NAND FLASH will be scanned whening yaffs2 mount.If not find checkpoint,yaffs2 will begin check chunk.But if get error information from NAND FLASH,yaffs2 may be run this code：

in = yaffs_retype_obj(in, oh ? oh->type : tags.extra_obj_type);

If in->variant_type ==YAFFS_OBJECT_TYPE_DIRECTORY ,It just put object's childrens in lost+found,but not deal with siblings list.It is need deal with siblings list?