daemonize git annex watch

Utility/Daemon.hs

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+{- daemon functions
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Utility.Daemon where
+
+import System.Posix
+import System.Directory
+import System.Exit
+import Control.Monad
+
+{- Run an action as a daemon, with all output sent to a file descriptor.
+ -
+ - Does not return. -}
+daemonize :: Fd -> Bool -> IO () -> IO ()
+daemonize logfd changedirectory a = do
+	_ <- forkProcess child1
+	end
+	where
+		child1 = do
+			_ <- createSession
+			_ <- forkProcess child2
+			end
+		child2 = do
+			when changedirectory $
+				setCurrentDirectory "/"
+			nullfd <- openFd "/dev/null" ReadOnly Nothing defaultFileFlags
+			_ <- redir nullfd stdInput
+			mapM_ (redir logfd) [stdOutput, stdError]
+			closeFd logfd
+			a
+			end
+		redir newh h = do
+			closeFd h
+			dupTo newh h
+		end = exitImmediately ExitSuccess