net/sctp/transport.c - LeafOS-Devices/android_kernel_samsung_gta4xl - Gitiles

 /* SCTP kernel implementation
  * Copyright (c) 1999-2000 Cisco, Inc.
  * Copyright (c) 1999-2001 Motorola, Inc.
  * Copyright (c) 2001-2003 International Business Machines Corp.
  * Copyright (c) 2001 Intel Corp.
  * Copyright (c) 2001 La Monte H.P. Yarroll
  *
  * This file is part of the SCTP kernel implementation
  *
  * This module provides the abstraction for an SCTP tranport representing
  * a remote transport address.  For local transport addresses, we just use
  * union sctp_addr.
  *
  * This SCTP implementation 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, or (at your option)
  * any later version.
  *
  * This SCTP implementation is distributed in the hope that it
  * will be useful, but WITHOUT ANY WARRANTY; without even the implied
  *                 ************************
  * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  * See the GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with GNU CC; see the file COPYING.  If not, see
  * <http://www.gnu.org/licenses/>.
  *
  * Please send any bug reports or fixes you make to the
  * email address(es):
  *    lksctp developers <linux-sctp@vger.kernel.org>
  *
  * Written or modified by:
  *    La Monte H.P. Yarroll <piggy@acm.org>
  *    Karl Knutson          <karl@athena.chicago.il.us>
  *    Jon Grimm             <jgrimm@us.ibm.com>
  *    Xingang Guo           <xingang.guo@intel.com>
  *    Hui Huang             <hui.huang@nokia.com>
  *    Sridhar Samudrala	    <sri@us.ibm.com>
  *    Ardelle Fan	    <ardelle.fan@intel.com>
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/random.h>
 #include <net/sctp/sctp.h>
 #include <net/sctp/sm.h>

 /* 1st Level Abstractions.  */

 /* Initialize a new transport from provided memory.  */
 static struct sctp_transport *sctp_transport_init(struct net *net,
 						  struct sctp_transport *peer,
 						  const union sctp_addr *addr,
 						  gfp_t gfp)
 {
 	/* Copy in the address.  */
 	peer->ipaddr = *addr;
 	peer->af_specific = sctp_get_af_specific(addr->sa.sa_family);
 	memset(&peer->saddr, 0, sizeof(union sctp_addr));

 	peer->sack_generation = 0;

 	/* From 6.3.1 RTO Calculation:
 	 *
 	 * C1) Until an RTT measurement has been made for a packet sent to the
 	 * given destination transport address, set RTO to the protocol
 	 * parameter 'RTO.Initial'.
 	 */
 	peer->rto = msecs_to_jiffies(net->sctp.rto_initial);

 	peer->last_time_heard = 0;
 	peer->last_time_ecne_reduced = jiffies;

 	peer->param_flags = SPP_HB_DISABLE |
 			    SPP_PMTUD_ENABLE |
 			    SPP_SACKDELAY_ENABLE;

 	/* Initialize the default path max_retrans.  */
 	peer->pathmaxrxt  = net->sctp.max_retrans_path;
 	peer->pf_retrans  = net->sctp.pf_retrans;

 	INIT_LIST_HEAD(&peer->transmitted);
 	INIT_LIST_HEAD(&peer->send_ready);
 	INIT_LIST_HEAD(&peer->transports);

 	setup_timer(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event,
 		    (unsigned long)peer);
 	setup_timer(&peer->hb_timer, sctp_generate_heartbeat_event,
 		    (unsigned long)peer);
 	setup_timer(&peer->reconf_timer, sctp_generate_reconf_event,
 		    (unsigned long)peer);
 	setup_timer(&peer->proto_unreach_timer,
 		    sctp_generate_proto_unreach_event, (unsigned long)peer);

 	/* Initialize the 64-bit random nonce sent with heartbeat. */
 	get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));

 	refcount_set(&peer->refcnt, 1);

 	return peer;
 }

 /* Allocate and initialize a new transport.  */
 struct sctp_transport *sctp_transport_new(struct net *net,
 					  const union sctp_addr *addr,
 					  gfp_t gfp)
 {
 	struct sctp_transport *transport;

 	transport = kzalloc(sizeof(*transport), gfp);
 	if (!transport)
 		goto fail;

 	if (!sctp_transport_init(net, transport, addr, gfp))
 		goto fail_init;

 	SCTP_DBG_OBJCNT_INC(transport);

 	return transport;

 fail_init:
 	kfree(transport);

 fail:
 	return NULL;
 }

 /* This transport is no longer needed.  Free up if possible, or
  * delay until it last reference count.
  */
 void sctp_transport_free(struct sctp_transport *transport)
 {
 	/* Try to delete the heartbeat timer.  */
 	if (del_timer(&transport->hb_timer))
 		sctp_transport_put(transport);

 	/* Delete the T3_rtx timer if it's active.
 	 * There is no point in not doing this now and letting
 	 * structure hang around in memory since we know
 	 * the tranport is going away.
 	 */
 	if (del_timer(&transport->T3_rtx_timer))
 		sctp_transport_put(transport);

 	if (del_timer(&transport->reconf_timer))
 		sctp_transport_put(transport);

 	/* Delete the ICMP proto unreachable timer if it's active. */
 	if (del_timer(&transport->proto_unreach_timer))
 		sctp_transport_put(transport);

 	sctp_transport_put(transport);
 }

 static void sctp_transport_destroy_rcu(struct rcu_head *head)
 {
 	struct sctp_transport *transport;

 	transport = container_of(head, struct sctp_transport, rcu);

 	dst_release(transport->dst);
 	kfree(transport);
 	SCTP_DBG_OBJCNT_DEC(transport);
 }

 /* Destroy the transport data structure.
  * Assumes there are no more users of this structure.
  */
 static void sctp_transport_destroy(struct sctp_transport *transport)
 {
 	if (unlikely(refcount_read(&transport->refcnt))) {
 		WARN(1, "Attempt to destroy undead transport %p!\n", transport);
 		return;
 	}

 	sctp_packet_free(&transport->packet);

 	if (transport->asoc)
 		sctp_association_put(transport->asoc);

 	call_rcu(&transport->rcu, sctp_transport_destroy_rcu);
 }

 /* Start T3_rtx timer if it is not already running and update the heartbeat
  * timer.  This routine is called every time a DATA chunk is sent.
  */
 void sctp_transport_reset_t3_rtx(struct sctp_transport *transport)
 {
 	/* RFC 2960 6.3.2 Retransmission Timer Rules
 	 *
 	 * R1) Every time a DATA chunk is sent to any address(including a
 	 * retransmission), if the T3-rtx timer of that address is not running
 	 * start it running so that it will expire after the RTO of that
 	 * address.
 	 */

 	if (!timer_pending(&transport->T3_rtx_timer))
 		if (!mod_timer(&transport->T3_rtx_timer,
 			       jiffies + transport->rto))
 			sctp_transport_hold(transport);
 }

 void sctp_transport_reset_hb_timer(struct sctp_transport *transport)
 {
 	unsigned long expires;

 	/* When a data chunk is sent, reset the heartbeat interval.  */
 	expires = jiffies + sctp_transport_timeout(transport);
 	if ((time_before(transport->hb_timer.expires, expires) ||
 	     !timer_pending(&transport->hb_timer)) &&
 	    !mod_timer(&transport->hb_timer,
 		       expires + prandom_u32_max(transport->rto)))
 		sctp_transport_hold(transport);
 }

 void sctp_transport_reset_reconf_timer(struct sctp_transport *transport)
 {
 	if (!timer_pending(&transport->reconf_timer))
 		if (!mod_timer(&transport->reconf_timer,
 			       jiffies + transport->rto))
 			sctp_transport_hold(transport);
 }

 /* This transport has been assigned to an association.
  * Initialize fields from the association or from the sock itself.
  * Register the reference count in the association.
  */
 void sctp_transport_set_owner(struct sctp_transport *transport,
 			      struct sctp_association *asoc)
 {
 	transport->asoc = asoc;
 	sctp_association_hold(asoc);
 }

 /* Initialize the pmtu of a transport. */
 void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)
 {
 	/* If we don't have a fresh route, look one up */
 	if (!transport->dst || transport->dst->obsolete) {
 		sctp_transport_dst_release(transport);
 		transport->af_specific->get_dst(transport, &transport->saddr,
 						&transport->fl, sk);
 	}

 	if (transport->dst) {
 		transport->pathmtu = SCTP_TRUNC4(dst_mtu(transport->dst));
 	} else
 		transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
 }

 bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
 {
 	struct dst_entry *dst = sctp_transport_dst_check(t);
 	struct sock *sk = t->asoc->base.sk;
 	bool change = true;

 	if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
 		pr_warn_ratelimited("%s: Reported pmtu %d too low, using default minimum of %d\n",
 				    __func__, pmtu, SCTP_DEFAULT_MINSEGMENT);
 		/* Use default minimum segment instead */
 		pmtu = SCTP_DEFAULT_MINSEGMENT;
 	}
 	pmtu = SCTP_TRUNC4(pmtu);

 	if (dst) {
 		struct sctp_pf *pf = sctp_get_pf_specific(dst->ops->family);
 		union sctp_addr addr;

 		pf->af->from_sk(&addr, sk);
 		pf->to_sk_daddr(&t->ipaddr, sk);
 		dst->ops->update_pmtu(dst, sk, NULL, pmtu, true);
 		pf->to_sk_daddr(&addr, sk);

 		dst = sctp_transport_dst_check(t);
 	}

 	if (!dst) {
 		t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
 		dst = t->dst;
 	}

 	if (dst) {
 		/* Re-fetch, as under layers may have a higher minimum size */
 		pmtu = SCTP_TRUNC4(dst_mtu(dst));
 		change = t->pathmtu != pmtu;
 	}
 	t->pathmtu = pmtu;

 	return change;
 }

 /* Caches the dst entry and source address for a transport's destination
  * address.
  */
 void sctp_transport_route(struct sctp_transport *transport,
 			  union sctp_addr *saddr, struct sctp_sock *opt)
 {
 	struct sctp_association *asoc = transport->asoc;
 	struct sctp_af *af = transport->af_specific;

 	af->get_dst(transport, saddr, &transport->fl, sctp_opt2sk(opt));

 	if (saddr)
 		memcpy(&transport->saddr, saddr, sizeof(union sctp_addr));
 	else
 		af->get_saddr(opt, transport, &transport->fl);

 	if ((transport->param_flags & SPP_PMTUD_DISABLE) && transport->pathmtu) {
 		return;
 	}
 	if (transport->dst) {
 		transport->pathmtu = SCTP_TRUNC4(dst_mtu(transport->dst));

 		/* Initialize sk->sk_rcv_saddr, if the transport is the
 		 * association's active path for getsockname().
 		 */
 		if (asoc && (!asoc->peer.primary_path ||
 				(transport == asoc->peer.active_path)))
 			opt->pf->to_sk_saddr(&transport->saddr,
 					     asoc->base.sk);
 	} else
 		transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
 }

 /* Hold a reference to a transport.  */
 int sctp_transport_hold(struct sctp_transport *transport)
 {
 	return refcount_inc_not_zero(&transport->refcnt);
 }

 /* Release a reference to a transport and clean up
  * if there are no more references.
  */
 void sctp_transport_put(struct sctp_transport *transport)
 {
 	if (refcount_dec_and_test(&transport->refcnt))
 		sctp_transport_destroy(transport);
 }

 /* Update transport's RTO based on the newly calculated RTT. */
 void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
 {
 	if (unlikely(!tp->rto_pending))
 		/* We should not be doing any RTO updates unless rto_pending is set.  */
 		pr_debug("%s: rto_pending not set on transport %p!\n", __func__, tp);

 	if (tp->rttvar || tp->srtt) {
 		struct net *net = sock_net(tp->asoc->base.sk);
 		/* 6.3.1 C3) When a new RTT measurement R' is made, set
 		 * RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'|
 		 * SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'
 		 */

 		/* Note:  The above algorithm has been rewritten to
 		 * express rto_beta and rto_alpha as inverse powers
 		 * of two.
 		 * For example, assuming the default value of RTO.Alpha of
 		 * 1/8, rto_alpha would be expressed as 3.
 		 */
 		tp->rttvar = tp->rttvar - (tp->rttvar >> net->sctp.rto_beta)
 			+ (((__u32)abs((__s64)tp->srtt - (__s64)rtt)) >> net->sctp.rto_beta);
 		tp->srtt = tp->srtt - (tp->srtt >> net->sctp.rto_alpha)
 			+ (rtt >> net->sctp.rto_alpha);
 	} else {
 		/* 6.3.1 C2) When the first RTT measurement R is made, set
 		 * SRTT <- R, RTTVAR <- R/2.
 		 */
 		tp->srtt = rtt;
 		tp->rttvar = rtt >> 1;
 	}

 	/* 6.3.1 G1) Whenever RTTVAR is computed, if RTTVAR = 0, then
 	 * adjust RTTVAR <- G, where G is the CLOCK GRANULARITY.
 	 */
 	if (tp->rttvar == 0)
 		tp->rttvar = SCTP_CLOCK_GRANULARITY;

 	/* 6.3.1 C3) After the computation, update RTO <- SRTT + 4 * RTTVAR. */
 	tp->rto = tp->srtt + (tp->rttvar << 2);

 	/* 6.3.1 C6) Whenever RTO is computed, if it is less than RTO.Min
 	 * seconds then it is rounded up to RTO.Min seconds.
 	 */
 	if (tp->rto < tp->asoc->rto_min)
 		tp->rto = tp->asoc->rto_min;

 	/* 6.3.1 C7) A maximum value may be placed on RTO provided it is
 	 * at least RTO.max seconds.
 	 */
 	if (tp->rto > tp->asoc->rto_max)
 		tp->rto = tp->asoc->rto_max;

 	sctp_max_rto(tp->asoc, tp);
 	tp->rtt = rtt;

 	/* Reset rto_pending so that a new RTT measurement is started when a
 	 * new data chunk is sent.
 	 */
 	tp->rto_pending = 0;

 	pr_debug("%s: transport:%p, rtt:%d, srtt:%d rttvar:%d, rto:%ld\n",
 		 __func__, tp, rtt, tp->srtt, tp->rttvar, tp->rto);
 }

 /* This routine updates the transport's cwnd and partial_bytes_acked
  * parameters based on the bytes acked in the received SACK.
  */
 void sctp_transport_raise_cwnd(struct sctp_transport *transport,
 			       __u32 sack_ctsn, __u32 bytes_acked)
 {
 	struct sctp_association *asoc = transport->asoc;
 	__u32 cwnd, ssthresh, flight_size, pba, pmtu;

 	cwnd = transport->cwnd;
 	flight_size = transport->flight_size;

 	/* See if we need to exit Fast Recovery first */
 	if (asoc->fast_recovery &&
 	    TSN_lte(asoc->fast_recovery_exit, sack_ctsn))
 		asoc->fast_recovery = 0;

 	ssthresh = transport->ssthresh;
 	pba = transport->partial_bytes_acked;
 	pmtu = transport->asoc->pathmtu;

 	if (cwnd <= ssthresh) {
 		/* RFC 4960 7.2.1
 		 * o  When cwnd is less than or equal to ssthresh, an SCTP
 		 *    endpoint MUST use the slow-start algorithm to increase
 		 *    cwnd only if the current congestion window is being fully
 		 *    utilized, an incoming SACK advances the Cumulative TSN
 		 *    Ack Point, and the data sender is not in Fast Recovery.
 		 *    Only when these three conditions are met can the cwnd be
 		 *    increased; otherwise, the cwnd MUST not be increased.
 		 *    If these conditions are met, then cwnd MUST be increased
 		 *    by, at most, the lesser of 1) the total size of the
 		 *    previously outstanding DATA chunk(s) acknowledged, and
 		 *    2) the destination's path MTU.  This upper bound protects
 		 *    against the ACK-Splitting attack outlined in [SAVAGE99].
 		 */
 		if (asoc->fast_recovery)
 			return;

 		/* The appropriate cwnd increase algorithm is performed
 		 * if, and only if the congestion window is being fully
 		 * utilized.  Note that RFC4960 Errata 3.22 removed the
 		 * other condition on ctsn moving.
 		 */
 		if (flight_size < cwnd)
 			return;

 		if (bytes_acked > pmtu)
 			cwnd += pmtu;
 		else
 			cwnd += bytes_acked;

 		pr_debug("%s: slow start: transport:%p, bytes_acked:%d, "
 			 "cwnd:%d, ssthresh:%d, flight_size:%d, pba:%d\n",
 			 __func__, transport, bytes_acked, cwnd, ssthresh,
 			 flight_size, pba);
 	} else {
 		/* RFC 2960 7.2.2 Whenever cwnd is greater than ssthresh,
 		 * upon each SACK arrival, increase partial_bytes_acked
 		 * by the total number of bytes of all new chunks
 		 * acknowledged in that SACK including chunks
 		 * acknowledged by the new Cumulative TSN Ack and by Gap
 		 * Ack Blocks. (updated by RFC4960 Errata 3.22)
 		 *
 		 * When partial_bytes_acked is greater than cwnd and
 		 * before the arrival of the SACK the sender had less
 		 * bytes of data outstanding than cwnd (i.e., before
 		 * arrival of the SACK, flightsize was less than cwnd),
 		 * reset partial_bytes_acked to cwnd. (RFC 4960 Errata
 		 * 3.26)
 		 *
 		 * When partial_bytes_acked is equal to or greater than
 		 * cwnd and before the arrival of the SACK the sender
 		 * had cwnd or more bytes of data outstanding (i.e.,
 		 * before arrival of the SACK, flightsize was greater
 		 * than or equal to cwnd), partial_bytes_acked is reset
 		 * to (partial_bytes_acked - cwnd). Next, cwnd is
 		 * increased by MTU. (RFC 4960 Errata 3.12)
 		 */
 		pba += bytes_acked;
 		if (pba > cwnd && flight_size < cwnd)
 			pba = cwnd;
 		if (pba >= cwnd && flight_size >= cwnd) {
 			pba = pba - cwnd;
 			cwnd += pmtu;
 		}

 		pr_debug("%s: congestion avoidance: transport:%p, "
 			 "bytes_acked:%d, cwnd:%d, ssthresh:%d, "
 			 "flight_size:%d, pba:%d\n", __func__,
 			 transport, bytes_acked, cwnd, ssthresh,
 			 flight_size, pba);
 	}

 	transport->cwnd = cwnd;
 	transport->partial_bytes_acked = pba;
 }

 /* This routine is used to lower the transport's cwnd when congestion is
  * detected.
  */
 void sctp_transport_lower_cwnd(struct sctp_transport *transport,
 			       enum sctp_lower_cwnd reason)
 {
 	struct sctp_association *asoc = transport->asoc;

 	switch (reason) {
 	case SCTP_LOWER_CWND_T3_RTX:
 		/* RFC 2960 Section 7.2.3, sctpimpguide
 		 * When the T3-rtx timer expires on an address, SCTP should
 		 * perform slow start by:
 		 *      ssthresh = max(cwnd/2, 4*MTU)
 		 *      cwnd = 1*MTU
 		 *      partial_bytes_acked = 0
 		 */
 		transport->ssthresh = max(transport->cwnd/2,
 					  4*asoc->pathmtu);
 		transport->cwnd = asoc->pathmtu;

 		/* T3-rtx also clears fast recovery */
 		asoc->fast_recovery = 0;
 		break;

 	case SCTP_LOWER_CWND_FAST_RTX:
 		/* RFC 2960 7.2.4 Adjust the ssthresh and cwnd of the
 		 * destination address(es) to which the missing DATA chunks
 		 * were last sent, according to the formula described in
 		 * Section 7.2.3.
 		 *
 		 * RFC 2960 7.2.3, sctpimpguide Upon detection of packet
 		 * losses from SACK (see Section 7.2.4), An endpoint
 		 * should do the following:
 		 *      ssthresh = max(cwnd/2, 4*MTU)
 		 *      cwnd = ssthresh
 		 *      partial_bytes_acked = 0
 		 */
 		if (asoc->fast_recovery)
 			return;

 		/* Mark Fast recovery */
 		asoc->fast_recovery = 1;
 		asoc->fast_recovery_exit = asoc->next_tsn - 1;

 		transport->ssthresh = max(transport->cwnd/2,
 					  4*asoc->pathmtu);
 		transport->cwnd = transport->ssthresh;
 		break;

 	case SCTP_LOWER_CWND_ECNE:
 		/* RFC 2481 Section 6.1.2.
 		 * If the sender receives an ECN-Echo ACK packet
 		 * then the sender knows that congestion was encountered in the
 		 * network on the path from the sender to the receiver. The
 		 * indication of congestion should be treated just as a
 		 * congestion loss in non-ECN Capable TCP. That is, the TCP
 		 * source halves the congestion window "cwnd" and reduces the
 		 * slow start threshold "ssthresh".
 		 * A critical condition is that TCP does not react to
 		 * congestion indications more than once every window of
 		 * data (or more loosely more than once every round-trip time).
 		 */
 		if (time_after(jiffies, transport->last_time_ecne_reduced +
 					transport->rtt)) {
 			transport->ssthresh = max(transport->cwnd/2,
 						  4*asoc->pathmtu);
 			transport->cwnd = transport->ssthresh;
 			transport->last_time_ecne_reduced = jiffies;
 		}
 		break;

 	case SCTP_LOWER_CWND_INACTIVE:
 		/* RFC 2960 Section 7.2.1, sctpimpguide
 		 * When the endpoint does not transmit data on a given
 		 * transport address, the cwnd of the transport address
 		 * should be adjusted to max(cwnd/2, 4*MTU) per RTO.
 		 * NOTE: Although the draft recommends that this check needs
 		 * to be done every RTO interval, we do it every hearbeat
 		 * interval.
 		 */
 		transport->cwnd = max(transport->cwnd/2,
 					 4*asoc->pathmtu);
 		/* RFC 4960 Errata 3.27.2: also adjust sshthresh */
 		transport->ssthresh = transport->cwnd;
 		break;
 	}

 	transport->partial_bytes_acked = 0;

 	pr_debug("%s: transport:%p, reason:%d, cwnd:%d, ssthresh:%d\n",
 		 __func__, transport, reason, transport->cwnd,
 		 transport->ssthresh);
 }

 /* Apply Max.Burst limit to the congestion window:
  * sctpimpguide-05 2.14.2
  * D) When the time comes for the sender to
  * transmit new DATA chunks, the protocol parameter Max.Burst MUST
  * first be applied to limit how many new DATA chunks may be sent.
  * The limit is applied by adjusting cwnd as follows:
  * 	if ((flightsize+ Max.Burst * MTU) < cwnd)
  * 		cwnd = flightsize + Max.Burst * MTU
  */

 void sctp_transport_burst_limited(struct sctp_transport *t)
 {
 	struct sctp_association *asoc = t->asoc;
 	u32 old_cwnd = t->cwnd;
 	u32 max_burst_bytes;

 	if (t->burst_limited || asoc->max_burst == 0)
 		return;

 	max_burst_bytes = t->flight_size + (asoc->max_burst * asoc->pathmtu);
 	if (max_burst_bytes < old_cwnd) {
 		t->cwnd = max_burst_bytes;
 		t->burst_limited = old_cwnd;
 	}
 }

 /* Restore the old cwnd congestion window, after the burst had it's
  * desired effect.
  */
 void sctp_transport_burst_reset(struct sctp_transport *t)
 {
 	if (t->burst_limited) {
 		t->cwnd = t->burst_limited;
 		t->burst_limited = 0;
 	}
 }

 /* What is the next timeout value for this transport? */
 unsigned long sctp_transport_timeout(struct sctp_transport *trans)
 {
 	/* RTO + timer slack +/- 50% of RTO */
 	unsigned long timeout = trans->rto >> 1;

 	if (trans->state != SCTP_UNCONFIRMED &&
 	    trans->state != SCTP_PF)
 		timeout += trans->hbinterval;

 	return max_t(unsigned long, timeout, HZ / 5);
 }

 /* Reset transport variables to their initial values */
 void sctp_transport_reset(struct sctp_transport *t)
 {
 	struct sctp_association *asoc = t->asoc;

 	/* RFC 2960 (bis), Section 5.2.4
 	 * All the congestion control parameters (e.g., cwnd, ssthresh)
 	 * related to this peer MUST be reset to their initial values
 	 * (see Section 6.2.1)
 	 */
 	t->cwnd = min(4*asoc->pathmtu, max_t(__u32, 2*asoc->pathmtu, 4380));
 	t->burst_limited = 0;
 	t->ssthresh = asoc->peer.i.a_rwnd;
 	t->rto = asoc->rto_initial;
 	sctp_max_rto(asoc, t);
 	t->rtt = 0;
 	t->srtt = 0;
 	t->rttvar = 0;

 	/* Reset these additional variables so that we have a clean slate. */
 	t->partial_bytes_acked = 0;
 	t->flight_size = 0;
 	t->error_count = 0;
 	t->rto_pending = 0;
 	t->hb_sent = 0;

 	/* Initialize the state information for SFR-CACC */
 	t->cacc.changeover_active = 0;
 	t->cacc.cycling_changeover = 0;
 	t->cacc.next_tsn_at_change = 0;
 	t->cacc.cacc_saw_newack = 0;
 }

 /* Schedule retransmission on the given transport */
 void sctp_transport_immediate_rtx(struct sctp_transport *t)
 {
 	/* Stop pending T3_rtx_timer */
 	if (del_timer(&t->T3_rtx_timer))
 		sctp_transport_put(t);

 	sctp_retransmit(&t->asoc->outqueue, t, SCTP_RTXR_T3_RTX);
 	if (!timer_pending(&t->T3_rtx_timer)) {
 		if (!mod_timer(&t->T3_rtx_timer, jiffies + t->rto))
 			sctp_transport_hold(t);
 	}
 }

 /* Drop dst */
 void sctp_transport_dst_release(struct sctp_transport *t)
 {
 	dst_release(t->dst);
 	t->dst = NULL;
 	t->dst_pending_confirm = 0;
 }

 /* Schedule neighbour confirm */
 void sctp_transport_dst_confirm(struct sctp_transport *t)
 {
 	t->dst_pending_confirm = 1;
 }
	/* SCTP kernel implementation
	* Copyright (c) 1999-2000 Cisco, Inc.
	* Copyright (c) 1999-2001 Motorola, Inc.
	* Copyright (c) 2001-2003 International Business Machines Corp.
	* Copyright (c) 2001 Intel Corp.
	* Copyright (c) 2001 La Monte H.P. Yarroll
	*
	* This file is part of the SCTP kernel implementation
	*
	* This module provides the abstraction for an SCTP tranport representing
	* a remote transport address. For local transport addresses, we just use
	* union sctp_addr.
	*
	* This SCTP implementation 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, or (at your option)
	* any later version.
	*
	* This SCTP implementation is distributed in the hope that it
	* will be useful, but WITHOUT ANY WARRANTY; without even the implied
	* ************************
	* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
	* See the GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with GNU CC; see the file COPYING. If not, see
	* <http://www.gnu.org/licenses/>.
	*
	* Please send any bug reports or fixes you make to the
	* email address(es):
	* lksctp developers <linux-sctp@vger.kernel.org>
	*
	* Written or modified by:
	* La Monte H.P. Yarroll <piggy@acm.org>
	* Karl Knutson <karl@athena.chicago.il.us>
	* Jon Grimm <jgrimm@us.ibm.com>
	* Xingang Guo <xingang.guo@intel.com>
	* Hui Huang <hui.huang@nokia.com>
	* Sridhar Samudrala <sri@us.ibm.com>
	* Ardelle Fan <ardelle.fan@intel.com>
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/slab.h>
	#include <linux/types.h>
	#include <linux/random.h>
	#include <net/sctp/sctp.h>
	#include <net/sctp/sm.h>

	/* 1st Level Abstractions. */

	/* Initialize a new transport from provided memory. */
	static struct sctp_transport sctp_transport_init(struct net net,
	struct sctp_transport *peer,
	const union sctp_addr *addr,
	gfp_t gfp)
	{
	/* Copy in the address. */
	peer->ipaddr = *addr;
	peer->af_specific = sctp_get_af_specific(addr->sa.sa_family);
	memset(&peer->saddr, 0, sizeof(union sctp_addr));

	peer->sack_generation = 0;

	/* From 6.3.1 RTO Calculation:
	*
	* C1) Until an RTT measurement has been made for a packet sent to the
	* given destination transport address, set RTO to the protocol
	* parameter 'RTO.Initial'.
	*/
	peer->rto = msecs_to_jiffies(net->sctp.rto_initial);

	peer->last_time_heard = 0;
	peer->last_time_ecne_reduced = jiffies;

	peer->param_flags = SPP_HB_DISABLE \|
	SPP_PMTUD_ENABLE \|
	SPP_SACKDELAY_ENABLE;

	/* Initialize the default path max_retrans. */
	peer->pathmaxrxt = net->sctp.max_retrans_path;
	peer->pf_retrans = net->sctp.pf_retrans;

	INIT_LIST_HEAD(&peer->transmitted);
	INIT_LIST_HEAD(&peer->send_ready);
	INIT_LIST_HEAD(&peer->transports);

	setup_timer(&peer->T3_rtx_timer, sctp_generate_t3_rtx_event,
	(unsigned long)peer);
	setup_timer(&peer->hb_timer, sctp_generate_heartbeat_event,
	(unsigned long)peer);
	setup_timer(&peer->reconf_timer, sctp_generate_reconf_event,
	(unsigned long)peer);
	setup_timer(&peer->proto_unreach_timer,
	sctp_generate_proto_unreach_event, (unsigned long)peer);

	/* Initialize the 64-bit random nonce sent with heartbeat. */
	get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));

	refcount_set(&peer->refcnt, 1);

	return peer;
	}

	/* Allocate and initialize a new transport. */
	struct sctp_transport sctp_transport_new(struct net net,
	const union sctp_addr *addr,
	gfp_t gfp)
	{
	struct sctp_transport *transport;

	transport = kzalloc(sizeof(*transport), gfp);
	if (!transport)
	goto fail;

	if (!sctp_transport_init(net, transport, addr, gfp))
	goto fail_init;

	SCTP_DBG_OBJCNT_INC(transport);

	return transport;

	fail_init:
	kfree(transport);

	fail:
	return NULL;
	}

	/* This transport is no longer needed. Free up if possible, or
	* delay until it last reference count.
	*/
	void sctp_transport_free(struct sctp_transport *transport)
	{
	/* Try to delete the heartbeat timer. */
	if (del_timer(&transport->hb_timer))
	sctp_transport_put(transport);

	/* Delete the T3_rtx timer if it's active.
	* There is no point in not doing this now and letting
	* structure hang around in memory since we know
	* the tranport is going away.
	*/
	if (del_timer(&transport->T3_rtx_timer))
	sctp_transport_put(transport);

	if (del_timer(&transport->reconf_timer))
	sctp_transport_put(transport);

	/* Delete the ICMP proto unreachable timer if it's active. */
	if (del_timer(&transport->proto_unreach_timer))
	sctp_transport_put(transport);

	sctp_transport_put(transport);
	}

	static void sctp_transport_destroy_rcu(struct rcu_head *head)
	{
	struct sctp_transport *transport;

	transport = container_of(head, struct sctp_transport, rcu);

	dst_release(transport->dst);
	kfree(transport);
	SCTP_DBG_OBJCNT_DEC(transport);
	}

	/* Destroy the transport data structure.
	* Assumes there are no more users of this structure.
	*/
	static void sctp_transport_destroy(struct sctp_transport *transport)
	{
	if (unlikely(refcount_read(&transport->refcnt))) {
	WARN(1, "Attempt to destroy undead transport %p!\n", transport);
	return;
	}

	sctp_packet_free(&transport->packet);

	if (transport->asoc)
	sctp_association_put(transport->asoc);

	call_rcu(&transport->rcu, sctp_transport_destroy_rcu);
	}

	/* Start T3_rtx timer if it is not already running and update the heartbeat
	* timer. This routine is called every time a DATA chunk is sent.
	*/
	void sctp_transport_reset_t3_rtx(struct sctp_transport *transport)
	{
	/* RFC 2960 6.3.2 Retransmission Timer Rules
	*
	* R1) Every time a DATA chunk is sent to any address(including a
	* retransmission), if the T3-rtx timer of that address is not running
	* start it running so that it will expire after the RTO of that
	* address.
	*/

	if (!timer_pending(&transport->T3_rtx_timer))
	if (!mod_timer(&transport->T3_rtx_timer,
	jiffies + transport->rto))
	sctp_transport_hold(transport);
	}

	void sctp_transport_reset_hb_timer(struct sctp_transport *transport)
	{
	unsigned long expires;

	/* When a data chunk is sent, reset the heartbeat interval. */
	expires = jiffies + sctp_transport_timeout(transport);
	if ((time_before(transport->hb_timer.expires, expires) \|\|
	!timer_pending(&transport->hb_timer)) &&
	!mod_timer(&transport->hb_timer,
	expires + prandom_u32_max(transport->rto)))
	sctp_transport_hold(transport);
	}

	void sctp_transport_reset_reconf_timer(struct sctp_transport *transport)
	{
	if (!timer_pending(&transport->reconf_timer))
	if (!mod_timer(&transport->reconf_timer,
	jiffies + transport->rto))
	sctp_transport_hold(transport);
	}

	/* This transport has been assigned to an association.
	* Initialize fields from the association or from the sock itself.
	* Register the reference count in the association.
	*/
	void sctp_transport_set_owner(struct sctp_transport *transport,
	struct sctp_association *asoc)
	{
	transport->asoc = asoc;
	sctp_association_hold(asoc);
	}

	/* Initialize the pmtu of a transport. */
	void sctp_transport_pmtu(struct sctp_transport transport, struct sock sk)
	{
	/* If we don't have a fresh route, look one up */
	if (!transport->dst \|\| transport->dst->obsolete) {
	sctp_transport_dst_release(transport);
	transport->af_specific->get_dst(transport, &transport->saddr,
	&transport->fl, sk);
	}

	if (transport->dst) {
	transport->pathmtu = SCTP_TRUNC4(dst_mtu(transport->dst));
	} else
	transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
	}

	bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu)
	{
	struct dst_entry *dst = sctp_transport_dst_check(t);
	struct sock *sk = t->asoc->base.sk;
	bool change = true;

	if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) {
	pr_warn_ratelimited("%s: Reported pmtu %d too low, using default minimum of %d\n",
	__func__, pmtu, SCTP_DEFAULT_MINSEGMENT);
	/* Use default minimum segment instead */
	pmtu = SCTP_DEFAULT_MINSEGMENT;
	}
	pmtu = SCTP_TRUNC4(pmtu);

	if (dst) {
	struct sctp_pf *pf = sctp_get_pf_specific(dst->ops->family);
	union sctp_addr addr;

	pf->af->from_sk(&addr, sk);
	pf->to_sk_daddr(&t->ipaddr, sk);
	dst->ops->update_pmtu(dst, sk, NULL, pmtu, true);
	pf->to_sk_daddr(&addr, sk);

	dst = sctp_transport_dst_check(t);
	}

	if (!dst) {
	t->af_specific->get_dst(t, &t->saddr, &t->fl, sk);
	dst = t->dst;
	}

	if (dst) {
	/* Re-fetch, as under layers may have a higher minimum size */
	pmtu = SCTP_TRUNC4(dst_mtu(dst));
	change = t->pathmtu != pmtu;
	}
	t->pathmtu = pmtu;

	return change;
	}

	/* Caches the dst entry and source address for a transport's destination
	* address.
	*/
	void sctp_transport_route(struct sctp_transport *transport,
	union sctp_addr saddr, struct sctp_sock opt)
	{
	struct sctp_association *asoc = transport->asoc;
	struct sctp_af *af = transport->af_specific;

	af->get_dst(transport, saddr, &transport->fl, sctp_opt2sk(opt));

	if (saddr)
	memcpy(&transport->saddr, saddr, sizeof(union sctp_addr));
	else
	af->get_saddr(opt, transport, &transport->fl);

	if ((transport->param_flags & SPP_PMTUD_DISABLE) && transport->pathmtu) {
	return;
	}
	if (transport->dst) {
	transport->pathmtu = SCTP_TRUNC4(dst_mtu(transport->dst));

	/* Initialize sk->sk_rcv_saddr, if the transport is the
	* association's active path for getsockname().
	*/
	if (asoc && (!asoc->peer.primary_path \|\|
	(transport == asoc->peer.active_path)))
	opt->pf->to_sk_saddr(&transport->saddr,
	asoc->base.sk);
	} else
	transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT;
	}

	/* Hold a reference to a transport. */
	int sctp_transport_hold(struct sctp_transport *transport)
	{
	return refcount_inc_not_zero(&transport->refcnt);
	}

	/* Release a reference to a transport and clean up
	* if there are no more references.
	*/
	void sctp_transport_put(struct sctp_transport *transport)
	{
	if (refcount_dec_and_test(&transport->refcnt))
	sctp_transport_destroy(transport);
	}

	/* Update transport's RTO based on the newly calculated RTT. */
	void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt)
	{
	if (unlikely(!tp->rto_pending))
	/* We should not be doing any RTO updates unless rto_pending is set. */
	pr_debug("%s: rto_pending not set on transport %p!\n", __func__, tp);

	if (tp->rttvar \|\| tp->srtt) {
	struct net *net = sock_net(tp->asoc->base.sk);
	/* 6.3.1 C3) When a new RTT measurement R' is made, set
	* RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * \|SRTT - R'\|
	* SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R'
	*/

	/* Note: The above algorithm has been rewritten to
	* express rto_beta and rto_alpha as inverse powers
	* of two.
	* For example, assuming the default value of RTO.Alpha of
	* 1/8, rto_alpha would be expressed as 3.
	*/
	tp->rttvar = tp->rttvar - (tp->rttvar >> net->sctp.rto_beta)
	+ (((__u32)abs((__s64)tp->srtt - (__s64)rtt)) >> net->sctp.rto_beta);
	tp->srtt = tp->srtt - (tp->srtt >> net->sctp.rto_alpha)
	+ (rtt >> net->sctp.rto_alpha);
	} else {
	/* 6.3.1 C2) When the first RTT measurement R is made, set
	* SRTT <- R, RTTVAR <- R/2.
	*/
	tp->srtt = rtt;
	tp->rttvar = rtt >> 1;
	}

	/* 6.3.1 G1) Whenever RTTVAR is computed, if RTTVAR = 0, then
	* adjust RTTVAR <- G, where G is the CLOCK GRANULARITY.
	*/
	if (tp->rttvar == 0)
	tp->rttvar = SCTP_CLOCK_GRANULARITY;

	/* 6.3.1 C3) After the computation, update RTO <- SRTT + 4 * RTTVAR. */
	tp->rto = tp->srtt + (tp->rttvar << 2);

	/* 6.3.1 C6) Whenever RTO is computed, if it is less than RTO.Min
	* seconds then it is rounded up to RTO.Min seconds.
	*/
	if (tp->rto < tp->asoc->rto_min)
	tp->rto = tp->asoc->rto_min;

	/* 6.3.1 C7) A maximum value may be placed on RTO provided it is
	* at least RTO.max seconds.
	*/
	if (tp->rto > tp->asoc->rto_max)
	tp->rto = tp->asoc->rto_max;

	sctp_max_rto(tp->asoc, tp);
	tp->rtt = rtt;

	/* Reset rto_pending so that a new RTT measurement is started when a
	* new data chunk is sent.
	*/
	tp->rto_pending = 0;

	pr_debug("%s: transport:%p, rtt:%d, srtt:%d rttvar:%d, rto:%ld\n",
	__func__, tp, rtt, tp->srtt, tp->rttvar, tp->rto);
	}

	/* This routine updates the transport's cwnd and partial_bytes_acked
	* parameters based on the bytes acked in the received SACK.
	*/
	void sctp_transport_raise_cwnd(struct sctp_transport *transport,
	__u32 sack_ctsn, __u32 bytes_acked)
	{
	struct sctp_association *asoc = transport->asoc;
	__u32 cwnd, ssthresh, flight_size, pba, pmtu;

	cwnd = transport->cwnd;
	flight_size = transport->flight_size;

	/* See if we need to exit Fast Recovery first */
	if (asoc->fast_recovery &&
	TSN_lte(asoc->fast_recovery_exit, sack_ctsn))
	asoc->fast_recovery = 0;

	ssthresh = transport->ssthresh;
	pba = transport->partial_bytes_acked;
	pmtu = transport->asoc->pathmtu;

	if (cwnd <= ssthresh) {
	/* RFC 4960 7.2.1
	* o When cwnd is less than or equal to ssthresh, an SCTP
	* endpoint MUST use the slow-start algorithm to increase
	* cwnd only if the current congestion window is being fully
	* utilized, an incoming SACK advances the Cumulative TSN
	* Ack Point, and the data sender is not in Fast Recovery.
	* Only when these three conditions are met can the cwnd be
	* increased; otherwise, the cwnd MUST not be increased.
	* If these conditions are met, then cwnd MUST be increased
	* by, at most, the lesser of 1) the total size of the
	* previously outstanding DATA chunk(s) acknowledged, and
	* 2) the destination's path MTU. This upper bound protects
	* against the ACK-Splitting attack outlined in [SAVAGE99].
	*/
	if (asoc->fast_recovery)
	return;

	/* The appropriate cwnd increase algorithm is performed
	* if, and only if the congestion window is being fully
	* utilized. Note that RFC4960 Errata 3.22 removed the
	* other condition on ctsn moving.
	*/
	if (flight_size < cwnd)
	return;

	if (bytes_acked > pmtu)
	cwnd += pmtu;
	else
	cwnd += bytes_acked;

	pr_debug("%s: slow start: transport:%p, bytes_acked:%d, "
	"cwnd:%d, ssthresh:%d, flight_size:%d, pba:%d\n",
	__func__, transport, bytes_acked, cwnd, ssthresh,
	flight_size, pba);
	} else {
	/* RFC 2960 7.2.2 Whenever cwnd is greater than ssthresh,
	* upon each SACK arrival, increase partial_bytes_acked
	* by the total number of bytes of all new chunks
	* acknowledged in that SACK including chunks
	* acknowledged by the new Cumulative TSN Ack and by Gap
	* Ack Blocks. (updated by RFC4960 Errata 3.22)
	*
	* When partial_bytes_acked is greater than cwnd and
	* before the arrival of the SACK the sender had less
	* bytes of data outstanding than cwnd (i.e., before
	* arrival of the SACK, flightsize was less than cwnd),
	* reset partial_bytes_acked to cwnd. (RFC 4960 Errata
	* 3.26)
	*
	* When partial_bytes_acked is equal to or greater than
	* cwnd and before the arrival of the SACK the sender
	* had cwnd or more bytes of data outstanding (i.e.,
	* before arrival of the SACK, flightsize was greater
	* than or equal to cwnd), partial_bytes_acked is reset
	* to (partial_bytes_acked - cwnd). Next, cwnd is
	* increased by MTU. (RFC 4960 Errata 3.12)
	*/
	pba += bytes_acked;
	if (pba > cwnd && flight_size < cwnd)
	pba = cwnd;
	if (pba >= cwnd && flight_size >= cwnd) {
	pba = pba - cwnd;
	cwnd += pmtu;
	}

	pr_debug("%s: congestion avoidance: transport:%p, "
	"bytes_acked:%d, cwnd:%d, ssthresh:%d, "
	"flight_size:%d, pba:%d\n", __func__,
	transport, bytes_acked, cwnd, ssthresh,
	flight_size, pba);
	}

	transport->cwnd = cwnd;
	transport->partial_bytes_acked = pba;
	}

	/* This routine is used to lower the transport's cwnd when congestion is
	* detected.
	*/
	void sctp_transport_lower_cwnd(struct sctp_transport *transport,
	enum sctp_lower_cwnd reason)
	{
	struct sctp_association *asoc = transport->asoc;

	switch (reason) {
	case SCTP_LOWER_CWND_T3_RTX:
	/* RFC 2960 Section 7.2.3, sctpimpguide
	* When the T3-rtx timer expires on an address, SCTP should
	* perform slow start by:
	* ssthresh = max(cwnd/2, 4*MTU)
	* cwnd = 1*MTU
	* partial_bytes_acked = 0
	*/
	transport->ssthresh = max(transport->cwnd/2,
	4*asoc->pathmtu);
	transport->cwnd = asoc->pathmtu;

	/* T3-rtx also clears fast recovery */
	asoc->fast_recovery = 0;
	break;

	case SCTP_LOWER_CWND_FAST_RTX:
	/* RFC 2960 7.2.4 Adjust the ssthresh and cwnd of the
	* destination address(es) to which the missing DATA chunks
	* were last sent, according to the formula described in
	* Section 7.2.3.
	*
	* RFC 2960 7.2.3, sctpimpguide Upon detection of packet
	* losses from SACK (see Section 7.2.4), An endpoint
	* should do the following:
	* ssthresh = max(cwnd/2, 4*MTU)
	* cwnd = ssthresh
	* partial_bytes_acked = 0
	*/
	if (asoc->fast_recovery)
	return;

	/* Mark Fast recovery */
	asoc->fast_recovery = 1;
	asoc->fast_recovery_exit = asoc->next_tsn - 1;

	transport->ssthresh = max(transport->cwnd/2,
	4*asoc->pathmtu);
	transport->cwnd = transport->ssthresh;
	break;

	case SCTP_LOWER_CWND_ECNE:
	/* RFC 2481 Section 6.1.2.
	* If the sender receives an ECN-Echo ACK packet
	* then the sender knows that congestion was encountered in the
	* network on the path from the sender to the receiver. The
	* indication of congestion should be treated just as a
	* congestion loss in non-ECN Capable TCP. That is, the TCP
	* source halves the congestion window "cwnd" and reduces the
	* slow start threshold "ssthresh".
	* A critical condition is that TCP does not react to
	* congestion indications more than once every window of
	* data (or more loosely more than once every round-trip time).
	*/
	if (time_after(jiffies, transport->last_time_ecne_reduced +
	transport->rtt)) {
	transport->ssthresh = max(transport->cwnd/2,
	4*asoc->pathmtu);
	transport->cwnd = transport->ssthresh;
	transport->last_time_ecne_reduced = jiffies;
	}
	break;

	case SCTP_LOWER_CWND_INACTIVE:
	/* RFC 2960 Section 7.2.1, sctpimpguide
	* When the endpoint does not transmit data on a given
	* transport address, the cwnd of the transport address
	* should be adjusted to max(cwnd/2, 4*MTU) per RTO.
	* NOTE: Although the draft recommends that this check needs
	* to be done every RTO interval, we do it every hearbeat
	* interval.
	*/
	transport->cwnd = max(transport->cwnd/2,
	4*asoc->pathmtu);
	/* RFC 4960 Errata 3.27.2: also adjust sshthresh */
	transport->ssthresh = transport->cwnd;
	break;
	}

	transport->partial_bytes_acked = 0;

	pr_debug("%s: transport:%p, reason:%d, cwnd:%d, ssthresh:%d\n",
	__func__, transport, reason, transport->cwnd,
	transport->ssthresh);
	}

	/* Apply Max.Burst limit to the congestion window:
	* sctpimpguide-05 2.14.2
	* D) When the time comes for the sender to
	* transmit new DATA chunks, the protocol parameter Max.Burst MUST
	* first be applied to limit how many new DATA chunks may be sent.
	* The limit is applied by adjusting cwnd as follows:
	* if ((flightsize+ Max.Burst * MTU) < cwnd)
	* cwnd = flightsize + Max.Burst * MTU
	*/

	void sctp_transport_burst_limited(struct sctp_transport *t)
	{
	struct sctp_association *asoc = t->asoc;
	u32 old_cwnd = t->cwnd;
	u32 max_burst_bytes;

	if (t->burst_limited \|\| asoc->max_burst == 0)
	return;

	max_burst_bytes = t->flight_size + (asoc->max_burst * asoc->pathmtu);
	if (max_burst_bytes < old_cwnd) {
	t->cwnd = max_burst_bytes;
	t->burst_limited = old_cwnd;
	}
	}

	/* Restore the old cwnd congestion window, after the burst had it's
	* desired effect.
	*/
	void sctp_transport_burst_reset(struct sctp_transport *t)
	{
	if (t->burst_limited) {
	t->cwnd = t->burst_limited;
	t->burst_limited = 0;
	}
	}

	/* What is the next timeout value for this transport? */
	unsigned long sctp_transport_timeout(struct sctp_transport *trans)
	{
	/* RTO + timer slack +/- 50% of RTO */
	unsigned long timeout = trans->rto >> 1;

	if (trans->state != SCTP_UNCONFIRMED &&
	trans->state != SCTP_PF)
	timeout += trans->hbinterval;

	return max_t(unsigned long, timeout, HZ / 5);
	}

	/* Reset transport variables to their initial values */
	void sctp_transport_reset(struct sctp_transport *t)
	{
	struct sctp_association *asoc = t->asoc;

	/* RFC 2960 (bis), Section 5.2.4
	* All the congestion control parameters (e.g., cwnd, ssthresh)
	* related to this peer MUST be reset to their initial values
	* (see Section 6.2.1)
	*/
	t->cwnd = min(4asoc->pathmtu, max_t(__u32, 2asoc->pathmtu, 4380));
	t->burst_limited = 0;
	t->ssthresh = asoc->peer.i.a_rwnd;
	t->rto = asoc->rto_initial;
	sctp_max_rto(asoc, t);
	t->rtt = 0;
	t->srtt = 0;
	t->rttvar = 0;

	/* Reset these additional variables so that we have a clean slate. */
	t->partial_bytes_acked = 0;
	t->flight_size = 0;
	t->error_count = 0;
	t->rto_pending = 0;
	t->hb_sent = 0;

	/* Initialize the state information for SFR-CACC */
	t->cacc.changeover_active = 0;
	t->cacc.cycling_changeover = 0;
	t->cacc.next_tsn_at_change = 0;
	t->cacc.cacc_saw_newack = 0;
	}

	/* Schedule retransmission on the given transport */
	void sctp_transport_immediate_rtx(struct sctp_transport *t)
	{
	/* Stop pending T3_rtx_timer */
	if (del_timer(&t->T3_rtx_timer))
	sctp_transport_put(t);

	sctp_retransmit(&t->asoc->outqueue, t, SCTP_RTXR_T3_RTX);
	if (!timer_pending(&t->T3_rtx_timer)) {
	if (!mod_timer(&t->T3_rtx_timer, jiffies + t->rto))
	sctp_transport_hold(t);
	}
	}

	/* Drop dst */
	void sctp_transport_dst_release(struct sctp_transport *t)
	{
	dst_release(t->dst);
	t->dst = NULL;
	t->dst_pending_confirm = 0;
	}

	/* Schedule neighbour confirm */
	void sctp_transport_dst_confirm(struct sctp_transport *t)
	{
	t->dst_pending_confirm = 1;
	}