text: /*
   * 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>
  
  struct pcpu_lstats {
  	u64			packets;
  	u64			bytes;
  	struct u64_stats_sync	syncp;
  };
  
  /* 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 int loopback_get_ts_info(struct net_device *netdev,
  				struct ethtool_ts_info *ts_info)
  {
  	ts_info->so_timestamping = SOF_TIMESTAMPING_TX_SOFTWARE |
  				   SOF_TIMESTAMPING_RX_SOFTWARE |
  				   SOF_TIMESTAMPING_SOFTWARE;
  
  	ts_info->phc_index = -1;
  
  	return 0;
  };
  
  static const struct ethtool_ops loopback_ethtool_ops = {
  	.get_link		= always_on,
  	.get_ts_info		= loopback_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,
  };
  