Btrfs: add leaf data casting helper

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.h

@@ -401,6 +401,10 @@ static inline void btrfs_set_super_blocksize(struct btrfs_super_block *s,
 	s->blocksize = cpu_to_le16(val);
 }
 
+/* helper function to cast into the data area of the leaf. */
+#define btrfs_item_ptr(leaf, slot, type) \
+	((type *)((leaf)->data + btrfs_item_offset((leaf)->items + (slot))))
+
 struct btrfs_buffer *btrfs_alloc_free_block(struct btrfs_root *root);
 int btrfs_inc_ref(struct btrfs_root *root, struct btrfs_buffer *buf);
 int btrfs_free_extent(struct btrfs_root *root, u64 blocknr, u64 num_blocks);

fs/btrfs/extent-tree.c

@@ -41,9 +41,7 @@ static int inc_block_ref(struct btrfs_root *root, u64 blocknr)
 		BUG();
 	BUG_ON(ret != 0);
 	l = &path.nodes[0]->leaf;
-	item = (struct btrfs_extent_item *)(l->data +
-					    btrfs_item_offset(l->items +
-							      path.slots[0]));
+	item = btrfs_item_ptr(l, path.slots[0], struct btrfs_extent_item);
 	refs = btrfs_extent_refs(item);
 	btrfs_set_extent_refs(item, refs + 1);
 
@@ -69,9 +67,7 @@ static int lookup_block_ref(struct btrfs_root *root, u64 blocknr, u32 *refs)
 	if (ret != 0)
 		BUG();
 	l = &path.nodes[0]->leaf;
-	item = (struct btrfs_extent_item *)(l->data +
-				      btrfs_item_offset(l->items +
-							path.slots[0]));
+	item = btrfs_item_ptr(l, path.slots[0], struct btrfs_extent_item);
 	*refs = btrfs_extent_refs(item);
 	btrfs_release_path(root->extent_root, &path);
 	return 0;

fs/btrfs/print-tree.c

@@ -26,11 +26,10 @@ void btrfs_print_leaf(struct btrfs_leaf *l)
 			btrfs_item_size(item));
 		printf("\t\titem data %.*s\n", btrfs_item_size(item),
 			l->data + btrfs_item_offset(item));
-		ei = (struct btrfs_extent_item *)(l->data +
-						  btrfs_item_offset(item));
+		ei = btrfs_item_ptr(l, i, struct btrfs_extent_item);
 		printf("\t\textent data refs %u owner %Lu\n",
 			btrfs_extent_refs(ei), btrfs_extent_owner(ei));
-		ri = (struct btrfs_root_item *)ei;
+		ri = btrfs_item_ptr(l, i, struct btrfs_root_item);
 		printf("\t\troot data blocknr %Lu refs %u\n",
 			btrfs_root_blocknr(ri), btrfs_root_refs(ri));
 		fflush(stdout);