220 lines
7.0 KiB
ReStructuredText
220 lines
7.0 KiB
ReStructuredText
Introduction
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============
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The Linux kernel uses `Sphinx`_ to generate pretty documentation from
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`reStructuredText`_ files under ``Documentation``. To build the documentation in
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HTML or PDF formats, use ``make htmldocs`` or ``make pdfdocs``. The generated
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documentation is placed in ``Documentation/output``.
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.. _Sphinx: http://www.sphinx-doc.org/
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.. _reStructuredText: http://docutils.sourceforge.net/rst.html
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The reStructuredText files may contain directives to include structured
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documentation comments, or kernel-doc comments, from source files. Usually these
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are used to describe the functions and types and design of the code. The
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kernel-doc comments have some special structure and formatting, but beyond that
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they are also treated as reStructuredText.
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There is also the deprecated DocBook toolchain to generate documentation from
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DocBook XML template files under ``Documentation/DocBook``. The DocBook files
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are to be converted to reStructuredText, and the toolchain is slated to be
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removed.
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Finally, there are thousands of plain text documentation files scattered around
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``Documentation``. Some of these will likely be converted to reStructuredText
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over time, but the bulk of them will remain in plain text.
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Sphinx Build
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============
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The usual way to generate the documentation is to run ``make htmldocs`` or
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``make pdfdocs``. There are also other formats available, see the documentation
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section of ``make help``. The generated documentation is placed in
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format-specific subdirectories under ``Documentation/output``.
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To generate documentation, Sphinx (``sphinx-build``) must obviously be
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installed. For prettier HTML output, the Read the Docs Sphinx theme
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(``sphinx_rtd_theme``) is used if available. For PDF output, ``rst2pdf`` is also
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needed. All of these are widely available and packaged in distributions.
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To pass extra options to Sphinx, you can use the ``SPHINXOPTS`` make
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variable. For example, use ``make SPHINXOPTS=-v htmldocs`` to get more verbose
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output.
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To remove the generated documentation, run ``make cleandocs``.
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Writing Documentation
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=====================
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Adding new documentation can be as simple as:
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1. Add a new ``.rst`` file somewhere under ``Documentation``.
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2. Refer to it from the Sphinx main `TOC tree`_ in ``Documentation/index.rst``.
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.. _TOC tree: http://www.sphinx-doc.org/en/stable/markup/toctree.html
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This is usually good enough for simple documentation (like the one you're
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reading right now), but for larger documents it may be advisable to create a
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subdirectory (or use an existing one). For example, the graphics subsystem
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documentation is under ``Documentation/gpu``, split to several ``.rst`` files,
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and has a separate ``index.rst`` (with a ``toctree`` of its own) referenced from
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the main index.
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See the documentation for `Sphinx`_ and `reStructuredText`_ on what you can do
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with them. In particular, the Sphinx `reStructuredText Primer`_ is a good place
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to get started with reStructuredText. There are also some `Sphinx specific
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markup constructs`_.
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.. _reStructuredText Primer: http://www.sphinx-doc.org/en/stable/rest.html
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.. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html
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Specific guidelines for the kernel documentation
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------------------------------------------------
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Here are some specific guidelines for the kernel documentation:
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* Please don't go overboard with reStructuredText markup. Keep it simple.
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* Please stick to this order of heading adornments:
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1. ``=`` with overline for document title::
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==============
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Document title
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==============
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2. ``=`` for chapters::
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Chapters
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========
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3. ``-`` for sections::
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Section
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-------
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4. ``~`` for subsections::
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Subsection
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~~~~~~~~~~
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Although RST doesn't mandate a specific order ("Rather than imposing a fixed
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number and order of section title adornment styles, the order enforced will be
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the order as encountered."), having the higher levels the same overall makes
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it easier to follow the documents.
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the C domain
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------------
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The `Sphinx C Domain`_ (name c) is suited for documentation of C API. E.g. a
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function prototype:
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.. code-block:: rst
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.. c:function:: int ioctl( int fd, int request )
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The C domain of the kernel-doc has some additional features. E.g. you can
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*rename* the reference name of a function with a common name like ``open`` or
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``ioctl``:
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.. code-block:: rst
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.. c:function:: int ioctl( int fd, int request )
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:name: VIDIOC_LOG_STATUS
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The func-name (e.g. ioctl) remains in the output but the ref-name changed from
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``ioctl`` to ``VIDIOC_LOG_STATUS``. The index entry for this function is also
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changed to ``VIDIOC_LOG_STATUS`` and the function can now referenced by:
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.. code-block:: rst
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:c:func:`VIDIOC_LOG_STATUS`
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list tables
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-----------
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We recommend the use of *list table* formats. The *list table* formats are
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double-stage lists. Compared to the ASCII-art they might not be as
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comfortable for
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readers of the text files. Their advantage is that they are easy to
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create or modify and that the diff of a modification is much more meaningful,
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because it is limited to the modified content.
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The ``flat-table`` is a double-stage list similar to the ``list-table`` with
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some additional features:
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* column-span: with the role ``cspan`` a cell can be extended through
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additional columns
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* row-span: with the role ``rspan`` a cell can be extended through
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additional rows
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* auto span rightmost cell of a table row over the missing cells on the right
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side of that table-row. With Option ``:fill-cells:`` this behavior can
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changed from *auto span* to *auto fill*, which automatically inserts (empty)
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cells instead of spanning the last cell.
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options:
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* ``:header-rows:`` [int] count of header rows
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* ``:stub-columns:`` [int] count of stub columns
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* ``:widths:`` [[int] [int] ... ] widths of columns
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* ``:fill-cells:`` instead of auto-spanning missing cells, insert missing cells
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roles:
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* ``:cspan:`` [int] additional columns (*morecols*)
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* ``:rspan:`` [int] additional rows (*morerows*)
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The example below shows how to use this markup. The first level of the staged
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list is the *table-row*. In the *table-row* there is only one markup allowed,
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the list of the cells in this *table-row*. Exceptions are *comments* ( ``..`` )
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and *targets* (e.g. a ref to ``:ref:`last row <last row>``` / :ref:`last row
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<last row>`).
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.. code-block:: rst
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.. flat-table:: table title
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:widths: 2 1 1 3
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* - head col 1
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- head col 2
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- head col 3
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- head col 4
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* - column 1
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- field 1.1
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- field 1.2 with autospan
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* - column 2
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- field 2.1
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- :rspan:`1` :cspan:`1` field 2.2 - 3.3
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* .. _`last row`:
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- column 3
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Rendered as:
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.. flat-table:: table title
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:widths: 2 1 1 3
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* - head col 1
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- head col 2
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- head col 3
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- head col 4
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* - column 1
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- field 1.1
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- field 1.2 with autospan
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* - column 2
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- field 2.1
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- :rspan:`1` :cspan:`1` field 2.2 - 3.3
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* .. _`last row`:
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- column 3
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