Make Hroller present master node last

If in the list of nodes to be scheduled for maintaince,
one is marked as being the master node, schedule it
as the last node in the last group.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

src/Ganeti/HTools/Program/Hroller.hs

@@ -98,6 +98,14 @@ filterOutput g l =
       nonNullOnly = filter (not . null)
   in nonNullOnly (map (onlineOnly . byGroupOnly g) l)
 
+-- | Put the master node last.
+-- Reorder a list of lists of nodes such that the master node (if present)
+-- is the last node of the last group.
+masterLast :: [[Node.Node]] -> [[Node.Node]]
+masterLast rebootgroups =
+  map (uncurry (++)) . uncurry (++) . partition (null . snd) $
+  map (partition (not . Node.isMaster)) rebootgroups
+
 -- | Main function.
 main :: Options -> [String] -> IO ()
 main opts args = do
@@ -121,7 +129,6 @@ main opts args = do
       Just grp -> return (Just grp)
 
   -- TODO: fail if instances are running (with option to warn only)
-  -- TODO: identify master node, and put it last
 
   nodeGraph <- case Node.mkNodeGraph nlf ilf of
                      Nothing -> exitErr "Cannot create node graph"
@@ -138,7 +145,8 @@ main opts args = do
         (snd . minimumBy (comparing (IntMap.size . snd))) colorings
       idToNode = (`Container.find` nlf)
       nodesRebootGroups = map (map idToNode) $ IntMap.elems smallestColoring
-      outputRebootGroups = filterOutput wantedGroup nodesRebootGroups
+      outputRebootGroups = masterLast $
+                           filterOutput wantedGroup nodesRebootGroups
       outputRebootNames = map (map Node.name) outputRebootGroups
 
   when (verbose > 1) . putStrLn $ getStats colorings