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diff --git a/Annex/InodeSentinal.hs b/Annex/InodeSentinal.hs
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+{- git-annex inode sentinal file
+ -
+ - Copyright 2012-2015 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+{-# LANGUAGE CPP #-}
+
+module Annex.InodeSentinal where
+
+import Common.Annex
+import qualified Annex
+import Utility.InodeCache
+import Annex.Perms
+
+{- Some filesystems get new inodes each time they are mounted.
+ - In order to work on such a filesystem, a sentinal file is used to detect
+ - when the inodes have changed.
+ -
+ - If the sentinal file does not exist, we have to assume that the
+ - inodes have changed.
+ -}
+inodesChanged :: Annex Bool
+inodesChanged = sentinalInodesChanged <$> sentinalStatus
+
+withTSDelta :: (TSDelta -> Annex a) -> Annex a
+withTSDelta a = a =<< getTSDelta
+
+getTSDelta :: Annex TSDelta
+#ifdef mingw32_HOST_OS
+getTSDelta = sentinalTSDelta <$> sentinalStatus
+#else
+getTSDelta = pure noTSDelta -- optimisation
+#endif
+
+sentinalStatus :: Annex SentinalStatus
+sentinalStatus = maybe check return =<< Annex.getState Annex.sentinalstatus
+  where
+	check = do
+		sc <- liftIO . checkSentinalFile =<< annexSentinalFile
+		Annex.changeState $ \s -> s { Annex.sentinalstatus = Just sc }
+		return sc
+
+{- The sentinal file is only created when first initializing a repository.
+ - If there are any annexed objects in the repository already, creating
+ - the file would invalidate their inode caches. -}
+createInodeSentinalFile :: Bool -> Annex ()
+createInodeSentinalFile evenwithobjects = 
+	unlessM (alreadyexists <||> hasobjects) $ do
+		s <- annexSentinalFile
+		createAnnexDirectory (parentDir (sentinalFile s))
+		liftIO $ writeSentinalFile s
+  where
+	alreadyexists = liftIO. sentinalFileExists =<< annexSentinalFile
+	hasobjects
+		| evenwithobjects = pure False
+		| otherwise = liftIO . doesDirectoryExist =<< fromRepo gitAnnexObjectDir
+
+annexSentinalFile :: Annex SentinalFile
+annexSentinalFile = do
+	sentinalfile <- fromRepo gitAnnexInodeSentinal
+	sentinalcachefile <- fromRepo gitAnnexInodeSentinalCache
+	return SentinalFile
+		{ sentinalFile = sentinalfile
+		, sentinalCacheFile = sentinalcachefile
+		}