docs-rst: doc-guide: split the kernel-documentation.rst contents

Having the kernel-documentation at the topmost level doesn't
allow generating a separate PDF file for it. Also, makes harder
to add extra contents. So, place it on a sub-dir.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 219 insertions, 0 deletions

diff --git a/Documentation/doc-guide/sphinx.rst b/Documentation/doc-guide/sphinx.rst
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+Introduction
+============
+
+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: http://www.sphinx-doc.org/
+.. _reStructuredText: http://docutils.sourceforge.net/rst.html
+
+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.
+
+There is also the deprecated DocBook toolchain to generate documentation from
+DocBook XML template files under ``Documentation/DocBook``. The DocBook files
+are to be converted to reStructuredText, and the toolchain is slated to be
+removed.
+
+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 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, ``rst2pdf`` is also
+needed. 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
+output.
+
+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: http://www.sphinx-doc.org/en/stable/markup/toctree.html
+
+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: http://www.sphinx-doc.org/en/stable/rest.html
+.. _Sphinx specific markup constructs: http://www.sphinx-doc.org/en/stable/markup/index.html
+
+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.
+
+* Please stick to this order of heading adornments:
+
+  1. ``=`` with overline for document title::
+
+       ==============
+       Document title
+       ==============
+
+  2. ``=`` for chapters::
+
+       Chapters
+       ========
+
+  3. ``-`` for sections::
+
+       Section
+       -------
+
+  4. ``~`` for subsections::
+
+       Subsection
+       ~~~~~~~~~~
+
+  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.
+
+
+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
+``ioctl``:
+
+.. code-block:: rst
+
+     .. c:function:: int ioctl( int fd, int request )
+        :name: VIDIOC_LOG_STATUS
+
+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`` and the function can now referenced by:
+
+.. code-block:: rst
+
+     :c:func:`VIDIOC_LOG_STATUS`
+
+
+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.
+
+options:
+
+* ``: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
+
+roles:
+
+* ``: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
+
+      * - column 1
+        - field 1.1
+        - field 1.2 with autospan
+
+      * - column 2
+        - field 2.1
+        - :rspan:`1` :cspan:`1` field 2.2 - 3.3
+
+      * .. _`last row`:
+
+        - column 3
+
+Rendered as:
+
+   .. flat-table:: table title
+      :widths: 2 1 1 3
+
+      * - head col 1
+        - head col 2
+        - head col 3
+        - head col 4
+
+      * - column 1
+        - field 1.1
+        - field 1.2 with autospan
+
+      * - column 2
+        - field 2.1
+        - :rspan:`1` :cspan:`1` field 2.2 - 3.3
+
+      * .. _`last row`:
+
+        - column 3