// SPDX-License-Identifier: GPL-2.0-or-later

  /*
   * 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.

   */
  #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>

  /* blackhole_netdev - a device used for dsts that are marked expired!
   * This is global device (instead of per-net-ns) since it's not needed
   * to be per-ns and gets initialized at boot time.
   */
  struct net_device *blackhole_netdev;
  EXPORT_SYMBOL(blackhole_netdev);

  /* 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,

  };

  static void gen_lo_setup(struct net_device *dev,
  			 unsigned int mtu,
  			 const struct ethtool_ops *eth_ops,
  			 const struct header_ops *hdr_ops,
  			 const struct net_device_ops *dev_ops,
  			 void (*dev_destructor)(struct net_device *dev))

  {

  	dev->mtu		= mtu;

  	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	= eth_ops;
  	dev->header_ops		= hdr_ops;
  	dev->netdev_ops		= dev_ops;

  	dev->needs_free_netdev	= true;

  	dev->priv_destructor	= dev_destructor;
  }
  
  /* The loopback device is special. There is only one instance
   * per network namespace.
   */
  static void loopback_setup(struct net_device *dev)
  {
  	gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, &eth_header_ops,
  		     &loopback_ops, 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
  ", err);
  	return err;

  }

  /* Registered in net/core/dev.c */
  struct pernet_operations __net_initdata loopback_net_ops = {

  	.init = loopback_net_init,

  };

  
  /* blackhole netdevice */
  static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
  					 struct net_device *dev)
  {
  	kfree_skb(skb);
  	net_warn_ratelimited("%s(): Dropping skb.
  ", __func__);
  	return NETDEV_TX_OK;
  }
  
  static const struct net_device_ops blackhole_netdev_ops = {
  	.ndo_start_xmit = blackhole_netdev_xmit,
  };
  
  /* This is a dst-dummy device used specifically for invalidated
   * DSTs and unlike loopback, this is not per-ns.
   */
  static void blackhole_netdev_setup(struct net_device *dev)
  {
  	gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
  }
  
  /* Setup and register the blackhole_netdev. */
  static int __init blackhole_netdev_init(void)
  {
  	blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
  					blackhole_netdev_setup);
  	if (!blackhole_netdev)
  		return -ENOMEM;

  	rtnl_lock();

  	dev_init_scheduler(blackhole_netdev);
  	dev_activate(blackhole_netdev);

  	rtnl_unlock();

  
  	blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
  	dev_net_set(blackhole_netdev, &init_net);
  
  	return 0;
  }
  
  device_initcall(blackhole_netdev_init);