optimise sending to encrypted rsync

With an encrypted rsync remote, the encrpyted file can be renamed, rather
than being copied, in crippled filesystem mode. This gets back to just as
fast as non-crippled mode for this very common case.

Remote/Rsync.hs

@@ -102,14 +102,14 @@ rsyncUrls o k = map use annexHashes
 	f = keyFile k
 
 store :: RsyncOpts -> Key -> AssociatedFile -> MeterUpdate -> Annex Bool
-store o k _f p = sendAnnex k (void $ remove o k) $ rsyncSend o p k
+store o k _f p = sendAnnex k (void $ remove o k) $ rsyncSend o p k False
 
 storeEncrypted :: RsyncOpts -> (Cipher, Key) -> Key -> MeterUpdate -> Annex Bool
 storeEncrypted o (cipher, enck) k p = withTmp enck $ \tmp ->
 	sendAnnex k (void $ remove o enck) $ \src -> do
 		liftIO $ encrypt cipher (feedFile src) $
 			readBytes $ L.writeFile tmp
-		rsyncSend o p enck tmp
+		rsyncSend o p enck True tmp
 
 retrieve :: RsyncOpts -> Key -> AssociatedFile -> FilePath -> Annex Bool
 retrieve o k _ f = untilTrue (rsyncUrls o k) $ \u -> rsyncRemote o Nothing
@@ -216,16 +216,18 @@ rsyncRemote o callback params = do
  - (When we have the right hash directory structure, we can just
  - pass --include=X --include=X/Y --include=X/Y/file --exclude=*)
  -}
-rsyncSend :: RsyncOpts -> MeterUpdate -> Key -> FilePath -> Annex Bool
+rsyncSend :: RsyncOpts -> MeterUpdate -> Key -> Bool -> FilePath -> Annex Bool
-rsyncSend o callback k src = withRsyncScratchDir $ \tmp -> do
+rsyncSend o callback k canrename src = withRsyncScratchDir $ \tmp -> do
 	let dest = tmp </> Prelude.head (keyPaths k)
 	liftIO $ createDirectoryIfMissing True $ parentDir dest
-	ok <- ifM crippledFileSystem
+	ok <- if canrename
-		( liftIO $ copyFileExternal src dest
+		then liftIO $ renameFile src dest
-		, do
+		else ifM crippledFileSystem
-			liftIO $ createLink src dest
+			( liftIO $ copyFileExternal src dest
-			return True
+			, do
-		)
+				liftIO $ createLink src dest
+				return True
+			)
 	if ok
 		then rsyncRemote o (Just callback)
 			[ Param "--recursive"