text: /*-
   * SPDX-License-Identifier: BSD-3-Clause
   *
   * Copyright (c) 1982, 1986, 1988, 1993
   *	The Regents of the University of California.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   *	@(#)if_ether.c	8.1 (Berkeley) 6/10/93
   */
  
  /*
   * Ethernet address resolution protocol.
   * TODO:
   *	add "inuse/lock" bit (or ref. count) along with valid bit
   */
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD$");
  
  #include "opt_inet.h"
  
  #include <sys/param.h>
  #include <sys/eventhandler.h>
  #include <sys/kernel.h>
  #include <sys/lock.h>
  #include <sys/queue.h>
  #include <sys/sysctl.h>
  #include <sys/systm.h>
  #include <sys/mbuf.h>
  #include <sys/malloc.h>
  #include <sys/proc.h>
  #include <sys/rmlock.h>
  #include <sys/socket.h>
  #include <sys/syslog.h>
  
  #include <net/if.h>
  #include <net/if_var.h>
  #include <net/if_dl.h>
  #include <net/if_types.h>
  #include <net/netisr.h>
  #include <net/ethernet.h>
  #include <net/route.h>
  #include <net/vnet.h>
  
  #include <netinet/in.h>
  #include <netinet/in_fib.h>
  #include <netinet/in_var.h>
  #include <net/if_llatbl.h>
  #include <netinet/if_ether.h>
  #ifdef INET
  #include <netinet/ip_carp.h>
  #endif
  
  #include <security/mac/mac_framework.h>
  
  #define SIN(s) ((const struct sockaddr_in *)(s))
  
  static struct timeval arp_lastlog;
  static int arp_curpps;
  static int arp_maxpps = 1;
  
  /* Simple ARP state machine */
  enum arp_llinfo_state {
  	ARP_LLINFO_INCOMPLETE = 0, /* No LLE data */
  	ARP_LLINFO_REACHABLE,	/* LLE is valid */
  	ARP_LLINFO_VERIFY,	/* LLE is valid, need refresh */
  	ARP_LLINFO_DELETED,	/* LLE is deleted */
  };
  
  SYSCTL_DECL(_net_link_ether);
  static SYSCTL_NODE(_net_link_ether, PF_INET, inet,
      CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
      "");
  static SYSCTL_NODE(_net_link_ether, PF_ARP, arp,
      CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
      "");
  
  /* timer values */
  VNET_DEFINE_STATIC(int, arpt_keep) = (20*60);	/* once resolved, good for 20
  						 * minutes */
  VNET_DEFINE_STATIC(int, arp_maxtries) = 5;
  VNET_DEFINE_STATIC(int, arp_proxyall) = 0;
  VNET_DEFINE_STATIC(int, arpt_down) = 20;	/* keep incomplete entries for
  						 * 20 seconds */
  VNET_DEFINE_STATIC(int, arpt_rexmit) = 1;	/* retransmit arp entries, sec*/
  VNET_PCPUSTAT_DEFINE(struct arpstat, arpstat);  /* ARP statistics, see if_arp.h */
  VNET_PCPUSTAT_SYSINIT(arpstat);
  
  #ifdef VIMAGE
  VNET_PCPUSTAT_SYSUNINIT(arpstat);
  #endif /* VIMAGE */
  
  VNET_DEFINE_STATIC(int, arp_maxhold) = 1;
  
  #define	V_arpt_keep		VNET(arpt_keep)
  #define	V_arpt_down		VNET(arpt_down)
  #define	V_arpt_rexmit		VNET(arpt_rexmit)
  #define	V_arp_maxtries		VNET(arp_maxtries)
  #define	V_arp_proxyall		VNET(arp_proxyall)
  #define	V_arp_maxhold		VNET(arp_maxhold)
  
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, max_age, CTLFLAG_VNET | CTLFLAG_RW,
  	&VNET_NAME(arpt_keep), 0,
  	"ARP entry lifetime in seconds");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, maxtries, CTLFLAG_VNET | CTLFLAG_RW,
  	&VNET_NAME(arp_maxtries), 0,
  	"ARP resolution attempts before returning error");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, proxyall, CTLFLAG_VNET | CTLFLAG_RW,
  	&VNET_NAME(arp_proxyall), 0,
  	"Enable proxy ARP for all suitable requests");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, wait, CTLFLAG_VNET | CTLFLAG_RW,
  	&VNET_NAME(arpt_down), 0,
  	"Incomplete ARP entry lifetime in seconds");
  SYSCTL_VNET_PCPUSTAT(_net_link_ether_arp, OID_AUTO, stats, struct arpstat,
      arpstat, "ARP statistics (struct arpstat, net/if_arp.h)");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, maxhold, CTLFLAG_VNET | CTLFLAG_RW,
  	&VNET_NAME(arp_maxhold), 0,
  	"Number of packets to hold per ARP entry");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, max_log_per_second,
  	CTLFLAG_RW, &arp_maxpps, 0,
  	"Maximum number of remotely triggered ARP messages that can be "
  	"logged per second");
  
  /*
   * Due to the exponential backoff algorithm used for the interval between GARP
   * retransmissions, the maximum number of retransmissions is limited for
   * sanity. This limit corresponds to a maximum interval between retransmissions
   * of 2^16 seconds ~= 18 hours.
   *
   * Making this limit more dynamic is more complicated than worthwhile,
   * especially since sending out GARPs spaced days apart would be of little
   * use. A maximum dynamic limit would look something like:
   *
   * const int max = fls(INT_MAX / hz) - 1;
   */
  #define MAX_GARP_RETRANSMITS 16
  static int sysctl_garp_rexmit(SYSCTL_HANDLER_ARGS);
  static int garp_rexmit_count = 0; /* GARP retransmission setting. */
  
  SYSCTL_PROC(_net_link_ether_inet, OID_AUTO, garp_rexmit_count,
      CTLTYPE_INT|CTLFLAG_RW|CTLFLAG_MPSAFE,
      &garp_rexmit_count, 0, sysctl_garp_rexmit, "I",
      "Number of times to retransmit GARP packets;"
      " 0 to disable, maximum of 16");
  
  VNET_DEFINE_STATIC(int, arp_log_level) = LOG_INFO;	/* Min. log(9) level. */
  #define	V_arp_log_level		VNET(arp_log_level)
  SYSCTL_INT(_net_link_ether_arp, OID_AUTO, log_level, CTLFLAG_VNET | CTLFLAG_RW,
  	&VNET_NAME(arp_log_level), 0,
  	"Minimum log(9) level for recording rate limited arp log messages. "
  	"The higher will be log more (emerg=0, info=6 (default), debug=7).");
  #define	ARP_LOG(pri, ...)	do {					\
  	if ((pri) <= V_arp_log_level &&					\
  	    ppsratecheck(&arp_lastlog, &arp_curpps, arp_maxpps))	\
  		log((pri), "arp: " __VA_ARGS__);			\
  } while (0)
  
  
  static void	arpintr(struct mbuf *);
  static void	arptimer(void *);
  #ifdef INET
  static void	in_arpinput(struct mbuf *);
  #endif
  
  static void arp_check_update_lle(struct arphdr *ah, struct in_addr isaddr,
      struct ifnet *ifp, int bridged, struct llentry *la);
  static void arp_mark_lle_reachable(struct llentry *la);
  static void arp_iflladdr(void *arg __unused, struct ifnet *ifp);
  
  static eventhandler_tag iflladdr_tag;
  
  static const struct netisr_handler arp_nh = {
  	.nh_name = "arp",
  	.nh_handler = arpintr,
  	.nh_proto = NETISR_ARP,
  	.nh_policy = NETISR_POLICY_SOURCE,
  };
  
  /*
   * Timeout routine.  Age arp_tab entries periodically.
   */
  static void
  arptimer(void *arg)
  {
  	struct llentry *lle = (struct llentry *)arg;
  	struct ifnet *ifp;
  	int r_skip_req;
  
  	if (lle->la_flags & LLE_STATIC) {
  		return;
  	}
  	LLE_WLOCK(lle);
  	if (callout_pending(&lle->lle_timer)) {
  		/*
  		 * Here we are a bit odd here in the treatment of
  		 * active/pending. If the pending bit is set, it got
  		 * rescheduled before I ran. The active
  		 * bit we ignore, since if it was stopped
  		 * in ll_tablefree() and was currently running
  		 * it would have return 0 so the code would
  		 * not have deleted it since the callout could
  		 * not be stopped so we want to go through
  		 * with the delete here now. If the callout
  		 * was restarted, the pending bit will be back on and
  		 * we just want to bail since the callout_reset would
  		 * return 1 and our reference would have been removed
  		 * by arpresolve() below.
  		 */
  		LLE_WUNLOCK(lle);
   		return;
   	}
  	ifp = lle->lle_tbl->llt_ifp;
  	CURVNET_SET(ifp->if_vnet);
  
  	switch (lle->ln_state) {
  	case ARP_LLINFO_REACHABLE:
  
  		/*
  		 * Expiration time is approaching.
  		 * Let's try to refresh entry if it is still
  		 * in use.
  		 *
  		 * Set r_skip_req to get feedback from
  		 * fast path. Change state and re-schedule
  		 * ourselves.
  		 */
  		LLE_REQ_LOCK(lle);
  		lle->r_skip_req = 1;
  		LLE_REQ_UNLOCK(lle);
  		lle->ln_state = ARP_LLINFO_VERIFY;
  		callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
  		LLE_WUNLOCK(lle);
  		CURVNET_RESTORE();
  		return;
  	case ARP_LLINFO_VERIFY:
  		LLE_REQ_LOCK(lle);
  		r_skip_req = lle->r_skip_req;
  		LLE_REQ_UNLOCK(lle);
  
  		if (r_skip_req == 0 && lle->la_preempt > 0) {
  			/* Entry was used, issue refresh request */
  			struct epoch_tracker et;
  			struct in_addr dst;
  
  			dst = lle->r_l3addr.addr4;
  			lle->la_preempt--;
  			callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
  			LLE_WUNLOCK(lle);
  			NET_EPOCH_ENTER(et);
  			arprequest(ifp, NULL, &dst, NULL);
  			NET_EPOCH_EXIT(et);
  			CURVNET_RESTORE();
  			return;
  		}
  		/* Nothing happened. Reschedule if not too late */
  		if (lle->la_expire > time_uptime) {
  			callout_schedule(&lle->lle_timer, hz * V_arpt_rexmit);
  			LLE_WUNLOCK(lle);
  			CURVNET_RESTORE();
  			return;
  		}
  		break;
  	case ARP_LLINFO_INCOMPLETE:
  	case ARP_LLINFO_DELETED:
  		break;
  	}
  
  	if ((lle->la_flags & LLE_DELETED) == 0) {
  		int evt;
  
  		if (lle->la_flags & LLE_VALID)
  			evt = LLENTRY_EXPIRED;
  		else
  			evt = LLENTRY_TIMEDOUT;
  		EVENTHANDLER_INVOKE(lle_event, lle, evt);
  	}
  
  	callout_stop(&lle->lle_timer);
  
  	/* XXX: LOR avoidance. We still have ref on lle. */
  	LLE_WUNLOCK(lle);
  	IF_AFDATA_LOCK(ifp);
  	LLE_WLOCK(lle);
  
  	/* Guard against race with other llentry_free(). */
  	if (lle->la_flags & LLE_LINKED) {
  		LLE_REMREF(lle);
  		lltable_unlink_entry(lle->lle_tbl, lle);
  	}
  	IF_AFDATA_UNLOCK(ifp);
  
  	size_t pkts_dropped = llentry_free(lle);
  
  	ARPSTAT_ADD(dropped, pkts_dropped);
  	ARPSTAT_INC(timeouts);
  
  	CURVNET_RESTORE();
  }
  
  /*
   * Stores link-layer header for @ifp in format suitable for if_output()
   * into buffer @buf. Resulting header length is stored in @bufsize.
   *
   * Returns 0 on success.
   */
  static int
  arp_fillheader(struct ifnet *ifp, struct arphdr *ah, int bcast, u_char *buf,
      size_t *bufsize)
  {
  	struct if_encap_req ereq;
  	int error;
  
  	bzero(buf, *bufsize);
  	bzero(&ereq, sizeof(ereq));
  	ereq.buf = buf;
  	ereq.bufsize = *bufsize;
  	ereq.rtype = IFENCAP_LL;
  	ereq.family = AF_ARP;
  	ereq.lladdr = ar_tha(ah);
  	ereq.hdata = (u_char *)ah;
  	if (bcast)
  		ereq.flags = IFENCAP_FLAG_BROADCAST;
  	error = ifp->if_requestencap(ifp, &ereq);
  	if (error == 0)
  		*bufsize = ereq.bufsize;
  
  	return (error);
  }
  
  
  /*
   * Broadcast an ARP request. Caller specifies:
   *	- arp header source ip address
   *	- arp header target ip address
   *	- arp header source ethernet address
   */
  static int
  arprequest_internal(struct ifnet *ifp, const struct in_addr *sip,
      const struct in_addr *tip, u_char *enaddr)
  {
  	struct mbuf *m;
  	struct arphdr *ah;
  	struct sockaddr sa;
  	u_char *carpaddr = NULL;
  	uint8_t linkhdr[LLE_MAX_LINKHDR];
  	size_t linkhdrsize;
  	struct route ro;
  	int error;
  
  	NET_EPOCH_ASSERT();
  
  	if (sip == NULL) {
  		/*
  		 * The caller did not supply a source address, try to find
  		 * a compatible one among those assigned to this interface.
  		 */
  		struct ifaddr *ifa;
  
  		CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
  			if (ifa->ifa_addr->sa_family != AF_INET)
  				continue;
  
  			if (ifa->ifa_carp) {
  				if ((*carp_iamatch_p)(ifa, &carpaddr) == 0)
  					continue;
  				sip = &IA_SIN(ifa)->sin_addr;
  			} else {
  				carpaddr = NULL;
  				sip = &IA_SIN(ifa)->sin_addr;
  			}
  
  			if (0 == ((sip->s_addr ^ tip->s_addr) &
  			    IA_MASKSIN(ifa)->sin_addr.s_addr))
  				break;  /* found it. */
  		}
  		if (sip == NULL) {
  			printf("%s: cannot find matching address\n", __func__);
  			return (EADDRNOTAVAIL);
  		}
  	}
  	if (enaddr == NULL)
  		enaddr = carpaddr ? carpaddr : (u_char *)IF_LLADDR(ifp);
  
  	if ((m = m_gethdr(M_NOWAIT, MT_DATA)) == NULL)
  		return (ENOMEM);
  	m->m_len = sizeof(*ah) + 2 * sizeof(struct in_addr) +
  		2 * ifp->if_addrlen;
  	m->m_pkthdr.len = m->m_len;
  	M_ALIGN(m, m->m_len);
  	ah = mtod(m, struct arphdr *);
  	bzero((caddr_t)ah, m->m_len);
  #ifdef MAC
  	mac_netinet_arp_send(ifp, m);
  #endif
  	ah->ar_pro = htons(ETHERTYPE_IP);
  	ah->ar_hln = ifp->if_addrlen;		/* hardware address length */
  	ah->ar_pln = sizeof(struct in_addr);	/* protocol address length */
  	ah->ar_op = htons(ARPOP_REQUEST);
  	bcopy(enaddr, ar_sha(ah), ah->ar_hln);
  	bcopy(sip, ar_spa(ah), ah->ar_pln);
  	bcopy(tip, ar_tpa(ah), ah->ar_pln);
  	sa.sa_family = AF_ARP;
  	sa.sa_len = 2;
  
  	/* Calculate link header for sending frame */
  	bzero(&ro, sizeof(ro));
  	linkhdrsize = sizeof(linkhdr);
  	error = arp_fillheader(ifp, ah, 1, linkhdr, &linkhdrsize);
  	if (error != 0 && error != EAFNOSUPPORT) {
  		ARP_LOG(LOG_ERR, "Failed to calculate ARP header on %s: %d\n",
  		    if_name(ifp), error);
  		return (error);
  	}
  
  	ro.ro_prepend = linkhdr;
  	ro.ro_plen = linkhdrsize;
  	ro.ro_flags = 0;
  
  	m->m_flags |= M_BCAST;
  	m_clrprotoflags(m);	/* Avoid confusing lower layers. */
  	error = (*ifp->if_output)(ifp, m, &sa, &ro);
  	ARPSTAT_INC(txrequests);
  	if (error) {
  		ARPSTAT_INC(txerrors);
  		ARP_LOG(LOG_DEBUG, "Failed to send ARP packet on %s: %d\n",
  		    if_name(ifp), error);
  	}
  	return (error);
  }
  
  void
  arprequest(struct ifnet *ifp, const struct in_addr *sip,
      const struct in_addr *tip, u_char *enaddr)
  {
  
  	(void) arprequest_internal(ifp, sip, tip, enaddr);
  }
  
  /*
   * Resolve an IP address into an ethernet address - heavy version.
   * Used internally by arpresolve().
   * We have already checked that we can't use an existing lle without
   * modification so we have to acquire an LLE_EXCLUSIVE lle lock.
   *
   * On success, desten and pflags are filled in and the function returns 0;
   * If the packet must be held pending resolution, we return EWOULDBLOCK
   * On other errors, we return the corresponding error code.
   * Note that m_freem() handles NULL.
   */
  static int
  arpresolve_full(struct ifnet *ifp, int is_gw, int flags, struct mbuf *m,
  	const struct sockaddr *dst, u_char *desten, uint32_t *pflags,
  	struct llentry **plle)
  {
  	struct llentry *la = NULL, *la_tmp;
  	struct mbuf *curr = NULL;
  	struct mbuf *next = NULL;
  	int error, renew;
  	char *lladdr;
  	int ll_len;
  
  	NET_EPOCH_ASSERT();
  
  	if (pflags != NULL)
  		*pflags = 0;
  	if (plle != NULL)
  		*plle = NULL;
  
  	if ((flags & LLE_CREATE) == 0)
  		la = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
  	if (la == NULL && (ifp->if_flags & (IFF_NOARP | IFF_STATICARP)) == 0) {
  		la = lltable_alloc_entry(LLTABLE(ifp), 0, dst);
  		if (la == NULL) {
  			char addrbuf[INET_ADDRSTRLEN];
  
  			log(LOG_DEBUG,
  			    "arpresolve: can't allocate llinfo for %s on %s\n",
  			    inet_ntoa_r(SIN(dst)->sin_addr, addrbuf),
  			    if_name(ifp));
  			m_freem(m);
  			return (EINVAL);
  		}
  
  		IF_AFDATA_WLOCK(ifp);
  		LLE_WLOCK(la);
  		la_tmp = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
  		/* Prefer ANY existing lle over newly-created one */
  		if (la_tmp == NULL)
  			lltable_link_entry(LLTABLE(ifp), la);
  		IF_AFDATA_WUNLOCK(ifp);
  		if (la_tmp != NULL) {
  			lltable_free_entry(LLTABLE(ifp), la);
  			la = la_tmp;
  		}
  	}
  	if (la == NULL) {
  		m_freem(m);
  		return (EINVAL);
  	}
  
  	if ((la->la_flags & LLE_VALID) &&
  	    ((la->la_flags & LLE_STATIC) || la->la_expire > time_uptime)) {
  		if (flags & LLE_ADDRONLY) {
  			lladdr = la->ll_addr;
  			ll_len = ifp->if_addrlen;
  		} else {
  			lladdr = la->r_linkdata;
  			ll_len = la->r_hdrlen;
  		}
  		bcopy(lladdr, desten, ll_len);
  
  		/* Notify LLE code that the entry was used by datapath */
  		llentry_mark_used(la);
  		if (pflags != NULL)
  			*pflags = la->la_flags & (LLE_VALID|LLE_IFADDR);
  		if (plle) {
  			LLE_ADDREF(la);
  			*plle = la;
  		}
  		LLE_WUNLOCK(la);
  		return (0);
  	}
  
  	renew = (la->la_asked == 0 || la->la_expire != time_uptime);
  	/*
  	 * There is an arptab entry, but no ethernet address
  	 * response yet.  Add the mbuf to the list, dropping
  	 * the oldest packet if we have exceeded the system
  	 * setting.
  	 */
  	if (m != NULL) {
  		if (la->la_numheld >= V_arp_maxhold) {
  			if (la->la_hold != NULL) {
  				next = la->la_hold->m_nextpkt;
  				m_freem(la->la_hold);
  				la->la_hold = next;
  				la->la_numheld--;
  				ARPSTAT_INC(dropped);
  			}
  		}
  		if (la->la_hold != NULL) {
  			curr = la->la_hold;
  			while (curr->m_nextpkt != NULL)
  				curr = curr->m_nextpkt;
  			curr->m_nextpkt = m;
  		} else
  			la->la_hold = m;
  		la->la_numheld++;
  	}
  	/*
  	 * Return EWOULDBLOCK if we have tried less than arp_maxtries. It
  	 * will be masked by ether_output(). Return EHOSTDOWN/EHOSTUNREACH
  	 * if we have already sent arp_maxtries ARP requests. Retransmit the
  	 * ARP request, but not faster than one request per second.
  	 */
  	if (la->la_asked < V_arp_maxtries)
  		error = EWOULDBLOCK;	/* First request. */
  	else
  		error = is_gw != 0 ? EHOSTUNREACH : EHOSTDOWN;
  
  	if (renew) {
  		int canceled, e;
  
  		LLE_ADDREF(la);
  		la->la_expire = time_uptime;
  		canceled = callout_reset(&la->lle_timer, hz * V_arpt_down,
  		    arptimer, la);
  		if (canceled)
  			LLE_REMREF(la);
  		la->la_asked++;
  		LLE_WUNLOCK(la);
  		e = arprequest_internal(ifp, NULL, &SIN(dst)->sin_addr, NULL);
  		/*
  		 * Only overwrite 'error' in case of error; in case of success
  		 * the proper return value was already set above.
  		 */
  		if (e != 0)
  			return (e);
  		return (error);
  	}
  
  	LLE_WUNLOCK(la);
  	return (error);
  }
  
  /*
   * Lookups link header based on an IP address.
   * On input:
   *    ifp is the interface we use
   *    is_gw != 0 if @dst represents gateway to some destination
   *    m is the mbuf. May be NULL if we don't have a packet.
   *    dst is the next hop,
   *    desten is the storage to put LL header.
   *    flags returns subset of lle flags: LLE_VALID | LLE_IFADDR
   *
   * On success, full/partial link header and flags are filled in and
   * the function returns 0.
   * If the packet must be held pending resolution, we return EWOULDBLOCK
   * On other errors, we return the corresponding error code.
   * Note that m_freem() handles NULL.
   */
  int
  arpresolve(struct ifnet *ifp, int is_gw, struct mbuf *m,
  	const struct sockaddr *dst, u_char *desten, uint32_t *pflags,
  	struct llentry **plle)
  {
  	struct llentry *la = NULL;
  
  	NET_EPOCH_ASSERT();
  
  	if (pflags != NULL)
  		*pflags = 0;
  	if (plle != NULL)
  		*plle = NULL;
  
  	if (m != NULL) {
  		if (m->m_flags & M_BCAST) {
  			/* broadcast */
  			(void)memcpy(desten,
  			    ifp->if_broadcastaddr, ifp->if_addrlen);
  			return (0);
  		}
  		if (m->m_flags & M_MCAST) {
  			/* multicast */
  			ETHER_MAP_IP_MULTICAST(&SIN(dst)->sin_addr, desten);
  			return (0);
  		}
  	}
  
  	la = lla_lookup(LLTABLE(ifp), plle ? LLE_EXCLUSIVE : LLE_UNLOCKED, dst);
  	if (la != NULL && (la->r_flags & RLLE_VALID) != 0) {
  		/* Entry found, let's copy lle info */
  		bcopy(la->r_linkdata, desten, la->r_hdrlen);
  		if (pflags != NULL)
  			*pflags = LLE_VALID | (la->r_flags & RLLE_IFADDR);
  		/* Notify the LLE handling code that the entry was used. */
  		llentry_mark_used(la);
  		if (plle) {
  			LLE_ADDREF(la);
  			*plle = la;
  			LLE_WUNLOCK(la);
  		}
  		return (0);
  	}
  	if (plle && la)
  		LLE_WUNLOCK(la);
  
  	return (arpresolve_full(ifp, is_gw, la == NULL ? LLE_CREATE : 0, m, dst,
  	    desten, pflags, plle));
  }
  
  /*
   * Common length and type checks are done here,
   * then the protocol-specific routine is called.
   */
  static void
  arpintr(struct mbuf *m)
  {
  	struct arphdr *ar;
  	struct ifnet *ifp;
  	char *layer;
  	int hlen;
  
  	ifp = m->m_pkthdr.rcvif;
  
  	if (m->m_len < sizeof(struct arphdr) &&
  	    ((m = m_pullup(m, sizeof(struct arphdr))) == NULL)) {
  		ARP_LOG(LOG_NOTICE, "packet with short header received on %s\n",
  		    if_name(ifp));
  		return;
  	}
  	ar = mtod(m, struct arphdr *);
  
  	/* Check if length is sufficient */
  	if (m->m_len <  arphdr_len(ar)) {
  		m = m_pullup(m, arphdr_len(ar));
  		if (m == NULL) {
  			ARP_LOG(LOG_NOTICE, "short packet received on %s\n",
  			    if_name(ifp));
  			return;
  		}
  		ar = mtod(m, struct arphdr *);
  	}
  
  	hlen = 0;
  	layer = "";
  	switch (ntohs(ar->ar_hrd)) {
  	case ARPHRD_ETHER:
  		hlen = ETHER_ADDR_LEN; /* RFC 826 */
  		layer = "ethernet";
  		break;
  	case ARPHRD_INFINIBAND:
  		hlen = 20;	/* RFC 4391, INFINIBAND_ALEN */
  		layer = "infiniband";
  		break;
  	case ARPHRD_IEEE1394:
  		hlen = 0; /* SHALL be 16 */ /* RFC 2734 */
  		layer = "firewire";
  
  		/*
  		 * Restrict too long hardware addresses.
  		 * Currently we are capable of handling 20-byte
  		 * addresses ( sizeof(lle->ll_addr) )
  		 */
  		if (ar->ar_hln >= 20)
  			hlen = 16;
  		break;
  	default:
  		ARP_LOG(LOG_NOTICE,
  		    "packet with unknown hardware format 0x%02d received on "
  		    "%s\n", ntohs(ar->ar_hrd), if_name(ifp));
  		m_freem(m);
  		return;
  	}
  
  	if (hlen != 0 && hlen != ar->ar_hln) {
  		ARP_LOG(LOG_NOTICE,
  		    "packet with invalid %s address length %d received on %s\n",
  		    layer, ar->ar_hln, if_name(ifp));
  		m_freem(m);
  		return;
  	}
  
  	ARPSTAT_INC(received);
  	switch (ntohs(ar->ar_pro)) {
  #ifdef INET
  	case ETHERTYPE_IP:
  		in_arpinput(m);
  		return;
  #endif
  	}
  	m_freem(m);
  }
  
  #ifdef INET
  /*
   * ARP for Internet protocols on 10 Mb/s Ethernet.
   * Algorithm is that given in RFC 826.
   * In addition, a sanity check is performed on the sender
   * protocol address, to catch impersonators.
   * We no longer handle negotiations for use of trailer protocol:
   * Formerly, ARP replied for protocol type ETHERTYPE_TRAIL sent
   * along with IP replies if we wanted trailers sent to us,
   * and also sent them in response to IP replies.
   * This allowed either end to announce the desire to receive
   * trailer packets.
   * We no longer reply to requests for ETHERTYPE_TRAIL protocol either,
   * but formerly didn't normally send requests.
   */
  static int log_arp_wrong_iface = 1;
  static int log_arp_movements = 1;
  static int log_arp_permanent_modify = 1;
  static int allow_multicast = 0;
  
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_wrong_iface, CTLFLAG_RW,
  	&log_arp_wrong_iface, 0,
  	"log arp packets arriving on the wrong interface");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_movements, CTLFLAG_RW,
  	&log_arp_movements, 0,
  	"log arp replies from MACs different than the one in the cache");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_permanent_modify, CTLFLAG_RW,
  	&log_arp_permanent_modify, 0,
  	"log arp replies from MACs different than the one in the permanent arp entry");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, allow_multicast, CTLFLAG_RW,
  	&allow_multicast, 0, "accept multicast addresses");
  
  static void
  in_arpinput(struct mbuf *m)
  {
  	struct rm_priotracker in_ifa_tracker;
  	struct arphdr *ah;
  	struct ifnet *ifp = m->m_pkthdr.rcvif;
  	struct llentry *la = NULL, *la_tmp;
  	struct ifaddr *ifa;
  	struct in_ifaddr *ia;
  	struct sockaddr sa;
  	struct in_addr isaddr, itaddr, myaddr;
  	u_int8_t *enaddr = NULL;
  	int op;
  	int bridged = 0, is_bridge = 0;
  	int carped;
  	struct sockaddr_in sin;
  	struct sockaddr *dst;
  	struct nhop4_basic nh4;
  	uint8_t linkhdr[LLE_MAX_LINKHDR];
  	struct route ro;
  	size_t linkhdrsize;
  	int lladdr_off;
  	int error;
  	char addrbuf[INET_ADDRSTRLEN];
  
  	NET_EPOCH_ASSERT();
  
  	sin.sin_len = sizeof(struct sockaddr_in);
  	sin.sin_family = AF_INET;
  	sin.sin_addr.s_addr = 0;
  
  	if (ifp->if_bridge)
  		bridged = 1;
  	if (ifp->if_type == IFT_BRIDGE)
  		is_bridge = 1;
  
  	/*
  	 * We already have checked that mbuf contains enough contiguous data
  	 * to hold entire arp message according to the arp header.
  	 */
  	ah = mtod(m, struct arphdr *);
  
  	/*
  	 * ARP is only for IPv4 so we can reject packets with
  	 * a protocol length not equal to an IPv4 address.
  	 */
  	if (ah->ar_pln != sizeof(struct in_addr)) {
  		ARP_LOG(LOG_NOTICE, "requested protocol length != %zu\n",
  		    sizeof(struct in_addr));
  		goto drop;
  	}
  
  	if (allow_multicast == 0 && ETHER_IS_MULTICAST(ar_sha(ah))) {
  		ARP_LOG(LOG_NOTICE, "%*D is multicast\n",
  		    ifp->if_addrlen, (u_char *)ar_sha(ah), ":");
  		goto drop;
  	}
  
  	op = ntohs(ah->ar_op);
  	(void)memcpy(&isaddr, ar_spa(ah), sizeof (isaddr));
  	(void)memcpy(&itaddr, ar_tpa(ah), sizeof (itaddr));
  
  	if (op == ARPOP_REPLY)
  		ARPSTAT_INC(rxreplies);
  
  	/*
  	 * For a bridge, we want to check the address irrespective
  	 * of the receive interface. (This will change slightly
  	 * when we have clusters of interfaces).
  	 */
  	IN_IFADDR_RLOCK(&in_ifa_tracker);
  	LIST_FOREACH(ia, INADDR_HASH(itaddr.s_addr), ia_hash) {
  		if (((bridged && ia->ia_ifp->if_bridge == ifp->if_bridge) ||
  		    ia->ia_ifp == ifp) &&
  		    itaddr.s_addr == ia->ia_addr.sin_addr.s_addr &&
  		    (ia->ia_ifa.ifa_carp == NULL ||
  		    (*carp_iamatch_p)(&ia->ia_ifa, &enaddr))) {
  			ifa_ref(&ia->ia_ifa);
  			IN_IFADDR_RUNLOCK(&in_ifa_tracker);
  			goto match;
  		}
  	}
  	LIST_FOREACH(ia, INADDR_HASH(isaddr.s_addr), ia_hash)
  		if (((bridged && ia->ia_ifp->if_bridge == ifp->if_bridge) ||
  		    ia->ia_ifp == ifp) &&
  		    isaddr.s_addr == ia->ia_addr.sin_addr.s_addr) {
  			ifa_ref(&ia->ia_ifa);
  			IN_IFADDR_RUNLOCK(&in_ifa_tracker);
  			goto match;
  		}
  
  #define BDG_MEMBER_MATCHES_ARP(addr, ifp, ia)				\
    (ia->ia_ifp->if_bridge == ifp->if_softc &&				\
    !bcmp(IF_LLADDR(ia->ia_ifp), IF_LLADDR(ifp), ifp->if_addrlen) &&	\
    addr == ia->ia_addr.sin_addr.s_addr)
  	/*
  	 * Check the case when bridge shares its MAC address with
  	 * some of its children, so packets are claimed by bridge
  	 * itself (bridge_input() does it first), but they are really
  	 * meant to be destined to the bridge member.
  	 */
  	if (is_bridge) {
  		LIST_FOREACH(ia, INADDR_HASH(itaddr.s_addr), ia_hash) {
  			if (BDG_MEMBER_MATCHES_ARP(itaddr.s_addr, ifp, ia)) {
  				ifa_ref(&ia->ia_ifa);
  				ifp = ia->ia_ifp;
  				IN_IFADDR_RUNLOCK(&in_ifa_tracker);
  				goto match;
  			}
  		}
  	}
  #undef BDG_MEMBER_MATCHES_ARP
  	IN_IFADDR_RUNLOCK(&in_ifa_tracker);
  
  	/*
  	 * No match, use the first inet address on the receive interface
  	 * as a dummy address for the rest of the function.
  	 */
  	CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link)
  		if (ifa->ifa_addr->sa_family == AF_INET &&
  		    (ifa->ifa_carp == NULL ||
  		    (*carp_iamatch_p)(ifa, &enaddr))) {
  			ia = ifatoia(ifa);
  			ifa_ref(ifa);
  			goto match;
  		}
  
  	/*
  	 * If bridging, fall back to using any inet address.
  	 */
  	IN_IFADDR_RLOCK(&in_ifa_tracker);
  	if (!bridged || (ia = CK_STAILQ_FIRST(&V_in_ifaddrhead)) == NULL) {
  		IN_IFADDR_RUNLOCK(&in_ifa_tracker);
  		goto drop;
  	}
  	ifa_ref(&ia->ia_ifa);
  	IN_IFADDR_RUNLOCK(&in_ifa_tracker);
  match:
  	if (!enaddr)
  		enaddr = (u_int8_t *)IF_LLADDR(ifp);
  	carped = (ia->ia_ifa.ifa_carp != NULL);
  	myaddr = ia->ia_addr.sin_addr;
  	ifa_free(&ia->ia_ifa);
  	if (!bcmp(ar_sha(ah), enaddr, ifp->if_addrlen))
  		goto drop;	/* it's from me, ignore it. */
  	if (!bcmp(ar_sha(ah), ifp->if_broadcastaddr, ifp->if_addrlen)) {
  		ARP_LOG(LOG_NOTICE, "link address is broadcast for IP address "
  		    "%s!\n", inet_ntoa_r(isaddr, addrbuf));
  		goto drop;
  	}
  
  	if (ifp->if_addrlen != ah->ar_hln) {
  		ARP_LOG(LOG_WARNING, "from %*D: addr len: new %d, "
  		    "i/f %d (ignored)\n", ifp->if_addrlen,
  		    (u_char *) ar_sha(ah), ":", ah->ar_hln,
  		    ifp->if_addrlen);
  		goto drop;
  	}
  
  	/*
  	 * Warn if another host is using the same IP address, but only if the
  	 * IP address isn't 0.0.0.0, which is used for DHCP only, in which
  	 * case we suppress the warning to avoid false positive complaints of
  	 * potential misconfiguration.
  	 */
  	if (!bridged && !carped && isaddr.s_addr == myaddr.s_addr &&
  	    myaddr.s_addr != 0) {
  		ARP_LOG(LOG_ERR, "%*D is using my IP address %s on %s!\n",
  		   ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
  		   inet_ntoa_r(isaddr, addrbuf), ifp->if_xname);
  		itaddr = myaddr;
  		ARPSTAT_INC(dupips);
  		goto reply;
  	}
  	if (ifp->if_flags & IFF_STATICARP)
  		goto reply;
  
  	bzero(&sin, sizeof(sin));
  	sin.sin_len = sizeof(struct sockaddr_in);
  	sin.sin_family = AF_INET;
  	sin.sin_addr = isaddr;
  	dst = (struct sockaddr *)&sin;
  	la = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
  	if (la != NULL)
  		arp_check_update_lle(ah, isaddr, ifp, bridged, la);
  	else if (itaddr.s_addr == myaddr.s_addr) {
  		/*
  		 * Request/reply to our address, but no lle exists yet.
  		 * Calculate full link prepend to use in lle.
  		 */
  		linkhdrsize = sizeof(linkhdr);
  		if (lltable_calc_llheader(ifp, AF_INET, ar_sha(ah), linkhdr,
  		    &linkhdrsize, &lladdr_off) != 0)
  			goto reply;
  
  		/* Allocate new entry */
  		la = lltable_alloc_entry(LLTABLE(ifp), 0, dst);
  		if (la == NULL) {
  
  			/*
  			 * lle creation may fail if source address belongs
  			 * to non-directly connected subnet. However, we
  			 * will try to answer the request instead of dropping
  			 * frame.
  			 */
  			goto reply;
  		}
  		lltable_set_entry_addr(ifp, la, linkhdr, linkhdrsize,
  		    lladdr_off);
  
  		IF_AFDATA_WLOCK(ifp);
  		LLE_WLOCK(la);
  		la_tmp = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
  
  		/*
  		 * Check if lle still does not exists.
  		 * If it does, that means that we either
  		 * 1) have configured it explicitly, via
  		 * 1a) 'arp -s' static entry or
  		 * 1b) interface address static record
  		 * or
  		 * 2) it was the result of sending first packet to-host
  		 * or
  		 * 3) it was another arp reply packet we handled in
  		 * different thread.
  		 *
  		 * In all cases except 3) we definitely need to prefer
  		 * existing lle. For the sake of simplicity, prefer any
  		 * existing lle over newly-create one.
  		 */
  		if (la_tmp == NULL)
  			lltable_link_entry(LLTABLE(ifp), la);
  		IF_AFDATA_WUNLOCK(ifp);
  
  		if (la_tmp == NULL) {
  			arp_mark_lle_reachable(la);
  			LLE_WUNLOCK(la);
  		} else {
  			/* Free newly-create entry and handle packet */
  			lltable_free_entry(LLTABLE(ifp), la);
  			la = la_tmp;
  			la_tmp = NULL;
  			arp_check_update_lle(ah, isaddr, ifp, bridged, la);
  			/* arp_check_update_lle() returns @la unlocked */
  		}
  		la = NULL;
  	}
  reply:
  	if (op != ARPOP_REQUEST)
  		goto drop;
  	ARPSTAT_INC(rxrequests);
  
  	if (itaddr.s_addr == myaddr.s_addr) {
  		/* Shortcut.. the receiving interface is the target. */
  		(void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
  		(void)memcpy(ar_sha(ah), enaddr, ah->ar_hln);
  	} else {
  		struct llentry *lle = NULL;
  
  		sin.sin_addr = itaddr;
  		lle = lla_lookup(LLTABLE(ifp), 0, (struct sockaddr *)&sin);
  
  		if ((lle != NULL) && (lle->la_flags & LLE_PUB)) {
  			(void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
  			(void)memcpy(ar_sha(ah), lle->ll_addr, ah->ar_hln);
  			LLE_RUNLOCK(lle);
  		} else {
  
  			if (lle != NULL)
  				LLE_RUNLOCK(lle);
  
  			if (!V_arp_proxyall)
  				goto drop;
  
  			/* XXX MRT use table 0 for arp reply  */
  			if (fib4_lookup_nh_basic(0, itaddr, 0, 0, &nh4) != 0)
  				goto drop;
  
  			/*
  			 * Don't send proxies for nodes on the same interface
  			 * as this one came out of, or we'll get into a fight
  			 * over who claims what Ether address.
  			 */
  			if (nh4.nh_ifp == ifp)
  				goto drop;
  
  			(void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
  			(void)memcpy(ar_sha(ah), enaddr, ah->ar_hln);
  
  			/*
  			 * Also check that the node which sent the ARP packet
  			 * is on the interface we expect it to be on. This
  			 * avoids ARP chaos if an interface is connected to the
  			 * wrong network.
  			 */
  
  			/* XXX MRT use table 0 for arp checks */
  			if (fib4_lookup_nh_basic(0, isaddr, 0, 0, &nh4) != 0)
  				goto drop;
  			if (nh4.nh_ifp != ifp) {
  				ARP_LOG(LOG_INFO, "proxy: ignoring request"
  				    " from %s via %s\n",
  				    inet_ntoa_r(isaddr, addrbuf),
  				    ifp->if_xname);
  				goto drop;
  			}
  
  #ifdef DEBUG_PROXY
  			printf("arp: proxying for %s\n",
  			    inet_ntoa_r(itaddr, addrbuf));
  #endif
  		}
  	}
  
  	if (itaddr.s_addr == myaddr.s_addr &&
  	    IN_LINKLOCAL(ntohl(itaddr.s_addr))) {
  		/* RFC 3927 link-local IPv4; always reply by broadcast. */
  #ifdef DEBUG_LINKLOCAL
  		printf("arp: sending reply for link-local addr %s\n",
  		    inet_ntoa_r(itaddr, addrbuf));
  #endif
  		m->m_flags |= M_BCAST;
  		m->m_flags &= ~M_MCAST;
  	} else {
  		/* default behaviour; never reply by broadcast. */
  		m->m_flags &= ~(M_BCAST|M_MCAST);
  	}
  	(void)memcpy(ar_tpa(ah), ar_spa(ah), ah->ar_pln);
  	(void)memcpy(ar_spa(ah), &itaddr, ah->ar_pln);
  	ah->ar_op = htons(ARPOP_REPLY);
  	ah->ar_pro = htons(ETHERTYPE_IP); /* let's be sure! */
  	m->m_len = sizeof(*ah) + (2 * ah->ar_pln) + (2 * ah->ar_hln);
  	m->m_pkthdr.len = m->m_len;
  	m->m_pkthdr.rcvif = NULL;
  	sa.sa_family = AF_ARP;
  	sa.sa_len = 2;
  
  	/* Calculate link header for sending frame */
  	bzero(&ro, sizeof(ro));
  	linkhdrsize = sizeof(linkhdr);
  	error = arp_fillheader(ifp, ah, 0, linkhdr, &linkhdrsize);
  
  	/*
  	 * arp_fillheader() may fail due to lack of support inside encap request
  	 * routing. This is not necessary an error, AF_ARP can/should be handled
  	 * by if_output().
  	 */
  	if (error != 0 && error != EAFNOSUPPORT) {
  		ARP_LOG(LOG_ERR, "Failed to calculate ARP header on %s: %d\n",
  		    if_name(ifp), error);
  		return;
  	}
  
  	ro.ro_prepend = linkhdr;
  	ro.ro_plen = linkhdrsize;
  	ro.ro_flags = 0;
  
  	m_clrprotoflags(m);	/* Avoid confusing lower layers. */
  	(*ifp->if_output)(ifp, m, &sa, &ro);
  	ARPSTAT_INC(txreplies);
  	return;
  
  drop:
  	m_freem(m);
  }
  #endif
  
  /*
   * Checks received arp data against existing @la.
   * Updates lle state/performs notification if necessary.
   */
  static void
  arp_check_update_lle(struct arphdr *ah, struct in_addr isaddr, struct ifnet *ifp,
      int bridged, struct llentry *la)
  {
  	struct sockaddr sa;
  	struct mbuf *m_hold, *m_hold_next;
  	uint8_t linkhdr[LLE_MAX_LINKHDR];
  	size_t linkhdrsize;
  	int lladdr_off;
  	char addrbuf[INET_ADDRSTRLEN];
  
  	LLE_WLOCK_ASSERT(la);
  
  	/* the following is not an error when doing bridging */
  	if (!bridged && la->lle_tbl->llt_ifp != ifp) {
  		if (log_arp_wrong_iface)
  			ARP_LOG(LOG_WARNING, "%s is on %s "
  			    "but got reply from %*D on %s\n",
  			    inet_ntoa_r(isaddr, addrbuf),
  			    la->lle_tbl->llt_ifp->if_xname,
  			    ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
  			    ifp->if_xname);
  		LLE_WUNLOCK(la);
  		return;
  	}
  	if ((la->la_flags & LLE_VALID) &&
  	    bcmp(ar_sha(ah), la->ll_addr, ifp->if_addrlen)) {
  		if (la->la_flags & LLE_STATIC) {
  			LLE_WUNLOCK(la);
  			if (log_arp_permanent_modify)
  				ARP_LOG(LOG_ERR,
  				    "%*D attempts to modify "
  				    "permanent entry for %s on %s\n",
  				    ifp->if_addrlen,
  				    (u_char *)ar_sha(ah), ":",
  				    inet_ntoa_r(isaddr, addrbuf),
  				    ifp->if_xname);
  			return;
  		}
  		if (log_arp_movements) {
  			ARP_LOG(LOG_INFO, "%s moved from %*D "
  			    "to %*D on %s\n",
  			    inet_ntoa_r(isaddr, addrbuf),
  			    ifp->if_addrlen,
  			    (u_char *)la->ll_addr, ":",
  			    ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
  			    ifp->if_xname);
  		}
  	}
  
  	/* Calculate full link prepend to use in lle */
  	linkhdrsize = sizeof(linkhdr);
  	if (lltable_calc_llheader(ifp, AF_INET, ar_sha(ah), linkhdr,
  	    &linkhdrsize, &lladdr_off) != 0)
  		return;
  
  	/* Check if something has changed */
  	if (memcmp(la->r_linkdata, linkhdr, linkhdrsize) != 0 ||
  	    (la->la_flags & LLE_VALID) == 0) {
  		/* Try to perform LLE update */
  		if (lltable_try_set_entry_addr(ifp, la, linkhdr, linkhdrsize,
  		    lladdr_off) == 0)
  			return;
  
  		/* Clear fast path feedback request if set */
  		la->r_skip_req = 0;
  	}
  
  	arp_mark_lle_reachable(la);
  
  	/*
  	 * The packets are all freed within the call to the output
  	 * routine.
  	 *
  	 * NB: The lock MUST be released before the call to the
  	 * output routine.
  	 */
  	if (la->la_hold != NULL) {
  		m_hold = la->la_hold;
  		la->la_hold = NULL;
  		la->la_numheld = 0;
  		lltable_fill_sa_entry(la, &sa);
  		LLE_WUNLOCK(la);
  		for (; m_hold != NULL; m_hold = m_hold_next) {
  			m_hold_next = m_hold->m_nextpkt;
  			m_hold->m_nextpkt = NULL;
  			/* Avoid confusing lower layers. */
  			m_clrprotoflags(m_hold);
  			(*ifp->if_output)(ifp, m_hold, &sa, NULL);
  		}
  	} else
  		LLE_WUNLOCK(la);
  }
  
  static void
  arp_mark_lle_reachable(struct llentry *la)
  {
  	int canceled, wtime;
  
  	LLE_WLOCK_ASSERT(la);
  
  	la->ln_state = ARP_LLINFO_REACHABLE;
  	EVENTHANDLER_INVOKE(lle_event, la, LLENTRY_RESOLVED);
  
  	if (!(la->la_flags & LLE_STATIC)) {
  		LLE_ADDREF(la);
  		la->la_expire = time_uptime + V_arpt_keep;
  		wtime = V_arpt_keep - V_arp_maxtries * V_arpt_rexmit;
  		if (wtime < 0)
  			wtime = V_arpt_keep;
  		canceled = callout_reset(&la->lle_timer,
  		    hz * wtime, arptimer, la);
  		if (canceled)
  			LLE_REMREF(la);
  	}
  	la->la_asked = 0;
  	la->la_preempt = V_arp_maxtries;
  }
  
  /*
   * Add permanent link-layer record for given interface address.
   */
  static __noinline void
  arp_add_ifa_lle(struct ifnet *ifp, const struct sockaddr *dst)
  {
  	struct llentry *lle, *lle_tmp;
  
  	/*
  	 * Interface address LLE record is considered static
  	 * because kernel code relies on LLE_STATIC flag to check
  	 * if these entries can be rewriten by arp updates.
  	 */
  	lle = lltable_alloc_entry(LLTABLE(ifp), LLE_IFADDR | LLE_STATIC, dst);
  	if (lle == NULL) {
  		log(LOG_INFO, "arp_ifinit: cannot create arp "
  		    "entry for interface address\n");
  		return;
  	}
  
  	IF_AFDATA_WLOCK(ifp);
  	LLE_WLOCK(lle);
  	/* Unlink any entry if exists */
  	lle_tmp = lla_lookup(LLTABLE(ifp), LLE_EXCLUSIVE, dst);
  	if (lle_tmp != NULL)
  		lltable_unlink_entry(LLTABLE(ifp), lle_tmp);
  
  	lltable_link_entry(LLTABLE(ifp), lle);
  	IF_AFDATA_WUNLOCK(ifp);
  
  	if (lle_tmp != NULL)
  		EVENTHANDLER_INVOKE(lle_event, lle_tmp, LLENTRY_EXPIRED);
  
  	EVENTHANDLER_INVOKE(lle_event, lle, LLENTRY_RESOLVED);
  	LLE_WUNLOCK(lle);
  	if (lle_tmp != NULL)
  		lltable_free_entry(LLTABLE(ifp), lle_tmp);
  }
  
  /*
   * Handle the garp_rexmit_count. Like sysctl_handle_int(), but limits the range
   * of valid values.
   */
  static int
  sysctl_garp_rexmit(SYSCTL_HANDLER_ARGS)
  {
  	int error;
  	int rexmit_count = *(int *)arg1;
  
  	error = sysctl_handle_int(oidp, &rexmit_count, 0, req);
  
  	/* Enforce limits on any new value that may have been set. */
  	if (!error && req->newptr) {
  		/* A new value was set. */
  		if (rexmit_count < 0) {
  			rexmit_count = 0;
  		} else if (rexmit_count > MAX_GARP_RETRANSMITS) {
  			rexmit_count = MAX_GARP_RETRANSMITS;
  		}
  		*(int *)arg1 = rexmit_count;
  	}
  
  	return (error);
  }
  
  /*
   * Retransmit a Gratuitous ARP (GARP) and, if necessary, schedule a callout to
   * retransmit it again. A pending callout owns a reference to the ifa.
   */
  static void
  garp_rexmit(void *arg)
  {
  	struct in_ifaddr *ia = arg;
  
  	if (callout_pending(&ia->ia_garp_timer) ||
  	    !callout_active(&ia->ia_garp_timer)) {
  		IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);
  		ifa_free(&ia->ia_ifa);
  		return;
  	}
  
  	CURVNET_SET(ia->ia_ifa.ifa_ifp->if_vnet);
  
  	/*
  	 * Drop lock while the ARP request is generated.
  	 */
  	IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);
  
  	arprequest(ia->ia_ifa.ifa_ifp, &IA_SIN(ia)->sin_addr,
  	    &IA_SIN(ia)->sin_addr, IF_LLADDR(ia->ia_ifa.ifa_ifp));
  
  	/*
  	 * Increment the count of retransmissions. If the count has reached the
  	 * maximum value, stop sending the GARP packets. Otherwise, schedule
  	 * the callout to retransmit another GARP packet.
  	 */
  	++ia->ia_garp_count;
  	if (ia->ia_garp_count >= garp_rexmit_count) {
  		ifa_free(&ia->ia_ifa);
  	} else {
  		int rescheduled;
  		IF_ADDR_WLOCK(ia->ia_ifa.ifa_ifp);
  		rescheduled = callout_reset(&ia->ia_garp_timer,
  		    (1 << ia->ia_garp_count) * hz,
  		    garp_rexmit, ia);
  		IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);
  		if (rescheduled) {
  			ifa_free(&ia->ia_ifa);
  		}
  	}
  
  	CURVNET_RESTORE();
  }
  
  /*
   * Start the GARP retransmit timer.
   *
   * A single GARP is always transmitted when an IPv4 address is added
   * to an interface and that is usually sufficient. However, in some
   * circumstances, such as when a shared address is passed between
   * cluster nodes, this single GARP may occasionally be dropped or
   * lost. This can lead to neighbors on the network link working with a
   * stale ARP cache and sending packets destined for that address to
   * the node that previously owned the address, which may not respond.
   *
   * To avoid this situation, GARP retransmits can be enabled by setting
   * the net.link.ether.inet.garp_rexmit_count sysctl to a value greater
   * than zero. The setting represents the maximum number of
   * retransmissions. The interval between retransmissions is calculated
   * using an exponential backoff algorithm, doubling each time, so the
   * retransmission intervals are: {1, 2, 4, 8, 16, ...} (seconds).
   */
  static void
  garp_timer_start(struct ifaddr *ifa)
  {
  	struct in_ifaddr *ia = (struct in_ifaddr *) ifa;
  
  	IF_ADDR_WLOCK(ia->ia_ifa.ifa_ifp);
  	ia->ia_garp_count = 0;
  	if (callout_reset(&ia->ia_garp_timer, (1 << ia->ia_garp_count) * hz,
  	    garp_rexmit, ia) == 0) {
  		ifa_ref(ifa);
  	}
  	IF_ADDR_WUNLOCK(ia->ia_ifa.ifa_ifp);
  }
  
  void
  arp_ifinit(struct ifnet *ifp, struct ifaddr *ifa)
  {
  	struct epoch_tracker et;
  	const struct sockaddr_in *dst_in;
  	const struct sockaddr *dst;
  
  	if (ifa->ifa_carp != NULL)
  		return;
  
  	dst = ifa->ifa_addr;
  	dst_in = (const struct sockaddr_in *)dst;
  
  	if (ntohl(dst_in->sin_addr.s_addr) == INADDR_ANY)
  		return;
  	NET_EPOCH_ENTER(et);
  	arp_announce_ifaddr(ifp, dst_in->sin_addr, IF_LLADDR(ifp));
  	NET_EPOCH_EXIT(et);
  	if (garp_rexmit_count > 0) {
  		garp_timer_start(ifa);
  	}
  
  	arp_add_ifa_lle(ifp, dst);
  }
  
  void
  arp_announce_ifaddr(struct ifnet *ifp, struct in_addr addr, u_char *enaddr)
  {
  
  	if (ntohl(addr.s_addr) != INADDR_ANY)
  		arprequest(ifp, &addr, &addr, enaddr);
  }
  
  /*
   * Sends gratuitous ARPs for each ifaddr to notify other
   * nodes about the address change.
   */
  static __noinline void
  arp_handle_ifllchange(struct ifnet *ifp)
  {
  	struct ifaddr *ifa;
  
  	CK_STAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
  		if (ifa->ifa_addr->sa_family == AF_INET)
  			arp_ifinit(ifp, ifa);
  	}
  }
  
  /*
   * A handler for interface link layer address change event.
   */
  static void
  arp_iflladdr(void *arg __unused, struct ifnet *ifp)
  {
  
  	lltable_update_ifaddr(LLTABLE(ifp));
  
  	if ((ifp->if_flags & IFF_UP) != 0)
  		arp_handle_ifllchange(ifp);
  }
  
  static void
  vnet_arp_init(void)
  {
  
  	if (IS_DEFAULT_VNET(curvnet)) {
  		netisr_register(&arp_nh);
  		iflladdr_tag = EVENTHANDLER_REGISTER(iflladdr_event,
  		    arp_iflladdr, NULL, EVENTHANDLER_PRI_ANY);
  	}
  #ifdef VIMAGE
  	else
  		netisr_register_vnet(&arp_nh);
  #endif
  }
  VNET_SYSINIT(vnet_arp_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_SECOND,
      vnet_arp_init, 0);
  
  #ifdef VIMAGE
  /*
   * We have to unregister ARP along with IP otherwise we risk doing INADDR_HASH
   * lookups after destroying the hash.  Ideally this would go on SI_ORDER_3.5.
   */
  static void
  vnet_arp_destroy(__unused void *arg)
  {
  
  	netisr_unregister_vnet(&arp_nh);
  }
  VNET_SYSUNINIT(vnet_arp_uninit, SI_SUB_PROTO_DOMAIN, SI_ORDER_THIRD,
      vnet_arp_destroy, NULL);
  #endif
  