Mysterious network interface

Any types of Linux network interface drivers will initialise an instance of net_device data structure. Here is a very concise summary of what is happening between NIC hardware and before IP Protocol stack is invoked.

Packet reception:

DMA packet memory copy is completed -> NIC hardware interrupt ISR is invoked -> Receive interrupt detected -> gather the buffer containing raw packet into a socket buffer (avoid coping: we can set up socket buffer to point directly at DMA space.) -> place packet onto queue (by protocol input function) -> Queuing layer kicks in -> softIRQ threads to process the scheduled interface

Packet transmission:

(Based on registered queuing discipline and scheduler) Queuing layer (dev_queue_xmit) invokes Hard_start_xmit -> Hard_start_xmit checks hardware buffer -> Hard_start_xmit puts socket buffer in driver's local queue and enable the Transmit Interrupt

Status notifier chain: This is really just a linkedlist of functions to be called on event for notification, nice and simple (to my like). Registering is actually appending callback function point to the list in this case. netdev_chain is the implementation for NIC.

As a bonus for whoever is reading this, the following are comments for in the include/linux/netdevice.h

/*

 * The DEVICE structure.

 * Actually, this whole structure is a big mistake.  It mixes I/O

 * data with strictly "high-level" data, and it has to know about

 * almost every data structure used in the INET module.

 *

 * FIXME: cleanup struct net_device such that network protocol info

 * moves out.

 */

struct net_device {...}