35
How the kernel interacts with a qdisc

enqueue is called from dev_queue_xmit() 
in net/core/dev.c:

/* Grab device queue */
spin_lock_bh(&dev->queue_lock);  
q = dev->qdisc;
if (q->enqueue) {
  int ret = q->enqueue(skb, q);
  qdisc_run(dev);
  spin_unlock_bh(&dev->queue_lock);
  return ret == NET_XMIT_BYPASS ? 
    NET_XMIT_SUCCESS : ret;
}