Add file info RPC call

Due to the need to determine the size of the temporary disk used for
the VM helper, an RPC call capable of supplying this information has
been added. It can be extended as needed to supply additional
information provided by Python's os.stat.
Signed-off-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Jose A. Lopes <jabolopes@google.com>

lib/backend.py

@@ -4675,6 +4675,30 @@ def ConfigureOVS(ovs_name, ovs_link):
             result.output), log=True)
 
 
+def GetFileInfo(file_path):
+  """ Checks if a file exists and returns information related to it.
+
+  Currently returned information:
+    - file size: int, size in bytes
+
+  @type file_path: string
+  @param file_path: Name of file to examine.
+
+  @rtype: tuple of bool, dict
+  @return: Whether the file exists, and a dictionary of information about the
+           file gathered by os.stat.
+
+  """
+  try:
+    stat_info = os.stat(file_path)
+    values_dict = {
+      constants.STAT_SIZE: stat_info.st_size,
+    }
+    return True, values_dict
+  except IOError:
+    return False, {}
+
+
 class HooksRunner(object):
   """Hook runner.
 

lib/rpc_defs.py

@@ -560,6 +560,9 @@ _MISC_CALLS = [
   ("set_watcher_pause", MULTI, None, constants.RPC_TMO_URGENT, [
     ("until", None, None),
     ], None, None, "Set watcher pause end"),
+  ("get_file_info", SINGLE, None, constants.RPC_TMO_FAST, [
+    ("file_path", None, None),
+    ], None, None, "Checks if a file exists and reports on it"),
   ]
 
 CALLS = {

lib/server/noded.py

@@ -969,6 +969,14 @@ class NodeRequestHandler(http.server.HttpServerHandler):
     (until, ) = params
     return backend.SetWatcherPause(until)
 
+  @staticmethod
+  def perspective_get_file_info(params):
+    """Get info on whether a file exists and its properties.
+
+    """
+    (path, ) = params
+    return backend.GetFileInfo(path)
+
   # os -----------------------
 
   @staticmethod

src/Ganeti/Constants.hs

@@ -4873,3 +4873,12 @@ debugModeConfidentialityWarning :: String
 debugModeConfidentialityWarning =
   "ALERT: %s started in debug mode.\n\
   \ Private and secret parameters WILL be logged!\n"
+
+-- * Stat dictionary entries
+--
+-- The get_file_info RPC returns a number of values as a dictionary, and the
+-- following constants are both descriptions and means of accessing them.
+
+-- | The size of the file
+statSize :: String
+statSize = "size"