1Introduction
2============
3
4The Linux kernel uses `Sphinx`_ to generate pretty documentation from
5`reStructuredText`_ files under ``Documentation``. To build the documentation in
6HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated
7documentation is placed in ``Documentation/output``.
8
9.. _Sphinx: http://www.sphinx-doc.org/
10.. _reStructuredText: http://docutils.sourceforge.net/rst.html
11
12The reStructuredText files may contain directives to include structured
13documentation comments, or kernel-doc comments, from source files. Usually these
14are used to describe the functions and types and design of the code. The
15kernel-doc comments have some special structure and formatting, but beyond that
16they are also treated as reStructuredText.
17
18Finally, there are thousands of plain text documentation files scattered around
19``Documentation``. Some of these will likely be converted to reStructuredText
20over time, but the bulk of them will remain in plain text.
21
22.. _sphinx_install:
23
24Sphinx Install
25==============
26
27The ReST markups currently used by the Documentation/ files are meant to be
28built with ``Sphinx`` version 1.3 or upper. If you're desiring to build
29PDF outputs, it is recommended to use version 1.4.6 or upper.
30
31There's a script that checks for the Spinx requirements. Please see
32:ref:`sphinx-pre-install` for further details.
33
34Most distributions are shipped with Sphinx, but its toolchain is fragile,
35and it is not uncommon that upgrading it or some other Python packages
36on your machine would cause the documentation build to break.
37
38A way to get rid of that is to use a different version than the one shipped
39on your distributions. In order to do that, it is recommended to install
40Sphinx inside a virtual environment, using ``virtualenv-3``
41or ``virtualenv``, depending on how your distribution packaged Python 3.
42
43.. note::
44
45   #) Sphinx versions below 1.5 don't work properly with Python's
46      docutils version 0.13.1 or upper. So, if you're willing to use
47      those versions, you should run ``pip install 'docutils==0.12'``.
48
49   #) It is recommended to use the RTD theme for html output. Depending
50      on the Sphinx version, it should be installed  in separate,
51      with ``pip install sphinx_rtd_theme``.
52
53   #) Some ReST pages contain math expressions. Due to the way Sphinx work,
54      those expressions are written using LaTeX notation. It needs texlive
55      installed with amdfonts and amsmath in order to evaluate them.
56
57In summary, if you want to install Sphinx version 1.4.9, you should do::
58
59       $ virtualenv sphinx_1.4
60       $ . sphinx_1.4/bin/activate
61       (sphinx_1.4) $ pip install -r Documentation/sphinx/requirements.txt
62
63After running ``. sphinx_1.4/bin/activate``, the prompt will change,
64in order to indicate that you're using the new environment. If you
65open a new shell, you need to rerun this command to enter again at
66the virtual environment before building the documentation.
67
68Image output
69------------
70
71The kernel documentation build system contains an extension that
72handles images on both GraphViz and SVG formats (see
73:ref:`sphinx_kfigure`).
74
75For it to work, you need to install both GraphViz and ImageMagick
76packages. If those packages are not installed, the build system will
77still build the documentation, but won't include any images at the
78output.
79
80PDF and LaTeX builds
81--------------------
82
83Such builds are currently supported only with Sphinx versions 1.4 and upper.
84
85For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265.
86
87Depending on the distribution, you may also need to install a series of
88``texlive`` packages that provide the minimal set of functionalities
89required for ``XeLaTeX`` to work.
90
91.. _sphinx-pre-install:
92
93Checking for Sphinx dependencies
94--------------------------------
95
96There's a script that automatically check for Sphinx dependencies. If it can
97recognize your distribution, it will also give a hint about the install
98command line options for your distro::
99
100	$ ./scripts/sphinx-pre-install
101	Checking if the needed tools for Fedora release 26 (Twenty Six) are available
102	Warning: better to also install "texlive-luatex85".
103	You should run:
104
105		sudo dnf install -y texlive-luatex85
106		/usr/bin/virtualenv sphinx_1.4
107		. sphinx_1.4/bin/activate
108		pip install -r Documentation/sphinx/requirements.txt
109
110	Can't build as 1 mandatory dependency is missing at ./scripts/sphinx-pre-install line 468.
111
112By default, it checks all the requirements for both html and PDF, including
113the requirements for images, math expressions and LaTeX build, and assumes
114that a virtual Python environment will be used. The ones needed for html
115builds are assumed to be mandatory; the others to be optional.
116
117It supports two optional parameters:
118
119``--no-pdf``
120	Disable checks for PDF;
121
122``--no-virtualenv``
123	Use OS packaging for Sphinx instead of Python virtual environment.
124
125
126Sphinx Build
127============
128
129The usual way to generate the documentation is to run ``make htmldocs`` or
130``make pdfdocs``. There are also other formats available, see the documentation
131section of ``make help``. The generated documentation is placed in
132format-specific subdirectories under ``Documentation/output``.
133
134To generate documentation, Sphinx (``sphinx-build``) must obviously be
135installed. For prettier HTML output, the Read the Docs Sphinx theme
136(``sphinx_rtd_theme``) is used if available. For PDF output you'll also need
137``XeLaTeX`` and ``convert(1)`` from ImageMagick (https://www.imagemagick.org).
138All of these are widely available and packaged in distributions.
139
140To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make
141variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose
142output.
143
144To remove the generated documentation, run ``make cleandocs``.
145
146Writing Documentation
147=====================
148
149Adding new documentation can be as simple as:
150
1511. Add a new ``.rst`` file somewhere under ``Documentation``.
1522. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.
153
154.. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html
155
156This is usually good enough for simple documentation (like the one you're
157reading right now), but for larger documents it may be advisable to create a
158subdirectory (or use an existing one). For example, the graphics subsystem
159documentation is under ``Documentation/gpu``, split to several ``.rst`` files,
160and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from
161the main index.
162
163See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do
164with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place
165to get started with reStructuredText. There are also some `Sphinx specific
166markup constructs`_.
167
168.. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html
169.. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html
170
171Specific guidelines for the kernel documentation
172------------------------------------------------
173
174Here are some specific guidelines for the kernel documentation:
175
176* Please don't go overboard with reStructuredText markup. Keep it
177  simple. For the most part the documentation should be plain text with
178  just enough consistency in formatting that it can be converted to
179  other formats.
180
181* Please keep the formatting changes minimal when converting existing
182  documentation to reStructuredText.
183
184* Also update the content, not just the formatting, when converting
185  documentation.
186
187* Please stick to this order of heading adornments:
188
189  1. ``=`` with overline for document title::
190
191       ==============
192       Document title
193       ==============
194
195  2. ``=`` for chapters::
196
197       Chapters
198       ========
199
200  3. ``-`` for sections::
201
202       Section
203       -------
204
205  4. ``~`` for subsections::
206
207       Subsection
208       ~~~~~~~~~~
209
210  Although RST doesn't mandate a specific order ("Rather than imposing a fixed
211  number and order of section title adornment styles, the order enforced will be
212  the order as encountered."), having the higher levels the same overall makes
213  it easier to follow the documents.
214
215* For inserting fixed width text blocks (for code examples, use case
216  examples, etc.), use ``::`` for anything that doesn't really benefit
217  from syntax highlighting, especially short snippets. Use
218  ``.. code-block:: <language>`` for longer code blocks that benefit
219  from highlighting.
220
221
222the C domain
223------------
224
225The **Sphinx C Domain** (name c) is suited for documentation of C API. E.g. a
226function prototype:
227
228.. code-block:: rst
229
230    .. c:function:: int ioctl( int fd, int request )
231
232The C domain of the kernel-doc has some additional features. E.g. you can
233*rename* the reference name of a function with a common name like ``open`` or
234``ioctl``:
235
236.. code-block:: rst
237
238     .. c:function:: int ioctl( int fd, int request )
239        :name: VIDIOC_LOG_STATUS
240
241The func-name (e.g. ioctl) remains in the output but the ref-name changed from
242``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also
243changed to ``VIDIOC_LOG_STATUS`` and the function can now referenced by:
244
245.. code-block:: rst
246
247     :c:func:`VIDIOC_LOG_STATUS`
248
249
250list tables
251-----------
252
253We recommend the use of *list table* formats. The *list table* formats are
254double-stage lists. Compared to the ASCII-art they might not be as
255comfortable for
256readers of the text files. Their advantage is that they are easy to
257create or modify and that the diff of a modification is much more meaningful,
258because it is limited to the modified content.
259
260The ``flat-table`` is a double-stage list similar to the ``list-table`` with
261some additional features:
262
263* column-span: with the role ``cspan`` a cell can be extended through
264  additional columns
265
266* row-span: with the role ``rspan`` a cell can be extended through
267  additional rows
268
269* auto span rightmost cell of a table row over the missing cells on the right
270  side of that table-row.  With Option ``:fill-cells:`` this behavior can
271  changed from *auto span* to *auto fill*, which automatically inserts (empty)
272  cells instead of spanning the last cell.
273
274options:
275
276* ``:header-rows:``   [int] count of header rows
277* ``:stub-columns:``  [int] count of stub columns
278* ``:widths:``        [[int] [int] ... ] widths of columns
279* ``:fill-cells:``    instead of auto-spanning missing cells, insert missing cells
280
281roles:
282
283* ``:cspan:`` [int] additional columns (*morecols*)
284* ``:rspan:`` [int] additional rows (*morerows*)
285
286The example below shows how to use this markup.  The first level of the staged
287list is the *table-row*. In the *table-row* there is only one markup allowed,
288the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` )
289and *targets* (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row
290<last row>`).
291
292.. code-block:: rst
293
294   .. flat-table:: table title
295      :widths: 2 1 1 3
296
297      * - head col 1
298        - head col 2
299        - head col 3
300        - head col 4
301
302      * - column 1
303        - field 1.1
304        - field 1.2 with autospan
305
306      * - column 2
307        - field 2.1
308        - :rspan:`1` :cspan:`1` field 2.2 - 3.3
309
310      * .. _`last row`:
311
312        - column 3
313
314Rendered as:
315
316   .. flat-table:: table title
317      :widths: 2 1 1 3
318
319      * - head col 1
320        - head col 2
321        - head col 3
322        - head col 4
323
324      * - column 1
325        - field 1.1
326        - field 1.2 with autospan
327
328      * - column 2
329        - field 2.1
330        - :rspan:`1` :cspan:`1` field 2.2 - 3.3
331
332      * .. _`last row`:
333
334        - column 3
335
336.. _sphinx_kfigure:
337
338Figures & Images
339================
340
341If you want to add an image, you should use the ``kernel-figure`` and
342``kernel-image`` directives. E.g. to insert a figure with a scalable
343image format use SVG (:ref:`svg_image_example`)::
344
345    .. kernel-figure::  svg_image.svg
346       :alt:    simple SVG image
347
348       SVG image example
349
350.. _svg_image_example:
351
352.. kernel-figure::  svg_image.svg
353   :alt:    simple SVG image
354
355   SVG image example
356
357The kernel figure (and image) directive support **DOT** formated files, see
358
359* DOT: http://graphviz.org/pdf/dotguide.pdf
360* Graphviz: http://www.graphviz.org/content/dot-language
361
362A simple example (:ref:`hello_dot_file`)::
363
364  .. kernel-figure::  hello.dot
365     :alt:    hello world
366
367     DOT's hello world example
368
369.. _hello_dot_file:
370
371.. kernel-figure::  hello.dot
372   :alt:    hello world
373
374   DOT's hello world example
375
376Embed *render* markups (or languages) like Graphviz's **DOT** is provided by the
377``kernel-render`` directives.::
378
379  .. kernel-render:: DOT
380     :alt: foobar digraph
381     :caption: Embedded **DOT** (Graphviz) code
382
383     digraph foo {
384      "bar" -> "baz";
385     }
386
387How this will be rendered depends on the installed tools. If Graphviz is
388installed, you will see an vector image. If not the raw markup is inserted as
389*literal-block* (:ref:`hello_dot_render`).
390
391.. _hello_dot_render:
392
393.. kernel-render:: DOT
394   :alt: foobar digraph
395   :caption: Embedded **DOT** (Graphviz) code
396
397   digraph foo {
398      "bar" -> "baz";
399   }
400
401The *render* directive has all the options known from the *figure* directive,
402plus option ``caption``.  If ``caption`` has a value, a *figure* node is
403inserted. If not, a *image* node is inserted. A ``caption`` is also needed, if
404you want to refer it (:ref:`hello_svg_render`).
405
406Embedded **SVG**::
407
408  .. kernel-render:: SVG
409     :caption: Embedded **SVG** markup
410     :alt: so-nw-arrow
411
412     <?xml version="1.0" encoding="UTF-8"?>
413     <svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>
414        ...
415     </svg>
416
417.. _hello_svg_render:
418
419.. kernel-render:: SVG
420   :caption: Embedded **SVG** markup
421   :alt: so-nw-arrow
422
423   <?xml version="1.0" encoding="UTF-8"?>
424   <svg xmlns="http://www.w3.org/2000/svg"
425     version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">
426   <line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>
427   <polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>
428   </svg>
429