/* * 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 *		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/jiffies.h>#include <linux/module.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 <linux/ethtool.h>#include <net/sock.h>#include <net/checksum.h>#include <linux/if_ether.h>	/* For the statistics structure. */#include <linux/if_arp.h>	/* For ARPHRD_ETHER */#include <linux/ip.h>#include <linux/tcp.h>#include <linux/percpu.h>#include <net/net_namespace.h> struct pcpu_lstats {	unsigned long packets;	unsigned long bytes;}; /* * 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 pcpu_lstats *pcpu_lstats, *lb_stats; 	skb_orphan(skb); 	skb->protocol = eth_type_trans(skb,dev); #ifdef LOOPBACK_TSO	if (skb_is_gso(skb)) {		BUG_ON(skb->protocol != htons(ETH_P_IP));		BUG_ON(ip_hdr(skb)->protocol != IPPROTO_TCP); 		emulate_large_send_offload(skb);		return 0;	}#endif	dev->last_rx = jiffies; 	/* it's OK to use per_cpu_ptr() because BHs are off */	pcpu_lstats = dev->ml_priv;	lb_stats = per_cpu_ptr(pcpu_lstats, smp_processor_id());	lb_stats->bytes += skb->len;	lb_stats->packets++; 	netif_rx(skb); 	return 0;} static struct net_device_stats *get_stats(struct net_device *dev){	const struct pcpu_lstats *pcpu_lstats;	struct net_device_stats *stats = &dev->stats;	unsigned long bytes = 0;	unsigned long packets = 0;	int i; 	pcpu_lstats = dev->ml_priv;	for_each_possible_cpu(i) {		const struct pcpu_lstats *lb_stats; 		lb_stats = per_cpu_ptr(pcpu_lstats, i);		bytes   += lb_stats->bytes;		packets += lb_stats->packets;	}	stats->rx_packets = packets;	stats->tx_packets = packets;	stats->rx_bytes = bytes;	stats->tx_bytes = bytes;	return stats;} static u32 always_on(struct net_device *dev){	return 1;} static const struct ethtool_ops loopback_ethtool_ops = {	.get_link		= always_on,	.set_tso		= ethtool_op_set_tso,	.get_tx_csum		= always_on,	.get_sg			= always_on,	.get_rx_csum		= always_on,}; static int loopback_dev_init(struct net_device *dev){	struct pcpu_lstats *lstats; 	lstats = alloc_percpu(struct pcpu_lstats);	if (!lstats)		return -ENOMEM; 	dev->ml_priv = lstats;	return 0;} static void loopback_dev_free(struct net_device *dev){	struct pcpu_lstats *lstats = dev->ml_priv; 	free_percpu(lstats);	free_netdev(dev);} /* * The loopback device is special. There is only one instance * per network namespace. */static void loopback_setup(struct net_device *dev){	dev->get_stats		= &get_stats;	dev->mtu		= (16 * 1024) + 20 + 20 + 12;	dev->hard_start_xmit	= loopback_xmit;	dev->hard_header_len	= ETH_HLEN;	/* 14	*/	dev->addr_len		= ETH_ALEN;	/* 6	*/	dev->tx_queue_len	= 0;	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001*/	dev->flags		= IFF_LOOPBACK;	dev->features 		= NETIF_F_SG | NETIF_F_FRAGLIST		| NETIF_F_TSO		| NETIF_F_NO_CSUM		| NETIF_F_HIGHDMA		| NETIF_F_LLTX		| NETIF_F_NETNS_LOCAL;	dev->ethtool_ops	= &loopback_ethtool_ops;	dev->header_ops		= &eth_header_ops;	dev->init = loopback_dev_init;	dev->destructor = loopback_dev_free;} /* Setup and register the loopback device. */static __net_init int loopback_net_init(struct net *net){	struct net_device *dev;	int err; 	err = -ENOMEM;	dev = alloc_netdev(0, "lo", loopback_setup);	if (!dev)		goto out; 	dev_net_set(dev, net);	err = register_netdev(dev);	if (err)		goto out_free_netdev; 	net->loopback_dev = dev;	return 0;  out_free_netdev:	free_netdev(dev);out:	if (net == &init_net)		panic("loopback: Failed to register netdevice: %d\n", err);	return err;} static __net_exit void loopback_net_exit(struct net *net){	struct net_device *dev = net->loopback_dev; 	unregister_netdev(dev);} static struct pernet_operations __net_initdata loopback_net_ops = {       .init = loopback_net_init,       .exit = loopback_net_exit,}; static int __init loopback_init(void){	return register_pernet_device(&loopback_net_ops);} /* Loopback is special. It should be initialized before any other network * device and network subsystem. */fs_initcall(loopback_init);