :alt: foobar digraph

            
               :caption: Embedded **DOT** (Graphviz) code


               digraph foo {

            
                  "bar" -> "baz";

            
               }


            The *render* directive has all the options known from the *figure* directive,

            
            plus option ``caption``.  If ``caption`` has a value, a *figure* node is

            
            inserted. If not, an *image* node is inserted. A ``caption`` is also needed, if

            
            you want to refer to it (:ref:`hello_svg_render`).


            Embedded **SVG**::


              .. kernel-render:: SVG

            
                 :caption: Embedded **SVG** markup

            
                 :alt: so-nw-arrow


                 <?xml version="1.0" encoding="UTF-8"?>

            
                 <svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>

            
                    ...

            
                 </svg>


            .. _hello_svg_render:


            .. kernel-render:: SVG

            
               :caption: Embedded **SVG** markup

            
               :alt: so-nw-arrow


               <?xml version="1.0" encoding="UTF-8"?>

            
               <svg xmlns="http://www.w3.org/2000/svg"

            
                 version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">

            
               <line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>

            
               <polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>

            
               </svg>
	.. _sphinxdoc:

	=====================================
	Using Sphinx for kernel documentation
	=====================================

	The Linux kernel uses `Sphinx`_ to generate pretty documentation from
	`reStructuredText`_ files under ``Documentation``. To build the documentation in
	HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated
	documentation is placed in ``Documentation/output``.

	.. _Sphinx: http://www.sphinx-doc.org/
	.. _reStructuredText: http://docutils.sourceforge.net/rst.html

	The reStructuredText files may contain directives to include structured
	documentation comments, or kernel-doc comments, from source files. Usually these
	are used to describe the functions and types and design of the code. The
	kernel-doc comments have some special structure and formatting, but beyond that
	they are also treated as reStructuredText.

	Finally, there are thousands of plain text documentation files scattered around
	``Documentation``. Some of these will likely be converted to reStructuredText
	over time, but the bulk of them will remain in plain text.

	.. _sphinx_install:

	Sphinx Install
	==============

	The ReST markups currently used by the Documentation/ files are meant to be
	built with ``Sphinx`` version 3.4.3 or higher.

	There's a script that checks for the Sphinx requirements. Please see
	:ref:`sphinx-pre-install` for further details.

	Most distributions are shipped with Sphinx, but its toolchain is fragile,
	and it is not uncommon that upgrading it or some other Python packages
	on your machine would cause the documentation build to break.

	A way to avoid that is to use a different version than the one shipped
	with your distributions. In order to do so, it is recommended to install
	Sphinx inside a virtual environment, using ``virtualenv-3``
	or ``virtualenv``, depending on how your distribution packaged Python 3.

	In summary, if you want to install the latest version of Sphinx, you
	should do::

	$ virtualenv sphinx_latest
	$ . sphinx_latest/bin/activate
	(sphinx_latest) $ pip install -r Documentation/sphinx/requirements.txt

	After running ``. sphinx_latest/bin/activate``, the prompt will change,
	in order to indicate that you're using the new environment. If you
	open a new shell, you need to rerun this command to enter again at
	the virtual environment before building the documentation.

	Image output
	------------

	The kernel documentation build system contains an extension that
	handles images in both GraphViz and SVG formats (see :ref:`sphinx_kfigure`).

	For it to work, you need to install both GraphViz and ImageMagick
	packages. If those packages are not installed, the build system will
	still build the documentation, but won't include any images at the
	output.

	PDF and LaTeX builds
	--------------------

	Such builds are currently supported only with Sphinx versions 2.4 and higher.

	For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265.

	Depending on the distribution, you may also need to install a series of
	``texlive`` packages that provide the minimal set of functionalities
	required for ``XeLaTeX`` to work.

	Math Expressions in HTML
	------------------------

	Some ReST pages contain math expressions. Due to the way Sphinx works,
	those expressions are written using LaTeX notation.
	There are two options for Sphinx to render math expressions in html output.
	One is an extension called `imgmath`_ which converts math expressions into
	images and embeds them in html pages.
	The other is an extension called `mathjax`_ which delegates math rendering
	to JavaScript capable web browsers.
	The former was the only option for pre-6.1 kernel documentation and it
	requires quite a few texlive packages including amsfonts and amsmath among
	others.

	Since kernel release 6.1, html pages with math expressions can be built
	without installing any texlive packages. See `Choice of Math Renderer`_ for
	further info.

	.. _imgmath: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.imgmath
	.. _mathjax: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.mathjax

	.. _sphinx-pre-install:

	Checking for Sphinx dependencies
	--------------------------------

	There's a script that automatically checks for Sphinx dependencies. If it can
	recognize your distribution, it will also give a hint about the install
	command line options for your distro::

	$ ./tools/docs/sphinx-pre-install
	Checking if the needed tools for Fedora release 26 (Twenty Six) are available
	Warning: better to also install "texlive-luatex85".
	You should run:

	sudo dnf install -y texlive-luatex85
	/usr/bin/virtualenv sphinx_2.4.4
	. sphinx_2.4.4/bin/activate
	pip install -r Documentation/sphinx/requirements.txt

	Can't build as 1 mandatory dependency is missing at ./tools/docs/sphinx-pre-install line 468.

	By default, it checks all the requirements for both html and PDF, including
	the requirements for images, math expressions and LaTeX build, and assumes
	that a virtual Python environment will be used. The ones needed for html
	builds are assumed to be mandatory; the others to be optional.

	It supports two optional parameters:

	``--no-pdf``
	Disable checks for PDF;

	``--no-virtualenv``
	Use OS packaging for Sphinx instead of Python virtual environment.

	Installing Sphinx Minimal Version
	---------------------------------

	When changing Sphinx build system, it is important to ensure that
	the minimal version will still be supported. Nowadays, it is
	becoming harder to do that on modern distributions, as it is not
	possible to install with Python 3.13 and above.

	Testing with the lowest supported Python version as defined at
	Documentation/process/changes.rst can be done by creating
	a venv with it with, and install minimal requirements with::

	/usr/bin/python3.9 -m venv sphinx_min
	. sphinx_min/bin/activate
	pip install -r Documentation/sphinx/min_requirements.txt

	A more comprehensive test can be done by using:

	tools/docs/test_doc_build.py

	Such script create one Python venv per supported version,
	optionally building documentation for a range of Sphinx versions.


	Sphinx Build
	============

	The usual way to generate the documentation is to run ``make htmldocs`` or
	``make pdfdocs``. There are also other formats available: see the documentation
	section of ``make help``. The generated documentation is placed in
	format-specific subdirectories under ``Documentation/output``.

	To generate documentation, Sphinx (``sphinx-build``) must obviously be
	installed. For PDF output you'll also need ``XeLaTeX`` and ``convert(1)``
	from ImageMagick (https://www.imagemagick.org).\ [#ink]_ All of these are
	widely available and packaged in distributions.

	To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make
	variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose
	output.

	It is also possible to pass an extra DOCS_CSS overlay file, in order to customize
	the html layout, by using the ``DOCS_CSS`` make variable.

	By default, the "Alabaster" theme is used to build the HTML documentation;
	this theme is bundled with Sphinx and need not be installed separately.
	The Sphinx theme can be overridden by using the ``DOCS_THEME`` make variable.

	.. note::

	Some people might prefer to use the RTD theme for html output.
	Depending on the Sphinx version, it should be installed separately,
	with ``pip install sphinx_rtd_theme``.

	There is another make variable ``SPHINXDIRS``, which is useful when test
	building a subset of documentation. For example, you can build documents
	under ``Documentation/doc-guide`` by running
	``make SPHINXDIRS=doc-guide htmldocs``.
	The documentation section of ``make help`` will show you the list of
	subdirectories you can specify.

	To remove the generated documentation, run ``make cleandocs``.

	.. [#ink] Having ``inkscape(1)`` from Inkscape (https://inkscape.org)
	as well would improve the quality of images embedded in PDF
	documents, especially for kernel releases 5.18 and later.

	Choice of Math Renderer
	-----------------------

	Since kernel release 6.1, mathjax works as a fallback math renderer for
	html output.\ [#sph1_8]_

	Math renderer is chosen depending on available commands as shown below:

	.. table:: Math Renderer Choices for HTML

	============= ================= ============
	Math renderer Required commands Image format
	============= ================= ============
	imgmath latex, dvipng PNG (raster)
	mathjax
	============= ================= ============

	The choice can be overridden by setting an environment variable
	``SPHINX_IMGMATH`` as shown below:

	.. table:: Effect of Setting ``SPHINX_IMGMATH``

	====================== ========
	Setting Renderer
	====================== ========
	``SPHINX_IMGMATH=yes`` imgmath
	``SPHINX_IMGMATH=no`` mathjax
	====================== ========

	.. [#sph1_8] Fallback of math renderer requires Sphinx >=1.8.


	Writing Documentation
	=====================

	Adding new documentation can be as simple as:

	1. Add a new ``.rst`` file somewhere under ``Documentation``.
	2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.

	.. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html

	This is usually good enough for simple documentation (like the one you're
	reading right now), but for larger documents it may be advisable to create a
	subdirectory (or use an existing one). For example, the graphics subsystem
	documentation is under ``Documentation/gpu``, split to several ``.rst`` files,
	and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from
	the main index.

	See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do
	with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place
	to get started with reStructuredText. There are also some `Sphinx specific
	markup constructs`_.

	.. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html
	.. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html

	Specific guidelines for the kernel documentation
	------------------------------------------------

	Here are some specific guidelines for the kernel documentation:

	* Please don't go overboard with reStructuredText markup. Keep it
	simple. For the most part the documentation should be plain text with
	just enough consistency in formatting that it can be converted to
	other formats.

	* Please keep the formatting changes minimal when converting existing
	documentation to reStructuredText.

	* Also update the content, not just the formatting, when converting
	documentation.

	* Please stick to this order of heading adornments:

	1. ``=`` with overline for document title::

	==============
	Document title
	==============

	2. ``=`` for chapters::

	Chapters
	========

	3. ``-`` for sections::

	Section
	-------

	4. ``~`` for subsections::

	Subsection
	~~~~~~~~~~

	Although RST doesn't mandate a specific order ("Rather than imposing a fixed
	number and order of section title adornment styles, the order enforced will be
	the order as encountered."), having the higher levels the same overall makes
	it easier to follow the documents.

	* For inserting fixed width text blocks (for code examples, use case
	examples, etc.), use ``::`` for anything that doesn't really benefit
	from syntax highlighting, especially short snippets. Use
	``.. code-block:: <language>`` for longer code blocks that benefit
	from highlighting. For a short snippet of code embedded in the text, use \`\`.


	The C domain
	------------

	The Sphinx C Domain (name c) is suited for documentation of C API. E.g. a
	function prototype:

	.. code-block:: rst

	.. c:function:: int ioctl( int fd, int request )

	The C domain of the kernel-doc has some additional features. E.g. you can
	rename the reference name of a function with a common name like ``open`` or
	``ioctl``:

	.. code-block:: rst

	.. c:function:: int ioctl( int fd, int request )
	:name: VIDIOC_LOG_STATUS

	The func-name (e.g. ioctl) remains in the output but the ref-name changed from
	``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also
	changed to ``VIDIOC_LOG_STATUS``.

	Please note that there is no need to use ``c:func:`` to generate cross
	references to function documentation. Due to some Sphinx extension magic,
	the documentation build system will automatically turn a reference to
	``function()`` into a cross reference if an index entry for the given
	function name exists. If you see ``c:func:`` use in a kernel document,
	please feel free to remove it.

	Tables
	------

	ReStructuredText provides several options for table syntax. Kernel style for
	tables is to prefer simple table syntax or grid table syntax. See the
	`reStructuredText user reference for table syntax`_ for more details.

	.. _reStructuredText user reference for table syntax:
	https://docutils.sourceforge.io/docs/user/rst/quickref.html#tables

	list tables
	~~~~~~~~~~~

	The list-table formats can be useful for tables that are not easily laid
	out in the usual Sphinx ASCII-art formats. These formats are nearly
	impossible for readers of the plain-text documents to understand, though,
	and should be avoided in the absence of a strong justification for their
	use.

	The ``flat-table`` is a double-stage list similar to the ``list-table`` with
	some additional features:

	* column-span: with the role ``cspan`` a cell can be extended through
	additional columns

	* row-span: with the role ``rspan`` a cell can be extended through
	additional rows

	* auto span rightmost cell of a table row over the missing cells on the right
	side of that table-row. With Option ``:fill-cells:`` this behavior can
	changed from auto span to auto fill, which automatically inserts (empty)
	cells instead of spanning the last cell.

	options:

	* ``:header-rows:`` [int] count of header rows
	* ``:stub-columns:`` [int] count of stub columns
	* ``:widths:`` [[int] [int] ... ] widths of columns
	* ``:fill-cells:`` instead of auto-spanning missing cells, insert missing cells

	roles:

	* ``:cspan:`` [int] additional columns (morecols)
	* ``:rspan:`` [int] additional rows (morerows)

	The example below shows how to use this markup. The first level of the staged
	list is the table-row. In the table-row there is only one markup allowed,
	the list of the cells in this table-row. Exceptions are comments ( ``..`` )
	and targets (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row
	<last row>`).

	.. code-block:: rst

	.. flat-table:: table title
	:widths: 2 1 1 3

	* - head col 1
	- head col 2
	- head col 3
	- head col 4

	* - row 1
	- field 1.1
	- field 1.2 with autospan

	* - row 2
	- field 2.1
	- :rspan:`1` :cspan:`1` field 2.2 - 3.3

	* .. _`last row`:

	- row 3

	Rendered as:

	.. flat-table:: table title
	:widths: 2 1 1 3

	* - head col 1
	- head col 2
	- head col 3
	- head col 4

	* - row 1
	- field 1.1
	- field 1.2 with autospan

	* - row 2
	- field 2.1
	- :rspan:`1` :cspan:`1` field 2.2 - 3.3

	* .. _`last row`:

	- row 3

	Cross-referencing
	-----------------

	Cross-referencing from one documentation page to another can be done simply by
	writing the path to the document file, no special syntax required. The path can
	be either absolute or relative. For absolute paths, start it with
	"Documentation/". For example, to cross-reference to this page, all the
	following are valid options, depending on the current document's directory (note
	that the ``.rst`` extension is required)::

	See Documentation/doc-guide/sphinx.rst. This always works.
	Take a look at sphinx.rst, which is at this same directory.
	Read ../sphinx.rst, which is one directory above.

	If you want the link to have a different rendered text other than the document's
	title, you need to use Sphinx's ``doc`` role. For example::

	See :doc:`my custom link text for document sphinx <sphinx>`.

	For most use cases, the former is preferred, as it is cleaner and more suited
	for people reading the source files. If you come across a ``:doc:`` usage that
	isn't adding any value, please feel free to convert it to just the document
	path.

	For information on cross-referencing to kernel-doc functions or types, see
	Documentation/doc-guide/kernel-doc.rst.

	Referencing commits
	~~~~~~~~~~~~~~~~~~~

	References to git commits are automatically hyperlinked given that they are
	written in one of these formats::

	commit 72bf4f1767f0
	commit 72bf4f1767f0 ("net: do not leave an empty skb in write queue")

	.. _sphinx_kfigure:

	Figures & Images
	================

	If you want to add an image, you should use the ``kernel-figure`` and
	``kernel-image`` directives. E.g. to insert a figure with a scalable
	image format, use SVG (:ref:`svg_image_example`)::

	.. kernel-figure:: svg_image.svg
	:alt: simple SVG image

	SVG image example

	.. _svg_image_example:

	.. kernel-figure:: svg_image.svg
	:alt: simple SVG image

	SVG image example

	The kernel figure (and image) directive supports DOT formatted files, see

	* DOT: http://graphviz.org/pdf/dotguide.pdf
	* Graphviz: http://www.graphviz.org/content/dot-language

	A simple example (:ref:`hello_dot_file`)::

	.. kernel-figure:: hello.dot
	:alt: hello world

	DOT's hello world example

	.. _hello_dot_file:

	.. kernel-figure:: hello.dot
	:alt: hello world

	DOT's hello world example

	Embedded render markups (or languages) like Graphviz's DOT are provided by the
	``kernel-render`` directives.::

	.. kernel-render:: DOT
	:alt: foobar digraph
	:caption: Embedded DOT (Graphviz) code

	digraph foo {
	"bar" -> "baz";
	}

	How this will be rendered depends on the installed tools. If Graphviz is
	installed, you will see a vector image. If not, the raw markup is inserted as
	literal-block (:ref:`hello_dot_render`).

	.. _hello_dot_render:

	.. kernel-render:: DOT
	:alt: foobar digraph
	:caption: Embedded DOT (Graphviz) code

	digraph foo {
	"bar" -> "baz";
	}

	The render directive has all the options known from the figure directive,
	plus option ``caption``. If ``caption`` has a value, a figure node is
	inserted. If not, an image node is inserted. A ``caption`` is also needed, if
	you want to refer to it (:ref:`hello_svg_render`).

	Embedded SVG::

	.. kernel-render:: SVG
	:caption: Embedded SVG markup
	:alt: so-nw-arrow

	<?xml version="1.0" encoding="UTF-8"?>
	<svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>
	...
	</svg>

	.. _hello_svg_render:

	.. kernel-render:: SVG
	:caption: Embedded SVG markup
	:alt: so-nw-arrow

	<?xml version="1.0" encoding="UTF-8"?>
	<svg xmlns="http://www.w3.org/2000/svg"
	version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">
	<line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>
	<polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>
	</svg>