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 There is also the deprecated DocBook toolchain to generate documentation from
19 DocBook XML template files under ``Documentation/DocBook``. The DocBook files
20 are to be converted to reStructuredText, and the toolchain is slated to be
23 Finally, there are thousands of plain text documentation files scattered around
24 ``Documentation``. Some of these will likely be converted to reStructuredText
25 over time, but the bulk of them will remain in plain text.
30 The usual way to generate the documentation is to run ``make htmldocs`` or
31 ``make pdfdocs``. There are also other formats available, see the documentation
32 section of ``make help``. The generated documentation is placed in
33 format-specific subdirectories under ``Documentation/output``.
35 To generate documentation, Sphinx (``sphinx-build``) must obviously be
36 installed. For prettier HTML output, the Read the Docs Sphinx theme
37 (``sphinx_rtd_theme``) is used if available. For PDF output you'll also need
38 ``XeLaTeX`` and ``convert(1)`` from ImageMagick (https://www.imagemagick.org).
39 All of these are widely available and packaged in distributions.
41 To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make
42 variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose
45 To remove the generated documentation, run ``make cleandocs``.
50 Adding new documentation can be as simple as:
52 1. Add a new ``.rst`` file somewhere under ``Documentation``.
53 2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.
55 .. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html
57 This is usually good enough for simple documentation (like the one you're
58 reading right now), but for larger documents it may be advisable to create a
59 subdirectory (or use an existing one). For example, the graphics subsystem
60 documentation is under ``Documentation/gpu``, split to several ``.rst`` files,
61 and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from
64 See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do
65 with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place
66 to get started with reStructuredText. There are also some `Sphinx specific
69 .. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html
70 .. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html
72 Specific guidelines for the kernel documentation
73 ------------------------------------------------
75 Here are some specific guidelines for the kernel documentation:
77 * Please don't go overboard with reStructuredText markup. Keep it
78 simple. For the most part the documentation should be plain text with
79 just enough consistency in formatting that it can be converted to
82 * Please keep the formatting changes minimal when converting existing
83 documentation to reStructuredText.
85 * Also update the content, not just the formatting, when converting
88 * Please stick to this order of heading adornments:
90 1. ``=`` with overline for document title::
96 2. ``=`` for chapters::
101 3. ``-`` for sections::
106 4. ``~`` for subsections::
111 Although RST doesn't mandate a specific order ("Rather than imposing a fixed
112 number and order of section title adornment styles, the order enforced will be
113 the order as encountered."), having the higher levels the same overall makes
114 it easier to follow the documents.
116 * For inserting fixed width text blocks (for code examples, use case
117 examples, etc.), use ``::`` for anything that doesn't really benefit
118 from syntax highlighting, especially short snippets. Use
119 ``.. code-block:: <language>`` for longer code blocks that benefit
126 The `Sphinx C Domain`_ (name c) is suited for documentation of C API. E.g. a
131 .. c:function:: int ioctl( int fd, int request )
133 The C domain of the kernel-doc has some additional features. E.g. you can
134 *rename* the reference name of a function with a common name like ``open`` or
139 .. c:function:: int ioctl( int fd, int request )
140 :name: VIDIOC_LOG_STATUS
142 The func-name (e.g. ioctl) remains in the output but the ref-name changed from
143 ``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also
144 changed to ``VIDIOC_LOG_STATUS`` and the function can now referenced by:
148 :c:func:`VIDIOC_LOG_STATUS`
154 We recommend the use of *list table* formats. The *list table* formats are
155 double-stage lists. Compared to the ASCII-art they might not be as
157 readers of the text files. Their advantage is that they are easy to
158 create or modify and that the diff of a modification is much more meaningful,
159 because it is limited to the modified content.
161 The ``flat-table`` is a double-stage list similar to the ``list-table`` with
162 some additional features:
164 * column-span: with the role ``cspan`` a cell can be extended through
167 * row-span: with the role ``rspan`` a cell can be extended through
170 * auto span rightmost cell of a table row over the missing cells on the right
171 side of that table-row. With Option ``:fill-cells:`` this behavior can
172 changed from *auto span* to *auto fill*, which automatically inserts (empty)
173 cells instead of spanning the last cell.
177 * ``:header-rows:`` [int] count of header rows
178 * ``:stub-columns:`` [int] count of stub columns
179 * ``:widths:`` [[int] [int] ... ] widths of columns
180 * ``:fill-cells:`` instead of auto-spanning missing cells, insert missing cells
184 * ``:cspan:`` [int] additional columns (*morecols*)
185 * ``:rspan:`` [int] additional rows (*morerows*)
187 The example below shows how to use this markup. The first level of the staged
188 list is the *table-row*. In the *table-row* there is only one markup allowed,
189 the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` )
190 and *targets* (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row
195 .. flat-table:: table title
205 - field 1.2 with autospan
209 - :rspan:`1` :cspan:`1` field 2.2 - 3.3
217 .. flat-table:: table title
227 - field 1.2 with autospan
231 - :rspan:`1` :cspan:`1` field 2.2 - 3.3
241 If you want to add an image, you should use the ``kernel-figure`` and
242 ``kernel-image`` directives. E.g. to insert a figure with a scalable
243 image format use SVG (:ref:`svg_image_example`)::
245 .. kernel-figure:: svg_image.svg
246 :alt: simple SVG image
250 .. _svg_image_example:
252 .. kernel-figure:: svg_image.svg
253 :alt: simple SVG image
257 The kernel figure (and image) directive support **DOT** formated files, see
259 * DOT: http://graphviz.org/pdf/dotguide.pdf
260 * Graphviz: http://www.graphviz.org/content/dot-language
262 A simple example (:ref:`hello_dot_file`)::
264 .. kernel-figure:: hello.dot
267 DOT's hello world example
271 .. kernel-figure:: hello.dot
274 DOT's hello world example
276 Embed *render* markups (or languages) like Graphviz's **DOT** is provided by the
277 ``kernel-render`` directives.::
279 .. kernel-render:: DOT
281 :caption: Embedded **DOT** (Graphviz) code
287 How this will be rendered depends on the installed tools. If Graphviz is
288 installed, you will see an vector image. If not the raw markup is inserted as
289 *literal-block* (:ref:`hello_dot_render`).
291 .. _hello_dot_render:
293 .. kernel-render:: DOT
295 :caption: Embedded **DOT** (Graphviz) code
301 The *render* directive has all the options known from the *figure* directive,
302 plus option ``caption``. If ``caption`` has a value, a *figure* node is
303 inserted. If not, a *image* node is inserted. A ``caption`` is also needed, if
304 you want to refer it (:ref:`hello_svg_render`).
308 .. kernel-render:: SVG
309 :caption: Embedded **SVG** markup
312 <?xml version="1.0" encoding="UTF-8"?>
313 <svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>
317 .. _hello_svg_render:
319 .. kernel-render:: SVG
320 :caption: Embedded **SVG** markup
323 <?xml version="1.0" encoding="UTF-8"?>
324 <svg xmlns="http://www.w3.org/2000/svg"
325 version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">
326 <line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>
327 <polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>