/* * 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/uaccess.h>#include <linux/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 <linux/net_tstamp.h>#include <net/net_namespace.h>#include <linux/u64_stats_sync.h> /* The higher levels take care of making this non-reentrant (it's * called with bh's disabled). */static netdev_tx_t loopback_xmit(struct sk_buff *skb,				 struct net_device *dev){	struct pcpu_lstats *lb_stats;	int len; 	skb_tx_timestamp(skb); 	/* do not fool net_timestamp_check() with various clock bases */	skb->tstamp = 0; 	skb_orphan(skb); 	/* Before queueing this packet to netif_rx(),	 * make sure dst is refcounted.	 */	skb_dst_force(skb); 	skb->protocol = eth_type_trans(skb, dev); 	/* it's OK to use per_cpu_ptr() because BHs are off */	lb_stats = this_cpu_ptr(dev->lstats); 	len = skb->len;	if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {		u64_stats_update_begin(&lb_stats->syncp);		lb_stats->bytes += len;		lb_stats->packets++;		u64_stats_update_end(&lb_stats->syncp);	} 	return NETDEV_TX_OK;} static void loopback_get_stats64(struct net_device *dev,				 struct rtnl_link_stats64 *stats){	u64 bytes = 0;	u64 packets = 0;	int i; 	for_each_possible_cpu(i) {		const struct pcpu_lstats *lb_stats;		u64 tbytes, tpackets;		unsigned int start; 		lb_stats = per_cpu_ptr(dev->lstats, i);		do {			start = u64_stats_fetch_begin_irq(&lb_stats->syncp);			tbytes = lb_stats->bytes;			tpackets = lb_stats->packets;		} while (u64_stats_fetch_retry_irq(&lb_stats->syncp, start));		bytes   += tbytes;		packets += tpackets;	}	stats->rx_packets = packets;	stats->tx_packets = packets;	stats->rx_bytes   = bytes;	stats->tx_bytes   = bytes;} static u32 always_on(struct net_device *dev){	return 1;} static const struct ethtool_ops loopback_ethtool_ops = {	.get_link		= always_on,	.get_ts_info		= ethtool_op_get_ts_info,}; static int loopback_dev_init(struct net_device *dev){	dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);	if (!dev->lstats)		return -ENOMEM;	return 0;} static void loopback_dev_free(struct net_device *dev){	dev_net(dev)->loopback_dev = NULL;	free_percpu(dev->lstats);} static const struct net_device_ops loopback_ops = {	.ndo_init        = loopback_dev_init,	.ndo_start_xmit  = loopback_xmit,	.ndo_get_stats64 = loopback_get_stats64,	.ndo_set_mac_address = eth_mac_addr,}; /* The loopback device is special. There is only one instance * per network namespace. */static void loopback_setup(struct net_device *dev){	dev->mtu		= 64 * 1024;	dev->hard_header_len	= ETH_HLEN;	/* 14	*/	dev->min_header_len	= ETH_HLEN;	/* 14	*/	dev->addr_len		= ETH_ALEN;	/* 6	*/	dev->type		= ARPHRD_LOOPBACK;	/* 0x0001*/	dev->flags		= IFF_LOOPBACK;	dev->priv_flags		|= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;	netif_keep_dst(dev);	dev->hw_features	= NETIF_F_GSO_SOFTWARE;	dev->features		= NETIF_F_SG | NETIF_F_FRAGLIST		| NETIF_F_GSO_SOFTWARE		| NETIF_F_HW_CSUM		| NETIF_F_RXCSUM		| NETIF_F_SCTP_CRC		| NETIF_F_HIGHDMA		| NETIF_F_LLTX		| NETIF_F_NETNS_LOCAL		| NETIF_F_VLAN_CHALLENGED		| NETIF_F_LOOPBACK;	dev->ethtool_ops	= &loopback_ethtool_ops;	dev->header_ops		= &eth_header_ops;	dev->netdev_ops		= &loopback_ops;	dev->needs_free_netdev	= true;	dev->priv_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", NET_NAME_UNKNOWN, loopback_setup);	if (!dev)		goto out; 	dev_net_set(dev, net);	err = register_netdev(dev);	if (err)		goto out_free_netdev; 	BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);	net->loopback_dev = dev;	return 0; out_free_netdev:	free_netdev(dev);out:	if (net_eq(net, &init_net))		panic("loopback: Failed to register netdevice: %d\n", err);	return err;} /* Registered in net/core/dev.c */struct pernet_operations __net_initdata loopback_net_ops = {	.init = loopback_net_init,};