Add a function changing the priority of an opcode

This pure function follows the semantic that an opcode, including
its priority, may only be changed if the opcode is not finalized.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

src/Ganeti/JQueue.hs

@@ -31,6 +31,7 @@ module Ganeti.JQueue
     , InputOpCode(..)
     , queuedOpCodeFromMetaOpCode
     , queuedJobFromOpCodes
+    , changeOpCodePriority
     , cancelQueuedJob
     , Timestamp
     , fromClockTime
@@ -213,6 +214,14 @@ queuedJobFromOpCodes jobid ops = do
 setReceivedTimestamp :: Timestamp -> QueuedJob -> QueuedJob
 setReceivedTimestamp ts job = job { qjReceivedTimestamp = Just ts }
 
+-- | Change the priority of a QueuedOpCode, if it is not already
+-- finalized.
+changeOpCodePriority :: Int -> QueuedOpCode -> QueuedOpCode
+changeOpCodePriority prio op =
+  if qoStatus op > OP_STATUS_RUNNING
+     then op
+     else op { qoPriority = prio }
+
 -- | Set the state of a QueuedOpCode to canceled.
 cancelOpCode :: Timestamp -> QueuedOpCode -> QueuedOpCode
 cancelOpCode now op =