Add option --one-step-only to hroller

Add a new option to hroller to only output information about the first
reboot group. Together with the option --node-tags this allows for the
following work flow. First tag all nodes; then repeatedly compute the
first node group, handle these nodes and remove the tags. In between
these steps, other operations can be carried out on the cluster.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Thomas Thrainer <thomasth@google.com>

man/hroller.rst

@@ -33,6 +33,7 @@ Reporting options:
 
 **[ -v... | -q ]**
 **[ -S *file* ]**
+**[ --one-step-only ]**
 
 DESCRIPTION
 -----------
@@ -65,6 +66,9 @@ For a description of the standard options check **htools**\(7) and
 \--node-tags *tag,...*
   Restrict to nodes having at least one of the given tags.
 
+\--one-step-only
+  Restrict to the first reboot group. Output the group one node per line.
+
 \--force
   Do not fail, even if the master node cannot be determined.
 

src/Ganeti/HTools/CLI.hs

@@ -71,6 +71,7 @@ module Ganeti.HTools.CLI
   , oNodeSim
   , oNodeTags
   , oOfflineNode
+  , oOneStepOnly
   , oOutputDir
   , oPrintCommands
   , oPrintInsts
@@ -138,6 +139,7 @@ data Options = Options
   , optNodeSim     :: [String]       -- ^ Cluster simulation mode
   , optNodeTags    :: Maybe [String] -- ^ List of node tags to restrict to 
   , optOffline     :: [String]       -- ^ Names of offline nodes
+  , optOneStepOnly :: Bool           -- ^ Only do the first step
   , optOutPath     :: FilePath       -- ^ Path to the output directory
   , optSaveCluster :: Maybe FilePath -- ^ Save cluster state to this file
   , optShowCmds    :: Maybe FilePath -- ^ Whether to show the command list
@@ -186,6 +188,7 @@ defaultOptions  = Options
   , optNodeSim     = []
   , optNodeTags    = Nothing
   , optOffline     = []
+  , optOneStepOnly = False
   , optOutPath     = "."
   , optSaveCluster = Nothing
   , optShowCmds    = Nothing
@@ -469,6 +472,13 @@ oOfflineNode =
    "set node as offline",
    OptComplOneNode)
 
+oOneStepOnly :: OptType
+oOneStepOnly =
+  (Option "" ["one-step-only"]
+   (NoArg (\ opts -> Ok opts {optOneStepOnly = True}))
+   "Only do the first step",
+   OptComplNone)
+
 oOutputDir :: OptType
 oOutputDir =
   (Option "d" ["output-dir"]

src/Ganeti/HTools/Program/Hroller.hs

@@ -65,6 +65,7 @@ options = do
     , oSaveCluster
     , oGroup
     , oForce
+    , oOneStepOnly
     ]
 
 -- | The list of arguments supported by the program.
@@ -169,6 +170,15 @@ main opts args = do
 
   when (verbose > 1) . putStrLn $ getStats colorings
 
-  unless (optNoHeaders opts) $
-         putStrLn "'Node Reboot Groups'"
-  mapM_ (putStrLn . commaJoin) outputRebootNames
+  if optOneStepOnly opts
+     then do
+       unless (optNoHeaders opts) $
+              putStrLn "'First Reboot Group'"
+       case outputRebootNames of
+         [] -> return ()
+         y : _ -> mapM_ putStrLn y
+     else do
+       unless (optNoHeaders opts) $
+              putStrLn "'Node Reboot Groups'"
+       mapM_ (putStrLn . commaJoin) outputRebootNames
+