convert incremental fsck to using sqlite database

Did not keep backwards compat for sticky bit records. An incremental fsck
that is already in progress will start over on upgrade to this version.

This is not yet ready for merging. The autobuilders need to have sqlite
installed.

Also, interrupting a fsck --incremental does not commit the database.
So, resuming with fsck --more restarts from beginning.

Memory: Constant during a fsck of tens of thousands of files.
(But, it does seem to buffer whole transation in memory, so
may really scale with number of files.)

CPU: ?

Command/Fsck.hs

@@ -1,6 +1,6 @@
 {- git-annex command
  -
- - Copyright 2010-2013 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2015 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU GPL version 3 or higher.
  -}
@@ -26,13 +26,13 @@ import Logs.Trust
 import Config.NumCopies
 import Annex.UUID
 import Utility.DataUnits
-import Utility.FileMode
 import Config
 import Types.Key
 import Types.CleanupActions
 import Utility.HumanTime
 import Git.FilePath
 import Utility.PID
+import qualified Database.Fsck as FsckDb
 
 import Data.Time.Clock.POSIX
 import Data.Time
@@ -72,6 +72,7 @@ seek ps = do
 		(\k -> startKey i k =<< getNumCopies)
 		(withFilesInGit $ whenAnnexed $ start from i)
 		ps
+	withFsckDb i (liftIO . FsckDb.closeDb)
 
 getIncremental :: Annex Incremental
 getIncremental = do
@@ -82,15 +83,17 @@ getIncremental = do
 	case (i, starti, morei) of
 		(False, False, False) -> return NonIncremental
 		(False, True, False) -> startIncremental
-		(False ,False, True) -> ContIncremental <$> getStartTime
+		(False ,False, True) -> contIncremental
 		(True, False, False) ->
-			maybe startIncremental (return . ContIncremental . Just)
+			maybe startIncremental (const contIncremental)
 				=<< getStartTime
 		_ -> error "Specify only one of --incremental, --more, or --incremental-schedule"
   where
 	startIncremental = do
 		recordStartTime
-		return StartIncremental
+		FsckDb.newPass
+		StartIncremental <$> FsckDb.openDb
+	contIncremental = ContIncremental <$> FsckDb.openDb
 
 	checkschedule Nothing = error "bad --incremental-schedule value"
 	checkschedule (Just delta) = do
@@ -415,8 +418,7 @@ badContentRemote remote key = do
 	return $ (if ok then "dropped from " else "failed to drop from ")
 		++ Remote.name remote
 
-data Incremental = StartIncremental | ContIncremental (Maybe EpochTime) | NonIncremental
-	deriving (Eq, Show)
+data Incremental = StartIncremental FsckDb.DbHandle | ContIncremental FsckDb.DbHandle | NonIncremental
 
 runFsck :: Incremental -> FilePath -> Key -> Annex Bool -> CommandStart
 runFsck inc file key a = ifM (needFsck inc key)
@@ -425,48 +427,23 @@ runFsck inc file key a = ifM (needFsck inc key)
 		next $ do
 			ok <- a
 			when ok $
-				recordFsckTime key
+				recordFsckTime inc key
 			next $ return ok
 	, stop
 	)
 
 {- Check if a key needs to be fscked, with support for incremental fscks. -}
 needFsck :: Incremental -> Key -> Annex Bool
-needFsck (ContIncremental Nothing) _ = return True
-needFsck (ContIncremental starttime) key = do
-	fscktime <- getFsckTime key
-	return $ fscktime < starttime
+needFsck (ContIncremental h) key = not <$> FsckDb.inDb h key
 needFsck _ _ = return True
 
-{- To record the time that a key was last fscked, without
- - modifying its mtime, we set the timestamp of its parent directory.
- - Each annexed file is the only thing in its directory, so this is fine.
- -
- - To record that the file was fscked, the directory's sticky bit is set.
- - (None of the normal unix behaviors of the sticky bit should matter, so
- - we can reuse this permission bit.)
- -
- - Note that this relies on the parent directory being deleted when a file
- - is dropped. That way, if it's later added back, the fsck record
- - won't still be present.
- -}
-recordFsckTime :: Key -> Annex ()
-recordFsckTime key = do
-	parent <- parentDir <$> calcRepo (gitAnnexLocation key)
-	liftIO $ void $ tryIO $ do
-		touchFile parent
-#ifndef mingw32_HOST_OS
-		setSticky parent
-#endif
+withFsckDb :: Incremental -> (FsckDb.DbHandle -> Annex ()) -> Annex ()
+withFsckDb (ContIncremental h) a = a h
+withFsckDb (StartIncremental h) a = a h
+withFsckDb NonIncremental _ = noop
 
-getFsckTime :: Key -> Annex (Maybe EpochTime)
-getFsckTime key = do
-	parent <- parentDir <$> calcRepo (gitAnnexLocation key)
-	liftIO $ catchDefaultIO Nothing $ do
-		s <- getFileStatus parent
-		return $ if isSticky $ fileMode s
-			then Just $ modificationTime s
-			else Nothing
+recordFsckTime :: Incremental -> Key -> Annex ()
+recordFsckTime inc key = withFsckDb inc $ \h -> FsckDb.addDb h key
 
 {- Records the start time of an incremental fsck.
  -