RPC to start/stop a daemon on a node

This RPC will be needed so that changes to the cluster parameters for
enabled hypervisors, user shutdown, and vm capable nodes, can
start/stop the KVM daemon as necessary.
Signed-off-by: Jose A. Lopes <jabolopes@google.com>
Reviewed-by: Hrvoje Ribicic <riba@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>

lib/backend.py

@@ -1247,6 +1247,32 @@ def GetCryptoTokens(token_requests):
   return tokens
 
 
+def EnsureDaemon(daemon_name, run):
+  """Ensures the given daemon is running or stopped.
+
+  @type daemon_name: string
+  @param daemon_name: name of the daemon (e.g., constants.KVMD)
+
+  @type run: bool
+  @param run: whether to start or stop the daemon
+
+  @rtype: bool
+  @return: 'True' if daemon successfully started/stopped,
+           'False' otherwise
+
+  """
+  allowed_daemons = [constants.KVMD]
+
+  if daemon_name not in allowed_daemons:
+    fn = lambda _: False
+  elif run:
+    fn = utils.EnsureDaemon
+  else:
+    fn = utils.StopDaemon
+
+  return fn(daemon_name)
+
+
 def GetBlockDevSizes(devices):
   """Return the size of the given block devices
 

lib/rpc_defs.py

@@ -509,6 +509,10 @@ _NODE_CALLS = [
     ("token_request", None,
      "List of tuples of requested crypto token types, actions"),
     ], None, None, "Handle crypto tokens of the node."),
+  ("node_ensure_daemon", MULTI, None, constants.RPC_TMO_URGENT, [
+    ("daemon", None, "Daemon name"),
+    ("run", None, "Whether the daemon should be running or stopped"),
+    ], None, None, "Ensure daemon is running on the node."),
   ]
 
 _MISC_CALLS = [

lib/server/noded.py

@@ -872,6 +872,14 @@ class NodeRequestHandler(http.server.HttpServerHandler):
     token_requests = params[0]
     return backend.GetCryptoTokens(token_requests)
 
+  @staticmethod
+  def perspective_node_ensure_daemon(params):
+    """Ensure daemon is running.
+
+    """
+    (daemon_name, run) = params
+    return backend.EnsureDaemon(daemon_name, run)
+
   # cluster --------------------------
 
   @staticmethod

lib/utils/__init__.py

@@ -469,6 +469,13 @@ def WaitForFdCondition(fdobj, event, timeout):
 def EnsureDaemon(name):
   """Check for and start daemon if not alive.
 
+  @type name: string
+  @param name: daemon name
+
+  @rtype: bool
+  @return: 'True' if daemon successfully started,
+           'False' otherwise
+
   """
   result = RunCmd([pathutils.DAEMON_UTIL, "check-and-start", name])
   if result.failed:
@@ -482,6 +489,13 @@ def EnsureDaemon(name):
 def StopDaemon(name):
   """Stop daemon
 
+  @type name: string
+  @param name: daemon name
+
+  @rtype: bool
+  @return: 'True' if daemon successfully stopped,
+           'False' otherwise
+
   """
   result = RunCmd([pathutils.DAEMON_UTIL, "stop", name])
   if result.failed: