xfs: vectorise encoding/decoding directory headers

Conversion from on-disk structures to in-core header structures
currently relies on magic number checks. If the magic number is
wrong, but one of the supported values, we do the wrong thing with
the encode/decode operation. Split these functions so that there are
discrete operations for the specific directory format we are
handling.

In doing this, move all the header encode/decode functions to
xfs_da_format.c as they are directly manipulating the on-disk
format. It should be noted that all the growth in binary size is
from xfs_da_format.c - the rest of the code actaully shrinks.

   text    data     bss     dec     hex filename
 794490   96802    1096  892388   d9de4 fs/xfs/xfs.o.orig
 792986   96802    1096  890884   d9804 fs/xfs/xfs.o.p1
 792350   96802    1096  890248   d9588 fs/xfs/xfs.o.p2
 789293   96802    1096  887191   d8997 fs/xfs/xfs.o.p3
 789005   96802    1096  886903   d8997 fs/xfs/xfs.o.p4
 789061   96802    1096  886959   d88af fs/xfs/xfs.o.p5
 789733   96802    1096  887631   d8b4f fs/xfs/xfs.o.p6
 791421   96802    1096  889319   d91e7 fs/xfs/xfs.o.p7

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_attr_inactive.c

@@ -231,7 +231,7 @@ xfs_attr3_node_inactive(
 	}
 
 	node = bp->b_addr;
-	xfs_da3_node_hdr_from_disk(&ichdr, node);
+	dp->d_ops->node_hdr_from_disk(&ichdr, node);
 	parent_blkno = bp->b_bn;
 	if (!ichdr.count) {
 		xfs_trans_brelse(*trans, bp);

fs/xfs/xfs_attr_leaf.c

@@ -916,7 +916,7 @@ xfs_attr3_leaf_to_node(
 	if (error)
 		goto out;
 	node = bp1->b_addr;
-	xfs_da3_node_hdr_from_disk(&icnodehdr, node);
+	dp->d_ops->node_hdr_from_disk(&icnodehdr, node);
 	btree = dp->d_ops->node_tree_p(node);
 
 	leaf = bp2->b_addr;
@@ -927,7 +927,7 @@ xfs_attr3_leaf_to_node(
 	btree[0].hashval = entries[icleafhdr.count - 1].hashval;
 	btree[0].before = cpu_to_be32(blkno);
 	icnodehdr.count = 1;
-	xfs_da3_node_hdr_to_disk(node, &icnodehdr);
+	dp->d_ops->node_hdr_to_disk(node, &icnodehdr);
 	xfs_trans_log_buf(args->trans, bp1, 0, XFS_LBSIZE(mp) - 1);
 	error = 0;
 out:

fs/xfs/xfs_attr_list.c

@@ -311,7 +311,7 @@ xfs_attr_node_list(xfs_attr_list_context_t *context)
 				return XFS_ERROR(EFSCORRUPTED);
 			}
 
-			xfs_da3_node_hdr_from_disk(&nodehdr, node);
+			dp->d_ops->node_hdr_from_disk(&nodehdr, node);
 			btree = dp->d_ops->node_tree_p(node);
 			for (i = 0; i < nodehdr.count; btree++, i++) {
 				if (cursor->hashval