tc_fifo_qopt
struct tc_fifo_qopt *ctl = nla_data(opt);
struct tc_fifo_qopt opt = { .limit = READ_ONCE(sch->limit) };
nla = kmalloc(nla_attr_size(sizeof(struct tc_fifo_qopt)), GFP_KERNEL);
nla->nla_len = nla_attr_size(sizeof(struct tc_fifo_qopt));
((struct tc_fifo_qopt *)nla_data(nla))->limit = limit;