docs: Provide separate conf.py for each manual we want

By default Sphinx wants to build a single manual at once.
For QEMU, this doesn't suit us, because we want to have
separate manuals for "Developer's Guide", "User Manual",
and so on, and we don't want to ship the Developer's Guide
to end-users. However, we don't want to completely duplicate
conf.py for each manual, and we'd like to continue to
support "build all docs in one run" for third-party sites
like readthedocs.org.

Make the top-level conf.py support two usage forms:
 (1) as a common config file which is included by the conf.py
 for each of QEMU's manuals: in this case sphinx-build is run
 multiple times, once per subdirectory.
 (2) as a top level conf file which will result in building all
 the manuals into a single document: in this case sphinx-build is
 run once, on the top-level docs directory.

Provide per-manual conf.py files and top level pages for
our first two manuals:
 * QEMU Developer's Guide (docs/devel)
 * QEMU System Emulation Management and Interoperability Guide
   (docs/interop)

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Message-id: 20190305172139.32662-9-peter.maydell@linaro.org
Message-id: 20190228145624.24885-9-peter.maydell@linaro.org

docs/conf.py

@@ -3,6 +3,20 @@
 # QEMU documentation build configuration file, created by
 # sphinx-quickstart on Thu Jan 31 16:40:14 2019.
 #
+# This config file can be used in one of two ways:
+# (1) as a common config file which is included by the conf.py
+# for each of QEMU's manuals: in this case sphinx-build is run multiple
+# times, once per subdirectory.
+# (2) as a top level conf file which will result in building all
+# the manuals into a single document: in this case sphinx-build is
+# run once, on the top-level docs directory.
+#
+# QEMU's makefiles take option (1), which allows us to install
+# only the ones the user cares about (in particular we don't want
+# to ship the 'devel' manual to end-users).
+# Third-party sites such as readthedocs.org will take option (2).
+#
+#
 # This file is execfile()d with the current directory set to its
 # containing dir.
 #
@@ -12,13 +26,22 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
+import os
+import sys
+
+# The per-manual conf.py will set qemu_docdir for a single-manual build;
+# otherwise set it here if this is an entire-manual-set build.
+# This is always the absolute path of the docs/ directory in the source tree.
+try:
+    qemu_docdir
+except NameError:
+    qemu_docdir = os.path.abspath(".")
+
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
-# documentation root, use os.path.abspath to make it absolute, like shown here.
+# documentation root, use an absolute path starting from qemu_docdir.
 #
-# import os
-# import sys
-# sys.path.insert(0, os.path.abspath('.'))
+# sys.path.insert(0, os.path.join(qemu_docdir, "my_subdir"))
 
 
 # -- General configuration ------------------------------------------------
@@ -91,8 +114,10 @@ html_theme = 'alabaster'
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#
-# html_theme_options = {}
+# We initialize this to empty here, so the per-manual conf.py can just
+# add individual key/value entries.
+html_theme_options = {
+}
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,

docs/devel/conf.py

@@ -0,0 +1,15 @@
+# -*- coding: utf-8 -*-
+#
+# QEMU documentation build configuration file for the 'devel' manual.
+#
+# This includes the top level conf file and then makes any necessary tweaks.
+import sys
+import os
+
+qemu_docdir = os.path.abspath("..")
+parent_config = os.path.join(qemu_docdir, "conf.py")
+exec(compile(open(parent_config, "rb").read(), parent_config, 'exec'))
+
+# This slightly misuses the 'description', but is the best way to get
+# the manual title to appear in the sidebar.
+html_theme_options['description'] = u'Developer''s Guide'

docs/devel/index.rst

@@ -0,0 +1,21 @@
+.. This is the top level page for the 'devel' manual.
+
+
+QEMU Developer's Guide
+======================
+
+This manual documents various parts of the internals of QEMU.
+You only need to read it if you are interested in reading or
+modifying QEMU's source code.
+
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   loads-stores
+   memory
+   migration
+   stable-process
+   testing
+

docs/index.rst

@@ -10,11 +10,6 @@ Welcome to QEMU's documentation!
    :maxdepth: 2
    :caption: Contents:
 
+   interop/index
+   devel/index
 
-
-Indices and tables
-==================
-
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`

docs/interop/conf.py

@@ -0,0 +1,15 @@
+# -*- coding: utf-8 -*-
+#
+# QEMU documentation build configuration file for the 'interop' manual.
+#
+# This includes the top level conf file and then makes any necessary tweaks.
+import sys
+import os
+
+qemu_docdir = os.path.abspath("..")
+parent_config = os.path.join(qemu_docdir, "conf.py")
+exec(compile(open(parent_config, "rb").read(), parent_config, 'exec'))
+
+# This slightly misuses the 'description', but is the best way to get
+# the manual title to appear in the sidebar.
+html_theme_options['description'] = u'System Emulation Management and Interoperability Guide'

docs/interop/index.rst

@@ -0,0 +1,18 @@
+.. This is the top level page for the 'interop' manual.
+
+
+QEMU System Emulation Management and Interoperability Guide
+===========================================================
+
+This manual contains documents and specifications that are useful
+for making QEMU interoperate with other software.
+
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   bitmaps
+   live-block-operations
+   pr-helper
+