If the result of a dynamic inventory script contains a "_meta" hash at top level

and the _meta hash contains a "hostvars", don't call --host hostname for any elements
and just serve them directly for performance enhancements with the external inventory
script and a large number of hosts.

lib/ansible/inventory/script.py

@@ -42,6 +42,8 @@ class InventoryScript(object):
             raise errors.AnsibleError("problem running %s (%s)" % (' '.join(cmd), e))
         (stdout, stderr) = sp.communicate()
         self.data = stdout
+        # see comment about _meta below
+        self.host_vars_from_top = None
         self.groups = self._parse(stderr)
 
     def _parse(self, err):
@@ -52,11 +54,23 @@ class InventoryScript(object):
         groups    = dict(all=all)
         group     = None
 
+
         if 'failed' in self.raw:
             sys.stderr.write(err + "\n")
             raise errors.AnsibleError("failed to parse executable inventory script results: %s" % self.raw)
 
         for (group_name, data) in self.raw.items():
+ 
+            # in Ansible 1.3 and later, a "_meta" subelement may contain
+            # a variable "hostvars" which contains a hash for each host
+            # if this "hostvars" exists at all then do not call --host for each
+            # host.  This is for efficiency and scripts should still return data
+            # if called with --host for backwards compat with 1.2 and earlier.
+
+            if group_name == '_meta':
+                if 'hostvars' in data:
+                    self.host_vars_from_top = data['hostvars']
+                    continue
 
             group = groups[group_name] = Group(group_name)
             host = None
@@ -85,6 +99,8 @@ class InventoryScript(object):
 
         # Separate loop to ensure all groups are defined
         for (group_name, data) in self.raw.items():
+            if group_name == '_meta':
+                continue
             if isinstance(data, dict) and 'children' in data:
                 for child_name in data['children']:
                     if child_name in groups:
@@ -93,6 +109,11 @@ class InventoryScript(object):
 
     def get_host_variables(self, host):
         """ Runs <script> --host <hostname> to determine additional host variables """
+        if self.host_vars_from_top is not None:
+            got = self.host_vars_from_top.get(host, {})
+            return got
+
+
         cmd = [self.filename, "--host", host.name]
         try:
             sp = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)