void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info);
int exit_ro_spine(struct ro_spine *s);
int ro_step(struct ro_spine *s, dm_block_t new_child);
void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info);
int exit_ro_spine(struct ro_spine *s);
int ro_step(struct ro_spine *s, dm_block_t new_child);