VPP-57 Add Doxygen to VPP

- Configures Doxygen.
- Adds a source filter to do magic on our use of the preprocessor to do
  constructor stuff to make Doxygen grok it better.
- Adds a convenience helper to the root Makefile.
- Adds a README.md to the root directory (and which Doxygem uses as its
  "mainpage".
- Add several other documentative files.
- Currently using SVG for call graphs, though this may have a
  load-time performance impact in browsers.

Change-Id: I25fc6fb5bf634319dcb36a7f0e32031921c125ac
Signed-off-by: Chris Luke <chrisy@flirble.org>

doxygen/filter_c.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python
+
+import sys, re
+
+if len(sys.argv) < 2:
+    sys.stderr.write("Usage: %s <filename>\n" % (sys.argv[0]))
+    sys.exit(1)
+
+patterns = [
+    # Search for VLIB_CLI_COMMAND, extract its parameter and add a docblock for it
+    ( re.compile("(?P<m>VLIB_CLI_COMMAND)\s*[(](?P<name>[a-zA-Z0-9_]+)(,[^)]*)?[)]"), r"/** @brief (@em constructor) \g<m> (\g<name>) */ vlib_cli_command_t \g<name>"),
+
+    # Search for VLIB_REGISTER_NODE, extract its parameter and add a docblock for it
+    ( re.compile("(?P<m>VLIB_REGISTER_NODE)\s*[(](?P<name>[a-zA-Z0-9_]+)(,[^)]*)?[)]"), r"/** @brief (@em constructor) \g<m> (\g<name>) */ vlib_node_registration_t \g<name>"),
+
+    # Search for VLIB_INIT_FUNCTION, extract its parameter and add a docblock for it
+    ( re.compile("(?P<m>VLIB_INIT_FUNCTION)\s*[(](?P<name>[a-zA-Z0-9_]+)[)]"), r"/** @brief (@em constructor) \g<m> (@ref \g<name>) */ vlib_init_function_t * _vlib_init_function_\g<name>"),
+    ( re.compile("(?P<m>VLIB_DECLARE_INIT_FUNCTION)\s*[(](?P<name>[a-zA-Z0-9_]+)[)]"), r"/** @brief (@em constructor) \g<m> (@ref \g<name>) */ vlib_init_function_t * _vlib_init_function_\g<name>"),
+
+    # Search for VLIB_LOOP_ENTER_FUNCTION, extract the 1st parameter (ignore any others) and add a docblock for it
+    ( re.compile("(?P<m>VLIB_MAIN_LOOP_ENTER_FUNCTION)\s*[(](?P<name>[a-zA-Z0-9_]+)(,[^)]*)?[)]"), r"/** @brief (@em constructor) \g<m> (@ref \g<name>) */ _vlib_main_loop_enter_\g<name>"),
+    ( re.compile("(?P<m>VLIB_MAIN_LOOP_EXIT_FUNCTION)\s*[(](?P<name>[a-zA-Z0-9_]+)(,[^)]*)?[)]"), r"/** @brief (@em constructor) \g<m> (@ref \g<name>) */ _vlib_main_loop_exit_\g<name>"),
+
+    # Search for VLIB_CONFIG_FUNCTION, extract the 1st parameter (ignore any others) and add a docblock for it
+    ( re.compile("(?P<m>VLIB_CONFIG_FUNCTION)\s*[(](?P<name>[a-zA-Z0-9_]+),\s*(?P<n>\"[^\"]+\")(,[^)]*)?[)]"), r"/** @brief (@em constructor) \g<m> (\g<name>, \g<n>) */ vlib_config_function_runtime_t _vlib_config_function_\g<name>"),
+    ( re.compile("(?P<m>VLIB_EARLY_CONFIG_FUNCTION)\s*[(](?P<name>[a-zA-Z0-9_]+),\s*(?P<n>\"[^\"]+\")(,[^)]*)?[)]"), r"/** @brief (@em constructor) \g<m> (\g<name>, \g<n>) */ vlib_config_function_runtime_t _vlib_config_function_\g<name>"),
+
+    # Search for "format_thing" and "unformat_thing" when used as a function pointer and add parens
+    ( re.compile("(?P<pre>(^|,)\s*)(?P<name>(un)?format_[a-zA-Z0-9_]+)(?P<post>\s*(,|$))") , r"\g<pre>\g<name>()\g<post>" ),
+]
+
+with open(sys.argv[1]) as fd:
+    for line in fd:
+        str = line
+        for p in patterns:
+            str = p[0].sub(p[1], str)
+        sys.stdout.write(str)