[PATCH 3/4] btrfs-progs: Introduce function to find next sibling tree block

[Qu Wenruo <wqu@xxxxxxxx>]

Introduce a new function, btrfs_next_sibling_tree_block(), which could
find any sibling tree blocks at path->lowest_level, unlike level 0
limited btrfs_next_leaf().

Since this function is more generic than btrfs_next_leaf(), also make
btrfs_next_leaf() a wrapper of btrfs_next_sibling_tree_block(), to keep
the interface the same as kernel.

This would provide the basis for later breadth-first search print-tree.

Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
 ctree.c | 14 +++++++++-----
 ctree.h | 15 ++++++++++++++-
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/ctree.c b/ctree.c
index 042fae19344d..43d47f19c9cd 100644
--- a/ctree.c
+++ b/ctree.c
@@ -2875,18 +2875,22 @@ int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path)
 }
 
 /*
- * walk up the tree as far as required to find the next leaf.
+ * walk up the tree as far as required to find the next sibling tree block.
+ * more generic version of btrfs_next_leaf(), as it could find sibling nodes
+ * if @path->lowest_level is not 0.
+ *
  * returns 0 if it found something or 1 if there are no greater leaves.
  * returns < 0 on io errors.
  */
-int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
+int btrfs_next_sibling_tree_block(struct btrfs_fs_info *fs_info,
+				  struct btrfs_path *path)
 {
 	int slot;
-	int level = 1;
+	int level = path->lowest_level + 1;
 	struct extent_buffer *c;
 	struct extent_buffer *next = NULL;
-	struct btrfs_fs_info *fs_info = root->fs_info;
 
+	BUG_ON(path->lowest_level + 1 >= BTRFS_MAX_LEVEL);
 	while(level < BTRFS_MAX_LEVEL) {
 		if (!path->nodes[level])
 			return 1;
@@ -2915,7 +2919,7 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
 		free_extent_buffer(c);
 		path->nodes[level] = next;
 		path->slots[level] = 0;
-		if (!level)
+		if (level == path->lowest_level)
 			break;
 		if (path->reada)
 			reada_for_search(fs_info, path, level, 0, 0);
diff --git a/ctree.h b/ctree.h
index 6df6075865c2..939c584d0301 100644
--- a/ctree.h
+++ b/ctree.h
@@ -2633,7 +2633,20 @@ static inline int btrfs_insert_empty_item(struct btrfs_trans_handle *trans,
 	return btrfs_insert_empty_items(trans, root, path, key, &data_size, 1);
 }
 
-int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path);
+int btrfs_next_sibling_tree_block(struct btrfs_fs_info *fs_info,
+				  struct btrfs_path *path);
+/*
+ * walk up the tree as far as required to find the next leaf.
+ * returns 0 if it found something or 1 if there are no greater leaves.
+ * returns < 0 on io errors.
+ */
+static inline int btrfs_next_leaf(struct btrfs_root *root,
+				  struct btrfs_path *path)
+{
+	path->lowest_level = 0;
+	return btrfs_next_sibling_tree_block(root->fs_info, path);
+}
+
 static inline int btrfs_next_item(struct btrfs_root *root,
 				  struct btrfs_path *p)
 {
-- 
2.18.0