xfs: introduce XFS_SB_LOG_RES() for transactions that modify sb on disk

Introduce a new transaction space reservation XFS_SB_LOG_RES() for
those transactions that need to modify the superblock on disk.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
CC: Dave Chinner <david@fromorbit.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index 57339e40..d06919e 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -267,6 +267,7 @@
 #define XFS_QM_DQALLOC_LOG_RES(mp)	((mp)->m_reservations.tr_qm_dqalloc)
 #define XFS_QM_QUOTAOFF_LOG_RES(mp)	((mp)->m_reservations.tr_qm_quotaoff)
 #define XFS_QM_QUOTAOFF_END_LOG_RES(mp)	((mp)->m_reservations.tr_qm_equotaoff)
+#define XFS_SB_LOG_RES(mp)		((mp)->m_reservations.tr_sb)
 
 /*
  * Various log count values.