drivers/net/loopback.c

/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		Pseudo-driver for the loopback interface.
 *
 * Version:	@(#)loopback.c	1.0.4b	08/16/93
 *
 * Authors:	Ross Biro, <bir7@leland.Stanford.Edu>
 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *		Donald Becker, <becker@scyld.com>
 *
 *		Alan Cox	:	Fixed oddments for NET3.014
 *		Alan Cox	:	Rejig for NET3.029 snap #3
 *		Alan Cox	: 	Fixed NET3.029 bugs and sped up
 *		Larry McVoy	:	Tiny tweak to double performance
 *		Alan Cox	:	Backed out LMV's tweak - the linux mm
 *					can't take it...
 *              Michael Griffith:       Don't bother computing the checksums
 *                                      on packets received on the loopback
 *                                      interface.
 *		Alexey Kuznetsov:	Potential hang under some extreme
 *					cases removed.
 *
 *		This program is free software; you can redistribute it and/or
 *		modify it under the terms of the GNU General Public License
 *		as published by the Free Software Foundation; either version
 *		2 of the License, or (at your option) any later version.
 */
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/socket.h>
#include <linux/errno.h>
#include <linux/fcntl.h>
#include <linux/in.h>
#include <linux/init.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/io.h>

#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <linux/if_ether.h>	/* For the statistics structure. */
#include <linux/if_arp.h>	/* For ARPHRD_ETHER */

#define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)

/*
 * The higher levels take care of making this non-reentrant (it's
 * called with bh's disabled).
 */
static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct net_device_stats *stats = (struct net_device_stats *)dev->priv;

	/*
	 *	Optimise so buffers with skb->free=1 are not copied but
	 *	instead are lobbed from tx queue to rx queue 
	 */

	if(atomic_read(&skb->users) != 1)
	{
	  	struct sk_buff *skb2=skb;
	  	skb=skb_clone(skb, GFP_ATOMIC);		/* Clone the buffer */
	  	if(skb==NULL) {
			kfree_skb(skb2);
			return 0;
		}
	  	kfree_skb(skb2);
	}
	else
		skb_orphan(skb);

	skb->protocol=eth_type_trans(skb,dev);
	skb->dev=dev;
#ifndef LOOPBACK_MUST_CHECKSUM
	skb->ip_summed = CHECKSUM_UNNECESSARY;
#endif

	dev->last_rx = jiffies;
	stats->rx_bytes+=skb->len;
	stats->tx_bytes+=skb->len;
	stats->rx_packets++;
	stats->tx_packets++;

	netif_rx(skb);

	return(0);
}

static struct net_device_stats *get_stats(struct net_device *dev)
{
	return (struct net_device_stats *)dev->priv;
}

/* Initialize the rest of the LOOPBACK device. */
int __init loopback_init(struct net_device *dev)
{
	dev->mtu		= (16 * 1024) + 20 + 20 + 12;
	dev->hard_start_xmit	= loopback_xmit;
	dev->hard_header	= eth_header;
	dev->hard_header_cache	= eth_header_cache;
	dev->header_cache_update= eth_header_cache_update;
	dev->hard_header_len	= ETH_HLEN;		/* 14			*/
	dev->addr_len		= ETH_ALEN;		/* 6			*/
	dev->tx_queue_len	= 0;
	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001		*/
	dev->rebuild_header	= eth_rebuild_header;
	dev->flags		= IFF_LOOPBACK;
	dev->features		= NETIF_F_SG|NETIF_F_FRAGLIST|NETIF_F_NO_CSUM|NETIF_F_HIGHDMA;
	dev->priv = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
	if (dev->priv == NULL)
			return -ENOMEM;
	memset(dev->priv, 0, sizeof(struct net_device_stats));
	dev->get_stats = get_stats;

	/*
	 *	Fill in the generic fields of the device structure. 
	 */
   
	return(0);
};