xfs: refactor space log reservation for XFS_TRANS_ATTR_SET

Currently, we calculate the attribute set transaction
log space reservation at runtime in two parts:

1) XFS_ATTRSET_LOG_RES() which is calcuated out at mount time.

2) ((ext * (mp)->m_sb.sb_sectsize) + \
    (ext * XFS_FSB_TO_B((mp), XFS_BM_MAXLEVELS(mp, XFS_ATTR_FORK))) + \
    (128 * (ext + (ext * XFS_BM_MAXLEVELS(mp, XFS_ATTR_FORK))))))
which is calculated out at runtime since it depend on the given extent length in blocks.

This patch renamed XFS_ATTRSET_LOG_RES(mp) to XFS_ATTRSETM_LOG_RES(mp) to indicate
that it is figured out at mount time.  Introduce XFS_ATTRSETRT_LOG_RES(mp) which would
be used to calculate out the unit of the log space reservation for one block.

In this way, the total runtime space for the given extent length can be figured out by:
XFS_ATTRSETM_LOG_RES(mp) + XFS_ATTRSETRT_LOG_RES(mp) * ext

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>

fs/xfs/xfs_mount.h

@@ -34,7 +34,8 @@ typedef struct xfs_trans_reservations {
 	uint	tr_addafork;	/* cvt inode to attributed trans */
 	uint	tr_writeid;	/* write setuid/setgid file */
 	uint	tr_attrinval;	/* attr fork buffer invalidation */
-	uint	tr_attrset;	/* set/create an attribute */
+	uint	tr_attrsetm;	/* set/create an attribute at mount time */
+	uint	tr_attrsetrt;	/* set/create an attribute at runtime */
 	uint	tr_attrrm;	/* remove an attribute */
 	uint	tr_clearagi;	/* clear bad agi unlinked ino bucket */
 	uint	tr_growrtalloc;	/* grow realtime allocations */