mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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![Jonathan Corbet](/assets/img/avatar_default.png)
We don't default to Read The Docs anymore; update the docs to match. Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
521 lines
17 KiB
ReStructuredText
521 lines
17 KiB
ReStructuredText
.. _sphinxdoc:
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=====================================
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Using Sphinx for kernel documentation
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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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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_install:
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Sphinx Install
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==============
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The ReST markups currently used by the Documentation/ files are meant to be
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built with ``Sphinx`` version 1.7 or higher.
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There's a script that checks for the Sphinx requirements. Please see
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:ref:`sphinx-pre-install` for further details.
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Most distributions are shipped with Sphinx, but its toolchain is fragile,
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and it is not uncommon that upgrading it or some other Python packages
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on your machine would cause the documentation build to break.
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A way to avoid that is to use a different version than the one shipped
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with your distributions. In order to do so, it is recommended to install
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Sphinx inside a virtual environment, using ``virtualenv-3``
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or ``virtualenv``, depending on how your distribution packaged Python 3.
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.. note::
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#) It is recommended to use the RTD theme for html output. Depending
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on the Sphinx version, it should be installed separately,
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with ``pip install sphinx_rtd_theme``.
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In summary, if you want to install Sphinx version 2.4.4, you should do::
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$ virtualenv sphinx_2.4.4
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$ . sphinx_2.4.4/bin/activate
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(sphinx_2.4.4) $ pip install -r Documentation/sphinx/requirements.txt
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After running ``. sphinx_2.4.4/bin/activate``, the prompt will change,
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in order to indicate that you're using the new environment. If you
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open a new shell, you need to rerun this command to enter again at
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the virtual environment before building the documentation.
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Image output
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------------
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The kernel documentation build system contains an extension that
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handles images on both GraphViz and SVG formats (see
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:ref:`sphinx_kfigure`).
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For it to work, you need to install both GraphViz and ImageMagick
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packages. If those packages are not installed, the build system will
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still build the documentation, but won't include any images at the
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output.
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PDF and LaTeX builds
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--------------------
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Such builds are currently supported only with Sphinx versions 2.4 and higher.
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For PDF and LaTeX output, you'll also need ``XeLaTeX`` version 3.14159265.
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Depending on the distribution, you may also need to install a series of
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``texlive`` packages that provide the minimal set of functionalities
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required for ``XeLaTeX`` to work.
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Math Expressions in HTML
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------------------------
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Some ReST pages contain math expressions. Due to the way Sphinx works,
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those expressions are written using LaTeX notation.
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There are two options for Sphinx to render math expressions in html output.
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One is an extension called `imgmath`_ which converts math expressions into
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images and embeds them in html pages.
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The other is an extension called `mathjax`_ which delegates math rendering
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to JavaScript capable web browsers.
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The former was the only option for pre-6.1 kernel documentation and it
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requires quite a few texlive packages including amsfonts and amsmath among
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others.
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Since kernel release 6.1, html pages with math expressions can be built
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without installing any texlive packages. See `Choice of Math Renderer`_ for
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further info.
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.. _imgmath: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.imgmath
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.. _mathjax: https://www.sphinx-doc.org/en/master/usage/extensions/math.html#module-sphinx.ext.mathjax
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.. _sphinx-pre-install:
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Checking for Sphinx dependencies
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--------------------------------
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There's a script that automatically check for Sphinx dependencies. If it can
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recognize your distribution, it will also give a hint about the install
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command line options for your distro::
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$ ./scripts/sphinx-pre-install
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Checking if the needed tools for Fedora release 26 (Twenty Six) are available
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Warning: better to also install "texlive-luatex85".
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You should run:
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sudo dnf install -y texlive-luatex85
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/usr/bin/virtualenv sphinx_2.4.4
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. sphinx_2.4.4/bin/activate
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pip install -r Documentation/sphinx/requirements.txt
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Can't build as 1 mandatory dependency is missing at ./scripts/sphinx-pre-install line 468.
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By default, it checks all the requirements for both html and PDF, including
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the requirements for images, math expressions and LaTeX build, and assumes
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that a virtual Python environment will be used. The ones needed for html
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builds are assumed to be mandatory; the others to be optional.
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It supports two optional parameters:
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``--no-pdf``
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Disable checks for PDF;
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``--no-virtualenv``
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Use OS packaging for Sphinx instead of Python virtual environment.
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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 PDF output you'll also need ``XeLaTeX`` and ``convert(1)``
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from ImageMagick (https://www.imagemagick.org).\ [#ink]_ All of these are
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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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It is also possible to pass an extra DOCS_CSS overlay file, in order to customize
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the html layout, by using the ``DOCS_CSS`` make variable.
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By default, the "Alabaster" theme is used to build the HTML documentation;
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this theme is bundled with Sphinx and need not be installed separately.
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The Sphinx theme can be overridden by using the ``DOCS_THEME`` make variable.
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There is another make variable ``SPHINXDIRS``, which is useful when test
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building a subset of documentation. For example, you can build documents
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under ``Documentation/doc-guide`` by running
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``make SPHINXDIRS=doc-guide htmldocs``.
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The documentation section of ``make help`` will show you the list of
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subdirectories you can specify.
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To remove the generated documentation, run ``make cleandocs``.
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.. [#ink] Having ``inkscape(1)`` from Inkscape (https://inkscape.org)
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as well would improve the quality of images embedded in PDF
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documents, especially for kernel releases 5.18 and later.
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Choice of Math Renderer
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-----------------------
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Since kernel release 6.1, mathjax works as a fallback math renderer for
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html output.\ [#sph1_8]_
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Math renderer is chosen depending on available commands as shown below:
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.. table:: Math Renderer Choices for HTML
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============= ================= ============
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Math renderer Required commands Image format
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============= ================= ============
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imgmath latex, dvipng PNG (raster)
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mathjax
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============= ================= ============
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The choice can be overridden by setting an environment variable
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``SPHINX_IMGMATH`` as shown below:
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.. table:: Effect of Setting ``SPHINX_IMGMATH``
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====================== ========
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Setting Renderer
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====================== ========
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``SPHINX_IMGMATH=yes`` imgmath
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``SPHINX_IMGMATH=no`` mathjax
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====================== ========
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.. [#sph1_8] Fallback of math renderer requires Sphinx >=1.8.
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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
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simple. For the most part the documentation should be plain text with
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just enough consistency in formatting that it can be converted to
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other formats.
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* Please keep the formatting changes minimal when converting existing
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documentation to reStructuredText.
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* Also update the content, not just the formatting, when converting
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documentation.
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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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* For inserting fixed width text blocks (for code examples, use case
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examples, etc.), use ``::`` for anything that doesn't really benefit
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from syntax highlighting, especially short snippets. Use
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``.. code-block:: <language>`` for longer code blocks that benefit
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from highlighting. For a short snippet of code embedded in the text, use \`\`.
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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``.
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Please note that there is no need to use ``c:func:`` to generate cross
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references to function documentation. Due to some Sphinx extension magic,
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the documentation build system will automatically turn a reference to
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``function()`` into a cross reference if an index entry for the given
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function name exists. If you see ``c:func:`` use in a kernel document,
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please feel free to remove it.
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list tables
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-----------
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The list-table formats can be useful for tables that are not easily laid
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out in the usual Sphinx ASCII-art formats. These formats are nearly
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impossible for readers of the plain-text documents to understand, though,
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and should be avoided in the absence of a strong justification for their
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use.
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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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* - row 1
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- field 1.1
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- field 1.2 with autospan
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* - row 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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- row 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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* - row 1
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- field 1.1
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- field 1.2 with autospan
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* - row 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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- row 3
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Cross-referencing
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-----------------
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Cross-referencing from one documentation page to another can be done simply by
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writing the path to the document file, no special syntax required. The path can
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be either absolute or relative. For absolute paths, start it with
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"Documentation/". For example, to cross-reference to this page, all the
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following are valid options, depending on the current document's directory (note
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that the ``.rst`` extension is required)::
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See Documentation/doc-guide/sphinx.rst. This always works.
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Take a look at sphinx.rst, which is at this same directory.
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Read ../sphinx.rst, which is one directory above.
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If you want the link to have a different rendered text other than the document's
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title, you need to use Sphinx's ``doc`` role. For example::
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See :doc:`my custom link text for document sphinx <sphinx>`.
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For most use cases, the former is preferred, as it is cleaner and more suited
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for people reading the source files. If you come across a ``:doc:`` usage that
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isn't adding any value, please feel free to convert it to just the document
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path.
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For information on cross-referencing to kernel-doc functions or types, see
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Documentation/doc-guide/kernel-doc.rst.
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.. _sphinx_kfigure:
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Figures & Images
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================
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If you want to add an image, you should use the ``kernel-figure`` and
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``kernel-image`` directives. E.g. to insert a figure with a scalable
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image format, use SVG (:ref:`svg_image_example`)::
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.. kernel-figure:: svg_image.svg
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:alt: simple SVG image
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SVG image example
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.. _svg_image_example:
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.. kernel-figure:: svg_image.svg
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:alt: simple SVG image
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SVG image example
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The kernel figure (and image) directive supports **DOT** formatted files, see
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* DOT: http://graphviz.org/pdf/dotguide.pdf
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* Graphviz: http://www.graphviz.org/content/dot-language
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A simple example (:ref:`hello_dot_file`)::
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.. kernel-figure:: hello.dot
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:alt: hello world
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DOT's hello world example
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.. _hello_dot_file:
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.. kernel-figure:: hello.dot
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:alt: hello world
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DOT's hello world example
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Embedded *render* markups (or languages) like Graphviz's **DOT** are provided by the
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``kernel-render`` directives.::
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.. kernel-render:: DOT
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:alt: foobar digraph
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:caption: Embedded **DOT** (Graphviz) code
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digraph foo {
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"bar" -> "baz";
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}
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How this will be rendered depends on the installed tools. If Graphviz is
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installed, you will see a vector image. If not, the raw markup is inserted as
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*literal-block* (:ref:`hello_dot_render`).
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.. _hello_dot_render:
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.. kernel-render:: DOT
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:alt: foobar digraph
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:caption: Embedded **DOT** (Graphviz) code
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digraph foo {
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"bar" -> "baz";
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}
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The *render* directive has all the options known from the *figure* directive,
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plus option ``caption``. If ``caption`` has a value, a *figure* node is
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inserted. If not, an *image* node is inserted. A ``caption`` is also needed, if
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you want to refer to it (:ref:`hello_svg_render`).
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Embedded **SVG**::
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.. kernel-render:: SVG
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:caption: Embedded **SVG** markup
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:alt: so-nw-arrow
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<?xml version="1.0" encoding="UTF-8"?>
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<svg xmlns="http://www.w3.org/2000/svg" version="1.1" ...>
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...
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</svg>
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.. _hello_svg_render:
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.. kernel-render:: SVG
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:caption: Embedded **SVG** markup
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:alt: so-nw-arrow
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<?xml version="1.0" encoding="UTF-8"?>
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<svg xmlns="http://www.w3.org/2000/svg"
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version="1.1" baseProfile="full" width="70px" height="40px" viewBox="0 0 700 400">
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<line x1="180" y1="370" x2="500" y2="50" stroke="black" stroke-width="15px"/>
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<polygon points="585 0 525 25 585 50" transform="rotate(135 525 25)"/>
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</svg>
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