4 The Linux kernel uses `Sphinx`_ to generate pretty documentation from
5 `reStructuredText`_ files under ``Documentation``. To build the documentation in
6 HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated
7 documentation is placed in ``Documentation/output``.
9 .. _Sphinx: http://www.sphinx-doc.org/
10 .. _reStructuredText: http://docutils.sourceforge.net/rst.html
12 The reStructuredText files may contain directives to include structured
13 documentation comments, or kernel-doc comments, from source files. Usually these
14 are used to describe the functions and types and design of the code. The
15 kernel-doc comments have some special structure and formatting, but beyond that
16 they are also treated as reStructuredText.
18 Finally, there are thousands of plain text documentation files scattered around
19 ``Documentation``. Some of these will likely be converted to reStructuredText
20 over time, but the bulk of them will remain in plain text.
25 The usual way to generate the documentation is to run ``make htmldocs`` or
26 ``make pdfdocs``. There are also other formats available, see the documentation
27 section of ``make help``. The generated documentation is placed in
28 format-specific subdirectories under ``Documentation/output``.
30 To generate documentation, Sphinx (``sphinx-build``) must obviously be
31 installed. For prettier HTML output, the Read the Docs Sphinx theme
32 (``sphinx_rtd_theme``) is used if available. For PDF output you'll also need
33 ``XeLaTeX`` and ``convert(1)`` from ImageMagick (https://www.imagemagick.org).
34 All of these are widely available and packaged in distributions.
36 To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make
37 variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose
40 To remove the generated documentation, run ``make cleandocs``.
45 Adding new documentation can be as simple as:
47 1. Add a new ``.rst`` file somewhere under ``Documentation``.
48 2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.
50 .. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html
52 This is usually good enough for simple documentation (like the one you're
53 reading right now), but for larger documents it may be advisable to create a
54 subdirectory (or use an existing one). For example, the graphics subsystem
55 documentation is under ``Documentation/gpu``, split to several ``.rst`` files,
56 and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from
59 See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do
60 with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place
61 to get started with reStructuredText. There are also some `Sphinx specific
64 .. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html
65 .. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html
67 Specific guidelines for the kernel documentation
68 ------------------------------------------------
70 Here are some specific guidelines for the kernel documentation:
72 * Please don't go overboard with reStructuredText markup. Keep it
73 simple. For the most part the documentation should be plain text with
74 just enough consistency in formatting that it can be converted to
77 * Please keep the formatting changes minimal when converting existing
78 documentation to reStructuredText.
80 * Also update the content, not just the formatting, when converting
83 * Please stick to this order of heading adornments:
85 1. ``=`` with overline for document title::
91 2. ``=`` for chapters::
96 3. ``-`` for sections::
101 4. ``~`` for subsections::
106 Although RST doesn't mandate a specific order ("Rather than imposing a fixed
107 number and order of section title adornment styles, the order enforced will be
108 the order as encountered."), having the higher levels the same overall makes
109 it easier to follow the documents.
111 * For inserting fixed width text blocks (for code examples, use case
112 examples, etc.), use ``::`` for anything that doesn't really benefit
113 from syntax highlighting, especially short snippets. Use
114 ``.. code-block:: <language>`` for longer code blocks that benefit
121 The `Sphinx C Domain`_ (name c) is suited for documentation of C API. E.g. a
126 .. c:function:: int ioctl( int fd, int request )
128 The C domain of the kernel-doc has some additional features. E.g. you can
129 *rename* the reference name of a function with a common name like ``open`` or
134 .. c:function:: int ioctl( int fd, int request )
135 :name: VIDIOC_LOG_STATUS
137 The func-name (e.g. ioctl) remains in the output but the ref-name changed from
138 ``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also
139 changed to ``VIDIOC_LOG_STATUS`` and the function can now referenced by:
143 :c:func:`VIDIOC_LOG_STATUS`
149 We recommend the use of *list table* formats. The *list table* formats are
150 double-stage lists. Compared to the ASCII-art they might not be as
152 readers of the text files. Their advantage is that they are easy to
153 create or modify and that the diff of a modification is much more meaningful,
154 because it is limited to the modified content.
156 The ``flat-table`` is a double-stage list similar to the ``list-table`` with
157 some additional features:
159 * column-span: with the role ``cspan`` a cell can be extended through
162 * row-span: with the role ``rspan`` a cell can be extended through
165 * auto span rightmost cell of a table row over the missing cells on the right
166 side of that table-row. With Option ``:fill-cells:`` this behavior can
167 changed from *auto span* to *auto fill*, which automatically inserts (empty)
168 cells instead of spanning the last cell.
172 * ``:header-rows:`` [int] count of header rows
173 * ``:stub-columns:`` [int] count of stub columns
174 * ``:widths:`` [[int] [int] ... ] widths of columns
175 * ``:fill-cells:`` instead of auto-spanning missing cells, insert missing cells
179 * ``:cspan:`` [int] additional columns (*morecols*)
180 * ``:rspan:`` [int] additional rows (*morerows*)
182 The example below shows how to use this markup. The first level of the staged
183 list is the *table-row*. In the *table-row* there is only one markup allowed,
184 the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` )
185 and *targets* (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row
190 .. flat-table:: table title
200 - field 1.2 with autospan
204 - :rspan:`1` :cspan:`1` field 2.2 - 3.3
212 .. flat-table:: table title
222 - field 1.2 with autospan
226 - :rspan:`1` :cspan:`1` field 2.2 - 3.3
236 If you want to add an image, you should use the ``kernel-figure`` and
237 ``kernel-image`` directives. E.g. to insert a figure with a scalable
238 image format use SVG (:ref:`svg_image_example`)::
240 .. kernel-figure:: svg_image.svg
241 :alt: simple SVG image
245 .. _svg_image_example:
247 .. kernel-figure:: svg_image.svg
248 :alt: simple SVG image
252 The kernel figure (and image) directive support **DOT** formated files, see
254 * DOT: http://graphviz.org/pdf/dotguide.pdf
255 * Graphviz: http://www.graphviz.org/content/dot-language
257 A simple example (:ref:`hello_dot_file`)::
259 .. kernel-figure:: hello.dot
262 DOT's hello world example
266 .. kernel-figure:: hello.dot
269 DOT's hello world example
271 Embed *render* markups (or languages) like Graphviz's **DOT** is provided by the
272 ``kernel-render`` directives.::
274 .. kernel-render:: DOT
276 :caption: Embedded **DOT** (Graphviz) code
282 How this will be rendered depends on the installed tools. If Graphviz is
283 installed, you will see an vector image. If not the raw markup is inserted as
284 *literal-block* (:ref:`hello_dot_render`).
286 .. _hello_dot_render:
288 .. kernel-render:: DOT
290 :caption: Embedded **DOT** (Graphviz) code
296 The *render* directive has all the options known from the *figure* directive,
297 plus option ``caption``. If ``caption`` has a value, a *figure* node is
298 inserted. If not, a *image* node is inserted. A ``caption`` is also needed, if
299 you want to refer it (:ref:`hello_svg_render`).
303 .. kernel-render:: SVG
304 :caption: Embedded **SVG** markup
307 <?xml version="1.0" encoding="UTF-8"?>
308 <svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>
312 .. _hello_svg_render:
314 .. kernel-render:: SVG
315 :caption: Embedded **SVG** markup
318 <?xml version="1.0" encoding="UTF-8"?>
319 <svg xmlns="http://www.w3.org/2000/svg"
320 version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">
321 <line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>
322 <polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>