TC相关操作

///sched/sch_api.c
static int __init pktsched_init(void)
{
	int err;

	err = register_pernet_subsys(&psched_net_ops);
	if (err) {
		pr_err("pktsched_init: "
		       "cannot initialize per netns operations\n");
		return err;
	}

	register_qdisc(&pfifo_qdisc_ops);
	register_qdisc(&bfifo_qdisc_ops);
	register_qdisc(&pfifo_head_drop_qdisc_ops);
	register_qdisc(&mq_qdisc_ops);

	rtnl_register(PF_UNSPEC, RTM_NEWQDISC, tc_modify_qdisc, NULL, NULL); /// new qdisc
	rtnl_register(PF_UNSPEC, RTM_DELQDISC, tc_get_qdisc, NULL, NULL);
	rtnl_register(PF_UNSPEC, RTM_GETQDISC, tc_get_qdisc, tc_dump_qdisc, NULL);
	rtnl_register(PF_UNSPEC, RTM_NEWTCLASS, tc_ctl_tclass, NULL, NULL);
	rtnl_register(PF_UNSPEC, RTM_DELTCLASS, tc_ctl_tclass, NULL, NULL);
	rtnl_register(PF_UNSPEC, RTM_GETTCLASS, tc_ctl_tclass, tc_dump_tclass, NULL);

	return 0;
}

/* Graft qdisc "new" to class "classid" of qdisc "parent" or
 * to device "dev".
 *
 * When appropriate send a netlink notification using 'skb'
 * and "n".
 *
 * On success, destroy old qdisc.
 */

static int qdisc_graft(struct net_device *dev, struct Qdisc *parent,
		       struct sk_buff *skb, struct nlmsghdr *n, u32 classid,
		       struct Qdisc *new, struct Qdisc *old)
{
	struct Qdisc *q = old;
	struct net *net = dev_net(dev);
	int err = 0;

	if (parent == NULL) {
		unsigned int i, num_q, ingress;

		ingress = 0;
		num_q = dev->num_tx_queues;
		if ((q && q->flags & TCQ_F_INGRESS) ||
		    (new && new->flags & TCQ_F_INGRESS)) {
			num_q = 1;
			ingress = 1;
			if (!dev_ingress_queue(dev))
				return -ENOENT;
		}

		if (dev->flags & IFF_UP)
			dev_deactivate(dev);

		if (new && new->ops->attach)
			goto skip;

		for (i = 0; i < num_q; i++) { ///设置所有队列
			struct netdev_queue *dev_queue = dev_ingress_queue(dev);

			if (!ingress)
				dev_queue = netdev_get_tx_queue(dev, i);

			old = dev_graft_qdisc(dev_queue, new);
			if (new && i > 0)
				atomic_inc(&new->refcnt);

			if (!ingress)
				qdisc_destroy(old);
		}

skip:
		if (!ingress) {
			notify_and_destroy(net, skb, n, classid,
					   dev->qdisc, new);
			if (new && !new->ops->attach)
				atomic_inc(&new->refcnt);
			dev->qdisc = new ? : &noop_qdisc;

			if (new && new->ops->attach)
				new->ops->attach(new);
		} else {
			notify_and_destroy(net, skb, n, classid, old, new);
		}

		if (dev->flags & IFF_UP)
			dev_activate(dev); ///active
	}
	

int dev_queue_xmit(struct sk_buff *skb)
{
///...
	txq = netdev_pick_tx(dev, skb);
	q = rcu_dereference_bh(txq->qdisc);

	trace_net_dev_queue(skb);
	if (q->enqueue) { ///pfifo_fast_ops
		rc = __dev_xmit_skb(skb, q, dev, txq);
		goto out;
	}
///...
}

static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
				 struct net_device *dev,
				 struct netdev_queue *txq)
{
///...
	spin_lock(root_lock);
	if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) {
		kfree_skb(skb);
		rc = NET_XMIT_DROP;
	} else if ((q->flags & TCQ_F_CAN_BYPASS) && !qdisc_qlen(q) &&
		   qdisc_run_begin(q)) {
		/*
		 * This is a work-conserving queue; there are no old skbs
		 * waiting to be sent out; and the qdisc is not running -
		 * xmit the skb directly.
		 */
		if (!(dev->priv_flags & IFF_XMIT_DST_RELEASE))
			skb_dst_force(skb);

		qdisc_bstats_update(q, skb);

		if (sch_direct_xmit(skb, q, dev, txq, root_lock)) {
			if (unlikely(contended)) {
				spin_unlock(&q->busylock);
				contended = false;
			}
			__qdisc_run(q);
		} else
			qdisc_run_end(q);

		rc = NET_XMIT_SUCCESS;
	} else {
		skb_dst_force(skb);
		rc = q->enqueue(skb, q) & NET_XMIT_MASK; /// enqueue qdisc queue
		if (qdisc_run_begin(q)) {
			if (unlikely(contended)) {
				spin_unlock(&q->busylock);
				contended = false;
			}
			__qdisc_run(q);
		}
	}
	spin_unlock(root_lock);

/ * Returns to the caller:
 *				0  - queue is empty or throttled.
 *				>0 - queue is not empty.
 *
 */
static inline int qdisc_restart(struct Qdisc *q)
{
	struct netdev_queue *txq;
	struct net_device *dev;
	spinlock_t *root_lock;
	struct sk_buff *skb;

	/* Dequeue packet */
	skb = dequeue_skb(q); /// dequeue skb from qdisc
	if (unlikely(!skb))
		return 0;
	WARN_ON_ONCE(skb_dst_is_noref(skb));
	root_lock = qdisc_lock(q);
	dev = qdisc_dev(q);
	txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));

	return sch_direct_xmit(skb, q, dev, txq, root_lock); /// send to driver
}

void __qdisc_run(struct Qdisc *q)
{
	int quota = weight_p;

	while (qdisc_restart(q)) {
		/*
		 * Ordered by possible occurrence: Postpone processing if
		 * 1. we've exceeded packet quota
		 * 2. another process needs the CPU;
		 */
		if (--quota <= 0 || need_resched()) {
			__netif_schedule(q);
			break;
		}
	}

	qdisc_run_end(q);
}

int br_add_bridge(struct net *net, const char *name)
{
	struct net_device *dev;
	int res;

	dev = alloc_netdev(sizeof(struct net_bridge), name,
			   br_dev_setup);
}

#define alloc_netdev(sizeof_priv, name, setup) \
	alloc_netdev_mqs(sizeof_priv, name, setup, 1, 1)