Features/Documentation: Difference between revisions

Revision as of 23:58, 7 November 2016

QEMU's documentation needs some reorganization.

Ultimately there should be five manuals:

QEMU user mode emulation (docs/qemu-user, Features/Documentation/qemu-user): currently in qemu-doc.texi
QEMU full-system emulation user's guide (docs/qemu-system, Features/Documentation/qemu-system): Category:User documentation; the largest part of qemu-doc.texi; also covers qemu-img, qemu-io; parts of docs/
QEMU full-system emulation management guide (docs/qemu-system-mgmt, Features/Documentation/qemu-system-mgmt): qmp-commands.txt; qemu-ga.texi; more pieces of docs/; docs/specs/vhost-user.txt; probably should include file format specs in docs/specs/
QEMU full-system emulation guest hardware specifications (docs/qemu-system-hw, Features/Documentation/qemu-system-hw): currently in docs/specs/
QEMU developer's guide (docs/qemu-devel, Features/Documentation/qemu-devel): Category:Developer documentation; the rest of docs/; the implementation notes in qemu-doc.texi; tcg/README; doc comments in the source code; automatically generated docs for Python classes in qemu-iotests and scripts/qmp

Choices

Based on experience from the Linux kernel, QEMU's docs pipeline is going to be based on Sphinx (sample developer doc, sample user doc. Sphinx is extensible and it is easy to add new input formats and input directives.

Currently, QEMU documentation is written in a mix of Texinfo and text files roughly based on Markdown. Sphinx's native format is reStructuredText (rST). Texinfo input is not supported by Sphinx, but Paolo has a docutils (Sphinx-compatible) parser for Docbook; Texinfo is able to convert .texi input files into Docbook. This parser was used to produce the sample user doc above.

Currently, QEMU doc comments have never been actually used together with a actual documentation generator in mind, but are roughly based on gtk-doc syntax. We will probably end up keeping a copy of the Linux kernel's kernel-doc script. kernel-doc currently supports rST and Docbook output.

As a first step, we should decide how to evolve this into something more structured.

For text, the two possible choices should ultimately be:

Convert everything to reStructuredText
Advantages: Flexible enough, native format for Sphinx, Linux is using it

Disadvantages: Less "obvious" than Markdown (though a basic conversion seems to be simple enough), looks somewhat weird when you use more advanced features, after Texinfo conversion (makeinfo --docbook + either Pandoc or db2rst.py) expect some hand editing.
Convert everything to Texinfo
Advantages: qemu-doc.texi and command-line doc comments are already written in Texinfo, QAPI automatically generated docs also use Texinfo in the current version of the patches; more traditional/"precise" markup

Disadvantages: Most different from basic ASCII text, markup not supported by kernel-doc, probably some rST is needed anyway for Sphinx-specific stuff (e.g., toctree directives)

Markdown (i.e. Sphinx's reCommonMark extension) is not going to be used.

For C doc comments, the three possible choices are:

Use reStructuredText markup
Advantages: Flexible enough, native format for Sphinx, Linux is using it

Disadvantages: Would not want to use rST for doc comments but not for the rest of docs/, or for command-line doc comments
Extend kernel-doc to support Texinfo markup, and convert that to Docbook
Advantages: qemu-doc.texi and command-line doc comments are already written in Texinfo

Disadvantages: More work to do, Rube Goldberg would be proud
Use no markup, apart from annotating fields, functions etc. using sigils (e.g. kernel-doc's &struct Foo or GtkDoc's %Foo).
Advantages: Simplest solution, can use any kernel-doc backend (DocBook and rST), doesn't conflict with chioce of format for docs/

Disadvantages: none?

We should also choose whether to place comments close to the definition or the declaration of functions. Linux seems to place comments close to the definition—the disadvantage being that struct comments must obviously be placed in headers.

Things to do

For now in no particular order:

Merge Marc-André's patches to automatically generate QAPI documentation
Prepare five wiki pages to work collaboratively on the manuals' table of contents, populate them with current qemu-doc.texi ToC and a list of docs/ files.
Split qemu-doc.texi so that the bulk of its contents is included from small files in docs/
Annotate developer documentation in docs/ with the corresponding C source code, so as to prioritize where to add doc comments

@@ Line 39: / Line 39: @@
 # Convert everything to reStructuredText
 #:'''Advantages:''' Flexible enough, native format for Sphinx, Linux is using it
-#:'''Disadvantages:''' Less "obvious" than Markdown (though a basic conversion seems to be simple enough), looks somewhat weird when you use more advanced features
+#:'''Disadvantages:''' Less "obvious" than Markdown (though a basic conversion seems to be simple enough), looks somewhat weird when you use more advanced features, after Texinfo conversion (makeinfo --docbook + either Pandoc or db2rst.py) expect some hand editing.
 # Convert everything to Texinfo
 #:'''Advantages:''' qemu-doc.texi and command-line doc comments are already written in Texinfo, QAPI automatically generated docs also use Texinfo in the current version of the patches; more traditional/"precise" markup
-#:'''Disadvantages:''' Most different from basic ASCII text, markup not supported by kernel-doc, probably need some rST anyway for toctree directives and the like
+#:'''Disadvantages:''' Most different from basic ASCII text, markup not supported by kernel-doc, probably some rST is needed anyway for Sphinx-specific stuff (e.g., toctree directives)
 Markdown (i.e. Sphinx's reCommonMark extension) is not going to be used.