outqueue.c

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/* 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, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <[email protected]>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <[email protected]>
 *    Karl Knutson          <[email protected]>
 *    Perry Melange         <[email protected]>
 *    Xingang Guo           <[email protected]>
 *    Hui Huang         <[email protected]>
 *    Sridhar Samudrala     <[email protected]>
 *    Jon Grimm             <[email protected]>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#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)
{
    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);

    q->fast_rtx = 0;
    q->outstanding_bytes = 0;
    q->empty = 1;
    q->cork  = 0;

    q->malloced = 0;
    q->out_qlen = 0;
}

/* Free the outqueue structure and any related pending chunks.
 */
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);
    }

    q->error = 0;

    /* 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);
    }
}

/* 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);

    /* If we were kmalloc()'d, free the memory.  */
    if (q->malloced)
        kfree(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;

    SCTP_DEBUG_PRINTK("sctp_outq_tail(%p, %p[%s])\n",
              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:
            SCTP_DEBUG_PRINTK("outqueueing (%p, %p[%s])\n",
              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);
            q->empty = 0;
            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;
            }

            /* 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);
        }
    }

    SCTP_DEBUG_PRINTK("%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_NAGLE_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->empty = 0;
            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)
{
    int error = 0;
    if (q->cork)
        q->cork = 0;
    error = sctp_outq_flush(q, 0);
    return error;
}


/*
 * 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 if (chunk->chunk_hdr->type == SCTP_CID_FWD_TSN) {
                /* PR-SCTP C5) If a FORWARD TSN is sent, the
                 * sender MUST assure that at least one T3-rtx
                 * timer is running.
                 */
                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);
            }

            SCTP_DEBUG_PRINTK("sctp_outq_flush(%p, %p[%s]), ",
                      q, chunk,
                      chunk && chunk->chunk_hdr ?
                      sctp_cname(SCTP_ST_CHUNK(
                          chunk->chunk_hdr->type))
                      : "Illegal Chunk");

            SCTP_DEBUG_PRINTK("TX TSN 0x%x skb->head "
                    "%p skb->users %d.\n",
                    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_NAGLE_DELAY:
                /* We could not append this chunk, so put
                 * the chunk back on the output queue.
                 */
                SCTP_DEBUG_PRINTK("sctp_outq_flush: could "
                    "not transmit TSN: 0x%x, status: %d\n",
                    ntohl(chunk->subh.data_hdr->tsn),
                    status);
                sctp_outq_head_data(q, chunk);
                goto sctp_flush_out;
                break;

            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;

                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);

            q->empty = 0;

            /* 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);
    /*
     * 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);

    SCTP_DEBUG_PRINTK("%s: sack Cumulative TSN Ack is 0x%x.\n",
              __func__, sack_ctsn);
    SCTP_DEBUG_PRINTK("%s: Cumulative TSN Ack of association, "
              "%p is 0x%x. Adv peer ack point: 0x%x\n",
              __func__, asoc, ctsn, asoc->adv_peer_ack_point);

    /* See if all chunks are acked.
     * Make sure the empty queue handler will get run later.
     */
    q->empty = (list_empty(&q->out_chunk_list) &&
            list_empty(&q->retransmit));
    if (!q->empty)
        goto finish;

    list_for_each_entry(transport, transport_list, transports) {
        q->empty = q->empty && list_empty(&transport->transmitted);
        if (!q->empty)
            goto finish;
    }

    SCTP_DEBUG_PRINTK("sack queue is empty.\n");
finish:
    return q->empty;
}

/* Is the outqueue empty?  */
int sctp_outq_is_empty(const struct sctp_outq *q)
{
    return q->empty;
}

/********************************************************************
 * 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;

    /* These state variables are for coherent debug output. --xguo */

#if SCTP_DEBUG
    __u32 dbg_ack_tsn = 0;  /* An ACKed TSN range starts here... */
    __u32 dbg_last_ack_tsn = 0;  /* ...and finishes here.        */
    __u32 dbg_kept_tsn = 0; /* An un-ACKed range starts here...  */
    __u32 dbg_last_kept_tsn = 0; /* ...and finishes here.        */

    /* 0 : The last TSN was ACKed.
     * 1 : The last TSN was NOT ACKed (i.e. KEPT).
     * -1: We need to initialize.
     */
    int dbg_prt_state = -1;
#endif /* SCTP_DEBUG */

    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->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;
                *highest_new_tsn_in_sack = tsn;
                bytes_acked += sctp_data_size(tchunk);
                if (!tchunk->transport)
                    migrate_bytes += sctp_data_size(tchunk);
            }

            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;

                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);
            }

#if SCTP_DEBUG
            switch (dbg_prt_state) {
            case 0: /* last TSN was ACKed */
                if (dbg_last_ack_tsn + 1 == tsn) {
                    /* This TSN belongs to the
                     * current ACK range.
                     */
                    break;
                }

                if (dbg_last_ack_tsn != dbg_ack_tsn) {
                    /* Display the end of the
                     * current range.
                     */
                    SCTP_DEBUG_PRINTK_CONT("-%08x",
                                   dbg_last_ack_tsn);
                }

                /* Start a new range.  */
                SCTP_DEBUG_PRINTK_CONT(",%08x", tsn);
                dbg_ack_tsn = tsn;
                break;

            case 1: /* The last TSN was NOT ACKed. */
                if (dbg_last_kept_tsn != dbg_kept_tsn) {
                    /* Display the end of current range. */
                    SCTP_DEBUG_PRINTK_CONT("-%08x",
                                   dbg_last_kept_tsn);
                }

                SCTP_DEBUG_PRINTK_CONT("\n");

                /* FALL THROUGH... */
            default:
                /* This is the first-ever TSN we examined.  */
                /* Start a new range of ACK-ed TSNs.  */
                SCTP_DEBUG_PRINTK("ACKed: %08x", tsn);
                dbg_prt_state = 0;
                dbg_ack_tsn = tsn;
            }

            dbg_last_ack_tsn = tsn;
#endif /* SCTP_DEBUG */

        } else {
            if (tchunk->tsn_gap_acked) {
                SCTP_DEBUG_PRINTK("%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 SCTP_DEBUG
            /* See the above comments on ACK-ed TSNs. */
            switch (dbg_prt_state) {
            case 1:
                if (dbg_last_kept_tsn + 1 == tsn)
                    break;

                if (dbg_last_kept_tsn != dbg_kept_tsn)
                    SCTP_DEBUG_PRINTK_CONT("-%08x",
                                   dbg_last_kept_tsn);

                SCTP_DEBUG_PRINTK_CONT(",%08x", tsn);
                dbg_kept_tsn = tsn;
                break;

            case 0:
                if (dbg_last_ack_tsn != dbg_ack_tsn)
                    SCTP_DEBUG_PRINTK_CONT("-%08x",
                                   dbg_last_ack_tsn);
                SCTP_DEBUG_PRINTK_CONT("\n");

                /* FALL THROUGH... */
            default:
                SCTP_DEBUG_PRINTK("KEPT: %08x",tsn);
                dbg_prt_state = 1;
                dbg_kept_tsn = tsn;
            }

            dbg_last_kept_tsn = tsn;
#endif /* SCTP_DEBUG */
        }
    }

#if SCTP_DEBUG
    /* Finish off the last range, displaying its ending TSN.  */
    switch (dbg_prt_state) {
    case 0:
        if (dbg_last_ack_tsn != dbg_ack_tsn) {
            SCTP_DEBUG_PRINTK_CONT("-%08x\n", dbg_last_ack_tsn);
        } else {
            SCTP_DEBUG_PRINTK_CONT("\n");
        }
    break;

    case 1:
        if (dbg_last_kept_tsn != dbg_kept_tsn) {
            SCTP_DEBUG_PRINTK_CONT("-%08x\n", dbg_last_kept_tsn);
        } else {
            SCTP_DEBUG_PRINTK_CONT("\n");
        }
    }
#endif /* SCTP_DEBUG */
    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;

            /*
             * 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) {
                SCTP_DEBUG_PRINTK("%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 (timer_pending(&transport->T3_rtx_timer) &&
                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);
        }
    }

    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++;

                SCTP_DEBUG_PRINTK(
                    "%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);

        SCTP_DEBUG_PRINTK("%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);
    }
}