diskreserve setting

Add annex.diskreserve config setting, to control how much free space to
reserve for other purposes and avoid using (defaults to 1 mb).

Content.hs

@@ -119,24 +119,23 @@ checkDiskSpace = checkDiskSpace' 0
 
 checkDiskSpace' :: Integer -> Key -> Annex ()
 checkDiskSpace' adjustment key = do
-	liftIO $ putStrLn $ "adjust " ++ show adjustment
 	g <- Annex.gitRepo
+	r <- Annex.repoConfig g "diskreserve" ""
+	let reserve = if null r then megabyte else (read r :: Integer)
 	stats <- liftIO $ getFileSystemStats (gitAnnexDir g)
 	case (stats, keySize key) of
 		(Nothing, _) -> return ()
 		(_, Nothing) -> return ()
 		(Just (FileSystemStats { fsStatBytesAvailable = have }), Just need) ->
-			if (need + overhead >= have + adjustment)
+			if (need + reserve > have + adjustment)
 				then error $ "not enough free space (have " ++ 
 					showsize (have + adjustment) ++ "; need " ++
-					showsize (need + overhead) ++ ")"
+					showsize (need + reserve) ++ ")"
 				else return ()
 	where
 		showsize i = show i
-		-- Adding a file to the annex requires some overhead beyond
+		megabyte :: Integer
-		-- just the file size; the git index must be updated, etc. 
+		megabyte = 1024 * 1024
-		-- This is an arbitrary value.
-		overhead = 1024 * 1024 -- 1 mb
 
 {- Removes the write bits from a file. -}
 preventWrite :: FilePath -> IO ()

debian/changelog

@@ -5,6 +5,8 @@ git-annex (0.20110321) UNRELEASED; urgency=low
     with git-annex 0.24 or earlier.) The code is believed to work on
     Linux, FreeBSD, and OSX; check compile-time messages to see if it
     is not enabled for your OS.
+  * Add annex.diskreserve config setting, to control how much free space
+    to reserve for other purposes and avoid using (defaults to 1 mb).
   * Add --fast flag, that can enable less expensive, but also less thurough
     versions of some commands.
   * fsck: In fast mode, avoid checking checksums.

doc/git-annex.mdwn

@@ -377,6 +377,14 @@ Here are all the supported configuration settings.
   Default ssh and rsync options to use if a remote does not have
   specific options.
 
+* `annex.diskreserve`
+
+  Amount of disk space to reserve. Disk space is checked when transferring
+  content to avoid running out, and additional free space can be reserved
+  via this option, to make space for more important content (such as git
+  commit logs). The units are bytes.
+  The default reserve is 1048576 (1 megabyte).
+
 * `annex.version`
 
   Automatically maintained, and used to automate upgrades between versions.