Network Devices (Slideshow)#

Module Initialization: Device Allocation #

struct net_device *alloc_netdev(
        int sizeof_priv, const char *name,
        void (*setup)(struct net_device *));

sizeof_priv: private driver data, both allocated alongside net device structure in one large chunk
```
priv = netdev_priv(dev);
```
name: can contain "%d" ⟶ kernel inserts device number
setup: setup function, see below

Helper funcion for ethernet devices:

#include <linux/etherdevice.h>

struct net_device *alloc_etherdev(int sizeof_priv);

Finally, deallocation on unload:

free_netdev(dev);

err = register_netdev(dev);
unregister_netdev(dev);

int (*open)(struct net_device *dev);

Called when activated by ifconfig. Allocates resources like interrupts, initializes devince, …
int (*stop)(struct net_device *dev);

The reverse of open()
int (*hard_start_xmit) (struct sk_buff *skb, struct net_device *dev);

Submits packet for transmission.
void (*tx_timeout)(struct net_device *dev);

Called by networking layer above when it detects that a packet hasn’t completed.
int weight;
int (*poll)(struct net_device *dev; int *quota);

Used to mitigate interrupt load on high speed networks. Interrupts are off, and polling is used in stead. NAPI (“New API”).
int (*do_ioctl)(struct net_device *dev, struct ifreq *ifr, int cmd);

Much like ioctl() in character devices.
(A lot more omitted)

void netif_start_queue(struct net_device *dev);

Usually called by open().
void netif_stop_queue(struct net_device *dev);

Stops a queue; usually called by the stop() method, or in situations where the device sees no way of handling further packets.
void netif_wake_queue(struct net_device *dev);

Called when the device has room for more packets, and had stopped the queue before.
(A lot more omitted)