/* linux/net/ipv4/arp.c

   *

   * Copyright (C) 1994 by Florian  La Roche
   *
   * This module implements the Address Resolution Protocol ARP (RFC 826),
   * which is used to convert IP addresses (or in the future maybe other
   * high-level addresses) into a low-level hardware address (like an Ethernet
   * address).
   *
   * 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.
   *
   * Fixes:

   *		Alan Cox	:	Removed the Ethernet assumptions in

   *					Florian's code

   *		Alan Cox	:	Fixed some small errors in the ARP

   *					logic
   *		Alan Cox	:	Allow >4K in /proc
   *		Alan Cox	:	Make ARP add its own protocol entry
   *		Ross Martin     :       Rewrote arp_rcv() and arp_get_info()
   *		Stephen Henson	:	Add AX25 support to arp_get_info()
   *		Alan Cox	:	Drop data when a device is downed.
   *		Alan Cox	:	Use init_timer().
   *		Alan Cox	:	Double lock fixes.
   *		Martin Seine	:	Move the arphdr structure
   *					to if_arp.h for compatibility.
   *					with BSD based programs.
   *		Andrew Tridgell :       Added ARP netmask code and
   *					re-arranged proxy handling.
   *		Alan Cox	:	Changed to use notifiers.
   *		Niibe Yutaka	:	Reply for this device or proxies only.
   *		Alan Cox	:	Don't proxy across hardware types!
   *		Jonathan Naylor :	Added support for NET/ROM.
   *		Mike Shaver     :       RFC1122 checks.
   *		Jonathan Naylor :	Only lookup the hardware address for
   *					the correct hardware type.
   *		Germano Caronni	:	Assorted subtle races.

   *		Craig Schlenter :	Don't modify permanent entry

   *					during arp_rcv.
   *		Russ Nelson	:	Tidied up a few bits.
   *		Alexey Kuznetsov:	Major changes to caching and behaviour,

   *					eg intelligent arp probing and

   *					generation
   *					of host down events.
   *		Alan Cox	:	Missing unlock in device events.
   *		Eckes		:	ARP ioctl control errors.
   *		Alexey Kuznetsov:	Arp free fix.
   *		Manuel Rodriguez:	Gratuitous ARP.

   *              Jonathan Layes  :       Added arpd support through kerneld

   *                                      message queue (960314)
   *		Mike Shaver	:	/proc/sys/net/ipv4/arp_* support
   *		Mike McLagan    :	Routing by source
   *		Stuart Cheshire	:	Metricom and grat arp fixes
   *					*** FOR 2.1 clean this up ***
   *		Lawrence V. Stefani: (08/12/96) Added FDDI support.

   *		Alan Cox	:	Took the AP1000 nasty FDDI hack and

   *					folded into the mainstream FDDI code.
   *					Ack spit, Linus how did you allow that
   *					one in...
   *		Jes Sorensen	:	Make FDDI work again in 2.1.x and
   *					clean up the APFDDI & gen. FDDI bits.
   *		Alexey Kuznetsov:	new arp state machine;
   *					now it is in net/core/neighbour.c.
   *		Krzysztof Halasa:	Added Frame Relay ARP support.
   *		Arnaldo C. Melo :	convert /proc/net/arp to seq_file
   *		Shmulik Hen:		Split arp_send to arp_create and
   *					arp_xmit so intermediate drivers like
   *					bonding can change the skb before
   *					sending (e.g. insert 8021q tag).
   *		Harald Welte	:	convert to make use of jenkins hash

   *		Jesper D. Brouer:       Proxy ARP PVLAN RFC 3069 support.

   */

  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

  #include <linux/module.h>
  #include <linux/types.h>
  #include <linux/string.h>
  #include <linux/kernel.h>

  #include <linux/capability.h>

  #include <linux/socket.h>
  #include <linux/sockios.h>
  #include <linux/errno.h>
  #include <linux/in.h>
  #include <linux/mm.h>
  #include <linux/inet.h>

  #include <linux/inetdevice.h>

  #include <linux/netdevice.h>
  #include <linux/etherdevice.h>
  #include <linux/fddidevice.h>
  #include <linux/if_arp.h>

  #include <linux/skbuff.h>
  #include <linux/proc_fs.h>
  #include <linux/seq_file.h>
  #include <linux/stat.h>
  #include <linux/init.h>
  #include <linux/net.h>
  #include <linux/rcupdate.h>

  #include <linux/slab.h>

  #ifdef CONFIG_SYSCTL
  #include <linux/sysctl.h>
  #endif

  #include <net/net_namespace.h>

  #include <net/ip.h>
  #include <net/icmp.h>
  #include <net/route.h>
  #include <net/protocol.h>
  #include <net/tcp.h>
  #include <net/sock.h>
  #include <net/arp.h>

  #include <net/ax25.h>

  #include <net/netrom.h>

  #include <net/dst_metadata.h>
  #include <net/ip_tunnels.h>

  #include <linux/uaccess.h>

  
  #include <linux/netfilter_arp.h>
  
  /*
   *	Interface to generic neighbour cache.
   */

  static u32 arp_hash(const void *pkey, const struct net_device *dev, __u32 *hash_rnd);

  static bool arp_key_eq(const struct neighbour *n, const void *pkey);

  static int arp_constructor(struct neighbour *neigh);
  static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb);
  static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb);
  static void parp_redo(struct sk_buff *skb);

  static const struct neigh_ops arp_generic_ops = {

  	.family =		AF_INET,
  	.solicit =		arp_solicit,
  	.error_report =		arp_error_report,
  	.output =		neigh_resolve_output,
  	.connected_output =	neigh_connected_output,

  };

  static const struct neigh_ops arp_hh_ops = {

  	.family =		AF_INET,
  	.solicit =		arp_solicit,
  	.error_report =		arp_error_report,
  	.output =		neigh_resolve_output,
  	.connected_output =	neigh_resolve_output,

  };

  static const struct neigh_ops arp_direct_ops = {

  	.family =		AF_INET,

  	.output =		neigh_direct_output,
  	.connected_output =	neigh_direct_output,

  };

  struct neigh_table arp_tbl = {

  	.family		= AF_INET,

  	.key_len	= 4,

  	.protocol	= cpu_to_be16(ETH_P_IP),

  	.hash		= arp_hash,

  	.key_eq		= arp_key_eq,

  	.constructor	= arp_constructor,
  	.proxy_redo	= parp_redo,
  	.id		= "arp_cache",
  	.parms		= {
  		.tbl			= &arp_tbl,

  		.reachable_time		= 30 * HZ,

  		.data	= {
  			[NEIGH_VAR_MCAST_PROBES] = 3,
  			[NEIGH_VAR_UCAST_PROBES] = 3,
  			[NEIGH_VAR_RETRANS_TIME] = 1 * HZ,
  			[NEIGH_VAR_BASE_REACHABLE_TIME] = 30 * HZ,
  			[NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,
  			[NEIGH_VAR_GC_STALETIME] = 60 * HZ,

  			[NEIGH_VAR_QUEUE_LEN_BYTES] = SK_WMEM_MAX,

  			[NEIGH_VAR_PROXY_QLEN] = 64,
  			[NEIGH_VAR_ANYCAST_DELAY] = 1 * HZ,
  			[NEIGH_VAR_PROXY_DELAY]	= (8 * HZ) / 10,
  			[NEIGH_VAR_LOCKTIME] = 1 * HZ,
  		},

  	},

  	.gc_interval	= 30 * HZ,
  	.gc_thresh1	= 128,
  	.gc_thresh2	= 512,
  	.gc_thresh3	= 1024,

  };

  EXPORT_SYMBOL(arp_tbl);

  int arp_mc_map(__be32 addr, u8 *haddr, struct net_device *dev, int dir)

  {
  	switch (dev->type) {
  	case ARPHRD_ETHER:
  	case ARPHRD_FDDI:
  	case ARPHRD_IEEE802:
  		ip_eth_mc_map(addr, haddr);

  		return 0;

  	case ARPHRD_INFINIBAND:

  		ip_ib_mc_map(addr, dev->broadcast, haddr);

  		return 0;

  	case ARPHRD_IPGRE:
  		ip_ipgre_mc_map(addr, dev->broadcast, haddr);
  		return 0;

  	default:
  		if (dir) {
  			memcpy(haddr, dev->broadcast, dev->addr_len);
  			return 0;
  		}
  	}
  	return -EINVAL;
  }

  static u32 arp_hash(const void *pkey,
  		    const struct net_device *dev,

  		    __u32 *hash_rnd)

  {

  	return arp_hashfn(pkey, dev, hash_rnd);
  }
  
  static bool arp_key_eq(const struct neighbour *neigh, const void *pkey)
  {
  	return neigh_key_eq32(neigh, pkey);

  }
  
  static int arp_constructor(struct neighbour *neigh)
  {

  	__be32 addr;

  	struct net_device *dev = neigh->dev;
  	struct in_device *in_dev;
  	struct neigh_parms *parms;

  	u32 inaddr_any = INADDR_ANY;

  	if (dev->flags & (IFF_LOOPBACK | IFF_POINTOPOINT))
  		memcpy(neigh->primary_key, &inaddr_any, arp_tbl.key_len);
  
  	addr = *(__be32 *)neigh->primary_key;

  	rcu_read_lock();

  	in_dev = __in_dev_get_rcu(dev);

  	if (!in_dev) {

  		rcu_read_unlock();
  		return -EINVAL;
  	}

  	neigh->type = inet_addr_type_dev_table(dev_net(dev), dev, addr);

  	parms = in_dev->arp_parms;
  	__neigh_parms_put(neigh->parms);
  	neigh->parms = neigh_parms_clone(parms);
  	rcu_read_unlock();

  	if (!dev->header_ops) {

  		neigh->nud_state = NUD_NOARP;
  		neigh->ops = &arp_direct_ops;

  		neigh->output = neigh_direct_output;

  	} else {
  		/* Good devices (checked by reading texts, but only Ethernet is
  		   tested)
  
  		   ARPHRD_ETHER: (ethernet, apfddi)
  		   ARPHRD_FDDI: (fddi)
  		   ARPHRD_IEEE802: (tr)
  		   ARPHRD_METRICOM: (strip)
  		   ARPHRD_ARCNET:
  		   etc. etc. etc.
  
  		   ARPHRD_IPDDP will also work, if author repairs it.
  		   I did not it, because this driver does not work even
  		   in old paradigm.
  		 */

  		if (neigh->type == RTN_MULTICAST) {
  			neigh->nud_state = NUD_NOARP;
  			arp_mc_map(addr, neigh->ha, dev, 1);

  		} else if (dev->flags & (IFF_NOARP | IFF_LOOPBACK)) {

  			neigh->nud_state = NUD_NOARP;
  			memcpy(neigh->ha, dev->dev_addr, dev->addr_len);

  		} else if (neigh->type == RTN_BROADCAST ||
  			   (dev->flags & IFF_POINTOPOINT)) {

  			neigh->nud_state = NUD_NOARP;
  			memcpy(neigh->ha, dev->broadcast, dev->addr_len);
  		}

  
  		if (dev->header_ops->cache)

  			neigh->ops = &arp_hh_ops;
  		else
  			neigh->ops = &arp_generic_ops;

  		if (neigh->nud_state & NUD_VALID)

  			neigh->output = neigh->ops->connected_output;
  		else
  			neigh->output = neigh->ops->output;
  	}
  	return 0;
  }
  
  static void arp_error_report(struct neighbour *neigh, struct sk_buff *skb)
  {
  	dst_link_failure(skb);
  	kfree_skb(skb);
  }

  /* Create and send an arp packet. */
  static void arp_send_dst(int type, int ptype, __be32 dest_ip,
  			 struct net_device *dev, __be32 src_ip,
  			 const unsigned char *dest_hw,
  			 const unsigned char *src_hw,

  			 const unsigned char *target_hw,
  			 struct dst_entry *dst)

  {
  	struct sk_buff *skb;
  
  	/* arp on this interface. */
  	if (dev->flags & IFF_NOARP)
  		return;
  
  	skb = arp_create(type, ptype, dest_ip, dev, src_ip,
  			 dest_hw, src_hw, target_hw);
  	if (!skb)
  		return;

  	skb_dst_set(skb, dst_clone(dst));

  	arp_xmit(skb);
  }
  
  void arp_send(int type, int ptype, __be32 dest_ip,
  	      struct net_device *dev, __be32 src_ip,
  	      const unsigned char *dest_hw, const unsigned char *src_hw,
  	      const unsigned char *target_hw)
  {
  	arp_send_dst(type, ptype, dest_ip, dev, src_ip, dest_hw, src_hw,
  		     target_hw, NULL);
  }
  EXPORT_SYMBOL(arp_send);

  static void arp_solicit(struct neighbour *neigh, struct sk_buff *skb)
  {

  	__be32 saddr = 0;

  	u8 dst_ha[MAX_ADDR_LEN], *dst_hw = NULL;

  	struct net_device *dev = neigh->dev;

  	__be32 target = *(__be32 *)neigh->primary_key;

  	int probes = atomic_read(&neigh->probes);

  	struct in_device *in_dev;

  	struct dst_entry *dst = NULL;

  	rcu_read_lock();
  	in_dev = __in_dev_get_rcu(dev);
  	if (!in_dev) {
  		rcu_read_unlock();

  		return;

  	}

  	switch (IN_DEV_ARP_ANNOUNCE(in_dev)) {
  	default:
  	case 0:		/* By default announce any local IP */

  		if (skb && inet_addr_type_dev_table(dev_net(dev), dev,

  					  ip_hdr(skb)->saddr) == RTN_LOCAL)

  			saddr = ip_hdr(skb)->saddr;

  		break;
  	case 1:		/* Restrict announcements of saddr in same subnet */
  		if (!skb)
  			break;

  		saddr = ip_hdr(skb)->saddr;

  		if (inet_addr_type_dev_table(dev_net(dev), dev,
  					     saddr) == RTN_LOCAL) {

  			/* saddr should be known to target */
  			if (inet_addr_onlink(in_dev, target, saddr))
  				break;
  		}
  		saddr = 0;
  		break;
  	case 2:		/* Avoid secondary IPs, get a primary/preferred one */
  		break;
  	}

  	rcu_read_unlock();

  	if (!saddr)
  		saddr = inet_select_addr(dev, target, RT_SCOPE_LINK);

  	probes -= NEIGH_VAR(neigh->parms, UCAST_PROBES);

  	if (probes < 0) {
  		if (!(neigh->nud_state & NUD_VALID))

  			pr_debug("trying to ucast probe in NUD_INVALID
  ");

  		neigh_ha_snapshot(dst_ha, neigh, dev);

  		dst_hw = dst_ha;

  	} else {

  		probes -= NEIGH_VAR(neigh->parms, APP_PROBES);

  		if (probes < 0) {

  			neigh_app_ns(neigh);

  			return;
  		}

  	}

  	if (skb && !(dev->priv_flags & IFF_XMIT_DST_RELEASE))

  		dst = skb_dst(skb);

  	arp_send_dst(ARPOP_REQUEST, ETH_P_ARP, target, dev, saddr,

  		     dst_hw, dev->dev_addr, NULL, dst);

  }

  static int arp_ignore(struct in_device *in_dev, __be32 sip, __be32 tip)

  {

  	struct net *net = dev_net(in_dev->dev);

  	int scope;
  
  	switch (IN_DEV_ARP_IGNORE(in_dev)) {
  	case 0:	/* Reply, the tip is already validated */
  		return 0;
  	case 1:	/* Reply only if tip is configured on the incoming interface */
  		sip = 0;
  		scope = RT_SCOPE_HOST;
  		break;
  	case 2:	/*
  		 * Reply only if tip is configured on the incoming interface
  		 * and is in same subnet as sip
  		 */
  		scope = RT_SCOPE_HOST;
  		break;
  	case 3:	/* Do not reply for scope host addresses */
  		sip = 0;
  		scope = RT_SCOPE_LINK;

  		in_dev = NULL;

  		break;
  	case 4:	/* Reserved */
  	case 5:
  	case 6:
  	case 7:
  		return 0;
  	case 8:	/* Do not reply */
  		return 1;
  	default:
  		return 0;
  	}

  	return !inet_confirm_addr(net, in_dev, sip, tip, scope);

  }

  static int arp_filter(__be32 sip, __be32 tip, struct net_device *dev)

  {

  	struct rtable *rt;

  	int flag = 0;

  	/*unsigned long now; */

  	struct net *net = dev_net(dev);

  	rt = ip_route_output(net, sip, tip, 0, l3mdev_master_ifindex_rcu(dev));

  	if (IS_ERR(rt))

  		return 1;

  	if (rt->dst.dev != dev) {

  		__NET_INC_STATS(net, LINUX_MIB_ARPFILTER);

  		flag = 1;

  	}
  	ip_rt_put(rt);
  	return flag;
  }

  /*
   * Check if we can use proxy ARP for this path
   */

  static inline int arp_fwd_proxy(struct in_device *in_dev,
  				struct net_device *dev,	struct rtable *rt)

  {
  	struct in_device *out_dev;
  	int imi, omi = -1;

  	if (rt->dst.dev == dev)

  		return 0;

  	if (!IN_DEV_PROXY_ARP(in_dev))
  		return 0;

  	imi = IN_DEV_MEDIUM_ID(in_dev);
  	if (imi == 0)

  		return 1;
  	if (imi == -1)
  		return 0;
  
  	/* place to check for proxy_arp for routes */

  	out_dev = __in_dev_get_rcu(rt->dst.dev);

  	if (out_dev)

  		omi = IN_DEV_MEDIUM_ID(out_dev);

  	return omi != imi && omi != -1;

  }
  
  /*

   * Check for RFC3069 proxy arp private VLAN (allow to send back to same dev)
   *
   * RFC3069 supports proxy arp replies back to the same interface.  This
   * is done to support (ethernet) switch features, like RFC 3069, where
   * the individual ports are not allowed to communicate with each
   * other, BUT they are allowed to talk to the upstream router.  As
   * described in RFC 3069, it is possible to allow these hosts to
   * communicate through the upstream router, by proxy_arp'ing.
   *
   * RFC 3069: "VLAN Aggregation for Efficient IP Address Allocation"
   *
   *  This technology is known by different names:
   *    In RFC 3069 it is called VLAN Aggregation.
   *    Cisco and Allied Telesyn call it Private VLAN.
   *    Hewlett-Packard call it Source-Port filtering or port-isolation.
   *    Ericsson call it MAC-Forced Forwarding (RFC Draft).
   *
   */
  static inline int arp_fwd_pvlan(struct in_device *in_dev,
  				struct net_device *dev,	struct rtable *rt,
  				__be32 sip, __be32 tip)
  {
  	/* Private VLAN is only concerned about the same ethernet segment */

  	if (rt->dst.dev != dev)

  		return 0;
  
  	/* Don't reply on self probes (often done by windowz boxes)*/
  	if (sip == tip)
  		return 0;
  
  	if (IN_DEV_PROXY_ARP_PVLAN(in_dev))
  		return 1;
  	else
  		return 0;
  }
  
  /*

   *	Interface to link layer: send routine and receive handler.
   */
  
  /*

   *	Create an arp packet. If dest_hw is not set, we create a broadcast

   *	message.
   */

  struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
  			   struct net_device *dev, __be32 src_ip,

  			   const unsigned char *dest_hw,
  			   const unsigned char *src_hw,
  			   const unsigned char *target_hw)

  {
  	struct sk_buff *skb;
  	struct arphdr *arp;
  	unsigned char *arp_ptr;

  	int hlen = LL_RESERVED_SPACE(dev);
  	int tlen = dev->needed_tailroom;

  
  	/*
  	 *	Allocate a buffer
  	 */

  	skb = alloc_skb(arp_hdr_len(dev) + hlen + tlen, GFP_ATOMIC);

  	if (!skb)

  		return NULL;

  	skb_reserve(skb, hlen);

  	skb_reset_network_header(skb);

  	arp = skb_put(skb, arp_hdr_len(dev));

  	skb->dev = dev;
  	skb->protocol = htons(ETH_P_ARP);

  	if (!src_hw)

  		src_hw = dev->dev_addr;

  	if (!dest_hw)

  		dest_hw = dev->broadcast;
  
  	/*
  	 *	Fill the device header for the ARP frame
  	 */

  	if (dev_hard_header(skb, dev, ptype, dest_hw, src_hw, skb->len) < 0)

  		goto out;
  
  	/*
  	 * Fill out the arp protocol part.
  	 *
  	 * The arp hardware type should match the device type, except for FDDI,
  	 * which (according to RFC 1390) should always equal 1 (Ethernet).
  	 */
  	/*
  	 *	Exceptions everywhere. AX.25 uses the AX.25 PID value not the
  	 *	DIX code for the protocol. Make these device structure fields.
  	 */
  	switch (dev->type) {
  	default:
  		arp->ar_hrd = htons(dev->type);
  		arp->ar_pro = htons(ETH_P_IP);
  		break;

  #if IS_ENABLED(CONFIG_AX25)

  	case ARPHRD_AX25:
  		arp->ar_hrd = htons(ARPHRD_AX25);
  		arp->ar_pro = htons(AX25_P_IP);
  		break;

  #if IS_ENABLED(CONFIG_NETROM)

  	case ARPHRD_NETROM:
  		arp->ar_hrd = htons(ARPHRD_NETROM);
  		arp->ar_pro = htons(AX25_P_IP);
  		break;
  #endif
  #endif

  #if IS_ENABLED(CONFIG_FDDI)

  	case ARPHRD_FDDI:
  		arp->ar_hrd = htons(ARPHRD_ETHER);
  		arp->ar_pro = htons(ETH_P_IP);
  		break;
  #endif

  	}
  
  	arp->ar_hln = dev->addr_len;
  	arp->ar_pln = 4;
  	arp->ar_op = htons(type);

  	arp_ptr = (unsigned char *)(arp + 1);

  
  	memcpy(arp_ptr, src_hw, dev->addr_len);

  	arp_ptr += dev->addr_len;
  	memcpy(arp_ptr, &src_ip, 4);
  	arp_ptr += 4;

  
  	switch (dev->type) {
  #if IS_ENABLED(CONFIG_FIREWIRE_NET)
  	case ARPHRD_IEEE1394:
  		break;
  #endif
  	default:

  		if (target_hw)

  			memcpy(arp_ptr, target_hw, dev->addr_len);
  		else
  			memset(arp_ptr, 0, dev->addr_len);
  		arp_ptr += dev->addr_len;
  	}

  	memcpy(arp_ptr, &dest_ip, 4);
  
  	return skb;
  
  out:
  	kfree_skb(skb);
  	return NULL;
  }

  EXPORT_SYMBOL(arp_create);

  static int arp_xmit_finish(struct net *net, struct sock *sk, struct sk_buff *skb)

  {
  	return dev_queue_xmit(skb);
  }

  /*
   *	Send an arp packet.
   */
  void arp_xmit(struct sk_buff *skb)
  {
  	/* Send it off, maybe filter it using firewalling first.  */

  	NF_HOOK(NFPROTO_ARP, NF_ARP_OUT,
  		dev_net(skb->dev), NULL, skb, NULL, skb->dev,
  		arp_xmit_finish);

  }

  EXPORT_SYMBOL(arp_xmit);

  static bool arp_is_garp(struct net *net, struct net_device *dev,
  			int *addr_type, __be16 ar_op,

  			__be32 sip, __be32 tip,
  			unsigned char *sha, unsigned char *tha)
  {

  	bool is_garp = tip == sip;

  
  	/* Gratuitous ARP _replies_ also require target hwaddr to be
  	 * the same as source.
  	 */
  	if (is_garp && ar_op == htons(ARPOP_REPLY))
  		is_garp =
  			/* IPv4 over IEEE 1394 doesn't provide target
  			 * hardware address field in its ARP payload.
  			 */
  			tha &&
  			!memcmp(tha, sha, dev->addr_len);

  	if (is_garp) {
  		*addr_type = inet_addr_type_dev_table(net, dev, sip);
  		if (*addr_type != RTN_UNICAST)
  			is_garp = false;
  	}

  	return is_garp;
  }

  /*

   *	Process an arp request.
   */

  static int arp_process(struct net *net, struct sock *sk, struct sk_buff *skb)

  {
  	struct net_device *dev = skb->dev;

  	struct in_device *in_dev = __in_dev_get_rcu(dev);

  	struct arphdr *arp;
  	unsigned char *arp_ptr;
  	struct rtable *rt;

  	unsigned char *sha;

  	unsigned char *tha = NULL;

  	__be32 sip, tip;

  	u16 dev_type = dev->type;
  	int addr_type;
  	struct neighbour *n;

  	struct dst_entry *reply_dst = NULL;

  	bool is_garp = false;

  
  	/* arp_rcv below verifies the ARP header and verifies the device
  	 * is ARP'able.
  	 */

  	if (!in_dev)

  		goto out_free_skb;

  	arp = arp_hdr(skb);

  
  	switch (dev_type) {

  	default:

  		if (arp->ar_pro != htons(ETH_P_IP) ||
  		    htons(dev_type) != arp->ar_hrd)

  			goto out_free_skb;

  		break;

  	case ARPHRD_ETHER:

  	case ARPHRD_FDDI:

  	case ARPHRD_IEEE802:

  		/*

  		 * ETHERNET, and Fibre Channel (which are IEEE 802

  		 * devices, according to RFC 2625) devices will accept ARP
  		 * hardware types of either 1 (Ethernet) or 6 (IEEE 802.2).
  		 * This is the case also of FDDI, where the RFC 1390 says that
  		 * FDDI devices should accept ARP hardware of (1) Ethernet,
  		 * however, to be more robust, we'll accept both 1 (Ethernet)
  		 * or 6 (IEEE 802.2)
  		 */
  		if ((arp->ar_hrd != htons(ARPHRD_ETHER) &&
  		     arp->ar_hrd != htons(ARPHRD_IEEE802)) ||
  		    arp->ar_pro != htons(ETH_P_IP))

  			goto out_free_skb;

  		break;

  	case ARPHRD_AX25:
  		if (arp->ar_pro != htons(AX25_P_IP) ||
  		    arp->ar_hrd != htons(ARPHRD_AX25))

  			goto out_free_skb;

  		break;

  	case ARPHRD_NETROM:
  		if (arp->ar_pro != htons(AX25_P_IP) ||
  		    arp->ar_hrd != htons(ARPHRD_NETROM))

  			goto out_free_skb;

  		break;

  	}
  
  	/* Understand only these message types */
  
  	if (arp->ar_op != htons(ARPOP_REPLY) &&
  	    arp->ar_op != htons(ARPOP_REQUEST))

  		goto out_free_skb;

  
  /*
   *	Extract fields
   */

  	arp_ptr = (unsigned char *)(arp + 1);

  	sha	= arp_ptr;
  	arp_ptr += dev->addr_len;
  	memcpy(&sip, arp_ptr, 4);
  	arp_ptr += 4;

  	switch (dev_type) {
  #if IS_ENABLED(CONFIG_FIREWIRE_NET)
  	case ARPHRD_IEEE1394:
  		break;
  #endif
  	default:

  		tha = arp_ptr;

  		arp_ptr += dev->addr_len;
  	}

  	memcpy(&tip, arp_ptr, 4);

  /*

   *	Check for bad requests for 127.x.x.x and requests for multicast
   *	addresses.  If this is one such, delete it.
   */

  	if (ipv4_is_multicast(tip) ||
  	    (!IN_DEV_ROUTE_LOCALNET(in_dev) && ipv4_is_loopback(tip)))

  		goto out_free_skb;

   /*
    *	For some 802.11 wireless deployments (and possibly other networks),
    *	there will be an ARP proxy and gratuitous ARP frames are attacks
    *	and thus should not be accepted.
    */
  	if (sip == tip && IN_DEV_ORCONF(in_dev, DROP_GRATUITOUS_ARP))

  		goto out_free_skb;

  /*
   *     Special case: We must set Frame Relay source Q.922 address
   */
  	if (dev_type == ARPHRD_DLCI)
  		sha = dev->broadcast;
  
  /*
   *  Process entry.  The idea here is we want to send a reply if it is a
   *  request for us or if it is a request for someone else that we hold
   *  a proxy for.  We want to add an entry to our cache if it is a reply

   *  to us or if it is a request for our address.
   *  (The assumption for this last is that if someone is requesting our
   *  address, they are probably intending to talk to us, so it saves time
   *  if we cache their address.  Their address is also probably not in

   *  our cache, since ours is not in their cache.)

   *

   *  Putting this another way, we only care about replies if they are to
   *  us, in which case we add them to the cache.  For requests, we care
   *  about those for us and those for our proxies.  We reply to both,

   *  and in the case of requests for us we add the requester to the arp

   *  cache.
   */

  	if (arp->ar_op == htons(ARPOP_REQUEST) && skb_metadata_dst(skb))
  		reply_dst = (struct dst_entry *)
  			    iptunnel_metadata_reply(skb_metadata_dst(skb),
  						    GFP_ATOMIC);

  	/* Special case: IPv4 duplicate address detection packet (RFC2131) */
  	if (sip == 0) {

  		if (arp->ar_op == htons(ARPOP_REQUEST) &&

  		    inet_addr_type_dev_table(net, dev, tip) == RTN_LOCAL &&

  		    !arp_ignore(in_dev, sip, tip))

  			arp_send_dst(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip,
  				     sha, dev->dev_addr, sha, reply_dst);

  		goto out_consume_skb;

  	}
  
  	if (arp->ar_op == htons(ARPOP_REQUEST) &&

  	    ip_route_input_noref(skb, tip, sip, 0, dev) == 0) {

  		rt = skb_rtable(skb);

  		addr_type = rt->rt_type;
  
  		if (addr_type == RTN_LOCAL) {

  			int dont_send;

  			dont_send = arp_ignore(in_dev, sip, tip);

  			if (!dont_send && IN_DEV_ARPFILTER(in_dev))

  				dont_send = arp_filter(sip, tip, dev);

  			if (!dont_send) {
  				n = neigh_event_ns(&arp_tbl, sha, &sip, dev);
  				if (n) {

  					arp_send_dst(ARPOP_REPLY, ETH_P_ARP,
  						     sip, dev, tip, sha,
  						     dev->dev_addr, sha,
  						     reply_dst);

  					neigh_release(n);
  				}

  			}

  			goto out_consume_skb;

  		} else if (IN_DEV_FORWARD(in_dev)) {

  			if (addr_type == RTN_UNICAST  &&
  			    (arp_fwd_proxy(in_dev, dev, rt) ||
  			     arp_fwd_pvlan(in_dev, dev, rt, sip, tip) ||

  			     (rt->dst.dev != dev &&
  			      pneigh_lookup(&arp_tbl, net, &tip, dev, 0)))) {

  				n = neigh_event_ns(&arp_tbl, sha, &sip, dev);
  				if (n)
  					neigh_release(n);

  				if (NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED ||

  				    skb->pkt_type == PACKET_HOST ||

  				    NEIGH_VAR(in_dev->arp_parms, PROXY_DELAY) == 0) {

  					arp_send_dst(ARPOP_REPLY, ETH_P_ARP,
  						     sip, dev, tip, sha,
  						     dev->dev_addr, sha,
  						     reply_dst);

  				} else {

  					pneigh_enqueue(&arp_tbl,
  						       in_dev->arp_parms, skb);

  					goto out_free_dst;

  				}

  				goto out_consume_skb;

  			}
  		}
  	}
  
  	/* Update our ARP tables */
  
  	n = __neigh_lookup(&arp_tbl, &sip, dev, 0);

  	addr_type = -1;

  	if (n || IN_DEV_ARP_ACCEPT(in_dev)) {

  		is_garp = arp_is_garp(net, dev, &addr_type, arp->ar_op,
  				      sip, tip, sha, tha);
  	}

  	if (IN_DEV_ARP_ACCEPT(in_dev)) {

  		/* Unsolicited ARP is not accepted by default.
  		   It is possible, that this option should be enabled for some
  		   devices (strip is candidate)
  		 */

  		if (!n &&

  		    (is_garp ||
  		     (arp->ar_op == htons(ARPOP_REPLY) &&
  		      (addr_type == RTN_UNICAST ||
  		       (addr_type < 0 &&
  			/* postpone calculation to as late as possible */
  			inet_addr_type_dev_table(net, dev, sip) ==
  				RTN_UNICAST)))))

  			n = __neigh_lookup(&arp_tbl, &sip, dev, 1);

  	}

  
  	if (n) {
  		int state = NUD_REACHABLE;
  		int override;
  
  		/* If several different ARP replies follows back-to-back,
  		   use the FIRST one. It is possible, if several proxy
  		   agents are active. Taking the first reply prevents
  		   arp trashing and chooses the fastest router.
  		 */

  		override = time_after(jiffies,
  				      n->updated +
  				      NEIGH_VAR(n->parms, LOCKTIME)) ||
  			   is_garp;

  
  		/* Broadcast replies and request packets
  		   do not assert neighbour reachability.
  		 */
  		if (arp->ar_op != htons(ARPOP_REPLY) ||
  		    skb->pkt_type != PACKET_HOST)
  			state = NUD_STALE;

  		neigh_update(n, sha, state,

  			     override ? NEIGH_UPDATE_F_OVERRIDE : 0, 0);

  		neigh_release(n);
  	}

  out_consume_skb:

  	consume_skb(skb);

  out_free_dst:
  	dst_release(reply_dst);

  	return NET_RX_SUCCESS;
  
  out_free_skb:
  	kfree_skb(skb);
  	return NET_RX_DROP;

  }

  static void parp_redo(struct sk_buff *skb)
  {

  	arp_process(dev_net(skb->dev), NULL, skb);

  }

  
  /*
   *	Receive an arp request from the device layer.
   */

  static int arp_rcv(struct sk_buff *skb, struct net_device *dev,
  		   struct packet_type *pt, struct net_device *orig_dev)

  {

  	const struct arphdr *arp;

  	/* do not tweak dropwatch on an ARP we will ignore */

  	if (dev->flags & IFF_NOARP ||
  	    skb->pkt_type == PACKET_OTHERHOST ||
  	    skb->pkt_type == PACKET_LOOPBACK)

  		goto consumeskb;

  
  	skb = skb_share_check(skb, GFP_ATOMIC);
  	if (!skb)
  		goto out_of_mem;

  
  	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */

  	if (!pskb_may_pull(skb, arp_hdr_len(dev)))

  		goto freeskb;

  	arp = arp_hdr(skb);

  	if (arp->ar_hln != dev->addr_len || arp->ar_pln != 4)

  		goto freeskb;

  	memset(NEIGH_CB(skb), 0, sizeof(struct neighbour_cb));

  	return NF_HOOK(NFPROTO_ARP, NF_ARP_IN,
  		       dev_net(dev), NULL, skb, dev, NULL,
  		       arp_process);

  consumeskb:
  	consume_skb(skb);

  	return NET_RX_SUCCESS;

  freeskb:
  	kfree_skb(skb);
  out_of_mem:

  	return NET_RX_DROP;

  }
  
  /*
   *	User level interface (ioctl)
   */
  
  /*
   *	Set (create) an ARP cache entry.
   */

  static int arp_req_set_proxy(struct net *net, struct net_device *dev, int on)

  {

  	if (!dev) {

  		IPV4_DEVCONF_ALL(net, PROXY_ARP) = on;

  		return 0;
  	}

  	if (__in_dev_get_rtnl(dev)) {
  		IN_DEV_CONF_SET(__in_dev_get_rtnl(dev), PROXY_ARP, on);

  		return 0;
  	}
  	return -ENXIO;
  }

  static int arp_req_set_public(struct net *net, struct arpreq *r,
  		struct net_device *dev)

  {
  	__be32 ip = ((struct sockaddr_in *)&r->arp_pa)->sin_addr.s_addr;
  	__be32 mask = ((struct sockaddr_in *)&r->arp_netmask)->sin_addr.s_addr;
  
  	if (mask && mask != htonl(0xFFFFFFFF))
  		return -EINVAL;
  	if (!dev && (r->arp_flags & ATF_COM)) {

  		dev = dev_getbyhwaddr_rcu(net, r->arp_ha.sa_family,

  				      r->arp_ha.sa_data);

  		if (!dev)
  			return -ENODEV;
  	}
  	if (mask) {

  		if (!pneigh_lookup(&arp_tbl, net, &ip, dev, 1))

  			return -ENOBUFS;
  		return 0;
  	}

  	return arp_req_set_proxy(net, dev, 1);

  }

  static int arp_req_set(struct net *net, struct arpreq *r,

  		       struct net_device *dev)

  {

  	__be32 ip;

  	struct neighbour *neigh;
  	int err;

  	if (r->arp_flags & ATF_PUBL)

  		return arp_req_set_public(net, r, dev);

  	ip = ((struct sockaddr_in *)&r->arp_pa)->sin_addr.s_addr;

  	if (r->arp_flags & ATF_PERM)
  		r->arp_flags |= ATF_COM;

  	if (!dev) {

  		struct rtable *rt = ip_route_output(net, ip, 0, RTO_ONLINK, 0);

  
  		if (IS_ERR(rt))
  			return PTR_ERR(rt);

  		dev = rt->dst.dev;

  		ip_rt_put(rt);
  		if (!dev)
  			return -EINVAL;
  	}
  	switch (dev->type) {

  #if IS_ENABLED(CONFIG_FDDI)

  	case ARPHRD_FDDI:
  		/*
  		 * According to RFC 1390, FDDI devices should accept ARP
  		 * hardware types of 1 (Ethernet).  However, to be more
  		 * robust, we'll accept hardware types of either 1 (Ethernet)
  		 * or 6 (IEEE 802.2).
  		 */
  		if (r->arp_ha.sa_family != ARPHRD_FDDI &&
  		    r->arp_ha.sa_family != ARPHRD_ETHER &&
  		    r->arp_ha.sa_family != ARPHRD_IEEE802)
  			return -EINVAL;
  		break;
  #endif
  	default:
  		if (r->arp_ha.sa_family != dev->type)
  			return -EINVAL;
  		break;
  	}
  
  	neigh = __neigh_lookup_errno(&arp_tbl, &ip, dev);
  	err = PTR_ERR(neigh);
  	if (!IS_ERR(neigh)) {

  		unsigned int state = NUD_STALE;

  		if (r->arp_flags & ATF_PERM)
  			state = NUD_PERMANENT;

  		err = neigh_update(neigh, (r->arp_flags & ATF_COM) ?

  				   r->arp_ha.sa_data : NULL, state,

  				   NEIGH_UPDATE_F_OVERRIDE |

  				   NEIGH_UPDATE_F_ADMIN, 0);

  		neigh_release(neigh);
  	}
  	return err;
  }

  static unsigned int arp_state_to_flags(struct neighbour *neigh)

  {

  	if (neigh->nud_state&NUD_PERMANENT)

  		return ATF_PERM | ATF_COM;

  	else if (neigh->nud_state&NUD_VALID)

  		return ATF_COM;
  	else
  		return 0;

  }
  
  /*
   *	Get an ARP cache entry.
   */
  
  static int arp_req_get(struct arpreq *r, struct net_device *dev)
  {

  	__be32 ip = ((struct sockaddr_in *) &r->arp_pa)->sin_addr.s_addr;

  	struct neighbour *neigh;
  	int err = -ENXIO;
  
  	neigh = neigh_lookup(&arp_tbl, &ip, dev);
  	if (neigh) {

  		if (!(neigh->nud_state & NUD_NOARP)) {
  			read_lock_bh(&neigh->lock);
  			memcpy(r->arp_ha.sa_data, neigh->ha, dev->addr_len);
  			r->arp_flags = arp_state_to_flags(neigh);
  			read_unlock_bh(&neigh->lock);
  			r->arp_ha.sa_family = dev->type;
  			strlcpy(r->arp_dev, dev->name, sizeof(r->arp_dev));
  			err = 0;
  		}

  		neigh_release(neigh);

  	}
  	return err;
  }

  static int arp_invalidate(struct net_device *dev, __be32 ip)

  {
  	struct neighbour *neigh = neigh_lookup(&arp_tbl, &ip, dev);
  	int err = -ENXIO;

  	struct neigh_table *tbl = &arp_tbl;

  
  	if (neigh) {
  		if (neigh->nud_state & ~NUD_NOARP)
  			err = neigh_update(neigh, NULL, NUD_FAILED,
  					   NEIGH_UPDATE_F_OVERRIDE|

  					   NEIGH_UPDATE_F_ADMIN, 0);

  		write_lock_bh(&tbl->lock);

  		neigh_release(neigh);

  		neigh_remove_one(neigh, tbl);
  		write_unlock_bh(&tbl->lock);

  	}
  
  	return err;
  }

  static int arp_req_delete_public(struct net *net, struct arpreq *r,
  		struct net_device *dev)

  {
  	__be32 ip = ((struct sockaddr_in *) &r->arp_pa)->sin_addr.s_addr;
  	__be32 mask = ((struct sockaddr_in *)&r->arp_netmask)->sin_addr.s_addr;
  
  	if (mask == htonl(0xFFFFFFFF))

  		return pneigh_delete(&arp_tbl, net, &ip, dev);

  	if (mask)
  		return -EINVAL;

  	return arp_req_set_proxy(net, dev, 0);

  }

  static int arp_req_delete(struct net *net, struct arpreq *r,

  			  struct net_device *dev)

  {

  	__be32 ip;

  	if (r->arp_flags & ATF_PUBL)

  		return arp_req_delete_public(net, r, dev);

  	ip = ((struct sockaddr_in *)&r->arp_pa)->sin_addr.s_addr;

  	if (!dev) {

  		struct rtable *rt = ip_route_output(net, ip, 0, RTO_ONLINK, 0);

  		if (IS_ERR(rt))
  			return PTR_ERR(rt);

  		dev = rt->dst.dev;

  		ip_rt_put(rt);
  		if (!dev)
  			return -EINVAL;
  	}

  	return arp_invalidate(dev, ip);

  }
  
  /*
   *	Handle an ARP layer I/O control request.
   */

  int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)

  {
  	int err;
  	struct arpreq r;
  	struct net_device *dev = NULL;
  
  	switch (cmd) {

  	case SIOCDARP:
  	case SIOCSARP:

  		if (!ns_capable(net->user_ns, CAP_NET_ADMIN))

  			return -EPERM;
  	case SIOCGARP:
  		err = copy_from_user(&r, arg, sizeof(struct arpreq));
  		if (err)
  			return -EFAULT;
  		break;
  	default:
  		return -EINVAL;

  	}
  
  	if (r.arp_pa.sa_family != AF_INET)
  		return -EPFNOSUPPORT;
  
  	if (!(r.arp_flags & ATF_PUBL) &&

  	    (r.arp_flags & (ATF_NETMASK | ATF_DONTPUB)))

  		return -EINVAL;
  	if (!(r.arp_flags & ATF_NETMASK))
  		((struct sockaddr_in *)&r.arp_netmask)->sin_addr.s_addr =
  							   htonl(0xFFFFFFFFUL);

  	rtnl_lock();

  	if (r.arp_dev[0]) {
  		err = -ENODEV;

  		dev = __dev_get_by_name(net, r.arp_dev);

  		if (!dev)

  			goto out;
  
  		/* Mmmm... It is wrong... ARPHRD_NETROM==0 */
  		if (!r.arp_ha.sa_family)
  			r.arp_ha.sa_family = dev->type;
  		err = -EINVAL;
  		if ((r.arp_flags & ATF_COM) && r.arp_ha.sa_family != dev->type)
  			goto out;
  	} else if (cmd == SIOCGARP) {
  		err = -ENODEV;
  		goto out;
  	}

  	switch (cmd) {

  	case SIOCDARP:

  		err = arp_req_delete(net, &r, dev);

  		break;
  	case SIOCSARP:

  		err = arp_req_set(net, &r, dev);

  		break;
  	case SIOCGARP:
  		err = arp_req_get(&r, dev);

  		break;
  	}
  out:

  	rtnl_unlock();

  	if (cmd == SIOCGARP && !err && copy_to_user(arg, &r, sizeof(r)))
  		err = -EFAULT;

  	return err;
  }

  static int arp_netdev_event(struct notifier_block *this, unsigned long event,
  			    void *ptr)

  {

  	struct net_device *dev = netdev_notifier_info_to_dev(ptr);

  	struct netdev_notifier_change_info *change_info;

  
  	switch (event) {
  	case NETDEV_CHANGEADDR:
  		neigh_changeaddr(&arp_tbl, dev);

  		rt_cache_flush(dev_net(dev));

  		break;

  	case NETDEV_CHANGE:
  		change_info = ptr;
  		if (change_info->flags_changed & IFF_NOARP)
  			neigh_changeaddr(&arp_tbl, dev);
  		break;

  	default:
  		break;
  	}
  
  	return NOTIFY_DONE;
  }
  
  static struct notifier_block arp_netdev_notifier = {
  	.notifier_call = arp_netdev_event,
  };
  
  /* Note, that it is not on notifier chain.
     It is necessary, that this routine was called after route cache will be
     flushed.
   */
  void arp_ifdown(struct net_device *dev)
  {
  	neigh_ifdown(&arp_tbl, dev);
  }
  
  
  /*
   *	Called once on startup.
   */

  static struct packet_type arp_packet_type __read_mostly = {

  	.type =	cpu_to_be16(ETH_P_ARP),

  	.func =	arp_rcv,
  };
  
  static int arp_proc_init(void);
  
  void __init arp_init(void)
  {

  	neigh_table_init(NEIGH_ARP_TABLE, &arp_tbl);

  
  	dev_add_pack(&arp_packet_type);
  	arp_proc_init();
  #ifdef CONFIG_SYSCTL

  	neigh_sysctl_register(NULL, &arp_tbl.parms, NULL);

  #endif
  	register_netdevice_notifier(&arp_netdev_notifier);
  }
  
  #ifdef CONFIG_PROC_FS

  #if IS_ENABLED(CONFIG_AX25)

  
  /* ------------------------------------------------------------------------ */
  /*
   *	ax25 -> ASCII conversion
   */

  static void ax2asc2(ax25_address *a, char *buf)

  {
  	char c, *s;
  	int n;
  
  	for (n = 0, s = buf; n < 6; n++) {
  		c = (a->ax25_call[n] >> 1) & 0x7F;

  		if (c != ' ')
  			*s++ = c;

  	}

  	*s++ = '-';

  	n = (a->ax25_call[6] >> 1) & 0x0F;
  	if (n > 9) {

  		*s++ = '1';
  		n -= 10;
  	}

  	*s++ = n + '0';
  	*s++ = '\0';

  	if (*buf == '\0' || *buf == '-') {
  		buf[0] = '*';
  		buf[1] = '\0';
  	}

  }
  #endif /* CONFIG_AX25 */
  
  #define HBUFFERLEN 30
  
  static void arp_format_neigh_entry(struct seq_file *seq,
  				   struct neighbour *n)
  {
  	char hbuffer[HBUFFERLEN];

  	int k, j;
  	char tbuf[16];
  	struct net_device *dev = n->dev;
  	int hatype = dev->type;
  
  	read_lock(&n->lock);
  	/* Convert hardware address to XX:XX:XX:XX ... form. */

  #if IS_ENABLED(CONFIG_AX25)

  	if (hatype == ARPHRD_AX25 || hatype == ARPHRD_NETROM)
  		ax2asc2((ax25_address *)n->ha, hbuffer);
  	else {
  #endif
  	for (k = 0, j = 0; k < HBUFFERLEN - 3 && j < dev->addr_len; j++) {

  		hbuffer[k++] = hex_asc_hi(n->ha[j]);
  		hbuffer[k++] = hex_asc_lo(n->ha[j]);

  		hbuffer[k++] = ':';
  	}

  	if (k != 0)
  		--k;
  	hbuffer[k] = 0;

  #if IS_ENABLED(CONFIG_AX25)

  	}
  #endif

  	sprintf(tbuf, "%pI4", n->primary_key);

  	seq_printf(seq, "%-16s 0x%-10x0x%-10x%-17s     *        %s
  ",

  		   tbuf, hatype, arp_state_to_flags(n), hbuffer, dev->name);
  	read_unlock(&n->lock);
  }
  
  static void arp_format_pneigh_entry(struct seq_file *seq,
  				    struct pneigh_entry *n)
  {
  	struct net_device *dev = n->dev;
  	int hatype = dev ? dev->type : 0;
  	char tbuf[16];

  	sprintf(tbuf, "%pI4", n->key);

  	seq_printf(seq, "%-16s 0x%-10x0x%-10x%s     *        %s
  ",
  		   tbuf, hatype, ATF_PUBL | ATF_PERM, "00:00:00:00:00:00",
  		   dev ? dev->name : "*");
  }
  
  static int arp_seq_show(struct seq_file *seq, void *v)
  {
  	if (v == SEQ_START_TOKEN) {
  		seq_puts(seq, "IP address       HW type     Flags       "
  			      "HW address            Mask     Device
  ");
  	} else {
  		struct neigh_seq_state *state = seq->private;
  
  		if (state->flags & NEIGH_SEQ_IS_PNEIGH)
  			arp_format_pneigh_entry(seq, v);
  		else
  			arp_format_neigh_entry(seq, v);
  	}
  
  	return 0;
  }
  
  static void *arp_seq_start(struct seq_file *seq, loff_t *pos)
  {
  	/* Don't want to confuse "arp -a" w/ magic entries,
  	 * so we tell the generic iterator to skip NUD_NOARP.
  	 */
  	return neigh_seq_start(seq, pos, &arp_tbl, NEIGH_SEQ_SKIP_NOARP);
  }
  
  /* ------------------------------------------------------------------------ */

  static const struct seq_operations arp_seq_ops = {

  	.start	= arp_seq_start,
  	.next	= neigh_seq_next,
  	.stop	= neigh_seq_stop,
  	.show	= arp_seq_show,

  };
  
  static int arp_seq_open(struct inode *inode, struct file *file)
  {

  	return seq_open_net(inode, file, &arp_seq_ops,
  			    sizeof(struct neigh_seq_state));

  }

  static const struct file_operations arp_seq_fops = {

  	.owner		= THIS_MODULE,
  	.open           = arp_seq_open,
  	.read           = seq_read,
  	.llseek         = seq_lseek,

  	.release	= seq_release_net,

  };

  
  static int __net_init arp_net_init(struct net *net)

  {

  	if (!proc_create("arp", S_IRUGO, net->proc_net, &arp_seq_fops))

  		return -ENOMEM;
  	return 0;
  }

  static void __net_exit arp_net_exit(struct net *net)
  {

  	remove_proc_entry("arp", net->proc_net);

  }
  
  static struct pernet_operations arp_net_ops = {
  	.init = arp_net_init,
  	.exit = arp_net_exit,
  };
  
  static int __init arp_proc_init(void)
  {
  	return register_pernet_subsys(&arp_net_ops);
  }

  #else /* CONFIG_PROC_FS */
  
  static int __init arp_proc_init(void)
  {
  	return 0;
  }
  
  #endif /* CONFIG_PROC_FS */