blob: e445cb146efebe1080c74dabf41a29bc1d9057f7 [file] [log] [blame]
.. _sphinxdoc:
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:
.. _reStructuredText:
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 1.7 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.
.. note::
#) It is recommended to use the RTD theme for html output. Depending
on the Sphinx version, it should be installed separately,
with ``pip install sphinx_rtd_theme``.
#) Some ReST pages contain math expressions. Due to the way Sphinx works,
those expressions are written using LaTeX notation. It needs texlive
installed with amsfonts and amsmath in order to evaluate them.
In summary, if you want to install Sphinx version 2.4.4, you should do::
$ virtualenv sphinx_2.4.4
$ . sphinx_2.4.4/bin/activate
(sphinx_2.4.4) $ pip install -r Documentation/sphinx/requirements.txt
After running ``. sphinx_2.4.4/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 on both GraphViz and SVG formats (see
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
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.
.. _sphinx-pre-install:
Checking for Sphinx dependencies
There's a script that automatically check for Sphinx dependencies. If it can
recognize your distribution, it will also give a hint about the install
command line options for your distro::
$ ./scripts/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 ./scripts/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:
Disable checks for PDF;
Use OS packaging for Sphinx instead of Python virtual environment.
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 prettier HTML output, the Read the Docs Sphinx theme
(``sphinx_rtd_theme``) is used if available. For PDF output you'll also need
``XeLaTeX`` and ``convert(1)`` from ImageMagick (
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
To remove the generated documentation, run ``make cleandocs``.
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:
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:
.. _Sphinx specific markup constructs:
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
* Please stick to this order of heading adornments:
1. ``=`` with overline for document title::
Document title
2. ``=`` for chapters::
3. ``-`` for sections::
4. ``~`` for subsections::
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
.. code-block:: rst
.. c:function:: int ioctl( int fd, int request )
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.
list tables
We recommend the use of *list table* formats. The *list table* formats are
double-stage lists. Compared to the ASCII-art they might not be as
comfortable for
readers of the text files. Their advantage is that they are easy to
create or modify and that the diff of a modification is much more meaningful,
because it is limited to the modified content.
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.
* ``: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
* ``: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 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
For information on cross-referencing to kernel-doc functions or types, see
.. _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:
* Graphviz:
A simple example (:ref:`hello_dot_file`)::
.. kernel-figure::
:alt: hello world
DOT's hello world example
.. _hello_dot_file:
.. kernel-figure::
: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="" version="1.1" ...>
.. _hello_svg_render:
.. kernel-render:: SVG
:caption: Embedded **SVG** markup
:alt: so-nw-arrow
<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns=""
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)"/>