Add a module to support virtual clusters

Virtual clusters are an efficient way to test how Ganeti behaves
on a large cluster without requiring a large number of machines.
Now that more tasks like job replication are done by luxid, provide
that functionality in Haskell as well.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

Makefile.am

@@ -745,7 +745,8 @@ HS_LIB_SRCS = \
 	src/Ganeti/THH/PyType.hs \
 	src/Ganeti/Types.hs \
 	src/Ganeti/UDSServer.hs \
-	src/Ganeti/Utils.hs
+	src/Ganeti/Utils.hs\
+	src/Ganeti/VCluster.hs
 
 HS_TEST_SRCS = \
 	test/hs/Test/AutoConf.hs \

src/Ganeti/VCluster.hs

+{-| Utilities for virtual clusters.
+
+-}
+
+{-
+
+Copyright (C) 2014 Google Inc.
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301, USA.
+
+-}
+
+module Ganeti.VCluster
+  ( makeVirtualPath
+  ) where
+
+import Control.Monad (liftM)
+import Data.Set (member)
+import System.Posix.Env (getEnv)
+import System.FilePath.Posix
+
+import Ganeti.ConstantUtils (unFrozenSet)
+import Ganeti.Constants
+
+getRootDirectory :: IO (Maybe FilePath)
+getRootDirectory = fmap normalise `liftM` getEnv vClusterRootdirEnvname
+
+-- | Pure computation of the virtual path from the original path
+-- and the vcluster root
+virtualPath :: FilePath -> FilePath -> FilePath
+virtualPath fpath root =
+  let relpath = makeRelative root fpath
+  in if member fpath (unFrozenSet vClusterVpathWhitelist)
+       then fpath
+       else vClusterVirtPathPrefix </> relpath
+
+-- | Given a path, make it a virtual one, if in a vcluster environment.
+-- Otherwise, return unchanged.
+makeVirtualPath :: FilePath -> IO FilePath
+makeVirtualPath fpath = maybe fpath (virtualPath fpath) `liftM` getRootDirectory