[XFS] add generic btree types

Add generic union types for btree pointers, keys and records. The generic
btree pointer contains either a 32 and 64bit big endian scalar for short
and long form btrees, and the key and record contain the relevant type for
each possible btree.

Split out from a bigger patch from Dave Chinner and simplified a little
further.

SGI-PV: 985583

SGI-Modid: xfs-linux-melb:xfs-kern:32178a
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>

fs/xfs/xfs_btree.h

@@ -79,6 +79,31 @@ typedef struct xfs_btree_block {
 	} bb_u;				/* rest */
 } xfs_btree_block_t;
 
+/*
+ * Generic key, ptr and record wrapper structures.
+ *
+ * These are disk format structures, and are converted where necessary
+ * by the btree specific code that needs to interpret them.
+ */
+union xfs_btree_ptr {
+	__be32			s;	/* short form ptr */
+	__be64			l;	/* long form ptr */
+};
+
+union xfs_btree_key {
+	xfs_bmbt_key_t		bmbt;
+	xfs_bmdr_key_t		bmbr;	/* bmbt root block */
+	xfs_alloc_key_t		alloc;
+	xfs_inobt_key_t		inobt;
+};
+
+union xfs_btree_rec {
+	xfs_bmbt_rec_t		bmbt;
+	xfs_bmdr_rec_t		bmbr;	/* bmbt root block */
+	xfs_alloc_rec_t		alloc;
+	xfs_inobt_rec_t		inobt;
+};
+
 /*
  * For logging record fields.
  */