bitmask_swap
bitmask_swap(&ctl->nh_idx_head, gr_idx_ptr, new_idx_items, &old_idx_ptr);
bitmask_swap(&ctl->nh_idx_head, nh_idx_ptr, new_idx_items, &old_idx_ptr);
void bitmask_swap(struct bitmask_head *bh, void *new_idx, uint32_t new_items, void **pidx);