网卡驱动dev_watchdog详解

1、初始化

2、开启watchdog

3、超时处理dev_watchdog

4、发送时间trans_start 更新

5、usbnet驱动

网络设备watchdog用于监控网卡驱动发送数据是否异常，如果异常就报错，并调用网卡驱动提供的超时处理函数。

基本原理：网卡设备初始化时，初始化watchdog定时器，用户空间打开网卡设备时，同时开启watchdog定时器，每次watchdog定时器超时，就检查网卡设备的发送队列发送数据是否超时，如果超时报错并调用网卡驱动提供的超时处理函数。然后重启watchdog定时器超时。

驱动位置：

linux3.10.xx
netdevice.h
\net\core\dev.c
\net\sched\sch_generic.c

1、初始化

网卡驱动在register_netdevice注册网络设备时，调用dev_init_scheduler初始化watchdog定时器，register_netdevice---->dev_init_scheduler

void dev_init_scheduler(struct net_device *dev)
{dev->qdisc = &noop_qdisc;netdev_for_each_tx_queue(dev, dev_init_scheduler_queue, &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); 初始化watchdog_timer
}

2、开启watchdog

网卡up时，开启watchdog。
__dev_change_flags–>__dev_open–>dev_activate(dev);

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 forvirtual interfaces*/if (dev->qdisc == &noop_qdisc) //流控策略初始化时为noop_qdiscattach_default_qdiscs(dev); //改变流控测试为默认pfifo_fastif (!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);// 判断是否开启watchdog，不为noqueue_qdisc，就开启watchdogif (dev_ingress_queue(dev))transition_one_qdisc(dev, dev_ingress_queue(dev), NULL);if (need_watchdog) {//前面判断开启dev->trans_start = jiffies; //记录开启时间dev_watchdog_up(dev); //开启watchdog}
}static void transition_one_qdisc(struct net_device *dev,struct netdev_queue *dev_queue,void *_need_watchdog)
{struct Qdisc *new_qdisc = dev_queue->qdisc_sleeping;int *need_watchdog_p = _need_watchdog;if (!(new_qdisc->flags & TCQ_F_BUILTIN))clear_bit(__QDISC_STATE_DEACTIVATED, &new_qdisc->state);rcu_assign_pointer(dev_queue->qdisc, new_qdisc);if (need_watchdog_p && new_qdisc != &noqueue_qdisc) { //不为noqueue_qdisc，就开启watchdogdev_queue->trans_start = 0;*need_watchdog_p = 1;}
}

dev_watchdog_up(dev); 开启watchdog

static void dev_watchdog_up(struct net_device *dev)
{__netdev_watchdog_up(dev);
}void __netdev_watchdog_up(struct net_device *dev)
{if (dev->netdev_ops->ndo_tx_timeout) {//ndo_tx_timeout为网卡驱动提供的发送超时处理函数if (dev->watchdog_timeo <= 0)dev->watchdog_timeo = 5*HZ; //默认超时处理 5*HZif (!mod_timer(&dev->watchdog_timer,round_jiffies(jiffies + dev->watchdog_timeo))) //开启定时器dev_hold(dev);}
}

3、超时处理dev_watchdog

dev_watchdog为watchdog定时器超时处理函数，只有网卡还在正常运行时，才进一步检查网卡发送队列是否超时。
判断发送队列是否超时：
1，netif_xmit_stopped发送队列已经停止
2，txq->trans_start最近一次发送数据的时间已经超过watchdog_timeo时间

static void dev_watchdog(unsigned long arg)
{struct net_device *dev = (struct net_device *)arg;netif_tx_lock(dev);判断if (!qdisc_tx_is_noop(dev)) { txq->qdisc不是noop_qdisc，if (netif_device_present(dev) &&  网卡设备还存在netif_running(dev) && 网卡设备还在运行netif_carrier_ok(dev)) { 网卡设备在线int some_queue_timedout = 0;unsigned int i;unsigned long trans_start;for (i = 0; i < dev->num_tx_queues; i++) {struct netdev_queue *txq;txq = netdev_get_tx_queue(dev, i);/** old device drivers set dev->trans_start*/trans_start = txq->trans_start ? : dev->trans_start; 记录最近一次网卡设备发送时间if (netif_xmit_stopped(txq) &&  网卡发送队列在运行，time_after(jiffies, (trans_start +dev->watchdog_timeo))) {  当前时间已经超过了最近一次网卡设备发送时间+watchdog_timeosome_queue_timedout = 1;txq->trans_timeout++;break;}}if (some_queue_timedout) { 超时后，告警，并调用网卡驱动的ndo_tx_timeoutWARN_ONCE(1, KERN_INFO "NETDEV WATCHDOG: %s (%s): transmit queue %u timed out\n",dev->name, netdev_drivername(dev), i);dev->netdev_ops->ndo_tx_timeout(dev);}if (!mod_timer(&dev->watchdog_timer,round_jiffies(jiffies +dev->watchdog_timeo)))重新开启定时器dev_hold(dev);}}netif_tx_unlock(dev);dev_put(dev);
}

网卡在open时，网卡驱动提供的ndo_open都会调用netif_start_queue (net); 开启网卡队列，这样dev_watchdog函数中netif_xmit_stopped返回0，就不会判断是否超时。网卡在异常或发送队列中长度超过了门限时会停止发送队列netif_xmit_stopped，netif_xmit_stopped就返回1，那就进一步判断最近一次发送数据时间是否超时。

enum netdev_queue_state_t {__QUEUE_STATE_DRV_XOFF,__QUEUE_STATE_STACK_XOFF,__QUEUE_STATE_FROZEN,
#define QUEUE_STATE_ANY_XOFF ((1 << __QUEUE_STATE_DRV_XOFF)        | \(1 << __QUEUE_STATE_STACK_XOFF))
#define QUEUE_STATE_ANY_XOFF_OR_FROZEN (QUEUE_STATE_ANY_XOFF        | \(1 << __QUEUE_STATE_FROZEN))
};

ndo_open都会调用netif_start_queue (net)，清除__QUEUE_STATE_DRV_XOFF

static inline void netif_tx_start_queue(struct netdev_queue *dev_queue)
{clear_bit(__QUEUE_STATE_DRV_XOFF, &dev_queue->state);
}static inline void netif_start_queue(struct net_device *dev)
{netif_tx_start_queue(netdev_get_tx_queue(dev, 0));
}

网卡在异常或发送队列中长度超过了门限时会停止发送队列netif_stop_queue，设置__QUEUE_STATE_DRV_XOFF

static inline void netif_tx_stop_queue(struct netdev_queue *dev_queue)
{if (WARN_ON(!dev_queue)) {pr_info("netif_stop_queue() cannot be called before register_netdev()\n");return;}set_bit(__QUEUE_STATE_DRV_XOFF, &dev_queue->state);
}/***    netif_stop_queue - stop transmitted packets*    @dev: network device**    Stop upper layers calling the device hard_start_xmit routine.*    Used for flow control when transmit resources are unavailable.*/
static inline void netif_stop_queue(struct net_device *dev)
{netif_tx_stop_queue(netdev_get_tx_queue(dev, 0));
}

判断是否停止，__QUEUE_STATE_DRV_XOFF

static inline bool netif_xmit_stopped(const struct netdev_queue *dev_queue)
{return dev_queue->state & QUEUE_STATE_ANY_XOFF;
}

4、发送时间trans_start 更新

dev_hard_start_xmit调用网卡驱动接口ndo_start_xmit发送完成数据后，调用txq_trans_update更新发送时间。

dev_hard_start_xmit：rc = ops->ndo_start_xmit(skb, dev);if (rc == NETDEV_TX_OK)txq_trans_update(txq);static inline void txq_trans_update(struct netdev_queue *txq)
{if (txq->xmit_lock_owner != -1)txq->trans_start = jiffies;
}

5、usbnet驱动

usbnet_open–>netif_start_queue (net);

发送完成回调函数中tx_complete调用netif_stop_queue

tx_completecase -EPROTO:case -ETIME:case -EILSEQ:usb_mark_last_busy(dev->udev);if (!timer_pending (&dev->delay)) {mod_timer (&dev->delay,jiffies + THROTTLE_JIFFIES);netif_dbg(dev, link, dev->net,"tx throttle %d\n", urb->status); }netif_stop_queue (dev->net); 异常停止发送队列break;

usbnet_start_xmit发送数据中，发送队列数据格式超过了门限

usbnet_start_xmitcase 0:net->trans_start = jiffies;更新每次发送数据更新发送时间__usbnet_queue_skb(&dev->txq, skb, tx_start);if (dev->txq.qlen >= TX_QLEN (dev)) 超过门限netif_stop_queue (net);