docs/how-to-build.md: use proper markup for directory names

[unleashed/tickless.git] / kernel / net / tcp / tcp_output.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2014 by Delphix. All rights reserved.
 */

/* This file contains all TCP output processing functions. */

#include <sys/types.h>
#include <sys/stream.h>
#include <sys/strsun.h>
#include <sys/strsubr.h>
#include <sys/stropts.h>
#include <sys/strlog.h>
#define _SUN_TPI_VERSION 2
#include <sys/tihdr.h>
#include <sys/suntpi.h>
#include <sys/xti_inet.h>
#include <sys/timod.h>
#include <sys/pattr.h>
#include <sys/squeue_impl.h>
#include <sys/squeue.h>
#include <sys/sockio.h>

#include <inet/common.h>
#include <inet/ip.h>
#include <inet/tcp.h>
#include <inet/tcp_impl.h>
#include <inet/snmpcom.h>
#include <inet/proto_set.h>
#include <inet/ipsec_impl.h>
#include <inet/ip_ndp.h>

static mblk_t   *tcp_get_seg_mp(tcp_t *, uint32_t, int32_t *);
static void     tcp_wput_cmdblk(queue_t *, mblk_t *);
static void     tcp_wput_flush(tcp_t *, mblk_t *);
static void     tcp_wput_iocdata(tcp_t *tcp, mblk_t *mp);
static int      tcp_xmit_end(tcp_t *);
static int      tcp_send(tcp_t *, const int, const int, const int,
                    const int, int *, uint_t *, int *, mblk_t **, mblk_t *);
static void     tcp_xmit_early_reset(char *, mblk_t *, uint32_t, uint32_t,
                    int, ip_recv_attr_t *, ip_stack_t *, conn_t *);
static boolean_t        tcp_send_rst_chk(tcp_stack_t *);
static void     tcp_process_shrunk_swnd(tcp_t *, uint32_t);
static void     tcp_fill_header(tcp_t *, uchar_t *, clock_t, int);

/*
 * Functions called directly via squeue having a prototype of edesc_t.
 */
static void     tcp_wput_nondata(void *, mblk_t *, void *, ip_recv_attr_t *);
static void     tcp_wput_ioctl(void *, mblk_t *, void *, ip_recv_attr_t *);
static void     tcp_wput_proto(void *, mblk_t *, void *, ip_recv_attr_t *);

/*
 * This controls how tiny a write must be before we try to copy it
 * into the mblk on the tail of the transmit queue.  Not much
 * speedup is observed for values larger than sixteen.  Zero will
 * disable the optimisation.
 */
static int tcp_tx_pull_len = 16;

void
tcp_wput(queue_t *q, mblk_t *mp)
{
        conn_t  *connp = Q_TO_CONN(q);
        tcp_t   *tcp;
        void (*output_proc)();
        t_scalar_t type;
        uchar_t *rptr;
        struct iocblk   *iocp;
        size_t size;

        ASSERT(connp->conn_ref >= 2);

        switch (DB_TYPE(mp)) {
        case M_DATA:
                tcp = connp->conn_tcp;
                ASSERT(tcp != NULL);

                size = msgdsize(mp);

                mutex_enter(&tcp->tcp_non_sq_lock);
                tcp->tcp_squeue_bytes += size;
                if (TCP_UNSENT_BYTES(tcp) > connp->conn_sndbuf) {
                        tcp_setqfull(tcp);
                }
                mutex_exit(&tcp->tcp_non_sq_lock);

                CONN_INC_REF(connp);
                SQUEUE_ENTER_ONE(connp->conn_sqp, mp, tcp_output, connp,
                    NULL, tcp_squeue_flag, SQTAG_TCP_OUTPUT);
                return;

        case M_CMD:
                tcp_wput_cmdblk(q, mp);
                return;

        case M_PROTO:
        case M_PCPROTO:
                /*
                 * if it is a snmp message, don't get behind the squeue
                 */
                tcp = connp->conn_tcp;
                rptr = mp->b_rptr;
                if ((mp->b_wptr - rptr) >= sizeof (t_scalar_t)) {
                        type = ((union T_primitives *)rptr)->type;
                } else {
                        if (connp->conn_debug) {
                                (void) strlog(TCP_MOD_ID, 0, 1,
                                    SL_ERROR|SL_TRACE,
                                    "tcp_wput_proto, dropping one...");
                        }
                        freemsg(mp);
                        return;
                }
                if (type == T_SVR4_OPTMGMT_REQ) {
                        /*
                         * All Solaris components should pass a db_credp
                         * for this TPI message, hence we ASSERT.
                         * But in case there is some other M_PROTO that looks
                         * like a TPI message sent by some other kernel
                         * component, we check and return an error.
                         */
                        cred_t  *cr = msg_getcred(mp, NULL);

                        ASSERT(cr != NULL);
                        if (cr == NULL) {
                                tcp_err_ack(tcp, mp, TSYSERR, EINVAL);
                                return;
                        }
                        if (snmpcom_req(q, mp, tcp_snmp_set, ip_snmp_get,
                            cr)) {
                                /*
                                 * This was a SNMP request
                                 */
                                return;
                        } else {
                                output_proc = tcp_wput_proto;
                        }
                } else {
                        output_proc = tcp_wput_proto;
                }
                break;
        case M_IOCTL:
                /*
                 * Most ioctls can be processed right away without going via
                 * squeues - process them right here. Those that do require
                 * squeue (currently _SIOCSOCKFALLBACK)
                 * are processed by tcp_wput_ioctl().
                 */
                iocp = (struct iocblk *)mp->b_rptr;
                tcp = connp->conn_tcp;

                switch (iocp->ioc_cmd) {
                case TCP_IOC_ABORT_CONN:
                        tcp_ioctl_abort_conn(q, mp);
                        return;
                case TI_GETPEERNAME:
                case TI_GETMYNAME:
                        mi_copyin(q, mp, NULL,
                            SIZEOF_STRUCT(strbuf, iocp->ioc_flag));
                        return;

                default:
                        output_proc = tcp_wput_ioctl;
                        break;
                }
                break;
        default:
                output_proc = tcp_wput_nondata;
                break;
        }

        CONN_INC_REF(connp);
        SQUEUE_ENTER_ONE(connp->conn_sqp, mp, output_proc, connp,
            NULL, tcp_squeue_flag, SQTAG_TCP_WPUT_OTHER);
}

/*
 * The TCP normal data output path.
 * NOTE: the logic of the fast path is duplicated from this function.
 */
void
tcp_wput_data(tcp_t *tcp, mblk_t *mp, boolean_t urgent)
{
        int             len;
        mblk_t          *local_time;
        mblk_t          *mp1;
        uint32_t        snxt;
        int             tail_unsent;
        int             tcpstate;
        int             usable = 0;
        mblk_t          *xmit_tail;
        int32_t         mss;
        int32_t         num_sack_blk = 0;
        int32_t         total_hdr_len;
        int32_t         tcp_hdr_len;
        int             rc;
        tcp_stack_t     *tcps = tcp->tcp_tcps;
        conn_t          *connp = tcp->tcp_connp;
        clock_t         now = LBOLT_FASTPATH;

        tcpstate = tcp->tcp_state;
        if (mp == NULL) {
                /*
                 * tcp_wput_data() with NULL mp should only be called when
                 * there is unsent data.
                 */
                ASSERT(tcp->tcp_unsent > 0);
                /* Really tacky... but we need this for detached closes. */
                len = tcp->tcp_unsent;
                goto data_null;
        }

        ASSERT(mp->b_datap->db_type == M_DATA);
        /*
         * Don't allow data after T_ORDREL_REQ or T_DISCON_REQ,
         * or before a connection attempt has begun.
         */
        if (tcpstate < TCPS_SYN_SENT || tcpstate > TCPS_CLOSE_WAIT ||
            (tcp->tcp_valid_bits & TCP_FSS_VALID) != 0) {
                if ((tcp->tcp_valid_bits & TCP_FSS_VALID) != 0) {
#ifdef DEBUG
                        cmn_err(CE_WARN,
                            "tcp_wput_data: data after ordrel, %s",
                            tcp_display(tcp, NULL,
                            DISP_ADDR_AND_PORT));
#else
                        if (connp->conn_debug) {
                                (void) strlog(TCP_MOD_ID, 0, 1,
                                    SL_TRACE|SL_ERROR,
                                    "tcp_wput_data: data after ordrel, %s\n",
                                    tcp_display(tcp, NULL,
                                    DISP_ADDR_AND_PORT));
                        }
#endif /* DEBUG */
                }
                if (tcp->tcp_snd_zcopy_aware &&
                    (mp->b_datap->db_struioflag & STRUIO_ZCNOTIFY))
                        tcp_zcopy_notify(tcp);
                freemsg(mp);
                mutex_enter(&tcp->tcp_non_sq_lock);
                if (tcp->tcp_flow_stopped &&
                    TCP_UNSENT_BYTES(tcp) <= connp->conn_sndlowat) {
                        tcp_clrqfull(tcp);
                }
                mutex_exit(&tcp->tcp_non_sq_lock);
                return;
        }

        /* Strip empties */
        for (;;) {
                ASSERT((uintptr_t)(mp->b_wptr - mp->b_rptr) <=
                    (uintptr_t)INT_MAX);
                len = (int)(mp->b_wptr - mp->b_rptr);
                if (len > 0)
                        break;
                mp1 = mp;
                mp = mp->b_cont;
                freeb(mp1);
                if (mp == NULL) {
                        return;
                }
        }

        /* If we are the first on the list ... */
        if (tcp->tcp_xmit_head == NULL) {
                tcp->tcp_xmit_head = mp;
                tcp->tcp_xmit_tail = mp;
                tcp->tcp_xmit_tail_unsent = len;
        } else {
                /* If tiny tx and room in txq tail, pullup to save mblks. */
                struct datab *dp;

                mp1 = tcp->tcp_xmit_last;
                if (len < tcp_tx_pull_len &&
                    (dp = mp1->b_datap)->db_ref == 1 &&
                    dp->db_lim - mp1->b_wptr >= len) {
                        ASSERT(len > 0);
                        ASSERT(!mp1->b_cont);
                        if (len == 1) {
                                *mp1->b_wptr++ = *mp->b_rptr;
                        } else {
                                bcopy(mp->b_rptr, mp1->b_wptr, len);
                                mp1->b_wptr += len;
                        }
                        if (mp1 == tcp->tcp_xmit_tail)
                                tcp->tcp_xmit_tail_unsent += len;
                        mp1->b_cont = mp->b_cont;
                        if (tcp->tcp_snd_zcopy_aware &&
                            (mp->b_datap->db_struioflag & STRUIO_ZCNOTIFY))
                                mp1->b_datap->db_struioflag |= STRUIO_ZCNOTIFY;
                        freeb(mp);
                        mp = mp1;
                } else {
                        tcp->tcp_xmit_last->b_cont = mp;
                }
                len += tcp->tcp_unsent;
        }

        /* Tack on however many more positive length mblks we have */
        if ((mp1 = mp->b_cont) != NULL) {
                do {
                        int tlen;
                        ASSERT((uintptr_t)(mp1->b_wptr - mp1->b_rptr) <=
                            (uintptr_t)INT_MAX);
                        tlen = (int)(mp1->b_wptr - mp1->b_rptr);
                        if (tlen <= 0) {
                                mp->b_cont = mp1->b_cont;
                                freeb(mp1);
                        } else {
                                len += tlen;
                                mp = mp1;
                        }
                } while ((mp1 = mp->b_cont) != NULL);
        }
        tcp->tcp_xmit_last = mp;
        tcp->tcp_unsent = len;

        if (urgent)
                usable = 1;

data_null:
        snxt = tcp->tcp_snxt;
        xmit_tail = tcp->tcp_xmit_tail;
        tail_unsent = tcp->tcp_xmit_tail_unsent;

        /*
         * Note that tcp_mss has been adjusted to take into account the
         * timestamp option if applicable.  Because SACK options do not
         * appear in every TCP segments and they are of variable lengths,
         * they cannot be included in tcp_mss.  Thus we need to calculate
         * the actual segment length when we need to send a segment which
         * includes SACK options.
         */
        if (tcp->tcp_snd_sack_ok && tcp->tcp_num_sack_blk > 0) {
                int32_t opt_len;

                num_sack_blk = MIN(tcp->tcp_max_sack_blk,
                    tcp->tcp_num_sack_blk);
                opt_len = num_sack_blk * sizeof (sack_blk_t) + TCPOPT_NOP_LEN *
                    2 + TCPOPT_HEADER_LEN;
                mss = tcp->tcp_mss - opt_len;
                total_hdr_len = connp->conn_ht_iphc_len + opt_len;
                tcp_hdr_len = connp->conn_ht_ulp_len + opt_len;
        } else {
                mss = tcp->tcp_mss;
                total_hdr_len = connp->conn_ht_iphc_len;
                tcp_hdr_len = connp->conn_ht_ulp_len;
        }

        if ((tcp->tcp_suna == snxt) && !tcp->tcp_localnet &&
            (TICK_TO_MSEC(now - tcp->tcp_last_recv_time) >= tcp->tcp_rto)) {
                TCP_SET_INIT_CWND(tcp, mss, tcps->tcps_slow_start_after_idle);
        }
        if (tcpstate == TCPS_SYN_RCVD) {
                /*
                 * The three-way connection establishment handshake is not
                 * complete yet. We want to queue the data for transmission
                 * after entering ESTABLISHED state (RFC793). A jump to
                 * "done" label effectively leaves data on the queue.
                 */
                goto done;
        } else {
                int usable_r;

                /*
                 * In the special case when cwnd is zero, which can only
                 * happen if the connection is ECN capable, return now.
                 * New segments is sent using tcp_timer().  The timer
                 * is set in tcp_input_data().
                 */
                if (tcp->tcp_cwnd == 0) {
                        /*
                         * Note that tcp_cwnd is 0 before 3-way handshake is
                         * finished.
                         */
                        ASSERT(tcp->tcp_ecn_ok ||
                            tcp->tcp_state < TCPS_ESTABLISHED);
                        return;
                }

                /* NOTE: trouble if xmitting while SYN not acked? */
                usable_r = snxt - tcp->tcp_suna;
                usable_r = tcp->tcp_swnd - usable_r;

                /*
                 * Check if the receiver has shrunk the window.  If
                 * tcp_wput_data() with NULL mp is called, tcp_fin_sent
                 * cannot be set as there is unsent data, so FIN cannot
                 * be sent out.  Otherwise, we need to take into account
                 * of FIN as it consumes an "invisible" sequence number.
                 */
                ASSERT(tcp->tcp_fin_sent == 0);
                if (usable_r < 0) {
                        /*
                         * The receiver has shrunk the window and we have sent
                         * -usable_r date beyond the window, re-adjust.
                         *
                         * If TCP window scaling is enabled, there can be
                         * round down error as the advertised receive window
                         * is actually right shifted n bits.  This means that
                         * the lower n bits info is wiped out.  It will look
                         * like the window is shrunk.  Do a check here to
                         * see if the shrunk amount is actually within the
                         * error in window calculation.  If it is, just
                         * return.  Note that this check is inside the
                         * shrunk window check.  This makes sure that even
                         * though tcp_process_shrunk_swnd() is not called,
                         * we will stop further processing.
                         */
                        if ((-usable_r >> tcp->tcp_snd_ws) > 0) {
                                tcp_process_shrunk_swnd(tcp, -usable_r);
                        }
                        return;
                }

                /* usable = MIN(swnd, cwnd) - unacked_bytes */
                if (tcp->tcp_swnd > tcp->tcp_cwnd)
                        usable_r -= tcp->tcp_swnd - tcp->tcp_cwnd;

                /* usable = MIN(usable, unsent) */
                if (usable_r > len)
                        usable_r = len;

                /* usable = MAX(usable, {1 for urgent, 0 for data}) */
                if (usable_r > 0) {
                        usable = usable_r;
                } else {
                        /* Bypass all other unnecessary processing. */
                        goto done;
                }
        }

        local_time = (mblk_t *)now;

        /*
         * "Our" Nagle Algorithm.  This is not the same as in the old
         * BSD.  This is more in line with the true intent of Nagle.
         *
         * The conditions are:
         * 1. The amount of unsent data (or amount of data which can be
         *    sent, whichever is smaller) is less than Nagle limit.
         * 2. The last sent size is also less than Nagle limit.
         * 3. There is unack'ed data.
         * 4. Urgent pointer is not set.  Send urgent data ignoring the
         *    Nagle algorithm.  This reduces the probability that urgent
         *    bytes get "merged" together.
         * 5. The app has not closed the connection.  This eliminates the
         *    wait time of the receiving side waiting for the last piece of
         *    (small) data.
         *
         * If all are satisified, exit without sending anything.  Note
         * that Nagle limit can be smaller than 1 MSS.  Nagle limit is
         * the smaller of 1 MSS and global tcp_naglim_def (default to be
         * 4095).
         */
        if (usable < (int)tcp->tcp_naglim &&
            tcp->tcp_naglim > tcp->tcp_last_sent_len &&
            snxt != tcp->tcp_suna &&
            !(tcp->tcp_valid_bits & TCP_URG_VALID) &&
            !(tcp->tcp_valid_bits & TCP_FSS_VALID)) {
                goto done;
        }

        /*
         * If tcp_zero_win_probe is not set and the tcp->tcp_cork option
         * is set, then we have to force TCP not to send partial segment
         * (smaller than MSS bytes). We are calculating the usable now
         * based on full mss and will save the rest of remaining data for
         * later. When tcp_zero_win_probe is set, TCP needs to send out
         * something to do zero window probe.
         */
        if (tcp->tcp_cork && !tcp->tcp_zero_win_probe) {
                if (usable < mss)
                        goto done;
                usable = (usable / mss) * mss;
        }

        /* Update the latest receive window size in TCP header. */
        tcp->tcp_tcpha->tha_win = htons(tcp->tcp_rwnd >> tcp->tcp_rcv_ws);

        /* Send the packet. */
        rc = tcp_send(tcp, mss, total_hdr_len, tcp_hdr_len,
            num_sack_blk, &usable, &snxt, &tail_unsent, &xmit_tail,
            local_time);

        /* Pretend that all we were trying to send really got sent */
        if (rc < 0 && tail_unsent < 0) {
                do {
                        xmit_tail = xmit_tail->b_cont;
                        xmit_tail->b_prev = local_time;
                        ASSERT((uintptr_t)(xmit_tail->b_wptr -
                            xmit_tail->b_rptr) <= (uintptr_t)INT_MAX);
                        tail_unsent += (int)(xmit_tail->b_wptr -
                            xmit_tail->b_rptr);
                } while (tail_unsent < 0);
        }
done:;
        tcp->tcp_xmit_tail = xmit_tail;
        tcp->tcp_xmit_tail_unsent = tail_unsent;
        len = tcp->tcp_snxt - snxt;
        if (len) {
                /*
                 * If new data was sent, need to update the notsack
                 * list, which is, afterall, data blocks that have
                 * not been sack'ed by the receiver.  New data is
                 * not sack'ed.
                 */
                if (tcp->tcp_snd_sack_ok && tcp->tcp_notsack_list != NULL) {
                        /* len is a negative value. */
                        tcp->tcp_pipe -= len;
                        tcp_notsack_update(&(tcp->tcp_notsack_list),
                            tcp->tcp_snxt, snxt,
                            &(tcp->tcp_num_notsack_blk),
                            &(tcp->tcp_cnt_notsack_list));
                }
                tcp->tcp_snxt = snxt + tcp->tcp_fin_sent;
                tcp->tcp_rack = tcp->tcp_rnxt;
                tcp->tcp_rack_cnt = 0;
                if ((snxt + len) == tcp->tcp_suna) {
                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                }
        } else if (snxt == tcp->tcp_suna && tcp->tcp_swnd == 0) {
                /*
                 * Didn't send anything. Make sure the timer is running
                 * so that we will probe a zero window.
                 */
                TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
        }
        /* Note that len is the amount we just sent but with a negative sign */
        tcp->tcp_unsent += len;
        mutex_enter(&tcp->tcp_non_sq_lock);
        if (tcp->tcp_flow_stopped) {
                if (TCP_UNSENT_BYTES(tcp) <= connp->conn_sndlowat) {
                        tcp_clrqfull(tcp);
                }
        } else if (TCP_UNSENT_BYTES(tcp) >= connp->conn_sndbuf) {
                if (!(tcp->tcp_detached))
                        tcp_setqfull(tcp);
        }
        mutex_exit(&tcp->tcp_non_sq_lock);
}

/*
 * Initial STREAMS write side put() procedure for sockets. It tries to
 * handle the T_CAPABILITY_REQ which sockfs sends down while setting
 * up the socket without using the squeue. Non T_CAPABILITY_REQ messages
 * are handled by tcp_wput() as usual.
 *
 * All further messages will also be handled by tcp_wput() because we cannot
 * be sure that the above short cut is safe later.
 */
void
tcp_wput_sock(queue_t *wq, mblk_t *mp)
{
        conn_t                  *connp = Q_TO_CONN(wq);
        tcp_t                   *tcp = connp->conn_tcp;
        struct T_capability_req *car = (struct T_capability_req *)mp->b_rptr;

        ASSERT(wq->q_qinfo == &tcp_sock_winit);
        wq->q_qinfo = &tcp_winit;

        ASSERT(IPCL_IS_TCP(connp));
        ASSERT(TCP_IS_SOCKET(tcp));

        if (DB_TYPE(mp) == M_PCPROTO &&
            MBLKL(mp) == sizeof (struct T_capability_req) &&
            car->PRIM_type == T_CAPABILITY_REQ) {
                tcp_capability_req(tcp, mp);
                return;
        }

        tcp_wput(wq, mp);
}

/* ARGSUSED */
void
tcp_wput_fallback(queue_t *wq, mblk_t *mp)
{
#ifdef DEBUG
        cmn_err(CE_CONT, "tcp_wput_fallback: Message during fallback \n");
#endif
        freemsg(mp);
}

/*
 * Call by tcp_wput() to handle misc non M_DATA messages.
 */
/* ARGSUSED */
static void
tcp_wput_nondata(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        conn_t  *connp = (conn_t *)arg;
        tcp_t   *tcp = connp->conn_tcp;

        ASSERT(DB_TYPE(mp) != M_IOCTL);
        /*
         * TCP is D_MP and qprocsoff() is done towards the end of the tcp_close.
         * Once the close starts, streamhead and sockfs will not let any data
         * packets come down (close ensures that there are no threads using the
         * queue and no new threads will come down) but since qprocsoff()
         * hasn't happened yet, a M_FLUSH or some non data message might
         * get reflected back (in response to our own FLUSHRW) and get
         * processed after tcp_close() is done. The conn would still be valid
         * because a ref would have added but we need to check the state
         * before actually processing the packet.
         */
        if (TCP_IS_DETACHED(tcp) || (tcp->tcp_state == TCPS_CLOSED)) {
                freemsg(mp);
                return;
        }

        switch (DB_TYPE(mp)) {
        case M_IOCDATA:
                tcp_wput_iocdata(tcp, mp);
                break;
        case M_FLUSH:
                tcp_wput_flush(tcp, mp);
                break;
        default:
                ip_wput_nondata(connp->conn_wq, mp);
                break;
        }
}

/* tcp_wput_flush is called by tcp_wput_nondata to handle M_FLUSH messages. */
static void
tcp_wput_flush(tcp_t *tcp, mblk_t *mp)
{
        uchar_t fval = *mp->b_rptr;
        mblk_t  *tail;
        conn_t  *connp = tcp->tcp_connp;
        queue_t *q = connp->conn_wq;

        /* TODO: How should flush interact with urgent data? */
        if ((fval & FLUSHW) && tcp->tcp_xmit_head != NULL &&
            !(tcp->tcp_valid_bits & TCP_URG_VALID)) {
                /*
                 * Flush only data that has not yet been put on the wire.  If
                 * we flush data that we have already transmitted, life, as we
                 * know it, may come to an end.
                 */
                tail = tcp->tcp_xmit_tail;
                tail->b_wptr -= tcp->tcp_xmit_tail_unsent;
                tcp->tcp_xmit_tail_unsent = 0;
                tcp->tcp_unsent = 0;
                if (tail->b_wptr != tail->b_rptr)
                        tail = tail->b_cont;
                if (tail) {
                        mblk_t **excess = &tcp->tcp_xmit_head;
                        for (;;) {
                                mblk_t *mp1 = *excess;
                                if (mp1 == tail)
                                        break;
                                tcp->tcp_xmit_tail = mp1;
                                tcp->tcp_xmit_last = mp1;
                                excess = &mp1->b_cont;
                        }
                        *excess = NULL;
                        tcp_close_mpp(&tail);
                        if (tcp->tcp_snd_zcopy_aware)
                                tcp_zcopy_notify(tcp);
                }
                /*
                 * We have no unsent data, so unsent must be less than
                 * conn_sndlowat, so re-enable flow.
                 */
                mutex_enter(&tcp->tcp_non_sq_lock);
                if (tcp->tcp_flow_stopped) {
                        tcp_clrqfull(tcp);
                }
                mutex_exit(&tcp->tcp_non_sq_lock);
        }
        /*
         * TODO: you can't just flush these, you have to increase rwnd for one
         * thing.  For another, how should urgent data interact?
         */
        if (fval & FLUSHR) {
                *mp->b_rptr = fval & ~FLUSHW;
                /* XXX */
                qreply(q, mp);
                return;
        }
        freemsg(mp);
}

/*
 * tcp_wput_iocdata is called by tcp_wput_nondata to handle all M_IOCDATA
 * messages.
 */
static void
tcp_wput_iocdata(tcp_t *tcp, mblk_t *mp)
{
        mblk_t          *mp1;
        struct iocblk   *iocp = (struct iocblk *)mp->b_rptr;
        STRUCT_HANDLE(strbuf, sb);
        uint_t          addrlen;
        conn_t          *connp = tcp->tcp_connp;
        queue_t         *q = connp->conn_wq;

        /* Make sure it is one of ours. */
        switch (iocp->ioc_cmd) {
        case TI_GETMYNAME:
        case TI_GETPEERNAME:
                break;
        default:
                /*
                 * If the conn is closing, then error the ioctl here. Otherwise
                 * use the CONN_IOCTLREF_* macros to hold off tcp_close until
                 * we're done here.
                 */
                mutex_enter(&connp->conn_lock);
                if (connp->conn_state_flags & CONN_CLOSING) {
                        mutex_exit(&connp->conn_lock);
                        iocp->ioc_error = EINVAL;
                        mp->b_datap->db_type = M_IOCNAK;
                        iocp->ioc_count = 0;
                        qreply(q, mp);
                        return;
                }

                CONN_INC_IOCTLREF_LOCKED(connp);
                ip_wput_nondata(q, mp);
                CONN_DEC_IOCTLREF(connp);
                return;
        }
        switch (mi_copy_state(q, mp, &mp1)) {
        case -1:
                return;
        case MI_COPY_CASE(MI_COPY_IN, 1):
                break;
        case MI_COPY_CASE(MI_COPY_OUT, 1):
                /* Copy out the strbuf. */
                mi_copyout(q, mp);
                return;
        case MI_COPY_CASE(MI_COPY_OUT, 2):
                /* All done. */
                mi_copy_done(q, mp, 0);
                return;
        default:
                mi_copy_done(q, mp, EPROTO);
                return;
        }
        /* Check alignment of the strbuf */
        if (!OK_32PTR(mp1->b_rptr)) {
                mi_copy_done(q, mp, EINVAL);
                return;
        }

        STRUCT_SET_HANDLE(sb, iocp->ioc_flag, (void *)mp1->b_rptr);

        if (connp->conn_family == AF_INET)
                addrlen = sizeof (sin_t);
        else
                addrlen = sizeof (sin6_t);

        if (STRUCT_FGET(sb, maxlen) < addrlen) {
                mi_copy_done(q, mp, EINVAL);
                return;
        }

        switch (iocp->ioc_cmd) {
        case TI_GETMYNAME:
                break;
        case TI_GETPEERNAME:
                if (tcp->tcp_state < TCPS_SYN_RCVD) {
                        mi_copy_done(q, mp, ENOTCONN);
                        return;
                }
                break;
        }
        mp1 = mi_copyout_alloc(q, mp, STRUCT_FGETP(sb, buf), addrlen, B_TRUE);
        if (!mp1)
                return;

        STRUCT_FSET(sb, len, addrlen);
        switch (((struct iocblk *)mp->b_rptr)->ioc_cmd) {
        case TI_GETMYNAME:
                (void) conn_getsockname(connp, (struct sockaddr *)mp1->b_wptr,
                    &addrlen);
                break;
        case TI_GETPEERNAME:
                (void) conn_getpeername(connp, (struct sockaddr *)mp1->b_wptr,
                    &addrlen);
                break;
        }
        mp1->b_wptr += addrlen;
        /* Copy out the address */
        mi_copyout(q, mp);
}

/*
 * tcp_wput_ioctl is called by tcp_wput_nondata() to handle all M_IOCTL
 * messages.
 */
/* ARGSUSED */
static void
tcp_wput_ioctl(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        conn_t          *connp = (conn_t *)arg;
        tcp_t           *tcp = connp->conn_tcp;
        queue_t         *q = connp->conn_wq;
        struct iocblk   *iocp;

        ASSERT(DB_TYPE(mp) == M_IOCTL);
        /*
         * Try and ASSERT the minimum possible references on the
         * conn early enough. Since we are executing on write side,
         * the connection is obviously not detached and that means
         * there is a ref each for TCP and IP. Since we are behind
         * the squeue, the minimum references needed are 3. If the
         * conn is in classifier hash list, there should be an
         * extra ref for that (we check both the possibilities).
         */
        ASSERT((connp->conn_fanout != NULL && connp->conn_ref >= 4) ||
            (connp->conn_fanout == NULL && connp->conn_ref >= 3));

        iocp = (struct iocblk *)mp->b_rptr;
        switch (iocp->ioc_cmd) {
        case _SIOCSOCKFALLBACK:
                /*
                 * Either sockmod is about to be popped and the socket
                 * would now be treated as a plain stream, or a module
                 * is about to be pushed so we could no longer use read-
                 * side synchronous streams for fused loopback tcp.
                 * Drain any queued data and disable direct sockfs
                 * interface from now on.
                 */
                if (!tcp->tcp_issocket) {
                        DB_TYPE(mp) = M_IOCNAK;
                        iocp->ioc_error = EINVAL;
                } else {
                        tcp_use_pure_tpi(tcp);
                        DB_TYPE(mp) = M_IOCACK;
                        iocp->ioc_error = 0;
                }
                iocp->ioc_count = 0;
                iocp->ioc_rval = 0;
                qreply(q, mp);
                return;
        }

        /*
         * If the conn is closing, then error the ioctl here. Otherwise bump the
         * conn_ioctlref to hold off tcp_close until we're done here.
         */
        mutex_enter(&(connp)->conn_lock);
        if ((connp)->conn_state_flags & CONN_CLOSING) {
                mutex_exit(&(connp)->conn_lock);
                iocp->ioc_error = EINVAL;
                mp->b_datap->db_type = M_IOCNAK;
                iocp->ioc_count = 0;
                qreply(q, mp);
                return;
        }

        CONN_INC_IOCTLREF_LOCKED(connp);
        ip_wput_nondata(q, mp);
        CONN_DEC_IOCTLREF(connp);
}

/*
 * This routine is called by tcp_wput() to handle all TPI requests.
 */
/* ARGSUSED */
static void
tcp_wput_proto(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        conn_t          *connp = (conn_t *)arg;
        tcp_t           *tcp = connp->conn_tcp;
        union T_primitives *tprim = (union T_primitives *)mp->b_rptr;
        uchar_t         *rptr;
        t_scalar_t      type;
        cred_t          *cr;

        /*
         * Try and ASSERT the minimum possible references on the
         * conn early enough. Since we are executing on write side,
         * the connection is obviously not detached and that means
         * there is a ref each for TCP and IP. Since we are behind
         * the squeue, the minimum references needed are 3. If the
         * conn is in classifier hash list, there should be an
         * extra ref for that (we check both the possibilities).
         */
        ASSERT((connp->conn_fanout != NULL && connp->conn_ref >= 4) ||
            (connp->conn_fanout == NULL && connp->conn_ref >= 3));

        rptr = mp->b_rptr;
        ASSERT((uintptr_t)(mp->b_wptr - rptr) <= (uintptr_t)INT_MAX);
        if ((mp->b_wptr - rptr) >= sizeof (t_scalar_t)) {
                type = ((union T_primitives *)rptr)->type;
                if (type == T_EXDATA_REQ) {
                        tcp_output_urgent(connp, mp, arg2, NULL);
                } else if (type != T_DATA_REQ) {
                        goto non_urgent_data;
                } else {
                        /* TODO: options, flags, ... from user */
                        /* Set length to zero for reclamation below */
                        tcp_wput_data(tcp, mp->b_cont, B_TRUE);
                        freeb(mp);
                }
                return;
        } else {
                if (connp->conn_debug) {
                        (void) strlog(TCP_MOD_ID, 0, 1, SL_ERROR|SL_TRACE,
                            "tcp_wput_proto, dropping one...");
                }
                freemsg(mp);
                return;
        }

non_urgent_data:

        switch ((int)tprim->type) {
        case O_T_BIND_REQ:      /* bind request */
        case T_BIND_REQ:        /* new semantics bind request */
                tcp_tpi_bind(tcp, mp);
                break;
        case T_UNBIND_REQ:      /* unbind request */
                tcp_tpi_unbind(tcp, mp);
                break;
        case O_T_CONN_RES:      /* old connection response XXX */
        case T_CONN_RES:        /* connection response */
                tcp_tli_accept(tcp, mp);
                break;
        case T_CONN_REQ:        /* connection request */
                tcp_tpi_connect(tcp, mp);
                break;
        case T_DISCON_REQ:      /* disconnect request */
                tcp_disconnect(tcp, mp);
                break;
        case T_CAPABILITY_REQ:
                tcp_capability_req(tcp, mp);    /* capability request */
                break;
        case T_INFO_REQ:        /* information request */
                tcp_info_req(tcp, mp);
                break;
        case T_SVR4_OPTMGMT_REQ:        /* manage options req */
        case T_OPTMGMT_REQ:
                /*
                 * Note:  no support for snmpcom_req() through new
                 * T_OPTMGMT_REQ. See comments in ip.c
                 */

                /*
                 * All Solaris components should pass a db_credp
                 * for this TPI message, hence we ASSERT.
                 * But in case there is some other M_PROTO that looks
                 * like a TPI message sent by some other kernel
                 * component, we check and return an error.
                 */
                cr = msg_getcred(mp, NULL);
                ASSERT(cr != NULL);
                if (cr == NULL) {
                        tcp_err_ack(tcp, mp, TSYSERR, EINVAL);
                        return;
                }
                /*
                 * If EINPROGRESS is returned, the request has been queued
                 * for subsequent processing by ip_restart_optmgmt(), which
                 * will do the CONN_DEC_REF().
                 */
                if ((int)tprim->type == T_SVR4_OPTMGMT_REQ) {
                        svr4_optcom_req(connp->conn_wq, mp, cr, &tcp_opt_obj);
                } else {
                        tpi_optcom_req(connp->conn_wq, mp, cr, &tcp_opt_obj);
                }
                break;

        case T_UNITDATA_REQ:    /* unitdata request */
                tcp_err_ack(tcp, mp, TNOTSUPPORT, 0);
                break;
        case T_ORDREL_REQ:      /* orderly release req */
                freemsg(mp);

                if (tcp->tcp_fused)
                        tcp_unfuse(tcp);

                if (tcp_xmit_end(tcp) != 0) {
                        /*
                         * We were crossing FINs and got a reset from
                         * the other side. Just ignore it.
                         */
                        if (connp->conn_debug) {
                                (void) strlog(TCP_MOD_ID, 0, 1,
                                    SL_ERROR|SL_TRACE,
                                    "tcp_wput_proto, T_ORDREL_REQ out of "
                                    "state %s",
                                    tcp_display(tcp, NULL,
                                    DISP_ADDR_AND_PORT));
                        }
                }
                break;
        case T_ADDR_REQ:
                tcp_addr_req(tcp, mp);
                break;
        default:
                if (connp->conn_debug) {
                        (void) strlog(TCP_MOD_ID, 0, 1, SL_ERROR|SL_TRACE,
                            "tcp_wput_proto, bogus TPI msg, type %d",
                            tprim->type);
                }
                /*
                 * We used to M_ERROR.  Sending TNOTSUPPORT gives the user
                 * to recover.
                 */
                tcp_err_ack(tcp, mp, TNOTSUPPORT, 0);
                break;
        }
}

/*
 * Handle special out-of-band ioctl requests (see PSARC/2008/265).
 */
static void
tcp_wput_cmdblk(queue_t *q, mblk_t *mp)
{
        void    *data;
        mblk_t  *datamp = mp->b_cont;
        conn_t  *connp = Q_TO_CONN(q);
        tcp_t   *tcp = connp->conn_tcp;
        cmdblk_t *cmdp = (cmdblk_t *)mp->b_rptr;

        if (datamp == NULL || MBLKL(datamp) < cmdp->cb_len) {
                cmdp->cb_error = EPROTO;
                qreply(q, mp);
                return;
        }

        data = datamp->b_rptr;

        switch (cmdp->cb_cmd) {
        case TI_GETPEERNAME:
                if (tcp->tcp_state < TCPS_SYN_RCVD)
                        cmdp->cb_error = ENOTCONN;
                else
                        cmdp->cb_error = conn_getpeername(connp, data,
                            &cmdp->cb_len);
                break;
        case TI_GETMYNAME:
                cmdp->cb_error = conn_getsockname(connp, data, &cmdp->cb_len);
                break;
        default:
                cmdp->cb_error = EINVAL;
                break;
        }

        qreply(q, mp);
}

/*
 * The TCP fast path write put procedure.
 * NOTE: the logic of the fast path is duplicated from tcp_wput_data()
 */
/* ARGSUSED */
void
tcp_output(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        int             len;
        int             hdrlen;
        int             plen;
        mblk_t          *mp1;
        uchar_t         *rptr;
        uint32_t        snxt;
        tcpha_t         *tcpha;
        struct datab    *db;
        uint32_t        suna;
        uint32_t        mss;
        ipaddr_t        *dst;
        ipaddr_t        *src;
        uint32_t        sum;
        int             usable;
        conn_t          *connp = (conn_t *)arg;
        tcp_t           *tcp = connp->conn_tcp;
        uint32_t        msize;
        tcp_stack_t     *tcps = tcp->tcp_tcps;
        ip_xmit_attr_t  *ixa;
        clock_t         now;

        /*
         * Try and ASSERT the minimum possible references on the
         * conn early enough. Since we are executing on write side,
         * the connection is obviously not detached and that means
         * there is a ref each for TCP and IP. Since we are behind
         * the squeue, the minimum references needed are 3. If the
         * conn is in classifier hash list, there should be an
         * extra ref for that (we check both the possibilities).
         */
        ASSERT((connp->conn_fanout != NULL && connp->conn_ref >= 4) ||
            (connp->conn_fanout == NULL && connp->conn_ref >= 3));

        ASSERT(DB_TYPE(mp) == M_DATA);
        msize = (mp->b_cont == NULL) ? MBLKL(mp) : msgdsize(mp);

        mutex_enter(&tcp->tcp_non_sq_lock);
        tcp->tcp_squeue_bytes -= msize;
        mutex_exit(&tcp->tcp_non_sq_lock);

        /* Bypass tcp protocol for fused tcp loopback */
        if (tcp->tcp_fused && tcp_fuse_output(tcp, mp, msize))
                return;

        mss = tcp->tcp_mss;
        /*
         * If ZEROCOPY has turned off, try not to send any zero-copy message
         * down. Do backoff, now.
         */
        if (tcp->tcp_snd_zcopy_aware && !tcp->tcp_snd_zcopy_on)
                mp = tcp_zcopy_backoff(tcp, mp, B_FALSE);


        ASSERT((uintptr_t)(mp->b_wptr - mp->b_rptr) <= (uintptr_t)INT_MAX);
        len = (int)(mp->b_wptr - mp->b_rptr);

        /*
         * Criteria for fast path:
         *
         *   1. no unsent data
         *   2. single mblk in request
         *   3. connection established
         *   4. data in mblk
         *   5. len <= mss
         *   6. no tcp_valid bits
         */
        if ((tcp->tcp_unsent != 0) ||
            (tcp->tcp_cork) ||
            (mp->b_cont != NULL) ||
            (tcp->tcp_state != TCPS_ESTABLISHED) ||
            (len == 0) ||
            (len > mss) ||
            (tcp->tcp_valid_bits != 0)) {
                tcp_wput_data(tcp, mp, B_FALSE);
                return;
        }

        ASSERT(tcp->tcp_xmit_tail_unsent == 0);
        ASSERT(tcp->tcp_fin_sent == 0);

        /* queue new packet onto retransmission queue */
        if (tcp->tcp_xmit_head == NULL) {
                tcp->tcp_xmit_head = mp;
        } else {
                tcp->tcp_xmit_last->b_cont = mp;
        }
        tcp->tcp_xmit_last = mp;
        tcp->tcp_xmit_tail = mp;

        /* find out how much we can send */
        /* BEGIN CSTYLED */
        /*
         *    un-acked     usable
         *  |--------------|-----------------|
         *  tcp_suna       tcp_snxt       tcp_suna+tcp_swnd
         */
        /* END CSTYLED */

        /* start sending from tcp_snxt */
        snxt = tcp->tcp_snxt;

        /*
         * Check to see if this connection has been idled for some
         * time and no ACK is expected.  If it is, we need to slow
         * start again to get back the connection's "self-clock" as
         * described in VJ's paper.
         *
         * Reinitialize tcp_cwnd after idle.
         */
        now = LBOLT_FASTPATH;
        if ((tcp->tcp_suna == snxt) && !tcp->tcp_localnet &&
            (TICK_TO_MSEC(now - tcp->tcp_last_recv_time) >= tcp->tcp_rto)) {
                TCP_SET_INIT_CWND(tcp, mss, tcps->tcps_slow_start_after_idle);
        }

        usable = tcp->tcp_swnd;         /* tcp window size */
        if (usable > tcp->tcp_cwnd)
                usable = tcp->tcp_cwnd; /* congestion window smaller */
        usable -= snxt;         /* subtract stuff already sent */
        suna = tcp->tcp_suna;
        usable += suna;
        /* usable can be < 0 if the congestion window is smaller */
        if (len > usable) {
                /* Can't send complete M_DATA in one shot */
                goto slow;
        }

        mutex_enter(&tcp->tcp_non_sq_lock);
        if (tcp->tcp_flow_stopped &&
            TCP_UNSENT_BYTES(tcp) <= connp->conn_sndlowat) {
                tcp_clrqfull(tcp);
        }
        mutex_exit(&tcp->tcp_non_sq_lock);

        /*
         * determine if anything to send (Nagle).
         *
         *   1. len < tcp_mss (i.e. small)
         *   2. unacknowledged data present
         *   3. len < nagle limit
         *   4. last packet sent < nagle limit (previous packet sent)
         */
        if ((len < mss) && (snxt != suna) &&
            (len < (int)tcp->tcp_naglim) &&
            (tcp->tcp_last_sent_len < tcp->tcp_naglim)) {
                /*
                 * This was the first unsent packet and normally
                 * mss < xmit_hiwater so there is no need to worry
                 * about flow control. The next packet will go
                 * through the flow control check in tcp_wput_data().
                 */
                /* leftover work from above */
                tcp->tcp_unsent = len;
                tcp->tcp_xmit_tail_unsent = len;

                return;
        }

        /*
         * len <= tcp->tcp_mss && len == unsent so no sender silly window.  Can
         * send now.
         */

        if (snxt == suna) {
                TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
        }

        /* we have always sent something */
        tcp->tcp_rack_cnt = 0;

        tcp->tcp_snxt = snxt + len;
        tcp->tcp_rack = tcp->tcp_rnxt;

        if ((mp1 = dupb(mp)) == 0)
                goto no_memory;
        mp->b_prev = (mblk_t *)(uintptr_t)now;
        mp->b_next = (mblk_t *)(uintptr_t)snxt;

        /* adjust tcp header information */
        tcpha = tcp->tcp_tcpha;
        tcpha->tha_flags = (TH_ACK|TH_PUSH);

        sum = len + connp->conn_ht_ulp_len + connp->conn_sum;
        sum = (sum >> 16) + (sum & 0xFFFF);
        tcpha->tha_sum = htons(sum);

        tcpha->tha_seq = htonl(snxt);

        TCPS_BUMP_MIB(tcps, tcpOutDataSegs);
        TCPS_UPDATE_MIB(tcps, tcpOutDataBytes, len);
        BUMP_LOCAL(tcp->tcp_obsegs);

        /* Update the latest receive window size in TCP header. */
        tcpha->tha_win = htons(tcp->tcp_rwnd >> tcp->tcp_rcv_ws);

        tcp->tcp_last_sent_len = (ushort_t)len;

        plen = len + connp->conn_ht_iphc_len;

        ixa = connp->conn_ixa;
        ixa->ixa_pktlen = plen;

        if (ixa->ixa_flags & IXAF_IS_IPV4) {
                tcp->tcp_ipha->ipha_length = htons(plen);
        } else {
                tcp->tcp_ip6h->ip6_plen = htons(plen - IPV6_HDR_LEN);
        }

        /* see if we need to allocate a mblk for the headers */
        hdrlen = connp->conn_ht_iphc_len;
        rptr = mp1->b_rptr - hdrlen;
        db = mp1->b_datap;
        if ((db->db_ref != 2) || rptr < db->db_base ||
            (!OK_32PTR(rptr))) {
                /* NOTE: we assume allocb returns an OK_32PTR */
                mp = allocb(hdrlen + tcps->tcps_wroff_xtra, BPRI_MED);
                if (!mp) {
                        freemsg(mp1);
                        goto no_memory;
                }
                mp->b_cont = mp1;
                mp1 = mp;
                /* Leave room for Link Level header */
                rptr = &mp1->b_rptr[tcps->tcps_wroff_xtra];
                mp1->b_wptr = &rptr[hdrlen];
        }
        mp1->b_rptr = rptr;

        /* Fill in the timestamp option. */
        if (tcp->tcp_snd_ts_ok) {
                uint32_t llbolt = (uint32_t)LBOLT_FASTPATH;

                U32_TO_BE32(llbolt,
                    (char *)tcpha + TCP_MIN_HEADER_LENGTH+4);
                U32_TO_BE32(tcp->tcp_ts_recent,
                    (char *)tcpha + TCP_MIN_HEADER_LENGTH+8);
        } else {
                ASSERT(connp->conn_ht_ulp_len == TCP_MIN_HEADER_LENGTH);
        }

        /* copy header into outgoing packet */
        dst = (ipaddr_t *)rptr;
        src = (ipaddr_t *)connp->conn_ht_iphc;
        dst[0] = src[0];
        dst[1] = src[1];
        dst[2] = src[2];
        dst[3] = src[3];
        dst[4] = src[4];
        dst[5] = src[5];
        dst[6] = src[6];
        dst[7] = src[7];
        dst[8] = src[8];
        dst[9] = src[9];
        if (hdrlen -= 40) {
                hdrlen >>= 2;
                dst += 10;
                src += 10;
                do {
                        *dst++ = *src++;
                } while (--hdrlen);
        }

        /*
         * Set the ECN info in the TCP header.  Note that this
         * is not the template header.
         */
        if (tcp->tcp_ecn_ok) {
                TCP_SET_ECT(tcp, rptr);

                tcpha = (tcpha_t *)(rptr + ixa->ixa_ip_hdr_length);
                if (tcp->tcp_ecn_echo_on)
                        tcpha->tha_flags |= TH_ECE;
                if (tcp->tcp_cwr && !tcp->tcp_ecn_cwr_sent) {
                        tcpha->tha_flags |= TH_CWR;
                        tcp->tcp_ecn_cwr_sent = B_TRUE;
                }
        }

        if (tcp->tcp_ip_forward_progress) {
                tcp->tcp_ip_forward_progress = B_FALSE;
                connp->conn_ixa->ixa_flags |= IXAF_REACH_CONF;
        } else {
                connp->conn_ixa->ixa_flags &= ~IXAF_REACH_CONF;
        }
        tcp_send_data(tcp, mp1);
        return;

        /*
         * If we ran out of memory, we pretend to have sent the packet
         * and that it was lost on the wire.
         */
no_memory:
        return;

slow:
        /* leftover work from above */
        tcp->tcp_unsent = len;
        tcp->tcp_xmit_tail_unsent = len;
        tcp_wput_data(tcp, NULL, B_FALSE);
}

/* ARGSUSED2 */
void
tcp_output_urgent(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        int len;
        uint32_t msize;
        conn_t *connp = (conn_t *)arg;
        tcp_t *tcp = connp->conn_tcp;

        msize = msgdsize(mp);

        len = msize - 1;
        if (len < 0) {
                freemsg(mp);
                return;
        }

        /*
         * Try to force urgent data out on the wire. Even if we have unsent
         * data this will at least send the urgent flag.
         * XXX does not handle more flag correctly.
         */
        len += tcp->tcp_unsent;
        len += tcp->tcp_snxt;
        tcp->tcp_urg = len;
        tcp->tcp_valid_bits |= TCP_URG_VALID;

        /* Bypass tcp protocol for fused tcp loopback */
        if (tcp->tcp_fused && tcp_fuse_output(tcp, mp, msize))
                return;

        /* Strip off the T_EXDATA_REQ if the data is from TPI */
        if (DB_TYPE(mp) != M_DATA) {
                mblk_t *mp1 = mp;
                ASSERT(!IPCL_IS_NONSTR(connp));
                mp = mp->b_cont;
                freeb(mp1);
        }
        tcp_wput_data(tcp, mp, B_TRUE);
}

/*
 * Called by streams close routine via squeues when our client blows off its
 * descriptor, we take this to mean: "close the stream state NOW, close the tcp
 * connection politely" When SO_LINGER is set (with a non-zero linger time and
 * it is not a nonblocking socket) then this routine sleeps until the FIN is
 * acked.
 *
 * NOTE: tcp_close potentially returns error when lingering.
 * However, the stream head currently does not pass these errors
 * to the application. 4.4BSD only returns EINTR and EWOULDBLOCK
 * errors to the application (from tsleep()) and not errors
 * like ECONNRESET caused by receiving a reset packet.
 */

/* ARGSUSED */
void
tcp_close_output(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        char    *msg;
        conn_t  *connp = (conn_t *)arg;
        tcp_t   *tcp = connp->conn_tcp;
        clock_t delta = 0;
        tcp_stack_t     *tcps = tcp->tcp_tcps;

        /*
         * When a non-STREAMS socket is being closed, it does not always
         * stick around waiting for tcp_close_output to run and can therefore
         * have dropped a reference already. So adjust the asserts accordingly.
         */
        ASSERT((connp->conn_fanout != NULL &&
            connp->conn_ref >= (IPCL_IS_NONSTR(connp) ? 3 : 4)) ||
            (connp->conn_fanout == NULL &&
            connp->conn_ref >= (IPCL_IS_NONSTR(connp) ? 2 : 3)));

        mutex_enter(&tcp->tcp_eager_lock);
        if (tcp->tcp_conn_req_cnt_q0 != 0 || tcp->tcp_conn_req_cnt_q != 0) {
                /*
                 * Cleanup for listener. For non-STREAM sockets sockfs will
                 * close all the eagers on 'q', so in that case only deal
                 * with 'q0'.
                 */
                tcp_eager_cleanup(tcp, IPCL_IS_NONSTR(connp) ? 1 : 0);
                tcp->tcp_wait_for_eagers = 1;
        }
        mutex_exit(&tcp->tcp_eager_lock);

        tcp->tcp_lso = B_FALSE;

        msg = NULL;
        switch (tcp->tcp_state) {
        case TCPS_CLOSED:
        case TCPS_IDLE:
                break;
        case TCPS_BOUND:
                if (tcp->tcp_listener != NULL) {
                        ASSERT(IPCL_IS_NONSTR(connp));
                        /*
                         * Unlink from the listener and drop the reference
                         * put on it by the eager. tcp_closei_local will not
                         * do it because tcp_tconnind_started is TRUE.
                         */
                        mutex_enter(&tcp->tcp_saved_listener->tcp_eager_lock);
                        tcp_eager_unlink(tcp);
                        mutex_exit(&tcp->tcp_saved_listener->tcp_eager_lock);
                        CONN_DEC_REF(tcp->tcp_saved_listener->tcp_connp);
                }
                break;
        case TCPS_LISTEN:
                break;
        case TCPS_SYN_SENT:
                msg = "tcp_close, during connect";
                break;
        case TCPS_SYN_RCVD:
                /*
                 * Close during the connect 3-way handshake
                 * but here there may or may not be pending data
                 * already on queue. Process almost same as in
                 * the ESTABLISHED state.
                 */
                /* FALLTHRU */
        default:
                if (tcp->tcp_fused)
                        tcp_unfuse(tcp);

                /*
                 * If SO_LINGER has set a zero linger time, abort the
                 * connection with a reset.
                 */
                if (connp->conn_linger && connp->conn_lingertime == 0) {
                        msg = "tcp_close, zero lingertime";
                        break;
                }

                /*
                 * Abort connection if there is unread data queued.
                 */
                if (tcp->tcp_rcv_list || tcp->tcp_reass_head) {
                        msg = "tcp_close, unread data";
                        break;
                }

                /*
                 * Abort connection if it is being closed without first
                 * being accepted. This can happen if a listening non-STREAM
                 * socket wants to get rid of the socket, for example, if the
                 * listener is closing.
                 */
                if (tcp->tcp_listener != NULL) {
                        ASSERT(IPCL_IS_NONSTR(connp));
                        msg = "tcp_close, close before accept";

                        /*
                         * Unlink from the listener and drop the reference
                         * put on it by the eager. tcp_closei_local will not
                         * do it because tcp_tconnind_started is TRUE.
                         */
                        mutex_enter(&tcp->tcp_saved_listener->tcp_eager_lock);
                        tcp_eager_unlink(tcp);
                        mutex_exit(&tcp->tcp_saved_listener->tcp_eager_lock);
                        CONN_DEC_REF(tcp->tcp_saved_listener->tcp_connp);
                        break;
                }

                /*
                 * Transmit the FIN before detaching the tcp_t.
                 * After tcp_detach returns this queue/perimeter
                 * no longer owns the tcp_t thus others can modify it.
                 */
                (void) tcp_xmit_end(tcp);

                /*
                 * If lingering on close then wait until the fin is acked,
                 * the SO_LINGER time passes, or a reset is sent/received.
                 */
                if (connp->conn_linger && connp->conn_lingertime > 0 &&
                    !(tcp->tcp_fin_acked) &&
                    tcp->tcp_state >= TCPS_ESTABLISHED) {
                        if (tcp->tcp_closeflags & (FNDELAY|FNONBLOCK)) {
                                tcp->tcp_client_errno = EWOULDBLOCK;
                        } else if (tcp->tcp_client_errno == 0) {

                                ASSERT(tcp->tcp_linger_tid == 0);

                                /* conn_lingertime is in sec. */
                                tcp->tcp_linger_tid = TCP_TIMER(tcp,
                                    tcp_close_linger_timeout,
                                    connp->conn_lingertime * MILLISEC);

                                /* tcp_close_linger_timeout will finish close */
                                if (tcp->tcp_linger_tid == 0)
                                        tcp->tcp_client_errno = ENOSR;
                                else
                                        return;
                        }

                        /*
                         * Check if we need to detach or just close
                         * the instance.
                         */
                        if (tcp->tcp_state <= TCPS_LISTEN)
                                break;
                }

                /*
                 * Make sure that no other thread will access the conn_rq of
                 * this instance (through lookups etc.) as conn_rq will go
                 * away shortly.
                 */
                tcp_acceptor_hash_remove(tcp);

                mutex_enter(&tcp->tcp_non_sq_lock);
                if (tcp->tcp_flow_stopped) {
                        tcp_clrqfull(tcp);
                }
                mutex_exit(&tcp->tcp_non_sq_lock);

                if (tcp->tcp_timer_tid != 0) {
                        delta = TCP_TIMER_CANCEL(tcp, tcp->tcp_timer_tid);
                        tcp->tcp_timer_tid = 0;
                }
                /*
                 * Need to cancel those timers which will not be used when
                 * TCP is detached.  This has to be done before the conn_wq
                 * is set to NULL.
                 */
                tcp_timers_stop(tcp);

                tcp->tcp_detached = B_TRUE;
                if (tcp->tcp_state == TCPS_TIME_WAIT) {
                        tcp_time_wait_append(tcp);
                        TCP_DBGSTAT(tcps, tcp_detach_time_wait);
                        ASSERT(connp->conn_ref >=
                            (IPCL_IS_NONSTR(connp) ? 2 : 3));
                        goto finish;
                }

                /*
                 * If delta is zero the timer event wasn't executed and was
                 * successfully canceled. In this case we need to restart it
                 * with the minimal delta possible.
                 */
                if (delta >= 0)
                        tcp->tcp_timer_tid = TCP_TIMER(tcp, tcp_timer,
                            delta ? delta : 1);

                ASSERT(connp->conn_ref >= (IPCL_IS_NONSTR(connp) ? 2 : 3));
                goto finish;
        }

        /* Detach did not complete. Still need to remove q from stream. */
        if (msg) {
                if (tcp->tcp_state == TCPS_ESTABLISHED ||
                    tcp->tcp_state == TCPS_CLOSE_WAIT)
                        TCPS_BUMP_MIB(tcps, tcpEstabResets);
                if (tcp->tcp_state == TCPS_SYN_SENT ||
                    tcp->tcp_state == TCPS_SYN_RCVD)
                        TCPS_BUMP_MIB(tcps, tcpAttemptFails);
                tcp_xmit_ctl(msg, tcp,  tcp->tcp_snxt, 0, TH_RST);
        }

        tcp_closei_local(tcp);
        CONN_DEC_REF(connp);
        ASSERT(connp->conn_ref >= (IPCL_IS_NONSTR(connp) ? 1 : 2));

finish:
        /*
         * Don't change the queues in the case of a listener that has
         * eagers in its q or q0. It could surprise the eagers.
         * Instead wait for the eagers outside the squeue.
         *
         * For non-STREAMS sockets tcp_wait_for_eagers implies that
         * we should delay the su_closed upcall until all eagers have
         * dropped their references.
         */
        if (!tcp->tcp_wait_for_eagers) {
                tcp->tcp_detached = B_TRUE;
                connp->conn_rq = NULL;
                connp->conn_wq = NULL;

                /* non-STREAM socket, release the upper handle */
                if (IPCL_IS_NONSTR(connp)) {
                        ASSERT(connp->conn_upper_handle != NULL);
                        (*connp->conn_upcalls->su_closed)
                            (connp->conn_upper_handle);
                        connp->conn_upper_handle = NULL;
                        connp->conn_upcalls = NULL;
                }
        }

        /* Signal tcp_close() to finish closing. */
        mutex_enter(&tcp->tcp_closelock);
        tcp->tcp_closed = 1;
        cv_signal(&tcp->tcp_closecv);
        mutex_exit(&tcp->tcp_closelock);
}

/* ARGSUSED */
void
tcp_shutdown_output(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        conn_t  *connp = (conn_t *)arg;
        tcp_t   *tcp = connp->conn_tcp;

        freemsg(mp);

        if (tcp->tcp_fused)
                tcp_unfuse(tcp);

        if (tcp_xmit_end(tcp) != 0) {
                /*
                 * We were crossing FINs and got a reset from
                 * the other side. Just ignore it.
                 */
                if (connp->conn_debug) {
                        (void) strlog(TCP_MOD_ID, 0, 1,
                            SL_ERROR|SL_TRACE,
                            "tcp_shutdown_output() out of state %s",
                            tcp_display(tcp, NULL, DISP_ADDR_AND_PORT));
                }
        }
}

#pragma inline(tcp_send_data)

void
tcp_send_data(tcp_t *tcp, mblk_t *mp)
{
        conn_t          *connp = tcp->tcp_connp;

        /*
         * Check here to avoid sending zero-copy message down to IP when
         * ZEROCOPY capability has turned off. We only need to deal with
         * the race condition between sockfs and the notification here.
         * Since we have tried to backoff the tcp_xmit_head when turning
         * zero-copy off and new messages in tcp_output(), we simply drop
         * the dup'ed packet here and let tcp retransmit, if tcp_xmit_zc_clean
         * is not true.
         */
        if (tcp->tcp_snd_zcopy_aware && !tcp->tcp_snd_zcopy_on &&
            !tcp->tcp_xmit_zc_clean) {
                ip_drop_output("TCP ZC was disabled but not clean", mp, NULL);
                freemsg(mp);
                return;
        }

        DTRACE_TCP5(send, mblk_t *, NULL, ip_xmit_attr_t *, connp->conn_ixa,
            __dtrace_tcp_void_ip_t *, mp->b_rptr, tcp_t *, tcp,
            __dtrace_tcp_tcph_t *,
            &mp->b_rptr[connp->conn_ixa->ixa_ip_hdr_length]);

        ASSERT(connp->conn_ixa->ixa_notify_cookie == connp->conn_tcp);
        (void) conn_ip_output(mp, connp->conn_ixa);
}

/* ARGSUSED2 */
void
tcp_send_synack(void *arg, mblk_t *mp, void *arg2, ip_recv_attr_t *dummy)
{
        conn_t  *econnp = (conn_t *)arg;
        tcp_t   *tcp = econnp->conn_tcp;
        ip_xmit_attr_t *ixa = econnp->conn_ixa;

        /* Guard against a RST having blown it away while on the squeue */
        if (tcp->tcp_state == TCPS_CLOSED) {
                freemsg(mp);
                return;
        }

        /*
         * In the off-chance that the eager received and responded to
         * some other packet while the SYN|ACK was queued, we recalculate
         * the ixa_pktlen. It would be better to fix the SYN/accept
         * multithreading scheme to avoid this complexity.
         */
        ixa->ixa_pktlen = msgdsize(mp);
        (void) conn_ip_output(mp, ixa);
}

/*
 * tcp_send() is called by tcp_wput_data() and returns one of the following:
 *
 * -1 = failed allocation.
 *  0 = We've either successfully sent data, or our usable send window is too
 *      small and we'd rather wait until later before sending again.
 */
static int
tcp_send(tcp_t *tcp, const int mss, const int total_hdr_len,
    const int tcp_hdr_len, const int num_sack_blk, int *usable,
    uint_t *snxt, int *tail_unsent, mblk_t **xmit_tail, mblk_t *local_time)
{
        int             num_lso_seg = 1;
        uint_t          lso_usable;
        boolean_t       do_lso_send = B_FALSE;
        tcp_stack_t     *tcps = tcp->tcp_tcps;
        conn_t          *connp = tcp->tcp_connp;
        ip_xmit_attr_t  *ixa = connp->conn_ixa;

        /*
         * Check LSO possibility. The value of tcp->tcp_lso indicates whether
         * the underlying connection is LSO capable. Will check whether having
         * enough available data to initiate LSO transmission in the for(){}
         * loops.
         */
        if (tcp->tcp_lso && (tcp->tcp_valid_bits & ~TCP_FSS_VALID) == 0)
                do_lso_send = B_TRUE;

        for (;;) {
                struct datab    *db;
                tcpha_t         *tcpha;
                uint32_t        sum;
                mblk_t          *mp, *mp1;
                uchar_t         *rptr;
                int             len;

                /*
                 * Calculate the maximum payload length we can send at one
                 * time.
                 */
                if (do_lso_send) {
                        /*
                         * Determine whether or not it's possible to do LSO,
                         * and if so, how much data we can send.
                         */
                        if ((*usable - 1) / mss >= 1) {
                                lso_usable = MIN(tcp->tcp_lso_max, *usable);
                                num_lso_seg = lso_usable / mss;
                                if (lso_usable % mss) {
                                        num_lso_seg++;
                                        tcp->tcp_last_sent_len = (ushort_t)
                                            (lso_usable % mss);
                                } else {
                                        tcp->tcp_last_sent_len = (ushort_t)mss;
                                }
                        } else {
                                do_lso_send = B_FALSE;
                                num_lso_seg = 1;
                                lso_usable = mss;
                        }
                }

                ASSERT(num_lso_seg <= IP_MAXPACKET / mss + 1);

                len = mss;
                if (len > *usable) {
                        ASSERT(do_lso_send == B_FALSE);

                        len = *usable;
                        if (len <= 0) {
                                /* Terminate the loop */
                                break;  /* success; too small */
                        }
                        /*
                         * Sender silly-window avoidance.
                         * Ignore this if we are going to send a
                         * zero window probe out.
                         *
                         * TODO: force data into microscopic window?
                         *      ==> (!pushed || (unsent > usable))
                         */
                        if (len < (tcp->tcp_max_swnd >> 1) &&
                            (tcp->tcp_unsent - (*snxt - tcp->tcp_snxt)) > len &&
                            !((tcp->tcp_valid_bits & TCP_URG_VALID) &&
                            len == 1) && (! tcp->tcp_zero_win_probe)) {
                                /*
                                 * If the retransmit timer is not running
                                 * we start it so that we will retransmit
                                 * in the case when the receiver has
                                 * decremented the window.
                                 */
                                if (*snxt == tcp->tcp_snxt &&
                                    *snxt == tcp->tcp_suna) {
                                        /*
                                         * We are not supposed to send
                                         * anything.  So let's wait a little
                                         * bit longer before breaking SWS
                                         * avoidance.
                                         *
                                         * What should the value be?
                                         * Suggestion: MAX(init rexmit time,
                                         * tcp->tcp_rto)
                                         */
                                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                                }
                                break;  /* success; too small */
                        }
                }

                tcpha = tcp->tcp_tcpha;

                /*
                 * The reason to adjust len here is that we need to set flags
                 * and calculate checksum.
                 */
                if (do_lso_send)
                        len = lso_usable;

                *usable -= len; /* Approximate - can be adjusted later */
                if (*usable > 0)
                        tcpha->tha_flags = TH_ACK;
                else
                        tcpha->tha_flags = (TH_ACK | TH_PUSH);

                /*
                 * Prime pump for IP's checksumming on our behalf.
                 * Include the adjustment for a source route if any.
                 * In case of LSO, the partial pseudo-header checksum should
                 * exclusive TCP length, so zero tha_sum before IP calculate
                 * pseudo-header checksum for partial checksum offload.
                 */
                if (do_lso_send) {
                        sum = 0;
                } else {
                        sum = len + tcp_hdr_len + connp->conn_sum;
                        sum = (sum >> 16) + (sum & 0xFFFF);
                }
                tcpha->tha_sum = htons(sum);
                tcpha->tha_seq = htonl(*snxt);

                /*
                 * Branch off to tcp_xmit_mp() if any of the VALID bits is
                 * set.  For the case when TCP_FSS_VALID is the only valid
                 * bit (normal active close), branch off only when we think
                 * that the FIN flag needs to be set.  Note for this case,
                 * that (snxt + len) may not reflect the actual seg_len,
                 * as len may be further reduced in tcp_xmit_mp().  If len
                 * gets modified, we will end up here again.
                 */
                if (tcp->tcp_valid_bits != 0 &&
                    (tcp->tcp_valid_bits != TCP_FSS_VALID ||
                    ((*snxt + len) == tcp->tcp_fss))) {
                        uchar_t         *prev_rptr;
                        uint32_t        prev_snxt = tcp->tcp_snxt;

                        if (*tail_unsent == 0) {
                                ASSERT((*xmit_tail)->b_cont != NULL);
                                *xmit_tail = (*xmit_tail)->b_cont;
                                prev_rptr = (*xmit_tail)->b_rptr;
                                *tail_unsent = (int)((*xmit_tail)->b_wptr -
                                    (*xmit_tail)->b_rptr);
                        } else {
                                prev_rptr = (*xmit_tail)->b_rptr;
                                (*xmit_tail)->b_rptr = (*xmit_tail)->b_wptr -
                                    *tail_unsent;
                        }
                        mp = tcp_xmit_mp(tcp, *xmit_tail, len, NULL, NULL,
                            *snxt, B_FALSE, (uint32_t *)&len, B_FALSE);
                        /* Restore tcp_snxt so we get amount sent right. */
                        tcp->tcp_snxt = prev_snxt;
                        if (prev_rptr == (*xmit_tail)->b_rptr) {
                                /*
                                 * If the previous timestamp is still in use,
                                 * don't stomp on it.
                                 */
                                if ((*xmit_tail)->b_next == NULL) {
                                        (*xmit_tail)->b_prev = local_time;
                                        (*xmit_tail)->b_next =
                                            (mblk_t *)(uintptr_t)(*snxt);
                                }
                        } else
                                (*xmit_tail)->b_rptr = prev_rptr;

                        if (mp == NULL) {
                                return (-1);
                        }
                        mp1 = mp->b_cont;

                        if (len <= mss) /* LSO is unusable (!do_lso_send) */
                                tcp->tcp_last_sent_len = (ushort_t)len;
                        while (mp1->b_cont) {
                                *xmit_tail = (*xmit_tail)->b_cont;
                                (*xmit_tail)->b_prev = local_time;
                                (*xmit_tail)->b_next =
                                    (mblk_t *)(uintptr_t)(*snxt);
                                mp1 = mp1->b_cont;
                        }
                        *snxt += len;
                        *tail_unsent = (*xmit_tail)->b_wptr - mp1->b_wptr;
                        BUMP_LOCAL(tcp->tcp_obsegs);
                        TCPS_BUMP_MIB(tcps, tcpOutDataSegs);
                        TCPS_UPDATE_MIB(tcps, tcpOutDataBytes, len);
                        tcp_send_data(tcp, mp);
                        continue;
                }

                *snxt += len;   /* Adjust later if we don't send all of len */
                TCPS_BUMP_MIB(tcps, tcpOutDataSegs);
                TCPS_UPDATE_MIB(tcps, tcpOutDataBytes, len);

                if (*tail_unsent) {
                        /* Are the bytes above us in flight? */
                        rptr = (*xmit_tail)->b_wptr - *tail_unsent;
                        if (rptr != (*xmit_tail)->b_rptr) {
                                *tail_unsent -= len;
                                if (len <= mss) /* LSO is unusable */
                                        tcp->tcp_last_sent_len = (ushort_t)len;
                                len += total_hdr_len;
                                ixa->ixa_pktlen = len;

                                if (ixa->ixa_flags & IXAF_IS_IPV4) {
                                        tcp->tcp_ipha->ipha_length = htons(len);
                                } else {
                                        tcp->tcp_ip6h->ip6_plen =
                                            htons(len - IPV6_HDR_LEN);
                                }

                                mp = dupb(*xmit_tail);
                                if (mp == NULL) {
                                        return (-1);    /* out_of_mem */
                                }
                                mp->b_rptr = rptr;
                                /*
                                 * If the old timestamp is no longer in use,
                                 * sample a new timestamp now.
                                 */
                                if ((*xmit_tail)->b_next == NULL) {
                                        (*xmit_tail)->b_prev = local_time;
                                        (*xmit_tail)->b_next =
                                            (mblk_t *)(uintptr_t)(*snxt-len);
                                }
                                goto must_alloc;
                        }
                } else {
                        *xmit_tail = (*xmit_tail)->b_cont;
                        ASSERT((uintptr_t)((*xmit_tail)->b_wptr -
                            (*xmit_tail)->b_rptr) <= (uintptr_t)INT_MAX);
                        *tail_unsent = (int)((*xmit_tail)->b_wptr -
                            (*xmit_tail)->b_rptr);
                }

                (*xmit_tail)->b_prev = local_time;
                (*xmit_tail)->b_next = (mblk_t *)(uintptr_t)(*snxt - len);

                *tail_unsent -= len;
                if (len <= mss) /* LSO is unusable (!do_lso_send) */
                        tcp->tcp_last_sent_len = (ushort_t)len;

                len += total_hdr_len;
                ixa->ixa_pktlen = len;

                if (ixa->ixa_flags & IXAF_IS_IPV4) {
                        tcp->tcp_ipha->ipha_length = htons(len);
                } else {
                        tcp->tcp_ip6h->ip6_plen = htons(len - IPV6_HDR_LEN);
                }

                mp = dupb(*xmit_tail);
                if (mp == NULL) {
                        return (-1);    /* out_of_mem */
                }

                len = total_hdr_len;
                /*
                 * There are four reasons to allocate a new hdr mblk:
                 *  1) The bytes above us are in use by another packet
                 *  2) We don't have good alignment
                 *  3) The mblk is being shared
                 *  4) We don't have enough room for a header
                 */
                rptr = mp->b_rptr - len;
                if (!OK_32PTR(rptr) ||
                    ((db = mp->b_datap), db->db_ref != 2) ||
                    rptr < db->db_base) {
                        /* NOTE: we assume allocb returns an OK_32PTR */

                must_alloc:;
                        mp1 = allocb(connp->conn_ht_iphc_allocated +
                            tcps->tcps_wroff_xtra, BPRI_MED);
                        if (mp1 == NULL) {
                                freemsg(mp);
                                return (-1);    /* out_of_mem */
                        }
                        mp1->b_cont = mp;
                        mp = mp1;
                        /* Leave room for Link Level header */
                        len = total_hdr_len;
                        rptr = &mp->b_rptr[tcps->tcps_wroff_xtra];
                        mp->b_wptr = &rptr[len];
                }

                /*
                 * Fill in the header using the template header, and add
                 * options such as time-stamp, ECN and/or SACK, as needed.
                 */
                tcp_fill_header(tcp, rptr, (clock_t)local_time, num_sack_blk);

                mp->b_rptr = rptr;

                if (*tail_unsent) {
                        int spill = *tail_unsent;

                        mp1 = mp->b_cont;
                        if (mp1 == NULL)
                                mp1 = mp;

                        /*
                         * If we're a little short, tack on more mblks until
                         * there is no more spillover.
                         */
                        while (spill < 0) {
                                mblk_t *nmp;
                                int nmpsz;

                                nmp = (*xmit_tail)->b_cont;
                                nmpsz = MBLKL(nmp);

                                /*
                                 * Excess data in mblk; can we split it?
                                 * If LSO is enabled for the connection,
                                 * keep on splitting as this is a transient
                                 * send path.
                                 */
                                if (!do_lso_send && (spill + nmpsz > 0)) {
                                        /*
                                         * Don't split if stream head was
                                         * told to break up larger writes
                                         * into smaller ones.
                                         */
                                        if (tcp->tcp_maxpsz_multiplier > 0)
                                                break;

                                        /*
                                         * Next mblk is less than SMSS/2
                                         * rounded up to nearest 64-byte;
                                         * let it get sent as part of the
                                         * next segment.
                                         */
                                        if (tcp->tcp_localnet &&
                                            !tcp->tcp_cork &&
                                            (nmpsz < roundup((mss >> 1), 64)))
                                                break;
                                }

                                *xmit_tail = nmp;
                                ASSERT((uintptr_t)nmpsz <= (uintptr_t)INT_MAX);
                                /* Stash for rtt use later */
                                (*xmit_tail)->b_prev = local_time;
                                (*xmit_tail)->b_next =
                                    (mblk_t *)(uintptr_t)(*snxt - len);
                                mp1->b_cont = dupb(*xmit_tail);
                                mp1 = mp1->b_cont;

                                spill += nmpsz;
                                if (mp1 == NULL) {
                                        *tail_unsent = spill;
                                        freemsg(mp);
                                        return (-1);    /* out_of_mem */
                                }
                        }

                        /* Trim back any surplus on the last mblk */
                        if (spill >= 0) {
                                mp1->b_wptr -= spill;
                                *tail_unsent = spill;
                        } else {
                                /*
                                 * We did not send everything we could in
                                 * order to remain within the b_cont limit.
                                 */
                                *usable -= spill;
                                *snxt += spill;
                                tcp->tcp_last_sent_len += spill;
                                TCPS_UPDATE_MIB(tcps, tcpOutDataBytes, spill);
                                /*
                                 * Adjust the checksum
                                 */
                                tcpha = (tcpha_t *)(rptr +
                                    ixa->ixa_ip_hdr_length);
                                sum += spill;
                                sum = (sum >> 16) + (sum & 0xFFFF);
                                tcpha->tha_sum = htons(sum);
                                if (connp->conn_ipversion == IPV4_VERSION) {
                                        sum = ntohs(
                                            ((ipha_t *)rptr)->ipha_length) +
                                            spill;
                                        ((ipha_t *)rptr)->ipha_length =
                                            htons(sum);
                                } else {
                                        sum = ntohs(
                                            ((ip6_t *)rptr)->ip6_plen) +
                                            spill;
                                        ((ip6_t *)rptr)->ip6_plen =
                                            htons(sum);
                                }
                                ixa->ixa_pktlen += spill;
                                *tail_unsent = 0;
                        }
                }
                if (tcp->tcp_ip_forward_progress) {
                        tcp->tcp_ip_forward_progress = B_FALSE;
                        ixa->ixa_flags |= IXAF_REACH_CONF;
                } else {
                        ixa->ixa_flags &= ~IXAF_REACH_CONF;
                }

                if (do_lso_send) {
                        /* Append LSO information to the mp. */
                        lso_info_set(mp, mss, HW_LSO);
                        ixa->ixa_fragsize = IP_MAXPACKET;
                        ixa->ixa_extra_ident = num_lso_seg - 1;

                        DTRACE_PROBE2(tcp_send_lso, int, num_lso_seg,
                            boolean_t, B_TRUE);

                        tcp_send_data(tcp, mp);

                        /*
                         * Restore values of ixa_fragsize and ixa_extra_ident.
                         */
                        ixa->ixa_fragsize = ixa->ixa_pmtu;
                        ixa->ixa_extra_ident = 0;
                        tcp->tcp_obsegs += num_lso_seg;
                        TCP_STAT(tcps, tcp_lso_times);
                        TCP_STAT_UPDATE(tcps, tcp_lso_pkt_out, num_lso_seg);
                } else {
                        /*
                         * Make sure to clean up LSO information. Wherever a
                         * new mp uses the prepended header room after dupb(),
                         * lso_info_cleanup() should be called.
                         */
                        lso_info_cleanup(mp);
                        tcp_send_data(tcp, mp);
                        BUMP_LOCAL(tcp->tcp_obsegs);
                }
        }

        return (0);
}

/*
 * Initiate closedown sequence on an active connection.  (May be called as
 * writer.)  Return value zero for OK return, non-zero for error return.
 */
static int
tcp_xmit_end(tcp_t *tcp)
{
        mblk_t          *mp;
        tcp_stack_t     *tcps = tcp->tcp_tcps;
        iulp_t          uinfo;
        ip_stack_t      *ipst = tcps->tcps_netstack->netstack_ip;
        conn_t          *connp = tcp->tcp_connp;

        if (tcp->tcp_state < TCPS_SYN_RCVD ||
            tcp->tcp_state > TCPS_CLOSE_WAIT) {
                /*
                 * Invalid state, only states TCPS_SYN_RCVD,
                 * TCPS_ESTABLISHED and TCPS_CLOSE_WAIT are valid
                 */
                return (-1);
        }

        tcp->tcp_fss = tcp->tcp_snxt + tcp->tcp_unsent;
        tcp->tcp_valid_bits |= TCP_FSS_VALID;
        /*
         * If there is nothing more unsent, send the FIN now.
         * Otherwise, it will go out with the last segment.
         */
        if (tcp->tcp_unsent == 0) {
                mp = tcp_xmit_mp(tcp, NULL, 0, NULL, NULL,
                    tcp->tcp_fss, B_FALSE, NULL, B_FALSE);

                if (mp) {
                        tcp_send_data(tcp, mp);
                } else {
                        /*
                         * Couldn't allocate msg.  Pretend we got it out.
                         * Wait for rexmit timeout.
                         */
                        tcp->tcp_snxt = tcp->tcp_fss + 1;
                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                }

                /*
                 * If needed, update tcp_rexmit_snxt as tcp_snxt is
                 * changed.
                 */
                if (tcp->tcp_rexmit && tcp->tcp_rexmit_nxt == tcp->tcp_fss) {
                        tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
                }
        } else {
                /*
                 * If tcp->tcp_cork is set, then the data will not get sent,
                 * so we have to check that and unset it first.
                 */
                if (tcp->tcp_cork)
                        tcp->tcp_cork = B_FALSE;
                tcp_wput_data(tcp, NULL, B_FALSE);
        }

        /*
         * If TCP does not get enough samples of RTT or tcp_rtt_updates
         * is 0, don't update the cache.
         */
        if (tcps->tcps_rtt_updates == 0 ||
            tcp->tcp_rtt_update < tcps->tcps_rtt_updates)
                return (0);

        /*
         * We do not have a good algorithm to update ssthresh at this time.
         * So don't do any update.
         */
        bzero(&uinfo, sizeof (uinfo));
        uinfo.iulp_rtt = tcp->tcp_rtt_sa;
        uinfo.iulp_rtt_sd = tcp->tcp_rtt_sd;

        /*
         * Note that uinfo is kept for conn_faddr in the DCE. Could update even
         * if source routed but we don't.
         */
        if (connp->conn_ipversion == IPV4_VERSION) {
                if (connp->conn_faddr_v4 !=  tcp->tcp_ipha->ipha_dst) {
                        return (0);
                }
                (void) dce_update_uinfo_v4(connp->conn_faddr_v4, &uinfo, ipst);
        } else {
                uint_t ifindex;

                if (!(IN6_ARE_ADDR_EQUAL(&connp->conn_faddr_v6,
                    &tcp->tcp_ip6h->ip6_dst))) {
                        return (0);
                }
                ifindex = 0;
                if (IN6_IS_ADDR_LINKSCOPE(&connp->conn_faddr_v6)) {
                        ip_xmit_attr_t *ixa = connp->conn_ixa;

                        /*
                         * If we are going to create a DCE we'd better have
                         * an ifindex
                         */
                        if (ixa->ixa_nce != NULL) {
                                ifindex = ixa->ixa_nce->nce_common->ncec_ill->
                                    ill_phyint->phyint_ifindex;
                        } else {
                                return (0);
                        }
                }

                (void) dce_update_uinfo(&connp->conn_faddr_v6, ifindex, &uinfo,
                    ipst);
        }
        return (0);
}

/*
 * Send out a control packet on the tcp connection specified.  This routine
 * is typically called where we need a simple ACK or RST generated.
 */
void
tcp_xmit_ctl(char *str, tcp_t *tcp, uint32_t seq, uint32_t ack, int ctl)
{
        uchar_t         *rptr;
        tcpha_t         *tcpha;
        ipha_t          *ipha = NULL;
        ip6_t           *ip6h = NULL;
        uint32_t        sum;
        int             total_hdr_len;
        int             ip_hdr_len;
        mblk_t          *mp;
        tcp_stack_t     *tcps = tcp->tcp_tcps;
        conn_t          *connp = tcp->tcp_connp;
        ip_xmit_attr_t  *ixa = connp->conn_ixa;

        /*
         * Save sum for use in source route later.
         */
        sum = connp->conn_ht_ulp_len + connp->conn_sum;
        total_hdr_len = connp->conn_ht_iphc_len;
        ip_hdr_len = ixa->ixa_ip_hdr_length;

        /* If a text string is passed in with the request, pass it to strlog. */
        if (str != NULL && connp->conn_debug) {
                (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
                    "tcp_xmit_ctl: '%s', seq 0x%x, ack 0x%x, ctl 0x%x",
                    str, seq, ack, ctl);
        }
        mp = allocb(connp->conn_ht_iphc_allocated + tcps->tcps_wroff_xtra,
            BPRI_MED);
        if (mp == NULL) {
                return;
        }
        rptr = &mp->b_rptr[tcps->tcps_wroff_xtra];
        mp->b_rptr = rptr;
        mp->b_wptr = &rptr[total_hdr_len];
        bcopy(connp->conn_ht_iphc, rptr, total_hdr_len);

        ixa->ixa_pktlen = total_hdr_len;

        if (ixa->ixa_flags & IXAF_IS_IPV4) {
                ipha = (ipha_t *)rptr;
                ipha->ipha_length = htons(total_hdr_len);
        } else {
                ip6h = (ip6_t *)rptr;
                ip6h->ip6_plen = htons(total_hdr_len - IPV6_HDR_LEN);
        }
        tcpha = (tcpha_t *)&rptr[ip_hdr_len];
        tcpha->tha_flags = (uint8_t)ctl;
        if (ctl & TH_RST) {
                TCPS_BUMP_MIB(tcps, tcpOutRsts);
                TCPS_BUMP_MIB(tcps, tcpOutControl);
                /*
                 * Don't send TSopt w/ TH_RST packets per RFC 1323.
                 */
                if (tcp->tcp_snd_ts_ok &&
                    tcp->tcp_state > TCPS_SYN_SENT) {
                        mp->b_wptr = &rptr[total_hdr_len - TCPOPT_REAL_TS_LEN];
                        *(mp->b_wptr) = TCPOPT_EOL;

                        ixa->ixa_pktlen = total_hdr_len - TCPOPT_REAL_TS_LEN;

                        if (connp->conn_ipversion == IPV4_VERSION) {
                                ipha->ipha_length = htons(total_hdr_len -
                                    TCPOPT_REAL_TS_LEN);
                        } else {
                                ip6h->ip6_plen = htons(total_hdr_len -
                                    IPV6_HDR_LEN - TCPOPT_REAL_TS_LEN);
                        }
                        tcpha->tha_offset_and_reserved -= (3 << 4);
                        sum -= TCPOPT_REAL_TS_LEN;
                }
        }
        if (ctl & TH_ACK) {
                if (tcp->tcp_snd_ts_ok) {
                        uint32_t llbolt = (uint32_t)LBOLT_FASTPATH;

                        U32_TO_BE32(llbolt,
                            (char *)tcpha + TCP_MIN_HEADER_LENGTH+4);
                        U32_TO_BE32(tcp->tcp_ts_recent,
                            (char *)tcpha + TCP_MIN_HEADER_LENGTH+8);
                }

                /* Update the latest receive window size in TCP header. */
                tcpha->tha_win = htons(tcp->tcp_rwnd >> tcp->tcp_rcv_ws);
                /* Track what we sent to the peer */
                tcp->tcp_tcpha->tha_win = tcpha->tha_win;
                tcp->tcp_rack = ack;
                tcp->tcp_rack_cnt = 0;
                TCPS_BUMP_MIB(tcps, tcpOutAck);
        }
        BUMP_LOCAL(tcp->tcp_obsegs);
        tcpha->tha_seq = htonl(seq);
        tcpha->tha_ack = htonl(ack);
        /*
         * Include the adjustment for a source route if any.
         */
        sum = (sum >> 16) + (sum & 0xFFFF);
        tcpha->tha_sum = htons(sum);
        tcp_send_data(tcp, mp);
}

/*
 * Generate a reset based on an inbound packet, connp is set by caller
 * when RST is in response to an unexpected inbound packet for which
 * there is active tcp state in the system.
 *
 * IPSEC NOTE : Try to send the reply with the same protection as it came
 * in.  We have the ip_recv_attr_t which is reversed to form the ip_xmit_attr_t.
 * That way the packet will go out at the same level of protection as it
 * came in with.
 */
static void
tcp_xmit_early_reset(char *str, mblk_t *mp, uint32_t seq, uint32_t ack, int ctl,
    ip_recv_attr_t *ira, ip_stack_t *ipst, conn_t *connp)
{
        ipha_t          *ipha = NULL;
        ip6_t           *ip6h = NULL;
        ushort_t        len;
        tcpha_t         *tcpha;
        int             i;
        ipaddr_t        v4addr;
        in6_addr_t      v6addr;
        netstack_t      *ns = ipst->ips_netstack;
        tcp_stack_t     *tcps = ns->netstack_tcp;
        ip_xmit_attr_t  ixas, *ixa;
        uint_t          ip_hdr_len = ira->ira_ip_hdr_length;
        boolean_t       need_refrele = B_FALSE;         /* ixa_refrele(ixa) */
        ushort_t        port;

        if (!tcp_send_rst_chk(tcps)) {
                TCP_STAT(tcps, tcp_rst_unsent);
                freemsg(mp);
                return;
        }

        /*
         * If connp != NULL we use conn_ixa to keep IP_NEXTHOP and other
         * options from the listener. In that case the caller must ensure that
         * we are running on the listener = connp squeue.
         *
         * We get a safe copy of conn_ixa so we don't need to restore anything
         * we or ip_output_simple might change in the ixa.
         */
        if (connp != NULL) {
                ASSERT(connp->conn_on_sqp);

                ixa = conn_get_ixa_exclusive(connp);
                if (ixa == NULL) {
                        TCP_STAT(tcps, tcp_rst_unsent);
                        freemsg(mp);
                        return;
                }
                need_refrele = B_TRUE;
        } else {
                bzero(&ixas, sizeof (ixas));
                ixa = &ixas;
                /*
                 * IXAF_VERIFY_SOURCE is overkill since we know the
                 * packet was for us.
                 */
                ixa->ixa_flags |= IXAF_SET_ULP_CKSUM | IXAF_VERIFY_SOURCE;
                ixa->ixa_protocol = IPPROTO_TCP;
                ixa->ixa_zoneid = ira->ira_zoneid;
                ixa->ixa_ifindex = 0;
                ixa->ixa_ipst = ipst;
                ixa->ixa_cred = kcred;
                ixa->ixa_cpid = NOPID;
        }

        if (str && tcps->tcps_dbg) {
                (void) strlog(TCP_MOD_ID, 0, 1, SL_TRACE,
                    "tcp_xmit_early_reset: '%s', seq 0x%x, ack 0x%x, "
                    "flags 0x%x",
                    str, seq, ack, ctl);
        }
        if (mp->b_datap->db_ref != 1) {
                mblk_t *mp1 = copyb(mp);
                freemsg(mp);
                mp = mp1;
                if (mp == NULL)
                        goto done;
        } else if (mp->b_cont) {
                freemsg(mp->b_cont);
                mp->b_cont = NULL;
                DB_CKSUMFLAGS(mp) = 0;
        }
        /*
         * We skip reversing source route here.
         * (for now we replace all IP options with EOL)
         */
        if (IPH_HDR_VERSION(mp->b_rptr) == IPV4_VERSION) {
                ipha = (ipha_t *)mp->b_rptr;
                for (i = IP_SIMPLE_HDR_LENGTH; i < (int)ip_hdr_len; i++)
                        mp->b_rptr[i] = IPOPT_EOL;
                /*
                 * Make sure that src address isn't flagrantly invalid.
                 * Not all broadcast address checking for the src address
                 * is possible, since we don't know the netmask of the src
                 * addr.  No check for destination address is done, since
                 * IP will not pass up a packet with a broadcast dest
                 * address to TCP.  Similar checks are done below for IPv6.
                 */
                if (ipha->ipha_src == 0 || ipha->ipha_src == INADDR_BROADCAST ||
                    CLASSD(ipha->ipha_src)) {
                        BUMP_MIB(&ipst->ips_ip_mib, ipIfStatsInDiscards);
                        ip_drop_input("ipIfStatsInDiscards", mp, NULL);
                        freemsg(mp);
                        goto done;
                }
        } else {
                ip6h = (ip6_t *)mp->b_rptr;

                if (IN6_IS_ADDR_UNSPECIFIED(&ip6h->ip6_src) ||
                    IN6_IS_ADDR_MULTICAST(&ip6h->ip6_src)) {
                        BUMP_MIB(&ipst->ips_ip6_mib, ipIfStatsInDiscards);
                        ip_drop_input("ipIfStatsInDiscards", mp, NULL);
                        freemsg(mp);
                        goto done;
                }

                /* Remove any extension headers assuming partial overlay */
                if (ip_hdr_len > IPV6_HDR_LEN) {
                        uint8_t *to;

                        to = mp->b_rptr + ip_hdr_len - IPV6_HDR_LEN;
                        ovbcopy(ip6h, to, IPV6_HDR_LEN);
                        mp->b_rptr += ip_hdr_len - IPV6_HDR_LEN;
                        ip_hdr_len = IPV6_HDR_LEN;
                        ip6h = (ip6_t *)mp->b_rptr;
                        ip6h->ip6_nxt = IPPROTO_TCP;
                }
        }
        tcpha = (tcpha_t *)&mp->b_rptr[ip_hdr_len];
        if (tcpha->tha_flags & TH_RST) {
                freemsg(mp);
                goto done;
        }
        tcpha->tha_offset_and_reserved = (5 << 4);
        len = ip_hdr_len + sizeof (tcpha_t);
        mp->b_wptr = &mp->b_rptr[len];
        if (IPH_HDR_VERSION(mp->b_rptr) == IPV4_VERSION) {
                ipha->ipha_length = htons(len);
                /* Swap addresses */
                v4addr = ipha->ipha_src;
                ipha->ipha_src = ipha->ipha_dst;
                ipha->ipha_dst = v4addr;
                ipha->ipha_ident = 0;
                ipha->ipha_ttl = (uchar_t)tcps->tcps_ipv4_ttl;
                ixa->ixa_flags |= IXAF_IS_IPV4;
                ixa->ixa_ip_hdr_length = ip_hdr_len;
        } else {
                ip6h->ip6_plen = htons(len - IPV6_HDR_LEN);
                /* Swap addresses */
                v6addr = ip6h->ip6_src;
                ip6h->ip6_src = ip6h->ip6_dst;
                ip6h->ip6_dst = v6addr;
                ip6h->ip6_hops = (uchar_t)tcps->tcps_ipv6_hoplimit;
                ixa->ixa_flags &= ~IXAF_IS_IPV4;

                if (IN6_IS_ADDR_LINKSCOPE(&ip6h->ip6_dst)) {
                        ixa->ixa_flags |= IXAF_SCOPEID_SET;
                        ixa->ixa_scopeid = ira->ira_ruifindex;
                }
                ixa->ixa_ip_hdr_length = IPV6_HDR_LEN;
        }
        ixa->ixa_pktlen = len;

        /* Swap the ports */
        port = tcpha->tha_fport;
        tcpha->tha_fport = tcpha->tha_lport;
        tcpha->tha_lport = port;

        tcpha->tha_ack = htonl(ack);
        tcpha->tha_seq = htonl(seq);
        tcpha->tha_win = 0;
        tcpha->tha_sum = htons(sizeof (tcpha_t));
        tcpha->tha_flags = (uint8_t)ctl;
        if (ctl & TH_RST) {
                if (ctl & TH_ACK) {
                        /*
                         * Probe connection rejection here.
                         * tcp_xmit_listeners_reset() drops non-SYN segments
                         * that do not specify TH_ACK in their flags without
                         * calling this function.  As a consequence, if this
                         * function is called with a TH_RST|TH_ACK ctl argument,
                         * it is being called in response to a SYN segment
                         * and thus the tcp:::accept-refused probe point
                         * is valid here.
                         */
                        DTRACE_TCP5(accept__refused, mblk_t *, NULL,
                            void, NULL, void_ip_t *, mp->b_rptr, tcp_t *, NULL,
                            tcph_t *, tcpha);
                }
                TCPS_BUMP_MIB(tcps, tcpOutRsts);
                TCPS_BUMP_MIB(tcps, tcpOutControl);
        }

        if (ira->ira_flags & IRAF_IPSEC_SECURE) {
                /*
                 * Apply IPsec based on how IPsec was applied to
                 * the packet that caused the RST.
                 */
                if (!ipsec_in_to_out(ira, ixa, mp, ipha, ip6h)) {
                        BUMP_MIB(&ipst->ips_ip_mib, ipIfStatsOutDiscards);
                        /* Note: mp already consumed and ip_drop_packet done */
                        goto done;
                }
        } else {
                /*
                 * This is in clear. The RST message we are building
                 * here should go out in clear, independent of our policy.
                 */
                ixa->ixa_flags |= IXAF_NO_IPSEC;
        }

        DTRACE_TCP5(send, mblk_t *, NULL, ip_xmit_attr_t *, ixa,
            __dtrace_tcp_void_ip_t *, mp->b_rptr, tcp_t *, NULL,
            __dtrace_tcp_tcph_t *, tcpha);

        /*
         * NOTE:  one might consider tracing a TCP packet here, but
         * this function has no active TCP state and no tcp structure
         * that has a trace buffer.  If we traced here, we would have
         * to keep a local trace buffer in tcp_record_trace().
         */

        (void) ip_output_simple(mp, ixa);
done:
        ixa_cleanup(ixa);
        if (need_refrele) {
                ASSERT(ixa != &ixas);
                ixa_refrele(ixa);
        }
}

/*
 * Generate a "no listener here" RST in response to an "unknown" segment.
 * connp is set by caller when RST is in response to an unexpected
 * inbound packet for which there is active tcp state in the system.
 * Note that we are reusing the incoming mp to construct the outgoing RST.
 */
void
tcp_xmit_listeners_reset(mblk_t *mp, ip_recv_attr_t *ira, ip_stack_t *ipst,
    conn_t *connp)
{
        uchar_t         *rptr;
        uint32_t        seg_len;
        tcpha_t         *tcpha;
        uint32_t        seg_seq;
        uint32_t        seg_ack;
        uint_t          flags;
        ipha_t          *ipha;
        ip6_t           *ip6h;
        boolean_t       policy_present;
        netstack_t      *ns = ipst->ips_netstack;
        tcp_stack_t     *tcps = ns->netstack_tcp;
        ipsec_stack_t   *ipss = tcps->tcps_netstack->netstack_ipsec;
        uint_t          ip_hdr_len = ira->ira_ip_hdr_length;

        TCP_STAT(tcps, tcp_no_listener);

        /*
         * DTrace this "unknown" segment as a tcp:::receive, as we did
         * just receive something that was TCP.
         */
        DTRACE_TCP5(receive, mblk_t *, NULL, ip_xmit_attr_t *, NULL,
            __dtrace_tcp_void_ip_t *, mp->b_rptr, tcp_t *, NULL,
            __dtrace_tcp_tcph_t *, &mp->b_rptr[ip_hdr_len]);

        if (IPH_HDR_VERSION(mp->b_rptr) == IPV4_VERSION) {
                policy_present = ipss->ipsec_inbound_v4_policy_present;
                ipha = (ipha_t *)mp->b_rptr;
                ip6h = NULL;
        } else {
                policy_present = ipss->ipsec_inbound_v6_policy_present;
                ipha = NULL;
                ip6h = (ip6_t *)mp->b_rptr;
        }

        if (policy_present) {
                /*
                 * The conn_t parameter is NULL because we already know
                 * nobody's home.
                 */
                mp = ipsec_check_global_policy(mp, (conn_t *)NULL, ipha, ip6h,
                    ira, ns);
                if (mp == NULL)
                        return;
        }
        rptr = mp->b_rptr;

        tcpha = (tcpha_t *)&rptr[ip_hdr_len];
        seg_seq = ntohl(tcpha->tha_seq);
        seg_ack = ntohl(tcpha->tha_ack);
        flags = tcpha->tha_flags;

        seg_len = msgdsize(mp) - (TCP_HDR_LENGTH(tcpha) + ip_hdr_len);
        if (flags & TH_RST) {
                freemsg(mp);
        } else if (flags & TH_ACK) {
                tcp_xmit_early_reset("no tcp, reset", mp, seg_ack, 0, TH_RST,
                    ira, ipst, connp);
        } else {
                if (flags & TH_SYN) {
                        seg_len++;
                } else {
                        /*
                         * Here we violate the RFC.  Note that a normal
                         * TCP will never send a segment without the ACK
                         * flag, except for RST or SYN segment.  This
                         * segment is neither.  Just drop it on the
                         * floor.
                         */
                        freemsg(mp);
                        TCP_STAT(tcps, tcp_rst_unsent);
                        return;
                }

                tcp_xmit_early_reset("no tcp, reset/ack", mp, 0,
                    seg_seq + seg_len, TH_RST | TH_ACK, ira, ipst, connp);
        }
}

/*
 * Helper function for tcp_xmit_mp() in handling connection set up flag
 * options setting.
 */
static void
tcp_xmit_mp_aux_iss(tcp_t *tcp, conn_t *connp, tcpha_t *tcpha, mblk_t *mp,
    uint_t *flags)
{
        uint32_t u1;
        uint8_t *wptr = mp->b_wptr;
        tcp_stack_t *tcps = tcp->tcp_tcps;
        boolean_t add_sack = B_FALSE;

        /*
         * If TCP_ISS_VALID and the seq number is tcp_iss,
         * TCP can only be in SYN-SENT, SYN-RCVD or
         * FIN-WAIT-1 state.  It can be FIN-WAIT-1 if
         * our SYN is not ack'ed but the app closes this
         * TCP connection.
         */
        ASSERT(tcp->tcp_state == TCPS_SYN_SENT ||
            tcp->tcp_state == TCPS_SYN_RCVD ||
            tcp->tcp_state == TCPS_FIN_WAIT_1);

        /*
         * Tack on the MSS option.  It is always needed
         * for both active and passive open.
         *
         * MSS option value should be interface MTU - MIN
         * TCP/IP header according to RFC 793 as it means
         * the maximum segment size TCP can receive.  But
         * to get around some broken middle boxes/end hosts
         * out there, we allow the option value to be the
         * same as the MSS option size on the peer side.
         * In this way, the other side will not send
         * anything larger than they can receive.
         *
         * Note that for SYN_SENT state, the ndd param
         * tcp_use_smss_as_mss_opt has no effect as we
         * don't know the peer's MSS option value. So
         * the only case we need to take care of is in
         * SYN_RCVD state, which is done later.
         */
        wptr[0] = TCPOPT_MAXSEG;
        wptr[1] = TCPOPT_MAXSEG_LEN;
        wptr += 2;
        u1 = tcp->tcp_initial_pmtu - (connp->conn_ipversion == IPV4_VERSION ?
            IP_SIMPLE_HDR_LENGTH : IPV6_HDR_LEN) - TCP_MIN_HEADER_LENGTH;
        U16_TO_BE16(u1, wptr);
        wptr += 2;

        /* Update the offset to cover the additional word */
        tcpha->tha_offset_and_reserved += (1 << 4);

        switch (tcp->tcp_state) {
        case TCPS_SYN_SENT:
                *flags = TH_SYN;

                if (tcp->tcp_snd_sack_ok)
                        add_sack = B_TRUE;

                if (tcp->tcp_snd_ts_ok) {
                        uint32_t llbolt = (uint32_t)LBOLT_FASTPATH;

                        if (add_sack) {
                                wptr[0] = TCPOPT_SACK_PERMITTED;
                                wptr[1] = TCPOPT_SACK_OK_LEN;
                                add_sack = B_FALSE;
                        } else {
                                wptr[0] = TCPOPT_NOP;
                                wptr[1] = TCPOPT_NOP;
                        }
                        wptr[2] = TCPOPT_TSTAMP;
                        wptr[3] = TCPOPT_TSTAMP_LEN;
                        wptr += 4;
                        U32_TO_BE32(llbolt, wptr);
                        wptr += 4;
                        ASSERT(tcp->tcp_ts_recent == 0);
                        U32_TO_BE32(0L, wptr);
                        wptr += 4;
                        tcpha->tha_offset_and_reserved += (3 << 4);
                }

                /*
                 * Set up all the bits to tell other side
                 * we are ECN capable.
                 */
                if (tcp->tcp_ecn_ok)
                        *flags |= (TH_ECE | TH_CWR);

                break;

        case TCPS_SYN_RCVD:
                *flags |= TH_SYN;

                /*
                 * Reset the MSS option value to be SMSS
                 * We should probably add back the bytes
                 * for timestamp option and IPsec.  We
                 * don't do that as this is a workaround
                 * for broken middle boxes/end hosts, it
                 * is better for us to be more cautious.
                 * They may not take these things into
                 * account in their SMSS calculation.  Thus
                 * the peer's calculated SMSS may be smaller
                 * than what it can be.  This should be OK.
                 */
                if (tcps->tcps_use_smss_as_mss_opt) {
                        u1 = tcp->tcp_mss;
                        /*
                         * Note that wptr points just past the MSS
                         * option value.
                         */
                        U16_TO_BE16(u1, wptr - 2);
                }

                /*
                 * tcp_snd_ts_ok can only be set in TCPS_SYN_RCVD
                 * when the peer also uses timestamps option.  And
                 * the TCP header template must have already been
                 * updated to include the timestamps option.
                 */
                if (tcp->tcp_snd_sack_ok) {
                        if (tcp->tcp_snd_ts_ok) {
                                uint8_t *tmp_wptr;

                                /*
                                 * Use the NOP in the header just
                                 * before timestamps opton.
                                 */
                                tmp_wptr = (uint8_t *)tcpha +
                                    TCP_MIN_HEADER_LENGTH;
                                ASSERT(tmp_wptr[0] == TCPOPT_NOP &&
                                    tmp_wptr[1] == TCPOPT_NOP);
                                tmp_wptr[0] = TCPOPT_SACK_PERMITTED;
                                tmp_wptr[1] = TCPOPT_SACK_OK_LEN;
                        } else {
                                add_sack = B_TRUE;
                        }
                }


                /*
                 * If the other side is ECN capable, reply
                 * that we are also ECN capable.
                 */
                if (tcp->tcp_ecn_ok)
                        *flags |= TH_ECE;
                break;

        default:
                /*
                 * The above ASSERT() makes sure that this
                 * must be FIN-WAIT-1 state.  Our SYN has
                 * not been ack'ed so retransmit it.
                 */
                *flags |= TH_SYN;
                break;
        }

        if (add_sack) {
                wptr[0] = TCPOPT_NOP;
                wptr[1] = TCPOPT_NOP;
                wptr[2] = TCPOPT_SACK_PERMITTED;
                wptr[3] = TCPOPT_SACK_OK_LEN;
                wptr += TCPOPT_REAL_SACK_OK_LEN;
                tcpha->tha_offset_and_reserved += (1 << 4);
        }

        if (tcp->tcp_snd_ws_ok) {
                wptr[0] =  TCPOPT_NOP;
                wptr[1] =  TCPOPT_WSCALE;
                wptr[2] =  TCPOPT_WS_LEN;
                wptr[3] = (uchar_t)tcp->tcp_rcv_ws;
                wptr += TCPOPT_REAL_WS_LEN;
                tcpha->tha_offset_and_reserved += (1 << 4);
        }

        mp->b_wptr = wptr;
        u1 = (int)(mp->b_wptr - mp->b_rptr);
        /*
         * Get IP set to checksum on our behalf
         * Include the adjustment for a source route if any.
         */
        u1 += connp->conn_sum;
        u1 = (u1 >> 16) + (u1 & 0xFFFF);
        tcpha->tha_sum = htons(u1);
        TCPS_BUMP_MIB(tcps, tcpOutControl);
}

/*
 * Helper function for tcp_xmit_mp() in handling connection tear down
 * flag setting and state changes.
 */
static void
tcp_xmit_mp_aux_fss(tcp_t *tcp, ip_xmit_attr_t *ixa, uint_t *flags)
{
        if (!tcp->tcp_fin_acked) {
                *flags |= TH_FIN;
                TCPS_BUMP_MIB(tcp->tcp_tcps, tcpOutControl);
        }
        if (!tcp->tcp_fin_sent) {
                tcp->tcp_fin_sent = B_TRUE;
                switch (tcp->tcp_state) {
                case TCPS_SYN_RCVD:
                        tcp->tcp_state = TCPS_FIN_WAIT_1;
                        DTRACE_TCP6(state__change, void, NULL,
                            ip_xmit_attr_t *, ixa, void, NULL,
                            tcp_t *, tcp, void, NULL,
                            int32_t, TCPS_SYN_RCVD);
                        break;
                case TCPS_ESTABLISHED:
                        tcp->tcp_state = TCPS_FIN_WAIT_1;
                        DTRACE_TCP6(state__change, void, NULL,
                            ip_xmit_attr_t *, ixa, void, NULL,
                            tcp_t *, tcp, void, NULL,
                            int32_t, TCPS_ESTABLISHED);
                        break;
                case TCPS_CLOSE_WAIT:
                        tcp->tcp_state = TCPS_LAST_ACK;
                        DTRACE_TCP6(state__change, void, NULL,
                            ip_xmit_attr_t *, ixa, void, NULL,
                            tcp_t *, tcp, void, NULL,
                            int32_t, TCPS_CLOSE_WAIT);
                        break;
                }
                if (tcp->tcp_suna == tcp->tcp_snxt)
                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                tcp->tcp_snxt = tcp->tcp_fss + 1;
        }
}

/*
 * tcp_xmit_mp is called to return a pointer to an mblk chain complete with
 * ip and tcp header ready to pass down to IP.  If the mp passed in is
 * non-NULL, then up to max_to_send bytes of data will be dup'ed off that
 * mblk. (If sendall is not set the dup'ing will stop at an mblk boundary
 * otherwise it will dup partial mblks.)
 * Otherwise, an appropriate ACK packet will be generated.  This
 * routine is not usually called to send new data for the first time.  It
 * is mostly called out of the timer for retransmits, and to generate ACKs.
 *
 * If offset is not NULL, the returned mblk chain's first mblk's b_rptr will
 * be adjusted by *offset.  And after dupb(), the offset and the ending mblk
 * of the original mblk chain will be returned in *offset and *end_mp.
 */
mblk_t *
tcp_xmit_mp(tcp_t *tcp, mblk_t *mp, int32_t max_to_send, int32_t *offset,
    mblk_t **end_mp, uint32_t seq, boolean_t sendall, uint32_t *seg_len,
    boolean_t rexmit)
{
        int     data_length;
        int32_t off = 0;
        uint_t  flags;
        mblk_t  *mp1;
        mblk_t  *mp2;
        uchar_t *rptr;
        tcpha_t *tcpha;
        int32_t num_sack_blk = 0;
        int32_t sack_opt_len = 0;
        tcp_stack_t     *tcps = tcp->tcp_tcps;
        conn_t          *connp = tcp->tcp_connp;
        ip_xmit_attr_t  *ixa = connp->conn_ixa;

        /* Allocate for our maximum TCP header + link-level */
        mp1 = allocb(connp->conn_ht_iphc_allocated + tcps->tcps_wroff_xtra,
            BPRI_MED);
        if (mp1 == NULL)
                return (NULL);
        data_length = 0;

        /*
         * Note that tcp_mss has been adjusted to take into account the
         * timestamp option if applicable.  Because SACK options do not
         * appear in every TCP segments and they are of variable lengths,
         * they cannot be included in tcp_mss.  Thus we need to calculate
         * the actual segment length when we need to send a segment which
         * includes SACK options.
         */
        if (tcp->tcp_snd_sack_ok && tcp->tcp_num_sack_blk > 0) {
                num_sack_blk = MIN(tcp->tcp_max_sack_blk,
                    tcp->tcp_num_sack_blk);
                sack_opt_len = num_sack_blk * sizeof (sack_blk_t) +
                    TCPOPT_NOP_LEN * 2 + TCPOPT_HEADER_LEN;
                if (max_to_send + sack_opt_len > tcp->tcp_mss)
                        max_to_send -= sack_opt_len;
        }

        if (offset != NULL) {
                off = *offset;
                /* We use offset as an indicator that end_mp is not NULL. */
                *end_mp = NULL;
        }
        for (mp2 = mp1; mp && data_length != max_to_send; mp = mp->b_cont) {
                /* This could be faster with cooperation from downstream */
                if (mp2 != mp1 && !sendall &&
                    data_length + (int)(mp->b_wptr - mp->b_rptr) >
                    max_to_send)
                        /*
                         * Don't send the next mblk since the whole mblk
                         * does not fit.
                         */
                        break;
                mp2->b_cont = dupb(mp);
                mp2 = mp2->b_cont;
                if (!mp2) {
                        freemsg(mp1);
                        return (NULL);
                }
                mp2->b_rptr += off;
                ASSERT((uintptr_t)(mp2->b_wptr - mp2->b_rptr) <=
                    (uintptr_t)INT_MAX);

                data_length += (int)(mp2->b_wptr - mp2->b_rptr);
                if (data_length > max_to_send) {
                        mp2->b_wptr -= data_length - max_to_send;
                        data_length = max_to_send;
                        off = mp2->b_wptr - mp->b_rptr;
                        break;
                } else {
                        off = 0;
                }
        }
        if (offset != NULL) {
                *offset = off;
                *end_mp = mp;
        }
        if (seg_len != NULL) {
                *seg_len = data_length;
        }

        /* Update the latest receive window size in TCP header. */
        tcp->tcp_tcpha->tha_win = htons(tcp->tcp_rwnd >> tcp->tcp_rcv_ws);

        rptr = mp1->b_rptr + tcps->tcps_wroff_xtra;
        mp1->b_rptr = rptr;
        mp1->b_wptr = rptr + connp->conn_ht_iphc_len + sack_opt_len;
        bcopy(connp->conn_ht_iphc, rptr, connp->conn_ht_iphc_len);
        tcpha = (tcpha_t *)&rptr[ixa->ixa_ip_hdr_length];
        tcpha->tha_seq = htonl(seq);

        /*
         * Use tcp_unsent to determine if the PUSH bit should be used assumes
         * that this function was called from tcp_wput_data. Thus, when called
         * to retransmit data the setting of the PUSH bit may appear some
         * what random in that it might get set when it should not. This
         * should not pose any performance issues.
         */
        if (data_length != 0 && (tcp->tcp_unsent == 0 ||
            tcp->tcp_unsent == data_length)) {
                flags = TH_ACK | TH_PUSH;
        } else {
                flags = TH_ACK;
        }

        if (tcp->tcp_ecn_ok) {
                if (tcp->tcp_ecn_echo_on)
                        flags |= TH_ECE;

                /*
                 * Only set ECT bit and ECN_CWR if a segment contains new data.
                 * There is no TCP flow control for non-data segments, and
                 * only data segment is transmitted reliably.
                 */
                if (data_length > 0 && !rexmit) {
                        TCP_SET_ECT(tcp, rptr);
                        if (tcp->tcp_cwr && !tcp->tcp_ecn_cwr_sent) {
                                flags |= TH_CWR;
                                tcp->tcp_ecn_cwr_sent = B_TRUE;
                        }
                }
        }

        /* Check if there is any special processing needs to be done. */
        if (tcp->tcp_valid_bits) {
                uint32_t u1;

                /* We don't allow having SYN and FIN in the same segment... */
                if ((tcp->tcp_valid_bits & TCP_ISS_VALID) &&
                    seq == tcp->tcp_iss) {
                        /* Need to do connection set up processing. */
                        tcp_xmit_mp_aux_iss(tcp, connp, tcpha, mp1, &flags);
                } else if ((tcp->tcp_valid_bits & TCP_FSS_VALID) &&
                    (seq + data_length) == tcp->tcp_fss) {
                        /* Need to do connection tear down processing. */
                        tcp_xmit_mp_aux_fss(tcp, ixa, &flags);
                }

                /*
                 * Need to do urgent pointer processing.
                 *
                 * Note the trick here.  u1 is unsigned.  When tcp_urg
                 * is smaller than seq, u1 will become a very huge value.
                 * So the comparison will fail.  Also note that tcp_urp
                 * should be positive, see RFC 793 page 17.
                 */
                u1 = tcp->tcp_urg - seq + TCP_OLD_URP_INTERPRETATION;
                if ((tcp->tcp_valid_bits & TCP_URG_VALID) && u1 != 0 &&
                    u1 < (uint32_t)(64 * 1024)) {
                        flags |= TH_URG;
                        TCPS_BUMP_MIB(tcps, tcpOutUrg);
                        tcpha->tha_urp = htons(u1);
                }
        }
        tcpha->tha_flags = (uchar_t)flags;
        tcp->tcp_rack = tcp->tcp_rnxt;
        tcp->tcp_rack_cnt = 0;

        /* Fill in the current value of timestamps option. */
        if (tcp->tcp_snd_ts_ok) {
                if (tcp->tcp_state != TCPS_SYN_SENT) {
                        uint32_t llbolt = (uint32_t)LBOLT_FASTPATH;

                        U32_TO_BE32(llbolt,
                            (char *)tcpha + TCP_MIN_HEADER_LENGTH+4);
                        U32_TO_BE32(tcp->tcp_ts_recent,
                            (char *)tcpha + TCP_MIN_HEADER_LENGTH+8);
                }
        }

        /* Fill in the SACK blocks. */
        if (num_sack_blk > 0) {
                uchar_t *wptr = (uchar_t *)tcpha + connp->conn_ht_ulp_len;
                sack_blk_t *tmp;
                int32_t i;

                wptr[0] = TCPOPT_NOP;
                wptr[1] = TCPOPT_NOP;
                wptr[2] = TCPOPT_SACK;
                wptr[3] = TCPOPT_HEADER_LEN + num_sack_blk *
                    sizeof (sack_blk_t);
                wptr += TCPOPT_REAL_SACK_LEN;

                tmp = tcp->tcp_sack_list;
                for (i = 0; i < num_sack_blk; i++) {
                        U32_TO_BE32(tmp[i].begin, wptr);
                        wptr += sizeof (tcp_seq);
                        U32_TO_BE32(tmp[i].end, wptr);
                        wptr += sizeof (tcp_seq);
                }
                tcpha->tha_offset_and_reserved += ((num_sack_blk * 2 + 1) << 4);
        }
        ASSERT((uintptr_t)(mp1->b_wptr - rptr) <= (uintptr_t)INT_MAX);
        data_length += (int)(mp1->b_wptr - rptr);

        ixa->ixa_pktlen = data_length;

        if (ixa->ixa_flags & IXAF_IS_IPV4) {
                ((ipha_t *)rptr)->ipha_length = htons(data_length);
        } else {
                ip6_t *ip6 = (ip6_t *)rptr;

                ip6->ip6_plen = htons(data_length - IPV6_HDR_LEN);
        }

        /*
         * Prime pump for IP
         * Include the adjustment for a source route if any.
         */
        data_length -= ixa->ixa_ip_hdr_length;
        data_length += connp->conn_sum;
        data_length = (data_length >> 16) + (data_length & 0xFFFF);
        tcpha->tha_sum = htons(data_length);
        if (tcp->tcp_ip_forward_progress) {
                tcp->tcp_ip_forward_progress = B_FALSE;
                connp->conn_ixa->ixa_flags |= IXAF_REACH_CONF;
        } else {
                connp->conn_ixa->ixa_flags &= ~IXAF_REACH_CONF;
        }
        return (mp1);
}

/*
 * If this routine returns B_TRUE, TCP can generate a RST in response
 * to a segment.  If it returns B_FALSE, TCP should not respond.
 */
static boolean_t
tcp_send_rst_chk(tcp_stack_t *tcps)
{
        int64_t now;

        /*
         * TCP needs to protect itself from generating too many RSTs.
         * This can be a DoS attack by sending us random segments
         * soliciting RSTs.
         *
         * What we do here is to have a limit of tcp_rst_sent_rate RSTs
         * in each 1 second interval.  In this way, TCP still generate
         * RSTs in normal cases but when under attack, the impact is
         * limited.
         */
        if (tcps->tcps_rst_sent_rate_enabled != 0) {
                now = ddi_get_lbolt64();
                if (TICK_TO_MSEC(now - tcps->tcps_last_rst_intrvl) >
                    1*SECONDS) {
                        tcps->tcps_last_rst_intrvl = now;
                        tcps->tcps_rst_cnt = 1;
                } else if (++tcps->tcps_rst_cnt > tcps->tcps_rst_sent_rate) {
                        return (B_FALSE);
                }
        }
        return (B_TRUE);
}

/*
 * This function handles all retransmissions if SACK is enabled for this
 * connection.  First it calculates how many segments can be retransmitted
 * based on tcp_pipe.  Then it goes thru the notsack list to find eligible
 * segments.  A segment is eligible if sack_cnt for that segment is greater
 * than or equal tcp_dupack_fast_retransmit.  After it has retransmitted
 * all eligible segments, it checks to see if TCP can send some new segments
 * (fast recovery).  If it can, set the appropriate flag for tcp_input_data().
 *
 * Parameters:
 *      tcp_t *tcp: the tcp structure of the connection.
 *      uint_t *flags: in return, appropriate value will be set for
 *      tcp_input_data().
 */
void
tcp_sack_rexmit(tcp_t *tcp, uint_t *flags)
{
        notsack_blk_t   *notsack_blk;
        int32_t         usable_swnd;
        int32_t         mss;
        uint32_t        seg_len;
        mblk_t          *xmit_mp;
        tcp_stack_t     *tcps = tcp->tcp_tcps;

        ASSERT(tcp->tcp_notsack_list != NULL);
        ASSERT(tcp->tcp_rexmit == B_FALSE);

        /* Defensive coding in case there is a bug... */
        if (tcp->tcp_notsack_list == NULL) {
                return;
        }
        notsack_blk = tcp->tcp_notsack_list;
        mss = tcp->tcp_mss;

        /*
         * Limit the num of outstanding data in the network to be
         * tcp_cwnd_ssthresh, which is half of the original congestion wnd.
         */
        usable_swnd = tcp->tcp_cwnd_ssthresh - tcp->tcp_pipe;

        /* At least retransmit 1 MSS of data. */
        if (usable_swnd <= 0) {
                usable_swnd = mss;
        }

        /* Make sure no new RTT samples will be taken. */
        tcp->tcp_csuna = tcp->tcp_snxt;

        notsack_blk = tcp->tcp_notsack_list;
        while (usable_swnd > 0) {
                mblk_t          *snxt_mp, *tmp_mp;
                tcp_seq         begin = tcp->tcp_sack_snxt;
                tcp_seq         end;
                int32_t         off;

                for (; notsack_blk != NULL; notsack_blk = notsack_blk->next) {
                        if (SEQ_GT(notsack_blk->end, begin) &&
                            (notsack_blk->sack_cnt >=
                            tcps->tcps_dupack_fast_retransmit)) {
                                end = notsack_blk->end;
                                if (SEQ_LT(begin, notsack_blk->begin)) {
                                        begin = notsack_blk->begin;
                                }
                                break;
                        }
                }
                /*
                 * All holes are filled.  Manipulate tcp_cwnd to send more
                 * if we can.  Note that after the SACK recovery, tcp_cwnd is
                 * set to tcp_cwnd_ssthresh.
                 */
                if (notsack_blk == NULL) {
                        usable_swnd = tcp->tcp_cwnd_ssthresh - tcp->tcp_pipe;
                        if (usable_swnd <= 0 || tcp->tcp_unsent == 0) {
                                tcp->tcp_cwnd = tcp->tcp_snxt - tcp->tcp_suna;
                                ASSERT(tcp->tcp_cwnd > 0);
                                return;
                        } else {
                                usable_swnd = usable_swnd / mss;
                                tcp->tcp_cwnd = tcp->tcp_snxt - tcp->tcp_suna +
                                    MAX(usable_swnd * mss, mss);
                                *flags |= TH_XMIT_NEEDED;
                                return;
                        }
                }

                /*
                 * Note that we may send more than usable_swnd allows here
                 * because of round off, but no more than 1 MSS of data.
                 */
                seg_len = end - begin;
                if (seg_len > mss)
                        seg_len = mss;
                snxt_mp = tcp_get_seg_mp(tcp, begin, &off);
                ASSERT(snxt_mp != NULL);
                /* This should not happen.  Defensive coding again... */
                if (snxt_mp == NULL) {
                        return;
                }

                xmit_mp = tcp_xmit_mp(tcp, snxt_mp, seg_len, &off,
                    &tmp_mp, begin, B_TRUE, &seg_len, B_TRUE);
                if (xmit_mp == NULL)
                        return;

                usable_swnd -= seg_len;
                tcp->tcp_pipe += seg_len;
                tcp->tcp_sack_snxt = begin + seg_len;

                tcp_send_data(tcp, xmit_mp);

                /*
                 * Update the send timestamp to avoid false retransmission.
                 */
                snxt_mp->b_prev = (mblk_t *)ddi_get_lbolt();

                TCPS_BUMP_MIB(tcps, tcpRetransSegs);
                TCPS_UPDATE_MIB(tcps, tcpRetransBytes, seg_len);
                TCPS_BUMP_MIB(tcps, tcpOutSackRetransSegs);
                /*
                 * Update tcp_rexmit_max to extend this SACK recovery phase.
                 * This happens when new data sent during fast recovery is
                 * also lost.  If TCP retransmits those new data, it needs
                 * to extend SACK recover phase to avoid starting another
                 * fast retransmit/recovery unnecessarily.
                 */
                if (SEQ_GT(tcp->tcp_sack_snxt, tcp->tcp_rexmit_max)) {
                        tcp->tcp_rexmit_max = tcp->tcp_sack_snxt;
                }
        }
}

/*
 * tcp_ss_rexmit() is called to do slow start retransmission after a timeout
 * or ICMP errors.
 */
void
tcp_ss_rexmit(tcp_t *tcp)
{
        uint32_t        snxt;
        uint32_t        smax;
        int32_t         win;
        int32_t         mss;
        int32_t         off;
        mblk_t          *snxt_mp;
        tcp_stack_t     *tcps = tcp->tcp_tcps;

        /*
         * Note that tcp_rexmit can be set even though TCP has retransmitted
         * all unack'ed segments.
         */
        if (SEQ_LT(tcp->tcp_rexmit_nxt, tcp->tcp_rexmit_max)) {
                smax = tcp->tcp_rexmit_max;
                snxt = tcp->tcp_rexmit_nxt;
                if (SEQ_LT(snxt, tcp->tcp_suna)) {
                        snxt = tcp->tcp_suna;
                }
                win = MIN(tcp->tcp_cwnd, tcp->tcp_swnd);
                win -= snxt - tcp->tcp_suna;
                mss = tcp->tcp_mss;
                snxt_mp = tcp_get_seg_mp(tcp, snxt, &off);

                while (SEQ_LT(snxt, smax) && (win > 0) && (snxt_mp != NULL)) {
                        mblk_t  *xmit_mp;
                        mblk_t  *old_snxt_mp = snxt_mp;
                        uint32_t cnt = mss;

                        if (win < cnt) {
                                cnt = win;
                        }
                        if (SEQ_GT(snxt + cnt, smax)) {
                                cnt = smax - snxt;
                        }
                        xmit_mp = tcp_xmit_mp(tcp, snxt_mp, cnt, &off,
                            &snxt_mp, snxt, B_TRUE, &cnt, B_TRUE);
                        if (xmit_mp == NULL)
                                return;

                        tcp_send_data(tcp, xmit_mp);

                        snxt += cnt;
                        win -= cnt;
                        /*
                         * Update the send timestamp to avoid false
                         * retransmission.
                         */
                        old_snxt_mp->b_prev = (mblk_t *)ddi_get_lbolt();
                        TCPS_BUMP_MIB(tcps, tcpRetransSegs);
                        TCPS_UPDATE_MIB(tcps, tcpRetransBytes, cnt);

                        tcp->tcp_rexmit_nxt = snxt;
                }
                /*
                 * If we have transmitted all we have at the time
                 * we started the retranmission, we can leave
                 * the rest of the job to tcp_wput_data().  But we
                 * need to check the send window first.  If the
                 * win is not 0, go on with tcp_wput_data().
                 */
                if (SEQ_LT(snxt, smax) || win == 0) {
                        return;
                }
        }
        /* Only call tcp_wput_data() if there is data to be sent. */
        if (tcp->tcp_unsent) {
                tcp_wput_data(tcp, NULL, B_FALSE);
        }
}

/*
 * Do slow start retransmission after ICMP errors of PMTU changes.
 */
void
tcp_rexmit_after_error(tcp_t *tcp)
{
        /*
         * All sent data has been acknowledged or no data left to send, just
         * to return.
         */
        if (!SEQ_LT(tcp->tcp_suna, tcp->tcp_snxt) ||
            (tcp->tcp_xmit_head == NULL))
                return;

        if ((tcp->tcp_valid_bits & TCP_FSS_VALID) && (tcp->tcp_unsent == 0))
                tcp->tcp_rexmit_max = tcp->tcp_fss;
        else
                tcp->tcp_rexmit_max = tcp->tcp_snxt;

        tcp->tcp_rexmit_nxt = tcp->tcp_suna;
        tcp->tcp_rexmit = B_TRUE;
        tcp->tcp_dupack_cnt = 0;
        tcp_ss_rexmit(tcp);
}

/*
 * tcp_get_seg_mp() is called to get the pointer to a segment in the
 * send queue which starts at the given sequence number. If the given
 * sequence number is equal to last valid sequence number (tcp_snxt), the
 * returned mblk is the last valid mblk, and off is set to the length of
 * that mblk.
 *
 * send queue which starts at the given seq. no.
 *
 * Parameters:
 *      tcp_t *tcp: the tcp instance pointer.
 *      uint32_t seq: the starting seq. no of the requested segment.
 *      int32_t *off: after the execution, *off will be the offset to
 *              the returned mblk which points to the requested seq no.
 *              It is the caller's responsibility to send in a non-null off.
 *
 * Return:
 *      A mblk_t pointer pointing to the requested segment in send queue.
 */
static mblk_t *
tcp_get_seg_mp(tcp_t *tcp, uint32_t seq, int32_t *off)
{
        int32_t cnt;
        mblk_t  *mp;

        /* Defensive coding.  Make sure we don't send incorrect data. */
        if (SEQ_LT(seq, tcp->tcp_suna) || SEQ_GT(seq, tcp->tcp_snxt))
                return (NULL);

        cnt = seq - tcp->tcp_suna;
        mp = tcp->tcp_xmit_head;
        while (cnt > 0 && mp != NULL) {
                cnt -= mp->b_wptr - mp->b_rptr;
                if (cnt <= 0) {
                        cnt += mp->b_wptr - mp->b_rptr;
                        break;
                }
                mp = mp->b_cont;
        }
        ASSERT(mp != NULL);
        *off = cnt;
        return (mp);
}

/*
 * This routine adjusts next-to-send sequence number variables, in the
 * case where the reciever has shrunk it's window.
 */
void
tcp_update_xmit_tail(tcp_t *tcp, uint32_t snxt)
{
        mblk_t *xmit_tail;
        int32_t offset;

        tcp->tcp_snxt = snxt;

        /* Get the mblk, and the offset in it, as per the shrunk window */
        xmit_tail = tcp_get_seg_mp(tcp, snxt, &offset);
        ASSERT(xmit_tail != NULL);
        tcp->tcp_xmit_tail = xmit_tail;
        tcp->tcp_xmit_tail_unsent = xmit_tail->b_wptr -
            xmit_tail->b_rptr - offset;
}

/*
 * This handles the case when the receiver has shrunk its win. Per RFC 1122
 * if the receiver shrinks the window, i.e. moves the right window to the
 * left, the we should not send new data, but should retransmit normally the
 * old unacked data between suna and suna + swnd. We might has sent data
 * that is now outside the new window, pretend that we didn't send  it.
 */
static void
tcp_process_shrunk_swnd(tcp_t *tcp, uint32_t shrunk_count)
{
        uint32_t        snxt = tcp->tcp_snxt;

        ASSERT(shrunk_count > 0);

        if (!tcp->tcp_is_wnd_shrnk) {
                tcp->tcp_snxt_shrunk = snxt;
                tcp->tcp_is_wnd_shrnk = B_TRUE;
        } else if (SEQ_GT(snxt, tcp->tcp_snxt_shrunk)) {
                tcp->tcp_snxt_shrunk = snxt;
        }

        /* Pretend we didn't send the data outside the window */
        snxt -= shrunk_count;

        /* Reset all the values per the now shrunk window */
        tcp_update_xmit_tail(tcp, snxt);
        tcp->tcp_unsent += shrunk_count;

        /*
         * If the SACK option is set, delete the entire list of
         * notsack'ed blocks.
         */
        TCP_NOTSACK_REMOVE_ALL(tcp->tcp_notsack_list, tcp);

        if (tcp->tcp_suna == tcp->tcp_snxt && tcp->tcp_swnd == 0)
                /*
                 * Make sure the timer is running so that we will probe a zero
                 * window.
                 */
                TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
}

/*
 * tcp_fill_header is called by tcp_send() to fill the outgoing TCP header
 * with the template header, as well as other options such as time-stamp,
 * ECN and/or SACK.
 */
static void
tcp_fill_header(tcp_t *tcp, uchar_t *rptr, clock_t now, int num_sack_blk)
{
        tcpha_t *tcp_tmpl, *tcpha;
        uint32_t *dst, *src;
        int hdrlen;
        conn_t *connp = tcp->tcp_connp;

        ASSERT(OK_32PTR(rptr));

        /* Template header */
        tcp_tmpl = tcp->tcp_tcpha;

        /* Header of outgoing packet */
        tcpha = (tcpha_t *)(rptr + connp->conn_ixa->ixa_ip_hdr_length);

        /* dst and src are opaque 32-bit fields, used for copying */
        dst = (uint32_t *)rptr;
        src = (uint32_t *)connp->conn_ht_iphc;
        hdrlen = connp->conn_ht_iphc_len;

        /* Fill time-stamp option if needed */
        if (tcp->tcp_snd_ts_ok) {
                U32_TO_BE32((uint32_t)now,
                    (char *)tcp_tmpl + TCP_MIN_HEADER_LENGTH + 4);
                U32_TO_BE32(tcp->tcp_ts_recent,
                    (char *)tcp_tmpl + TCP_MIN_HEADER_LENGTH + 8);
        } else {
                ASSERT(connp->conn_ht_ulp_len == TCP_MIN_HEADER_LENGTH);
        }

        /*
         * Copy the template header; is this really more efficient than
         * calling bcopy()?  For simple IPv4/TCP, it may be the case,
         * but perhaps not for other scenarios.
         */
        dst[0] = src[0];
        dst[1] = src[1];
        dst[2] = src[2];
        dst[3] = src[3];
        dst[4] = src[4];
        dst[5] = src[5];
        dst[6] = src[6];
        dst[7] = src[7];
        dst[8] = src[8];
        dst[9] = src[9];
        if (hdrlen -= 40) {
                hdrlen >>= 2;
                dst += 10;
                src += 10;
                do {
                        *dst++ = *src++;
                } while (--hdrlen);
        }

        /*
         * Set the ECN info in the TCP header if it is not a zero
         * window probe.  Zero window probe is only sent in
         * tcp_wput_data() and tcp_timer().
         */
        if (tcp->tcp_ecn_ok && !tcp->tcp_zero_win_probe) {
                TCP_SET_ECT(tcp, rptr);

                if (tcp->tcp_ecn_echo_on)
                        tcpha->tha_flags |= TH_ECE;
                if (tcp->tcp_cwr && !tcp->tcp_ecn_cwr_sent) {
                        tcpha->tha_flags |= TH_CWR;
                        tcp->tcp_ecn_cwr_sent = B_TRUE;
                }
        }

        /* Fill in SACK options */
        if (num_sack_blk > 0) {
                uchar_t *wptr = rptr + connp->conn_ht_iphc_len;
                sack_blk_t *tmp;
                int32_t i;

                wptr[0] = TCPOPT_NOP;
                wptr[1] = TCPOPT_NOP;
                wptr[2] = TCPOPT_SACK;
                wptr[3] = TCPOPT_HEADER_LEN + num_sack_blk *
                    sizeof (sack_blk_t);
                wptr += TCPOPT_REAL_SACK_LEN;

                tmp = tcp->tcp_sack_list;
                for (i = 0; i < num_sack_blk; i++) {
                        U32_TO_BE32(tmp[i].begin, wptr);
                        wptr += sizeof (tcp_seq);
                        U32_TO_BE32(tmp[i].end, wptr);
                        wptr += sizeof (tcp_seq);
                }
                tcpha->tha_offset_and_reserved +=
                    ((num_sack_blk * 2 + 1) << 4);
        }
}