init: Improve fifo test to detect NFS systems that support fifos but not well enough for sshcaching.

ssh tries to hard link a fifo, and if not, complains:

muxserver_listen: link mux listener .git/annex/ssh/SHARD1@iabak.archiveteam.org.QK8zOCbtNebI7q54 => .git/annex/ssh/SHARD1@iabak.archiveteam.org: Operation not permitted

Annex/Init.hs

@@ -162,13 +162,17 @@ probeFifoSupport = do
 #else
 	tmp <- fromRepo gitAnnexTmpMiscDir
 	let f = tmp </> "gaprobe"
+	let f2 = tmp </> "gaprobe2"
 	createAnnexDirectory tmp
 	liftIO $ do
 		nukeFile f
+		nukeFile f2
 		ms <- tryIO $ do
 			createNamedPipe f ownerReadMode
+			createLink f f2
 			getFileStatus f
 		nukeFile f
+		nukeFile f2
 		return $ either (const False) isNamedPipe ms
 #endif
 

debian/changelog

@@ -26,6 +26,8 @@ git-annex (5.20150328) UNRELEASED; urgency=medium
   * Significantly sped up processing of large numbers of directories
     passed to a single git-annex command.
   * version: Add --raw
+  * init: Improve fifo test to detect NFS systems that support fifos
+    but not well enough for sshcaching.
 
  -- Joey Hess <id@joeyh.name>  Fri, 27 Mar 2015 16:04:43 -0400