网络设备接收到报文后将其传入上层：

/* * Receive a packet: retrieve, encapsulate and pass over to upper levels */ void snull_rx(struct net_device *dev, int len, unsigned char *buf) { 　struct sk_buff *skb; 　struct snull_priv *priv = (struct snull_priv *) dev->priv; 　/* 　* The packet has been retrieved from the transmission 　* medium. Build an skb around it, so upper layers can handle it 　*/ 　skb = dev_alloc_skb(len+2); 　if (!skb) { 　　printk("snull rx: low on mem - packet dropped\n"); 　　priv->stats.rx_dropped++; 　　return; 　} 　skb_reserve(skb, 2); /* align IP on 16B boundary */ 　memcpy(skb_put(skb, len), buf, len); 　/* Write metadata, and then pass to the receive level */ 　skb->dev = dev; 　skb->protocol = eth_type_trans(skb, dev); 　skb->ip_summed = CHECKSUM_UNNECESSARY; /* don't check it */ 　priv->stats.rx_packets++; 　#ifndef LINUX_20 　　priv->stats.rx_bytes += len; 　#endif 　netif_rx(skb); 　return; }

　　在中断到来时接收报文信息：

void snull_interrupt(int irq, void *dev_id, struct pt_regs *regs) { 　int statusword; 　struct snull_priv *priv; 　/* 　* As usual, check the "device" pointer for shared handlers. 　* Then assign "struct device *dev" 　*/ 　struct net_device *dev = (struct net_device *)dev_id; 　/* ... and check with hw if it's really ours */ 　if (!dev /*paranoid*/ ) return; 　/* Lock the device */ 　priv = (struct snull_priv *) dev->priv; 　spin_lock(&priv->lock); 　/* retrieve statusword: real netdevices use I/O instructions */ 　statusword = priv->status; 　if (statusword & SNULL_RX_INTR) { 　　/* send it to snull_rx for handling */ 　　snull_rx(dev, priv->rx_packetlen, priv->rx_packetdata); 　}

if (statusword & SNULL_TX_INTR) { 　　/* a transmission is over: free the skb */ 　　priv->stats.tx_packets++; 　　priv->stats.tx_bytes += priv->tx_packetlen; 　　dev_kfree_skb(priv->skb); 　} 　/* Unlock the device and we are done */ 　spin_unlock(&priv->lock); 　return; }

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