Disable ssh connection caching if the path to the control socket would be too long (and use relative path to minimise path to the control socket).

Annex/Ssh.hs

@@ -42,7 +42,13 @@ sshInfo (host, port) = ifM caching
 	( do
 		dir <- fromRepo gitAnnexSshDir
 		let socketfile = dir </> hostport2socket host port
-	 	return (Just socketfile, cacheParams socketfile)
+		if valid_unix_socket_path socketfile
+			then return (Just socketfile, cacheParams socketfile)
+			else do
+				socketfile' <- liftIO $ relPathCwdToFile socketfile
+				if valid_unix_socket_path socketfile'
+					then return (Just socketfile', cacheParams socketfile')
+					else return (Nothing, [])
 	, return (Nothing, [])
 	)
 	where
@@ -118,3 +124,16 @@ isLock f = lockExt `isSuffixOf` f
 
 lockExt :: String
 lockExt = ".lock"
+
+{- This is the size of the sun_path component of sockaddr_un, which
+ - is the limit to the total length of the filename of a unix socket.
+ -
+ - On Linux, this is 108. On OSX, 104. TODO: Probe
+ -}
+sizeof_sockaddr_un_sun_path :: Int
+sizeof_sockaddr_un_sun_path = 100
+
+{- Note that this looks at the true length of the path in bytes, as it will
+ - appear on disk. -}
+valid_unix_socket_path :: FilePath -> Bool
+valid_unix_socket_path f = length (decodeW8 f) < sizeof_sockaddr_un_sun_path

debian/changelog

@@ -13,6 +13,8 @@ git-annex (3.20120826) UNRELEASED; urgency=low
   * test: Set a lot of git environment variables so testing works in strange
     environments that normally need git config to set names, etc.
     Closes: #682351 Thanks, gregor herrmann
+  * Disable ssh connection caching if the path to the control socket would be
+    too long (and use relative path to minimise path to the control socket).
 
  -- Joey Hess <joeyh@debian.org>  Mon, 27 Aug 2012 13:27:39 -0400
 

doc/bugs/ControlPath_too_long_for_Unix_domain_socket.mdwn

@@ -41,4 +41,10 @@ stdout snippet from git-annex webapp:
 
 This data appears on both the sending and receiving git-annex stdout. At least for the initial sync. For later syncs it only appears on the sender, though the client system is using a lot of resources.
 
-
+> I've made git-annex detect if the control path would be too long,
+> and disable ssh connection caching. It also tries a relative path
+> to the file, which tends to make it shorter, and I think would
+> keep ssh connection caching working in your example.
+> 
+> Please test and see if it works, and also if the "looping" problem
+> still happens. --[[Joey]]