Allow loading of product/vendor/package info from external file

Currently the version.py file hardcodes some basic info for
the NOVA_PRODUCT, NOVA_VENDOR and NOVA_PACKAGE constants. It
is desirable that OS distro vendors can override/extend this
data in packages they ship. Cloud providers may also desire
to do the same. This allows Nova to optionally load this
data from a /etc/nova/release file. That file should contain
the data in a trivial "ini" format. For example:

  [Nova]
  vendor = Fedora Project
  package = 1.fc18

Note that vendor sare not required to override all strings.
In this example, the 'product' field is not set, leaving
it on the default 'OpenStack Nova' value.

Change-Id: I3d8d32eaf35268c4b0908b0a93b7c9a2ea9c580a
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

nova/version.py

@@ -21,16 +21,63 @@ NOVA_VERSION = ['2013', '1', None]
 YEAR, COUNT, REVISION = NOVA_VERSION
 FINAL = False   # This becomes true at Release Candidate time
 
+loaded = False
+
+
+def _load_config():
+    # Don't load in global context, since we can't assume
+    # these modules are accessible when distutils uses
+    # this module
+    import ConfigParser
+
+    from nova.openstack.common import cfg
+    from nova.openstack.common import log as logging
+
+    global loaded, NOVA_VENDOR, NOVA_PRODUCT, NOVA_PACKAGE
+    if loaded:
+        return
+
+    loaded = True
+
+    cfgfile = cfg.CONF.find_file("release")
+    if cfgfile is None:
+        return
+
+    try:
+        cfg = ConfigParser.RawConfigParser()
+        cfg.read(cfgfile)
+
+        NOVA_VENDOR = cfg.get("Nova", "vendor")
+        if cfg.has_option("Nova", "vendor"):
+            NOVA_VENDOR = cfg.get("Nova", "vendor")
+
+        NOVA_PRODUCT = cfg.get("Nova", "product")
+        if cfg.has_option("Nova", "product"):
+            NOVA_PRODUCT = cfg.get("Nova", "product")
+
+        NOVA_PACKAGE = cfg.get("Nova", "package")
+        if cfg.has_option("Nova", "package"):
+            NOVA_PACKAGE = cfg.get("Nova", "package")
+    except Exception, ex:
+        LOG = logging.getLogger(__name__)
+        LOG.error("Failed to load %(cfgfile)s: %(ex)s" % locals())
+
 
 def vendor_string():
+    _load_config()
+
     return NOVA_VENDOR
 
 
 def product_string():
+    _load_config()
+
     return NOVA_PRODUCT
 
 
 def package_string():
+    _load_config()
+
     return NOVA_PACKAGE