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qdisc 的创建过程

http://blog.chinaunix.net/uid-26902809-id-4106161.html

register_netdevice会初始化netdev的Tx调度discipline, 缺省使用noop_qdisc

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register_netdevice
--->dev_init_scheduler


void dev_init_scheduler(struct net_device *dev)
{
	dev->qdisc = &noop_qdisc; //缺省为设备配置noop_qdisc
	netdev_for_each_tx_queue(dev, dev_init_scheduler_queue, &noop_qdisc); //缺省为每个队列配置noop_qdisc
	if (dev_ingress_queue(dev))
		dev_init_scheduler_queue(dev, dev_ingress_queue(dev), &noop_qdisc);

	setup_timer(&dev->watchdog_timer, dev_watchdog, (unsigned long)dev);
}
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dev_open
--->__dev_open
---->dev_activate
---->attach_default_qdiscs
---->attach_one_default_qdisc
为单队列的设备创建pfifo_fast的qdisc

static void attach_one_default_qdisc(struct net_device *dev,
				struct netdev_queue *dev_queue,
				void *_unused)
{
	struct Qdisc *qdisc = &noqueue_qdisc;

	if (dev->tx_queue_len) {
		qdisc = qdisc_create_dflt(dev_queue,
				&pfifo_fast_ops, TC_H_ROOT);
		if (!qdisc) {
			netdev_info(dev, "activation failed\n");
			return;
		}
	}
	dev_queue->qdisc_sleeping = qdisc;
}
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dev_open
--->__dev_open
---->dev_activate
---->attach_default_qdiscs
---->qdisc_create_dflt
为多队列的设备创建mq_qdisc, 创建完mq_qdisc, 接着调用mq_qdisc_ops->mq_init函数为每个队列创建pfifo_fast_ops的qdisc

struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
			struct Qdisc_ops *ops, unsigned int parentid)
{
	struct Qdisc *sch;

	sch = qdisc_alloc(dev_queue, ops);
	if (IS_ERR(sch))
		goto errout;
	sch->parent = parentid;

	if (!ops->init || ops->init(sch, NULL) == 0)
		return sch;

	qdisc_destroy(sch);
errout:
	return NULL;
}
EXPORT_SYMBOL(qdisc_create_dflt);
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dev_open
--->__dev_open
---->dev_activate
---->attach_default_qdiscs
static void attach_default_qdiscs(struct net_device *dev)
{
	struct netdev_queue *txq;
	struct Qdisc *qdisc;

	txq = netdev_get_tx_queue(dev, 0);

	if (!netif_is_multiqueue(dev) || dev->tx_queue_len == 0) {
		netdev_for_each_tx_queue(dev, attach_one_default_qdisc, NULL);
		dev->qdisc = txq->qdisc_sleeping;
		atomic_inc(&dev->qdisc->refcnt);
	} else {
		qdisc = qdisc_create_dflt(txq, &mq_qdisc_ops, TC_H_ROOT);
		if (qdisc) {
			qdisc->ops->attach(qdisc);
			dev->qdisc = qdisc;
		}
	}
}
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dev_open函数会调用dev_activate:
a. 为单队列的设备创建pfifo_fast的qdisc
b. 为多队列的设备创建mq_qdisc, 创建完mq_qdisc, 接着调用mq_qdisc_ops->mq_init函数为每个队列创建pfifo_fast_ops的qdisc
dev_open
--->__dev_open
---->dev_activate

void dev_activate(struct net_device *dev)
{
	int need_watchdog;

	/* No queueing discipline is attached to device;
	   create default one i.e. pfifo_fast for devices,
	   which need queueing and noqueue_qdisc for
	   virtual interfaces
	*/

	if (dev->qdisc == &noop_qdisc)
		attach_default_qdiscs(dev);

	if (!netif_carrier_ok(dev))
	/* Delay activation until next carrier-on event */
		return;

	need_watchdog = 0;
	netdev_for_each_tx_queue(dev, transition_one_qdisc, &need_watchdog);
	if (dev_ingress_queue(dev))
		transition_one_qdisc(dev, dev_ingress_queue(dev), NULL);

	if (need_watchdog) {
		dev->trans_start = jiffies;
		dev_watchdog_up(dev);
	}
}