doc-rst: generic way to build only sphinx sub-folders

Add a generic way to build only a reST sub-folder with or
without a individual *build-theme*.

* control *sub-folders* by environment SPHINXDIRS
* control *build-theme* by environment SPHINX_CONF

Folders with a conf.py file, matching $(srctree)/Documentation/*/conf.py
can be build and distributed *stand-alone*. E.g. to compile only the
html of 'media' and 'gpu' folder use::

  make SPHINXDIRS="media gpu" htmldocs

To use an additional sphinx-build configuration (*build-theme*) set the
name of the configuration file to SPHINX_CONF. E.g. to compile only the
html of 'media' with the *nit-picking* build use::

  make SPHINXDIRS=media SPHINX_CONF=conf_nitpick.py htmldocs

With this, the Documentation/conf.py is read first and updated with the
configuration values from the Documentation/media/conf_nitpick.py.

Signed-off-by: Markus Heiser <markus.heiser@darmarIT.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 32 insertions, 0 deletions

diff --git a/Documentation/sphinx/load_config.py b/Documentation/sphinx/load_config.py
new file mode 100644
index 000000000000..301a21aa4f63
--- /dev/null
+++ b/Documentation/sphinx/load_config.py
@@ -0,0 +1,32 @@
+# -*- coding: utf-8; mode: python -*-
+# pylint: disable=R0903, C0330, R0914, R0912, E0401
+
+import os
+import sys
+from sphinx.util.pycompat import execfile_
+
+# ------------------------------------------------------------------------------
+def loadConfig(namespace):
+# ------------------------------------------------------------------------------
+
+    u"""Load an additional configuration file into *namespace*.
+
+    The name of the configuration file is taken from the environment
+    ``SPHINX_CONF``. The external configuration file extends (or overwrites) the
+    configuration values from the origin ``conf.py``.  With this you are able to
+    maintain *build themes*.  """
+
+    config_file = os.environ.get("SPHINX_CONF", None)
+    if (config_file is not None
+        and os.path.normpath(namespace["__file__"]) != os.path.normpath(config_file) ):
+        config_file = os.path.abspath(config_file)
+
+        if os.path.isfile(config_file):
+            sys.stdout.write("load additional sphinx-config: %s\n" % config_file)
+            config = namespace.copy()
+            config['__file__'] = config_file
+            execfile_(config_file, config)
+            del config['__file__']
+            namespace.update(config)
+        else:
+            sys.stderr.write("WARNING: additional sphinx-config not found: %s\n" % config_file)