Linux network kernel does not allow virtual device is busy!!

http://lxr.linux.no/linux+v2.6.26.6/net/core/dev.c#L1733

                                rc = 0;

                                if (!dev_hard_start_xmit(skb, dev)) {

                                        HARD_TX_UNLOCK(dev); 

                                        goto out; 

                                } 

                        } 

                        HARD_TX_UNLOCK(dev); 

                        if (net_ratelimit()) 

                                printk(KERN_CRIT "Virtual device %s asks to " 

                                       "queue packet!\n", dev->name);

if dev_hard_start_xmit failed, it does not report the reason to upper layer.

Look, rc is zero (which means TX_OK),

How about 

rc = dev_hard_start_xmit(), to report that the virtual device is going crazy ?