loopback NIC 驱动剖析Series---(5)

static const struct net_device_ops loopback_ops = {
    .ndo_init = loopback_dev_init,
    .ndo_start_xmit= loopback_xmit,
    .ndo_get_stats = loopback_get_stats,
};

/*
 * The higher levels take care of making this non-reentrant (it's
 * called with bh's disabled).
 */
static netdev_tx_t loopback_xmit(struct sk_buff *skb,
                 struct net_device *dev)
{
    struct pcpu_lstats __percpu *pcpu_lstats;
    struct pcpu_lstats *lb_stats;
    int len;

    skb_orphan(skb);

    skb->protocol = eth_type_trans(skb, dev);

    /* it's OK to use per_cpu_ptr() because BHs are off */
    pcpu_lstats = (void __percpu __force *)dev->ml_priv;
    lb_stats = this_cpu_ptr(pcpu_lstats);

    len = skb->len;
    if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
        lb_stats->bytes += len;
        lb_stats->packets++;
    } else
        lb_stats->drops++;

    return NETDEV_TX_OK;
}