--- fs/btrfs/root-tree.c

+++ fs/btrfs/root-tree.c

@@ -459,3 +459,21 @@ again:

btrfs_free_path(path);

return 0;

}

+

+/*

+ * Old btrfs forgets to init root_item->flags and root_item->byte_limit

+ * for subvolumes. To work around this problem, we steal a bit from

+ * root_item->inode_item->flags, and use it to indicate if those fields

+ * have been properly initialized.

+ */

+void btrfs_check_and_init_root_item(struct btrfs_root_item *root_item)

+{

+ u64 inode_flags = le64_to_cpu(root_item->inode.flags);

+

+ if (!(inode_flags & BTRFS_INODE_ROOT_ITEM_INIT)) {

+ inode_flags |= BTRFS_INODE_ROOT_ITEM_INIT;

+ root_item->inode.flags = cpu_to_le64(inode_flags);

+ root_item->flags = 0;

+ root_item->byte_limit = 0;

+ }

+}