net/tipc/link.c

/*
 * net/tipc/link.c: TIPC link code
 *
 * Copyright (c) 1996-2007, 2012-2015, Ericsson AB
 * Copyright (c) 2004-2007, 2010-2013, Wind River Systems
 * 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 names of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * Alternatively, this software may be distributed under the terms of the
 * GNU General Public License ("GPL") version 2 as published by the Free
 * Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
 */

#include "core.h"
#include "subscr.h"
#include "link.h"
#include "bcast.h"
#include "socket.h"
#include "name_distr.h"
#include "discover.h"
#include "netlink.h"

#include <linux/pkt_sched.h>

/*
 * Error message prefixes
 */
static const char *link_co_err = "Link tunneling error, ";
static const char *link_rst_msg = "Resetting link ";

/* Properties valid for media, bearar and link */
static const struct nla_policy tipc_nl_prop_policy[TIPC_NLA_PROP_MAX + 1] = {
	[TIPC_NLA_PROP_UNSPEC]		= { .type = NLA_UNSPEC },
	[TIPC_NLA_PROP_PRIO]		= { .type = NLA_U32 },
	[TIPC_NLA_PROP_TOL]		= { .type = NLA_U32 },
	[TIPC_NLA_PROP_WIN]		= { .type = NLA_U32 }
};

/* Send states for broadcast NACKs
 */
enum {
	BC_NACK_SND_CONDITIONAL,
	BC_NACK_SND_UNCONDITIONAL,
	BC_NACK_SND_SUPPRESS,
};

/*
 * Interval between NACKs when packets arrive out of order
 */
#define TIPC_NACK_INTV (TIPC_MIN_LINK_WIN * 2)
/*
 * Out-of-range value for link session numbers
 */
#define WILDCARD_SESSION 0x10000

/* Link FSM states:
 */
enum {
	LINK_ESTABLISHED     = 0xe,
	LINK_ESTABLISHING    = 0xe  << 4,
	LINK_RESET           = 0x1  << 8,
	LINK_RESETTING       = 0x2  << 12,
	LINK_PEER_RESET      = 0xd  << 16,
	LINK_FAILINGOVER     = 0xf  << 20,
	LINK_SYNCHING        = 0xc  << 24
};

/* Link FSM state checking routines
 */
static int link_is_up(struct tipc_link *l)
{
	return l->state & (LINK_ESTABLISHED | LINK_SYNCHING);
}

static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
			       struct sk_buff_head *xmitq);
static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
				      u16 rcvgap, int tolerance, int priority,
				      struct sk_buff_head *xmitq);
static void link_print(struct tipc_link *l_ptr, const char *str);
static void tipc_link_build_nack_msg(struct tipc_link *l,
				     struct sk_buff_head *xmitq);
static void tipc_link_build_bc_init_msg(struct tipc_link *l,
					struct sk_buff_head *xmitq);
static bool tipc_link_release_pkts(struct tipc_link *l, u16 to);

/*
 *  Simple non-static link routines (i.e. referenced outside this file)
 */
bool tipc_link_is_up(struct tipc_link *l)
{
	return link_is_up(l);
}

bool tipc_link_peer_is_down(struct tipc_link *l)
{
	return l->state == LINK_PEER_RESET;
}

bool tipc_link_is_reset(struct tipc_link *l)
{
	return l->state & (LINK_RESET | LINK_FAILINGOVER | LINK_ESTABLISHING);
}

bool tipc_link_is_establishing(struct tipc_link *l)
{
	return l->state == LINK_ESTABLISHING;
}

bool tipc_link_is_synching(struct tipc_link *l)
{
	return l->state == LINK_SYNCHING;
}

bool tipc_link_is_failingover(struct tipc_link *l)
{
	return l->state == LINK_FAILINGOVER;
}

bool tipc_link_is_blocked(struct tipc_link *l)
{
	return l->state & (LINK_RESETTING | LINK_PEER_RESET | LINK_FAILINGOVER);
}

static bool link_is_bc_sndlink(struct tipc_link *l)
{
	return !l->bc_sndlink;
}

static bool link_is_bc_rcvlink(struct tipc_link *l)
{
	return ((l->bc_rcvlink == l) && !link_is_bc_sndlink(l));
}

int tipc_link_is_active(struct tipc_link *l)
{
	return l->active;
}

void tipc_link_set_active(struct tipc_link *l, bool active)
{
	l->active = active;
}

void tipc_link_add_bc_peer(struct tipc_link *snd_l,
			   struct tipc_link *uc_l,
			   struct sk_buff_head *xmitq)
{
	struct tipc_link *rcv_l = uc_l->bc_rcvlink;

	snd_l->ackers++;
	rcv_l->acked = snd_l->snd_nxt - 1;
	tipc_link_build_bc_init_msg(uc_l, xmitq);
}

void tipc_link_remove_bc_peer(struct tipc_link *snd_l,
			      struct tipc_link *rcv_l,
			      struct sk_buff_head *xmitq)
{
	u16 ack = snd_l->snd_nxt - 1;

	snd_l->ackers--;
	tipc_link_bc_ack_rcv(rcv_l, ack, xmitq);
	tipc_link_reset(rcv_l);
	rcv_l->state = LINK_RESET;
	if (!snd_l->ackers) {
		tipc_link_reset(snd_l);
		__skb_queue_purge(xmitq);
	}
}

int tipc_link_bc_peers(struct tipc_link *l)
{
	return l->ackers;
}

void tipc_link_set_mtu(struct tipc_link *l, int mtu)
{
	l->mtu = mtu;
}

int tipc_link_mtu(struct tipc_link *l)
{
	return l->mtu;
}

static u32 link_own_addr(struct tipc_link *l)
{
	return msg_prevnode(l->pmsg);
}

/**
 * tipc_link_create - create a new link
 * @n: pointer to associated node
 * @if_name: associated interface name
 * @bearer_id: id (index) of associated bearer
 * @tolerance: link tolerance to be used by link
 * @net_plane: network plane (A,B,c..) this link belongs to
 * @mtu: mtu to be advertised by link
 * @priority: priority to be used by link
 * @window: send window to be used by link
 * @session: session to be used by link
 * @ownnode: identity of own node
 * @peer: node id of peer node
 * @peer_caps: bitmap describing peer node capabilities
 * @bc_sndlink: the namespace global link used for broadcast sending
 * @bc_rcvlink: the peer specific link used for broadcast reception
 * @inputq: queue to put messages ready for delivery
 * @namedq: queue to put binding table update messages ready for delivery
 * @link: return value, pointer to put the created link
 *
 * Returns true if link was created, otherwise false
 */
bool tipc_link_create(struct net *net, char *if_name, int bearer_id,
		      int tolerance, char net_plane, u32 mtu, int priority,
		      int window, u32 session, u32 ownnode, u32 peer,
		      u16 peer_caps,
		      struct tipc_link *bc_sndlink,
		      struct tipc_link *bc_rcvlink,
		      struct sk_buff_head *inputq,
		      struct sk_buff_head *namedq,
		      struct tipc_link **link)
{
	struct tipc_link *l;
	struct tipc_msg *hdr;

	l = kzalloc(sizeof(*l), GFP_ATOMIC);
	if (!l)
		return false;
	*link = l;
	l->pmsg = (struct tipc_msg *)&l->proto_msg;
	hdr = l->pmsg;
	tipc_msg_init(ownnode, hdr, LINK_PROTOCOL, RESET_MSG, INT_H_SIZE, peer);
	msg_set_size(hdr, sizeof(l->proto_msg));
	msg_set_session(hdr, session);
	msg_set_bearer_id(hdr, l->bearer_id);

	/* Note: peer i/f name is completed by reset/activate message */
	sprintf(l->name, "%u.%u.%u:%s-%u.%u.%u:unknown",
		tipc_zone(ownnode), tipc_cluster(ownnode), tipc_node(ownnode),
		if_name, tipc_zone(peer), tipc_cluster(peer), tipc_node(peer));
	strcpy((char *)msg_data(hdr), if_name);

	l->addr = peer;
	l->peer_caps = peer_caps;
	l->net = net;
	l->peer_session = WILDCARD_SESSION;
	l->bearer_id = bearer_id;
	l->tolerance = tolerance;
	l->net_plane = net_plane;
	l->advertised_mtu = mtu;
	l->mtu = mtu;
	l->priority = priority;
	tipc_link_set_queue_limits(l, window);
	l->ackers = 1;
	l->bc_sndlink = bc_sndlink;
	l->bc_rcvlink = bc_rcvlink;
	l->inputq = inputq;
	l->namedq = namedq;
	l->state = LINK_RESETTING;
	__skb_queue_head_init(&l->transmq);
	__skb_queue_head_init(&l->backlogq);
	__skb_queue_head_init(&l->deferdq);
	skb_queue_head_init(&l->wakeupq);
	skb_queue_head_init(l->inputq);
	return true;
}

/**
 * tipc_link_bc_create - create new link to be used for broadcast
 * @n: pointer to associated node
 * @mtu: mtu to be used
 * @window: send window to be used
 * @inputq: queue to put messages ready for delivery
 * @namedq: queue to put binding table update messages ready for delivery
 * @link: return value, pointer to put the created link
 *
 * Returns true if link was created, otherwise false
 */
bool tipc_link_bc_create(struct net *net, u32 ownnode, u32 peer,
			 int mtu, int window, u16 peer_caps,
			 struct sk_buff_head *inputq,
			 struct sk_buff_head *namedq,
			 struct tipc_link *bc_sndlink,
			 struct tipc_link **link)
{
	struct tipc_link *l;

	if (!tipc_link_create(net, "", MAX_BEARERS, 0, 'Z', mtu, 0, window,
			      0, ownnode, peer, peer_caps, bc_sndlink,
			      NULL, inputq, namedq, link))
		return false;

	l = *link;
	strcpy(l->name, tipc_bclink_name);
	tipc_link_reset(l);
	l->state = LINK_RESET;
	l->ackers = 0;
	l->bc_rcvlink = l;

	/* Broadcast send link is always up */
	if (link_is_bc_sndlink(l))
		l->state = LINK_ESTABLISHED;

	return true;
}

/**
 * tipc_link_fsm_evt - link finite state machine
 * @l: pointer to link
 * @evt: state machine event to be processed
 */
int tipc_link_fsm_evt(struct tipc_link *l, int evt)
{
	int rc = 0;

	switch (l->state) {
	case LINK_RESETTING:
		switch (evt) {
		case LINK_PEER_RESET_EVT:
			l->state = LINK_PEER_RESET;
			break;
		case LINK_RESET_EVT:
			l->state = LINK_RESET;
			break;
		case LINK_FAILURE_EVT:
		case LINK_FAILOVER_BEGIN_EVT:
		case LINK_ESTABLISH_EVT:
		case LINK_FAILOVER_END_EVT:
		case LINK_SYNCH_BEGIN_EVT:
		case LINK_SYNCH_END_EVT:
		default:
			goto illegal_evt;
		}
		break;
	case LINK_RESET:
		switch (evt) {
		case LINK_PEER_RESET_EVT:
			l->state = LINK_ESTABLISHING;
			break;
		case LINK_FAILOVER_BEGIN_EVT:
			l->state = LINK_FAILINGOVER;
		case LINK_FAILURE_EVT:
		case LINK_RESET_EVT:
		case LINK_ESTABLISH_EVT:
		case LINK_FAILOVER_END_EVT:
			break;
		case LINK_SYNCH_BEGIN_EVT:
		case LINK_SYNCH_END_EVT:
		default:
			goto illegal_evt;
		}
		break;
	case LINK_PEER_RESET:
		switch (evt) {
		case LINK_RESET_EVT:
			l->state = LINK_ESTABLISHING;
			break;
		case LINK_PEER_RESET_EVT:
		case LINK_ESTABLISH_EVT:
		case LINK_FAILURE_EVT:
			break;
		case LINK_SYNCH_BEGIN_EVT:
		case LINK_SYNCH_END_EVT:
		case LINK_FAILOVER_BEGIN_EVT:
		case LINK_FAILOVER_END_EVT:
		default:
			goto illegal_evt;
		}
		break;
	case LINK_FAILINGOVER:
		switch (evt) {
		case LINK_FAILOVER_END_EVT:
			l->state = LINK_RESET;
			break;
		case LINK_PEER_RESET_EVT:
		case LINK_RESET_EVT:
		case LINK_ESTABLISH_EVT:
		case LINK_FAILURE_EVT:
			break;
		case LINK_FAILOVER_BEGIN_EVT:
		case LINK_SYNCH_BEGIN_EVT:
		case LINK_SYNCH_END_EVT:
		default:
			goto illegal_evt;
		}
		break;
	case LINK_ESTABLISHING:
		switch (evt) {
		case LINK_ESTABLISH_EVT:
			l->state = LINK_ESTABLISHED;
			break;
		case LINK_FAILOVER_BEGIN_EVT:
			l->state = LINK_FAILINGOVER;
			break;
		case LINK_RESET_EVT:
			l->state = LINK_RESET;
			break;
		case LINK_FAILURE_EVT:
		case LINK_PEER_RESET_EVT:
		case LINK_SYNCH_BEGIN_EVT:
		case LINK_FAILOVER_END_EVT:
			break;
		case LINK_SYNCH_END_EVT:
		default:
			goto illegal_evt;
		}
		break;
	case LINK_ESTABLISHED:
		switch (evt) {
		case LINK_PEER_RESET_EVT:
			l->state = LINK_PEER_RESET;
			rc |= TIPC_LINK_DOWN_EVT;
			break;
		case LINK_FAILURE_EVT:
			l->state = LINK_RESETTING;
			rc |= TIPC_LINK_DOWN_EVT;
			break;
		case LINK_RESET_EVT:
			l->state = LINK_RESET;
			break;
		case LINK_ESTABLISH_EVT:
		case LINK_SYNCH_END_EVT:
			break;
		case LINK_SYNCH_BEGIN_EVT:
			l->state = LINK_SYNCHING;
			break;
		case LINK_FAILOVER_BEGIN_EVT:
		case LINK_FAILOVER_END_EVT:
		default:
			goto illegal_evt;
		}
		break;
	case LINK_SYNCHING:
		switch (evt) {
		case LINK_PEER_RESET_EVT:
			l->state = LINK_PEER_RESET;
			rc |= TIPC_LINK_DOWN_EVT;
			break;
		case LINK_FAILURE_EVT:
			l->state = LINK_RESETTING;
			rc |= TIPC_LINK_DOWN_EVT;
			break;
		case LINK_RESET_EVT:
			l->state = LINK_RESET;
			break;
		case LINK_ESTABLISH_EVT:
		case LINK_SYNCH_BEGIN_EVT:
			break;
		case LINK_SYNCH_END_EVT:
			l->state = LINK_ESTABLISHED;
			break;
		case LINK_FAILOVER_BEGIN_EVT:
		case LINK_FAILOVER_END_EVT:
		default:
			goto illegal_evt;
		}
		break;
	default:
		pr_err("Unknown FSM state %x in %s\n", l->state, l->name);
	}
	return rc;
illegal_evt:
	pr_err("Illegal FSM event %x in state %x on link %s\n",
	       evt, l->state, l->name);
	return rc;
}

/* link_profile_stats - update statistical profiling of traffic
 */
static void link_profile_stats(struct tipc_link *l)
{
	struct sk_buff *skb;
	struct tipc_msg *msg;
	int length;

	/* Update counters used in statistical profiling of send traffic */
	l->stats.accu_queue_sz += skb_queue_len(&l->transmq);
	l->stats.queue_sz_counts++;

	skb = skb_peek(&l->transmq);
	if (!skb)
		return;
	msg = buf_msg(skb);
	length = msg_size(msg);

	if (msg_user(msg) == MSG_FRAGMENTER) {
		if (msg_type(msg) != FIRST_FRAGMENT)
			return;
		length = msg_size(msg_get_wrapped(msg));
	}
	l->stats.msg_lengths_total += length;
	l->stats.msg_length_counts++;
	if (length <= 64)
		l->stats.msg_length_profile[0]++;
	else if (length <= 256)
		l->stats.msg_length_profile[1]++;
	else if (length <= 1024)
		l->stats.msg_length_profile[2]++;
	else if (length <= 4096)
		l->stats.msg_length_profile[3]++;
	else if (length <= 16384)
		l->stats.msg_length_profile[4]++;
	else if (length <= 32768)
		l->stats.msg_length_profile[5]++;
	else
		l->stats.msg_length_profile[6]++;
}

/* tipc_link_timeout - perform periodic task as instructed from node timeout
 */
/* tipc_link_timeout - perform periodic task as instructed from node timeout
 */
int tipc_link_timeout(struct tipc_link *l, struct sk_buff_head *xmitq)
{
	int rc = 0;
	int mtyp = STATE_MSG;
	bool xmit = false;
	bool prb = false;
	u16 bc_snt = l->bc_sndlink->snd_nxt - 1;
	u16 bc_acked = l->bc_rcvlink->acked;
	bool bc_up = link_is_up(l->bc_rcvlink);

	link_profile_stats(l);

	switch (l->state) {
	case LINK_ESTABLISHED:
	case LINK_SYNCHING:
		if (!l->silent_intv_cnt) {
			if (bc_up && (bc_acked != bc_snt))
				xmit = true;
		} else if (l->silent_intv_cnt <= l->abort_limit) {
			xmit = true;
			prb = true;
		} else {
			rc |= tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
		}
		l->silent_intv_cnt++;
		break;
	case LINK_RESET:
		xmit = true;
		mtyp = RESET_MSG;
		break;
	case LINK_ESTABLISHING:
		xmit = true;
		mtyp = ACTIVATE_MSG;
		break;
	case LINK_PEER_RESET:
	case LINK_RESETTING:
	case LINK_FAILINGOVER:
		break;
	default:
		break;
	}

	if (xmit)
		tipc_link_build_proto_msg(l, mtyp, prb, 0, 0, 0, xmitq);

	return rc;
}

/**
 * link_schedule_user - schedule a message sender for wakeup after congestion
 * @link: congested link
 * @list: message that was attempted sent
 * Create pseudo msg to send back to user when congestion abates
 * Does not consume buffer list
 */
static int link_schedule_user(struct tipc_link *link, struct sk_buff_head *list)
{
	struct tipc_msg *msg = buf_msg(skb_peek(list));
	int imp = msg_importance(msg);
	u32 oport = msg_origport(msg);
	u32 addr = link_own_addr(link);
	struct sk_buff *skb;

	/* This really cannot happen...  */
	if (unlikely(imp > TIPC_CRITICAL_IMPORTANCE)) {
		pr_warn("%s<%s>, send queue full", link_rst_msg, link->name);
		return -ENOBUFS;
	}
	/* Non-blocking sender: */
	if (TIPC_SKB_CB(skb_peek(list))->wakeup_pending)
		return -ELINKCONG;

	/* Create and schedule wakeup pseudo message */
	skb = tipc_msg_create(SOCK_WAKEUP, 0, INT_H_SIZE, 0,
			      addr, addr, oport, 0, 0);
	if (!skb)
		return -ENOBUFS;
	TIPC_SKB_CB(skb)->chain_sz = skb_queue_len(list);
	TIPC_SKB_CB(skb)->chain_imp = imp;
	skb_queue_tail(&link->wakeupq, skb);
	link->stats.link_congs++;
	return -ELINKCONG;
}

/**
 * link_prepare_wakeup - prepare users for wakeup after congestion
 * @link: congested link
 * Move a number of waiting users, as permitted by available space in
 * the send queue, from link wait queue to node wait queue for wakeup
 */
void link_prepare_wakeup(struct tipc_link *l)
{
	int pnd[TIPC_SYSTEM_IMPORTANCE + 1] = {0,};
	int imp, lim;
	struct sk_buff *skb, *tmp;

	skb_queue_walk_safe(&l->wakeupq, skb, tmp) {
		imp = TIPC_SKB_CB(skb)->chain_imp;
		lim = l->window + l->backlog[imp].limit;
		pnd[imp] += TIPC_SKB_CB(skb)->chain_sz;
		if ((pnd[imp] + l->backlog[imp].len) >= lim)
			break;
		skb_unlink(skb, &l->wakeupq);
		skb_queue_tail(l->inputq, skb);
	}
}

void tipc_link_reset(struct tipc_link *l)
{
	/* Link is down, accept any session */
	l->peer_session = WILDCARD_SESSION;

	/* If peer is up, it only accepts an incremented session number */
	msg_set_session(l->pmsg, msg_session(l->pmsg) + 1);

	/* Prepare for renewed mtu size negotiation */
	l->mtu = l->advertised_mtu;

	/* Clean up all queues and counters: */
	__skb_queue_purge(&l->transmq);
	__skb_queue_purge(&l->deferdq);
	skb_queue_splice_init(&l->wakeupq, l->inputq);
	__skb_queue_purge(&l->backlogq);
	l->backlog[TIPC_LOW_IMPORTANCE].len = 0;
	l->backlog[TIPC_MEDIUM_IMPORTANCE].len = 0;
	l->backlog[TIPC_HIGH_IMPORTANCE].len = 0;
	l->backlog[TIPC_CRITICAL_IMPORTANCE].len = 0;
	l->backlog[TIPC_SYSTEM_IMPORTANCE].len = 0;
	kfree_skb(l->reasm_buf);
	kfree_skb(l->failover_reasm_skb);
	l->reasm_buf = NULL;
	l->failover_reasm_skb = NULL;
	l->rcv_unacked = 0;
	l->snd_nxt = 1;
	l->rcv_nxt = 1;
	l->acked = 0;
	l->silent_intv_cnt = 0;
	l->stats.recv_info = 0;
	l->stale_count = 0;
	l->bc_peer_is_up = false;
	link_reset_statistics(l);
}

/**
 * tipc_link_xmit(): enqueue buffer list according to queue situation
 * @link: link to use
 * @list: chain of buffers containing message
 * @xmitq: returned list of packets to be sent by caller
 *
 * Consumes the buffer chain, except when returning -ELINKCONG,
 * since the caller then may want to make more send attempts.
 * Returns 0 if success, or errno: -ELINKCONG, -EMSGSIZE or -ENOBUFS
 * Messages at TIPC_SYSTEM_IMPORTANCE are always accepted
 */
int tipc_link_xmit(struct tipc_link *l, struct sk_buff_head *list,
		   struct sk_buff_head *xmitq)
{
	struct tipc_msg *hdr = buf_msg(skb_peek(list));
	unsigned int maxwin = l->window;
	unsigned int i, imp = msg_importance(hdr);
	unsigned int mtu = l->mtu;
	u16 ack = l->rcv_nxt - 1;
	u16 seqno = l->snd_nxt;
	u16 bc_ack = l->bc_rcvlink->rcv_nxt - 1;
	struct sk_buff_head *transmq = &l->transmq;
	struct sk_buff_head *backlogq = &l->backlogq;
	struct sk_buff *skb, *_skb, *bskb;

	/* Match msg importance against this and all higher backlog limits: */
	for (i = imp; i <= TIPC_SYSTEM_IMPORTANCE; i++) {
		if (unlikely(l->backlog[i].len >= l->backlog[i].limit))
			return link_schedule_user(l, list);
	}
	if (unlikely(msg_size(hdr) > mtu))
		return -EMSGSIZE;

	/* Prepare each packet for sending, and add to relevant queue: */
	while (skb_queue_len(list)) {
		skb = skb_peek(list);
		hdr = buf_msg(skb);
		msg_set_seqno(hdr, seqno);
		msg_set_ack(hdr, ack);
		msg_set_bcast_ack(hdr, bc_ack);

		if (likely(skb_queue_len(transmq) < maxwin)) {
			_skb = skb_clone(skb, GFP_ATOMIC);
			if (!_skb)
				return -ENOBUFS;
			__skb_dequeue(list);
			__skb_queue_tail(transmq, skb);
			__skb_queue_tail(xmitq, _skb);
			TIPC_SKB_CB(skb)->ackers = l->ackers;
			l->rcv_unacked = 0;
			seqno++;
			continue;
		}
		if (tipc_msg_bundle(skb_peek_tail(backlogq), hdr, mtu)) {
			kfree_skb(__skb_dequeue(list));
			l->stats.sent_bundled++;
			continue;
		}
		if (tipc_msg_make_bundle(&bskb, hdr, mtu, l->addr)) {
			kfree_skb(__skb_dequeue(list));
			__skb_queue_tail(backlogq, bskb);
			l->backlog[msg_importance(buf_msg(bskb))].len++;
			l->stats.sent_bundled++;
			l->stats.sent_bundles++;
			continue;
		}
		l->backlog[imp].len += skb_queue_len(list);
		skb_queue_splice_tail_init(list, backlogq);
	}
	l->snd_nxt = seqno;
	return 0;
}

void tipc_link_advance_backlog(struct tipc_link *l, struct sk_buff_head *xmitq)
{
	struct sk_buff *skb, *_skb;
	struct tipc_msg *hdr;
	u16 seqno = l->snd_nxt;
	u16 ack = l->rcv_nxt - 1;
	u16 bc_ack = l->bc_rcvlink->rcv_nxt - 1;

	while (skb_queue_len(&l->transmq) < l->window) {
		skb = skb_peek(&l->backlogq);
		if (!skb)
			break;
		_skb = skb_clone(skb, GFP_ATOMIC);
		if (!_skb)
			break;
		__skb_dequeue(&l->backlogq);
		hdr = buf_msg(skb);
		l->backlog[msg_importance(hdr)].len--;
		__skb_queue_tail(&l->transmq, skb);
		__skb_queue_tail(xmitq, _skb);
		TIPC_SKB_CB(skb)->ackers = l->ackers;
		msg_set_seqno(hdr, seqno);
		msg_set_ack(hdr, ack);
		msg_set_bcast_ack(hdr, bc_ack);
		l->rcv_unacked = 0;
		seqno++;
	}
	l->snd_nxt = seqno;
}

static void link_retransmit_failure(struct tipc_link *l, struct sk_buff *skb)
{
	struct tipc_msg *hdr = buf_msg(skb);

	pr_warn("Retransmission failure on link <%s>\n", l->name);
	link_print(l, "Resetting link ");
	pr_info("Failed msg: usr %u, typ %u, len %u, err %u\n",
		msg_user(hdr), msg_type(hdr), msg_size(hdr), msg_errcode(hdr));
	pr_info("sqno %u, prev: %x, src: %x\n",
		msg_seqno(hdr), msg_prevnode(hdr), msg_orignode(hdr));
}

int tipc_link_retrans(struct tipc_link *l, u16 from, u16 to,
		      struct sk_buff_head *xmitq)
{
	struct sk_buff *_skb, *skb = skb_peek(&l->transmq);
	struct tipc_msg *hdr;
	u16 ack = l->rcv_nxt - 1;
	u16 bc_ack = l->bc_rcvlink->rcv_nxt - 1;

	if (!skb)
		return 0;

	/* Detect repeated retransmit failures on same packet */
	if (likely(l->last_retransm != buf_seqno(skb))) {
		l->last_retransm = buf_seqno(skb);
		l->stale_count = 1;
	} else if (++l->stale_count > 100) {
		link_retransmit_failure(l, skb);
		return tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
	}

	/* Move forward to where retransmission should start */
	skb_queue_walk(&l->transmq, skb) {
		if (!less(buf_seqno(skb), from))
			break;
	}

	skb_queue_walk_from(&l->transmq, skb) {
		if (more(buf_seqno(skb), to))
			break;
		hdr = buf_msg(skb);
		_skb = __pskb_copy(skb, MIN_H_SIZE, GFP_ATOMIC);
		if (!_skb)
			return 0;
		hdr = buf_msg(_skb);
		msg_set_ack(hdr, ack);
		msg_set_bcast_ack(hdr, bc_ack);
		_skb->priority = TC_PRIO_CONTROL;
		__skb_queue_tail(xmitq, _skb);
		l->stats.retransmitted++;
	}
	return 0;
}

/* tipc_data_input - deliver data and name distr msgs to upper layer
 *
 * Consumes buffer if message is of right type
 * Node lock must be held
 */
static bool tipc_data_input(struct tipc_link *l, struct sk_buff *skb,
			    struct sk_buff_head *inputq)
{
	switch (msg_user(buf_msg(skb))) {
	case TIPC_LOW_IMPORTANCE:
	case TIPC_MEDIUM_IMPORTANCE:
	case TIPC_HIGH_IMPORTANCE:
	case TIPC_CRITICAL_IMPORTANCE:
	case CONN_MANAGER:
		skb_queue_tail(inputq, skb);
		return true;
	case NAME_DISTRIBUTOR:
		l->bc_rcvlink->state = LINK_ESTABLISHED;
		skb_queue_tail(l->namedq, skb);
		return true;
	case MSG_BUNDLER:
	case TUNNEL_PROTOCOL:
	case MSG_FRAGMENTER:
	case BCAST_PROTOCOL:
		return false;
	default:
		pr_warn("Dropping received illegal msg type\n");
		kfree_skb(skb);
		return false;
	};
}

/* tipc_link_input - process packet that has passed link protocol check
 *
 * Consumes buffer
 */
static int tipc_link_input(struct tipc_link *l, struct sk_buff *skb,
			   struct sk_buff_head *inputq)
{
	struct tipc_msg *hdr = buf_msg(skb);
	struct sk_buff **reasm_skb = &l->reasm_buf;
	struct sk_buff *iskb;
	struct sk_buff_head tmpq;
	int usr = msg_user(hdr);
	int rc = 0;
	int pos = 0;
	int ipos = 0;

	if (unlikely(usr == TUNNEL_PROTOCOL)) {
		if (msg_type(hdr) == SYNCH_MSG) {
			__skb_queue_purge(&l->deferdq);
			goto drop;
		}
		if (!tipc_msg_extract(skb, &iskb, &ipos))
			return rc;
		kfree_skb(skb);
		skb = iskb;
		hdr = buf_msg(skb);
		if (less(msg_seqno(hdr), l->drop_point))
			goto drop;
		if (tipc_data_input(l, skb, inputq))
			return rc;
		usr = msg_user(hdr);
		reasm_skb = &l->failover_reasm_skb;
	}

	if (usr == MSG_BUNDLER) {
		skb_queue_head_init(&tmpq);
		l->stats.recv_bundles++;
		l->stats.recv_bundled += msg_msgcnt(hdr);
		while (tipc_msg_extract(skb, &iskb, &pos))
			tipc_data_input(l, iskb, &tmpq);
		tipc_skb_queue_splice_tail(&tmpq, inputq);
		return 0;
	} else if (usr == MSG_FRAGMENTER) {
		l->stats.recv_fragments++;
		if (tipc_buf_append(reasm_skb, &skb)) {
			l->stats.recv_fragmented++;
			tipc_data_input(l, skb, inputq);
		} else if (!*reasm_skb && !link_is_bc_rcvlink(l)) {
			pr_warn_ratelimited("Unable to build fragment list\n");
			return tipc_link_fsm_evt(l, LINK_FAILURE_EVT);
		}
		return 0;
	} else if (usr == BCAST_PROTOCOL) {
		tipc_bcast_lock(l->net);
		tipc_link_bc_init_rcv(l->bc_rcvlink, hdr);
		tipc_bcast_unlock(l->net);
	}
drop:
	kfree_skb(skb);
	return 0;
}

static bool tipc_link_release_pkts(struct tipc_link *l, u16 acked)
{
	bool released = false;
	struct sk_buff *skb, *tmp;

	skb_queue_walk_safe(&l->transmq, skb, tmp) {
		if (more(buf_seqno(skb), acked))
			break;
		__skb_unlink(skb, &l->transmq);
		kfree_skb(skb);
		released = true;
	}
	return released;
}

/* tipc_link_build_ack_msg: prepare link acknowledge message for transmission
 *
 * Note that sending of broadcast ack is coordinated among nodes, to reduce
 * risk of ack storms towards the sender
 */
int tipc_link_build_ack_msg(struct tipc_link *l, struct sk_buff_head *xmitq)
{
	if (!l)
		return 0;

	/* Broadcast ACK must be sent via a unicast link => defer to caller */
	if (link_is_bc_rcvlink(l)) {
		if (((l->rcv_nxt ^ link_own_addr(l)) & 0xf) != 0xf)
			return 0;
		l->rcv_unacked = 0;
		return TIPC_LINK_SND_BC_ACK;
	}

	/* Unicast ACK */
	l->rcv_unacked = 0;
	l->stats.sent_acks++;
	tipc_link_build_proto_msg(l, STATE_MSG, 0, 0, 0, 0, xmitq);
	return 0;
}

/* tipc_link_build_reset_msg: prepare link RESET or ACTIVATE message
 */
void tipc_link_build_reset_msg(struct tipc_link *l, struct sk_buff_head *xmitq)
{
	int mtyp = RESET_MSG;

	if (l->state == LINK_ESTABLISHING)
		mtyp = ACTIVATE_MSG;

	tipc_link_build_proto_msg(l, mtyp, 0, 0, 0, 0, xmitq);
}

/* tipc_link_build_nack_msg: prepare link nack message for transmission
 */
static void tipc_link_build_nack_msg(struct tipc_link *l,
				     struct sk_buff_head *xmitq)
{
	u32 def_cnt = ++l->stats.deferred_recv;

	if (link_is_bc_rcvlink(l))
		return;

	if ((skb_queue_len(&l->deferdq) == 1) || !(def_cnt % TIPC_NACK_INTV))
		tipc_link_build_proto_msg(l, STATE_MSG, 0, 0, 0, 0, xmitq);
}

/* tipc_link_rcv - process TIPC packets/messages arriving from off-node
 * @l: the link that should handle the message
 * @skb: TIPC packet
 * @xmitq: queue to place packets to be sent after this call
 */
int tipc_link_rcv(struct tipc_link *l, struct sk_buff *skb,
		  struct sk_buff_head *xmitq)
{
	struct sk_buff_head *defq = &l->deferdq;
	struct tipc_msg *hdr;
	u16 seqno, rcv_nxt, win_lim;
	int rc = 0;

	do {
		hdr = buf_msg(skb);
		seqno = msg_seqno(hdr);
		rcv_nxt = l->rcv_nxt;
		win_lim = rcv_nxt + TIPC_MAX_LINK_WIN;

		/* Verify and update link state */
		if (unlikely(msg_user(hdr) == LINK_PROTOCOL))
			return tipc_link_proto_rcv(l, skb, xmitq);

		if (unlikely(!link_is_up(l))) {
			if (l->state == LINK_ESTABLISHING)
				rc = TIPC_LINK_UP_EVT;
			goto drop;
		}

		/* Don't send probe at next timeout expiration */
		l->silent_intv_cnt = 0;

		/* Drop if outside receive window */
		if (unlikely(less(seqno, rcv_nxt) || more(seqno, win_lim))) {
			l->stats.duplicates++;
			goto drop;
		}

		/* Forward queues and wake up waiting users */
		if (likely(tipc_link_release_pkts(l, msg_ack(hdr)))) {
			tipc_link_advance_backlog(l, xmitq);
			if (unlikely(!skb_queue_empty(&l->wakeupq)))
				link_prepare_wakeup(l);
		}

		/* Defer delivery if sequence gap */
		if (unlikely(seqno != rcv_nxt)) {
			__tipc_skb_queue_sorted(defq, seqno, skb);
			tipc_link_build_nack_msg(l, xmitq);
			break;
		}

		/* Deliver packet */
		l->rcv_nxt++;
		l->stats.recv_info++;
		if (!tipc_data_input(l, skb, l->inputq))
			rc |= tipc_link_input(l, skb, l->inputq);
		if (unlikely(++l->rcv_unacked >= TIPC_MIN_LINK_WIN))
			rc |= tipc_link_build_ack_msg(l, xmitq);
		if (unlikely(rc & ~TIPC_LINK_SND_BC_ACK))
			break;
	} while ((skb = __skb_dequeue(defq)));

	return rc;
drop:
	kfree_skb(skb);
	return rc;
}

/*
 * Send protocol message to the other endpoint.
 */
void tipc_link_proto_xmit(struct tipc_link *l, u32 msg_typ, int probe_msg,
			  u32 gap, u32 tolerance, u32 priority)
{
	struct sk_buff *skb = NULL;
	struct sk_buff_head xmitq;

	__skb_queue_head_init(&xmitq);
	tipc_link_build_proto_msg(l, msg_typ, probe_msg, gap,
				  tolerance, priority, &xmitq);
	skb = __skb_dequeue(&xmitq);
	if (!skb)
		return;
	tipc_bearer_xmit_skb(l->net, l->bearer_id, skb, l->media_addr);
	l->rcv_unacked = 0;
}

static void tipc_link_build_proto_msg(struct tipc_link *l, int mtyp, bool probe,
				      u16 rcvgap, int tolerance, int priority,
				      struct sk_buff_head *xmitq)
{
	struct sk_buff *skb = NULL;
	struct tipc_msg *hdr = l->pmsg;
	bool node_up = link_is_up(l->bc_rcvlink);

	/* Don't send protocol message during reset or link failover */
	if (tipc_link_is_blocked(l))
		return;

	msg_set_type(hdr, mtyp);
	msg_set_net_plane(hdr, l->net_plane);
	msg_set_next_sent(hdr, l->snd_nxt);
	msg_set_ack(hdr, l->rcv_nxt - 1);
	msg_set_bcast_ack(hdr, l->bc_rcvlink->rcv_nxt - 1);
	msg_set_last_bcast(hdr, l->bc_sndlink->snd_nxt - 1);
	msg_set_link_tolerance(hdr, tolerance);
	msg_set_linkprio(hdr, priority);
	msg_set_redundant_link(hdr, node_up);
	msg_set_seq_gap(hdr, 0);

	/* Compatibility: created msg must not be in sequence with pkt flow */
	msg_set_seqno(hdr, l->snd_nxt + U16_MAX / 2);

	if (mtyp == STATE_MSG) {
		if (!tipc_link_is_up(l))
			return;

		/* Override rcvgap if there are packets in deferred queue */
		if (!skb_queue_empty(&l->deferdq))
			rcvgap = buf_seqno(skb_peek(&l->deferdq)) - l->rcv_nxt;
		if (rcvgap) {
			msg_set_seq_gap(hdr, rcvgap);
			l->stats.sent_nacks++;
		}
		msg_set_probe(hdr, probe);
		if (probe)
			l->stats.sent_probes++;
		l->stats.sent_states++;
		l->rcv_unacked = 0;
	} else {
		/* RESET_MSG or ACTIVATE_MSG */
		msg_set_max_pkt(hdr, l->advertised_mtu);
		msg_set_ack(hdr, l->rcv_nxt - 1);
		msg_set_next_sent(hdr, 1);
	}
	skb = tipc_buf_acquire(msg_size(hdr));
	if (!skb)
		return;
	skb_copy_to_linear_data(skb, hdr, msg_size(hdr));
	skb->priority = TC_PRIO_CONTROL;
	__skb_queue_tail(xmitq, skb);
}

/* tipc_link_tnl_prepare(): prepare and return a list of tunnel packets
 * with contents of the link's transmit and backlog queues.
 */
void tipc_link_tnl_prepare(struct tipc_link *l, struct tipc_link *tnl,
			   int mtyp, struct sk_buff_head *xmitq)
{
	struct sk_buff *skb, *tnlskb;
	struct tipc_msg *hdr, tnlhdr;
	struct sk_buff_head *queue = &l->transmq;
	struct sk_buff_head tmpxq, tnlq;
	u16 pktlen, pktcnt, seqno = l->snd_nxt;

	if (!tnl)
		return;

	skb_queue_head_init(&tnlq);
	skb_queue_head_init(&tmpxq);

	/* At least one packet required for safe algorithm => add dummy */
	skb = tipc_msg_create(TIPC_LOW_IMPORTANCE, TIPC_DIRECT_MSG,
			      BASIC_H_SIZE, 0, l->addr, link_own_addr(l),
			      0, 0, TIPC_ERR_NO_PORT);
	if (!skb) {
		pr_warn("%sunable to create tunnel packet\n", link_co_err);
		return;
	}
	skb_queue_tail(&tnlq, skb);
	tipc_link_xmit(l, &tnlq, &tmpxq);
	__skb_queue_purge(&tmpxq);

	/* Initialize reusable tunnel packet header */
	tipc_msg_init(link_own_addr(l), &tnlhdr, TUNNEL_PROTOCOL,
		      mtyp, INT_H_SIZE, l->addr);
	pktcnt = skb_queue_len(&l->transmq) + skb_queue_len(&l->backlogq);
	msg_set_msgcnt(&tnlhdr, pktcnt);
	msg_set_bearer_id(&tnlhdr, l->peer_bearer_id);
tnl:
	/* Wrap each packet into a tunnel packet */
	skb_queue_walk(queue, skb) {
		hdr = buf_msg(skb);
		if (queue == &l->backlogq)
			msg_set_seqno(hdr, seqno++);
		pktlen = msg_size(hdr);
		msg_set_size(&tnlhdr, pktlen + INT_H_SIZE);
		tnlskb = tipc_buf_acquire(pktlen + INT_H_SIZE);
		if (!tnlskb) {
			pr_warn("%sunable to send packet\n", link_co_err);
			return;
		}
		skb_copy_to_linear_data(tnlskb, &tnlhdr, INT_H_SIZE);
		skb_copy_to_linear_data_offset(tnlskb, INT_H_SIZE, hdr, pktlen);
		__skb_queue_tail(&tnlq, tnlskb);
	}
	if (queue != &l->backlogq) {
		queue = &l->backlogq;
		goto tnl;
	}

	tipc_link_xmit(tnl, &tnlq, xmitq);

	if (mtyp == FAILOVER_MSG) {
		tnl->drop_point = l->rcv_nxt;
		tnl->failover_reasm_skb = l->reasm_buf;
		l->reasm_buf = NULL;
	}
}

/* tipc_link_proto_rcv(): receive link level protocol message :
 * Note that network plane id propagates through the network, and may
 * change at any time. The node with lowest numerical id determines
 * network plane
 */
static int tipc_link_proto_rcv(struct tipc_link *l, struct sk_buff *skb,
			       struct sk_buff_head *xmitq)
{
	struct tipc_msg *hdr = buf_msg(skb);
	u16 rcvgap = 0;
	u16 ack = msg_ack(hdr);
	u16 gap = msg_seq_gap(hdr);
	u16 peers_snd_nxt =  msg_next_sent(hdr);
	u16 peers_tol = msg_link_tolerance(hdr);
	u16 peers_prio = msg_linkprio(hdr);
	u16 rcv_nxt = l->rcv_nxt;
	int mtyp = msg_type(hdr);
	char *if_name;
	int rc = 0;

	if (tipc_link_is_blocked(l) || !xmitq)
		goto exit;

	if (link_own_addr(l) > msg_prevnode(hdr))
		l->net_plane = msg_net_plane(hdr);

	switch (mtyp) {
	case RESET_MSG:

		/* Ignore duplicate RESET with old session number */
		if ((less_eq(msg_session(hdr), l->peer_session)) &&
		    (l->peer_session != WILDCARD_SESSION))
			break;
		/* fall thru' */

	case ACTIVATE_MSG:
		skb_linearize(skb);
		hdr = buf_msg(skb);

		/* Complete own link name with peer's interface name */
		if_name =  strrchr(l->name, ':') + 1;
		if (sizeof(l->name) - (if_name - l->name) <= TIPC_MAX_IF_NAME)
			break;
		if (msg_data_sz(hdr) < TIPC_MAX_IF_NAME)
			break;
		strncpy(if_name, msg_data(hdr),	TIPC_MAX_IF_NAME);

		/* Update own tolerance if peer indicates a non-zero value */
		if (in_range(peers_tol, TIPC_MIN_LINK_TOL, TIPC_MAX_LINK_TOL))
			l->tolerance = peers_tol;

		/* Update own priority if peer's priority is higher */
		if (in_range(peers_prio, l->priority + 1, TIPC_MAX_LINK_PRI))
			l->priority = peers_prio;

		/* ACTIVATE_MSG serves as PEER_RESET if link is already down */
		if ((mtyp == RESET_MSG) || !link_is_up(l))
			rc = tipc_link_fsm_evt(l, LINK_PEER_RESET_EVT);

		/* ACTIVATE_MSG takes up link if it was already locally reset */
		if ((mtyp == ACTIVATE_MSG) && (l->state == LINK_ESTABLISHING))
			rc = TIPC_LINK_UP_EVT;

		l->peer_session = msg_session(hdr);
		l->peer_bearer_id = msg_bearer_id(hdr);
		if (l->mtu > msg_max_pkt(hdr))
			l->mtu = msg_max_pkt(hdr);
		break;

	case STATE_MSG:

		/* Update own tolerance if peer indicates a non-zero value */
		if (in_range(peers_tol, TIPC_MIN_LINK_TOL, TIPC_MAX_LINK_TOL))
			l->tolerance = peers_tol;

		l->silent_intv_cnt = 0;
		l->stats.recv_states++;
		if (msg_probe(hdr))
			l->stats.recv_probes++;

		if (!link_is_up(l)) {
			if (l->state == LINK_ESTABLISHING)
				rc = TIPC_LINK_UP_EVT;
			break;
		}

		/* Send NACK if peer has sent pkts we haven't received yet */
		if (more(peers_snd_nxt, rcv_nxt) && !tipc_link_is_synching(l))
			rcvgap = peers_snd_nxt - l->rcv_nxt;
		if (rcvgap || (msg_probe(hdr)))
			tipc_link_build_proto_msg(l, STATE_MSG, 0, rcvgap,
						  0, 0, xmitq);
		tipc_link_release_pkts(l, ack);

		/* If NACK, retransmit will now start at right position */
		if (gap) {
			rc = tipc_link_retrans(l, ack + 1, ack + gap, xmitq);
			l->stats.recv_nacks++;
		}

		tipc_link_advance_backlog(l, xmitq);
		if (unlikely(!skb_queue_empty(&l->wakeupq)))
			link_prepare_wakeup(l);
	}
exit:
	kfree_skb(skb);
	return rc;
}

/* tipc_link_build_bc_proto_msg() - create broadcast protocol message
 */
static bool tipc_link_build_bc_proto_msg(struct tipc_link *l, bool bcast,
					 u16 peers_snd_nxt,
					 struct sk_buff_head *xmitq)
{
	struct sk_buff *skb;
	struct tipc_msg *hdr;
	struct sk_buff *dfrd_skb = skb_peek(&l->deferdq);
	u16 ack = l->rcv_nxt - 1;
	u16 gap_to = peers_snd_nxt - 1;

	skb = tipc_msg_create(BCAST_PROTOCOL, STATE_MSG, INT_H_SIZE,
			      0, l->addr, link_own_addr(l), 0, 0, 0);
	if (!skb)
		return false;
	hdr = buf_msg(skb);
	msg_set_last_bcast(hdr, l->bc_sndlink->snd_nxt - 1);
	msg_set_bcast_ack(hdr, ack);
	msg_set_bcgap_after(hdr, ack);
	if (dfrd_skb)
		gap_to = buf_seqno(dfrd_skb) - 1;
	msg_set_bcgap_to(hdr, gap_to);
	msg_set_non_seq(hdr, bcast);
	__skb_queue_tail(xmitq, skb);
	return true;
}

/* tipc_link_build_bc_init_msg() - synchronize broadcast link endpoints.
 *
 * Give a newly added peer node the sequence number where it should
 * start receiving and acking broadcast packets.
 */
static void tipc_link_build_bc_init_msg(struct tipc_link *l,
					struct sk_buff_head *xmitq)
{
	struct sk_buff_head list;

	__skb_queue_head_init(&list);
	if (!tipc_link_build_bc_proto_msg(l->bc_rcvlink, false, 0, &list))
		return;
	tipc_link_xmit(l, &list, xmitq);
}

/* tipc_link_bc_init_rcv - receive initial broadcast synch data from peer
 */
void tipc_link_bc_init_rcv(struct tipc_link *l, struct tipc_msg *hdr)
{
	int mtyp = msg_type(hdr);
	u16 peers_snd_nxt = msg_bc_snd_nxt(hdr);

	if (link_is_up(l))
		return;

	if (msg_user(hdr) == BCAST_PROTOCOL) {
		l->rcv_nxt = peers_snd_nxt;
		l->state = LINK_ESTABLISHED;
		return;
	}

	if (l->peer_caps & TIPC_BCAST_SYNCH)
		return;

	if (msg_peer_node_is_up(hdr))
		return;

	/* Compatibility: accept older, less safe initial synch data */
	if ((mtyp == RESET_MSG) || (mtyp == ACTIVATE_MSG))
		l->rcv_nxt = peers_snd_nxt;
}

/* tipc_link_bc_sync_rcv - update rcv link according to peer's send state
 */
void tipc_link_bc_sync_rcv(struct tipc_link *l, struct tipc_msg *hdr,
			   struct sk_buff_head *xmitq)
{
	u16 peers_snd_nxt = msg_bc_snd_nxt(hdr);

	if (!link_is_up(l))
		return;

	if (!msg_peer_node_is_up(hdr))
		return;

	l->bc_peer_is_up = true;

	/* Ignore if peers_snd_nxt goes beyond receive window */
	if (more(peers_snd_nxt, l->rcv_nxt + l->window))
		return;

	if (!more(peers_snd_nxt, l->rcv_nxt)) {
		l->nack_state = BC_NACK_SND_CONDITIONAL;
		return;
	}

	/* Don't NACK if one was recently sent or peeked */
	if (l->nack_state == BC_NACK_SND_SUPPRESS) {
		l->nack_state = BC_NACK_SND_UNCONDITIONAL;
		return;
	}

	/* Conditionally delay NACK sending until next synch rcv */
	if (l->nack_state == BC_NACK_SND_CONDITIONAL) {
		l->nack_state = BC_NACK_SND_UNCONDITIONAL;
		if ((peers_snd_nxt - l->rcv_nxt) < TIPC_MIN_LINK_WIN)
			return;
	}

	/* Send NACK now but suppress next one */
	tipc_link_build_bc_proto_msg(l, true, peers_snd_nxt, xmitq);
	l->nack_state = BC_NACK_SND_SUPPRESS;
}

void tipc_link_bc_ack_rcv(struct tipc_link *l, u16 acked,
			  struct sk_buff_head *xmitq)
{
	struct sk_buff *skb, *tmp;
	struct tipc_link *snd_l = l->bc_sndlink;

	if (!link_is_up(l) || !l->bc_peer_is_up)
		return;

	if (!more(acked, l->acked))
		return;

	/* Skip over packets peer has already acked */
	skb_queue_walk(&snd_l->transmq, skb) {
		if (more(buf_seqno(skb), l->acked))
			break;
	}

	/* Update/release the packets peer is acking now */
	skb_queue_walk_from_safe(&snd_l->transmq, skb, tmp) {
		if (more(buf_seqno(skb), acked))
			break;
		if (!--TIPC_SKB_CB(skb)->ackers) {
			__skb_unlink(skb, &snd_l->transmq);
			kfree_skb(skb);
		}
	}
	l->acked = acked;
	tipc_link_advance_backlog(snd_l, xmitq);
	if (unlikely(!skb_queue_empty(&snd_l->wakeupq)))
		link_prepare_wakeup(snd_l);
}

/* tipc_link_bc_nack_rcv(): receive broadcast nack message
 */
int tipc_link_bc_nack_rcv(struct tipc_link *l, struct sk_buff *skb,
			  struct sk_buff_head *xmitq)
{
	struct tipc_msg *hdr = buf_msg(skb);
	u32 dnode = msg_destnode(hdr);
	int mtyp = msg_type(hdr);
	u16 acked = msg_bcast_ack(hdr);
	u16 from = acked + 1;
	u16 to = msg_bcgap_to(hdr);
	u16 peers_snd_nxt = to + 1;
	int rc = 0;

	kfree_skb(skb);

	if (!tipc_link_is_up(l) || !l->bc_peer_is_up)
		return 0;

	if (mtyp != STATE_MSG)
		return 0;

	if (dnode == link_own_addr(l)) {
		tipc_link_bc_ack_rcv(l, acked, xmitq);
		rc = tipc_link_retrans(l->bc_sndlink, from, to, xmitq);
		l->stats.recv_nacks++;
		return rc;
	}

	/* Msg for other node => suppress own NACK at next sync if applicable */
	if (more(peers_snd_nxt, l->rcv_nxt) && !less(l->rcv_nxt, from))
		l->nack_state = BC_NACK_SND_SUPPRESS;

	return 0;
}

void tipc_link_set_queue_limits(struct tipc_link *l, u32 win)
{
	int max_bulk = TIPC_MAX_PUBLICATIONS / (l->mtu / ITEM_SIZE);

	l->window = win;
	l->backlog[TIPC_LOW_IMPORTANCE].limit      = win / 2;
	l->backlog[TIPC_MEDIUM_IMPORTANCE].limit   = win;
	l->backlog[TIPC_HIGH_IMPORTANCE].limit     = win / 2 * 3;
	l->backlog[TIPC_CRITICAL_IMPORTANCE].limit = win * 2;
	l->backlog[TIPC_SYSTEM_IMPORTANCE].limit   = max_bulk;
}

/**
 * link_reset_statistics - reset link statistics
 * @l_ptr: pointer to link
 */
void link_reset_statistics(struct tipc_link *l_ptr)
{
	memset(&l_ptr->stats, 0, sizeof(l_ptr->stats));
	l_ptr->stats.sent_info = l_ptr->snd_nxt;
	l_ptr->stats.recv_info = l_ptr->rcv_nxt;
}

static void link_print(struct tipc_link *l, const char *str)
{
	struct sk_buff *hskb = skb_peek(&l->transmq);
	u16 head = hskb ? msg_seqno(buf_msg(hskb)) : l->snd_nxt - 1;
	u16 tail = l->snd_nxt - 1;

	pr_info("%s Link <%s> state %x\n", str, l->name, l->state);
	pr_info("XMTQ: %u [%u-%u], BKLGQ: %u, SNDNX: %u, RCVNX: %u\n",
		skb_queue_len(&l->transmq), head, tail,
		skb_queue_len(&l->backlogq), l->snd_nxt, l->rcv_nxt);
}

/* Parse and validate nested (link) properties valid for media, bearer and link
 */
int tipc_nl_parse_link_prop(struct nlattr *prop, struct nlattr *props[])
{
	int err;

	err = nla_parse_nested(props, TIPC_NLA_PROP_MAX, prop,
			       tipc_nl_prop_policy);
	if (err)
		return err;

	if (props[TIPC_NLA_PROP_PRIO]) {
		u32 prio;

		prio = nla_get_u32(props[TIPC_NLA_PROP_PRIO]);
		if (prio > TIPC_MAX_LINK_PRI)
			return -EINVAL;
	}

	if (props[TIPC_NLA_PROP_TOL]) {
		u32 tol;

		tol = nla_get_u32(props[TIPC_NLA_PROP_TOL]);
		if ((tol < TIPC_MIN_LINK_TOL) || (tol > TIPC_MAX_LINK_TOL))
			return -EINVAL;
	}

	if (props[TIPC_NLA_PROP_WIN]) {
		u32 win;

		win = nla_get_u32(props[TIPC_NLA_PROP_WIN]);
		if ((win < TIPC_MIN_LINK_WIN) || (win > TIPC_MAX_LINK_WIN))
			return -EINVAL;
	}

	return 0;
}

static int __tipc_nl_add_stats(struct sk_buff *skb, struct tipc_stats *s)
{
	int i;
	struct nlattr *stats;

	struct nla_map {
		u32 key;
		u32 val;
	};

	struct nla_map map[] = {
		{TIPC_NLA_STATS_RX_INFO, s->recv_info},
		{TIPC_NLA_STATS_RX_FRAGMENTS, s->recv_fragments},
		{TIPC_NLA_STATS_RX_FRAGMENTED, s->recv_fragmented},
		{TIPC_NLA_STATS_RX_BUNDLES, s->recv_bundles},
		{TIPC_NLA_STATS_RX_BUNDLED, s->recv_bundled},
		{TIPC_NLA_STATS_TX_INFO, s->sent_info},
		{TIPC_NLA_STATS_TX_FRAGMENTS, s->sent_fragments},
		{TIPC_NLA_STATS_TX_FRAGMENTED, s->sent_fragmented},
		{TIPC_NLA_STATS_TX_BUNDLES, s->sent_bundles},
		{TIPC_NLA_STATS_TX_BUNDLED, s->sent_bundled},
		{TIPC_NLA_STATS_MSG_PROF_TOT, (s->msg_length_counts) ?
			s->msg_length_counts : 1},
		{TIPC_NLA_STATS_MSG_LEN_CNT, s->msg_length_counts},
		{TIPC_NLA_STATS_MSG_LEN_TOT, s->msg_lengths_total},
		{TIPC_NLA_STATS_MSG_LEN_P0, s->msg_length_profile[0]},
		{TIPC_NLA_STATS_MSG_LEN_P1, s->msg_length_profile[1]},
		{TIPC_NLA_STATS_MSG_LEN_P2, s->msg_length_profile[2]},
		{TIPC_NLA_STATS_MSG_LEN_P3, s->msg_length_profile[3]},
		{TIPC_NLA_STATS_MSG_LEN_P4, s->msg_length_profile[4]},
		{TIPC_NLA_STATS_MSG_LEN_P5, s->msg_length_profile[5]},
		{TIPC_NLA_STATS_MSG_LEN_P6, s->msg_length_profile[6]},
		{TIPC_NLA_STATS_RX_STATES, s->recv_states},
		{TIPC_NLA_STATS_RX_PROBES, s->recv_probes},
		{TIPC_NLA_STATS_RX_NACKS, s->recv_nacks},
		{TIPC_NLA_STATS_RX_DEFERRED, s->deferred_recv},
		{TIPC_NLA_STATS_TX_STATES, s->sent_states},
		{TIPC_NLA_STATS_TX_PROBES, s->sent_probes},
		{TIPC_NLA_STATS_TX_NACKS, s->sent_nacks},
		{TIPC_NLA_STATS_TX_ACKS, s->sent_acks},
		{TIPC_NLA_STATS_RETRANSMITTED, s->retransmitted},
		{TIPC_NLA_STATS_DUPLICATES, s->duplicates},
		{TIPC_NLA_STATS_LINK_CONGS, s->link_congs},
		{TIPC_NLA_STATS_MAX_QUEUE, s->max_queue_sz},
		{TIPC_NLA_STATS_AVG_QUEUE, s->queue_sz_counts ?
			(s->accu_queue_sz / s->queue_sz_counts) : 0}
	};

	stats = nla_nest_start(skb, TIPC_NLA_LINK_STATS);
	if (!stats)
		return -EMSGSIZE;

	for (i = 0; i <  ARRAY_SIZE(map); i++)
		if (nla_put_u32(skb, map[i].key, map[i].val))
			goto msg_full;

	nla_nest_end(skb, stats);

	return 0;
msg_full:
	nla_nest_cancel(skb, stats);

	return -EMSGSIZE;
}

/* Caller should hold appropriate locks to protect the link */
int __tipc_nl_add_link(struct net *net, struct tipc_nl_msg *msg,
		       struct tipc_link *link, int nlflags)
{
	int err;
	void *hdr;
	struct nlattr *attrs;
	struct nlattr *prop;
	struct tipc_net *tn = net_generic(net, tipc_net_id);

	hdr = genlmsg_put(msg->skb, msg->portid, msg->seq, &tipc_genl_family,
			  nlflags, TIPC_NL_LINK_GET);
	if (!hdr)
		return -EMSGSIZE;

	attrs = nla_nest_start(msg->skb, TIPC_NLA_LINK);
	if (!attrs)
		goto msg_full;

	if (nla_put_string(msg->skb, TIPC_NLA_LINK_NAME, link->name))
		goto attr_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_LINK_DEST,
			tipc_cluster_mask(tn->own_addr)))
		goto attr_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_LINK_MTU, link->mtu))
		goto attr_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_LINK_RX, link->rcv_nxt))
		goto attr_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_LINK_TX, link->snd_nxt))
		goto attr_msg_full;

	if (tipc_link_is_up(link))
		if (nla_put_flag(msg->skb, TIPC_NLA_LINK_UP))
			goto attr_msg_full;
	if (link->active)
		if (nla_put_flag(msg->skb, TIPC_NLA_LINK_ACTIVE))
			goto attr_msg_full;

	prop = nla_nest_start(msg->skb, TIPC_NLA_LINK_PROP);
	if (!prop)
		goto attr_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_PROP_PRIO, link->priority))
		goto prop_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_PROP_TOL, link->tolerance))
		goto prop_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_PROP_WIN,
			link->window))
		goto prop_msg_full;
	if (nla_put_u32(msg->skb, TIPC_NLA_PROP_PRIO, link->priority))
		goto prop_msg_full;
	nla_nest_end(msg->skb, prop);

	err = __tipc_nl_add_stats(msg->skb, &link->stats);
	if (err)
		goto attr_msg_full;

	nla_nest_end(msg->skb, attrs);
	genlmsg_end(msg->skb, hdr);

	return 0;

prop_msg_full:
	nla_nest_cancel(msg->skb, prop);
attr_msg_full:
	nla_nest_cancel(msg->skb, attrs);
msg_full:
	genlmsg_cancel(msg->skb, hdr);

	return -EMSGSIZE;
}