add lsof build deps

Check for it in configure; and add a --force option for people without it
who want to live dangerously.

Assistant.hs

@@ -49,8 +49,10 @@ import Assistant.DaemonStatus
 import Assistant.Watcher
 import Assistant.Committer
 import Assistant.SanityChecker
+import qualified Annex
 import qualified Utility.Daemon
 import Utility.LogFile
+import qualified Build.SysConfig as SysConfig
 
 import Control.Concurrent
 
@@ -64,7 +66,12 @@ startDaemon foreground
 		pidfile <- fromRepo gitAnnexPidFile
 		go $ Utility.Daemon.daemonize logfd (Just pidfile) False
 	where
-		go a = withThreadState $ \st -> do
+		go a
+			| SysConfig.lsof = start a
+			| otherwise =
+				ifM (Annex.getState Annex.force)
+					(start a, needlsof)
+		start a = withThreadState $ \st -> do
 			dstatus <- startDaemonStatus
 			liftIO $ a $ do
 				changechan <- newChangeChan
@@ -78,5 +85,17 @@ startDaemon foreground
 				_ <- forkIO $ sanityCheckerThread st dstatus changechan
 				watchThread st dstatus changechan
 
+		-- this message is optimised away when lsof is available
+		needlsof = error $ unlines
+			[ "The lsof command is needed for watch mode to be safe."
+			, "But this build of git-annex was made without lsof available. Giving up..."
+			, ""
+			, "You can use --force if lsof is available now. Please make very sure it is."
+			, "If run with --force and without lsof available, files can be added to the"
+			, "annex while a process still has them opened for writing. This can"
+			, "corrupt data in the annex, and make fsck complain."
+			, "Use the --force with caution, Luke!"
+			]
+
 stopDaemon :: Annex ()
 stopDaemon = liftIO . Utility.Daemon.stopDaemon =<< fromRepo gitAnnexPidFile

Build/Configure.hs

@@ -26,6 +26,7 @@ tests =
 	, TestCase "wget" $ testCmd "wget" "wget --version >/dev/null"
 	, TestCase "bup" $ testCmd "bup" "bup --version >/dev/null"
 	, TestCase "gpg" $ testCmd "gpg" "gpg --version >/dev/null"
+	, TestCase "lsof" $ testCmd "lsof" "lsof -v >/dev/null 2>&1"
 	, TestCase "ssh connection caching" getSshConnectionCaching
 	] ++ shaTestCases False [1, 512, 224, 384] ++ shaTestCases True [256]
 

Utility/Lsof.hs

@@ -26,11 +26,16 @@ data ProcessInfo = ProcessInfo ProcessID CmdLine
 queryDir :: FilePath -> IO [(FilePath, LsofOpenMode, ProcessInfo)]
 queryDir path = query ["+d", path]
 
+{- Runs lsof with some parameters.
+ -
+ - Ignores nonzero exit code; lsof returns that when no files are open.
+ -
+ - Note: If lsof is not available, this always returns [] !
+ -}
 query :: [String] -> IO [(FilePath, LsofOpenMode, ProcessInfo)]
 query opts = do
 	(pid, s) <- pipeFrom "lsof" ("-F0can" : opts)
 	let !r = parse s
-	-- ignore nonzero exit code; lsof returns that when no files are open
 	void $ getProcessStatus True False $ processID pid
 	return r
 

debian/control

@@ -28,6 +28,7 @@ Build-Depends:
 	uuid,
 	rsync,
 	openssh-client,
+	lsof,
 Maintainer: Joey Hess <joeyh@debian.org>
 Standards-Version: 3.9.3
 Vcs-Git: git://git.kitenet.net/git-annex
@@ -41,7 +42,8 @@ Depends: ${misc:Depends}, ${shlibs:Depends},
 	uuid,
 	rsync,
 	wget | curl,
-	openssh-client (>= 1:5.6p1)
+	openssh-client (>= 1:5.6p1),
+	lsof
 Suggests: graphviz, bup, gnupg
 Description: manage files with git, without checking their contents into git
  git-annex allows managing files with git, without checking the file

doc/install.mdwn

@@ -54,6 +54,8 @@ To build and use git-annex, you will need:
   * [sha1sum](ftp://ftp.gnu.org/gnu/coreutils/) (optional, but recommended;
     a sha1 command will also do)
   * [gpg](http://gnupg.org/) (optional; needed for encryption)
+  * [lsof](ftp://lsof.itap.purdue.edu/pub/tools/unix/lsof/)
+    (needed for watch mode)
   * [ikiwiki](http://ikiwiki.info) (optional; used to build the docs)
 
 Then just [[download]] git-annex and run: `make; make install`