git-annex/Assistant/Threads/MountWatcher.hs

{- git-annex assistant mount watcher, using either dbus or mtab polling
 -
 - Copyright 2012 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

{-# LANGUAGE CPP #-}
{-# LANGUAGE OverloadedStrings #-}

module Assistant.Threads.MountWatcher where

import Assistant.Common
import Assistant.DaemonStatus
import Assistant.Sync
import qualified Annex
import qualified Git
import Utility.ThreadScheduler
import Utility.Mounts
import Remote.List
import qualified Types.Remote as Remote
import Assistant.Types.UrlRenderer
import Assistant.Fsck

import qualified Data.Set as S

#if WITH_DBUS
import Utility.DBus
import DBus.Client
import DBus
import Data.Word (Word32)
import Control.Concurrent
import qualified Control.Exception as E
#else
#ifdef linux_HOST_OS
#warning Building without dbus support; will use mtab polling
#endif
#endif

mountWatcherThread :: UrlRenderer -> NamedThread
mountWatcherThread urlrenderer = namedThread "MountWatcher" $
#if WITH_DBUS
	dbusThread urlrenderer
#else
	pollingThread urlrenderer
#endif

#if WITH_DBUS

dbusThread :: UrlRenderer -> Assistant ()
dbusThread urlrenderer = do
	runclient <- asIO1 go
	r <- liftIO $ E.try $ runClient getSystemAddress runclient
	either onerr (const noop) r
  where
	go client = ifM (checkMountMonitor client)
		( do
			{- Store the current mount points in an MVar, to be
			 - compared later. We could in theory work out the
			 - mount point from the dbus message, but this is
			 - easier. -}
			mvar <- liftIO $ newMVar =<< currentMountPoints
			handleevent <- asIO1 $ \_event -> do
				nowmounted <- liftIO $ currentMountPoints
				wasmounted <- liftIO $ swapMVar mvar nowmounted
				handleMounts urlrenderer wasmounted nowmounted
			liftIO $ forM_ mountChanged $ \matcher ->
				void $ addMatch client matcher handleevent
		, do
			liftAnnex $
				warning "No known volume monitor available through dbus; falling back to mtab polling"
			pollingThread urlrenderer
		)
	onerr :: E.SomeException -> Assistant ()
	onerr e = do
		liftAnnex $
			warning $ "dbus failed; falling back to mtab polling (" ++ show e ++ ")"
		pollingThread urlrenderer

{- Examine the list of services connected to dbus, to see if there
 - are any we can use to monitor mounts. If not, will attempt to start one. -}
checkMountMonitor :: Client -> Assistant Bool
checkMountMonitor client = do
	running <- filter (`elem` usableservices)
		<$> liftIO (listServiceNames client)
	case running of
		[] -> startOneService client startableservices
		(service:_) -> do
			debug [ "Using running DBUS service"
				, service
				, "to monitor mount events."
				]
			return True
  where
	startableservices = [udisks2]
	usableservices = startableservices
	udisks2 = "org.freedesktop.UDisks2"

startOneService :: Client -> [ServiceName] -> Assistant Bool
startOneService _ [] = return False
startOneService client (x:xs) = do
	_ <- liftIO $ tryNonAsync $ callDBus client "StartServiceByName"
		[toVariant x, toVariant (0 :: Word32)]
	ifM (liftIO $ elem x <$> listServiceNames client)
		( do
			debug
				[ "Started DBUS service", x
				, "to monitor mount events."
				]
			return True
		, startOneService client xs
		)

{- Filter matching events recieved when drives are mounted and unmounted. -}	
mountChanged :: [MatchRule]
mountChanged = [udisks2mount, udisks2umount]
  where
	udisks2mount = matchAny
		{ matchPath = Just "/org/freedesktop/UDisks2"
		, matchInterface = Just "org.freedesktop.DBus.ObjectManager"
		, matchMember = Just "InterfacesAdded"
		}
	udisks2umount = matchAny
		{ matchPath = Just "/org/freedesktop/UDisks2"
		, matchInterface = Just "org.freedesktop.DBus.ObjectManager"
		, matchMember = Just "InterfacesRemoved"
		}
#endif

pollingThread :: UrlRenderer -> Assistant ()
pollingThread urlrenderer = go =<< liftIO currentMountPoints
  where
	go wasmounted = do
		liftIO $ threadDelaySeconds (Seconds 10)
		nowmounted <- liftIO currentMountPoints
		handleMounts urlrenderer wasmounted nowmounted
		go nowmounted

handleMounts :: UrlRenderer -> MountPoints -> MountPoints -> Assistant ()
handleMounts urlrenderer wasmounted nowmounted =
	mapM_ (handleMount urlrenderer . mnt_dir) $
		S.toList $ newMountPoints wasmounted nowmounted

handleMount :: UrlRenderer -> FilePath -> Assistant ()
handleMount urlrenderer dir = do
	debug ["detected mount of", dir]
	rs <- filterM (Git.repoIsLocal <$$> liftAnnex . Remote.getRepo)
		=<< remotesUnder dir
	mapM_ (fsckNudge urlrenderer . Just) rs
	reconnectRemotes rs

{- Finds remotes located underneath the mount point.
 -
 - Updates state to include the remotes.
 -
 - The config of git remotes is re-read, as it may not have been available
 - at startup time, or may have changed (it could even be a different
 - repository at the same remote location..)
 -}
remotesUnder :: FilePath -> Assistant [Remote]
remotesUnder dir = do
	repotop <- liftAnnex $ fromRepo Git.repoPath
	rs <- liftAnnex remoteList
	pairs <- liftAnnex $ mapM (checkremote repotop) rs
	let (waschanged, rs') = unzip pairs
	when (or waschanged) $ do
		liftAnnex $ Annex.changeState $ \s -> s { Annex.remotes = catMaybes rs' }
		updateSyncRemotes
	return $ mapMaybe snd $ filter fst pairs
  where
	checkremote repotop r = case Remote.localpath r of
		Just p | dirContains dir (absPathFrom repotop p) ->
			(,) <$> pure True <*> updateRemote r
		_ -> return (False, Just r)

type MountPoints = S.Set Mntent

currentMountPoints :: IO MountPoints
currentMountPoints = S.fromList <$> getMounts

newMountPoints :: MountPoints -> MountPoints -> MountPoints
newMountPoints old new = S.difference new old