Add a function for listing all MAC addresses in a cluster

.. collected from all network interfaces of all instances.
Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>

src/Ganeti/Config.hs

@@ -59,6 +59,8 @@ module Ganeti.Config
     , getFilledInstBeParams
     , getFilledInstOsParams
     , getNetwork
+    , MAC
+    , getAllMACs
     , buildLinkIpInstnameMap
     , instNodes
     ) where
@@ -475,6 +477,14 @@ getNetwork cfg name =
                               networks
                 in getItem "Network" name by_name
 
+-- ** MACs
+
+type MAC = String
+
+-- | Returns all MAC addresses used in the cluster.
+getAllMACs :: ConfigData -> [MAC]
+getAllMACs = F.foldMap (map nicMac . instNics) . configInstances
+
 -- * ND params
 
 -- | Type class denoting objects which have node parameters.