btrfs-progs: add a helper for clearing all the items in a tree

Used in clear_free_space_tree, this is a totally generic operation.
It will also be used for clearing the qgroup tree from btrfstune.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
[ Make remove_all_tree_items() to use btrfs_clear_tree() ]
Signed-off-by: Qu Wenruo <wqu@suse.com>

common/root-tree-utils.c

@@ -226,8 +226,6 @@ int btrfs_link_subvolume(struct btrfs_trans_handle *trans,
 static int remove_all_tree_items(struct btrfs_root *root)
 {
 	struct btrfs_trans_handle *trans;
-	struct btrfs_path path = { 0 };
-	struct btrfs_key key = { 0 };
 	int ret;
 
 	trans = btrfs_start_transaction(root, 1);
@@ -239,40 +237,13 @@ static int remove_all_tree_items(struct btrfs_root *root)
 			  root->root_key.objectid);
 		return ret;
 	}
-	while (true) {
-		int nr_items;
-
-		ret = btrfs_search_slot(trans, root, &key, &path, -1, 1);
-		if (ret < 0) {
-			errno = -ret;
-			error("failed to locate the first key of root %lld: %m",
-				root->root_key.objectid);
-			btrfs_abort_transaction(trans, ret);
-			return ret;
-		}
-		if (ret == 0) {
-			ret = -EUCLEAN;
-			errno = -ret;
-			error("unexpected all zero key found in root %lld",
-				root->root_key.objectid);
-			btrfs_abort_transaction(trans, ret);
-			return ret;
-		}
-		nr_items = btrfs_header_nritems(path.nodes[0]);
-		/* The tree is empty. */
-		if (nr_items == 0) {
-			btrfs_release_path(&path);
-			break;
-		}
-		ret = btrfs_del_items(trans, root, &path, 0, nr_items);
-		btrfs_release_path(&path);
-		if (ret < 0) {
-			errno = -ret;
-			error("failed to empty the first leaf of root %lld: %m",
-				root->root_key.objectid);
-			btrfs_abort_transaction(trans, ret);
-			return ret;
-		}
+	ret = btrfs_clear_tree(trans, root);
+	if (ret < 0) {
+		errno = -ret;
+		error("failed to empty root %lld: %m",
+			root->root_key.objectid);
+		btrfs_abort_transaction(trans, ret);
+		return ret;
 	}
 	ret = btrfs_commit_transaction(trans, root);
 	if (ret < 0) {

kernel-shared/disk-io.c

@@ -2342,6 +2342,45 @@ static bool is_global_root(struct btrfs_root *root)
 		return true;
 	return false;
 }
+
+int btrfs_clear_tree(struct btrfs_trans_handle *trans,
+		     struct btrfs_root *root)
+{
+	struct btrfs_path *path;
+	struct btrfs_key key;
+	struct extent_buffer *leaf = NULL;
+	int ret;
+	int nr = 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	key.objectid = 0;
+	key.offset = 0;
+	key.type = 0;
+
+	while (1) {
+		ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+		if (ret < 0)
+			goto out;
+		leaf = path->nodes[0];
+		nr = btrfs_header_nritems(leaf);
+		if (!nr)
+			break;
+		path->slots[0] = 0;
+		ret = btrfs_del_items(trans, root, path, 0, nr);
+		if (ret)
+			goto out;
+
+		btrfs_release_path(path);
+	}
+	ret = 0;
+out:
+	btrfs_free_path(path);
+	return ret;
+}
+
 int btrfs_delete_and_free_root(struct btrfs_trans_handle *trans,
 			       struct btrfs_root *root)
 {

kernel-shared/disk-io.h

@@ -240,6 +240,8 @@ int write_tree_block(struct btrfs_trans_handle *trans,
 int btrfs_fs_roots_compare_roots(const struct rb_node *node1, const struct rb_node *node2);
 struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
 				     struct btrfs_key *key);
+int btrfs_clear_tree(struct btrfs_trans_handle *trans,
+		     struct btrfs_root *root);
 int btrfs_delete_and_free_root(struct btrfs_trans_handle *trans,
 			       struct btrfs_root *root);
 struct btrfs_root *btrfs_csum_root(struct btrfs_fs_info *fs_info, u64 bytenr);

kernel-shared/free-space-tree.c

@@ -1228,44 +1228,6 @@ int remove_block_group_free_space(struct btrfs_trans_handle *trans,
 		btrfs_abort_transaction(trans, ret);
 	return ret;
 }
-static int clear_free_space_tree(struct btrfs_trans_handle *trans,
-				 struct btrfs_root *root)
-{
-	struct btrfs_path *path;
-	struct btrfs_key key;
-	int nr;
-	int ret;
-
-	path = btrfs_alloc_path();
-	if (!path)
-		return -ENOMEM;
-
-	key.objectid = 0;
-	key.type = 0;
-	key.offset = 0;
-
-	while (1) {
-		ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
-		if (ret < 0)
-			goto out;
-
-		nr = btrfs_header_nritems(path->nodes[0]);
-		if (!nr)
-			break;
-
-		path->slots[0] = 0;
-		ret = btrfs_del_items(trans, root, path, 0, nr);
-		if (ret)
-			goto out;
-
-		btrfs_release_path(path);
-	}
-
-	ret = 0;
-out:
-	btrfs_free_path(path);
-	return ret;
-}
 
 int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
 {
@@ -1288,7 +1250,7 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
 
 		while (key.offset < fs_info->nr_global_roots) {
 			free_space_root = btrfs_global_root(fs_info, &key);
-			ret = clear_free_space_tree(trans, free_space_root);
+			ret = btrfs_clear_tree(trans, free_space_root);
 			if (ret)
 				goto abort;
 			key.offset++;
@@ -1299,7 +1261,7 @@ int btrfs_clear_free_space_tree(struct btrfs_fs_info *fs_info)
 			      BTRFS_FEATURE_COMPAT_RO_FREE_SPACE_TREE);
 		btrfs_set_super_compat_ro_flags(fs_info->super_copy, features);
 
-		ret = clear_free_space_tree(trans, free_space_root);
+		ret = btrfs_clear_tree(trans, free_space_root);
 		if (ret)
 			goto abort;