static netdev_tx_t ifb_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct ifb_dev_private *dp = netdev_priv(dev);
	struct ifb_q_private *txp = dp->tx_private + skb_get_queue_mapping(skb);

	u64_stats_update_begin(&txp->rsync);
	txp->rx_packets++;
	txp->rx_bytes += skb->len;
	u64_stats_update_end(&txp->rsync);

	if (!skb->tc_redirected || !skb->skb_iif) {
		dev_kfree_skb(skb);
		dev->stats.rx_dropped++;
		return NETDEV_TX_OK;
	}

	if (skb_queue_len(&txp->rq) >= dev->tx_queue_len)
		netif_tx_stop_queue(netdev_get_tx_queue(dev, txp->txqnum));

	__skb_queue_tail(&txp->rq, skb);
	if (!txp->tasklet_pending) {
		txp->tasklet_pending = 1;
		tasklet_schedule(&txp->ifb_tasklet);
	}

	return NETDEV_TX_OK;
}

int vlan_dev_fastbridge_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
	int i = skb_get_queue_mapping(skb);
	struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
	unsigned short veth_TCI;

	/* Construct the second two bytes. This field looks something
	 * like:
	 * usr_priority: 3 bits	 (high bits)
	 * CFI		 1 bit
	 * VLAN ID	 12 bits (low bits)
	 */
	veth_TCI = vlan_dev_info(dev)->vlan_id;
	veth_TCI |= vlan_dev_get_egress_qos_mask(dev, skb);
	skb = __vlan_put_tag(skb, veth_TCI);

	if (!skb) {
		txq->tx_dropped++;
		return 0;
	}

	txq->tx_packets++;
	txq->tx_bytes +=  skb->len;
	skb->dev = vlan_dev_info(dev)->real_dev;
	
	return skb->dev->netdev_ops->ndo_start_xmit(skb, skb->dev);	 
}

static void mt76x0_complete_tx(struct urb *urb)
{
	struct mt76x0_tx_queue *q = urb->context;
	struct mt76x0_dev *dev = q->dev;
	struct sk_buff *skb;
	unsigned long flags;

	spin_lock_irqsave(&dev->tx_lock, flags);

	if (mt76x0_urb_has_error(urb))
		dev_err(dev->mt76.dev, "Error: TX urb failed:%d\n", urb->status);
	if (WARN_ONCE(q->e[q->start].urb != urb, "TX urb mismatch"))
		goto out;

	skb = q->e[q->start].skb;
	trace_mt76x0_tx_dma_done(&dev->mt76, skb);

	__skb_queue_tail(&dev->tx_skb_done, skb);
	tasklet_schedule(&dev->tx_tasklet);

	if (q->used == q->entries - q->entries / 8)
		ieee80211_wake_queue(dev->mt76.hw, skb_get_queue_mapping(skb));

	q->start = (q->start + 1) % q->entries;
	q->used--;
out:
	spin_unlock_irqrestore(&dev->tx_lock, flags);
}

static void rtw_check_xmit_resource(_adapter *padapter, _pkt *pkt)
{
	struct xmit_priv *pxmitpriv = &padapter->xmitpriv;
#if (LINUX_VERSION_CODE>=KERNEL_VERSION(2,6,35))
	u16	queue;

	queue = skb_get_queue_mapping(pkt);
	if (padapter->registrypriv.wifi_spec) {
		/* No free space for Tx, tx_worker is too slow */
		if (pxmitpriv->hwxmits[queue].accnt > WMM_XMIT_THRESHOLD) {
			//DBG_871X("%s(): stop netif_subqueue[%d]\n", __FUNCTION__, queue);
			netif_stop_subqueue(padapter->pnetdev, queue);
		}
	} else {
		if(pxmitpriv->free_xmitframe_cnt<=4) {
			if (!netif_tx_queue_stopped(netdev_get_tx_queue(padapter->pnetdev, queue)))
				netif_stop_subqueue(padapter->pnetdev, queue);
		}
	}
#else
	if(pxmitpriv->free_xmitframe_cnt<=4)
	{
		if (!rtw_netif_queue_stopped(padapter->pnetdev))
			rtw_netif_stop_queue(padapter->pnetdev);
	}
#endif
}

static netdev_tx_t vlan_dev_hwaccel_hard_start_xmit(struct sk_buff *skb,
						    struct net_device *dev)
{
	int i = skb_get_queue_mapping(skb);
	struct netdev_queue *txq = netdev_get_tx_queue(dev, i);
	u16 vlan_tci;
	unsigned int len;
	int ret;

	vlan_tci = vlan_dev_info(dev)->vlan_id;
	vlan_tci |= vlan_dev_get_egress_qos_mask(dev, skb);
	skb = __vlan_hwaccel_put_tag(skb, vlan_tci);

	skb->dev = vlan_dev_info(dev)->real_dev;
	len = skb->len;
	ret = dev_queue_xmit(skb);

	if (likely(ret == NET_XMIT_SUCCESS || ret == NET_XMIT_CN)) {
		txq->tx_packets++;
		txq->tx_bytes += len;
	} else
		txq->tx_dropped++;

	return ret;
}

int octeon_report_sent_bytes_to_bql(void *buf, int reqtype)
{
	struct octnet_buf_free_info *finfo;
	struct sk_buff *skb;
	struct octeon_soft_command *sc;
	struct netdev_queue *txq;

	switch (reqtype) {
	case REQTYPE_NORESP_NET:
	case REQTYPE_NORESP_NET_SG:
		finfo = buf;
		skb = finfo->skb;
		break;

	case REQTYPE_RESP_NET_SG:
	case REQTYPE_RESP_NET:
		sc = buf;
		skb = sc->callback_arg;
		break;

	default:
		return 0;
	}

	txq = netdev_get_tx_queue(skb->dev, skb_get_queue_mapping(skb));
	netdev_tx_sent_queue(txq, skb->len);

	return netif_xmit_stopped(txq);
}

static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct xenvif *vif = netdev_priv(dev);
	struct xenvif_queue *queue = NULL;
	unsigned int num_queues;
	u16 index;
	struct xenvif_rx_cb *cb;

	BUG_ON(skb->dev != dev);

	/* Drop the packet if queues are not set up.
	 * This handler should be called inside an RCU read section
	 * so we don't need to enter it here explicitly.
	 */
	num_queues = READ_ONCE(vif->num_queues);
	if (num_queues < 1)
		goto drop;

	/* Obtain the queue to be used to transmit this packet */
	index = skb_get_queue_mapping(skb);
	if (index >= num_queues) {
		pr_warn_ratelimited("Invalid queue %hu for packet on interface %s\n.",
				    index, vif->dev->name);
		index %= num_queues;
	}
	queue = &vif->queues[index];

	/* Drop the packet if queue is not ready */
	if (queue->task == NULL ||
	    queue->dealloc_task == NULL ||
	    !xenvif_schedulable(vif))
		goto drop;

	if (vif->multicast_control && skb->pkt_type == PACKET_MULTICAST) {
		struct ethhdr *eth = (struct ethhdr *)skb->data;

		if (!xenvif_mcast_match(vif, eth->h_dest))
			goto drop;
	}

	cb = XENVIF_RX_CB(skb);
	cb->expires = jiffies + vif->drain_timeout;

	/* If there is no hash algorithm configured then make sure there
	 * is no hash information in the socket buffer otherwise it
	 * would be incorrectly forwarded to the frontend.
	 */
	if (vif->hash.alg == XEN_NETIF_CTRL_HASH_ALGORITHM_NONE)
		skb_clear_hash(skb);

	xenvif_rx_queue_tail(queue, skb);
	xenvif_kick_thread(queue);

	return NETDEV_TX_OK;

 drop:
	vif->dev->stats.tx_dropped++;
	dev_kfree_skb(skb);
	return NETDEV_TX_OK;
}

static struct Qdisc *
multiq_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
{
	struct multiq_sched_data *q = qdisc_priv(sch);
	u32 band;
	struct tcf_result res;
	struct tcf_proto *fl = rcu_dereference_bh(q->filter_list);
	int err;

	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
	err = tcf_classify(skb, fl, &res, false);
#ifdef CONFIG_NET_CLS_ACT
	switch (err) {
	case TC_ACT_STOLEN:
	case TC_ACT_QUEUED:
	case TC_ACT_TRAP:
		*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
		/* fall through */
	case TC_ACT_SHOT:
		return NULL;
	}
#endif
	band = skb_get_queue_mapping(skb);

	if (band >= q->bands)
		return q->queues[0];

	return q->queues[band];
}

static struct Qdisc *
multiq_classify(struct sk_buff *skb, struct Qdisc *sch, int *qerr)
{
	struct multiq_sched_data *q = qdisc_priv(sch);
	u32 band;
	struct tcf_result res;
	int err;

	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
	err = tc_classify(skb, q->filter_list, &res);
#ifdef CONFIG_NET_CLS_ACT
	switch (err) {
	case TC_ACT_STOLEN:
	case TC_ACT_QUEUED:
		*qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
	case TC_ACT_SHOT:
		return NULL;
	}
#endif
	band = skb_get_queue_mapping(skb);

	if (band >= q->bands)
		return q->queues[0];

	return q->queues[band];
}

netdev_tx_t mlx5e_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct mlx5e_priv *priv = netdev_priv(dev);
	struct mlx5e_sq *sq = priv->txq_to_sq_map[skb_get_queue_mapping(skb)];

	return mlx5e_sq_xmit(sq, skb);
}

static void mt7601u_complete_tx(struct urb *urb)
{
	struct mt7601u_tx_queue *q = urb->context;
	struct mt7601u_dev *dev = q->dev;
	struct sk_buff *skb;
	unsigned long flags;

	spin_lock_irqsave(&dev->tx_lock, flags);

	if (mt7601u_urb_has_error(urb))
		dev_err(dev->dev, "Error: TX urb failed:%d\n", urb->status);
	if (WARN_ONCE(q->e[q->start].urb != urb, "TX urb mismatch"))
		goto out;

	skb = q->e[q->start].skb;
	trace_mt_tx_dma_done(dev, skb);

	mt7601u_tx_status(dev, skb);

	if (q->used == q->entries - q->entries / 8)
		ieee80211_wake_queue(dev->hw, skb_get_queue_mapping(skb));

	q->start = (q->start + 1) % q->entries;
	q->used--;

	if (urb->status)
		goto out;

	set_bit(MT7601U_STATE_MORE_STATS, &dev->state);
	if (!test_and_set_bit(MT7601U_STATE_READING_STATS, &dev->state))
		queue_delayed_work(dev->stat_wq, &dev->stat_work,
				   msecs_to_jiffies(10));
out:
	spin_unlock_irqrestore(&dev->tx_lock, flags);
}

/*
 * NOTE: Called under qdisc_lock(q) with locally disabled BH.
 *
 * __QDISC_STATE_RUNNING guarantees only one CPU can process
 * this qdisc at a time. qdisc_lock(q) serializes queue accesses for
 * this queue.
 *
 *  netif_tx_lock serializes accesses to device driver.
 *
 *  qdisc_lock(q) and netif_tx_lock are mutually exclusive,
 *  if one is grabbed, another must be free.
 *
 * Note, that this procedure can be called by a watchdog timer
 *
 * 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;
	int ret = NETDEV_TX_BUSY;
	struct net_device *dev;
	spinlock_t *root_lock;
	struct sk_buff *skb;

	/* Dequeue packet */
	//从队列上取下一个要发送的数据包.
	if (unlikely((skb = dequeue_skb(q)) == NULL))
		return 0;

	root_lock = qdisc_lock(q);

	/* And release qdisc */
	spin_unlock(root_lock);

	dev = qdisc_dev(q);
	txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));

	HARD_TX_LOCK(dev, txq, smp_processor_id());
	//调用dev_hard_start_xmit吧数据包通过实际的链路发送出去...
	if (!netif_tx_queue_stopped(txq) &&
	    !netif_tx_queue_frozen(txq))
		ret = dev_hard_start_xmit(skb, dev, txq);
	HARD_TX_UNLOCK(dev, txq);

	spin_lock(root_lock);

	switch (ret) {
	case NETDEV_TX_OK:
		/* Driver sent out skb successfully */
		ret = qdisc_qlen(q);
		break;

	case NETDEV_TX_LOCKED:
		/* Driver try lock failed */
		ret = handle_dev_cpu_collision(skb, txq, q);
		break;

	default:
		/* Driver returned NETDEV_TX_BUSY - requeue skb */
		if (unlikely (ret != NETDEV_TX_BUSY && net_ratelimit()))
			printk(KERN_WARNING "BUG %s code %d qlen %d\n",
			       dev->name, ret, q->q.qlen);

		ret = dev_requeue_skb(skb, q);
		break;
	}

	if (ret && (netif_tx_queue_stopped(txq) ||
		    netif_tx_queue_frozen(txq)))
		ret = 0;

	return ret;
}

static int mlx5i_xmit(struct net_device *dev, struct sk_buff *skb,
		      struct ib_ah *address, u32 dqpn)
{
	struct mlx5e_priv *epriv = mlx5i_epriv(dev);
	struct mlx5e_txqsq *sq   = epriv->txq2sq[skb_get_queue_mapping(skb)];
	struct mlx5_ib_ah *mah   = to_mah(address);
	struct mlx5i_priv *ipriv = epriv->ppriv;

	return mlx5i_sq_xmit(sq, skb, &mah->av, dqpn, ipriv->qkey);
}

/* Take mac80211 Q id from the skb and translate it to hardware Q id */
static u8 skb2q(struct sk_buff *skb)
{
	int qid = skb_get_queue_mapping(skb);

	if (WARN_ON(qid >= MT_TXQ_PSD)) {
		qid = MT_TXQ_BE;
		skb_set_queue_mapping(skb, qid);
	}

	return q2hwq(qid);
}

u16 generic_ndo_select_queue(struct ifnet *ifp, struct mbuf *m
#if NETMAP_LINUX_SELECT_QUEUE >= 3
                                , void *accel_priv
#if NETMAP_LINUX_SELECT_QUEUE >= 4
				, select_queue_fallback_t fallback
#endif /* >= 4 */
#endif /* >= 3 */
		)
{
    return skb_get_queue_mapping(m); // actually 0 on 2.6.23 and before
}

/* This variant of try_bulk_dequeue_skb() makes sure
 * all skbs in the chain are for the same txq
 */
static void try_bulk_dequeue_skb_slow(struct Qdisc *q,
				      struct sk_buff *skb,
				      int *packets)
{
	int mapping = skb_get_queue_mapping(skb);
	struct sk_buff *nskb;
	int cnt = 0;

	do {
		nskb = q->dequeue(q);
		if (!nskb)
			break;
		if (unlikely(skb_get_queue_mapping(nskb) != mapping)) {
			qdisc_enqueue_skb_bad_txq(q, nskb);
			break;
		}
		skb->next = nskb;
		skb = nskb;
	} while (++cnt < 8);
	(*packets) += cnt;
	skb->next = NULL;
}

static int cpmac_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
	int queue, len;
	struct cpmac_desc *desc;
	struct cpmac_priv *priv = netdev_priv(dev);

	if (unlikely(atomic_read(&priv->reset_pending)))
		return NETDEV_TX_BUSY;

	if (unlikely(skb_padto(skb, ETH_ZLEN)))
		return NETDEV_TX_OK;

	len = max(skb->len, ETH_ZLEN);
	queue = skb_get_queue_mapping(skb);
#ifdef CONFIG_NETDEVICES_MULTIQUEUE
	netif_stop_subqueue(dev, queue);
#else
	netif_stop_queue(dev);
#endif

	desc = &priv->desc_ring[queue];
	if (unlikely(desc->dataflags & CPMAC_OWN)) {
		if (netif_msg_tx_err(priv) && net_ratelimit())
			printk(KERN_WARNING "%s: tx dma ring full\n",
			       dev->name);
		return NETDEV_TX_BUSY;
	}

	spin_lock(&priv->lock);
	dev->trans_start = jiffies;
	spin_unlock(&priv->lock);
	desc->dataflags = CPMAC_SOP | CPMAC_EOP | CPMAC_OWN;
	desc->skb = skb;
	desc->data_mapping = dma_map_single(&dev->dev, skb->data, len,
					    DMA_TO_DEVICE);
	desc->hw_data = (u32)desc->data_mapping;
	desc->datalen = len;
	desc->buflen = len;
	if (unlikely(netif_msg_tx_queued(priv)))
		printk(KERN_DEBUG "%s: sending 0x%p, len=%d\n", dev->name, skb,
		       skb->len);
	if (unlikely(netif_msg_hw(priv)))
		cpmac_dump_desc(dev, desc);
	if (unlikely(netif_msg_pktdata(priv)))
		cpmac_dump_skb(dev, skb);
	cpmac_write(priv->regs, CPMAC_TX_PTR(queue), (u32)desc->mapping);

	return NETDEV_TX_OK;
}

/* Initiate a packet transmission.  We use one channel per CPU
 * (sharing when we have more CPUs than channels).  On Falcon, the TX
 * completion events will be directed back to the CPU that transmitted
 * the packet, which should be cache-efficient.
 *
 * Context: non-blocking.
 * Note that returning anything other than NETDEV_TX_OK will cause the
 * OS to free the skb.
 */
netdev_tx_t efx_hard_start_xmit(struct sk_buff *skb,
				      struct net_device *net_dev)
{
	struct efx_nic *efx = netdev_priv(net_dev);
	struct efx_tx_queue *tx_queue;

	if (unlikely(efx->port_inhibited))
		return NETDEV_TX_BUSY;

	tx_queue = efx_get_tx_queue(efx, skb_get_queue_mapping(skb),
				    skb->ip_summed == CHECKSUM_PARTIAL ?
				    EFX_TXQ_TYPE_OFFLOAD : 0);

	return efx_enqueue_skb(tx_queue, skb);
}

void rtw_os_pkt_complete23a(struct rtw_adapter *padapter, struct sk_buff *pkt)
{
	struct xmit_priv *pxmitpriv = &padapter->xmitpriv;
	u16	queue;

	queue = skb_get_queue_mapping(pkt);
	if (padapter->registrypriv.wifi_spec) {
		if (__netif_subqueue_stopped(padapter->pnetdev, queue) &&
		    (pxmitpriv->hwxmits[queue].accnt < WMM_XMIT_THRESHOLD))
			netif_wake_subqueue(padapter->pnetdev, queue);
	} else {
		if (__netif_subqueue_stopped(padapter->pnetdev, queue))
			netif_wake_subqueue(padapter->pnetdev, queue);
	}
	dev_kfree_skb_any(pkt);
}

static void rtw_check_xmit_resource(struct adapter *padapter, struct sk_buff *pkt)
{
	struct xmit_priv *pxmitpriv = &padapter->xmitpriv;
	u16	queue;

	queue = skb_get_queue_mapping(pkt);
	if (padapter->registrypriv.wifi_spec) {
		/* No free space for Tx, tx_worker is too slow */
		if (pxmitpriv->hwxmits[queue].accnt > WMM_XMIT_THRESHOLD)
			netif_stop_subqueue(padapter->pnetdev, queue);
	} else {
		if (pxmitpriv->free_xmitframe_cnt <= 4) {
			if (!netif_tx_queue_stopped(netdev_get_tx_queue(padapter->pnetdev, queue)))
				netif_stop_subqueue(padapter->pnetdev, queue);
		}
	}
}