[XFS] add get_maxrecs btree operation

Factor xfs_btree_maxrecs into a per-btree operation.

The get_maxrecs method is based on a patch from Dave Chinner.

SGI-PV: 985583

SGI-Modid: xfs-linux-melb:xfs-kern:32188a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Bill O'Donnell <billodo@sgi.com>
Signed-off-by: David Chinner <david@fromorbit.com>
diff --git a/fs/xfs/xfs_btree.h b/fs/xfs/xfs_btree.h
index 0647a0e..5398cd0 100644
--- a/fs/xfs/xfs_btree.h
+++ b/fs/xfs/xfs_btree.h
@@ -183,6 +183,9 @@
 	/* cursor operations */
 	struct xfs_btree_cur *(*dup_cursor)(struct xfs_btree_cur *);
 
+	/* records in block/level */
+	int	(*get_maxrecs)(struct xfs_btree_cur *cur, int level);
+
 	/* btree tracing */
 #ifdef XFS_BTREE_TRACE
 	void		(*trace_enter)(struct xfs_btree_cur *, const char *,