.. _acrn_doc:

ACRN documentation generation
#############################

These instructions will walk you through generating the Project ACRN's
documentation and publishing it to https://projectacrn.github.io.
You can also use these instructions to generate the ACRN documentation
on your local system.

Documentation overview
**********************

Project ACRN content is written using the reStructuredText markup
language (.rst file extension) with Sphinx extensions, and processed
using Sphinx to create a formatted stand-alone website. Developers can
view this content either in its raw form as .rst markup files, or you
can generate the HTML content and view it with a web browser directly on
your workstation.

You can read details about `reStructuredText`_, and `Sphinx`_ from
their respective websites.

The project's documentation contains the following items:

* ReStructuredText source files used to generate documentation found at the
  http://projectacrn.github.io website. All of the reStructuredText sources
  are found in the acrn-hypervisor/doc folder, or pulled in from sibling
  folders (such as /misc/) by the build scripts.

* Doxygen-generated material used to create all API-specific documents
  found at http://projectacrn.github.io/latest/api/.  The doc build
  process uses doxygen to scan source files in the hypervisor and
  device-model folders, and from sources in the acrn-kernel repo (as
  explained later).

The reStructuredText files are processed by the Sphinx documentation system,
and make use of the breathe extension for including the doxygen-generated API
material.


Set up the documentation working folders
****************************************

You'll need git installed to get the working folders set up:

* For an Ubuntu development system use:

  .. code-block:: bash

     sudo apt-get install git

* For a Fedora development system use

  .. code-block:: bash

     sudo dnf install git

We use the source header files to generate API docs and we use github.io
for publishing the generated documentation.  Here's the recommended
folder setup for documentation contributions and generation:

.. code-block: none

   projectacrn/
      acrn-hypervisor/
         devicemodel/
         doc/
         hypervisor/
      acrn-kernel/

The parent projectacrn folder is there because we'll also be creating a
publishing area later in these steps.  For API doc generation, we'll also
need the acrn-kernel repo contents in a sibling folder to the
acrn-hypervisor repo contents. 

It's best if the acrn-hypervisor
folder is an ssh clone of your personal fork of the upstream project
repos (though https clones work too):

#. Use your browser to visit https://github.com/projectacrn and do a
   fork of the **acrn-hypervisor** repo to your personal GitHub account.)

   .. image:: images/acrn-doc-fork.png
      :align: center

#. At a command prompt, create the working folder and clone the acrn-hypervisor
   repository to your local computer (and if you have publishing rights, the
   projectacrn.github.io repo).  If you don't have publishing rights
   you'll still be able to generate the docs locally, but not publish them:

   .. code-block:: bash

      cd ~
      mkdir projectacrn && cd projectacrn
      git clone git@github.com:<github-username>/projectacrn/acrn-hypervisor.git

#. For the cloned local repos, tell git about the upstream repo:

   .. code-block:: bash

      cd acrn-hypervisor
      git remote add upstream git@github.com:projectacrn/acrn-hypervisor.git

#. For API doc generation we'll also need the acrn-kernel repo available
   locally:

   .. code-block:: bash

      cd ..
      git clone git@github.com:projectacrn/acrn-kernel.git

   .. note:: We assume for doc generation that ``origin`` is pointed to
      the upstream repo.  If you're a developer and have the acrn-kernel
      repo already set up as a sibling folder to the acrn-hypervisor,
      you can skip this clone step.

#. If you haven't done so already, be sure to configure git with your name
   and email address for the ``signed-off-by`` line in your commit messages:

   .. code-block:: bash

      git config --global user.name "David Developer"
      git config --global user.email "david.developer@company.com"

Installing the documentation tools
**********************************

Our documentation processing has been tested to run with:

* Python 3.6.3
* Doxygen version 1.8.13
* Sphinx version 1.7.7
* Breathe version 4.9.1
* docutils version 0.14
* sphinx_rtd_theme version 0.4.0

Depending on your Linux version, install the needed tools:

* For Clear Linux OS: follow the :ref:`kbl-nuc-sdc` to install
  all the tools required

* For Ubuntu use:

  .. code-block:: bash

     sudo apt-get install doxygen python3-pip \
       python3-wheel make graphviz

* For Fedora use:

  .. code-block:: bash

     sudo dnf install doxygen python3-pip python3-wheel make graphviz

And for any of these Linux environments, install the remaining python-based
tools:

.. code-block:: bash

   cd ~/projectacrn/acrn-hypervisor/doc
   pip3 install --user -r scripts/requirements.txt

Add ``$HOME/.local/bin`` to the front of your ``PATH`` so the system will
find expected versions of python utilities such as ``sphinx-build`` and
``breathe``:

.. code-block:: bash

   printf "\nexport PATH=\$HOME/.local/bin:\$PATH" >> ~/.bashrc

.. note::

   You will need to open a new terminal for this change to be effective.
   Adding this to your ``~/.bashrc`` file ensures it is set by default.

And with that you're ready to generate the documentation.

.. note::

   We've provided a script you can run to show what versions of the
   doc building tools you have installed ::

      doc/scripts/show-versions.py

Documentation presentation theme
********************************

Sphinx supports easy customization of the generated documentation
appearance through the use of themes.  Replace the theme files and do
another ``make html`` and the output layout and style is changed. The
sphinx build system creates document cache information that attempts to
expedite doc rebuilds, but occasionally can cause an unexpected error or
warning to be generated.  Doing a ``make clean`` to create a clean doc
generation and a ``make html`` again generally cleans this up.

The ``read-the-docs`` theme is installed as part of the
``requirements.txt`` list above.  Tweaks to the standard
``read-the-docs`` look and feel are added by using CSS
and JavaScript customization found in ``doc/static``, and
theme template overrides found in ``doc/_templates``.

Running the documentation processors
************************************

The acrn-hypervisor/doc directory has all the .rst source files, extra
tools, and Makefile for generating a local copy of the ACRN technical
documentation.  For generating all the API documentation, there is a
dependency on having the ``acrn-kernel`` repo's contents available too
(as described previously).  You'll get a sphinx warning if that repo is
not set up as described, but you can be ignore that warning if you're
not planning to publish.

.. code-block:: bash

   cd ~/projectacrn/acrn-hypervisor/doc
   make html

Depending on your development system, it will take about 15 seconds to
collect and generate the HTML content.  When done, you can view the HTML
output with your browser started at
``~/projectacrn/acrn-hypervisor/doc/_build/html/index.html``.  You can
also ``cd`` to the ``doc/_build/html`` folder and run a local web server
with the command:

.. code-block:: bash

   python3 -m http.server

and use your web browser to open the URL:  ``http://localhost:8000``.

Publishing content
******************

If you have merge rights to the projectacrn repo called
projectacrn.github.io, you can update the public project documentation
found at https://projectacrn.github.io.

You'll need to do a one-time clone of the upstream repo (we publish
directly to the upstream repo rather than to a personal forked copy):

.. code-block:: bash

   cd ~/projectacrn
   git clone git@github.com:projectacrn/projectacrn.github.io.git

Then, after you've verified the generated HTML from ``make html`` looks
good, you can push directly to the publishing site with:

.. code-block:: bash

   make publish

This will delete everything in the publishing repo's **latest** folder
(in case the new version has deleted files) and push a copy of the
newly-generated HTML content directly to the GitHub pages publishing
repo.  The public site at https://projectacrn.github.io will be updated
(nearly) immediately so it's best to verify the locally generated html
before publishing.

Document Versioning
*******************

The https://projectacrn.github.io site has a document version selector
at the bottom of the left nav panel.  The contents of this version
selector are defined in the ``conf.py`` sphinx configuration file,
specifically:

.. code-block:: python

   html_context = {
      'current_version': current_version,
      'versions': ( ("latest", "/latest/"),
                    ("0.2", "/0.2/"),
                    ("0.1", "/0.1/"),
                  )
       }

As new versions of documentation are added, this ``versions`` selection
list should be updated to include the version number and publishing
folder.  Note that there's no direct selection to go to a newer version
from an older one, without going to ``latest`` first.

By default, doc build and publishing assumes we're generating
documentation for the master branch and publishing to the ``/latest/``
area on https://projectacrn.github.io. When we're generating the
documentation for a tagged version (e.g., 0.2), check out that version
of the repo, and add some extra flags to the make commands:

.. code-block:: bash

   cd ~/projectacrn/acrn-hypervisor/doc
   git checkout v0.2
   make clean
   make DOC_TAG=release RELEASE=0.2 html
   make DOC_TAG=release RELEASE=0.2 publish

Filtering expected warnings
***************************

Alas, there are some known issues with the doxygen/Sphinx/Breathe
processing that generates warnings for some constructs, in particular
around unnamed structures in nested unions or structs.
While these issues are being considered for fixing in
Sphinx/Breathe, we've added a post-processing filter on the output of
the documentation build process to check for "expected" messages from the
generation process output.

The output from the Sphinx build is processed by the python script
``scripts/filter-known-issues.py`` together with a set of filter
configuration files in the ``.known-issues/doc`` folder.  (This
filtering is done as part of the ``Makefile``.)

If you're contributing components included in the ACRN API
documentation and run across these warnings, you can include filtering
them out as "expected" warnings by adding or editing a conf file in the
``.known-issues/doc`` folder, following the example of other conf files
found there.

.. _reStructuredText: http://sphinx-doc.org/rest.html
.. _Sphinx: http://sphinx-doc.org/