xfs: remove the if_ext_max field in struct xfs_ifork

We spent a lot of effort to maintain this field, but it always equals to the
fork size divided by the constant size of an extent.  The prime use of it is
to assert that the two stay in sync.  Just divide the fork size by the extent
size in the few places that we actually use it and remove the overhead
of maintaining it.  Also introduce a few helpers to consolidate the places
where we actually care about the value.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_inode.h

@@ -66,7 +66,6 @@ typedef struct xfs_ifork {
 	struct xfs_btree_block	*if_broot;	/* file's incore btree root */
 	short			if_broot_bytes;	/* bytes allocated for root */
 	unsigned char		if_flags;	/* per-fork flags */
-	unsigned char		if_ext_max;	/* max # of extent records */
 	union {
 		xfs_bmbt_rec_host_t *if_extents;/* linear map file exts */
 		xfs_ext_irec_t	*if_ext_irec;	/* irec map file exts */
@@ -206,7 +205,8 @@ typedef struct xfs_icdinode {
 	((w) == XFS_DATA_FORK ? \
 		((ip)->i_d.di_nextents = (n)) : \
 		((ip)->i_d.di_anextents = (n)))
-
+#define XFS_IFORK_MAXEXT(ip, w) \
+	(XFS_IFORK_SIZE(ip, w) / sizeof(xfs_bmbt_rec_t))
 
 
 #ifdef __KERNEL__