xfs: refactor xfs_trans_reserve() interface

With the new xfs_trans_res structure has been introduced, the log
reservation size, log count as well as log flags are pre-initialized
at mount time.  So it's time to refine xfs_trans_reserve() interface
to be more neat.

Also, introduce a new helper M_RES() to return a pointer to the
mp->m_resv structure to simplify the input.

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

diff --git a/fs/xfs/xfs_bmap.c b/fs/xfs/xfs_bmap.c
index 51e07e7..6c2d89e 100644
--- a/fs/xfs/xfs_bmap.c
+++ b/fs/xfs/xfs_bmap.c
@@ -1148,8 +1148,8 @@
 	blks = XFS_ADDAFORK_SPACE_RES(mp);
 	if (rsvd)
 		tp->t_flags |= XFS_TRANS_RESERVE;
-	if ((error = xfs_trans_reserve(tp, blks, XFS_ADDAFORK_LOG_RES(mp), 0,
-			XFS_TRANS_PERM_LOG_RES, XFS_ADDAFORK_LOG_COUNT)))
+	error = xfs_trans_reserve(tp, &M_RES(mp)->tr_addafork, blks, 0);
+	if (error)
 		goto error0;
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 	error = xfs_trans_reserve_quota_nblks(tp, ip, blks, 0, rsvd ?