Merge branch 'linus' into core/softlockup

[linux-2.6] / net / sctp / output.c

/* SCTP kernel implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 *
 * This file is part of the SCTP kernel implementation
 *
 * These functions handle output processing.
 *
 * 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 <lksctp-developers@lists.sourceforge.net>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    La Monte H.P. Yarroll <piggy@acm.org>
 *    Karl Knutson          <karl@athena.chicago.il.us>
 *    Jon Grimm             <jgrimm@austin.ibm.com>
 *    Sridhar Samudrala     <sri@us.ibm.com>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/time.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/init.h>
#include <net/inet_ecn.h>
#include <net/icmp.h>

#ifndef TEST_FRAME
#include <net/tcp.h>
#endif /* TEST_FRAME (not defined) */

#include <linux/socket.h> /* for sa_family_t */
#include <net/sock.h>

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

/* Forward declarations for private helpers. */
static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
                                           struct sctp_chunk *chunk);

/* Config a packet.
 * This appears to be a followup set of initializations.
 */
struct sctp_packet *sctp_packet_config(struct sctp_packet *packet,
                                       __u32 vtag, int ecn_capable)
{
        struct sctp_chunk *chunk = NULL;

        SCTP_DEBUG_PRINTK("%s: packet:%p vtag:0x%x\n", __func__,
                          packet, vtag);

        packet->vtag = vtag;
        packet->has_cookie_echo = 0;
        packet->has_sack = 0;
        packet->has_auth = 0;
        packet->has_data = 0;
        packet->ipfragok = 0;
        packet->auth = NULL;

        if (ecn_capable && sctp_packet_empty(packet)) {
                chunk = sctp_get_ecne_prepend(packet->transport->asoc);

                /* If there a is a prepend chunk stick it on the list before
                 * any other chunks get appended.
                 */
                if (chunk)
                        sctp_packet_append_chunk(packet, chunk);
        }

        return packet;
}

/* Initialize the packet structure. */
struct sctp_packet *sctp_packet_init(struct sctp_packet *packet,
                                     struct sctp_transport *transport,
                                     __u16 sport, __u16 dport)
{
        struct sctp_association *asoc = transport->asoc;
        size_t overhead;

        SCTP_DEBUG_PRINTK("%s: packet:%p transport:%p\n", __func__,
                          packet, transport);

        packet->transport = transport;
        packet->source_port = sport;
        packet->destination_port = dport;
        INIT_LIST_HEAD(&packet->chunk_list);
        if (asoc) {
                struct sctp_sock *sp = sctp_sk(asoc->base.sk);
                overhead = sp->pf->af->net_header_len;
        } else {
                overhead = sizeof(struct ipv6hdr);
        }
        overhead += sizeof(struct sctphdr);
        packet->overhead = overhead;
        packet->size = overhead;
        packet->vtag = 0;
        packet->has_cookie_echo = 0;
        packet->has_sack = 0;
        packet->has_auth = 0;
        packet->has_data = 0;
        packet->ipfragok = 0;
        packet->malloced = 0;
        packet->auth = NULL;
        return packet;
}

/* Free a packet.  */
void sctp_packet_free(struct sctp_packet *packet)
{
        struct sctp_chunk *chunk, *tmp;

        SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);

        list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
                list_del_init(&chunk->list);
                sctp_chunk_free(chunk);
        }

        if (packet->malloced)
                kfree(packet);
}

/* This routine tries to append the chunk to the offered packet. If adding
 * the chunk causes the packet to exceed the path MTU and COOKIE_ECHO chunk
 * is not present in the packet, it transmits the input packet.
 * Data can be bundled with a packet containing a COOKIE_ECHO chunk as long
 * as it can fit in the packet, but any more data that does not fit in this
 * packet can be sent only after receiving the COOKIE_ACK.
 */
sctp_xmit_t sctp_packet_transmit_chunk(struct sctp_packet *packet,
                                       struct sctp_chunk *chunk)
{
        sctp_xmit_t retval;
        int error = 0;

        SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__,
                          packet, chunk);

        switch ((retval = (sctp_packet_append_chunk(packet, chunk)))) {
        case SCTP_XMIT_PMTU_FULL:
                if (!packet->has_cookie_echo) {
                        error = sctp_packet_transmit(packet);
                        if (error < 0)
                                chunk->skb->sk->sk_err = -error;

                        /* If we have an empty packet, then we can NOT ever
                         * return PMTU_FULL.
                         */
                        retval = sctp_packet_append_chunk(packet, chunk);
                }
                break;

        case SCTP_XMIT_RWND_FULL:
        case SCTP_XMIT_OK:
        case SCTP_XMIT_NAGLE_DELAY:
                break;
        }

        return retval;
}

/* Try to bundle an auth chunk into the packet. */
static sctp_xmit_t sctp_packet_bundle_auth(struct sctp_packet *pkt,
                                           struct sctp_chunk *chunk)
{
        struct sctp_association *asoc = pkt->transport->asoc;
        struct sctp_chunk *auth;
        sctp_xmit_t retval = SCTP_XMIT_OK;

        /* if we don't have an association, we can't do authentication */
        if (!asoc)
                return retval;

        /* See if this is an auth chunk we are bundling or if
         * auth is already bundled.
         */
        if (chunk->chunk_hdr->type == SCTP_CID_AUTH || pkt->auth)
                return retval;

        /* if the peer did not request this chunk to be authenticated,
         * don't do it
         */
        if (!chunk->auth)
                return retval;

        auth = sctp_make_auth(asoc);
        if (!auth)
                return retval;

        retval = sctp_packet_append_chunk(pkt, auth);

        return retval;
}

/* Try to bundle a SACK with the packet. */
static sctp_xmit_t sctp_packet_bundle_sack(struct sctp_packet *pkt,
                                           struct sctp_chunk *chunk)
{
        sctp_xmit_t retval = SCTP_XMIT_OK;

        /* If sending DATA and haven't aleady bundled a SACK, try to
         * bundle one in to the packet.
         */
        if (sctp_chunk_is_data(chunk) && !pkt->has_sack &&
            !pkt->has_cookie_echo) {
                struct sctp_association *asoc;
                asoc = pkt->transport->asoc;

                if (asoc->a_rwnd > asoc->rwnd) {
                        struct sctp_chunk *sack;
                        asoc->a_rwnd = asoc->rwnd;
                        sack = sctp_make_sack(asoc);
                        if (sack) {
                                struct timer_list *timer;
                                retval = sctp_packet_append_chunk(pkt, sack);
                                asoc->peer.sack_needed = 0;
                                timer = &asoc->timers[SCTP_EVENT_TIMEOUT_SACK];
                                if (timer_pending(timer) && del_timer(timer))
                                        sctp_association_put(asoc);
                        }
                }
        }
        return retval;
}

/* Append a chunk to the offered packet reporting back any inability to do
 * so.
 */
sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
                                     struct sctp_chunk *chunk)
{
        sctp_xmit_t retval = SCTP_XMIT_OK;
        __u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
        size_t psize;
        size_t pmtu;
        int too_big;

        SCTP_DEBUG_PRINTK("%s: packet:%p chunk:%p\n", __func__, packet,
                          chunk);

        /* Try to bundle AUTH chunk */
        retval = sctp_packet_bundle_auth(packet, chunk);
        if (retval != SCTP_XMIT_OK)
                goto finish;

        /* Try to bundle SACK chunk */
        retval = sctp_packet_bundle_sack(packet, chunk);
        if (retval != SCTP_XMIT_OK)
                goto finish;

        psize = packet->size;
        pmtu  = ((packet->transport->asoc) ?
                 (packet->transport->asoc->pathmtu) :
                 (packet->transport->pathmtu));

        too_big = (psize + chunk_len > pmtu);

        /* Decide if we need to fragment or resubmit later. */
        if (too_big) {
                /* It's OK to fragmet at IP level if any one of the following
                 * is true:
                 *      1. The packet is empty (meaning this chunk is greater
                 *         the MTU)
                 *      2. The chunk we are adding is a control chunk
                 *      3. The packet doesn't have any data in it yet and data
                 *      requires authentication.
                 */
                if (sctp_packet_empty(packet) || !sctp_chunk_is_data(chunk) ||
                    (!packet->has_data && chunk->auth)) {
                        /* We no longer do re-fragmentation.
                         * Just fragment at the IP layer, if we
                         * actually hit this condition
                         */
                        packet->ipfragok = 1;
                        goto append;

                } else {
                        retval = SCTP_XMIT_PMTU_FULL;
                        goto finish;
                }
        }

append:
        /* We believe that this chunk is OK to add to the packet (as
         * long as we have the cwnd for it).
         */

        /* DATA is a special case since we must examine both rwnd and cwnd
         * before we send DATA.
         */
        switch (chunk->chunk_hdr->type) {
            case SCTP_CID_DATA:
                retval = sctp_packet_append_data(packet, chunk);
                /* Disallow SACK bundling after DATA. */
                packet->has_sack = 1;
                /* Disallow AUTH bundling after DATA */
                packet->has_auth = 1;
                /* Let it be knows that packet has DATA in it */
                packet->has_data = 1;
                if (SCTP_XMIT_OK != retval)
                        goto finish;
                break;
            case SCTP_CID_COOKIE_ECHO:
                packet->has_cookie_echo = 1;
                break;

            case SCTP_CID_SACK:
                packet->has_sack = 1;
                break;

            case SCTP_CID_AUTH:
                packet->has_auth = 1;
                packet->auth = chunk;
                break;
        }

        /* It is OK to send this chunk.  */
        list_add_tail(&chunk->list, &packet->chunk_list);
        packet->size += chunk_len;
        chunk->transport = packet->transport;
finish:
        return retval;
}

/* All packets are sent to the network through this function from
 * sctp_outq_tail().
 *
 * The return value is a normal kernel error return value.
 */
int sctp_packet_transmit(struct sctp_packet *packet)
{
        struct sctp_transport *tp = packet->transport;
        struct sctp_association *asoc = tp->asoc;
        struct sctphdr *sh;
        __u32 crc32 = 0;
        struct sk_buff *nskb;
        struct sctp_chunk *chunk, *tmp;
        struct sock *sk;
        int err = 0;
        int padding;            /* How much padding do we need?  */
        __u8 has_data = 0;
        struct dst_entry *dst = tp->dst;
        unsigned char *auth = NULL;     /* pointer to auth in skb data */
        __u32 cksum_buf_len = sizeof(struct sctphdr);

        SCTP_DEBUG_PRINTK("%s: packet:%p\n", __func__, packet);

        /* Do NOT generate a chunkless packet. */
        if (list_empty(&packet->chunk_list))
                return err;

        /* Set up convenience variables... */
        chunk = list_entry(packet->chunk_list.next, struct sctp_chunk, list);
        sk = chunk->skb->sk;

        /* Allocate the new skb.  */
        nskb = alloc_skb(packet->size + LL_MAX_HEADER, GFP_ATOMIC);
        if (!nskb)
                goto nomem;

        /* Make sure the outbound skb has enough header room reserved. */
        skb_reserve(nskb, packet->overhead + LL_MAX_HEADER);

        /* Set the owning socket so that we know where to get the
         * destination IP address.
         */
        skb_set_owner_w(nskb, sk);

        /* The 'obsolete' field of dst is set to 2 when a dst is freed. */
        if (!dst || (dst->obsolete > 1)) {
                dst_release(dst);
                sctp_transport_route(tp, NULL, sctp_sk(sk));
                if (asoc && (asoc->param_flags & SPP_PMTUD_ENABLE)) {
                        sctp_assoc_sync_pmtu(asoc);
                }
        }
        nskb->dst = dst_clone(tp->dst);
        if (!nskb->dst)
                goto no_route;
        dst = nskb->dst;

        /* Build the SCTP header.  */
        sh = (struct sctphdr *)skb_push(nskb, sizeof(struct sctphdr));
        sh->source = htons(packet->source_port);
        sh->dest   = htons(packet->destination_port);

        /* From 6.8 Adler-32 Checksum Calculation:
         * After the packet is constructed (containing the SCTP common
         * header and one or more control or DATA chunks), the
         * transmitter shall:
         *
         * 1) Fill in the proper Verification Tag in the SCTP common
         *    header and initialize the checksum field to 0's.
         */
        sh->vtag     = htonl(packet->vtag);
        sh->checksum = 0;

        /**
         * 6.10 Bundling
         *
         *    An endpoint bundles chunks by simply including multiple
         *    chunks in one outbound SCTP packet.  ...
         */

        /**
         * 3.2  Chunk Field Descriptions
         *
         * The total length of a chunk (including Type, Length and
         * Value fields) MUST be a multiple of 4 bytes.  If the length
         * of the chunk is not a multiple of 4 bytes, the sender MUST
         * pad the chunk with all zero bytes and this padding is not
         * included in the chunk length field.  The sender should
         * never pad with more than 3 bytes.
         *
         * [This whole comment explains WORD_ROUND() below.]
         */
        SCTP_DEBUG_PRINTK("***sctp_transmit_packet***\n");
        list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
                list_del_init(&chunk->list);
                if (sctp_chunk_is_data(chunk)) {

                        if (!chunk->has_tsn) {
                                sctp_chunk_assign_ssn(chunk);
                                sctp_chunk_assign_tsn(chunk);

                        /* 6.3.1 C4) When data is in flight and when allowed
                         * by rule C5, a new RTT measurement MUST be made each
                         * round trip.  Furthermore, new RTT measurements
                         * SHOULD be made no more than once per round-trip
                         * for a given destination transport address.
                         */

                                if (!tp->rto_pending) {
                                        chunk->rtt_in_progress = 1;
                                        tp->rto_pending = 1;
                                }
                        } else
                                chunk->resent = 1;

                        chunk->sent_at = jiffies;
                        has_data = 1;
                }

                padding = WORD_ROUND(chunk->skb->len) - chunk->skb->len;
                if (padding)
                        memset(skb_put(chunk->skb, padding), 0, padding);

                /* if this is the auth chunk that we are adding,
                 * store pointer where it will be added and put
                 * the auth into the packet.
                 */
                if (chunk == packet->auth)
                        auth = skb_tail_pointer(nskb);

                cksum_buf_len += chunk->skb->len;
                memcpy(skb_put(nskb, chunk->skb->len),
                               chunk->skb->data, chunk->skb->len);

                SCTP_DEBUG_PRINTK("%s %p[%s] %s 0x%x, %s %d, %s %d, %s %d\n",
                                  "*** Chunk", chunk,
                                  sctp_cname(SCTP_ST_CHUNK(
                                          chunk->chunk_hdr->type)),
                                  chunk->has_tsn ? "TSN" : "No TSN",
                                  chunk->has_tsn ?
                                  ntohl(chunk->subh.data_hdr->tsn) : 0,
                                  "length", ntohs(chunk->chunk_hdr->length),
                                  "chunk->skb->len", chunk->skb->len,
                                  "rtt_in_progress", chunk->rtt_in_progress);

                /*
                 * If this is a control chunk, this is our last
                 * reference. Free data chunks after they've been
                 * acknowledged or have failed.
                 */
                if (!sctp_chunk_is_data(chunk))
                        sctp_chunk_free(chunk);
        }

        /* SCTP-AUTH, Section 6.2
         *    The sender MUST calculate the MAC as described in RFC2104 [2]
         *    using the hash function H as described by the MAC Identifier and
         *    the shared association key K based on the endpoint pair shared key
         *    described by the shared key identifier.  The 'data' used for the
         *    computation of the AUTH-chunk is given by the AUTH chunk with its
         *    HMAC field set to zero (as shown in Figure 6) followed by all
         *    chunks that are placed after the AUTH chunk in the SCTP packet.
         */
        if (auth)
                sctp_auth_calculate_hmac(asoc, nskb,
                                        (struct sctp_auth_chunk *)auth,
                                        GFP_ATOMIC);

        /* 2) Calculate the Adler-32 checksum of the whole packet,
         *    including the SCTP common header and all the
         *    chunks.
         *
         * Note: Adler-32 is no longer applicable, as has been replaced
         * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
         */
        if (!(dst->dev->features & NETIF_F_NO_CSUM)) {
                crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
                crc32 = sctp_end_cksum(crc32);
        }

        /* 3) Put the resultant value into the checksum field in the
         *    common header, and leave the rest of the bits unchanged.
         */
        sh->checksum = htonl(crc32);

        /* IP layer ECN support
         * From RFC 2481
         *  "The ECN-Capable Transport (ECT) bit would be set by the
         *   data sender to indicate that the end-points of the
         *   transport protocol are ECN-capable."
         *
         * Now setting the ECT bit all the time, as it should not cause
         * any problems protocol-wise even if our peer ignores it.
         *
         * Note: The works for IPv6 layer checks this bit too later
         * in transmission.  See IP6_ECN_flow_xmit().
         */
        (*tp->af_specific->ecn_capable)(nskb->sk);

        /* Set up the IP options.  */
        /* BUG: not implemented
         * For v4 this all lives somewhere in sk->sk_opt...
         */

        /* Dump that on IP!  */
        if (asoc && asoc->peer.last_sent_to != tp) {
                /* Considering the multiple CPU scenario, this is a
                 * "correcter" place for last_sent_to.  --xguo
                 */
                asoc->peer.last_sent_to = tp;
        }

        if (has_data) {
                struct timer_list *timer;
                unsigned long timeout;

                tp->last_time_used = jiffies;

                /* Restart the AUTOCLOSE timer when sending data. */
                if (sctp_state(asoc, ESTABLISHED) && asoc->autoclose) {
                        timer = &asoc->timers[SCTP_EVENT_TIMEOUT_AUTOCLOSE];
                        timeout = asoc->timeouts[SCTP_EVENT_TIMEOUT_AUTOCLOSE];

                        if (!mod_timer(timer, jiffies + timeout))
                                sctp_association_hold(asoc);
                }
        }

        SCTP_DEBUG_PRINTK("***sctp_transmit_packet*** skb len %d\n",
                          nskb->len);

        if (tp->param_flags & SPP_PMTUD_ENABLE)
                (*tp->af_specific->sctp_xmit)(nskb, tp, packet->ipfragok);
        else
                (*tp->af_specific->sctp_xmit)(nskb, tp, 1);

out:
        packet->size = packet->overhead;
        return err;
no_route:
        kfree_skb(nskb);
        IP_INC_STATS_BH(IPSTATS_MIB_OUTNOROUTES);

        /* FIXME: Returning the 'err' will effect all the associations
         * associated with a socket, although only one of the paths of the
         * association is unreachable.
         * The real failure of a transport or association can be passed on
         * to the user via notifications. So setting this error may not be
         * required.
         */
         /* err = -EHOSTUNREACH; */
err:
        /* Control chunks are unreliable so just drop them.  DATA chunks
         * will get resent or dropped later.
         */

        list_for_each_entry_safe(chunk, tmp, &packet->chunk_list, list) {
                list_del_init(&chunk->list);
                if (!sctp_chunk_is_data(chunk))
                        sctp_chunk_free(chunk);
        }
        goto out;
nomem:
        err = -ENOMEM;
        goto err;
}

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

/* This private function handles the specifics of appending DATA chunks.  */
static sctp_xmit_t sctp_packet_append_data(struct sctp_packet *packet,
                                           struct sctp_chunk *chunk)
{
        sctp_xmit_t retval = SCTP_XMIT_OK;
        size_t datasize, rwnd, inflight;
        struct sctp_transport *transport = packet->transport;
        __u32 max_burst_bytes;
        struct sctp_association *asoc = transport->asoc;
        struct sctp_sock *sp = sctp_sk(asoc->base.sk);
        struct sctp_outq *q = &asoc->outqueue;

        /* RFC 2960 6.1  Transmission of DATA Chunks
         *
         * A) At any given time, the data sender MUST NOT transmit new data to
         * any destination transport address if its peer's rwnd indicates
         * that the peer has no buffer space (i.e. rwnd is 0, see Section
         * 6.2.1).  However, regardless of the value of rwnd (including if it
         * is 0), the data sender can always have one DATA chunk in flight to
         * the receiver if allowed by cwnd (see rule B below).  This rule
         * allows the sender to probe for a change in rwnd that the sender
         * missed due to the SACK having been lost in transit from the data
         * receiver to the data sender.
         */

        rwnd = asoc->peer.rwnd;
        inflight = asoc->outqueue.outstanding_bytes;

        datasize = sctp_data_size(chunk);

        if (datasize > rwnd) {
                if (inflight > 0) {
                        /* We have (at least) one data chunk in flight,
                         * so we can't fall back to rule 6.1 B).
                         */
                        retval = SCTP_XMIT_RWND_FULL;
                        goto finish;
                }
        }

        /* sctpimpguide-05 2.14.2
         * D) When the time comes for the sender to
         * transmit new DATA chunks, the protocol parameter Max.Burst MUST
         * first be applied to limit how many new DATA chunks may be sent.
         * The limit is applied by adjusting cwnd as follows:
         *      if ((flightsize + Max.Burst * MTU) < cwnd)
         *              cwnd = flightsize + Max.Burst * MTU
         */
        max_burst_bytes = asoc->max_burst * asoc->pathmtu;
        if ((transport->flight_size + max_burst_bytes) < transport->cwnd) {
                transport->cwnd = transport->flight_size + max_burst_bytes;
                SCTP_DEBUG_PRINTK("%s: cwnd limited by max_burst: "
                                  "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);
        }

        /* RFC 2960 6.1  Transmission of DATA Chunks
         *
         * B) At any given time, the sender MUST NOT transmit new data
         * to a given transport address if it has cwnd or more bytes
         * of data outstanding to that transport address.
         */
        /* RFC 7.2.4 & the Implementers Guide 2.8.
         *
         * 3) ...
         *    When a Fast Retransmit is being performed the sender SHOULD
         *    ignore the value of cwnd and SHOULD NOT delay retransmission.
         */
        if (chunk->fast_retransmit <= 0)
                if (transport->flight_size >= transport->cwnd) {
                        retval = SCTP_XMIT_RWND_FULL;
                        goto finish;
                }

        /* Nagle's algorithm to solve small-packet problem:
         * Inhibit the sending of new chunks when new outgoing data arrives
         * if any previously transmitted data on the connection remains
         * unacknowledged.
         */
        if (!sp->nodelay && sctp_packet_empty(packet) &&
            q->outstanding_bytes && sctp_state(asoc, ESTABLISHED)) {
                unsigned len = datasize + q->out_qlen;

                /* Check whether this chunk and all the rest of pending
                 * data will fit or delay in hopes of bundling a full
                 * sized packet.
                 */
                if (len < asoc->frag_point) {
                        retval = SCTP_XMIT_NAGLE_DELAY;
                        goto finish;
                }
        }

        /* Keep track of how many bytes are in flight over this transport. */
        transport->flight_size += datasize;

        /* Keep track of how many bytes are in flight to the receiver. */
        asoc->outqueue.outstanding_bytes += datasize;

        /* Update our view of the receiver's rwnd. Include sk_buff overhead
         * while updating peer.rwnd so that it reduces the chances of a
         * receiver running out of receive buffer space even when receive
         * window is still open. This can happen when a sender is sending
         * sending small messages.
         */
        datasize += sizeof(struct sk_buff);
        if (datasize < rwnd)
                rwnd -= datasize;
        else
                rwnd = 0;

        asoc->peer.rwnd = rwnd;
        /* Has been accepted for transmission. */
        if (!asoc->peer.prsctp_capable)
                chunk->msg->can_abandon = 0;

finish:
        return retval;
}