Documenting Ceph

User documentation

The documentation on is generated from the reStructuredText sources in /doc/ in the Ceph git repository.

Please make sure that your changes are written in a way that is intended for end users of the software, unless you are making additions in /doc/dev/, which is the section for developers.

All pull requests that modify user-facing functionality must include corresponding updates to documentation: see Submitting Patches for more detail.

Check your .rst syntax is working as expected by using the “View” button in the github user interface when looking at a diff on an .rst file, or build the docs locally using the admin/build-doc script.

For more information about the Ceph documentation, see Documenting Ceph.

Code Documentation

C and C++ can be documented with Doxygen, using the subset of Doxygen markup supported by Breathe.

The general format for function documentation is

 * Short description
 * Detailed description when necessary
 * preconditons, postconditions, warnings, bugs or other notes
 * parameter reference
 * return value (if non-void)

This should be in the header where the function is declared, and functions should be grouped into logical categories. The librados C API provides a complete example. It is pulled into Sphinx by librados.rst, which is rendered at Librados (C).

To generate the doxygen documentation in HTML format use:

# cmake --build . --target doxygen

HTML output will be under: build-doc/doxygen/html

Drawing diagrams


You can use Graphviz, as explained in the Graphviz extension documentation.

digraph "example" { foo -> bar; bar -> baz; bar -> th }

Most of the time, you’ll want to put the actual DOT source in a separate file, like this:

.. graphviz::

See the Dot User’s Manual by Emden R. Gansner, Eleftherios Koutsofios, and Stephen North for examples of digraphs. This is especially useful if this is your first time encountering GraphViz.


You can use Ditaa:


If a use arises, we can integrate Blockdiag. It is a Graphviz-style declarative language for drawing things, and includes:


You can use Inkscape to generate scalable vector graphics. for restructedText documents.

If you generate diagrams with Inkscape, you should commit both the Scalable Vector Graphics (SVG) file and export a Portable Network Graphic (PNG) file. Reference the PNG file.

By committing the SVG file, others will be able to update the SVG diagrams using Inkscape.

HTML5 will support SVG inline.