snull.c

linux 驱动程序编程第3版

	}

	/* Unlock the device and we are done */
	spin_unlock(&priv->lock);
	if (pkt) snull_release_buffer(pkt); /* Do this outside the lock! */
	return;
}

/*
 * A NAPI interrupt handler.
 */
static void snull_napi_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 */

	/* paranoid */
	if (!dev)
		return;

	/* Lock the device */
	priv = netdev_priv(dev);
	spin_lock(&priv->lock);

	/* retrieve statusword: real netdevices use I/O instructions */
	statusword = priv->status;
	priv->status = 0;
	if (statusword & SNULL_RX_INTR) {
		snull_rx_ints(dev, 0);  /* Disable further interrupts */
		netif_rx_schedule(dev);
	}
	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;
}



/*
 * Transmit a packet (low level interface)
 */
static void snull_hw_tx(char *buf, int len, struct net_device *dev)
{
	/*
	 * This function deals with hw details. This interface loops
	 * back the packet to the other snull interface (if any).
	 * In other words, this function implements the snull behaviour,
	 * while all other procedures are rather device-independent
	 */
	struct iphdr *ih;
	struct net_device *dest;
	struct snull_priv *priv;
	u32 *saddr, *daddr;
	struct snull_packet *tx_buffer;
    
	/* I am paranoid. Ain't I? */
	if (len < sizeof(struct ethhdr) + sizeof(struct iphdr)) {
		printk("snull: Hmm... packet too short (%i octets)\n",
				len);
		return;
	}

	if (0) { /* enable this conditional to look at the data */
		int i;
		PDEBUG("len is %i\n" KERN_DEBUG "data:",len);
		for (i=14 ; i<len; i++)
			printk(" %02x",buf[i]&0xff);
		printk("\n");
	}
	/*
	 * Ethhdr is 14 bytes, but the kernel arranges for iphdr
	 * to be aligned (i.e., ethhdr is unaligned)
	 */
	ih = (struct iphdr *)(buf+sizeof(struct ethhdr));
	saddr = &ih->saddr;
	daddr = &ih->daddr;

	((u8 *)saddr)[2] ^= 1; /* change the third octet (class C) */
	((u8 *)daddr)[2] ^= 1;

	ih->check = 0;         /* and rebuild the checksum (ip needs it) */
	ih->check = ip_fast_csum((unsigned char *)ih,ih->ihl);

	if (dev == snull_devs[0])
		PDEBUGG("%08x:%05i --> %08x:%05i\n",
				ntohl(ih->saddr),ntohs(((struct tcphdr *)(ih+1))->source),
				ntohl(ih->daddr),ntohs(((struct tcphdr *)(ih+1))->dest));
	else
		PDEBUGG("%08x:%05i <-- %08x:%05i\n",
				ntohl(ih->daddr),ntohs(((struct tcphdr *)(ih+1))->dest),
				ntohl(ih->saddr),ntohs(((struct tcphdr *)(ih+1))->source));

	/*
	 * Ok, now the packet is ready for transmission: first simulate a
	 * receive interrupt on the twin device, then  a
	 * transmission-done on the transmitting device
	 */
	dest = snull_devs[dev == snull_devs[0] ? 1 : 0];
	priv = netdev_priv(dest);
	tx_buffer = snull_get_tx_buffer(dev);
	tx_buffer->datalen = len;
	memcpy(tx_buffer->data, buf, len);
	snull_enqueue_buf(dest, tx_buffer);
	if (priv->rx_int_enabled) {
		priv->status |= SNULL_RX_INTR;
		snull_interrupt(0, dest, NULL);
	}

	priv = netdev_priv(dev);
	priv->tx_packetlen = len;
	priv->tx_packetdata = buf;
	priv->status |= SNULL_TX_INTR;
	if (lockup && ((priv->stats.tx_packets + 1) % lockup) == 0) {
        	/* Simulate a dropped transmit interrupt */
		netif_stop_queue(dev);
		PDEBUG("Simulate lockup at %ld, txp %ld\n", jiffies,
				(unsigned long) priv->stats.tx_packets);
	}
	else
		snull_interrupt(0, dev, NULL);
}

/*
 * Transmit a packet (called by the kernel)
 */
int snull_tx(struct sk_buff *skb, struct net_device *dev)
{
	int len;
	char *data, shortpkt[ETH_ZLEN];
	struct snull_priv *priv = netdev_priv(dev);
	
	data = skb->data;
	len = skb->len;
	if (len < ETH_ZLEN) {
		memset(shortpkt, 0, ETH_ZLEN);
		memcpy(shortpkt, skb->data, skb->len);
		len = ETH_ZLEN;
		data = shortpkt;
	}
	dev->trans_start = jiffies; /* save the timestamp */

	/* Remember the skb, so we can free it at interrupt time */
	priv->skb = skb;

	/* actual deliver of data is device-specific, and not shown here */
	snull_hw_tx(data, len, dev);

	return 0; /* Our simple device can not fail */
}

/*
 * Deal with a transmit timeout.
 */
void snull_tx_timeout (struct net_device *dev)
{
	struct snull_priv *priv = netdev_priv(dev);

	PDEBUG("Transmit timeout at %ld, latency %ld\n", jiffies,
			jiffies - dev->trans_start);
        /* Simulate a transmission interrupt to get things moving */
	priv->status = SNULL_TX_INTR;
	snull_interrupt(0, dev, NULL);
	priv->stats.tx_errors++;
	netif_wake_queue(dev);
	return;
}



/*
 * Ioctl commands 
 */
int snull_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
{
	PDEBUG("ioctl\n");
	return 0;
}

/*
 * Return statistics to the caller
 */
struct net_device_stats *snull_stats(struct net_device *dev)
{
	struct snull_priv *priv = netdev_priv(dev);
	return &priv->stats;
}

/*
 * This function is called to fill up an eth header, since arp is not
 * available on the interface
 */
int snull_rebuild_header(struct sk_buff *skb)
{
	struct ethhdr *eth = (struct ethhdr *) skb->data;
	struct net_device *dev = skb->dev;
    
	memcpy(eth->h_source, dev->dev_addr, dev->addr_len);
	memcpy(eth->h_dest, dev->dev_addr, dev->addr_len);
	eth->h_dest[ETH_ALEN-1]   ^= 0x01;   /* dest is us xor 1 */
	return 0;
}


int snull_header(struct sk_buff *skb, struct net_device *dev,
                unsigned short type, void *daddr, void *saddr,
                unsigned int len)
{
	struct ethhdr *eth = (struct ethhdr *)skb_push(skb,ETH_HLEN);

	eth->h_proto = htons(type);
	memcpy(eth->h_source, saddr ? saddr : dev->dev_addr, dev->addr_len);
	memcpy(eth->h_dest,   daddr ? daddr : dev->dev_addr, dev->addr_len);
	eth->h_dest[ETH_ALEN-1]   ^= 0x01;   /* dest is us xor 1 */
	return (dev->hard_header_len);
}





/*
 * The "change_mtu" method is usually not needed.
 * If you need it, it must be like this.
 */
int snull_change_mtu(struct net_device *dev, int new_mtu)
{
	unsigned long flags;
	struct snull_priv *priv = netdev_priv(dev);
	spinlock_t *lock = &priv->lock;
    
	/* check ranges */
	if ((new_mtu < 68) || (new_mtu > 1500))
		return -EINVAL;
	/*
	 * Do anything you need, and the accept the value
	 */
	spin_lock_irqsave(lock, flags);
	dev->mtu = new_mtu;
	spin_unlock_irqrestore(lock, flags);
	return 0; /* success */
}

/*
 * The init function (sometimes called probe).
 * It is invoked by register_netdev()
 */
void snull_init(struct net_device *dev)
{
	struct snull_priv *priv;
#if 0
    	/*
	 * Make the usual checks: check_region(), probe irq, ...  -ENODEV
	 * should be returned if no device found.  No resource should be
	 * grabbed: this is done on open(). 
	 */
#endif

    	/* 
	 * Then, assign other fields in dev, using ether_setup() and some
	 * hand assignments
	 */
	ether_setup(dev); /* assign some of the fields */

	dev->open            = snull_open;
	dev->stop            = snull_release;
	dev->set_config      = snull_config;
	dev->hard_start_xmit = snull_tx;
	dev->do_ioctl        = snull_ioctl;
	dev->get_stats       = snull_stats;
	dev->change_mtu      = snull_change_mtu;  
	dev->rebuild_header  = snull_rebuild_header;
	dev->hard_header     = snull_header;
	dev->tx_timeout      = snull_tx_timeout;
	dev->watchdog_timeo = timeout;
	if (use_napi) {
		dev->poll        = snull_poll;
		dev->weight      = 2;
	}
	/* keep the default flags, just add NOARP */
	dev->flags           |= IFF_NOARP;
	dev->features        |= NETIF_F_NO_CSUM;
	dev->hard_header_cache = NULL;      /* Disable caching */

	/*
	 * Then, initialize the priv field. This encloses the statistics
	 * and a few private fields.
	 */
	priv = netdev_priv(dev);
	memset(priv, 0, sizeof(struct snull_priv));
	spin_lock_init(&priv->lock);
	snull_rx_ints(dev, 1);		/* enable receive interrupts */
	snull_setup_pool(dev);
}

/*
 * The devices
 */

struct net_device *snull_devs[2];



/*
 * Finally, the module stuff
 */

void snull_cleanup(void)
{
	int i;
    
	for (i = 0; i < 2;  i++) {
		if (snull_devs[i]) {
			unregister_netdev(snull_devs[i]);
			snull_teardown_pool(snull_devs[i]);
			free_netdev(snull_devs[i]);
		}
	}
	return;
}




int snull_init_module(void)
{
	int result, i, ret = -ENOMEM;

	snull_interrupt = use_napi ? snull_napi_interrupt : snull_regular_interrupt;

	/* Allocate the devices */
	snull_devs[0] = alloc_netdev(sizeof(struct snull_priv), "sn%d",
			snull_init);
	snull_devs[1] = alloc_netdev(sizeof(struct snull_priv), "sn%d",
			snull_init);
	if (snull_devs[0] == NULL || snull_devs[1] == NULL)
		goto out;

	ret = -ENODEV;
	for (i = 0; i < 2;  i++)
		if ((result = register_netdev(snull_devs[i])))
			printk("snull: error %i registering device \"%s\"\n",
					result, snull_devs[i]->name);
		else
			ret = 0;
   out:
	if (ret) 
		snull_cleanup();
	return ret;
}


module_init(snull_init_module);
module_exit(snull_cleanup);