Linux 4.1.16

[linux/fpc-iii.git] / net / sctp / outqueue.c

/* SCTP kernel implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001-2003 Intel Corp.
 *
 * This file is part of the SCTP kernel implementation
 *
 * These functions implement the sctp_outq class.   The outqueue handles
 * bundling and queueing of outgoing SCTP chunks.
 *
 * 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>
 *    Perry Melange         <pmelange@null.cc.uic.edu>
 *    Xingang Guo           <xingang.guo@intel.com>
 *    Hui Huang             <hui.huang@nokia.com>
 *    Sridhar Samudrala     <sri@us.ibm.com>
 *    Jon Grimm             <jgrimm@us.ibm.com>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/types.h>
#include <linux/list.h>   /* For struct list_head */
#include <linux/socket.h>
#include <linux/ip.h>
#include <linux/slab.h>
#include <net/sock.h>     /* For skb_set_owner_w */

#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>

/* Declare internal functions here.  */
static int sctp_acked(struct sctp_sackhdr *sack, __u32 tsn);
static void sctp_check_transmitted(struct sctp_outq *q,
                                   struct list_head *transmitted_queue,
                                   struct sctp_transport *transport,
                                   union sctp_addr *saddr,
                                   struct sctp_sackhdr *sack,
                                   __u32 *highest_new_tsn);

static void sctp_mark_missing(struct sctp_outq *q,
                              struct list_head *transmitted_queue,
                              struct sctp_transport *transport,
                              __u32 highest_new_tsn,
                              int count_of_newacks);

static void sctp_generate_fwdtsn(struct sctp_outq *q, __u32 sack_ctsn);

static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout);

/* Add data to the front of the queue. */
static inline void sctp_outq_head_data(struct sctp_outq *q,
                                        struct sctp_chunk *ch)
{
        list_add(&ch->list, &q->out_chunk_list);
        q->out_qlen += ch->skb->len;
}

/* Take data from the front of the queue. */
static inline struct sctp_chunk *sctp_outq_dequeue_data(struct sctp_outq *q)
{
        struct sctp_chunk *ch = NULL;

        if (!list_empty(&q->out_chunk_list)) {
                struct list_head *entry = q->out_chunk_list.next;

                ch = list_entry(entry, struct sctp_chunk, list);
                list_del_init(entry);
                q->out_qlen -= ch->skb->len;
        }
        return ch;
}
/* Add data chunk to the end of the queue. */
static inline void sctp_outq_tail_data(struct sctp_outq *q,
                                       struct sctp_chunk *ch)
{
        list_add_tail(&ch->list, &q->out_chunk_list);
        q->out_qlen += ch->skb->len;
}

/*
 * SFR-CACC algorithm:
 * D) If count_of_newacks is greater than or equal to 2
 * and t was not sent to the current primary then the
 * sender MUST NOT increment missing report count for t.
 */
static inline int sctp_cacc_skip_3_1_d(struct sctp_transport *primary,
                                       struct sctp_transport *transport,
                                       int count_of_newacks)
{
        if (count_of_newacks >= 2 && transport != primary)
                return 1;
        return 0;
}

/*
 * SFR-CACC algorithm:
 * F) If count_of_newacks is less than 2, let d be the
 * destination to which t was sent. If cacc_saw_newack
 * is 0 for destination d, then the sender MUST NOT
 * increment missing report count for t.
 */
static inline int sctp_cacc_skip_3_1_f(struct sctp_transport *transport,
                                       int count_of_newacks)
{
        if (count_of_newacks < 2 &&
                        (transport && !transport->cacc.cacc_saw_newack))
                return 1;
        return 0;
}

/*
 * SFR-CACC algorithm:
 * 3.1) If CYCLING_CHANGEOVER is 0, the sender SHOULD
 * execute steps C, D, F.
 *
 * C has been implemented in sctp_outq_sack
 */
static inline int sctp_cacc_skip_3_1(struct sctp_transport *primary,
                                     struct sctp_transport *transport,
                                     int count_of_newacks)
{
        if (!primary->cacc.cycling_changeover) {
                if (sctp_cacc_skip_3_1_d(primary, transport, count_of_newacks))
                        return 1;
                if (sctp_cacc_skip_3_1_f(transport, count_of_newacks))
                        return 1;
                return 0;
        }
        return 0;
}

/*
 * SFR-CACC algorithm:
 * 3.2) Else if CYCLING_CHANGEOVER is 1, and t is less
 * than next_tsn_at_change of the current primary, then
 * the sender MUST NOT increment missing report count
 * for t.
 */
static inline int sctp_cacc_skip_3_2(struct sctp_transport *primary, __u32 tsn)
{
        if (primary->cacc.cycling_changeover &&
            TSN_lt(tsn, primary->cacc.next_tsn_at_change))
                return 1;
        return 0;
}

/*
 * SFR-CACC algorithm:
 * 3) If the missing report count for TSN t is to be
 * incremented according to [RFC2960] and
 * [SCTP_STEWART-2002], and CHANGEOVER_ACTIVE is set,
 * then the sender MUST further execute steps 3.1 and
 * 3.2 to determine if the missing report count for
 * TSN t SHOULD NOT be incremented.
 *
 * 3.3) If 3.1 and 3.2 do not dictate that the missing
 * report count for t should not be incremented, then
 * the sender SHOULD increment missing report count for
 * t (according to [RFC2960] and [SCTP_STEWART_2002]).
 */
static inline int sctp_cacc_skip(struct sctp_transport *primary,
                                 struct sctp_transport *transport,
                                 int count_of_newacks,
                                 __u32 tsn)
{
        if (primary->cacc.changeover_active &&
            (sctp_cacc_skip_3_1(primary, transport, count_of_newacks) ||
             sctp_cacc_skip_3_2(primary, tsn)))
                return 1;
        return 0;
}

/* Initialize an existing sctp_outq.  This does the boring stuff.
 * You still need to define handlers if you really want to DO
 * something with this structure...
 */
void sctp_outq_init(struct sctp_association *asoc, struct sctp_outq *q)
{
        memset(q, 0, sizeof(struct sctp_outq));

        q->asoc = asoc;
        INIT_LIST_HEAD(&q->out_chunk_list);
        INIT_LIST_HEAD(&q->control_chunk_list);
        INIT_LIST_HEAD(&q->retransmit);
        INIT_LIST_HEAD(&q->sacked);
        INIT_LIST_HEAD(&q->abandoned);
}

/* Free the outqueue structure and any related pending chunks.
 */
static void __sctp_outq_teardown(struct sctp_outq *q)
{
        struct sctp_transport *transport;
        struct list_head *lchunk, *temp;
        struct sctp_chunk *chunk, *tmp;

        /* Throw away unacknowledged chunks. */
        list_for_each_entry(transport, &q->asoc->peer.transport_addr_list,
                        transports) {
                while ((lchunk = sctp_list_dequeue(&transport->transmitted)) != NULL) {
                        chunk = list_entry(lchunk, struct sctp_chunk,
                                           transmitted_list);
                        /* Mark as part of a failed message. */
                        sctp_chunk_fail(chunk, q->error);
                        sctp_chunk_free(chunk);
                }
        }

        /* Throw away chunks that have been gap ACKed.  */
        list_for_each_safe(lchunk, temp, &q->sacked) {
                list_del_init(lchunk);
                chunk = list_entry(lchunk, struct sctp_chunk,
                                   transmitted_list);
                sctp_chunk_fail(chunk, q->error);
                sctp_chunk_free(chunk);
        }

        /* Throw away any chunks in the retransmit queue. */
        list_for_each_safe(lchunk, temp, &q->retransmit) {
                list_del_init(lchunk);
                chunk = list_entry(lchunk, struct sctp_chunk,
                                   transmitted_list);
                sctp_chunk_fail(chunk, q->error);
                sctp_chunk_free(chunk);
        }

        /* Throw away any chunks that are in the abandoned queue. */
        list_for_each_safe(lchunk, temp, &q->abandoned) {
                list_del_init(lchunk);
                chunk = list_entry(lchunk, struct sctp_chunk,
                                   transmitted_list);
                sctp_chunk_fail(chunk, q->error);
                sctp_chunk_free(chunk);
        }

        /* Throw away any leftover data chunks. */
        while ((chunk = sctp_outq_dequeue_data(q)) != NULL) {

                /* Mark as send failure. */
                sctp_chunk_fail(chunk, q->error);
                sctp_chunk_free(chunk);
        }

        /* Throw away any leftover control chunks. */
        list_for_each_entry_safe(chunk, tmp, &q->control_chunk_list, list) {
                list_del_init(&chunk->list);
                sctp_chunk_free(chunk);
        }
}

void sctp_outq_teardown(struct sctp_outq *q)
{
        __sctp_outq_teardown(q);
        sctp_outq_init(q->asoc, q);
}

/* Free the outqueue structure and any related pending chunks.  */
void sctp_outq_free(struct sctp_outq *q)
{
        /* Throw away leftover chunks. */
        __sctp_outq_teardown(q);
}

/* Put a new chunk in an sctp_outq.  */
int sctp_outq_tail(struct sctp_outq *q, struct sctp_chunk *chunk)
{
        struct net *net = sock_net(q->asoc->base.sk);
        int error = 0;

        pr_debug("%s: outq:%p, chunk:%p[%s]\n", __func__, q, chunk,
                 chunk && chunk->chunk_hdr ?
                 sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type)) :
                 "illegal chunk");

        /* If it is data, queue it up, otherwise, send it
         * immediately.
         */
        if (sctp_chunk_is_data(chunk)) {
                /* Is it OK to queue data chunks?  */
                /* From 9. Termination of Association
                 *
                 * When either endpoint performs a shutdown, the
                 * association on each peer will stop accepting new
                 * data from its user and only deliver data in queue
                 * at the time of sending or receiving the SHUTDOWN
                 * chunk.
                 */
                switch (q->asoc->state) {
                case SCTP_STATE_CLOSED:
                case SCTP_STATE_SHUTDOWN_PENDING:
                case SCTP_STATE_SHUTDOWN_SENT:
                case SCTP_STATE_SHUTDOWN_RECEIVED:
                case SCTP_STATE_SHUTDOWN_ACK_SENT:
                        /* Cannot send after transport endpoint shutdown */
                        error = -ESHUTDOWN;
                        break;

                default:
                        pr_debug("%s: outqueueing: outq:%p, chunk:%p[%s])\n",
                                 __func__, q, chunk, chunk && chunk->chunk_hdr ?
                                 sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type)) :
                                 "illegal chunk");

                        sctp_outq_tail_data(q, chunk);
                        if (chunk->chunk_hdr->flags & SCTP_DATA_UNORDERED)
                                SCTP_INC_STATS(net, SCTP_MIB_OUTUNORDERCHUNKS);
                        else
                                SCTP_INC_STATS(net, SCTP_MIB_OUTORDERCHUNKS);
                        break;
                }
        } else {
                list_add_tail(&chunk->list, &q->control_chunk_list);
                SCTP_INC_STATS(net, SCTP_MIB_OUTCTRLCHUNKS);
        }

        if (error < 0)
                return error;

        if (!q->cork)
                error = sctp_outq_flush(q, 0);

        return error;
}

/* Insert a chunk into the sorted list based on the TSNs.  The retransmit list
 * and the abandoned list are in ascending order.
 */
static void sctp_insert_list(struct list_head *head, struct list_head *new)
{
        struct list_head *pos;
        struct sctp_chunk *nchunk, *lchunk;
        __u32 ntsn, ltsn;
        int done = 0;

        nchunk = list_entry(new, struct sctp_chunk, transmitted_list);
        ntsn = ntohl(nchunk->subh.data_hdr->tsn);

        list_for_each(pos, head) {
                lchunk = list_entry(pos, struct sctp_chunk, transmitted_list);
                ltsn = ntohl(lchunk->subh.data_hdr->tsn);
                if (TSN_lt(ntsn, ltsn)) {
                        list_add(new, pos->prev);
                        done = 1;
                        break;
                }
        }
        if (!done)
                list_add_tail(new, head);
}

/* Mark all the eligible packets on a transport for retransmission.  */
void sctp_retransmit_mark(struct sctp_outq *q,
                          struct sctp_transport *transport,
                          __u8 reason)
{
        struct list_head *lchunk, *ltemp;
        struct sctp_chunk *chunk;

        /* Walk through the specified transmitted queue.  */
        list_for_each_safe(lchunk, ltemp, &transport->transmitted) {
                chunk = list_entry(lchunk, struct sctp_chunk,
                                   transmitted_list);

                /* If the chunk is abandoned, move it to abandoned list. */
                if (sctp_chunk_abandoned(chunk)) {
                        list_del_init(lchunk);
                        sctp_insert_list(&q->abandoned, lchunk);

                        /* If this chunk has not been previousely acked,
                         * stop considering it 'outstanding'.  Our peer
                         * will most likely never see it since it will
                         * not be retransmitted
                         */
                        if (!chunk->tsn_gap_acked) {
                                if (chunk->transport)
                                        chunk->transport->flight_size -=
                                                        sctp_data_size(chunk);
                                q->outstanding_bytes -= sctp_data_size(chunk);
                                q->asoc->peer.rwnd += sctp_data_size(chunk);
                        }
                        continue;
                }

                /* If we are doing  retransmission due to a timeout or pmtu
                 * discovery, only the  chunks that are not yet acked should
                 * be added to the retransmit queue.
                 */
                if ((reason == SCTP_RTXR_FAST_RTX  &&
                            (chunk->fast_retransmit == SCTP_NEED_FRTX)) ||
                    (reason != SCTP_RTXR_FAST_RTX  && !chunk->tsn_gap_acked)) {
                        /* RFC 2960 6.2.1 Processing a Received SACK
                         *
                         * C) Any time a DATA chunk is marked for
                         * retransmission (via either T3-rtx timer expiration
                         * (Section 6.3.3) or via fast retransmit
                         * (Section 7.2.4)), add the data size of those
                         * chunks to the rwnd.
                         */
                        q->asoc->peer.rwnd += sctp_data_size(chunk);
                        q->outstanding_bytes -= sctp_data_size(chunk);
                        if (chunk->transport)
                                transport->flight_size -= sctp_data_size(chunk);

                        /* sctpimpguide-05 Section 2.8.2
                         * M5) If a T3-rtx timer expires, the
                         * 'TSN.Missing.Report' of all affected TSNs is set
                         * to 0.
                         */
                        chunk->tsn_missing_report = 0;

                        /* If a chunk that is being used for RTT measurement
                         * has to be retransmitted, we cannot use this chunk
                         * anymore for RTT measurements. Reset rto_pending so
                         * that a new RTT measurement is started when a new
                         * data chunk is sent.
                         */
                        if (chunk->rtt_in_progress) {
                                chunk->rtt_in_progress = 0;
                                transport->rto_pending = 0;
                        }

                        chunk->resent = 1;

                        /* Move the chunk to the retransmit queue. The chunks
                         * on the retransmit queue are always kept in order.
                         */
                        list_del_init(lchunk);
                        sctp_insert_list(&q->retransmit, lchunk);
                }
        }

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

/* Mark all the eligible packets on a transport for retransmission and force
 * one packet out.
 */
void sctp_retransmit(struct sctp_outq *q, struct sctp_transport *transport,
                     sctp_retransmit_reason_t reason)
{
        struct net *net = sock_net(q->asoc->base.sk);
        int error = 0;

        switch (reason) {
        case SCTP_RTXR_T3_RTX:
                SCTP_INC_STATS(net, SCTP_MIB_T3_RETRANSMITS);
                sctp_transport_lower_cwnd(transport, SCTP_LOWER_CWND_T3_RTX);
                /* Update the retran path if the T3-rtx timer has expired for
                 * the current retran path.
                 */
                if (transport == transport->asoc->peer.retran_path)
                        sctp_assoc_update_retran_path(transport->asoc);
                transport->asoc->rtx_data_chunks +=
                        transport->asoc->unack_data;
                break;
        case SCTP_RTXR_FAST_RTX:
                SCTP_INC_STATS(net, SCTP_MIB_FAST_RETRANSMITS);
                sctp_transport_lower_cwnd(transport, SCTP_LOWER_CWND_FAST_RTX);
                q->fast_rtx = 1;
                break;
        case SCTP_RTXR_PMTUD:
                SCTP_INC_STATS(net, SCTP_MIB_PMTUD_RETRANSMITS);
                break;
        case SCTP_RTXR_T1_RTX:
                SCTP_INC_STATS(net, SCTP_MIB_T1_RETRANSMITS);
                transport->asoc->init_retries++;
                break;
        default:
                BUG();
        }

        sctp_retransmit_mark(q, transport, reason);

        /* PR-SCTP A5) Any time the T3-rtx timer expires, on any destination,
         * the sender SHOULD try to advance the "Advanced.Peer.Ack.Point" by
         * following the procedures outlined in C1 - C5.
         */
        if (reason == SCTP_RTXR_T3_RTX)
                sctp_generate_fwdtsn(q, q->asoc->ctsn_ack_point);

        /* Flush the queues only on timeout, since fast_rtx is only
         * triggered during sack processing and the queue
         * will be flushed at the end.
         */
        if (reason != SCTP_RTXR_FAST_RTX)
                error = sctp_outq_flush(q, /* rtx_timeout */ 1);

        if (error)
                q->asoc->base.sk->sk_err = -error;
}

/*
 * Transmit DATA chunks on the retransmit queue.  Upon return from
 * sctp_outq_flush_rtx() the packet 'pkt' may contain chunks which
 * need to be transmitted by the caller.
 * We assume that pkt->transport has already been set.
 *
 * The return value is a normal kernel error return value.
 */
static int sctp_outq_flush_rtx(struct sctp_outq *q, struct sctp_packet *pkt,
                               int rtx_timeout, int *start_timer)
{
        struct list_head *lqueue;
        struct sctp_transport *transport = pkt->transport;
        sctp_xmit_t status;
        struct sctp_chunk *chunk, *chunk1;
        int fast_rtx;
        int error = 0;
        int timer = 0;
        int done = 0;

        lqueue = &q->retransmit;
        fast_rtx = q->fast_rtx;

        /* This loop handles time-out retransmissions, fast retransmissions,
         * and retransmissions due to opening of whindow.
         *
         * RFC 2960 6.3.3 Handle T3-rtx Expiration
         *
         * E3) Determine how many of the earliest (i.e., lowest TSN)
         * outstanding DATA chunks for the address for which the
         * T3-rtx has expired will fit into a single packet, subject
         * to the MTU constraint for the path corresponding to the
         * destination transport address to which the retransmission
         * is being sent (this may be different from the address for
         * which the timer expires [see Section 6.4]). Call this value
         * K. Bundle and retransmit those K DATA chunks in a single
         * packet to the destination endpoint.
         *
         * [Just to be painfully clear, if we are retransmitting
         * because a timeout just happened, we should send only ONE
         * packet of retransmitted data.]
         *
         * For fast retransmissions we also send only ONE packet.  However,
         * if we are just flushing the queue due to open window, we'll
         * try to send as much as possible.
         */
        list_for_each_entry_safe(chunk, chunk1, lqueue, transmitted_list) {
                /* If the chunk is abandoned, move it to abandoned list. */
                if (sctp_chunk_abandoned(chunk)) {
                        list_del_init(&chunk->transmitted_list);
                        sctp_insert_list(&q->abandoned,
                                         &chunk->transmitted_list);
                        continue;
                }

                /* Make sure that Gap Acked TSNs are not retransmitted.  A
                 * simple approach is just to move such TSNs out of the
                 * way and into a 'transmitted' queue and skip to the
                 * next chunk.
                 */
                if (chunk->tsn_gap_acked) {
                        list_move_tail(&chunk->transmitted_list,
                                       &transport->transmitted);
                        continue;
                }

                /* If we are doing fast retransmit, ignore non-fast_rtransmit
                 * chunks
                 */
                if (fast_rtx && !chunk->fast_retransmit)
                        continue;

redo:
                /* Attempt to append this chunk to the packet. */
                status = sctp_packet_append_chunk(pkt, chunk);

                switch (status) {
                case SCTP_XMIT_PMTU_FULL:
                        if (!pkt->has_data && !pkt->has_cookie_echo) {
                                /* If this packet did not contain DATA then
                                 * retransmission did not happen, so do it
                                 * again.  We'll ignore the error here since
                                 * control chunks are already freed so there
                                 * is nothing we can do.
                                 */
                                sctp_packet_transmit(pkt);
                                goto redo;
                        }

                        /* Send this packet.  */
                        error = sctp_packet_transmit(pkt);

                        /* If we are retransmitting, we should only
                         * send a single packet.
                         * Otherwise, try appending this chunk again.
                         */
                        if (rtx_timeout || fast_rtx)
                                done = 1;
                        else
                                goto redo;

                        /* Bundle next chunk in the next round.  */
                        break;

                case SCTP_XMIT_RWND_FULL:
                        /* Send this packet. */
                        error = sctp_packet_transmit(pkt);

                        /* Stop sending DATA as there is no more room
                         * at the receiver.
                         */
                        done = 1;
                        break;

                case SCTP_XMIT_DELAY:
                        /* Send this packet. */
                        error = sctp_packet_transmit(pkt);

                        /* Stop sending DATA because of nagle delay. */
                        done = 1;
                        break;

                default:
                        /* The append was successful, so add this chunk to
                         * the transmitted list.
                         */
                        list_move_tail(&chunk->transmitted_list,
                                       &transport->transmitted);

                        /* Mark the chunk as ineligible for fast retransmit
                         * after it is retransmitted.
                         */
                        if (chunk->fast_retransmit == SCTP_NEED_FRTX)
                                chunk->fast_retransmit = SCTP_DONT_FRTX;

                        q->asoc->stats.rtxchunks++;
                        break;
                }

                /* Set the timer if there were no errors */
                if (!error && !timer)
                        timer = 1;

                if (done)
                        break;
        }

        /* If we are here due to a retransmit timeout or a fast
         * retransmit and if there are any chunks left in the retransmit
         * queue that could not fit in the PMTU sized packet, they need
         * to be marked as ineligible for a subsequent fast retransmit.
         */
        if (rtx_timeout || fast_rtx) {
                list_for_each_entry(chunk1, lqueue, transmitted_list) {
                        if (chunk1->fast_retransmit == SCTP_NEED_FRTX)
                                chunk1->fast_retransmit = SCTP_DONT_FRTX;
                }
        }

        *start_timer = timer;

        /* Clear fast retransmit hint */
        if (fast_rtx)
                q->fast_rtx = 0;

        return error;
}

/* Cork the outqueue so queued chunks are really queued. */
int sctp_outq_uncork(struct sctp_outq *q)
{
        if (q->cork)
                q->cork = 0;

        return sctp_outq_flush(q, 0);
}


/*
 * Try to flush an outqueue.
 *
 * Description: Send everything in q which we legally can, subject to
 * congestion limitations.
 * * Note: This function can be called from multiple contexts so appropriate
 * locking concerns must be made.  Today we use the sock lock to protect
 * this function.
 */
static int sctp_outq_flush(struct sctp_outq *q, int rtx_timeout)
{
        struct sctp_packet *packet;
        struct sctp_packet singleton;
        struct sctp_association *asoc = q->asoc;
        __u16 sport = asoc->base.bind_addr.port;
        __u16 dport = asoc->peer.port;
        __u32 vtag = asoc->peer.i.init_tag;
        struct sctp_transport *transport = NULL;
        struct sctp_transport *new_transport;
        struct sctp_chunk *chunk, *tmp;
        sctp_xmit_t status;
        int error = 0;
        int start_timer = 0;
        int one_packet = 0;

        /* These transports have chunks to send. */
        struct list_head transport_list;
        struct list_head *ltransport;

        INIT_LIST_HEAD(&transport_list);
        packet = NULL;

        /*
         * 6.10 Bundling
         *   ...
         *   When bundling control chunks with DATA chunks, an
         *   endpoint MUST place control chunks first in the outbound
         *   SCTP packet.  The transmitter MUST transmit DATA chunks
         *   within a SCTP packet in increasing order of TSN.
         *   ...
         */

        list_for_each_entry_safe(chunk, tmp, &q->control_chunk_list, list) {
                /* RFC 5061, 5.3
                 * F1) This means that until such time as the ASCONF
                 * containing the add is acknowledged, the sender MUST
                 * NOT use the new IP address as a source for ANY SCTP
                 * packet except on carrying an ASCONF Chunk.
                 */
                if (asoc->src_out_of_asoc_ok &&
                    chunk->chunk_hdr->type != SCTP_CID_ASCONF)
                        continue;

                list_del_init(&chunk->list);

                /* Pick the right transport to use. */
                new_transport = chunk->transport;

                if (!new_transport) {
                        /*
                         * If we have a prior transport pointer, see if
                         * the destination address of the chunk
                         * matches the destination address of the
                         * current transport.  If not a match, then
                         * try to look up the transport with a given
                         * destination address.  We do this because
                         * after processing ASCONFs, we may have new
                         * transports created.
                         */
                        if (transport &&
                            sctp_cmp_addr_exact(&chunk->dest,
                                                &transport->ipaddr))
                                        new_transport = transport;
                        else
                                new_transport = sctp_assoc_lookup_paddr(asoc,
                                                                &chunk->dest);

                        /* if we still don't have a new transport, then
                         * use the current active path.
                         */
                        if (!new_transport)
                                new_transport = asoc->peer.active_path;
                } else if ((new_transport->state == SCTP_INACTIVE) ||
                           (new_transport->state == SCTP_UNCONFIRMED) ||
                           (new_transport->state == SCTP_PF)) {
                        /* If the chunk is Heartbeat or Heartbeat Ack,
                         * send it to chunk->transport, even if it's
                         * inactive.
                         *
                         * 3.3.6 Heartbeat Acknowledgement:
                         * ...
                         * A HEARTBEAT ACK is always sent to the source IP
                         * address of the IP datagram containing the
                         * HEARTBEAT chunk to which this ack is responding.
                         * ...
                         *
                         * ASCONF_ACKs also must be sent to the source.
                         */
                        if (chunk->chunk_hdr->type != SCTP_CID_HEARTBEAT &&
                            chunk->chunk_hdr->type != SCTP_CID_HEARTBEAT_ACK &&
                            chunk->chunk_hdr->type != SCTP_CID_ASCONF_ACK)
                                new_transport = asoc->peer.active_path;
                }

                /* Are we switching transports?
                 * Take care of transport locks.
                 */
                if (new_transport != transport) {
                        transport = new_transport;
                        if (list_empty(&transport->send_ready)) {
                                list_add_tail(&transport->send_ready,
                                              &transport_list);
                        }
                        packet = &transport->packet;
                        sctp_packet_config(packet, vtag,
                                           asoc->peer.ecn_capable);
                }

                switch (chunk->chunk_hdr->type) {
                /*
                 * 6.10 Bundling
                 *   ...
                 *   An endpoint MUST NOT bundle INIT, INIT ACK or SHUTDOWN
                 *   COMPLETE with any other chunks.  [Send them immediately.]
                 */
                case SCTP_CID_INIT:
                case SCTP_CID_INIT_ACK:
                case SCTP_CID_SHUTDOWN_COMPLETE:
                        sctp_packet_init(&singleton, transport, sport, dport);
                        sctp_packet_config(&singleton, vtag, 0);
                        sctp_packet_append_chunk(&singleton, chunk);
                        error = sctp_packet_transmit(&singleton);
                        if (error < 0)
                                return error;
                        break;

                case SCTP_CID_ABORT:
                        if (sctp_test_T_bit(chunk)) {
                                packet->vtag = asoc->c.my_vtag;
                        }
                /* The following chunks are "response" chunks, i.e.
                 * they are generated in response to something we
                 * received.  If we are sending these, then we can
                 * send only 1 packet containing these chunks.
                 */
                case SCTP_CID_HEARTBEAT_ACK:
                case SCTP_CID_SHUTDOWN_ACK:
                case SCTP_CID_COOKIE_ACK:
                case SCTP_CID_COOKIE_ECHO:
                case SCTP_CID_ERROR:
                case SCTP_CID_ECN_CWR:
                case SCTP_CID_ASCONF_ACK:
                        one_packet = 1;
                        /* Fall through */

                case SCTP_CID_SACK:
                case SCTP_CID_HEARTBEAT:
                case SCTP_CID_SHUTDOWN:
                case SCTP_CID_ECN_ECNE:
                case SCTP_CID_ASCONF:
                case SCTP_CID_FWD_TSN:
                        status = sctp_packet_transmit_chunk(packet, chunk,
                                                            one_packet);
                        if (status  != SCTP_XMIT_OK) {
                                /* put the chunk back */
                                list_add(&chunk->list, &q->control_chunk_list);
                        } else {
                                asoc->stats.octrlchunks++;
                                /* PR-SCTP C5) If a FORWARD TSN is sent, the
                                 * sender MUST assure that at least one T3-rtx
                                 * timer is running.
                                 */
                                if (chunk->chunk_hdr->type == SCTP_CID_FWD_TSN)
                                        sctp_transport_reset_timers(transport);
                        }
                        break;

                default:
                        /* We built a chunk with an illegal type! */
                        BUG();
                }
        }

        if (q->asoc->src_out_of_asoc_ok)
                goto sctp_flush_out;

        /* Is it OK to send data chunks?  */
        switch (asoc->state) {
        case SCTP_STATE_COOKIE_ECHOED:
                /* Only allow bundling when this packet has a COOKIE-ECHO
                 * chunk.
                 */
                if (!packet || !packet->has_cookie_echo)
                        break;

                /* fallthru */
        case SCTP_STATE_ESTABLISHED:
        case SCTP_STATE_SHUTDOWN_PENDING:
        case SCTP_STATE_SHUTDOWN_RECEIVED:
                /*
                 * RFC 2960 6.1  Transmission of DATA Chunks
                 *
                 * C) When the time comes for the sender to transmit,
                 * before sending new DATA chunks, the sender MUST
                 * first transmit any outstanding DATA chunks which
                 * are marked for retransmission (limited by the
                 * current cwnd).
                 */
                if (!list_empty(&q->retransmit)) {
                        if (asoc->peer.retran_path->state == SCTP_UNCONFIRMED)
                                goto sctp_flush_out;
                        if (transport == asoc->peer.retran_path)
                                goto retran;

                        /* Switch transports & prepare the packet.  */

                        transport = asoc->peer.retran_path;

                        if (list_empty(&transport->send_ready)) {
                                list_add_tail(&transport->send_ready,
                                              &transport_list);
                        }

                        packet = &transport->packet;
                        sctp_packet_config(packet, vtag,
                                           asoc->peer.ecn_capable);
                retran:
                        error = sctp_outq_flush_rtx(q, packet,
                                                    rtx_timeout, &start_timer);

                        if (start_timer)
                                sctp_transport_reset_timers(transport);

                        /* This can happen on COOKIE-ECHO resend.  Only
                         * one chunk can get bundled with a COOKIE-ECHO.
                         */
                        if (packet->has_cookie_echo)
                                goto sctp_flush_out;

                        /* Don't send new data if there is still data
                         * waiting to retransmit.
                         */
                        if (!list_empty(&q->retransmit))
                                goto sctp_flush_out;
                }

                /* Apply Max.Burst limitation to the current transport in
                 * case it will be used for new data.  We are going to
                 * rest it before we return, but we want to apply the limit
                 * to the currently queued data.
                 */
                if (transport)
                        sctp_transport_burst_limited(transport);

                /* Finally, transmit new packets.  */
                while ((chunk = sctp_outq_dequeue_data(q)) != NULL) {
                        /* RFC 2960 6.5 Every DATA chunk MUST carry a valid
                         * stream identifier.
                         */
                        if (chunk->sinfo.sinfo_stream >=
                            asoc->c.sinit_num_ostreams) {

                                /* Mark as failed send. */
                                sctp_chunk_fail(chunk, SCTP_ERROR_INV_STRM);
                                sctp_chunk_free(chunk);
                                continue;
                        }

                        /* Has this chunk expired? */
                        if (sctp_chunk_abandoned(chunk)) {
                                sctp_chunk_fail(chunk, 0);
                                sctp_chunk_free(chunk);
                                continue;
                        }

                        /* If there is a specified transport, use it.
                         * Otherwise, we want to use the active path.
                         */
                        new_transport = chunk->transport;
                        if (!new_transport ||
                            ((new_transport->state == SCTP_INACTIVE) ||
                             (new_transport->state == SCTP_UNCONFIRMED) ||
                             (new_transport->state == SCTP_PF)))
                                new_transport = asoc->peer.active_path;
                        if (new_transport->state == SCTP_UNCONFIRMED)
                                continue;

                        /* Change packets if necessary.  */
                        if (new_transport != transport) {
                                transport = new_transport;

                                /* Schedule to have this transport's
                                 * packet flushed.
                                 */
                                if (list_empty(&transport->send_ready)) {
                                        list_add_tail(&transport->send_ready,
                                                      &transport_list);
                                }

                                packet = &transport->packet;
                                sctp_packet_config(packet, vtag,
                                                   asoc->peer.ecn_capable);
                                /* We've switched transports, so apply the
                                 * Burst limit to the new transport.
                                 */
                                sctp_transport_burst_limited(transport);
                        }

                        pr_debug("%s: outq:%p, chunk:%p[%s], tx-tsn:0x%x skb->head:%p "
                                 "skb->users:%d\n",
                                 __func__, q, chunk, chunk && chunk->chunk_hdr ?
                                 sctp_cname(SCTP_ST_CHUNK(chunk->chunk_hdr->type)) :
                                 "illegal chunk", ntohl(chunk->subh.data_hdr->tsn),
                                 chunk->skb ? chunk->skb->head : NULL, chunk->skb ?
                                 atomic_read(&chunk->skb->users) : -1);

                        /* Add the chunk to the packet.  */
                        status = sctp_packet_transmit_chunk(packet, chunk, 0);

                        switch (status) {
                        case SCTP_XMIT_PMTU_FULL:
                        case SCTP_XMIT_RWND_FULL:
                        case SCTP_XMIT_DELAY:
                                /* We could not append this chunk, so put
                                 * the chunk back on the output queue.
                                 */
                                pr_debug("%s: could not transmit tsn:0x%x, status:%d\n",
                                         __func__, ntohl(chunk->subh.data_hdr->tsn),
                                         status);

                                sctp_outq_head_data(q, chunk);
                                goto sctp_flush_out;

                        case SCTP_XMIT_OK:
                                /* The sender is in the SHUTDOWN-PENDING state,
                                 * The sender MAY set the I-bit in the DATA
                                 * chunk header.
                                 */
                                if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING)
                                        chunk->chunk_hdr->flags |= SCTP_DATA_SACK_IMM;
                                if (chunk->chunk_hdr->flags & SCTP_DATA_UNORDERED)
                                        asoc->stats.ouodchunks++;
                                else
                                        asoc->stats.oodchunks++;

                                break;

                        default:
                                BUG();
                        }

                        /* BUG: We assume that the sctp_packet_transmit()
                         * call below will succeed all the time and add the
                         * chunk to the transmitted list and restart the
                         * timers.
                         * It is possible that the call can fail under OOM
                         * conditions.
                         *
                         * Is this really a problem?  Won't this behave
                         * like a lost TSN?
                         */
                        list_add_tail(&chunk->transmitted_list,
                                      &transport->transmitted);

                        sctp_transport_reset_timers(transport);

                        /* Only let one DATA chunk get bundled with a
                         * COOKIE-ECHO chunk.
                         */
                        if (packet->has_cookie_echo)
                                goto sctp_flush_out;
                }
                break;

        default:
                /* Do nothing.  */
                break;
        }

sctp_flush_out:

        /* Before returning, examine all the transports touched in
         * this call.  Right now, we bluntly force clear all the
         * transports.  Things might change after we implement Nagle.
         * But such an examination is still required.
         *
         * --xguo
         */
        while ((ltransport = sctp_list_dequeue(&transport_list)) != NULL) {
                struct sctp_transport *t = list_entry(ltransport,
                                                      struct sctp_transport,
                                                      send_ready);
                packet = &t->packet;
                if (!sctp_packet_empty(packet))
                        error = sctp_packet_transmit(packet);

                /* Clear the burst limited state, if any */
                sctp_transport_burst_reset(t);
        }

        return error;
}

/* Update unack_data based on the incoming SACK chunk */
static void sctp_sack_update_unack_data(struct sctp_association *assoc,
                                        struct sctp_sackhdr *sack)
{
        sctp_sack_variable_t *frags;
        __u16 unack_data;
        int i;

        unack_data = assoc->next_tsn - assoc->ctsn_ack_point - 1;

        frags = sack->variable;
        for (i = 0; i < ntohs(sack->num_gap_ack_blocks); i++) {
                unack_data -= ((ntohs(frags[i].gab.end) -
                                ntohs(frags[i].gab.start) + 1));
        }

        assoc->unack_data = unack_data;
}

/* This is where we REALLY process a SACK.
 *
 * Process the SACK against the outqueue.  Mostly, this just frees
 * things off the transmitted queue.
 */
int sctp_outq_sack(struct sctp_outq *q, struct sctp_chunk *chunk)
{
        struct sctp_association *asoc = q->asoc;
        struct sctp_sackhdr *sack = chunk->subh.sack_hdr;
        struct sctp_transport *transport;
        struct sctp_chunk *tchunk = NULL;
        struct list_head *lchunk, *transport_list, *temp;
        sctp_sack_variable_t *frags = sack->variable;
        __u32 sack_ctsn, ctsn, tsn;
        __u32 highest_tsn, highest_new_tsn;
        __u32 sack_a_rwnd;
        unsigned int outstanding;
        struct sctp_transport *primary = asoc->peer.primary_path;
        int count_of_newacks = 0;
        int gap_ack_blocks;
        u8 accum_moved = 0;

        /* Grab the association's destination address list. */
        transport_list = &asoc->peer.transport_addr_list;

        sack_ctsn = ntohl(sack->cum_tsn_ack);
        gap_ack_blocks = ntohs(sack->num_gap_ack_blocks);
        asoc->stats.gapcnt += gap_ack_blocks;
        /*
         * SFR-CACC algorithm:
         * On receipt of a SACK the sender SHOULD execute the
         * following statements.
         *
         * 1) If the cumulative ack in the SACK passes next tsn_at_change
         * on the current primary, the CHANGEOVER_ACTIVE flag SHOULD be
         * cleared. The CYCLING_CHANGEOVER flag SHOULD also be cleared for
         * all destinations.
         * 2) If the SACK contains gap acks and the flag CHANGEOVER_ACTIVE
         * is set the receiver of the SACK MUST take the following actions:
         *
         * A) Initialize the cacc_saw_newack to 0 for all destination
         * addresses.
         *
         * Only bother if changeover_active is set. Otherwise, this is
         * totally suboptimal to do on every SACK.
         */
        if (primary->cacc.changeover_active) {
                u8 clear_cycling = 0;

                if (TSN_lte(primary->cacc.next_tsn_at_change, sack_ctsn)) {
                        primary->cacc.changeover_active = 0;
                        clear_cycling = 1;
                }

                if (clear_cycling || gap_ack_blocks) {
                        list_for_each_entry(transport, transport_list,
                                        transports) {
                                if (clear_cycling)
                                        transport->cacc.cycling_changeover = 0;
                                if (gap_ack_blocks)
                                        transport->cacc.cacc_saw_newack = 0;
                        }
                }
        }

        /* Get the highest TSN in the sack. */
        highest_tsn = sack_ctsn;
        if (gap_ack_blocks)
                highest_tsn += ntohs(frags[gap_ack_blocks - 1].gab.end);

        if (TSN_lt(asoc->highest_sacked, highest_tsn))
                asoc->highest_sacked = highest_tsn;

        highest_new_tsn = sack_ctsn;

        /* Run through the retransmit queue.  Credit bytes received
         * and free those chunks that we can.
         */
        sctp_check_transmitted(q, &q->retransmit, NULL, NULL, sack, &highest_new_tsn);

        /* Run through the transmitted queue.
         * Credit bytes received and free those chunks which we can.
         *
         * This is a MASSIVE candidate for optimization.
         */
        list_for_each_entry(transport, transport_list, transports) {
                sctp_check_transmitted(q, &transport->transmitted,
                                       transport, &chunk->source, sack,
                                       &highest_new_tsn);
                /*
                 * SFR-CACC algorithm:
                 * C) Let count_of_newacks be the number of
                 * destinations for which cacc_saw_newack is set.
                 */
                if (transport->cacc.cacc_saw_newack)
                        count_of_newacks++;
        }

        /* Move the Cumulative TSN Ack Point if appropriate.  */
        if (TSN_lt(asoc->ctsn_ack_point, sack_ctsn)) {
                asoc->ctsn_ack_point = sack_ctsn;
                accum_moved = 1;
        }

        if (gap_ack_blocks) {

                if (asoc->fast_recovery && accum_moved)
                        highest_new_tsn = highest_tsn;

                list_for_each_entry(transport, transport_list, transports)
                        sctp_mark_missing(q, &transport->transmitted, transport,
                                          highest_new_tsn, count_of_newacks);
        }

        /* Update unack_data field in the assoc. */
        sctp_sack_update_unack_data(asoc, sack);

        ctsn = asoc->ctsn_ack_point;

        /* Throw away stuff rotting on the sack queue.  */
        list_for_each_safe(lchunk, temp, &q->sacked) {
                tchunk = list_entry(lchunk, struct sctp_chunk,
                                    transmitted_list);
                tsn = ntohl(tchunk->subh.data_hdr->tsn);
                if (TSN_lte(tsn, ctsn)) {
                        list_del_init(&tchunk->transmitted_list);
                        sctp_chunk_free(tchunk);
                }
        }

        /* ii) Set rwnd equal to the newly received a_rwnd minus the
         *     number of bytes still outstanding after processing the
         *     Cumulative TSN Ack and the Gap Ack Blocks.
         */

        sack_a_rwnd = ntohl(sack->a_rwnd);
        outstanding = q->outstanding_bytes;

        if (outstanding < sack_a_rwnd)
                sack_a_rwnd -= outstanding;
        else
                sack_a_rwnd = 0;

        asoc->peer.rwnd = sack_a_rwnd;

        sctp_generate_fwdtsn(q, sack_ctsn);

        pr_debug("%s: sack cumulative tsn ack:0x%x\n", __func__, sack_ctsn);
        pr_debug("%s: cumulative tsn ack of assoc:%p is 0x%x, "
                 "advertised peer ack point:0x%x\n", __func__, asoc, ctsn,
                 asoc->adv_peer_ack_point);

        return sctp_outq_is_empty(q);
}

/* Is the outqueue empty?
 * The queue is empty when we have not pending data, no in-flight data
 * and nothing pending retransmissions.
 */
int sctp_outq_is_empty(const struct sctp_outq *q)
{
        return q->out_qlen == 0 && q->outstanding_bytes == 0 &&
               list_empty(&q->retransmit);
}

/********************************************************************
 * 2nd Level Abstractions
 ********************************************************************/

/* Go through a transport's transmitted list or the association's retransmit
 * list and move chunks that are acked by the Cumulative TSN Ack to q->sacked.
 * The retransmit list will not have an associated transport.
 *
 * I added coherent debug information output.   --xguo
 *
 * Instead of printing 'sacked' or 'kept' for each TSN on the
 * transmitted_queue, we print a range: SACKED: TSN1-TSN2, TSN3, TSN4-TSN5.
 * KEPT TSN6-TSN7, etc.
 */
static void sctp_check_transmitted(struct sctp_outq *q,
                                   struct list_head *transmitted_queue,
                                   struct sctp_transport *transport,
                                   union sctp_addr *saddr,
                                   struct sctp_sackhdr *sack,
                                   __u32 *highest_new_tsn_in_sack)
{
        struct list_head *lchunk;
        struct sctp_chunk *tchunk;
        struct list_head tlist;
        __u32 tsn;
        __u32 sack_ctsn;
        __u32 rtt;
        __u8 restart_timer = 0;
        int bytes_acked = 0;
        int migrate_bytes = 0;
        bool forward_progress = false;

        sack_ctsn = ntohl(sack->cum_tsn_ack);

        INIT_LIST_HEAD(&tlist);

        /* The while loop will skip empty transmitted queues. */
        while (NULL != (lchunk = sctp_list_dequeue(transmitted_queue))) {
                tchunk = list_entry(lchunk, struct sctp_chunk,
                                    transmitted_list);

                if (sctp_chunk_abandoned(tchunk)) {
                        /* Move the chunk to abandoned list. */
                        sctp_insert_list(&q->abandoned, lchunk);

                        /* If this chunk has not been acked, stop
                         * considering it as 'outstanding'.
                         */
                        if (!tchunk->tsn_gap_acked) {
                                if (tchunk->transport)
                                        tchunk->transport->flight_size -=
                                                        sctp_data_size(tchunk);
                                q->outstanding_bytes -= sctp_data_size(tchunk);
                        }
                        continue;
                }

                tsn = ntohl(tchunk->subh.data_hdr->tsn);
                if (sctp_acked(sack, tsn)) {
                        /* If this queue is the retransmit queue, the
                         * retransmit timer has already reclaimed
                         * the outstanding bytes for this chunk, so only
                         * count bytes associated with a transport.
                         */
                        if (transport) {
                                /* If this chunk is being used for RTT
                                 * measurement, calculate the RTT and update
                                 * the RTO using this value.
                                 *
                                 * 6.3.1 C5) Karn's algorithm: RTT measurements
                                 * MUST NOT be made using packets that were
                                 * retransmitted (and thus for which it is
                                 * ambiguous whether the reply was for the
                                 * first instance of the packet or a later
                                 * instance).
                                 */
                                if (!tchunk->tsn_gap_acked &&
                                    !tchunk->resent &&
                                    tchunk->rtt_in_progress) {
                                        tchunk->rtt_in_progress = 0;
                                        rtt = jiffies - tchunk->sent_at;
                                        sctp_transport_update_rto(transport,
                                                                  rtt);
                                }
                        }

                        /* If the chunk hasn't been marked as ACKED,
                         * mark it and account bytes_acked if the
                         * chunk had a valid transport (it will not
                         * have a transport if ASCONF had deleted it
                         * while DATA was outstanding).
                         */
                        if (!tchunk->tsn_gap_acked) {
                                tchunk->tsn_gap_acked = 1;
                                if (TSN_lt(*highest_new_tsn_in_sack, tsn))
                                        *highest_new_tsn_in_sack = tsn;
                                bytes_acked += sctp_data_size(tchunk);
                                if (!tchunk->transport)
                                        migrate_bytes += sctp_data_size(tchunk);
                                forward_progress = true;
                        }

                        if (TSN_lte(tsn, sack_ctsn)) {
                                /* RFC 2960  6.3.2 Retransmission Timer Rules
                                 *
                                 * R3) Whenever a SACK is received
                                 * that acknowledges the DATA chunk
                                 * with the earliest outstanding TSN
                                 * for that address, restart T3-rtx
                                 * timer for that address with its
                                 * current RTO.
                                 */
                                restart_timer = 1;
                                forward_progress = true;

                                if (!tchunk->tsn_gap_acked) {
                                        /*
                                         * SFR-CACC algorithm:
                                         * 2) If the SACK contains gap acks
                                         * and the flag CHANGEOVER_ACTIVE is
                                         * set the receiver of the SACK MUST
                                         * take the following action:
                                         *
                                         * B) For each TSN t being acked that
                                         * has not been acked in any SACK so
                                         * far, set cacc_saw_newack to 1 for
                                         * the destination that the TSN was
                                         * sent to.
                                         */
                                        if (transport &&
                                            sack->num_gap_ack_blocks &&
                                            q->asoc->peer.primary_path->cacc.
                                            changeover_active)
                                                transport->cacc.cacc_saw_newack
                                                        = 1;
                                }

                                list_add_tail(&tchunk->transmitted_list,
                                              &q->sacked);
                        } else {
                                /* RFC2960 7.2.4, sctpimpguide-05 2.8.2
                                 * M2) Each time a SACK arrives reporting
                                 * 'Stray DATA chunk(s)' record the highest TSN
                                 * reported as newly acknowledged, call this
                                 * value 'HighestTSNinSack'. A newly
                                 * acknowledged DATA chunk is one not
                                 * previously acknowledged in a SACK.
                                 *
                                 * When the SCTP sender of data receives a SACK
                                 * chunk that acknowledges, for the first time,
                                 * the receipt of a DATA chunk, all the still
                                 * unacknowledged DATA chunks whose TSN is
                                 * older than that newly acknowledged DATA
                                 * chunk, are qualified as 'Stray DATA chunks'.
                                 */
                                list_add_tail(lchunk, &tlist);
                        }
                } else {
                        if (tchunk->tsn_gap_acked) {
                                pr_debug("%s: receiver reneged on data TSN:0x%x\n",
                                         __func__, tsn);

                                tchunk->tsn_gap_acked = 0;

                                if (tchunk->transport)
                                        bytes_acked -= sctp_data_size(tchunk);

                                /* RFC 2960 6.3.2 Retransmission Timer Rules
                                 *
                                 * R4) Whenever a SACK is received missing a
                                 * TSN that was previously acknowledged via a
                                 * Gap Ack Block, start T3-rtx for the
                                 * destination address to which the DATA
                                 * chunk was originally
                                 * transmitted if it is not already running.
                                 */
                                restart_timer = 1;
                        }

                        list_add_tail(lchunk, &tlist);
                }
        }

        if (transport) {
                if (bytes_acked) {
                        struct sctp_association *asoc = transport->asoc;

                        /* We may have counted DATA that was migrated
                         * to this transport due to DEL-IP operation.
                         * Subtract those bytes, since the were never
                         * send on this transport and shouldn't be
                         * credited to this transport.
                         */
                        bytes_acked -= migrate_bytes;

                        /* 8.2. When an outstanding TSN is acknowledged,
                         * the endpoint shall clear the error counter of
                         * the destination transport address to which the
                         * DATA chunk was last sent.
                         * The association's overall error counter is
                         * also cleared.
                         */
                        transport->error_count = 0;
                        transport->asoc->overall_error_count = 0;
                        forward_progress = true;

                        /*
                         * While in SHUTDOWN PENDING, we may have started
                         * the T5 shutdown guard timer after reaching the
                         * retransmission limit. Stop that timer as soon
                         * as the receiver acknowledged any data.
                         */
                        if (asoc->state == SCTP_STATE_SHUTDOWN_PENDING &&
                            del_timer(&asoc->timers
                                [SCTP_EVENT_TIMEOUT_T5_SHUTDOWN_GUARD]))
                                        sctp_association_put(asoc);

                        /* Mark the destination transport address as
                         * active if it is not so marked.
                         */
                        if ((transport->state == SCTP_INACTIVE ||
                             transport->state == SCTP_UNCONFIRMED) &&
                            sctp_cmp_addr_exact(&transport->ipaddr, saddr)) {
                                sctp_assoc_control_transport(
                                        transport->asoc,
                                        transport,
                                        SCTP_TRANSPORT_UP,
                                        SCTP_RECEIVED_SACK);
                        }

                        sctp_transport_raise_cwnd(transport, sack_ctsn,
                                                  bytes_acked);

                        transport->flight_size -= bytes_acked;
                        if (transport->flight_size == 0)
                                transport->partial_bytes_acked = 0;
                        q->outstanding_bytes -= bytes_acked + migrate_bytes;
                } else {
                        /* RFC 2960 6.1, sctpimpguide-06 2.15.2
                         * When a sender is doing zero window probing, it
                         * should not timeout the association if it continues
                         * to receive new packets from the receiver. The
                         * reason is that the receiver MAY keep its window
                         * closed for an indefinite time.
                         * A sender is doing zero window probing when the
                         * receiver's advertised window is zero, and there is
                         * only one data chunk in flight to the receiver.
                         *
                         * Allow the association to timeout while in SHUTDOWN
                         * PENDING or SHUTDOWN RECEIVED in case the receiver
                         * stays in zero window mode forever.
                         */
                        if (!q->asoc->peer.rwnd &&
                            !list_empty(&tlist) &&
                            (sack_ctsn+2 == q->asoc->next_tsn) &&
                            q->asoc->state < SCTP_STATE_SHUTDOWN_PENDING) {
                                pr_debug("%s: sack received for zero window "
                                         "probe:%u\n", __func__, sack_ctsn);

                                q->asoc->overall_error_count = 0;
                                transport->error_count = 0;
                        }
                }

                /* RFC 2960 6.3.2 Retransmission Timer Rules
                 *
                 * R2) Whenever all outstanding data sent to an address have
                 * been acknowledged, turn off the T3-rtx timer of that
                 * address.
                 */
                if (!transport->flight_size) {
                        if (del_timer(&transport->T3_rtx_timer))
                                sctp_transport_put(transport);
                } else if (restart_timer) {
                        if (!mod_timer(&transport->T3_rtx_timer,
                                       jiffies + transport->rto))
                                sctp_transport_hold(transport);
                }

                if (forward_progress) {
                        if (transport->dst)
                                dst_confirm(transport->dst);
                }
        }

        list_splice(&tlist, transmitted_queue);
}

/* Mark chunks as missing and consequently may get retransmitted. */
static void sctp_mark_missing(struct sctp_outq *q,
                              struct list_head *transmitted_queue,
                              struct sctp_transport *transport,
                              __u32 highest_new_tsn_in_sack,
                              int count_of_newacks)
{
        struct sctp_chunk *chunk;
        __u32 tsn;
        char do_fast_retransmit = 0;
        struct sctp_association *asoc = q->asoc;
        struct sctp_transport *primary = asoc->peer.primary_path;

        list_for_each_entry(chunk, transmitted_queue, transmitted_list) {

                tsn = ntohl(chunk->subh.data_hdr->tsn);

                /* RFC 2960 7.2.4, sctpimpguide-05 2.8.2 M3) Examine all
                 * 'Unacknowledged TSN's', if the TSN number of an
                 * 'Unacknowledged TSN' is smaller than the 'HighestTSNinSack'
                 * value, increment the 'TSN.Missing.Report' count on that
                 * chunk if it has NOT been fast retransmitted or marked for
                 * fast retransmit already.
                 */
                if (chunk->fast_retransmit == SCTP_CAN_FRTX &&
                    !chunk->tsn_gap_acked &&
                    TSN_lt(tsn, highest_new_tsn_in_sack)) {

                        /* SFR-CACC may require us to skip marking
                         * this chunk as missing.
                         */
                        if (!transport || !sctp_cacc_skip(primary,
                                                chunk->transport,
                                                count_of_newacks, tsn)) {
                                chunk->tsn_missing_report++;

                                pr_debug("%s: tsn:0x%x missing counter:%d\n",
                                         __func__, tsn, chunk->tsn_missing_report);
                        }
                }
                /*
                 * M4) If any DATA chunk is found to have a
                 * 'TSN.Missing.Report'
                 * value larger than or equal to 3, mark that chunk for
                 * retransmission and start the fast retransmit procedure.
                 */

                if (chunk->tsn_missing_report >= 3) {
                        chunk->fast_retransmit = SCTP_NEED_FRTX;
                        do_fast_retransmit = 1;
                }
        }

        if (transport) {
                if (do_fast_retransmit)
                        sctp_retransmit(q, transport, SCTP_RTXR_FAST_RTX);

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

/* Is the given TSN acked by this packet?  */
static int sctp_acked(struct sctp_sackhdr *sack, __u32 tsn)
{
        int i;
        sctp_sack_variable_t *frags;
        __u16 gap;
        __u32 ctsn = ntohl(sack->cum_tsn_ack);

        if (TSN_lte(tsn, ctsn))
                goto pass;

        /* 3.3.4 Selective Acknowledgement (SACK) (3):
         *
         * Gap Ack Blocks:
         *  These fields contain the Gap Ack Blocks. They are repeated
         *  for each Gap Ack Block up to the number of Gap Ack Blocks
         *  defined in the Number of Gap Ack Blocks field. All DATA
         *  chunks with TSNs greater than or equal to (Cumulative TSN
         *  Ack + Gap Ack Block Start) and less than or equal to
         *  (Cumulative TSN Ack + Gap Ack Block End) of each Gap Ack
         *  Block are assumed to have been received correctly.
         */

        frags = sack->variable;
        gap = tsn - ctsn;
        for (i = 0; i < ntohs(sack->num_gap_ack_blocks); ++i) {
                if (TSN_lte(ntohs(frags[i].gab.start), gap) &&
                    TSN_lte(gap, ntohs(frags[i].gab.end)))
                        goto pass;
        }

        return 0;
pass:
        return 1;
}

static inline int sctp_get_skip_pos(struct sctp_fwdtsn_skip *skiplist,
                                    int nskips, __be16 stream)
{
        int i;

        for (i = 0; i < nskips; i++) {
                if (skiplist[i].stream == stream)
                        return i;
        }
        return i;
}

/* Create and add a fwdtsn chunk to the outq's control queue if needed. */
static void sctp_generate_fwdtsn(struct sctp_outq *q, __u32 ctsn)
{
        struct sctp_association *asoc = q->asoc;
        struct sctp_chunk *ftsn_chunk = NULL;
        struct sctp_fwdtsn_skip ftsn_skip_arr[10];
        int nskips = 0;
        int skip_pos = 0;
        __u32 tsn;
        struct sctp_chunk *chunk;
        struct list_head *lchunk, *temp;

        if (!asoc->peer.prsctp_capable)
                return;

        /* PR-SCTP C1) Let SackCumAck be the Cumulative TSN ACK carried in the
         * received SACK.
         *
         * If (Advanced.Peer.Ack.Point < SackCumAck), then update
         * Advanced.Peer.Ack.Point to be equal to SackCumAck.
         */
        if (TSN_lt(asoc->adv_peer_ack_point, ctsn))
                asoc->adv_peer_ack_point = ctsn;

        /* PR-SCTP C2) Try to further advance the "Advanced.Peer.Ack.Point"
         * locally, that is, to move "Advanced.Peer.Ack.Point" up as long as
         * the chunk next in the out-queue space is marked as "abandoned" as
         * shown in the following example:
         *
         * Assuming that a SACK arrived with the Cumulative TSN ACK 102
         * and the Advanced.Peer.Ack.Point is updated to this value:
         *
         *   out-queue at the end of  ==>   out-queue after Adv.Ack.Point
         *   normal SACK processing           local advancement
         *                ...                           ...
         *   Adv.Ack.Pt-> 102 acked                     102 acked
         *                103 abandoned                 103 abandoned
         *                104 abandoned     Adv.Ack.P-> 104 abandoned
         *                105                           105
         *                106 acked                     106 acked
         *                ...                           ...
         *
         * In this example, the data sender successfully advanced the
         * "Advanced.Peer.Ack.Point" from 102 to 104 locally.
         */
        list_for_each_safe(lchunk, temp, &q->abandoned) {
                chunk = list_entry(lchunk, struct sctp_chunk,
                                        transmitted_list);
                tsn = ntohl(chunk->subh.data_hdr->tsn);

                /* Remove any chunks in the abandoned queue that are acked by
                 * the ctsn.
                 */
                if (TSN_lte(tsn, ctsn)) {
                        list_del_init(lchunk);
                        sctp_chunk_free(chunk);
                } else {
                        if (TSN_lte(tsn, asoc->adv_peer_ack_point+1)) {
                                asoc->adv_peer_ack_point = tsn;
                                if (chunk->chunk_hdr->flags &
                                         SCTP_DATA_UNORDERED)
                                        continue;
                                skip_pos = sctp_get_skip_pos(&ftsn_skip_arr[0],
                                                nskips,
                                                chunk->subh.data_hdr->stream);
                                ftsn_skip_arr[skip_pos].stream =
                                        chunk->subh.data_hdr->stream;
                                ftsn_skip_arr[skip_pos].ssn =
                                         chunk->subh.data_hdr->ssn;
                                if (skip_pos == nskips)
                                        nskips++;
                                if (nskips == 10)
                                        break;
                        } else
                                break;
                }
        }

        /* PR-SCTP C3) If, after step C1 and C2, the "Advanced.Peer.Ack.Point"
         * is greater than the Cumulative TSN ACK carried in the received
         * SACK, the data sender MUST send the data receiver a FORWARD TSN
         * chunk containing the latest value of the
         * "Advanced.Peer.Ack.Point".
         *
         * C4) For each "abandoned" TSN the sender of the FORWARD TSN SHOULD
         * list each stream and sequence number in the forwarded TSN. This
         * information will enable the receiver to easily find any
         * stranded TSN's waiting on stream reorder queues. Each stream
         * SHOULD only be reported once; this means that if multiple
         * abandoned messages occur in the same stream then only the
         * highest abandoned stream sequence number is reported. If the
         * total size of the FORWARD TSN does NOT fit in a single MTU then
         * the sender of the FORWARD TSN SHOULD lower the
         * Advanced.Peer.Ack.Point to the last TSN that will fit in a
         * single MTU.
         */
        if (asoc->adv_peer_ack_point > ctsn)
                ftsn_chunk = sctp_make_fwdtsn(asoc, asoc->adv_peer_ack_point,
                                              nskips, &ftsn_skip_arr[0]);

        if (ftsn_chunk) {
                list_add_tail(&ftsn_chunk->list, &q->control_chunk_list);
                SCTP_INC_STATS(sock_net(asoc->base.sk), SCTP_MIB_OUTCTRLCHUNKS);
        }
}