btrfs: backref: implement btrfs_backref_iter_next()

This function will go to the next inline/keyed backref for
btrfs_backref_iter infrastructure.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/backref.c

@@ -2405,3 +2405,63 @@ int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr)
 	btrfs_backref_iter_release(iter);
 	return ret;
 }
+
+/*
+ * Go to the next backref item of current bytenr, can be either inlined or
+ * keyed.
+ *
+ * Caller needs to check whether it's inline ref or not by iter->cur_key.
+ *
+ * Return 0 if we get next backref without problem.
+ * Return >0 if there is no extra backref for this bytenr.
+ * Return <0 if there is something wrong happened.
+ */
+int btrfs_backref_iter_next(struct btrfs_backref_iter *iter)
+{
+	struct extent_buffer *eb = btrfs_backref_get_eb(iter);
+	struct btrfs_path *path = iter->path;
+	struct btrfs_extent_inline_ref *iref;
+	int ret;
+	u32 size;
+
+	if (btrfs_backref_iter_is_inline_ref(iter)) {
+		/* We're still inside the inline refs */
+		ASSERT(iter->cur_ptr < iter->end_ptr);
+
+		if (btrfs_backref_has_tree_block_info(iter)) {
+			/* First tree block info */
+			size = sizeof(struct btrfs_tree_block_info);
+		} else {
+			/* Use inline ref type to determine the size */
+			int type;
+
+			iref = (struct btrfs_extent_inline_ref *)
+				((unsigned long)iter->cur_ptr);
+			type = btrfs_extent_inline_ref_type(eb, iref);
+
+			size = btrfs_extent_inline_ref_size(type);
+		}
+		iter->cur_ptr += size;
+		if (iter->cur_ptr < iter->end_ptr)
+			return 0;
+
+		/* All inline items iterated, fall through */
+	}
+
+	/* We're at keyed items, there is no inline item, go to the next one */
+	ret = btrfs_next_item(iter->fs_info->extent_root, iter->path);
+	if (ret)
+		return ret;
+
+	btrfs_item_key_to_cpu(path->nodes[0], &iter->cur_key, path->slots[0]);
+	if (iter->cur_key.objectid != iter->bytenr ||
+	    (iter->cur_key.type != BTRFS_TREE_BLOCK_REF_KEY &&
+	     iter->cur_key.type != BTRFS_SHARED_BLOCK_REF_KEY))
+		return 1;
+	iter->item_ptr = (u32)btrfs_item_ptr_offset(path->nodes[0],
+					path->slots[0]);
+	iter->cur_ptr = iter->item_ptr;
+	iter->end_ptr = iter->item_ptr + (u32)btrfs_item_size_nr(path->nodes[0],
+						path->slots[0]);
+	return 0;
+}

fs/btrfs/backref.h

@@ -104,8 +104,42 @@ static inline void btrfs_backref_iter_free(struct btrfs_backref_iter *iter)
 	kfree(iter);
 }
 
+static inline struct extent_buffer *btrfs_backref_get_eb(
+		struct btrfs_backref_iter *iter)
+{
+	if (!iter)
+		return NULL;
+	return iter->path->nodes[0];
+}
+
+/*
+ * For metadata with EXTENT_ITEM key (non-skinny) case, the first inline data
+ * is btrfs_tree_block_info, without a btrfs_extent_inline_ref header.
+ *
+ * This helper determines if that's the case.
+ */
+static inline bool btrfs_backref_has_tree_block_info(
+		struct btrfs_backref_iter *iter)
+{
+	if (iter->cur_key.type == BTRFS_EXTENT_ITEM_KEY &&
+	    iter->cur_ptr - iter->item_ptr == sizeof(struct btrfs_extent_item))
+		return true;
+	return false;
+}
+
 int btrfs_backref_iter_start(struct btrfs_backref_iter *iter, u64 bytenr);
 
+int btrfs_backref_iter_next(struct btrfs_backref_iter *iter);
+
+static inline bool btrfs_backref_iter_is_inline_ref(
+		struct btrfs_backref_iter *iter)
+{
+	if (iter->cur_key.type == BTRFS_EXTENT_ITEM_KEY ||
+	    iter->cur_key.type == BTRFS_METADATA_ITEM_KEY)
+		return true;
+	return false;
+}
+
 static inline void btrfs_backref_iter_release(struct btrfs_backref_iter *iter)
 {
 	iter->bytenr = 0;