虚拟网卡驱动

alloc_netdev

#define alloc_netdev(sizeof_priv, name, setup) 
	alloc_netdev_mq(sizeof_priv, name, setup, 1)

/**
 *	alloc_netdev_mq - allocate network device
 *	@sizeof_priv:	size of private data to allocate space for
 *	@name:		device name format string
 *	@setup:		callback to initialize device
 *	@queue_count:	the number of subqueues to allocate
 *
 *	Allocates a struct net_device with private data area for driver use
 *	and performs basic initialization.  Also allocates subquue structs
 *	for each queue on the device at the end of the netdevice.
 */
struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
		void (*setup)(struct net_device *), unsigned int queue_count)
{
	struct netdev_queue *tx;
	struct net_device *dev;
	size_t alloc_size;
	struct net_device *p;

	BUG_ON(strlen(name) >= sizeof(dev->name));

	alloc_size = sizeof(struct net_device);
	if (sizeof_priv) {
		/* ensure 32-byte alignment of private area */
		alloc_size = ALIGN(alloc_size, NETDEV_ALIGN);
		alloc_size += sizeof_priv;
	}
	/* ensure 32-byte alignment of whole construct */
	alloc_size += NETDEV_ALIGN - 1;

	p = kzalloc(alloc_size, GFP_KERNEL);
	if (!p) {
		printk(KERN_ERR "alloc_netdev: Unable to allocate device.
");
		return NULL;
	}

	tx = kcalloc(queue_count, sizeof(struct netdev_queue), GFP_KERNEL);
	if (!tx) {
		printk(KERN_ERR "alloc_netdev: Unable to allocate "
		       "tx qdiscs.
");
		goto free_p;
	}

	dev = PTR_ALIGN(p, NETDEV_ALIGN);
	dev->padded = (char *)dev - (char *)p;

	if (dev_addr_init(dev))
		goto free_tx;

	dev_unicast_init(dev);

	dev_net_set(dev, &init_net);

	dev->_tx = tx;
	dev->num_tx_queues = queue_count;
	dev->real_num_tx_queues = queue_count;

	dev->gso_max_size = GSO_MAX_SIZE;

	netdev_init_queues(dev);

	INIT_LIST_HEAD(&dev->napi_list);
	dev->priv_flags = IFF_XMIT_DST_RELEASE;
	setup(dev);
	strcpy(dev->name, name);
	return dev;

free_tx:
	kfree(tx);

free_p:
	kfree(p);
	return NULL;
}
EXPORT_SYMBOL(alloc_netdev_mq);

sizeof_priv：私有数据大小
name：设备名
setup：net_device部分成员初始化

alloc_etherdev

#define alloc_etherdev(sizeof_priv) alloc_etherdev_mq(sizeof_priv, 1)

struct net_device *alloc_etherdev_mq(int sizeof_priv, unsigned int queue_count)
{
	return alloc_netdev_mq(sizeof_priv, "eth%d", ether_setup, queue_count);
}

alloc_etherdev相比alloc_netdev更常用

网络接口的打开与关闭

static inline void netif_start_queue(struct net_device *dev)
static inline void netif_stop_queue(struct net_device *dev)

netdev_priv

#define netdev_priv(dev) (dev->priv)

存取私有数据指针

dev_hold
设备的引用计数器加1

dev_put
设备的引用计数器减1

dev_get_by_name
取得设备指针
记得dev_put取消设备引用

/**
 *	dev_get_by_name		- find a device by its name
 *	@net: the applicable net namespace
 *	@name: name to find
 *
 *	Find an interface by name. This can be called from any
 *	context and does its own locking. The returned handle has
 *	the usage count incremented and the caller must use dev_put() to
 *	release it when it is no longer needed. %NULL is returned if no
 *	matching device is found.
 */

struct net_device *dev_get_by_name(struct net *net, const char *name)
{
	struct net_device *dev;

	read_lock(&dev_base_lock);
	dev = __dev_get_by_name(net, name);
	if (dev)
		dev_hold(dev);
	read_unlock(&dev_base_lock);
	return dev;
}

举例

#include <linux/init.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/ethtool.h>

static struct net_device *dev = NULL;

static int net_open(struct net_device *dev)
{
	netif_start_queue(dev);
	
	return 0;
}

static int net_start_xmit(struct sk_buf *skb, struct net_device *dev)
{
	netif_start_queue(dev);

	dev->stats.tx_packets++;
	dev->stats.tx_bytes += skb->len;
	
	/* this is normally done in the interrupt when tx finishes */
//	netif_wake_queue(dev);	

	netif_stop_queue(dev);
	
	return 0;
}

static int net_close(struct net_device *dev)
{
	netif_stop_queue(dev);
	
	return 0;
}

static int __init net_init(void)
{
	dev = alloc_etherdev(0);
	
	dev->open = net_open;
	dev->hard_start_xmit = &net_start_xmit;
	dev->stop = net_close;
	dev->tx_timeout = net_tx_timeout;
	
	ether_setup(dev);
	
	//注册网卡设备
	register_netdev(dev);
	
	return 0;
}

//出口函数
static void __exit net_exit(void)
{
	unregister_netdev(dev);
	free_netdev(dev);
	
	return;
}

module_init(net_init);
module_exit(net_exit);

启动网卡

# ifconfig "eth%d" 192.168.1.1 up