[XFS] Ensure that 2 GiB xfs logs work properly.

We found this while experimenting with 2GiB xfs logs. The previous code
never assumed that xfs logs would ever get so large.

SGI-PV: 981502
SGI-Modid: xfs-linux-melb:xfs-kern:31058a

Signed-off-by: Michael Nishimoto <miken@agami.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

fs/xfs/xfs_log.c

@@ -226,20 +226,24 @@ xlog_grant_sub_space(struct log *log, int bytes)
 static void
 xlog_grant_add_space_write(struct log *log, int bytes)
 {
-	log->l_grant_write_bytes += bytes;
-	if (log->l_grant_write_bytes > log->l_logsize) {
-		log->l_grant_write_bytes -= log->l_logsize;
+	int tmp = log->l_logsize - log->l_grant_write_bytes;
+	if (tmp > bytes)
+		log->l_grant_write_bytes += bytes;
+	else {
 		log->l_grant_write_cycle++;
+		log->l_grant_write_bytes = bytes - tmp;
 	}
 }
 
 static void
 xlog_grant_add_space_reserve(struct log *log, int bytes)
 {
-	log->l_grant_reserve_bytes += bytes;
-	if (log->l_grant_reserve_bytes > log->l_logsize) {
-		log->l_grant_reserve_bytes -= log->l_logsize;
+	int tmp = log->l_logsize - log->l_grant_reserve_bytes;
+	if (tmp > bytes)
+		log->l_grant_reserve_bytes += bytes;
+	else {
 		log->l_grant_reserve_cycle++;
+		log->l_grant_reserve_bytes = bytes - tmp;
 	}
 }