8322 nl: misleading-indentation

[unleashed/tickless.git] / usr / src / stand / lib / tcp / tcp.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 2006 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 * Copyright (c) 2016 by Delphix. All rights reserved.
 *
 * tcp.c, Code implementing the TCP protocol.
 */

#pragma ident   "%Z%%M% %I%     %E% SMI"

#include <sys/types.h>
#include <socket_impl.h>
#include <socket_inet.h>
#include <sys/sysmacros.h>
#include <sys/promif.h>
#include <sys/socket.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <net/if_types.h>
#include <sys/salib.h>

#include "ipv4.h"
#include "ipv4_impl.h"
#include "mac.h"
#include "mac_impl.h"
#include "v4_sum_impl.h"
#include <sys/bootdebug.h>
#include "tcp_inet.h"
#include "tcp_sack.h"
#include <inet/common.h>
#include <inet/mib2.h>

/*
 * We need to redefine BUMP_MIB/UPDATE_MIB to not have DTrace probes.
 */
#undef BUMP_MIB
#define BUMP_MIB(x) (x)++

#undef UPDATE_MIB
#define UPDATE_MIB(x, y) x += y

/*
 * MIB-2 stuff for SNMP
 */
mib2_tcp_t      tcp_mib;        /* SNMP fixed size info */

/* The TCP mib does not include the following errors. */
static uint_t tcp_cksum_errors;
static uint_t tcp_drops;

/* Macros for timestamp comparisons */
#define TSTMP_GEQ(a, b) ((int32_t)((a)-(b)) >= 0)
#define TSTMP_LT(a, b)  ((int32_t)((a)-(b)) < 0)

/*
 * Parameters for TCP Initial Send Sequence number (ISS) generation.
 * The ISS is calculated by adding three components: a time component
 * which grows by 1 every 4096 nanoseconds (versus every 4 microseconds
 * suggested by RFC 793, page 27);
 * a per-connection component which grows by 125000 for every new connection;
 * and an "extra" component that grows by a random amount centered
 * approximately on 64000.  This causes the the ISS generator to cycle every
 * 4.89 hours if no TCP connections are made, and faster if connections are
 * made.
 */
#define ISS_INCR        250000
#define ISS_NSEC_SHT    0

static uint32_t tcp_iss_incr_extra;     /* Incremented for each connection */

#define TCP_XMIT_LOWATER        4096
#define TCP_XMIT_HIWATER        49152
#define TCP_RECV_LOWATER        2048
#define TCP_RECV_HIWATER        49152

/*
 *  PAWS needs a timer for 24 days.  This is the number of ms in 24 days
 */
#define PAWS_TIMEOUT    ((uint32_t)(24*24*60*60*1000))

/*
 * TCP options struct returned from tcp_parse_options.
 */
typedef struct tcp_opt_s {
        uint32_t        tcp_opt_mss;
        uint32_t        tcp_opt_wscale;
        uint32_t        tcp_opt_ts_val;
        uint32_t        tcp_opt_ts_ecr;
        tcp_t           *tcp;
} tcp_opt_t;

/*
 * RFC1323-recommended phrasing of TSTAMP option, for easier parsing
 */

#ifdef _BIG_ENDIAN
#define TCPOPT_NOP_NOP_TSTAMP ((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) | \
        (TCPOPT_TSTAMP << 8) | 10)
#else
#define TCPOPT_NOP_NOP_TSTAMP ((10 << 24) | (TCPOPT_TSTAMP << 16) | \
        (TCPOPT_NOP << 8) | TCPOPT_NOP)
#endif

/*
 * Flags returned from tcp_parse_options.
 */
#define TCP_OPT_MSS_PRESENT     1
#define TCP_OPT_WSCALE_PRESENT  2
#define TCP_OPT_TSTAMP_PRESENT  4
#define TCP_OPT_SACK_OK_PRESENT 8
#define TCP_OPT_SACK_PRESENT    16

/* TCP option length */
#define TCPOPT_NOP_LEN          1
#define TCPOPT_MAXSEG_LEN       4
#define TCPOPT_WS_LEN           3
#define TCPOPT_REAL_WS_LEN      (TCPOPT_WS_LEN+1)
#define TCPOPT_TSTAMP_LEN       10
#define TCPOPT_REAL_TS_LEN      (TCPOPT_TSTAMP_LEN+2)
#define TCPOPT_SACK_OK_LEN      2
#define TCPOPT_REAL_SACK_OK_LEN (TCPOPT_SACK_OK_LEN+2)
#define TCPOPT_REAL_SACK_LEN    4
#define TCPOPT_MAX_SACK_LEN     36
#define TCPOPT_HEADER_LEN       2

/* TCP cwnd burst factor. */
#define TCP_CWND_INFINITE       65535
#define TCP_CWND_SS             3
#define TCP_CWND_NORMAL         5

/* Named Dispatch Parameter Management Structure */
typedef struct tcpparam_s {
        uint32_t        tcp_param_min;
        uint32_t        tcp_param_max;
        uint32_t        tcp_param_val;
        char            *tcp_param_name;
} tcpparam_t;

/* Max size IP datagram is 64k - 1 */
#define TCP_MSS_MAX_IPV4 (IP_MAXPACKET - (sizeof (struct ip) + \
        sizeof (tcph_t)))

/* Max of the above */
#define TCP_MSS_MAX     TCP_MSS_MAX_IPV4

/* Largest TCP port number */
#define TCP_MAX_PORT    (64 * 1024 - 1)

/* Round up the value to the nearest mss. */
#define MSS_ROUNDUP(value, mss)         ((((value) - 1) / (mss) + 1) * (mss))

#define MS      1L
#define SECONDS (1000 * MS)
#define MINUTES (60 * SECONDS)
#define HOURS   (60 * MINUTES)
#define DAYS    (24 * HOURS)

/* All NDD params in the core TCP became static variables. */
static int      tcp_time_wait_interval = 1 * MINUTES;
static int      tcp_conn_req_max_q = 128;
static int      tcp_conn_req_max_q0 = 1024;
static int      tcp_conn_req_min = 1;
static int      tcp_conn_grace_period = 0 * SECONDS;
static int      tcp_cwnd_max_ = 1024 * 1024;
static int      tcp_smallest_nonpriv_port = 1024;
static int      tcp_ip_abort_cinterval = 3 * MINUTES;
static int      tcp_ip_abort_linterval = 3 * MINUTES;
static int      tcp_ip_abort_interval = 8 * MINUTES;
static int      tcp_ip_notify_cinterval = 10 * SECONDS;
static int      tcp_ip_notify_interval = 10 * SECONDS;
static int      tcp_ipv4_ttl = 64;
static int      tcp_mss_def_ipv4 = 536;
static int      tcp_mss_max_ipv4 = TCP_MSS_MAX_IPV4;
static int      tcp_mss_min = 108;
static int      tcp_naglim_def = (4*1024)-1;
static int      tcp_rexmit_interval_initial = 3 * SECONDS;
static int      tcp_rexmit_interval_max = 60 * SECONDS;
static int      tcp_rexmit_interval_min = 400 * MS;
static int      tcp_dupack_fast_retransmit = 3;
static int      tcp_smallest_anon_port = 32 * 1024;
static int      tcp_largest_anon_port = TCP_MAX_PORT;
static int      tcp_xmit_lowat = TCP_XMIT_LOWATER;
static int      tcp_recv_hiwat_minmss = 4;
static int      tcp_fin_wait_2_flush_interval = 1 * MINUTES;
static int      tcp_max_buf = 1024 * 1024;
static int      tcp_wscale_always = 1;
static int      tcp_tstamp_always = 1;
static int      tcp_tstamp_if_wscale = 1;
static int      tcp_rexmit_interval_extra = 0;
static int      tcp_slow_start_after_idle = 2;
static int      tcp_slow_start_initial = 2;
static int      tcp_sack_permitted = 2;
static int      tcp_ecn_permitted = 2;

/* Extra room to fit in headers. */
static uint_t   tcp_wroff_xtra;

/* Hint for next port to try. */
static in_port_t        tcp_next_port_to_try = 32*1024;

/*
 * Figure out the value of window scale opton.  Note that the rwnd is
 * ASSUMED to be rounded up to the nearest MSS before the calculation.
 * We cannot find the scale value and then do a round up of tcp_rwnd
 * because the scale value may not be correct after that.
 */
#define SET_WS_VALUE(tcp) \
{ \
        int i; \
        uint32_t rwnd = (tcp)->tcp_rwnd; \
        for (i = 0; rwnd > TCP_MAXWIN && i < TCP_MAX_WINSHIFT; \
            i++, rwnd >>= 1) \
                ; \
        (tcp)->tcp_rcv_ws = i; \
}

/*
 * Set ECN capable transport (ECT) code point in IP header.
 *
 * Note that there are 2 ECT code points '01' and '10', which are called
 * ECT(1) and ECT(0) respectively.  Here we follow the original ECT code
 * point ECT(0) for TCP as described in RFC 2481.
 */
#define SET_ECT(tcp, iph) \
        if ((tcp)->tcp_ipversion == IPV4_VERSION) { \
                /* We need to clear the code point first. */ \
                ((struct ip *)(iph))->ip_tos &= 0xFC; \
                ((struct ip *)(iph))->ip_tos |= IPH_ECN_ECT0; \
        }

/*
 * The format argument to pass to tcp_display().
 * DISP_PORT_ONLY means that the returned string has only port info.
 * DISP_ADDR_AND_PORT means that the returned string also contains the
 * remote and local IP address.
 */
#define DISP_PORT_ONLY          1
#define DISP_ADDR_AND_PORT      2

/*
 * TCP reassembly macros.  We hide starting and ending sequence numbers in
 * b_next and b_prev of messages on the reassembly queue.  The messages are
 * chained using b_cont.  These macros are used in tcp_reass() so we don't
 * have to see the ugly casts and assignments.
 * Note. use uintptr_t to suppress the gcc warning.
 */
#define TCP_REASS_SEQ(mp)               ((uint32_t)(uintptr_t)((mp)->b_next))
#define TCP_REASS_SET_SEQ(mp, u)        ((mp)->b_next = \
                                            (mblk_t *)((uintptr_t)(u)))
#define TCP_REASS_END(mp)               ((uint32_t)(uintptr_t)((mp)->b_prev))
#define TCP_REASS_SET_END(mp, u)        ((mp)->b_prev = \
                                            (mblk_t *)((uintptr_t)(u)))

#define TCP_TIMER_RESTART(tcp, intvl) \
        (tcp)->tcp_rto_timeout = prom_gettime() + intvl; \
        (tcp)->tcp_timer_running = B_TRUE;

static int tcp_accept_comm(tcp_t *, tcp_t *, mblk_t *, uint_t);
static mblk_t *tcp_ack_mp(tcp_t *);
static in_port_t tcp_bindi(in_port_t, in_addr_t *, boolean_t, boolean_t);
static uint16_t tcp_cksum(uint16_t *, uint32_t);
static void tcp_clean_death(int, tcp_t *, int err);
static tcp_t *tcp_conn_request(tcp_t *, mblk_t *mp, uint_t, uint_t);
static char *tcp_display(tcp_t *, char *, char);
static int tcp_drain_input(tcp_t *, int, int);
static void tcp_drain_needed(int, tcp_t *);
static boolean_t tcp_drop_q0(tcp_t *);
static mblk_t *tcp_get_seg_mp(tcp_t *, uint32_t, int32_t *);
static int tcp_header_len(struct inetgram *);
static in_port_t tcp_report_ports(uint16_t *, enum Ports);
static int tcp_input(int);
static void tcp_iss_init(tcp_t *);
static tcp_t *tcp_lookup_ipv4(struct ip *, tcpha_t *, int, int *);
static tcp_t *tcp_lookup_listener_ipv4(in_addr_t, in_port_t, int *);
static int tcp_conn_check(tcp_t *);
static int tcp_close(int);
static void tcp_close_detached(tcp_t *);
static void tcp_eager_cleanup(tcp_t *, boolean_t, int);
static void tcp_eager_unlink(tcp_t *);
static void tcp_free(tcp_t *);
static int tcp_header_init_ipv4(tcp_t *);
static void tcp_mss_set(tcp_t *, uint32_t);
static int tcp_parse_options(tcph_t *, tcp_opt_t *);
static boolean_t tcp_paws_check(tcp_t *, tcph_t *, tcp_opt_t *);
static void tcp_process_options(tcp_t *, tcph_t *);
static int tcp_random(void);
static void tcp_random_init(void);
static mblk_t *tcp_reass(tcp_t *, mblk_t *, uint32_t);
static void tcp_reass_elim_overlap(tcp_t *, mblk_t *);
static void tcp_rcv_drain(int sock_id, tcp_t *);
static void tcp_rcv_enqueue(tcp_t *, mblk_t *, uint_t);
static void tcp_rput_data(tcp_t *, mblk_t *, int);
static int tcp_rwnd_set(tcp_t *, uint32_t);
static int32_t tcp_sack_rxmit(tcp_t *, int);
static void tcp_set_cksum(mblk_t *);
static void tcp_set_rto(tcp_t *, int32_t);
static void tcp_ss_rexmit(tcp_t *, int);
static int tcp_state_wait(int, tcp_t *, int);
static void tcp_timer(tcp_t *, int);
static void tcp_time_wait_append(tcp_t *);
static void tcp_time_wait_collector(void);
static void tcp_time_wait_processing(tcp_t *, mblk_t *, uint32_t,
    uint32_t, int, tcph_t *, int sock_id);
static void tcp_time_wait_remove(tcp_t *);
static in_port_t tcp_update_next_port(in_port_t);
static int tcp_verify_cksum(mblk_t *);
static void tcp_wput_data(tcp_t *, mblk_t *, int);
static void tcp_xmit_ctl(char *, tcp_t *, mblk_t *, uint32_t, uint32_t,
    int, uint_t, int);
static void tcp_xmit_early_reset(char *, int, mblk_t *, uint32_t, uint32_t,
    int, uint_t);
static int tcp_xmit_end(tcp_t *, int);
static void tcp_xmit_listeners_reset(int, mblk_t *, uint_t);
static mblk_t *tcp_xmit_mp(tcp_t *, mblk_t *, int32_t, int32_t *,
    mblk_t **, uint32_t, boolean_t, uint32_t *, boolean_t);
static int tcp_init_values(tcp_t *, struct inetboot_socket *);

#if DEBUG > 1
#define TCP_DUMP_PACKET(str, mp) \
{ \
        int len = (mp)->b_wptr - (mp)->b_rptr; \
\
        printf("%s: dump TCP(%d): \n", (str), len); \
        hexdump((char *)(mp)->b_rptr, len); \
}
#else
#define TCP_DUMP_PACKET(str, mp)
#endif

#ifdef DEBUG
#define DEBUG_1(str, arg)               printf(str, (arg))
#define DEBUG_2(str, arg1, arg2)        printf(str, (arg1), (arg2))
#define DEBUG_3(str, arg1, arg2, arg3)  printf(str, (arg1), (arg2), (arg3))
#else
#define DEBUG_1(str, arg)
#define DEBUG_2(str, arg1, arg2)
#define DEBUG_3(str, arg1, arg2, arg3)
#endif

/* Whether it is the first time TCP is used. */
static boolean_t tcp_initialized = B_FALSE;

/* TCP time wait list. */
static tcp_t *tcp_time_wait_head;
static tcp_t *tcp_time_wait_tail;
static uint32_t tcp_cum_timewait;
/* When the tcp_time_wait_collector is run. */
static uint32_t tcp_time_wait_runtime;

#define TCP_RUN_TIME_WAIT_COLLECTOR() \
        if (prom_gettime() > tcp_time_wait_runtime) \
                tcp_time_wait_collector();

/*
 * Accept will return with an error if there is no connection coming in
 * after this (in ms).
 */
static int tcp_accept_timeout = 60000;

/*
 * Initialize the TCP-specific parts of a socket.
 */
void
tcp_socket_init(struct inetboot_socket *isp)
{
        /* Do some initializations. */
        if (!tcp_initialized) {
                tcp_random_init();
                /* Extra head room for the MAC layer address. */
                if ((tcp_wroff_xtra = mac_get_hdr_len()) & 0x3) {
                        tcp_wroff_xtra = (tcp_wroff_xtra & ~0x3) + 0x4;
                }
                /* Schedule the first time wait cleanup time */
                tcp_time_wait_runtime = prom_gettime() + tcp_time_wait_interval;
                tcp_initialized = B_TRUE;
        }
        TCP_RUN_TIME_WAIT_COLLECTOR();

        isp->proto = IPPROTO_TCP;
        isp->input[TRANSPORT_LVL] = tcp_input;
        /* Socket layer should call tcp_send() directly. */
        isp->output[TRANSPORT_LVL] = NULL;
        isp->close[TRANSPORT_LVL] = tcp_close;
        isp->headerlen[TRANSPORT_LVL] = tcp_header_len;
        isp->ports = tcp_report_ports;
        if ((isp->pcb = bkmem_alloc(sizeof (tcp_t))) == NULL) {
                errno = ENOBUFS;
                return;
        }
        if ((errno = tcp_init_values((tcp_t *)isp->pcb, isp)) != 0) {
                bkmem_free(isp->pcb, sizeof (tcp_t));
                return;
        }
        /*
         * This is set last because this field is used to determine if
         * a socket is in use or not.
         */
        isp->type = INETBOOT_STREAM;
}

/*
 * Return the size of a TCP header including TCP option.
 */
static int
tcp_header_len(struct inetgram *igm)
{
        mblk_t *pkt;
        int ipvers;

        /* Just returns the standard TCP header without option */
        if (igm == NULL)
                return (sizeof (tcph_t));

        if ((pkt = igm->igm_mp) == NULL)
                return (0);

        ipvers = ((struct ip *)pkt->b_rptr)->ip_v;
        if (ipvers == IPV4_VERSION) {
                return (TCP_HDR_LENGTH((tcph_t *)(pkt + IPH_HDR_LENGTH(pkt))));
        } else {
                dprintf("tcp_header_len: non-IPv4 packet.\n");
                return (0);
        }
}

/*
 * Return the requested port number in network order.
 */
static in_port_t
tcp_report_ports(uint16_t *tcphp, enum Ports request)
{
        if (request == SOURCE)
                return (*(uint16_t *)(((tcph_t *)tcphp)->th_lport));
        return (*(uint16_t *)(((tcph_t *)tcphp)->th_fport));
}

/*
 * Because inetboot is not interrupt driven, TCP can only poll.  This
 * means that there can be packets stuck in the NIC buffer waiting to
 * be processed.  Thus we need to drain them before, for example, sending
 * anything because an ACK may actually be stuck there.
 *
 * The timeout arguments determine how long we should wait for draining.
 */
static int
tcp_drain_input(tcp_t *tcp, int sock_id, int timeout)
{
        struct inetgram *in_gram;
        struct inetgram *old_in_gram;
        int old_timeout;
        mblk_t *mp;
        int i;

        dprintf("tcp_drain_input(%d): %s\n", sock_id,
            tcp_display(tcp, NULL, DISP_ADDR_AND_PORT));

        /*
         * Since the driver uses the in_timeout value in the socket
         * structure to determine the timeout value, we need to save
         * the original one so that we can restore that after draining.
         */
        old_timeout = sockets[sock_id].in_timeout;
        sockets[sock_id].in_timeout = timeout;

        /*
         * We do this because the input queue may have some user
         * data already.
         */
        old_in_gram = sockets[sock_id].inq;
        sockets[sock_id].inq = NULL;

        /* Go out and check the wire */
        for (i = MEDIA_LVL; i < TRANSPORT_LVL; i++) {
                if (sockets[sock_id].input[i] != NULL) {
                        if (sockets[sock_id].input[i](sock_id) < 0) {
                                sockets[sock_id].in_timeout = old_timeout;
                                if (sockets[sock_id].inq != NULL)
                                        nuke_grams(&sockets[sock_id].inq);
                                sockets[sock_id].inq = old_in_gram;
                                return (-1);
                        }
                }
        }
#if DEBUG
        printf("tcp_drain_input: done with checking packets\n");
#endif
        while ((in_gram = sockets[sock_id].inq) != NULL) {
                /* Remove unknown inetgrams from the head of inq. */
                if (in_gram->igm_level != TRANSPORT_LVL) {
#if DEBUG
                        printf("tcp_drain_input: unexpected packet "
                            "level %d frame found\n", in_gram->igm_level);
#endif
                        del_gram(&sockets[sock_id].inq, in_gram, B_TRUE);
                        continue;
                }
                mp = in_gram->igm_mp;
                del_gram(&sockets[sock_id].inq, in_gram, B_FALSE);
                bkmem_free((caddr_t)in_gram, sizeof (struct inetgram));
                tcp_rput_data(tcp, mp, sock_id);
                sockets[sock_id].in_timeout = old_timeout;

                /*
                 * The other side may have closed this connection or
                 * RST us.  But we need to continue to process other
                 * packets in the socket's queue because they may be
                 * belong to another TCP connections.
                 */
                if (sockets[sock_id].pcb == NULL)
                        tcp = NULL;
        }

        if (tcp == NULL || sockets[sock_id].pcb == NULL) {
                if (sockets[sock_id].so_error != 0)
                        return (-1);
                else
                        return (0);
        }
#if DEBUG
        printf("tcp_drain_input: done with processing packets\n");
#endif
        sockets[sock_id].in_timeout = old_timeout;
        sockets[sock_id].inq = old_in_gram;

        /*
         * Data may have been received so indicate it is available
         */
        tcp_drain_needed(sock_id, tcp);
        return (0);
}

/*
 * The receive entry point for upper layer to call to get data.  Note
 * that this follows the current architecture that lower layer receive
 * routines have been called already.  Thus if the inq of socket is
 * not NULL, the packets must be for us.
 */
static int
tcp_input(int sock_id)
{
        struct inetgram *in_gram;
        mblk_t *mp;
        tcp_t *tcp;

        TCP_RUN_TIME_WAIT_COLLECTOR();

        if ((tcp = sockets[sock_id].pcb) == NULL)
                return (-1);

        while ((in_gram = sockets[sock_id].inq) != NULL) {
                /* Remove unknown inetgrams from the head of inq. */
                if (in_gram->igm_level != TRANSPORT_LVL) {
#ifdef DEBUG
                        printf("tcp_input: unexpected packet "
                            "level %d frame found\n", in_gram->igm_level);
#endif
                        del_gram(&sockets[sock_id].inq, in_gram, B_TRUE);
                        continue;
                }
                mp = in_gram->igm_mp;
                del_gram(&sockets[sock_id].inq, in_gram, B_FALSE);
                bkmem_free((caddr_t)in_gram, sizeof (struct inetgram));
                tcp_rput_data(tcp, mp, sock_id);
                /* The TCP may be gone because it gets a RST. */
                if (sockets[sock_id].pcb == NULL)
                        return (-1);
        }

        /* Flush the receive list. */
        if (tcp->tcp_rcv_list != NULL) {
                tcp_rcv_drain(sock_id, tcp);
        } else {
                /* The other side has closed the connection, report this up. */
                if (tcp->tcp_state == TCPS_CLOSE_WAIT) {
                        sockets[sock_id].so_state |= SS_CANTRCVMORE;
                        return (0);
                }
        }
        return (0);
}

/*
 * The send entry point for upper layer to call to send data.  In order
 * to minimize changes to the core TCP code, we need to put the
 * data into mblks.
 */
int
tcp_send(int sock_id, tcp_t *tcp, const void *msg, int len)
{
        mblk_t *mp;
        mblk_t *head = NULL;
        mblk_t *tail;
        int mss = tcp->tcp_mss;
        int cnt = 0;
        int win_size;
        char *buf = (char *)msg;

        TCP_RUN_TIME_WAIT_COLLECTOR();

        /* We don't want to append 0 size mblk. */
        if (len == 0)
                return (0);
        while (len > 0) {
                if (len < mss) {
                        mss = len;
                }
                /*
                 * If we cannot allocate more buffer, stop here and
                 * the number of bytes buffered will be returned.
                 *
                 * Note that we follow the core TCP optimization that
                 * each mblk contains only MSS bytes data.
                 */
                if ((mp = allocb(mss + tcp->tcp_ip_hdr_len +
                    TCP_MAX_HDR_LENGTH + tcp_wroff_xtra, 0)) == NULL) {
                        break;
                }
                mp->b_rptr += tcp->tcp_hdr_len + tcp_wroff_xtra;
                bcopy(buf, mp->b_rptr, mss);
                mp->b_wptr = mp->b_rptr + mss;
                buf += mss;
                cnt += mss;
                len -= mss;

                if (head == NULL) {
                        head = mp;
                        tail = mp;
                } else {
                        tail->b_cont = mp;
                        tail = mp;
                }
        }

        /*
         * Since inetboot is not interrupt driven, there may be
         * some ACKs in the MAC's buffer.  Drain them first,
         * otherwise, we may not be able to send.
         *
         * We expect an ACK in two cases:
         *
         * 1) We have un-ACK'ed data.
         *
         * 2) All ACK's have been received and the sender's window has been
         * closed.  We need an ACK back to open the window so that we can
         * send.  In this case, call tcp_drain_input() if the window size is
         * less than 2 * MSS.
         */

        /* window size = MIN(swnd, cwnd) - unacked bytes */
        win_size = (tcp->tcp_swnd > tcp->tcp_cwnd) ? tcp->tcp_cwnd :
                tcp->tcp_swnd;
        win_size -= tcp->tcp_snxt;
        win_size += tcp->tcp_suna;
        if (win_size < (2 * tcp->tcp_mss))
                if (tcp_drain_input(tcp, sock_id, 5) < 0)
                        return (-1);

        tcp_wput_data(tcp, head, sock_id);
        /*
         * errno should be reset here as it may be
         * set to ETIMEDOUT. This may be set by
         * the MAC driver in case it has timed out
         * waiting for ARP reply. Any segment which
         * was not transmitted because of ARP timeout
         * will be retransmitted by TCP.
         */
        if (errno == ETIMEDOUT)
                errno = 0;
        return (cnt);
}

/* Free up all TCP related stuff */
static void
tcp_free(tcp_t *tcp)
{
        if (tcp->tcp_iphc != NULL) {
                bkmem_free((caddr_t)tcp->tcp_iphc, tcp->tcp_iphc_len);
                tcp->tcp_iphc = NULL;
        }
        if (tcp->tcp_xmit_head != NULL) {
                freemsg(tcp->tcp_xmit_head);
                tcp->tcp_xmit_head = NULL;
        }
        if (tcp->tcp_rcv_list != NULL) {
                freemsg(tcp->tcp_rcv_list);
                tcp->tcp_rcv_list = NULL;
        }
        if (tcp->tcp_reass_head != NULL) {
                freemsg(tcp->tcp_reass_head);
                tcp->tcp_reass_head = NULL;
        }
        if (tcp->tcp_sack_info != NULL) {
                bkmem_free((caddr_t)tcp->tcp_sack_info,
                    sizeof (tcp_sack_info_t));
                tcp->tcp_sack_info = NULL;
        }
}

static void
tcp_close_detached(tcp_t *tcp)
{
        if (tcp->tcp_listener != NULL)
                tcp_eager_unlink(tcp);
        tcp_free(tcp);
        bkmem_free((caddr_t)tcp, sizeof (tcp_t));
}

/*
 * If we are an eager connection hanging off a listener that hasn't
 * formally accepted the connection yet, get off its list and blow off
 * any data that we have accumulated.
 */
static void
tcp_eager_unlink(tcp_t *tcp)
{
        tcp_t   *listener = tcp->tcp_listener;

        assert(listener != NULL);
        if (tcp->tcp_eager_next_q0 != NULL) {
                assert(tcp->tcp_eager_prev_q0 != NULL);

                /* Remove the eager tcp from q0 */
                tcp->tcp_eager_next_q0->tcp_eager_prev_q0 =
                    tcp->tcp_eager_prev_q0;
                tcp->tcp_eager_prev_q0->tcp_eager_next_q0 =
                    tcp->tcp_eager_next_q0;
                listener->tcp_conn_req_cnt_q0--;
        } else {
                tcp_t   **tcpp = &listener->tcp_eager_next_q;
                tcp_t   *prev = NULL;

                for (; tcpp[0]; tcpp = &tcpp[0]->tcp_eager_next_q) {
                        if (tcpp[0] == tcp) {
                                if (listener->tcp_eager_last_q == tcp) {
                                        /*
                                         * If we are unlinking the last
                                         * element on the list, adjust
                                         * tail pointer. Set tail pointer
                                         * to nil when list is empty.
                                         */
                                        assert(tcp->tcp_eager_next_q == NULL);
                                        if (listener->tcp_eager_last_q ==
                                            listener->tcp_eager_next_q) {
                                                listener->tcp_eager_last_q =
                                                NULL;
                                        } else {
                                                /*
                                                 * We won't get here if there
                                                 * is only one eager in the
                                                 * list.
                                                 */
                                                assert(prev != NULL);
                                                listener->tcp_eager_last_q =
                                                    prev;
                                        }
                                }
                                tcpp[0] = tcp->tcp_eager_next_q;
                                tcp->tcp_eager_next_q = NULL;
                                tcp->tcp_eager_last_q = NULL;
                                listener->tcp_conn_req_cnt_q--;
                                break;
                        }
                        prev = tcpp[0];
                }
        }
        tcp->tcp_listener = NULL;
}

/*
 * Reset any eager connection hanging off this listener
 * and then reclaim it's resources.
 */
static void
tcp_eager_cleanup(tcp_t *listener, boolean_t q0_only, int sock_id)
{
        tcp_t   *eager;

        if (!q0_only) {
                /* First cleanup q */
                while ((eager = listener->tcp_eager_next_q) != NULL) {
                        assert(listener->tcp_eager_last_q != NULL);
                        tcp_xmit_ctl("tcp_eager_cleanup, can't wait",
                            eager, NULL, eager->tcp_snxt, 0, TH_RST, 0,
                            sock_id);
                        tcp_close_detached(eager);
                }
                assert(listener->tcp_eager_last_q == NULL);
        }
        /* Then cleanup q0 */
        while ((eager = listener->tcp_eager_next_q0) != listener) {
                tcp_xmit_ctl("tcp_eager_cleanup, can't wait",
                    eager, NULL, eager->tcp_snxt, 0, TH_RST, 0, sock_id);
                tcp_close_detached(eager);
        }
}

/*
 * To handle the shutdown request. Called from shutdown()
 */
int
tcp_shutdown(int sock_id)
{
        tcp_t   *tcp;

        DEBUG_1("tcp_shutdown: sock_id %x\n", sock_id);

        if ((tcp = sockets[sock_id].pcb) == NULL) {
                return (-1);
        }

        /*
         * Since inetboot is not interrupt driven, there may be
         * some ACKs in the MAC's buffer.  Drain them first,
         * otherwise, we may not be able to send.
         */
        if (tcp_drain_input(tcp, sock_id, 5) < 0) {
                /*
                 * If we return now without freeing TCP, there will be
                 * a memory leak.
                 */
                if (sockets[sock_id].pcb != NULL)
                        tcp_clean_death(sock_id, tcp, 0);
                return (-1);
        }

        DEBUG_1("tcp_shutdown: tcp_state %x\n", tcp->tcp_state);
        switch (tcp->tcp_state) {

        case TCPS_SYN_RCVD:
                /*
                 * Shutdown during the connect 3-way handshake
                 */
        case TCPS_ESTABLISHED:
                /*
                 * Transmit the FIN
                 * wait for the FIN to be ACKed,
                 * then remain in FIN_WAIT_2
                 */
                dprintf("tcp_shutdown: sending fin\n");
                if (tcp_xmit_end(tcp, sock_id) == 0 &&
                        tcp_state_wait(sock_id, tcp, TCPS_FIN_WAIT_2) < 0) {
                        /* During the wait, TCP may be gone... */
                        if (sockets[sock_id].pcb == NULL)
                                return (-1);
                }
                dprintf("tcp_shutdown: done\n");
                break;

        default:
                break;

        }
        return (0);
}

/* To handle closing of the socket */
static int
tcp_close(int sock_id)
{
        char    *msg;
        tcp_t   *tcp;
        int     error = 0;

        if ((tcp = sockets[sock_id].pcb) == NULL) {
                return (-1);
        }

        TCP_RUN_TIME_WAIT_COLLECTOR();

        /*
         * Since inetboot is not interrupt driven, there may be
         * some ACKs in the MAC's buffer.  Drain them first,
         * otherwise, we may not be able to send.
         */
        if (tcp_drain_input(tcp, sock_id, 5) < 0) {
                /*
                 * If we return now without freeing TCP, there will be
                 * a memory leak.
                 */
                if (sockets[sock_id].pcb != NULL)
                        tcp_clean_death(sock_id, tcp, 0);
                return (-1);
        }

        if (tcp->tcp_conn_req_cnt_q0 != 0 || tcp->tcp_conn_req_cnt_q != 0) {
                /* Cleanup for listener */
                tcp_eager_cleanup(tcp, 0, sock_id);
        }

        msg = NULL;
        switch (tcp->tcp_state) {
        case TCPS_CLOSED:
        case TCPS_IDLE:
        case TCPS_BOUND:
        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 SO_LINGER has set a zero linger time, abort the
                 * connection with a reset.
                 */
                if (tcp->tcp_linger && tcp->tcp_lingertime == 0) {
                        msg = "tcp_close, zero lingertime";
                        break;
                }

                /*
                 * Abort connection if there is unread data queued.
                 */
                if (tcp->tcp_rcv_list != NULL ||
                                tcp->tcp_reass_head != NULL) {
                        msg = "tcp_close, unread data";
                        break;
                }
                if (tcp->tcp_state <= TCPS_LISTEN)
                        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.
                 * The TCP could be closed in tcp_state_wait called by
                 * tcp_wput_data called by tcp_xmit_end.
                 */
                (void) tcp_xmit_end(tcp, sock_id);
                if (sockets[sock_id].pcb == NULL)
                        return (0);

                /*
                 * If lingering on close then wait until the fin is acked,
                 * the SO_LINGER time passes, or a reset is sent/received.
                 */
                if (tcp->tcp_linger && tcp->tcp_lingertime > 0 &&
                    !(tcp->tcp_fin_acked) &&
                    tcp->tcp_state >= TCPS_ESTABLISHED) {
                        uint32_t stoptime; /* in ms */

                        tcp->tcp_client_errno = 0;
                        stoptime = prom_gettime() +
                            (tcp->tcp_lingertime * 1000);
                        while (!(tcp->tcp_fin_acked) &&
                            tcp->tcp_state >= TCPS_ESTABLISHED &&
                            tcp->tcp_client_errno == 0 &&
                            ((int32_t)(stoptime - prom_gettime()) > 0)) {
                                if (tcp_drain_input(tcp, sock_id, 5) < 0) {
                                        if (sockets[sock_id].pcb != NULL) {
                                                tcp_clean_death(sock_id,
                                                    tcp, 0);
                                        }
                                        return (-1);
                                }
                        }
                        tcp->tcp_client_errno = 0;
                }
                if (tcp_state_wait(sock_id, tcp, TCPS_TIME_WAIT) < 0) {
                        /* During the wait, TCP may be gone... */
                        if (sockets[sock_id].pcb == NULL)
                                return (0);
                        msg = "tcp_close, couldn't detach";
                } else {
                        return (0);
                }
                break;
        }

        /* Something went wrong...  Send a RST and report the error */
        if (msg != NULL) {
                if (tcp->tcp_state == TCPS_ESTABLISHED ||
                    tcp->tcp_state == TCPS_CLOSE_WAIT)
                        BUMP_MIB(tcp_mib.tcpEstabResets);
                if (tcp->tcp_state == TCPS_SYN_SENT ||
                    tcp->tcp_state == TCPS_SYN_RCVD)
                        BUMP_MIB(tcp_mib.tcpAttemptFails);
                tcp_xmit_ctl(msg, tcp, NULL, tcp->tcp_snxt, 0, TH_RST, 0,
                    sock_id);
        }

        tcp_free(tcp);
        bkmem_free((caddr_t)tcp, sizeof (tcp_t));
        sockets[sock_id].pcb = NULL;
        return (error);
}

/* To make an endpoint a listener. */
int
tcp_listen(int sock_id, int backlog)
{
        tcp_t *tcp;

        if ((tcp = (tcp_t *)(sockets[sock_id].pcb)) == NULL) {
                errno = EINVAL;
                return (-1);
        }
        /* We allow calling listen() multiple times to change the backlog. */
        if (tcp->tcp_state > TCPS_LISTEN || tcp->tcp_state < TCPS_BOUND) {
                errno = EOPNOTSUPP;
                return (-1);
        }
        /* The following initialization should only be done once. */
        if (tcp->tcp_state != TCPS_LISTEN) {
                tcp->tcp_eager_next_q0 = tcp->tcp_eager_prev_q0 = tcp;
                tcp->tcp_eager_next_q = NULL;
                tcp->tcp_state = TCPS_LISTEN;
                tcp->tcp_second_ctimer_threshold = tcp_ip_abort_linterval;
        }
        if ((tcp->tcp_conn_req_max = backlog) > tcp_conn_req_max_q) {
                tcp->tcp_conn_req_max = tcp_conn_req_max_q;
        }
        if (tcp->tcp_conn_req_max < tcp_conn_req_min) {
                tcp->tcp_conn_req_max = tcp_conn_req_min;
        }
        return (0);
}

/* To accept connections. */
int
tcp_accept(int sock_id, struct sockaddr *addr, socklen_t *addr_len)
{
        tcp_t *listener;
        tcp_t *eager;
        int sd, new_sock_id;
        struct sockaddr_in *new_addr = (struct sockaddr_in *)addr;
        int timeout;

        /* Sanity check. */
        if ((listener = (tcp_t *)(sockets[sock_id].pcb)) == NULL ||
            new_addr == NULL || addr_len == NULL ||
            *addr_len < sizeof (struct sockaddr_in) ||
            listener->tcp_state != TCPS_LISTEN) {
                errno = EINVAL;
                return (-1);
        }

        if (sockets[sock_id].in_timeout > tcp_accept_timeout)
                timeout = prom_gettime() + sockets[sock_id].in_timeout;
        else
                timeout = prom_gettime() + tcp_accept_timeout;
        while (listener->tcp_eager_next_q == NULL &&
            timeout > prom_gettime()) {
#if DEBUG
                printf("tcp_accept: Waiting in tcp_accept()\n");
#endif
                if (tcp_drain_input(listener, sock_id, 5) < 0) {
                        return (-1);
                }
        }
        /* If there is an eager, don't timeout... */
        if (timeout <= prom_gettime() && listener->tcp_eager_next_q == NULL) {
#if DEBUG
                printf("tcp_accept: timeout\n");
#endif
                errno = ETIMEDOUT;
                return (-1);
        }
#if DEBUG
        printf("tcp_accept: got a connection\n");
#endif

        /* Now create the socket for this new TCP. */
        if ((sd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
                return (-1);
        }
        if ((new_sock_id = so_check_fd(sd, &errno)) == -1)
                /* This should not happen! */
                prom_panic("so_check_fd() fails in tcp_accept()");
        /* Free the TCP PCB in the original socket. */
        bkmem_free((caddr_t)(sockets[new_sock_id].pcb), sizeof (tcp_t));
        /* Dequeue the eager and attach it to the socket. */
        eager = listener->tcp_eager_next_q;
        listener->tcp_eager_next_q = eager->tcp_eager_next_q;
        if (listener->tcp_eager_last_q == eager)
                listener->tcp_eager_last_q = NULL;
        eager->tcp_eager_next_q = NULL;
        sockets[new_sock_id].pcb = eager;
        listener->tcp_conn_req_cnt_q--;

        /* Copy in the address info. */
        bcopy(&eager->tcp_remote, &new_addr->sin_addr.s_addr,
            sizeof (in_addr_t));
        bcopy(&eager->tcp_fport, &new_addr->sin_port, sizeof (in_port_t));
        new_addr->sin_family = AF_INET;

#ifdef DEBUG
        printf("tcp_accept(), new sock_id: %d\n", sd);
#endif
        return (sd);
}

/* Update the next anonymous port to use.  */
static in_port_t
tcp_update_next_port(in_port_t port)
{
        /* Don't allow the port to fall out of the anonymous port range. */
        if (port < tcp_smallest_anon_port || port > tcp_largest_anon_port)
                port = (in_port_t)tcp_smallest_anon_port;

        if (port < tcp_smallest_nonpriv_port)
                port = (in_port_t)tcp_smallest_nonpriv_port;
        return (port);
}

/* To check whether a bind to a port is allowed. */
static in_port_t
tcp_bindi(in_port_t port, in_addr_t *addr, boolean_t reuseaddr,
    boolean_t bind_to_req_port_only)
{
        int i, count;
        tcp_t *tcp;

        count = tcp_largest_anon_port - tcp_smallest_anon_port;
try_again:
        for (i = 0; i < MAXSOCKET; i++) {
                if (sockets[i].type != INETBOOT_STREAM ||
                    ((tcp = (tcp_t *)sockets[i].pcb) == NULL) ||
                    ntohs(tcp->tcp_lport) != port) {
                        continue;
                }
                /*
                 * Both TCPs have the same port.  If SO_REUSEDADDR is
                 * set and the bound TCP has a state greater than
                 * TCPS_LISTEN, it is fine.
                 */
                if (reuseaddr && tcp->tcp_state > TCPS_LISTEN) {
                        continue;
                }
                if (tcp->tcp_bound_source != INADDR_ANY &&
                    *addr != INADDR_ANY &&
                    tcp->tcp_bound_source != *addr) {
                        continue;
                }
                if (bind_to_req_port_only) {
                        return (0);
                }
                if (--count > 0) {
                        port = tcp_update_next_port(++port);
                        goto try_again;
                } else {
                        return (0);
                }
        }
        return (port);
}

/* To handle the bind request. */
int
tcp_bind(int sock_id)
{
        tcp_t *tcp;
        in_port_t requested_port, allocated_port;
        boolean_t bind_to_req_port_only;
        boolean_t reuseaddr;

        if ((tcp = (tcp_t *)sockets[sock_id].pcb) == NULL) {
                errno = EINVAL;
                return (-1);
        }

        if (tcp->tcp_state >= TCPS_BOUND) {
                /* We don't allow multiple bind(). */
                errno = EPROTO;
                return (-1);
        }

        requested_port = ntohs(sockets[sock_id].bind.sin_port);

        /* The bound source can be INADDR_ANY. */
        tcp->tcp_bound_source = sockets[sock_id].bind.sin_addr.s_addr;

        tcp->tcp_ipha->ip_src.s_addr = tcp->tcp_bound_source;

        /* Verify the port is available. */
        if (requested_port == 0)
                bind_to_req_port_only = B_FALSE;
        else                    /* T_BIND_REQ and requested_port != 0 */
                bind_to_req_port_only = B_TRUE;

        if (requested_port == 0) {
                requested_port = tcp_update_next_port(++tcp_next_port_to_try);
        }
        reuseaddr = sockets[sock_id].so_opt & SO_REUSEADDR;
        allocated_port = tcp_bindi(requested_port, &(tcp->tcp_bound_source),
            reuseaddr, bind_to_req_port_only);

        if (allocated_port == 0) {
                errno = EADDRINUSE;
                return (-1);
        }
        tcp->tcp_lport = htons(allocated_port);
        *(uint16_t *)tcp->tcp_tcph->th_lport = tcp->tcp_lport;
        sockets[sock_id].bind.sin_port = tcp->tcp_lport;
        tcp->tcp_state = TCPS_BOUND;
        return (0);
}

/*
 * Check for duplicate TCP connections.
 */
static int
tcp_conn_check(tcp_t *tcp)
{
        int i;
        tcp_t *tmp_tcp;

        for (i = 0; i < MAXSOCKET; i++) {
                if (sockets[i].type != INETBOOT_STREAM)
                        continue;
                /* Socket may not be closed but the TCP can be gone. */
                if ((tmp_tcp = (tcp_t *)sockets[i].pcb) == NULL)
                        continue;
                /* We only care about TCP in states later than SYN_SENT. */
                if (tmp_tcp->tcp_state < TCPS_SYN_SENT)
                        continue;
                if (tmp_tcp->tcp_lport != tcp->tcp_lport ||
                    tmp_tcp->tcp_fport != tcp->tcp_fport ||
                    tmp_tcp->tcp_bound_source != tcp->tcp_bound_source ||
                    tmp_tcp->tcp_remote != tcp->tcp_remote) {
                        continue;
                } else {
                        return (-1);
                }
        }
        return (0);
}

/* To handle a connect request. */
int
tcp_connect(int sock_id)
{
        tcp_t *tcp;
        in_addr_t dstaddr;
        in_port_t dstport;
        tcph_t  *tcph;
        int mss;
        mblk_t *syn_mp;

        if ((tcp = (tcp_t *)(sockets[sock_id].pcb)) == NULL) {
                errno = EINVAL;
                return (-1);
        }

        TCP_RUN_TIME_WAIT_COLLECTOR();

        dstaddr = sockets[sock_id].remote.sin_addr.s_addr;
        dstport = sockets[sock_id].remote.sin_port;

        /*
         * Check for attempt to connect to INADDR_ANY or non-unicast addrress.
         * We don't have enough info to check for broadcast addr, except
         * for the all 1 broadcast.
         */
        if (dstaddr == INADDR_ANY || IN_CLASSD(ntohl(dstaddr)) ||
            dstaddr == INADDR_BROADCAST)  {
                /*
                 * SunOS 4.x and 4.3 BSD allow an application
                 * to connect a TCP socket to INADDR_ANY.
                 * When they do this, the kernel picks the
                 * address of one interface and uses it
                 * instead.  The kernel usually ends up
                 * picking the address of the loopback
                 * interface.  This is an undocumented feature.
                 * However, we provide the same thing here
                 * in order to have source and binary
                 * compatibility with SunOS 4.x.
                 * Update the T_CONN_REQ (sin/sin6) since it is used to
                 * generate the T_CONN_CON.
                 *
                 * Fail this for inetboot TCP.
                 */
                errno = EINVAL;
                return (-1);
        }

        /* It is not bound to any address yet... */
        if (tcp->tcp_bound_source == INADDR_ANY) {
                ipv4_getipaddr(&(sockets[sock_id].bind.sin_addr));
                /* We don't have an address! */
                if (ntohl(sockets[sock_id].bind.sin_addr.s_addr) ==
                    INADDR_ANY) {
                        errno = EPROTO;
                        return (-1);
                }
                tcp->tcp_bound_source = sockets[sock_id].bind.sin_addr.s_addr;
                tcp->tcp_ipha->ip_src.s_addr = tcp->tcp_bound_source;
        }

        /*
         * Don't let an endpoint connect to itself.
         */
        if (dstaddr == tcp->tcp_ipha->ip_src.s_addr &&
            dstport == tcp->tcp_lport) {
                errno = EINVAL;
                return (-1);
        }

        tcp->tcp_ipha->ip_dst.s_addr = dstaddr;
        tcp->tcp_remote = dstaddr;
        tcph = tcp->tcp_tcph;
        *(uint16_t *)tcph->th_fport = dstport;
        tcp->tcp_fport = dstport;

        /*
         * Don't allow this connection to completely duplicate
         * an existing connection.
         */
        if (tcp_conn_check(tcp) < 0) {
                errno = EADDRINUSE;
                return (-1);
        }

        /*
         * Just make sure our rwnd is at
         * least tcp_recv_hiwat_mss * MSS
         * large, and round up to the nearest
         * MSS.
         *
         * We do the round up here because
         * we need to get the interface
         * MTU first before we can do the
         * round up.
         */
        mss = tcp->tcp_mss - tcp->tcp_hdr_len;
        tcp->tcp_rwnd = MAX(MSS_ROUNDUP(tcp->tcp_rwnd, mss),
            tcp_recv_hiwat_minmss * mss);
        tcp->tcp_rwnd_max = tcp->tcp_rwnd;
        SET_WS_VALUE(tcp);
        U32_TO_ABE16((tcp->tcp_rwnd >> tcp->tcp_rcv_ws),
            tcp->tcp_tcph->th_win);
        if (tcp->tcp_rcv_ws > 0 || tcp_wscale_always)
                tcp->tcp_snd_ws_ok = B_TRUE;

        /*
         * Set tcp_snd_ts_ok to true
         * so that tcp_xmit_mp will
         * include the timestamp
         * option in the SYN segment.
         */
        if (tcp_tstamp_always ||
            (tcp->tcp_rcv_ws && tcp_tstamp_if_wscale)) {
                tcp->tcp_snd_ts_ok = B_TRUE;
        }

        if (tcp_sack_permitted == 2 ||
            tcp->tcp_snd_sack_ok) {
                assert(tcp->tcp_sack_info == NULL);
                if ((tcp->tcp_sack_info = (tcp_sack_info_t *)bkmem_zalloc(
                    sizeof (tcp_sack_info_t))) == NULL) {
                        tcp->tcp_snd_sack_ok = B_FALSE;
                } else {
                        tcp->tcp_snd_sack_ok = B_TRUE;
                }
        }
        /*
         * Should we use ECN?  Note that the current
         * default value (SunOS 5.9) of tcp_ecn_permitted
         * is 2.  The reason for doing this is that there
         * are equipments out there that will drop ECN
         * enabled IP packets.  Setting it to 1 avoids
         * compatibility problems.
         */
        if (tcp_ecn_permitted == 2)
                tcp->tcp_ecn_ok = B_TRUE;

        tcp_iss_init(tcp);
        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
        tcp->tcp_active_open = B_TRUE;

        tcp->tcp_state = TCPS_SYN_SENT;
        syn_mp = tcp_xmit_mp(tcp, NULL, 0, NULL, NULL, tcp->tcp_iss, B_FALSE,
            NULL, B_FALSE);
        if (syn_mp != NULL) {
                int ret;

                /* Dump the packet when debugging. */
                TCP_DUMP_PACKET("tcp_connect", syn_mp);
                /* Send out the SYN packet. */
                ret = ipv4_tcp_output(sock_id, syn_mp);
                freeb(syn_mp);
                /*
                 * errno ETIMEDOUT is set by the mac driver
                 * in case it is not able to receive ARP reply.
                 * TCP will retransmit this segment so we can
                 * ignore the ARP timeout.
                 */
                if ((ret < 0) && (errno != ETIMEDOUT)) {
                        return (-1);
                }
                /* tcp_state_wait() will finish the 3 way handshake. */
                return (tcp_state_wait(sock_id, tcp, TCPS_ESTABLISHED));
        } else {
                errno = ENOBUFS;
                return (-1);
        }
}

/*
 * Common accept code.  Called by tcp_conn_request.
 * cr_pkt is the SYN packet.
 */
static int
tcp_accept_comm(tcp_t *listener, tcp_t *acceptor, mblk_t *cr_pkt,
    uint_t ip_hdr_len)
{
        tcph_t          *tcph;

#ifdef DEBUG
        printf("tcp_accept_comm #######################\n");
#endif

        /*
         * When we get here, we know that the acceptor header template
         * has already been initialized.
         * However, it may not match the listener if the listener
         * includes options...
         * It may also not match the listener if the listener is v6 and
         * and the acceptor is v4
         */
        acceptor->tcp_lport = listener->tcp_lport;

        if (listener->tcp_ipversion == acceptor->tcp_ipversion) {
                if (acceptor->tcp_iphc_len != listener->tcp_iphc_len) {
                        /*
                         * Listener had options of some sort; acceptor inherits.
                         * Free up the acceptor template and allocate one
                         * of the right size.
                         */
                        bkmem_free(acceptor->tcp_iphc, acceptor->tcp_iphc_len);
                        acceptor->tcp_iphc = bkmem_zalloc(
                            listener->tcp_iphc_len);
                        if (acceptor->tcp_iphc == NULL) {
                                acceptor->tcp_iphc_len = 0;
                                return (ENOMEM);
                        }
                        acceptor->tcp_iphc_len = listener->tcp_iphc_len;
                }
                acceptor->tcp_hdr_len = listener->tcp_hdr_len;
                acceptor->tcp_ip_hdr_len = listener->tcp_ip_hdr_len;
                acceptor->tcp_tcp_hdr_len = listener->tcp_tcp_hdr_len;

                /*
                 * Copy the IP+TCP header template from listener to acceptor
                 */
                bcopy(listener->tcp_iphc, acceptor->tcp_iphc,
                    listener->tcp_hdr_len);
                acceptor->tcp_ipha = (struct ip *)acceptor->tcp_iphc;
                acceptor->tcp_tcph = (tcph_t *)(acceptor->tcp_iphc +
                    acceptor->tcp_ip_hdr_len);
        } else {
                prom_panic("tcp_accept_comm: version not equal");
        }

        /* Copy our new dest and fport from the connection request packet */
        if (acceptor->tcp_ipversion == IPV4_VERSION) {
                struct ip *ipha;

                ipha = (struct ip *)cr_pkt->b_rptr;
                acceptor->tcp_ipha->ip_dst = ipha->ip_src;
                acceptor->tcp_remote = ipha->ip_src.s_addr;
                acceptor->tcp_ipha->ip_src = ipha->ip_dst;
                acceptor->tcp_bound_source = ipha->ip_dst.s_addr;
                tcph = (tcph_t *)&cr_pkt->b_rptr[ip_hdr_len];
        } else {
                prom_panic("tcp_accept_comm: not IPv4");
        }
        bcopy(tcph->th_lport, acceptor->tcp_tcph->th_fport, sizeof (in_port_t));
        bcopy(acceptor->tcp_tcph->th_fport, &acceptor->tcp_fport,
            sizeof (in_port_t));
        /*
         * For an all-port proxy listener, the local port is determined by
         * the port number field in the SYN packet.
         */
        if (listener->tcp_lport == 0) {
                acceptor->tcp_lport = *(in_port_t *)tcph->th_fport;
                bcopy(tcph->th_fport, acceptor->tcp_tcph->th_lport,
                    sizeof (in_port_t));
        }
        /* Inherit various TCP parameters from the listener */
        acceptor->tcp_naglim = listener->tcp_naglim;
        acceptor->tcp_first_timer_threshold =
            listener->tcp_first_timer_threshold;
        acceptor->tcp_second_timer_threshold =
            listener->tcp_second_timer_threshold;

        acceptor->tcp_first_ctimer_threshold =
            listener->tcp_first_ctimer_threshold;
        acceptor->tcp_second_ctimer_threshold =
            listener->tcp_second_ctimer_threshold;

        acceptor->tcp_xmit_hiwater = listener->tcp_xmit_hiwater;

        acceptor->tcp_state = TCPS_LISTEN;
        tcp_iss_init(acceptor);

        /* Process all TCP options. */
        tcp_process_options(acceptor, tcph);

        /* Is the other end ECN capable? */
        if (tcp_ecn_permitted >= 1 &&
            (tcph->th_flags[0] & (TH_ECE|TH_CWR)) == (TH_ECE|TH_CWR)) {
                acceptor->tcp_ecn_ok = B_TRUE;
        }

        /*
         * listener->tcp_rq->q_hiwat should be the default window size or a
         * window size changed via SO_RCVBUF option.  First round up the
         * acceptor's tcp_rwnd to the nearest MSS.  Then find out the window
         * scale option value if needed.  Call tcp_rwnd_set() to finish the
         * setting.
         *
         * Note if there is a rpipe metric associated with the remote host,
         * we should not inherit receive window size from listener.
         */
        acceptor->tcp_rwnd = MSS_ROUNDUP(
            (acceptor->tcp_rwnd == 0 ? listener->tcp_rwnd_max :
            acceptor->tcp_rwnd), acceptor->tcp_mss);
        if (acceptor->tcp_snd_ws_ok)
                SET_WS_VALUE(acceptor);
        /*
         * Note that this is the only place tcp_rwnd_set() is called for
         * accepting a connection.  We need to call it here instead of
         * after the 3-way handshake because we need to tell the other
         * side our rwnd in the SYN-ACK segment.
         */
        (void) tcp_rwnd_set(acceptor, acceptor->tcp_rwnd);

        return (0);
}

/*
 * Defense for the SYN attack -
 * 1. When q0 is full, drop from the tail (tcp_eager_prev_q0) the oldest
 *    one that doesn't have the dontdrop bit set.
 * 2. Don't drop a SYN request before its first timeout. This gives every
 *    request at least til the first timeout to complete its 3-way handshake.
 * 3. The current threshold is - # of timeout > q0len/4 => SYN alert on
 *    # of timeout drops back to <= q0len/32 => SYN alert off
 */
static boolean_t
tcp_drop_q0(tcp_t *tcp)
{
        tcp_t   *eager;

        assert(tcp->tcp_eager_next_q0 != tcp->tcp_eager_prev_q0);
        /*
         * New one is added after next_q0 so prev_q0 points to the oldest
         * Also do not drop any established connections that are deferred on
         * q0 due to q being full
         */

        eager = tcp->tcp_eager_prev_q0;
        while (eager->tcp_dontdrop || eager->tcp_conn_def_q0) {
                /* XXX should move the eager to the head */
                eager = eager->tcp_eager_prev_q0;
                if (eager == tcp) {
                        eager = tcp->tcp_eager_prev_q0;
                        break;
                }
        }
        dprintf("tcp_drop_q0: listen half-open queue (max=%d) overflow"
            " (%d pending) on %s, drop one", tcp_conn_req_max_q0,
            tcp->tcp_conn_req_cnt_q0,
            tcp_display(tcp, NULL, DISP_PORT_ONLY));

        BUMP_MIB(tcp_mib.tcpHalfOpenDrop);
        bkmem_free((caddr_t)eager, sizeof (tcp_t));
        return (B_TRUE);
}

/* ARGSUSED */
static tcp_t *
tcp_conn_request(tcp_t *tcp, mblk_t *mp, uint_t sock_id, uint_t ip_hdr_len)
{
        tcp_t   *eager;
        struct ip *ipha;
        int     err;

#ifdef DEBUG
        printf("tcp_conn_request ###################\n");
#endif

        if (tcp->tcp_conn_req_cnt_q >= tcp->tcp_conn_req_max) {
                BUMP_MIB(tcp_mib.tcpListenDrop);
                dprintf("tcp_conn_request: listen backlog (max=%d) "
                    "overflow (%d pending) on %s",
                    tcp->tcp_conn_req_max, tcp->tcp_conn_req_cnt_q,
                    tcp_display(tcp, NULL, DISP_PORT_ONLY));
                return (NULL);
        }

        assert(OK_32PTR(mp->b_rptr));

        if (tcp->tcp_conn_req_cnt_q0 >=
            tcp->tcp_conn_req_max + tcp_conn_req_max_q0) {
                /*
                 * Q0 is full. Drop a pending half-open req from the queue
                 * to make room for the new SYN req. Also mark the time we
                 * drop a SYN.
                 */
                tcp->tcp_last_rcv_lbolt = prom_gettime();
                if (!tcp_drop_q0(tcp)) {
                        freemsg(mp);
                        BUMP_MIB(tcp_mib.tcpListenDropQ0);
                        dprintf("tcp_conn_request: listen half-open queue "
                            "(max=%d) full (%d pending) on %s",
                            tcp_conn_req_max_q0,
                            tcp->tcp_conn_req_cnt_q0,
                            tcp_display(tcp, NULL, DISP_PORT_ONLY));
                        return (NULL);
                }
        }

        ipha = (struct ip *)mp->b_rptr;
        if (IN_CLASSD(ntohl(ipha->ip_src.s_addr)) ||
            ipha->ip_src.s_addr == INADDR_BROADCAST ||
            ipha->ip_src.s_addr == INADDR_ANY ||
            ipha->ip_dst.s_addr == INADDR_BROADCAST) {
                freemsg(mp);
                return (NULL);
        }
        /*
         * We allow the connection to proceed
         * by generating a detached tcp state vector and put it in
         * the eager queue.  When an accept happens, it will be
         * dequeued sequentially.
         */
        if ((eager = (tcp_t *)bkmem_alloc(sizeof (tcp_t))) == NULL) {
                freemsg(mp);
                errno = ENOBUFS;
                return (NULL);
        }
        if ((errno = tcp_init_values(eager, NULL)) != 0) {
                freemsg(mp);
                bkmem_free((caddr_t)eager, sizeof (tcp_t));
                return (NULL);
        }

        /*
         * Eager connection inherits address form from its listener,
         * but its packet form comes from the version of the received
         * SYN segment.
         */
        eager->tcp_family = tcp->tcp_family;

        err = tcp_accept_comm(tcp, eager, mp, ip_hdr_len);
        if (err) {
                bkmem_free((caddr_t)eager, sizeof (tcp_t));
                return (NULL);
        }

        tcp->tcp_eager_next_q0->tcp_eager_prev_q0 = eager;
        eager->tcp_eager_next_q0 = tcp->tcp_eager_next_q0;
        tcp->tcp_eager_next_q0 = eager;
        eager->tcp_eager_prev_q0 = tcp;

        /* Set tcp_listener before adding it to tcp_conn_fanout */
        eager->tcp_listener = tcp;
        tcp->tcp_conn_req_cnt_q0++;

        return (eager);
}

/*
 * To get around the non-interrupt problem of inetboot.
 * Keep on processing packets until a certain state is reached or the
 * TCP is destroyed because of getting a RST packet.
 */
static int
tcp_state_wait(int sock_id, tcp_t *tcp, int state)
{
        int i;
        struct inetgram *in_gram;
        mblk_t *mp;
        int timeout;
        boolean_t changed = B_FALSE;

        /*
         * We need to make sure that the MAC does not wait longer
         * than RTO for any packet so that TCP can do retransmission.
         * But if the MAC timeout is less than tcp_rto, we are fine
         * and do not need to change it.
         */
        timeout = sockets[sock_id].in_timeout;
        if (timeout > tcp->tcp_rto) {
                sockets[sock_id].in_timeout = tcp->tcp_rto;
                changed = B_TRUE;
        }
retry:
        if (sockets[sock_id].inq == NULL) {
                /* Go out and check the wire */
                for (i = MEDIA_LVL; i < TRANSPORT_LVL; i++) {
                        if (sockets[sock_id].input[i] != NULL) {
                                if (sockets[sock_id].input[i](sock_id) < 0) {
                                        if (changed) {
                                                sockets[sock_id].in_timeout =
                                                    timeout;
                                        }
                                        return (-1);
                                }
                        }
                }
        }

        while ((in_gram = sockets[sock_id].inq) != NULL) {
                if (tcp != NULL && tcp->tcp_state == state)
                        break;

                /* Remove unknown inetgrams from the head of inq. */
                if (in_gram->igm_level != TRANSPORT_LVL) {
#ifdef DEBUG
                        printf("tcp_state_wait for state %d: unexpected "
                            "packet level %d frame found\n", state,
                            in_gram->igm_level);
#endif
                        del_gram(&sockets[sock_id].inq, in_gram, B_TRUE);
                        continue;
                }
                mp = in_gram->igm_mp;
                del_gram(&sockets[sock_id].inq, in_gram, B_FALSE);
                bkmem_free((caddr_t)in_gram, sizeof (struct inetgram));
                tcp_rput_data(tcp, mp, sock_id);

                /*
                 * The other side may have closed this connection or
                 * RST us.  But we need to continue to process other
                 * packets in the socket's queue because they may be
                 * belong to another TCP connections.
                 */
                if (sockets[sock_id].pcb == NULL) {
                        tcp = NULL;
                }
        }

        /* If the other side has closed the connection, just return. */
        if (tcp == NULL || sockets[sock_id].pcb == NULL) {
#ifdef DEBUG
                printf("tcp_state_wait other side dead: state %d "
                    "error %d\n", state, sockets[sock_id].so_error);
#endif
                if (sockets[sock_id].so_error != 0)
                        return (-1);
                else
                        return (0);
        }
        /*
         * TCPS_ALL_ACKED is not a valid TCP state, it is just used as an
         * indicator to tcp_state_wait to mean that it is being called
         * to wait till we have received acks for all the new segments sent.
         */
        if ((state == TCPS_ALL_ACKED) && (tcp->tcp_suna == tcp->tcp_snxt)) {
                goto done;
        }
        if (tcp->tcp_state != state) {
                if (prom_gettime() > tcp->tcp_rto_timeout)
                        tcp_timer(tcp, sock_id);
                goto retry;
        }
done:
        if (changed)
                sockets[sock_id].in_timeout = timeout;

        tcp_drain_needed(sock_id, tcp);
        return (0);
}

/* Verify the checksum of a segment. */
static int
tcp_verify_cksum(mblk_t *mp)
{
        struct ip *iph;
        tcpha_t *tcph;
        int len;
        uint16_t old_sum;

        iph = (struct ip *)mp->b_rptr;
        tcph = (tcpha_t *)(iph + 1);
        len = ntohs(iph->ip_len);

        /*
         * Calculate the TCP checksum.  Need to include the psuedo header,
         * which is similar to the real IP header starting at the TTL field.
         */
        iph->ip_sum = htons(len - IP_SIMPLE_HDR_LENGTH);
        old_sum = tcph->tha_sum;
        tcph->tha_sum = 0;
        iph->ip_ttl = 0;
        if (old_sum == tcp_cksum((uint16_t *)&(iph->ip_ttl),
            len - IP_SIMPLE_HDR_LENGTH + 12)) {
                return (0);
        } else {
                tcp_cksum_errors++;
                return (-1);
        }
}

/* To find a TCP connection matching the incoming segment. */
static tcp_t *
tcp_lookup_ipv4(struct ip *iph, tcpha_t *tcph, int min_state, int *sock_id)
{
        int i;
        tcp_t *tcp;

        for (i = 0; i < MAXSOCKET; i++) {
                if (sockets[i].type == INETBOOT_STREAM &&
                    (tcp = (tcp_t *)sockets[i].pcb) != NULL) {
                        if (tcph->tha_lport == tcp->tcp_fport &&
                            tcph->tha_fport == tcp->tcp_lport &&
                            iph->ip_src.s_addr == tcp->tcp_remote &&
                            iph->ip_dst.s_addr == tcp->tcp_bound_source &&
                            tcp->tcp_state >= min_state) {
                                *sock_id = i;
                                return (tcp);
                        }
                }
        }
        /* Find it in the time wait list. */
        for (tcp = tcp_time_wait_head; tcp != NULL;
            tcp = tcp->tcp_time_wait_next) {
                if (tcph->tha_lport == tcp->tcp_fport &&
                    tcph->tha_fport == tcp->tcp_lport &&
                    iph->ip_src.s_addr == tcp->tcp_remote &&
                    iph->ip_dst.s_addr == tcp->tcp_bound_source &&
                    tcp->tcp_state >= min_state) {
                        *sock_id = -1;
                        return (tcp);
                }
        }
        return (NULL);
}

/* To find a TCP listening connection matching the incoming segment. */
static tcp_t *
tcp_lookup_listener_ipv4(in_addr_t addr, in_port_t port, int *sock_id)
{
        int i;
        tcp_t *tcp;

        for (i = 0; i < MAXSOCKET; i++) {
                if (sockets[i].type == INETBOOT_STREAM &&
                    (tcp = (tcp_t *)sockets[i].pcb) != NULL) {
                        if (tcp->tcp_lport == port &&
                            (tcp->tcp_bound_source == addr ||
                            tcp->tcp_bound_source == INADDR_ANY)) {
                                *sock_id = i;
                                return (tcp);
                        }
                }
        }

        return (NULL);
}

/* To find a TCP eager matching the incoming segment. */
static tcp_t *
tcp_lookup_eager_ipv4(tcp_t *listener, struct ip *iph, tcpha_t *tcph)
{
        tcp_t *tcp;

#ifdef DEBUG
        printf("tcp_lookup_eager_ipv4 ###############\n");
#endif
        for (tcp = listener->tcp_eager_next_q; tcp != NULL;
            tcp = tcp->tcp_eager_next_q) {
                if (tcph->tha_lport == tcp->tcp_fport &&
                    tcph->tha_fport == tcp->tcp_lport &&
                    iph->ip_src.s_addr == tcp->tcp_remote &&
                    iph->ip_dst.s_addr == tcp->tcp_bound_source) {
                        return (tcp);
                }
        }

        for (tcp = listener->tcp_eager_next_q0; tcp != listener;
            tcp = tcp->tcp_eager_next_q0) {
                if (tcph->tha_lport == tcp->tcp_fport &&
                    tcph->tha_fport == tcp->tcp_lport &&
                    iph->ip_src.s_addr == tcp->tcp_remote &&
                    iph->ip_dst.s_addr == tcp->tcp_bound_source) {
                        return (tcp);
                }
        }
#ifdef DEBUG
        printf("No eager found\n");
#endif
        return (NULL);
}

/* To destroy a TCP control block. */
static void
tcp_clean_death(int sock_id, tcp_t *tcp, int err)
{
        tcp_free(tcp);
        if (tcp->tcp_state == TCPS_TIME_WAIT)
                tcp_time_wait_remove(tcp);

        if (sock_id >= 0) {
                sockets[sock_id].pcb = NULL;
                if (err != 0)
                        sockets[sock_id].so_error = err;
        }
        bkmem_free((caddr_t)tcp, sizeof (tcp_t));
}

/*
 * tcp_rwnd_set() is called to adjust the receive window to a desired value.
 * We do not allow the receive window to shrink.  After setting rwnd,
 * set the flow control hiwat of the stream.
 *
 * This function is called in 2 cases:
 *
 * 1) Before data transfer begins, in tcp_accept_comm() for accepting a
 *    connection (passive open) and in tcp_rput_data() for active connect.
 *    This is called after tcp_mss_set() when the desired MSS value is known.
 *    This makes sure that our window size is a mutiple of the other side's
 *    MSS.
 * 2) Handling SO_RCVBUF option.
 *
 * It is ASSUMED that the requested size is a multiple of the current MSS.
 *
 * XXX - Should allow a lower rwnd than tcp_recv_hiwat_minmss * mss if the
 * user requests so.
 */
static int
tcp_rwnd_set(tcp_t *tcp, uint32_t rwnd)
{
        uint32_t        mss = tcp->tcp_mss;
        uint32_t        old_max_rwnd;
        uint32_t        max_transmittable_rwnd;

        if (tcp->tcp_rwnd_max != 0)
                old_max_rwnd = tcp->tcp_rwnd_max;
        else
                old_max_rwnd = tcp->tcp_rwnd;

        /*
         * Insist on a receive window that is at least
         * tcp_recv_hiwat_minmss * MSS (default 4 * MSS) to avoid
         * funny TCP interactions of Nagle algorithm, SWS avoidance
         * and delayed acknowledgement.
         */
        rwnd = MAX(rwnd, tcp_recv_hiwat_minmss * mss);

        /*
         * If window size info has already been exchanged, TCP should not
         * shrink the window.  Shrinking window is doable if done carefully.
         * We may add that support later.  But so far there is not a real
         * need to do that.
         */
        if (rwnd < old_max_rwnd && tcp->tcp_state > TCPS_SYN_SENT) {
                /* MSS may have changed, do a round up again. */
                rwnd = MSS_ROUNDUP(old_max_rwnd, mss);
        }

        /*
         * tcp_rcv_ws starts with TCP_MAX_WINSHIFT so the following check
         * can be applied even before the window scale option is decided.
         */
        max_transmittable_rwnd = TCP_MAXWIN << tcp->tcp_rcv_ws;
        if (rwnd > max_transmittable_rwnd) {
                rwnd = max_transmittable_rwnd -
                    (max_transmittable_rwnd % mss);
                if (rwnd < mss)
                        rwnd = max_transmittable_rwnd;
                /*
                 * If we're over the limit we may have to back down tcp_rwnd.
                 * The increment below won't work for us. So we set all three
                 * here and the increment below will have no effect.
                 */
                tcp->tcp_rwnd = old_max_rwnd = rwnd;
        }

        /*
         * Increment the current rwnd by the amount the maximum grew (we
         * can not overwrite it since we might be in the middle of a
         * connection.)
         */
        tcp->tcp_rwnd += rwnd - old_max_rwnd;
        U32_TO_ABE16(tcp->tcp_rwnd >> tcp->tcp_rcv_ws, tcp->tcp_tcph->th_win);
        if ((tcp->tcp_rcv_ws > 0) && rwnd > tcp->tcp_cwnd_max)
                tcp->tcp_cwnd_max = rwnd;
        tcp->tcp_rwnd_max = rwnd;

        return (rwnd);
}

/*
 * Extract option values from a tcp header.  We put any found values into the
 * tcpopt struct and return a bitmask saying which options were found.
 */
static int
tcp_parse_options(tcph_t *tcph, tcp_opt_t *tcpopt)
{
        uchar_t         *endp;
        int             len;
        uint32_t        mss;
        uchar_t         *up = (uchar_t *)tcph;
        int             found = 0;
        int32_t         sack_len;
        tcp_seq         sack_begin, sack_end;
        tcp_t           *tcp;

        endp = up + TCP_HDR_LENGTH(tcph);
        up += TCP_MIN_HEADER_LENGTH;
        while (up < endp) {
                len = endp - up;
                switch (*up) {
                case TCPOPT_EOL:
                        break;

                case TCPOPT_NOP:
                        up++;
                        continue;

                case TCPOPT_MAXSEG:
                        if (len < TCPOPT_MAXSEG_LEN ||
                            up[1] != TCPOPT_MAXSEG_LEN)
                                break;

                        mss = BE16_TO_U16(up+2);
                        /* Caller must handle tcp_mss_min and tcp_mss_max_* */
                        tcpopt->tcp_opt_mss = mss;
                        found |= TCP_OPT_MSS_PRESENT;

                        up += TCPOPT_MAXSEG_LEN;
                        continue;

                case TCPOPT_WSCALE:
                        if (len < TCPOPT_WS_LEN || up[1] != TCPOPT_WS_LEN)
                                break;

                        if (up[2] > TCP_MAX_WINSHIFT)
                                tcpopt->tcp_opt_wscale = TCP_MAX_WINSHIFT;
                        else
                                tcpopt->tcp_opt_wscale = up[2];
                        found |= TCP_OPT_WSCALE_PRESENT;

                        up += TCPOPT_WS_LEN;
                        continue;

                case TCPOPT_SACK_PERMITTED:
                        if (len < TCPOPT_SACK_OK_LEN ||
                            up[1] != TCPOPT_SACK_OK_LEN)
                                break;
                        found |= TCP_OPT_SACK_OK_PRESENT;
                        up += TCPOPT_SACK_OK_LEN;
                        continue;

                case TCPOPT_SACK:
                        if (len <= 2 || up[1] <= 2 || len < up[1])
                                break;

                        /* If TCP is not interested in SACK blks... */
                        if ((tcp = tcpopt->tcp) == NULL) {
                                up += up[1];
                                continue;
                        }
                        sack_len = up[1] - TCPOPT_HEADER_LEN;
                        up += TCPOPT_HEADER_LEN;

                        /*
                         * If the list is empty, allocate one and assume
                         * nothing is sack'ed.
                         */
                        assert(tcp->tcp_sack_info != NULL);
                        if (tcp->tcp_notsack_list == NULL) {
                                tcp_notsack_update(&(tcp->tcp_notsack_list),
                                    tcp->tcp_suna, tcp->tcp_snxt,
                                    &(tcp->tcp_num_notsack_blk),
                                    &(tcp->tcp_cnt_notsack_list));

                                /*
                                 * Make sure tcp_notsack_list is not NULL.
                                 * This happens when kmem_alloc(KM_NOSLEEP)
                                 * returns NULL.
                                 */
                                if (tcp->tcp_notsack_list == NULL) {
                                        up += sack_len;
                                        continue;
                                }
                                tcp->tcp_fack = tcp->tcp_suna;
                        }

                        while (sack_len > 0) {
                                if (up + 8 > endp) {
                                        up = endp;
                                        break;
                                }
                                sack_begin = BE32_TO_U32(up);
                                up += 4;
                                sack_end = BE32_TO_U32(up);
                                up += 4;
                                sack_len -= 8;
                                /*
                                 * Bounds checking.  Make sure the SACK
                                 * info is within tcp_suna and tcp_snxt.
                                 * If this SACK blk is out of bound, ignore
                                 * it but continue to parse the following
                                 * blks.
                                 */
                                if (SEQ_LEQ(sack_end, sack_begin) ||
                                    SEQ_LT(sack_begin, tcp->tcp_suna) ||
                                    SEQ_GT(sack_end, tcp->tcp_snxt)) {
                                        continue;
                                }
                                tcp_notsack_insert(&(tcp->tcp_notsack_list),
                                    sack_begin, sack_end,
                                    &(tcp->tcp_num_notsack_blk),
                                    &(tcp->tcp_cnt_notsack_list));
                                if (SEQ_GT(sack_end, tcp->tcp_fack)) {
                                        tcp->tcp_fack = sack_end;
                                }
                        }
                        found |= TCP_OPT_SACK_PRESENT;
                        continue;

                case TCPOPT_TSTAMP:
                        if (len < TCPOPT_TSTAMP_LEN ||
                            up[1] != TCPOPT_TSTAMP_LEN)
                                break;

                        tcpopt->tcp_opt_ts_val = BE32_TO_U32(up+2);
                        tcpopt->tcp_opt_ts_ecr = BE32_TO_U32(up+6);

                        found |= TCP_OPT_TSTAMP_PRESENT;

                        up += TCPOPT_TSTAMP_LEN;
                        continue;

                default:
                        if (len <= 1 || len < (int)up[1] || up[1] == 0)
                                break;
                        up += up[1];
                        continue;
                }
                break;
        }
        return (found);
}

/*
 * Set the mss associated with a particular tcp based on its current value,
 * and a new one passed in. Observe minimums and maximums, and reset
 * other state variables that we want to view as multiples of mss.
 *
 * This function is called in various places mainly because
 * 1) Various stuffs, tcp_mss, tcp_cwnd, ... need to be adjusted when the
 *    other side's SYN/SYN-ACK packet arrives.
 * 2) PMTUd may get us a new MSS.
 * 3) If the other side stops sending us timestamp option, we need to
 *    increase the MSS size to use the extra bytes available.
 */
static void
tcp_mss_set(tcp_t *tcp, uint32_t mss)
{
        uint32_t        mss_max;

        mss_max = tcp_mss_max_ipv4;

        if (mss < tcp_mss_min)
                mss = tcp_mss_min;
        if (mss > mss_max)
                mss = mss_max;
        /*
         * Unless naglim has been set by our client to
         * a non-mss value, force naglim to track mss.
         * This can help to aggregate small writes.
         */
        if (mss < tcp->tcp_naglim || tcp->tcp_mss == tcp->tcp_naglim)
                tcp->tcp_naglim = mss;
        /*
         * TCP should be able to buffer at least 4 MSS data for obvious
         * performance reason.
         */
        if ((mss << 2) > tcp->tcp_xmit_hiwater)
                tcp->tcp_xmit_hiwater = mss << 2;
        tcp->tcp_mss = mss;
        /*
         * Initialize cwnd according to draft-floyd-incr-init-win-01.txt.
         * Previously, we use tcp_slow_start_initial to control the size
         * of the initial cwnd.  Now, when tcp_slow_start_initial * mss
         * is smaller than the cwnd calculated from the formula suggested in
         * the draft, we use tcp_slow_start_initial * mss as the cwnd.
         * Otherwise, use the cwnd from the draft's formula.  The default
         * of tcp_slow_start_initial is 2.
         */
        tcp->tcp_cwnd = MIN(tcp_slow_start_initial * mss,
            MIN(4 * mss, MAX(2 * mss, 4380 / mss * mss)));
        tcp->tcp_cwnd_cnt = 0;
}

/*
 * Process all TCP option in SYN segment.
 *
 * This function sets up the correct tcp_mss value according to the
 * MSS option value and our header size.  It also sets up the window scale
 * and timestamp values, and initialize SACK info blocks.  But it does not
 * change receive window size after setting the tcp_mss value.  The caller
 * should do the appropriate change.
 */
void
tcp_process_options(tcp_t *tcp, tcph_t *tcph)
{
        int options;
        tcp_opt_t tcpopt;
        uint32_t mss_max;
        char *tmp_tcph;

        tcpopt.tcp = NULL;
        options = tcp_parse_options(tcph, &tcpopt);

        /*
         * Process MSS option.  Note that MSS option value does not account
         * for IP or TCP options.  This means that it is equal to MTU - minimum
         * IP+TCP header size, which is 40 bytes for IPv4 and 60 bytes for
         * IPv6.
         */
        if (!(options & TCP_OPT_MSS_PRESENT)) {
                tcpopt.tcp_opt_mss = tcp_mss_def_ipv4;
        } else {
                if (tcp->tcp_ipversion == IPV4_VERSION)
                        mss_max = tcp_mss_max_ipv4;
                if (tcpopt.tcp_opt_mss < tcp_mss_min)
                        tcpopt.tcp_opt_mss = tcp_mss_min;
                else if (tcpopt.tcp_opt_mss > mss_max)
                        tcpopt.tcp_opt_mss = mss_max;
        }

        /* Process Window Scale option. */
        if (options & TCP_OPT_WSCALE_PRESENT) {
                tcp->tcp_snd_ws = tcpopt.tcp_opt_wscale;
                tcp->tcp_snd_ws_ok = B_TRUE;
        } else {
                tcp->tcp_snd_ws = B_FALSE;
                tcp->tcp_snd_ws_ok = B_FALSE;
                tcp->tcp_rcv_ws = B_FALSE;
        }

        /* Process Timestamp option. */
        if ((options & TCP_OPT_TSTAMP_PRESENT) &&
            (tcp->tcp_snd_ts_ok || !tcp->tcp_active_open)) {
                tmp_tcph = (char *)tcp->tcp_tcph;

                tcp->tcp_snd_ts_ok = B_TRUE;
                tcp->tcp_ts_recent = tcpopt.tcp_opt_ts_val;
                tcp->tcp_last_rcv_lbolt = prom_gettime();
                assert(OK_32PTR(tmp_tcph));
                assert(tcp->tcp_tcp_hdr_len == TCP_MIN_HEADER_LENGTH);

                /* Fill in our template header with basic timestamp option. */
                tmp_tcph += tcp->tcp_tcp_hdr_len;
                tmp_tcph[0] = TCPOPT_NOP;
                tmp_tcph[1] = TCPOPT_NOP;
                tmp_tcph[2] = TCPOPT_TSTAMP;
                tmp_tcph[3] = TCPOPT_TSTAMP_LEN;
                tcp->tcp_hdr_len += TCPOPT_REAL_TS_LEN;
                tcp->tcp_tcp_hdr_len += TCPOPT_REAL_TS_LEN;
                tcp->tcp_tcph->th_offset_and_rsrvd[0] += (3 << 4);
        } else {
                tcp->tcp_snd_ts_ok = B_FALSE;
        }

        /*
         * Process SACK options.  If SACK is enabled for this connection,
         * then allocate the SACK info structure.
         */
        if ((options & TCP_OPT_SACK_OK_PRESENT) &&
            (tcp->tcp_snd_sack_ok ||
            (tcp_sack_permitted != 0 && !tcp->tcp_active_open))) {
                /* This should be true only in the passive case. */
                if (tcp->tcp_sack_info == NULL) {
                        tcp->tcp_sack_info = (tcp_sack_info_t *)bkmem_zalloc(
                            sizeof (tcp_sack_info_t));
                }
                if (tcp->tcp_sack_info == NULL) {
                        tcp->tcp_snd_sack_ok = B_FALSE;
                } else {
                        tcp->tcp_snd_sack_ok = B_TRUE;
                        if (tcp->tcp_snd_ts_ok) {
                                tcp->tcp_max_sack_blk = 3;
                        } else {
                                tcp->tcp_max_sack_blk = 4;
                        }
                }
        } else {
                /*
                 * Resetting tcp_snd_sack_ok to B_FALSE so that
                 * no SACK info will be used for this
                 * connection.  This assumes that SACK usage
                 * permission is negotiated.  This may need
                 * to be changed once this is clarified.
                 */
                if (tcp->tcp_sack_info != NULL) {
                        bkmem_free((caddr_t)tcp->tcp_sack_info,
                            sizeof (tcp_sack_info_t));
                        tcp->tcp_sack_info = NULL;
                }
                tcp->tcp_snd_sack_ok = B_FALSE;
        }

        /*
         * Now we know the exact TCP/IP header length, subtract
         * that from tcp_mss to get our side's MSS.
         */
        tcp->tcp_mss -= tcp->tcp_hdr_len;
        /*
         * Here we assume that the other side's header size will be equal to
         * our header size.  We calculate the real MSS accordingly.  Need to
         * take into additional stuffs IPsec puts in.
         *
         * Real MSS = Opt.MSS - (our TCP/IP header - min TCP/IP header)
         */
        tcpopt.tcp_opt_mss -= tcp->tcp_hdr_len -
            (IP_SIMPLE_HDR_LENGTH + TCP_MIN_HEADER_LENGTH);

        /*
         * Set MSS to the smaller one of both ends of the connection.
         * We should not have called tcp_mss_set() before, but our
         * side of the MSS should have been set to a proper value
         * by tcp_adapt_ire().  tcp_mss_set() will also set up the
         * STREAM head parameters properly.
         *
         * If we have a larger-than-16-bit window but the other side
         * didn't want to do window scale, tcp_rwnd_set() will take
         * care of that.
         */
        tcp_mss_set(tcp, MIN(tcpopt.tcp_opt_mss, tcp->tcp_mss));
}

/*
 * This function does PAWS protection check.  Returns B_TRUE if the
 * segment passes the PAWS test, else returns B_FALSE.
 */
boolean_t
tcp_paws_check(tcp_t *tcp, tcph_t *tcph, tcp_opt_t *tcpoptp)
{
        uint8_t flags;
        int     options;
        uint8_t *up;

        flags = (unsigned int)tcph->th_flags[0] & 0xFF;
        /*
         * If timestamp option is aligned nicely, get values inline,
         * otherwise call general routine to parse.  Only do that
         * if timestamp is the only option.
         */
        if (TCP_HDR_LENGTH(tcph) == (uint32_t)TCP_MIN_HEADER_LENGTH +
            TCPOPT_REAL_TS_LEN &&
            OK_32PTR((up = ((uint8_t *)tcph) +
            TCP_MIN_HEADER_LENGTH)) &&
            *(uint32_t *)up == TCPOPT_NOP_NOP_TSTAMP) {
                tcpoptp->tcp_opt_ts_val = ABE32_TO_U32((up+4));
                tcpoptp->tcp_opt_ts_ecr = ABE32_TO_U32((up+8));

                options = TCP_OPT_TSTAMP_PRESENT;
        } else {
                if (tcp->tcp_snd_sack_ok) {
                        tcpoptp->tcp = tcp;
                } else {
                        tcpoptp->tcp = NULL;
                }
                options = tcp_parse_options(tcph, tcpoptp);
        }

        if (options & TCP_OPT_TSTAMP_PRESENT) {
                /*
                 * Do PAWS per RFC 1323 section 4.2.  Accept RST
                 * regardless of the timestamp, page 18 RFC 1323.bis.
                 */
                if ((flags & TH_RST) == 0 &&
                    TSTMP_LT(tcpoptp->tcp_opt_ts_val,
                    tcp->tcp_ts_recent)) {
                        if (TSTMP_LT(prom_gettime(),
                            tcp->tcp_last_rcv_lbolt + PAWS_TIMEOUT)) {
                                /* This segment is not acceptable. */
                                return (B_FALSE);
                        } else {
                                /*
                                 * Connection has been idle for
                                 * too long.  Reset the timestamp
                                 * and assume the segment is valid.
                                 */
                                tcp->tcp_ts_recent =
                                    tcpoptp->tcp_opt_ts_val;
                        }
                }
        } else {
                /*
                 * If we don't get a timestamp on every packet, we
                 * figure we can't really trust 'em, so we stop sending
                 * and parsing them.
                 */
                tcp->tcp_snd_ts_ok = B_FALSE;

                tcp->tcp_hdr_len -= TCPOPT_REAL_TS_LEN;
                tcp->tcp_tcp_hdr_len -= TCPOPT_REAL_TS_LEN;
                tcp->tcp_tcph->th_offset_and_rsrvd[0] -= (3 << 4);
                tcp_mss_set(tcp, tcp->tcp_mss + TCPOPT_REAL_TS_LEN);
                if (tcp->tcp_snd_sack_ok) {
                        assert(tcp->tcp_sack_info != NULL);
                        tcp->tcp_max_sack_blk = 4;
                }
        }
        return (B_TRUE);
}

/*
 * tcp_get_seg_mp() is called to get the pointer to a segment in the
 * 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.
 *
 * 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_GEQ(seq, tcp->tcp_snxt) ||
            off == NULL) {
                return (NULL);
        }
        cnt = seq - tcp->tcp_suna;
        mp = tcp->tcp_xmit_head;
        while (cnt > 0 && mp) {
                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 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, it returns 1.  Otherwise it returns 0.
 *
 * Parameters:
 *      tcp_t *tcp: the tcp structure of the connection.
 *
 * Return:
 *      1 if the pipe is not full (new data can be sent), 0 otherwise
 */
static int32_t
tcp_sack_rxmit(tcp_t *tcp, int sock_id)
{
        notsack_blk_t   *notsack_blk;
        int32_t         usable_swnd;
        int32_t         mss;
        uint32_t        seg_len;
        mblk_t          *xmit_mp;

        assert(tcp->tcp_sack_info != NULL);
        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 (0);
        }
        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 >=
                            tcp_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_cwnd = tcp->tcp_snxt - tcp->tcp_suna;
                                assert(tcp->tcp_cwnd > 0);
                                return (0);
                        } else {
                                usable_swnd = usable_swnd / mss;
                                tcp->tcp_cwnd = tcp->tcp_snxt - tcp->tcp_suna +
                                    MAX(usable_swnd * mss, mss);
                                return (1);
                        }
                }

                /*
                 * 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 (0);
                }

                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 (0);

                usable_swnd -= seg_len;
                tcp->tcp_pipe += seg_len;
                tcp->tcp_sack_snxt = begin + seg_len;
                TCP_DUMP_PACKET("tcp_sack_rxmit", xmit_mp);
                (void) ipv4_tcp_output(sock_id, xmit_mp);
                freeb(xmit_mp);

                /*
                 * Update the send timestamp to avoid false retransmission.
                 * Note. use uintptr_t to suppress the gcc warning.
                 */
                snxt_mp->b_prev = (mblk_t *)(uintptr_t)prom_gettime();

                BUMP_MIB(tcp_mib.tcpRetransSegs);
                UPDATE_MIB(tcp_mib.tcpRetransBytes, seg_len);
                BUMP_MIB(tcp_mib.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;
                }
        }
        return (0);
}

static void
tcp_rput_data(tcp_t *tcp, mblk_t *mp, int sock_id)
{
        uchar_t         *rptr;
        struct ip       *iph;
        tcp_t           *tcp1;
        tcpha_t         *tcph;
        uint32_t        seg_ack;
        int             seg_len;
        uint_t          ip_hdr_len;
        uint32_t        seg_seq;
        mblk_t          *mp1;
        uint_t          flags;
        uint32_t        new_swnd = 0;
        int             mss;
        boolean_t       ofo_seg = B_FALSE; /* Out of order segment */
        int32_t         gap;
        int32_t         rgap;
        tcp_opt_t       tcpopt;
        int32_t         bytes_acked;
        int             npkt;
        uint32_t        cwnd;
        uint32_t        add;

#ifdef DEBUG
        printf("tcp_rput_data sock %d mp %x mp_datap %x #################\n",
            sock_id, mp, mp->b_datap);
#endif

        /* Dump the packet when debugging. */
        TCP_DUMP_PACKET("tcp_rput_data", mp);

        assert(OK_32PTR(mp->b_rptr));

        rptr = mp->b_rptr;
        iph = (struct ip *)rptr;
        ip_hdr_len = IPH_HDR_LENGTH(rptr);
        if (ip_hdr_len != IP_SIMPLE_HDR_LENGTH) {
#ifdef DEBUG
                printf("Not simple IP header\n");
#endif
                /* We cannot handle IP option yet... */
                tcp_drops++;
                freeb(mp);
                return;
        }
        /* The TCP header must be aligned. */
        tcph = (tcpha_t *)&rptr[ip_hdr_len];
        seg_seq = ntohl(tcph->tha_seq);
        seg_ack = ntohl(tcph->tha_ack);
        assert((uintptr_t)(mp->b_wptr - rptr) <= (uintptr_t)INT_MAX);
        seg_len = (int)(mp->b_wptr - rptr) -
            (ip_hdr_len + TCP_HDR_LENGTH(((tcph_t *)tcph)));
        /* In inetboot, b_cont should always be NULL. */
        assert(mp->b_cont == NULL);

        /* Verify the checksum. */
        if (tcp_verify_cksum(mp) < 0) {
#ifdef DEBUG
                printf("tcp_rput_data: wrong cksum\n");
#endif
                freemsg(mp);
                return;
        }

        /*
         * This segment is not for us, try to find its
         * intended receiver.
         */
        if (tcp == NULL ||
            tcph->tha_lport != tcp->tcp_fport ||
            tcph->tha_fport != tcp->tcp_lport ||
            iph->ip_src.s_addr != tcp->tcp_remote ||
            iph->ip_dst.s_addr != tcp->tcp_bound_source) {
#ifdef DEBUG
                printf("tcp_rput_data: not for us, state %d\n",
                    tcp->tcp_state);
#endif
                /*
                 * First try to find a established connection.  If none
                 * is found, look for a listener.
                 *
                 * If a listener is found, we need to check to see if the
                 * incoming segment is for one of its eagers.  If it is,
                 * give it to the eager.  If not, listener should take care
                 * of it.
                 */
                if ((tcp1 = tcp_lookup_ipv4(iph, tcph, TCPS_SYN_SENT,
                    &sock_id)) != NULL ||
                    (tcp1 = tcp_lookup_listener_ipv4(iph->ip_dst.s_addr,
                    tcph->tha_fport, &sock_id)) != NULL) {
                        if (tcp1->tcp_state == TCPS_LISTEN) {
                                if ((tcp = tcp_lookup_eager_ipv4(tcp1,
                                    iph, tcph)) == NULL) {
                                        /* No eager... sent to listener */
#ifdef DEBUG
                                        printf("found the listener: %s\n",
                                            tcp_display(tcp1, NULL,
                                            DISP_ADDR_AND_PORT));
#endif
                                        tcp = tcp1;
                                }
#ifdef DEBUG
                                else {
                                        printf("found the eager: %s\n",
                                            tcp_display(tcp, NULL,
                                            DISP_ADDR_AND_PORT));
                                }
#endif
                        } else {
                                /* Non listener found... */
#ifdef DEBUG
                                printf("found the connection: %s\n",
                                    tcp_display(tcp1, NULL,
                                    DISP_ADDR_AND_PORT));
#endif
                                tcp = tcp1;
                        }
                } else {
                        /*
                         * No connection for this segment...
                         * Send a RST to the other side.
                         */
                        tcp_xmit_listeners_reset(sock_id, mp, ip_hdr_len);
                        return;
                }
        }

        flags = tcph->tha_flags & 0xFF;
        BUMP_MIB(tcp_mib.tcpInSegs);
        if (tcp->tcp_state == TCPS_TIME_WAIT) {
                tcp_time_wait_processing(tcp, mp, seg_seq, seg_ack,
                    seg_len, (tcph_t *)tcph, sock_id);
                return;
        }
        /*
         * From this point we can assume that the tcp is not compressed,
         * since we would have branched off to tcp_time_wait_processing()
         * in such a case.
         */
        assert(tcp != NULL && tcp->tcp_state != TCPS_TIME_WAIT);

        /*
         * After this point, we know we have the correct TCP, so update
         * the receive time.
         */
        tcp->tcp_last_recv_time = prom_gettime();

        /* In inetboot, we do not handle urgent pointer... */
        if (flags & TH_URG) {
                freemsg(mp);
                DEBUG_1("tcp_rput_data(%d): received segment with urgent "
                    "pointer\n", sock_id);
                tcp_drops++;
                return;
        }

        switch (tcp->tcp_state) {
        case TCPS_LISTEN:
                if ((flags & (TH_RST | TH_ACK | TH_SYN)) != TH_SYN) {
                        if (flags & TH_RST) {
                                freemsg(mp);
                                return;
                        }
                        if (flags & TH_ACK) {
                                tcp_xmit_early_reset("TCPS_LISTEN-TH_ACK",
                                    sock_id, mp, seg_ack, 0, TH_RST,
                                    ip_hdr_len);
                                return;
                        }
                        if (!(flags & TH_SYN)) {
                                freemsg(mp);
                                return;
                        }
                        printf("tcp_rput_data: %d\n", __LINE__);
                        prom_panic("inetboot");
                }
                if (tcp->tcp_conn_req_max > 0) {
                        tcp = tcp_conn_request(tcp, mp, sock_id, ip_hdr_len);
                        if (tcp == NULL) {
                                freemsg(mp);
                                return;
                        }
#ifdef DEBUG
                        printf("tcp_rput_data: new tcp created\n");
#endif
                }
                tcp->tcp_irs = seg_seq;
                tcp->tcp_rack = seg_seq;
                tcp->tcp_rnxt = seg_seq + 1;
                U32_TO_ABE32(tcp->tcp_rnxt, tcp->tcp_tcph->th_ack);
                BUMP_MIB(tcp_mib.tcpPassiveOpens);
                goto syn_rcvd;
        case TCPS_SYN_SENT:
                if (flags & TH_ACK) {
                        /*
                         * Note that our stack cannot send data before a
                         * connection is established, therefore the
                         * following check is valid.  Otherwise, it has
                         * to be changed.
                         */
                        if (SEQ_LEQ(seg_ack, tcp->tcp_iss) ||
                            SEQ_GT(seg_ack, tcp->tcp_snxt)) {
                                if (flags & TH_RST) {
                                        freemsg(mp);
                                        return;
                                }
                                tcp_xmit_ctl("TCPS_SYN_SENT-Bad_seq",
                                    tcp, mp, seg_ack, 0, TH_RST,
                                    ip_hdr_len, sock_id);
                                return;
                        }
                        assert(tcp->tcp_suna + 1 == seg_ack);
                }
                if (flags & TH_RST) {
                        freemsg(mp);
                        if (flags & TH_ACK) {
                                tcp_clean_death(sock_id, tcp, ECONNREFUSED);
                        }
                        return;
                }
                if (!(flags & TH_SYN)) {
                        freemsg(mp);
                        return;
                }

                /* Process all TCP options. */
                tcp_process_options(tcp, (tcph_t *)tcph);
                /*
                 * The following changes our rwnd to be a multiple of the
                 * MIN(peer MSS, our MSS) for performance reason.
                 */
                (void) tcp_rwnd_set(tcp, MSS_ROUNDUP(tcp->tcp_rwnd,
                    tcp->tcp_mss));

                /* Is the other end ECN capable? */
                if (tcp->tcp_ecn_ok) {
                        if ((flags & (TH_ECE|TH_CWR)) != TH_ECE) {
                                tcp->tcp_ecn_ok = B_FALSE;
                        }
                }
                /*
                 * Clear ECN flags because it may interfere with later
                 * processing.
                 */
                flags &= ~(TH_ECE|TH_CWR);

                tcp->tcp_irs = seg_seq;
                tcp->tcp_rack = seg_seq;
                tcp->tcp_rnxt = seg_seq + 1;
                U32_TO_ABE32(tcp->tcp_rnxt, tcp->tcp_tcph->th_ack);

                if (flags & TH_ACK) {
                        /* One for the SYN */
                        tcp->tcp_suna = tcp->tcp_iss + 1;
                        tcp->tcp_valid_bits &= ~TCP_ISS_VALID;
                        tcp->tcp_state = TCPS_ESTABLISHED;

                        /*
                         * If SYN was retransmitted, need to reset all
                         * retransmission info.  This is because this
                         * segment will be treated as a dup ACK.
                         */
                        if (tcp->tcp_rexmit) {
                                tcp->tcp_rexmit = B_FALSE;
                                tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
                                tcp->tcp_rexmit_max = tcp->tcp_snxt;
                                tcp->tcp_snd_burst = TCP_CWND_NORMAL;

                                /*
                                 * Set tcp_cwnd back to 1 MSS, per
                                 * recommendation from
                                 * draft-floyd-incr-init-win-01.txt,
                                 * Increasing TCP's Initial Window.
                                 */
                                tcp->tcp_cwnd = tcp->tcp_mss;
                        }

                        tcp->tcp_swl1 = seg_seq;
                        tcp->tcp_swl2 = seg_ack;

                        new_swnd = BE16_TO_U16(((tcph_t *)tcph)->th_win);
                        tcp->tcp_swnd = new_swnd;
                        if (new_swnd > tcp->tcp_max_swnd)
                                tcp->tcp_max_swnd = new_swnd;

                        /*
                         * Always send the three-way handshake ack immediately
                         * in order to make the connection complete as soon as
                         * possible on the accepting host.
                         */
                        flags |= TH_ACK_NEEDED;
                        /*
                         * Check to see if there is data to be sent.  If
                         * yes, set the transmit flag.  Then check to see
                         * if received data processing needs to be done.
                         * If not, go straight to xmit_check.  This short
                         * cut is OK as we don't support T/TCP.
                         */
                        if (tcp->tcp_unsent)
                                flags |= TH_XMIT_NEEDED;

                        if (seg_len == 0) {
                                freemsg(mp);
                                goto xmit_check;
                        }

                        flags &= ~TH_SYN;
                        seg_seq++;
                        break;
                }
                syn_rcvd:
                tcp->tcp_state = TCPS_SYN_RCVD;
                mp1 = tcp_xmit_mp(tcp, tcp->tcp_xmit_head, tcp->tcp_mss,
                    NULL, NULL, tcp->tcp_iss, B_FALSE, NULL, B_FALSE);
                if (mp1 != NULL) {
                        TCP_DUMP_PACKET("tcp_rput_data replying SYN", mp1);
                        (void) ipv4_tcp_output(sock_id, mp1);
                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                        freeb(mp1);
                        /*
                         * Let's wait till our SYN has been ACKED since we
                         * don't have a timer.
                         */
                        if (tcp_state_wait(sock_id, tcp, TCPS_ALL_ACKED) < 0) {
                                freemsg(mp);
                                return;
                        }
                }
                freemsg(mp);
                return;
        default:
                break;
        }
        mp->b_rptr = (uchar_t *)tcph + TCP_HDR_LENGTH((tcph_t *)tcph);
        new_swnd = ntohs(tcph->tha_win) <<
            ((flags & TH_SYN) ? 0 : tcp->tcp_snd_ws);
        mss = tcp->tcp_mss;

        if (tcp->tcp_snd_ts_ok) {
                if (!tcp_paws_check(tcp, (tcph_t *)tcph, &tcpopt)) {
                        /*
                         * This segment is not acceptable.
                         * Drop it and send back an ACK.
                         */
                        freemsg(mp);
                        flags |= TH_ACK_NEEDED;
                        goto ack_check;
                }
        } else if (tcp->tcp_snd_sack_ok) {
                assert(tcp->tcp_sack_info != NULL);
                tcpopt.tcp = tcp;
                /*
                 * SACK info in already updated in tcp_parse_options.  Ignore
                 * all other TCP options...
                 */
                (void) tcp_parse_options((tcph_t *)tcph, &tcpopt);
        }
try_again:;
        gap = seg_seq - tcp->tcp_rnxt;
        rgap = tcp->tcp_rwnd - (gap + seg_len);
        /*
         * gap is the amount of sequence space between what we expect to see
         * and what we got for seg_seq.  A positive value for gap means
         * something got lost.  A negative value means we got some old stuff.
         */
        if (gap < 0) {
                /* Old stuff present.  Is the SYN in there? */
                if (seg_seq == tcp->tcp_irs && (flags & TH_SYN) &&
                    (seg_len != 0)) {
                        flags &= ~TH_SYN;
                        seg_seq++;
                        /* Recompute the gaps after noting the SYN. */
                        goto try_again;
                }
                BUMP_MIB(tcp_mib.tcpInDataDupSegs);
                UPDATE_MIB(tcp_mib.tcpInDataDupBytes,
                    (seg_len > -gap ? -gap : seg_len));
                /* Remove the old stuff from seg_len. */
                seg_len += gap;
                /*
                 * Anything left?
                 * Make sure to check for unack'd FIN when rest of data
                 * has been previously ack'd.
                 */
                if (seg_len < 0 || (seg_len == 0 && !(flags & TH_FIN))) {
                        /*
                         * Resets are only valid if they lie within our offered
                         * window.  If the RST bit is set, we just ignore this
                         * segment.
                         */
                        if (flags & TH_RST) {
                                freemsg(mp);
                                return;
                        }

                        /*
                         * This segment is "unacceptable".  None of its
                         * sequence space lies within our advertized window.
                         *
                         * Adjust seg_len to the original value for tracing.
                         */
                        seg_len -= gap;
#ifdef DEBUG
                        printf("tcp_rput: unacceptable, gap %d, rgap "
                            "%d, flags 0x%x, seg_seq %u, seg_ack %u, "
                            "seg_len %d, rnxt %u, snxt %u, %s",
                            gap, rgap, flags, seg_seq, seg_ack,
                            seg_len, tcp->tcp_rnxt, tcp->tcp_snxt,
                            tcp_display(tcp, NULL, DISP_ADDR_AND_PORT));
#endif

                        /*
                         * Arrange to send an ACK in response to the
                         * unacceptable segment per RFC 793 page 69. There
                         * is only one small difference between ours and the
                         * acceptability test in the RFC - we accept ACK-only
                         * packet with SEG.SEQ = RCV.NXT+RCV.WND and no ACK
                         * will be generated.
                         *
                         * Note that we have to ACK an ACK-only packet at least
                         * for stacks that send 0-length keep-alives with
                         * SEG.SEQ = SND.NXT-1 as recommended by RFC1122,
                         * section 4.2.3.6. As long as we don't ever generate
                         * an unacceptable packet in response to an incoming
                         * packet that is unacceptable, it should not cause
                         * "ACK wars".
                         */
                        flags |=  TH_ACK_NEEDED;

                        /*
                         * Continue processing this segment in order to use the
                         * ACK information it contains, but skip all other
                         * sequence-number processing.  Processing the ACK
                         * information is necessary in order to
                         * re-synchronize connections that may have lost
                         * synchronization.
                         *
                         * We clear seg_len and flag fields related to
                         * sequence number processing as they are not
                         * to be trusted for an unacceptable segment.
                         */
                        seg_len = 0;
                        flags &= ~(TH_SYN | TH_FIN | TH_URG);
                        goto process_ack;
                }

                /* Fix seg_seq, and chew the gap off the front. */
                seg_seq = tcp->tcp_rnxt;
                do {
                        mblk_t  *mp2;
                        assert((uintptr_t)(mp->b_wptr - mp->b_rptr) <=
                            (uintptr_t)UINT_MAX);
                        gap += (uint_t)(mp->b_wptr - mp->b_rptr);
                        if (gap > 0) {
                                mp->b_rptr = mp->b_wptr - gap;
                                break;
                        }
                        mp2 = mp;
                        mp = mp->b_cont;
                        freeb(mp2);
                } while (gap < 0);
        }
        /*
         * rgap is the amount of stuff received out of window.  A negative
         * value is the amount out of window.
         */
        if (rgap < 0) {
                mblk_t  *mp2;

                if (tcp->tcp_rwnd == 0)
                        BUMP_MIB(tcp_mib.tcpInWinProbe);
                else {
                        BUMP_MIB(tcp_mib.tcpInDataPastWinSegs);
                        UPDATE_MIB(tcp_mib.tcpInDataPastWinBytes, -rgap);
                }

                /*
                 * seg_len does not include the FIN, so if more than
                 * just the FIN is out of window, we act like we don't
                 * see it.  (If just the FIN is out of window, rgap
                 * will be zero and we will go ahead and acknowledge
                 * the FIN.)
                 */
                flags &= ~TH_FIN;

                /* Fix seg_len and make sure there is something left. */
                seg_len += rgap;
                if (seg_len <= 0) {
                        /*
                         * Resets are only valid if they lie within our offered
                         * window.  If the RST bit is set, we just ignore this
                         * segment.
                         */
                        if (flags & TH_RST) {
                                freemsg(mp);
                                return;
                        }

                        /* Per RFC 793, we need to send back an ACK. */
                        flags |= TH_ACK_NEEDED;

                        /*
                         * If this is a zero window probe, continue to
                         * process the ACK part.  But we need to set seg_len
                         * to 0 to avoid data processing.  Otherwise just
                         * drop the segment and send back an ACK.
                         */
                        if (tcp->tcp_rwnd == 0 && seg_seq == tcp->tcp_rnxt) {
                                flags &= ~(TH_SYN | TH_URG);
                                seg_len = 0;
                                /* Let's see if we can update our rwnd */
                                tcp_rcv_drain(sock_id, tcp);
                                goto process_ack;
                        } else {
                                freemsg(mp);
                                goto ack_check;
                        }
                }
                /* Pitch out of window stuff off the end. */
                rgap = seg_len;
                mp2 = mp;
                do {
                        assert((uintptr_t)(mp2->b_wptr -
                            mp2->b_rptr) <= (uintptr_t)INT_MAX);
                        rgap -= (int)(mp2->b_wptr - mp2->b_rptr);
                        if (rgap < 0) {
                                mp2->b_wptr += rgap;
                                if ((mp1 = mp2->b_cont) != NULL) {
                                        mp2->b_cont = NULL;
                                        freemsg(mp1);
                                }
                                break;
                        }
                } while ((mp2 = mp2->b_cont) != NULL);
        }
ok:;
        /*
         * TCP should check ECN info for segments inside the window only.
         * Therefore the check should be done here.
         */
        if (tcp->tcp_ecn_ok) {
                uchar_t tos = ((struct ip *)rptr)->ip_tos;

                if (flags & TH_CWR) {
                        tcp->tcp_ecn_echo_on = B_FALSE;
                }
                /*
                 * Note that both ECN_CE and CWR can be set in the
                 * same segment.  In this case, we once again turn
                 * on ECN_ECHO.
                 */
                if ((tos & IPH_ECN_CE) == IPH_ECN_CE) {
                        tcp->tcp_ecn_echo_on = B_TRUE;
                }
        }

        /*
         * Check whether we can update tcp_ts_recent.  This test is
         * NOT the one in RFC 1323 3.4.  It is from Braden, 1993, "TCP
         * Extensions for High Performance: An Update", Internet Draft.
         */
        if (tcp->tcp_snd_ts_ok &&
            TSTMP_GEQ(tcpopt.tcp_opt_ts_val, tcp->tcp_ts_recent) &&
            SEQ_LEQ(seg_seq, tcp->tcp_rack)) {
                tcp->tcp_ts_recent = tcpopt.tcp_opt_ts_val;
                tcp->tcp_last_rcv_lbolt = prom_gettime();
        }

        if (seg_seq != tcp->tcp_rnxt || tcp->tcp_reass_head) {
                /*
                 * FIN in an out of order segment.  We record this in
                 * tcp_valid_bits and the seq num of FIN in tcp_ofo_fin_seq.
                 * Clear the FIN so that any check on FIN flag will fail.
                 * Remember that FIN also counts in the sequence number
                 * space.  So we need to ack out of order FIN only segments.
                 */
                if (flags & TH_FIN) {
                        tcp->tcp_valid_bits |= TCP_OFO_FIN_VALID;
                        tcp->tcp_ofo_fin_seq = seg_seq + seg_len;
                        flags &= ~TH_FIN;
                        flags |= TH_ACK_NEEDED;
                }
                if (seg_len > 0) {
                        /* Fill in the SACK blk list. */
                        if (tcp->tcp_snd_sack_ok) {
                                assert(tcp->tcp_sack_info != NULL);
                                tcp_sack_insert(tcp->tcp_sack_list,
                                    seg_seq, seg_seq + seg_len,
                                    &(tcp->tcp_num_sack_blk));
                        }

                        /*
                         * Attempt reassembly and see if we have something
                         * ready to go.
                         */
                        mp = tcp_reass(tcp, mp, seg_seq);
                        /* Always ack out of order packets */
                        flags |= TH_ACK_NEEDED | TH_PUSH;
                        if (mp != NULL) {
                                assert((uintptr_t)(mp->b_wptr -
                                    mp->b_rptr) <= (uintptr_t)INT_MAX);
                                seg_len = mp->b_cont ? msgdsize(mp) :
                                        (int)(mp->b_wptr - mp->b_rptr);
                                seg_seq = tcp->tcp_rnxt;
                                /*
                                 * A gap is filled and the seq num and len
                                 * of the gap match that of a previously
                                 * received FIN, put the FIN flag back in.
                                 */
                                if ((tcp->tcp_valid_bits & TCP_OFO_FIN_VALID) &&
                                    seg_seq + seg_len == tcp->tcp_ofo_fin_seq) {
                                        flags |= TH_FIN;
                                        tcp->tcp_valid_bits &=
                                            ~TCP_OFO_FIN_VALID;
                                }
                        } else {
                                /*
                                 * Keep going even with NULL mp.
                                 * There may be a useful ACK or something else
                                 * we don't want to miss.
                                 *
                                 * But TCP should not perform fast retransmit
                                 * because of the ack number.  TCP uses
                                 * seg_len == 0 to determine if it is a pure
                                 * ACK.  And this is not a pure ACK.
                                 */
                                seg_len = 0;
                                ofo_seg = B_TRUE;
                        }
                }
        } else if (seg_len > 0) {
                BUMP_MIB(tcp_mib.tcpInDataInorderSegs);
                UPDATE_MIB(tcp_mib.tcpInDataInorderBytes, seg_len);
                /*
                 * If an out of order FIN was received before, and the seq
                 * num and len of the new segment match that of the FIN,
                 * put the FIN flag back in.
                 */
                if ((tcp->tcp_valid_bits & TCP_OFO_FIN_VALID) &&
                    seg_seq + seg_len == tcp->tcp_ofo_fin_seq) {
                        flags |= TH_FIN;
                        tcp->tcp_valid_bits &= ~TCP_OFO_FIN_VALID;
                }
        }
        if ((flags & (TH_RST | TH_SYN | TH_URG | TH_ACK)) != TH_ACK) {
        if (flags & TH_RST) {
                freemsg(mp);
                switch (tcp->tcp_state) {
                case TCPS_SYN_RCVD:
                        (void) tcp_clean_death(sock_id, tcp, ECONNREFUSED);
                        break;
                case TCPS_ESTABLISHED:
                case TCPS_FIN_WAIT_1:
                case TCPS_FIN_WAIT_2:
                case TCPS_CLOSE_WAIT:
                        (void) tcp_clean_death(sock_id, tcp, ECONNRESET);
                        break;
                case TCPS_CLOSING:
                case TCPS_LAST_ACK:
                        (void) tcp_clean_death(sock_id, tcp, 0);
                        break;
                default:
                        assert(tcp->tcp_state != TCPS_TIME_WAIT);
                        (void) tcp_clean_death(sock_id, tcp, ENXIO);
                        break;
                }
                return;
        }
        if (flags & TH_SYN) {
                /*
                 * See RFC 793, Page 71
                 *
                 * The seq number must be in the window as it should
                 * be "fixed" above.  If it is outside window, it should
                 * be already rejected.  Note that we allow seg_seq to be
                 * rnxt + rwnd because we want to accept 0 window probe.
                 */
                assert(SEQ_GEQ(seg_seq, tcp->tcp_rnxt) &&
                    SEQ_LEQ(seg_seq, tcp->tcp_rnxt + tcp->tcp_rwnd));
                freemsg(mp);
                /*
                 * If the ACK flag is not set, just use our snxt as the
                 * seq number of the RST segment.
                 */
                if (!(flags & TH_ACK)) {
                        seg_ack = tcp->tcp_snxt;
                }
                tcp_xmit_ctl("TH_SYN", tcp, NULL, seg_ack,
                    seg_seq + 1, TH_RST|TH_ACK, 0, sock_id);
                assert(tcp->tcp_state != TCPS_TIME_WAIT);
                (void) tcp_clean_death(sock_id, tcp, ECONNRESET);
                return;
        }

process_ack:
        if (!(flags & TH_ACK)) {
#ifdef DEBUG
                printf("No ack in segment, dropped it, seq:%x\n", seg_seq);
#endif
                freemsg(mp);
                goto xmit_check;
        }
        }
        bytes_acked = (int)(seg_ack - tcp->tcp_suna);

        if (tcp->tcp_state == TCPS_SYN_RCVD) {
                tcp_t   *listener = tcp->tcp_listener;
#ifdef DEBUG
                printf("Done with eager 3-way handshake\n");
#endif
                /*
                 * NOTE: RFC 793 pg. 72 says this should be 'bytes_acked < 0'
                 * but that would mean we have an ack that ignored our SYN.
                 */
                if (bytes_acked < 1 || SEQ_GT(seg_ack, tcp->tcp_snxt)) {
                        freemsg(mp);
                        tcp_xmit_ctl("TCPS_SYN_RCVD-bad_ack",
                            tcp, NULL, seg_ack, 0, TH_RST, 0, sock_id);
                        return;
                }

                /*
                 * if the conn_req_q is full defer processing
                 * until space is availabe after accept()
                 * processing
                 */
                if (listener->tcp_conn_req_cnt_q <
                    listener->tcp_conn_req_max) {
                        tcp_t *tail;

                        listener->tcp_conn_req_cnt_q0--;
                        listener->tcp_conn_req_cnt_q++;

                        /* Move from SYN_RCVD to ESTABLISHED list  */
                        tcp->tcp_eager_next_q0->tcp_eager_prev_q0 =
                                tcp->tcp_eager_prev_q0;
                        tcp->tcp_eager_prev_q0->tcp_eager_next_q0 =
                                tcp->tcp_eager_next_q0;
                        tcp->tcp_eager_prev_q0 = NULL;
                        tcp->tcp_eager_next_q0 = NULL;

                        /*
                         * Insert at end of the queue because sockfs
                         * sends down T_CONN_RES in chronological
                         * order. Leaving the older conn indications
                         * at front of the queue helps reducing search
                         * time.
                         */
                        tail = listener->tcp_eager_last_q;
                        if (tail != NULL) {
                                tail->tcp_eager_next_q = tcp;
                        } else {
                                listener->tcp_eager_next_q = tcp;
                        }
                        listener->tcp_eager_last_q = tcp;
                        tcp->tcp_eager_next_q = NULL;
                } else {
                        /*
                         * Defer connection on q0 and set deferred
                         * connection bit true
                         */
                        tcp->tcp_conn_def_q0 = B_TRUE;

                        /* take tcp out of q0 ... */
                        tcp->tcp_eager_prev_q0->tcp_eager_next_q0 =
                            tcp->tcp_eager_next_q0;
                        tcp->tcp_eager_next_q0->tcp_eager_prev_q0 =
                            tcp->tcp_eager_prev_q0;

                        /* ... and place it at the end of q0 */
                        tcp->tcp_eager_prev_q0 = listener->tcp_eager_prev_q0;
                        tcp->tcp_eager_next_q0 = listener;
                        listener->tcp_eager_prev_q0->tcp_eager_next_q0 = tcp;
                        listener->tcp_eager_prev_q0 = tcp;
                }

                tcp->tcp_suna = tcp->tcp_iss + 1;       /* One for the SYN */
                bytes_acked--;

                /*
                 * If SYN was retransmitted, need to reset all
                 * retransmission info as this segment will be
                 * treated as a dup ACK.
                 */
                if (tcp->tcp_rexmit) {
                        tcp->tcp_rexmit = B_FALSE;
                        tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
                        tcp->tcp_rexmit_max = tcp->tcp_snxt;
                        tcp->tcp_snd_burst = TCP_CWND_NORMAL;
                        tcp->tcp_ms_we_have_waited = 0;
                        tcp->tcp_cwnd = mss;
                }

                /*
                 * We set the send window to zero here.
                 * This is needed if there is data to be
                 * processed already on the queue.
                 * Later (at swnd_update label), the
                 * "new_swnd > tcp_swnd" condition is satisfied
                 * the XMIT_NEEDED flag is set in the current
                 * (SYN_RCVD) state. This ensures tcp_wput_data() is
                 * called if there is already data on queue in
                 * this state.
                 */
                tcp->tcp_swnd = 0;

                if (new_swnd > tcp->tcp_max_swnd)
                        tcp->tcp_max_swnd = new_swnd;
                tcp->tcp_swl1 = seg_seq;
                tcp->tcp_swl2 = seg_ack;
                tcp->tcp_state = TCPS_ESTABLISHED;
                tcp->tcp_valid_bits &= ~TCP_ISS_VALID;
        }
        /* This code follows 4.4BSD-Lite2 mostly. */
        if (bytes_acked < 0)
                goto est;

        /*
         * If TCP is ECN capable and the congestion experience bit is
         * set, reduce tcp_cwnd and tcp_ssthresh.  But this should only be
         * done once per window (or more loosely, per RTT).
         */
        if (tcp->tcp_cwr && SEQ_GT(seg_ack, tcp->tcp_cwr_snd_max))
                tcp->tcp_cwr = B_FALSE;
        if (tcp->tcp_ecn_ok && (flags & TH_ECE)) {
                if (!tcp->tcp_cwr) {
                        npkt = (MIN(tcp->tcp_cwnd, tcp->tcp_swnd) >> 1) / mss;
                        tcp->tcp_cwnd_ssthresh = MAX(npkt, 2) * mss;
                        tcp->tcp_cwnd = npkt * mss;
                        /*
                         * If the cwnd is 0, use the timer to clock out
                         * new segments.  This is required by the ECN spec.
                         */
                        if (npkt == 0) {
                                TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                                /*
                                 * This makes sure that when the ACK comes
                                 * back, we will increase tcp_cwnd by 1 MSS.
                                 */
                                tcp->tcp_cwnd_cnt = 0;
                        }
                        tcp->tcp_cwr = B_TRUE;
                        /*
                         * This marks the end of the current window of in
                         * flight data.  That is why we don't use
                         * tcp_suna + tcp_swnd.  Only data in flight can
                         * provide ECN info.
                         */
                        tcp->tcp_cwr_snd_max = tcp->tcp_snxt;
                        tcp->tcp_ecn_cwr_sent = B_FALSE;
                }
        }

        mp1 = tcp->tcp_xmit_head;
        if (bytes_acked == 0) {
                if (!ofo_seg && seg_len == 0 && new_swnd == tcp->tcp_swnd) {
                        int dupack_cnt;

                        BUMP_MIB(tcp_mib.tcpInDupAck);
                        /*
                         * Fast retransmit.  When we have seen exactly three
                         * identical ACKs while we have unacked data
                         * outstanding we take it as a hint that our peer
                         * dropped something.
                         *
                         * If TCP is retransmitting, don't do fast retransmit.
                         */
                        if (mp1 != NULL && tcp->tcp_suna != tcp->tcp_snxt &&
                            ! tcp->tcp_rexmit) {
                                /* Do Limited Transmit */
                                if ((dupack_cnt = ++tcp->tcp_dupack_cnt) <
                                    tcp_dupack_fast_retransmit) {
                                        /*
                                         * RFC 3042
                                         *
                                         * What we need to do is temporarily
                                         * increase tcp_cwnd so that new
                                         * data can be sent if it is allowed
                                         * by the receive window (tcp_rwnd).
                                         * tcp_wput_data() will take care of
                                         * the rest.
                                         *
                                         * If the connection is SACK capable,
                                         * only do limited xmit when there
                                         * is SACK info.
                                         *
                                         * Note how tcp_cwnd is incremented.
                                         * The first dup ACK will increase
                                         * it by 1 MSS.  The second dup ACK
                                         * will increase it by 2 MSS.  This
                                         * means that only 1 new segment will
                                         * be sent for each dup ACK.
                                         */
                                        if (tcp->tcp_unsent > 0 &&
                                            (!tcp->tcp_snd_sack_ok ||
                                            (tcp->tcp_snd_sack_ok &&
                                            tcp->tcp_notsack_list != NULL))) {
                                                tcp->tcp_cwnd += mss <<
                                                    (tcp->tcp_dupack_cnt - 1);
                                                flags |= TH_LIMIT_XMIT;
                                        }
                                } else if (dupack_cnt ==
                                    tcp_dupack_fast_retransmit) {

                                BUMP_MIB(tcp_mib.tcpOutFastRetrans);
                                /*
                                 * If we have reduced tcp_ssthresh
                                 * because of ECN, do not reduce it again
                                 * unless it is already one window of data
                                 * away.  After one window of data, tcp_cwr
                                 * should then be cleared.  Note that
                                 * for non ECN capable connection, tcp_cwr
                                 * should always be false.
                                 *
                                 * Adjust cwnd since the duplicate
                                 * ack indicates that a packet was
                                 * dropped (due to congestion.)
                                 */
                                if (!tcp->tcp_cwr) {
                                        npkt = (MIN(tcp->tcp_cwnd,
                                            tcp->tcp_swnd) >> 1) / mss;
                                        if (npkt < 2)
                                                npkt = 2;
                                        tcp->tcp_cwnd_ssthresh = npkt * mss;
                                        tcp->tcp_cwnd = (npkt +
                                            tcp->tcp_dupack_cnt) * mss;
                                }
                                if (tcp->tcp_ecn_ok) {
                                        tcp->tcp_cwr = B_TRUE;
                                        tcp->tcp_cwr_snd_max = tcp->tcp_snxt;
                                        tcp->tcp_ecn_cwr_sent = B_FALSE;
                                }

                                /*
                                 * We do Hoe's algorithm.  Refer to her
                                 * paper "Improving the Start-up Behavior
                                 * of a Congestion Control Scheme for TCP,"
                                 * appeared in SIGCOMM'96.
                                 *
                                 * Save highest seq no we have sent so far.
                                 * Be careful about the invisible FIN byte.
                                 */
                                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;
                                }

                                /*
                                 * Do not allow bursty traffic during.
                                 * fast recovery.  Refer to Fall and Floyd's
                                 * paper "Simulation-based Comparisons of
                                 * Tahoe, Reno and SACK TCP" (in CCR ??)
                                 * This is a best current practise.
                                 */
                                tcp->tcp_snd_burst = TCP_CWND_SS;

                                /*
                                 * For SACK:
                                 * Calculate tcp_pipe, which is the
                                 * estimated number of bytes in
                                 * network.
                                 *
                                 * tcp_fack is the highest sack'ed seq num
                                 * TCP has received.
                                 *
                                 * tcp_pipe is explained in the above quoted
                                 * Fall and Floyd's paper.  tcp_fack is
                                 * explained in Mathis and Mahdavi's
                                 * "Forward Acknowledgment: Refining TCP
                                 * Congestion Control" in SIGCOMM '96.
                                 */
                                if (tcp->tcp_snd_sack_ok) {
                                        assert(tcp->tcp_sack_info != NULL);
                                        if (tcp->tcp_notsack_list != NULL) {
                                                tcp->tcp_pipe = tcp->tcp_snxt -
                                                    tcp->tcp_fack;
                                                tcp->tcp_sack_snxt = seg_ack;
                                                flags |= TH_NEED_SACK_REXMIT;
                                        } else {
                                                /*
                                                 * Always initialize tcp_pipe
                                                 * even though we don't have
                                                 * any SACK info.  If later
                                                 * we get SACK info and
                                                 * tcp_pipe is not initialized,
                                                 * funny things will happen.
                                                 */
                                                tcp->tcp_pipe =
                                                    tcp->tcp_cwnd_ssthresh;
                                        }
                                } else {
                                        flags |= TH_REXMIT_NEEDED;
                                } /* tcp_snd_sack_ok */

                                } else {
                                        /*
                                         * Here we perform congestion
                                         * avoidance, but NOT slow start.
                                         * This is known as the Fast
                                         * Recovery Algorithm.
                                         */
                                        if (tcp->tcp_snd_sack_ok &&
                                            tcp->tcp_notsack_list != NULL) {
                                                flags |= TH_NEED_SACK_REXMIT;
                                                tcp->tcp_pipe -= mss;
                                                if (tcp->tcp_pipe < 0)
                                                        tcp->tcp_pipe = 0;
                                        } else {
                                        /*
                                         * We know that one more packet has
                                         * left the pipe thus we can update
                                         * cwnd.
                                         */
                                        cwnd = tcp->tcp_cwnd + mss;
                                        if (cwnd > tcp->tcp_cwnd_max)
                                                cwnd = tcp->tcp_cwnd_max;
                                        tcp->tcp_cwnd = cwnd;
                                        flags |= TH_XMIT_NEEDED;
                                        }
                                }
                        }
                } else if (tcp->tcp_zero_win_probe) {
                        /*
                         * If the window has opened, need to arrange
                         * to send additional data.
                         */
                        if (new_swnd != 0) {
                                /* tcp_suna != tcp_snxt */
                                /* Packet contains a window update */
                                BUMP_MIB(tcp_mib.tcpInWinUpdate);
                                tcp->tcp_zero_win_probe = 0;
                                tcp->tcp_timer_backoff = 0;
                                tcp->tcp_ms_we_have_waited = 0;

                                /*
                                 * Transmit starting with tcp_suna since
                                 * the one byte probe is not ack'ed.
                                 * If TCP has sent more than one identical
                                 * probe, tcp_rexmit will be set.  That means
                                 * tcp_ss_rexmit() will send out the one
                                 * byte along with new data.  Otherwise,
                                 * fake the retransmission.
                                 */
                                flags |= TH_XMIT_NEEDED;
                                if (!tcp->tcp_rexmit) {
                                        tcp->tcp_rexmit = B_TRUE;
                                        tcp->tcp_dupack_cnt = 0;
                                        tcp->tcp_rexmit_nxt = tcp->tcp_suna;
                                        tcp->tcp_rexmit_max = tcp->tcp_suna + 1;
                                }
                        }
                }
                goto swnd_update;
        }

        /*
         * Check for "acceptability" of ACK value per RFC 793, pages 72 - 73.
         * If the ACK value acks something that we have not yet sent, it might
         * be an old duplicate segment.  Send an ACK to re-synchronize the
         * other side.
         * Note: reset in response to unacceptable ACK in SYN_RECEIVE
         * state is handled above, so we can always just drop the segment and
         * send an ACK here.
         *
         * Should we send ACKs in response to ACK only segments?
         */
        if (SEQ_GT(seg_ack, tcp->tcp_snxt)) {
                BUMP_MIB(tcp_mib.tcpInAckUnsent);
                /* drop the received segment */
                freemsg(mp);

                /* Send back an ACK. */
                mp = tcp_ack_mp(tcp);

                if (mp == NULL) {
                        return;
                }
                BUMP_MIB(tcp_mib.tcpOutAck);
                (void) ipv4_tcp_output(sock_id, mp);
                freeb(mp);
                return;
        }

        /*
         * TCP gets a new ACK, update the notsack'ed list to delete those
         * blocks that are covered by this ACK.
         */
        if (tcp->tcp_snd_sack_ok && tcp->tcp_notsack_list != NULL) {
                tcp_notsack_remove(&(tcp->tcp_notsack_list), seg_ack,
                    &(tcp->tcp_num_notsack_blk), &(tcp->tcp_cnt_notsack_list));
        }

        /*
         * If we got an ACK after fast retransmit, check to see
         * if it is a partial ACK.  If it is not and the congestion
         * window was inflated to account for the other side's
         * cached packets, retract it.  If it is, do Hoe's algorithm.
         */
        if (tcp->tcp_dupack_cnt >= tcp_dupack_fast_retransmit) {
                assert(tcp->tcp_rexmit == B_FALSE);
                if (SEQ_GEQ(seg_ack, tcp->tcp_rexmit_max)) {
                        tcp->tcp_dupack_cnt = 0;
                        /*
                         * Restore the orig tcp_cwnd_ssthresh after
                         * fast retransmit phase.
                         */
                        if (tcp->tcp_cwnd > tcp->tcp_cwnd_ssthresh) {
                                tcp->tcp_cwnd = tcp->tcp_cwnd_ssthresh;
                        }
                        tcp->tcp_rexmit_max = seg_ack;
                        tcp->tcp_cwnd_cnt = 0;
                        tcp->tcp_snd_burst = TCP_CWND_NORMAL;

                        /*
                         * Remove all notsack info to avoid confusion with
                         * the next fast retrasnmit/recovery phase.
                         */
                        if (tcp->tcp_snd_sack_ok &&
                            tcp->tcp_notsack_list != NULL) {
                                TCP_NOTSACK_REMOVE_ALL(tcp->tcp_notsack_list);
                        }
                } else {
                        if (tcp->tcp_snd_sack_ok &&
                            tcp->tcp_notsack_list != NULL) {
                                flags |= TH_NEED_SACK_REXMIT;
                                tcp->tcp_pipe -= mss;
                                if (tcp->tcp_pipe < 0)
                                        tcp->tcp_pipe = 0;
                        } else {
                                /*
                                 * Hoe's algorithm:
                                 *
                                 * Retransmit the unack'ed segment and
                                 * restart fast recovery.  Note that we
                                 * need to scale back tcp_cwnd to the
                                 * original value when we started fast
                                 * recovery.  This is to prevent overly
                                 * aggressive behaviour in sending new
                                 * segments.
                                 */
                                tcp->tcp_cwnd = tcp->tcp_cwnd_ssthresh +
                                        tcp_dupack_fast_retransmit * mss;
                                tcp->tcp_cwnd_cnt = tcp->tcp_cwnd;
                                BUMP_MIB(tcp_mib.tcpOutFastRetrans);
                                flags |= TH_REXMIT_NEEDED;
                        }
                }
        } else {
                tcp->tcp_dupack_cnt = 0;
                if (tcp->tcp_rexmit) {
                        /*
                         * TCP is retranmitting.  If the ACK ack's all
                         * outstanding data, update tcp_rexmit_max and
                         * tcp_rexmit_nxt.  Otherwise, update tcp_rexmit_nxt
                         * to the correct value.
                         *
                         * Note that SEQ_LEQ() is used.  This is to avoid
                         * unnecessary fast retransmit caused by dup ACKs
                         * received when TCP does slow start retransmission
                         * after a time out.  During this phase, TCP may
                         * send out segments which are already received.
                         * This causes dup ACKs to be sent back.
                         */
                        if (SEQ_LEQ(seg_ack, tcp->tcp_rexmit_max)) {
                                if (SEQ_GT(seg_ack, tcp->tcp_rexmit_nxt)) {
                                        tcp->tcp_rexmit_nxt = seg_ack;
                                }
                                if (seg_ack != tcp->tcp_rexmit_max) {
                                        flags |= TH_XMIT_NEEDED;
                                }
                        } else {
                                tcp->tcp_rexmit = B_FALSE;
                                tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
                                tcp->tcp_snd_burst = TCP_CWND_NORMAL;
                        }
                        tcp->tcp_ms_we_have_waited = 0;
                }
        }

        BUMP_MIB(tcp_mib.tcpInAckSegs);
        UPDATE_MIB(tcp_mib.tcpInAckBytes, bytes_acked);
        tcp->tcp_suna = seg_ack;
        if (tcp->tcp_zero_win_probe != 0) {
                tcp->tcp_zero_win_probe = 0;
                tcp->tcp_timer_backoff = 0;
        }

        /*
         * If tcp_xmit_head is NULL, then it must be the FIN being ack'ed.
         * Note that it cannot be the SYN being ack'ed.  The code flow
         * will not reach here.
         */
        if (mp1 == NULL) {
                goto fin_acked;
        }

        /*
         * Update the congestion window.
         *
         * If TCP is not ECN capable or TCP is ECN capable but the
         * congestion experience bit is not set, increase the tcp_cwnd as
         * usual.
         */
        if (!tcp->tcp_ecn_ok || !(flags & TH_ECE)) {
                cwnd = tcp->tcp_cwnd;
                add = mss;

                if (cwnd >= tcp->tcp_cwnd_ssthresh) {
                        /*
                         * This is to prevent an increase of less than 1 MSS of
                         * tcp_cwnd.  With partial increase, tcp_wput_data()
                         * may send out tinygrams in order to preserve mblk
                         * boundaries.
                         *
                         * By initializing tcp_cwnd_cnt to new tcp_cwnd and
                         * decrementing it by 1 MSS for every ACKs, tcp_cwnd is
                         * increased by 1 MSS for every RTTs.
                         */
                        if (tcp->tcp_cwnd_cnt <= 0) {
                                tcp->tcp_cwnd_cnt = cwnd + add;
                        } else {
                                tcp->tcp_cwnd_cnt -= add;
                                add = 0;
                        }
                }
                tcp->tcp_cwnd = MIN(cwnd + add, tcp->tcp_cwnd_max);
        }

        /* Can we update the RTT estimates? */
        if (tcp->tcp_snd_ts_ok) {
                /* Ignore zero timestamp echo-reply. */
                if (tcpopt.tcp_opt_ts_ecr != 0) {
                        tcp_set_rto(tcp, (int32_t)(prom_gettime() -
                            tcpopt.tcp_opt_ts_ecr));
                }

                /* If needed, restart the timer. */
                if (tcp->tcp_set_timer == 1) {
                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                        tcp->tcp_set_timer = 0;
                }
                /*
                 * Update tcp_csuna in case the other side stops sending
                 * us timestamps.
                 */
                tcp->tcp_csuna = tcp->tcp_snxt;
        } else if (SEQ_GT(seg_ack, tcp->tcp_csuna)) {
                /*
                 * An ACK sequence we haven't seen before, so get the RTT
                 * and update the RTO.
                 * Note. use uintptr_t to suppress the gcc warning.
                 */
                tcp_set_rto(tcp, (int32_t)(prom_gettime() -
                    (uint32_t)(uintptr_t)mp1->b_prev));

                /* Remeber the last sequence to be ACKed */
                tcp->tcp_csuna = seg_ack;
                if (tcp->tcp_set_timer == 1) {
                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                        tcp->tcp_set_timer = 0;
                }
        } else {
                BUMP_MIB(tcp_mib.tcpRttNoUpdate);
        }

        /* Eat acknowledged bytes off the xmit queue. */
        for (;;) {
                mblk_t  *mp2;
                uchar_t *wptr;

                wptr = mp1->b_wptr;
                assert((uintptr_t)(wptr - mp1->b_rptr) <= (uintptr_t)INT_MAX);
                bytes_acked -= (int)(wptr - mp1->b_rptr);
                if (bytes_acked < 0) {
                        mp1->b_rptr = wptr + bytes_acked;
                        break;
                }
                mp1->b_prev = NULL;
                mp2 = mp1;
                mp1 = mp1->b_cont;
                freeb(mp2);
                if (bytes_acked == 0) {
                        if (mp1 == NULL) {
                                /* Everything is ack'ed, clear the tail. */
                                tcp->tcp_xmit_tail = NULL;
                                goto pre_swnd_update;
                        }
                        if (mp2 != tcp->tcp_xmit_tail)
                                break;
                        tcp->tcp_xmit_tail = mp1;
                        assert((uintptr_t)(mp1->b_wptr -
                            mp1->b_rptr) <= (uintptr_t)INT_MAX);
                        tcp->tcp_xmit_tail_unsent = (int)(mp1->b_wptr -
                            mp1->b_rptr);
                        break;
                }
                if (mp1 == NULL) {
                        /*
                         * More was acked but there is nothing more
                         * outstanding.  This means that the FIN was
                         * just acked or that we're talking to a clown.
                         */
fin_acked:
                        assert(tcp->tcp_fin_sent);
                        tcp->tcp_xmit_tail = NULL;
                        if (tcp->tcp_fin_sent) {
                                tcp->tcp_fin_acked = B_TRUE;
                        } else {
                                /*
                                 * We should never got here because
                                 * we have already checked that the
                                 * number of bytes ack'ed should be
                                 * smaller than or equal to what we
                                 * have sent so far (it is the
                                 * acceptability check of the ACK).
                                 * We can only get here if the send
                                 * queue is corrupted.
                                 *
                                 * Terminate the connection and
                                 * panic the system.  It is better
                                 * for us to panic instead of
                                 * continuing to avoid other disaster.
                                 */
                                tcp_xmit_ctl(NULL, tcp, NULL, tcp->tcp_snxt,
                                    tcp->tcp_rnxt, TH_RST|TH_ACK, 0, sock_id);
                                printf("Memory corruption "
                                    "detected for connection %s.\n",
                                    tcp_display(tcp, NULL,
                                        DISP_ADDR_AND_PORT));
                                /* We should never get here... */
                                prom_panic("tcp_rput_data");
                                return;
                        }
                        goto pre_swnd_update;
                }
                assert(mp2 != tcp->tcp_xmit_tail);
        }
        if (tcp->tcp_unsent) {
                flags |= TH_XMIT_NEEDED;
        }
pre_swnd_update:
        tcp->tcp_xmit_head = mp1;
swnd_update:
        /*
         * The following check is different from most other implementations.
         * For bi-directional transfer, when segments are dropped, the
         * "normal" check will not accept a window update in those
         * retransmitted segemnts.  Failing to do that, TCP may send out
         * segments which are outside receiver's window.  As TCP accepts
         * the ack in those retransmitted segments, if the window update in
         * the same segment is not accepted, TCP will incorrectly calculates
         * that it can send more segments.  This can create a deadlock
         * with the receiver if its window becomes zero.
         */
        if (SEQ_LT(tcp->tcp_swl2, seg_ack) ||
            SEQ_LT(tcp->tcp_swl1, seg_seq) ||
            (tcp->tcp_swl1 == seg_seq && new_swnd > tcp->tcp_swnd)) {
                /*
                 * The criteria for update is:
                 *
                 * 1. the segment acknowledges some data.  Or
                 * 2. the segment is new, i.e. it has a higher seq num. Or
                 * 3. the segment is not old and the advertised window is
                 * larger than the previous advertised window.
                 */
                if (tcp->tcp_unsent && new_swnd > tcp->tcp_swnd)
                        flags |= TH_XMIT_NEEDED;
                tcp->tcp_swnd = new_swnd;
                if (new_swnd > tcp->tcp_max_swnd)
                        tcp->tcp_max_swnd = new_swnd;
                tcp->tcp_swl1 = seg_seq;
                tcp->tcp_swl2 = seg_ack;
        }
est:
        if (tcp->tcp_state > TCPS_ESTABLISHED) {
                switch (tcp->tcp_state) {
                case TCPS_FIN_WAIT_1:
                        if (tcp->tcp_fin_acked) {
                                tcp->tcp_state = TCPS_FIN_WAIT_2;
                                /*
                                 * We implement the non-standard BSD/SunOS
                                 * FIN_WAIT_2 flushing algorithm.
                                 * If there is no user attached to this
                                 * TCP endpoint, then this TCP struct
                                 * could hang around forever in FIN_WAIT_2
                                 * state if the peer forgets to send us
                                 * a FIN.  To prevent this, we wait only
                                 * 2*MSL (a convenient time value) for
                                 * the FIN to arrive.  If it doesn't show up,
                                 * we flush the TCP endpoint.  This algorithm,
                                 * though a violation of RFC-793, has worked
                                 * for over 10 years in BSD systems.
                                 * Note: SunOS 4.x waits 675 seconds before
                                 * flushing the FIN_WAIT_2 connection.
                                 */
                                TCP_TIMER_RESTART(tcp,
                                    tcp_fin_wait_2_flush_interval);
                        }
                        break;
                case TCPS_FIN_WAIT_2:
                        break;  /* Shutdown hook? */
                case TCPS_LAST_ACK:
                        freemsg(mp);
                        if (tcp->tcp_fin_acked) {
                                (void) tcp_clean_death(sock_id, tcp, 0);
                                return;
                        }
                        goto xmit_check;
                case TCPS_CLOSING:
                        if (tcp->tcp_fin_acked) {
                                tcp->tcp_state = TCPS_TIME_WAIT;
                                tcp_time_wait_append(tcp);
                                TCP_TIMER_RESTART(tcp, tcp_time_wait_interval);
                        }
                        /*FALLTHRU*/
                case TCPS_CLOSE_WAIT:
                        freemsg(mp);
                        goto xmit_check;
                default:
                        assert(tcp->tcp_state != TCPS_TIME_WAIT);
                        break;
                }
        }
        if (flags & TH_FIN) {
                /* Make sure we ack the fin */
                flags |= TH_ACK_NEEDED;
                if (!tcp->tcp_fin_rcvd) {
                        tcp->tcp_fin_rcvd = B_TRUE;
                        tcp->tcp_rnxt++;
                        U32_TO_ABE32(tcp->tcp_rnxt, tcp->tcp_tcph->th_ack);

                        switch (tcp->tcp_state) {
                        case TCPS_SYN_RCVD:
                        case TCPS_ESTABLISHED:
                                tcp->tcp_state = TCPS_CLOSE_WAIT;
                                /* Keepalive? */
                                break;
                        case TCPS_FIN_WAIT_1:
                                if (!tcp->tcp_fin_acked) {
                                        tcp->tcp_state = TCPS_CLOSING;
                                        break;
                                }
                                /* FALLTHRU */
                        case TCPS_FIN_WAIT_2:
                                tcp->tcp_state = TCPS_TIME_WAIT;
                                tcp_time_wait_append(tcp);
                                TCP_TIMER_RESTART(tcp, tcp_time_wait_interval);
                                if (seg_len) {
                                        /*
                                         * implies data piggybacked on FIN.
                                         * break to handle data.
                                         */
                                        break;
                                }
                                freemsg(mp);
                                goto ack_check;
                        }
                }
        }
        if (mp == NULL)
                goto xmit_check;
        if (seg_len == 0) {
                freemsg(mp);
                goto xmit_check;
        }
        if (mp->b_rptr == mp->b_wptr) {
                /*
                 * The header has been consumed, so we remove the
                 * zero-length mblk here.
                 */
                mp1 = mp;
                mp = mp->b_cont;
                freeb(mp1);
        }
        /*
         * ACK every other segments, unless the input queue is empty
         * as we don't have a timer available.
         */
        if (++tcp->tcp_rack_cnt == 2 || sockets[sock_id].inq == NULL) {
                flags |= TH_ACK_NEEDED;
                tcp->tcp_rack_cnt = 0;
        }
        tcp->tcp_rnxt += seg_len;
        U32_TO_ABE32(tcp->tcp_rnxt, tcp->tcp_tcph->th_ack);

        /* Update SACK list */
        if (tcp->tcp_snd_sack_ok && tcp->tcp_num_sack_blk > 0) {
                tcp_sack_remove(tcp->tcp_sack_list, tcp->tcp_rnxt,
                    &(tcp->tcp_num_sack_blk));
        }

        if (tcp->tcp_listener) {
                /*
                 * Side queue inbound data until the accept happens.
                 * tcp_accept/tcp_rput drains this when the accept happens.
                 */
                tcp_rcv_enqueue(tcp, mp, seg_len);
        } else {
                /* Just queue the data until the app calls read. */
                tcp_rcv_enqueue(tcp, mp, seg_len);
                /*
                 * Make sure the timer is running if we have data waiting
                 * for a push bit. This provides resiliency against
                 * implementations that do not correctly generate push bits.
                 */
                if (tcp->tcp_rcv_list != NULL)
                        flags |= TH_TIMER_NEEDED;
        }

xmit_check:
        /* Is there anything left to do? */
        if ((flags & (TH_REXMIT_NEEDED|TH_XMIT_NEEDED|TH_ACK_NEEDED|
            TH_NEED_SACK_REXMIT|TH_LIMIT_XMIT|TH_TIMER_NEEDED)) == 0)
                return;

        /* Any transmit work to do and a non-zero window? */
        if ((flags & (TH_REXMIT_NEEDED|TH_XMIT_NEEDED|TH_NEED_SACK_REXMIT|
            TH_LIMIT_XMIT)) && tcp->tcp_swnd != 0) {
                if (flags & TH_REXMIT_NEEDED) {
                        uint32_t snd_size = tcp->tcp_snxt - tcp->tcp_suna;

                        if (snd_size > mss)
                                snd_size = mss;
                        if (snd_size > tcp->tcp_swnd)
                                snd_size = tcp->tcp_swnd;
                        mp1 = tcp_xmit_mp(tcp, tcp->tcp_xmit_head, snd_size,
                            NULL, NULL, tcp->tcp_suna, B_TRUE, &snd_size,
                            B_TRUE);

                        if (mp1 != NULL) {
                                /* use uintptr_t to suppress the gcc warning */
                                tcp->tcp_xmit_head->b_prev =
                                    (mblk_t *)(uintptr_t)prom_gettime();
                                tcp->tcp_csuna = tcp->tcp_snxt;
                                BUMP_MIB(tcp_mib.tcpRetransSegs);
                                UPDATE_MIB(tcp_mib.tcpRetransBytes, snd_size);
                                (void) ipv4_tcp_output(sock_id, mp1);
                                freeb(mp1);
                        }
                }
                if (flags & TH_NEED_SACK_REXMIT) {
                        if (tcp_sack_rxmit(tcp, sock_id) != 0) {
                                flags |= TH_XMIT_NEEDED;
                        }
                }
                /*
                 * For TH_LIMIT_XMIT, tcp_wput_data() is called to send
                 * out new segment.  Note that tcp_rexmit should not be
                 * set, otherwise TH_LIMIT_XMIT should not be set.
                 */
                if (flags & (TH_XMIT_NEEDED|TH_LIMIT_XMIT)) {
                        if (!tcp->tcp_rexmit) {
                                tcp_wput_data(tcp, NULL, sock_id);
                        } else {
                                tcp_ss_rexmit(tcp, sock_id);
                        }
                        /*
                         * The TCP could be closed in tcp_state_wait via
                         * tcp_wput_data (tcp_ss_rexmit could call
                         * tcp_wput_data as well).
                         */
                        if (sockets[sock_id].pcb == NULL)
                                return;
                }
                /*
                 * Adjust tcp_cwnd back to normal value after sending
                 * new data segments.
                 */
                if (flags & TH_LIMIT_XMIT) {
                        tcp->tcp_cwnd -= mss << (tcp->tcp_dupack_cnt - 1);
                }

                /* Anything more to do? */
                if ((flags & (TH_ACK_NEEDED|TH_TIMER_NEEDED)) == 0)
                        return;
        }
ack_check:
        if (flags & TH_ACK_NEEDED) {
                /*
                 * Time to send an ack for some reason.
                 */
                if ((mp1 = tcp_ack_mp(tcp)) != NULL) {
                        TCP_DUMP_PACKET("tcp_rput_data: ack mp", mp1);
                        (void) ipv4_tcp_output(sock_id, mp1);
                        BUMP_MIB(tcp_mib.tcpOutAck);
                        freeb(mp1);
                }
        }
}

/*
 * tcp_ss_rexmit() is called in tcp_rput_data() to do slow start
 * retransmission after a timeout.
 *
 * To limit the number of duplicate segments, we limit the number of segment
 * to be sent in one time to tcp_snd_burst, the burst variable.
 */
static void
tcp_ss_rexmit(tcp_t *tcp, int sock_id)
{
        uint32_t        snxt;
        uint32_t        smax;
        int32_t         win;
        int32_t         mss;
        int32_t         off;
        int32_t         burst = tcp->tcp_snd_burst;
        mblk_t          *snxt_mp;

        /*
         * 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) &&
                    (burst > 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;

                        (void) ipv4_tcp_output(sock_id, xmit_mp);
                        freeb(xmit_mp);

                        snxt += cnt;
                        win -= cnt;
                        /*
                         * Update the send timestamp to avoid false
                         * retransmission.
                         * Note. use uintptr_t to suppress the gcc warning.
                         */
                        old_snxt_mp->b_prev =
                            (mblk_t *)(uintptr_t)prom_gettime();
                        BUMP_MIB(tcp_mib.tcpRetransSegs);
                        UPDATE_MIB(tcp_mib.tcpRetransBytes, cnt);

                        tcp->tcp_rexmit_nxt = snxt;
                        burst--;
                }
                /*
                 * 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, sock_id);
        }
}

/*
 * tcp_timer is the timer service routine.  It handles all timer events for
 * a tcp instance except keepalives.  It figures out from the state of the
 * tcp instance what kind of action needs to be done at the time it is called.
 */
static void
tcp_timer(tcp_t *tcp, int sock_id)
{
        mblk_t          *mp;
        uint32_t        first_threshold;
        uint32_t        second_threshold;
        uint32_t        ms;
        uint32_t        mss;

        first_threshold =  tcp->tcp_first_timer_threshold;
        second_threshold = tcp->tcp_second_timer_threshold;
        switch (tcp->tcp_state) {
        case TCPS_IDLE:
        case TCPS_BOUND:
        case TCPS_LISTEN:
                return;
        case TCPS_SYN_RCVD:
        case TCPS_SYN_SENT:
                first_threshold =  tcp->tcp_first_ctimer_threshold;
                second_threshold = tcp->tcp_second_ctimer_threshold;
                break;
        case TCPS_ESTABLISHED:
        case TCPS_FIN_WAIT_1:
        case TCPS_CLOSING:
        case TCPS_CLOSE_WAIT:
        case TCPS_LAST_ACK:
                /* If we have data to rexmit */
                if (tcp->tcp_suna != tcp->tcp_snxt) {
                        int32_t time_to_wait;

                        BUMP_MIB(tcp_mib.tcpTimRetrans);
                        if (tcp->tcp_xmit_head == NULL)
                                break;
                        /* use uintptr_t to suppress the gcc warning */
                        time_to_wait = (int32_t)(prom_gettime() -
                            (uint32_t)(uintptr_t)tcp->tcp_xmit_head->b_prev);
                        time_to_wait = tcp->tcp_rto - time_to_wait;
                        if (time_to_wait > 0) {
                                /*
                                 * Timer fired too early, so restart it.
                                 */
                                TCP_TIMER_RESTART(tcp, time_to_wait);
                                return;
                        }
                        /*
                         * When we probe zero windows, we force the swnd open.
                         * If our peer acks with a closed window swnd will be
                         * set to zero by tcp_rput(). As long as we are
                         * receiving acks tcp_rput will
                         * reset 'tcp_ms_we_have_waited' so as not to trip the
                         * first and second interval actions.  NOTE: the timer
                         * interval is allowed to continue its exponential
                         * backoff.
                         */
                        if (tcp->tcp_swnd == 0 || tcp->tcp_zero_win_probe) {
                                DEBUG_1("tcp_timer (%d): zero win", sock_id);
                                break;
                        } else {
                                /*
                                 * After retransmission, we need to do
                                 * slow start.  Set the ssthresh to one
                                 * half of current effective window and
                                 * cwnd to one MSS.  Also reset
                                 * tcp_cwnd_cnt.
                                 *
                                 * Note that if tcp_ssthresh is reduced because
                                 * of ECN, do not reduce it again unless it is
                                 * already one window of data away (tcp_cwr
                                 * should then be cleared) or this is a
                                 * timeout for a retransmitted segment.
                                 */
                                uint32_t npkt;

                                if (!tcp->tcp_cwr || tcp->tcp_rexmit) {
                                        npkt = (MIN((tcp->tcp_timer_backoff ?
                                            tcp->tcp_cwnd_ssthresh :
                                            tcp->tcp_cwnd),
                                            tcp->tcp_swnd) >> 1) /
                                            tcp->tcp_mss;
                                        if (npkt < 2)
                                                npkt = 2;
                                        tcp->tcp_cwnd_ssthresh = npkt *
                                            tcp->tcp_mss;
                                }
                                tcp->tcp_cwnd = tcp->tcp_mss;
                                tcp->tcp_cwnd_cnt = 0;
                                if (tcp->tcp_ecn_ok) {
                                        tcp->tcp_cwr = B_TRUE;
                                        tcp->tcp_cwr_snd_max = tcp->tcp_snxt;
                                        tcp->tcp_ecn_cwr_sent = B_FALSE;
                                }
                        }
                        break;
                }
                /*
                 * We have something to send yet we cannot send.  The
                 * reason can be:
                 *
                 * 1. Zero send window: we need to do zero window probe.
                 * 2. Zero cwnd: because of ECN, we need to "clock out
                 * segments.
                 * 3. SWS avoidance: receiver may have shrunk window,
                 * reset our knowledge.
                 *
                 * Note that condition 2 can happen with either 1 or
                 * 3.  But 1 and 3 are exclusive.
                 */
                if (tcp->tcp_unsent != 0) {
                        if (tcp->tcp_cwnd == 0) {
                                /*
                                 * Set tcp_cwnd to 1 MSS so that a
                                 * new segment can be sent out.  We
                                 * are "clocking out" new data when
                                 * the network is really congested.
                                 */
                                assert(tcp->tcp_ecn_ok);
                                tcp->tcp_cwnd = tcp->tcp_mss;
                        }
                        if (tcp->tcp_swnd == 0) {
                                /* Extend window for zero window probe */
                                tcp->tcp_swnd++;
                                tcp->tcp_zero_win_probe = B_TRUE;
                                BUMP_MIB(tcp_mib.tcpOutWinProbe);
                        } else {
                                /*
                                 * Handle timeout from sender SWS avoidance.
                                 * Reset our knowledge of the max send window
                                 * since the receiver might have reduced its
                                 * receive buffer.  Avoid setting tcp_max_swnd
                                 * to one since that will essentially disable
                                 * the SWS checks.
                                 *
                                 * Note that since we don't have a SWS
                                 * state variable, if the timeout is set
                                 * for ECN but not for SWS, this
                                 * code will also be executed.  This is
                                 * fine as tcp_max_swnd is updated
                                 * constantly and it will not affect
                                 * anything.
                                 */
                                tcp->tcp_max_swnd = MAX(tcp->tcp_swnd, 2);
                        }
                        tcp_wput_data(tcp, NULL, sock_id);
                        return;
                }
                /* Is there a FIN that needs to be to re retransmitted? */
                if ((tcp->tcp_valid_bits & TCP_FSS_VALID) &&
                    !tcp->tcp_fin_acked)
                        break;
                /* Nothing to do, return without restarting timer. */
                return;
        case TCPS_FIN_WAIT_2:
                /*
                 * User closed the TCP endpoint and peer ACK'ed our FIN.
                 * We waited some time for for peer's FIN, but it hasn't
                 * arrived.  We flush the connection now to avoid
                 * case where the peer has rebooted.
                 */
                /* FALLTHRU */
        case TCPS_TIME_WAIT:
                (void) tcp_clean_death(sock_id, tcp, 0);
                return;
        default:
                DEBUG_3("tcp_timer (%d): strange state (%d) %s", sock_id,
                    tcp->tcp_state, tcp_display(tcp, NULL,
                    DISP_PORT_ONLY));
                return;
        }
        if ((ms = tcp->tcp_ms_we_have_waited) > second_threshold) {
                /*
                 * For zero window probe, we need to send indefinitely,
                 * unless we have not heard from the other side for some
                 * time...
                 */
                if ((tcp->tcp_zero_win_probe == 0) ||
                    ((prom_gettime() - tcp->tcp_last_recv_time) >
                    second_threshold)) {
                        BUMP_MIB(tcp_mib.tcpTimRetransDrop);
                        /*
                         * If TCP is in SYN_RCVD state, send back a
                         * RST|ACK as BSD does.  Note that tcp_zero_win_probe
                         * should be zero in TCPS_SYN_RCVD state.
                         */
                        if (tcp->tcp_state == TCPS_SYN_RCVD) {
                                tcp_xmit_ctl("tcp_timer: RST sent on timeout "
                                    "in SYN_RCVD",
                                    tcp, NULL, tcp->tcp_snxt,
                                    tcp->tcp_rnxt, TH_RST | TH_ACK, 0, sock_id);
                        }
                        (void) tcp_clean_death(sock_id, tcp,
                            tcp->tcp_client_errno ?
                            tcp->tcp_client_errno : ETIMEDOUT);
                        return;
                } else {
                        /*
                         * Set tcp_ms_we_have_waited to second_threshold
                         * so that in next timeout, we will do the above
                         * check (lbolt - tcp_last_recv_time).  This is
                         * also to avoid overflow.
                         *
                         * We don't need to decrement tcp_timer_backoff
                         * to avoid overflow because it will be decremented
                         * later if new timeout value is greater than
                         * tcp_rexmit_interval_max.  In the case when
                         * tcp_rexmit_interval_max is greater than
                         * second_threshold, it means that we will wait
                         * longer than second_threshold to send the next
                         * window probe.
                         */
                        tcp->tcp_ms_we_have_waited = second_threshold;
                }
        } else if (ms > first_threshold && tcp->tcp_rtt_sa != 0) {
                /*
                 * We have been retransmitting for too long...  The RTT
                 * we calculated is probably incorrect.  Reinitialize it.
                 * Need to compensate for 0 tcp_rtt_sa.  Reset
                 * tcp_rtt_update so that we won't accidentally cache a
                 * bad value.  But only do this if this is not a zero
                 * window probe.
                 */
                if (tcp->tcp_zero_win_probe == 0) {
                        tcp->tcp_rtt_sd += (tcp->tcp_rtt_sa >> 3) +
                            (tcp->tcp_rtt_sa >> 5);
                        tcp->tcp_rtt_sa = 0;
                        tcp->tcp_rtt_update = 0;
                }
        }
        tcp->tcp_timer_backoff++;
        if ((ms = (tcp->tcp_rtt_sa >> 3) + tcp->tcp_rtt_sd +
            tcp_rexmit_interval_extra + (tcp->tcp_rtt_sa >> 5)) <
            tcp_rexmit_interval_min) {
                /*
                 * This means the original RTO is tcp_rexmit_interval_min.
                 * So we will use tcp_rexmit_interval_min as the RTO value
                 * and do the backoff.
                 */
                ms = tcp_rexmit_interval_min << tcp->tcp_timer_backoff;
        } else {
                ms <<= tcp->tcp_timer_backoff;
        }
        if (ms > tcp_rexmit_interval_max) {
                ms = tcp_rexmit_interval_max;
                /*
                 * ms is at max, decrement tcp_timer_backoff to avoid
                 * overflow.
                 */
                tcp->tcp_timer_backoff--;
        }
        tcp->tcp_ms_we_have_waited += ms;
        if (tcp->tcp_zero_win_probe == 0) {
                tcp->tcp_rto = ms;
        }
        TCP_TIMER_RESTART(tcp, ms);
        /*
         * This is after a timeout and tcp_rto is backed off.  Set
         * tcp_set_timer to 1 so that next time RTO is updated, we will
         * restart the timer with a correct value.
         */
        tcp->tcp_set_timer = 1;
        mss = tcp->tcp_snxt - tcp->tcp_suna;
        if (mss > tcp->tcp_mss)
                mss = tcp->tcp_mss;
        if (mss > tcp->tcp_swnd && tcp->tcp_swnd != 0)
                mss = tcp->tcp_swnd;

        if ((mp = tcp->tcp_xmit_head) != NULL) {
                /* use uintptr_t to suppress the gcc warning */
                mp->b_prev = (mblk_t *)(uintptr_t)prom_gettime();
        }
        mp = tcp_xmit_mp(tcp, mp, mss, NULL, NULL, tcp->tcp_suna, B_TRUE, &mss,
            B_TRUE);
        if (mp == NULL)
                return;
        tcp->tcp_csuna = tcp->tcp_snxt;
        BUMP_MIB(tcp_mib.tcpRetransSegs);
        UPDATE_MIB(tcp_mib.tcpRetransBytes, mss);
        /* Dump the packet when debugging. */
        TCP_DUMP_PACKET("tcp_timer", mp);

        (void) ipv4_tcp_output(sock_id, mp);
        freeb(mp);

        /*
         * When slow start after retransmission begins, start with
         * this seq no.  tcp_rexmit_max marks the end of special slow
         * start phase.  tcp_snd_burst controls how many segments
         * can be sent because of an ack.
         */
        tcp->tcp_rexmit_nxt = tcp->tcp_suna;
        tcp->tcp_snd_burst = TCP_CWND_SS;
        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 = B_TRUE;
        tcp->tcp_dupack_cnt = 0;

        /*
         * Remove all rexmit SACK blk to start from fresh.
         */
        if (tcp->tcp_snd_sack_ok && tcp->tcp_notsack_list != NULL) {
                TCP_NOTSACK_REMOVE_ALL(tcp->tcp_notsack_list);
                tcp->tcp_num_notsack_blk = 0;
                tcp->tcp_cnt_notsack_list = 0;
        }
}

/*
 * The TCP normal data output path.
 * NOTE: the logic of the fast path is duplicated from this function.
 */
static void
tcp_wput_data(tcp_t *tcp, mblk_t *mp, int sock_id)
{
        int             len;
        mblk_t          *local_time;
        mblk_t          *mp1;
        uchar_t         *rptr;
        uint32_t        snxt;
        int             tail_unsent;
        int             tcpstate;
        int             usable = 0;
        mblk_t          *xmit_tail;
        int32_t         num_burst_seg;
        int32_t         mss;
        int32_t         num_sack_blk = 0;
        int32_t         tcp_hdr_len;
        ipaddr_t        *dst;
        ipaddr_t        *src;

#ifdef DEBUG
        printf("tcp_wput_data(%d) ##############################\n", sock_id);
#endif
        tcpstate = tcp->tcp_state;
        if (mp == NULL) {
                /* Really tacky... but we need this for detached closes. */
                len = tcp->tcp_unsent;
                goto data_null;
        }

        /*
         * Don't allow data after T_ORDREL_REQ or T_DISCON_REQ,
         * or before a connection attempt has begun.
         *
         * The following should not happen in inetboot....
         */
        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) {
                        printf("tcp_wput_data: data after ordrel, %s\n",
                            tcp_display(tcp, NULL, DISP_ADDR_AND_PORT));
                }
                freemsg(mp);
                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 {
                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;

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;
                tcp_hdr_len = tcp->tcp_hdr_len + opt_len;
        } else {
                mss = tcp->tcp_mss;
                tcp_hdr_len = tcp->tcp_hdr_len;
        }

        if ((tcp->tcp_suna == snxt) &&
            (prom_gettime() - tcp->tcp_last_recv_time) >= tcp->tcp_rto) {
                tcp->tcp_cwnd = MIN(tcp_slow_start_after_idle * mss,
                    MIN(4 * mss, MAX(2 * mss, 4380 / mss * mss)));
        }
        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). Setting usable to
                 * zero cause a jump to "done" label effectively leaving data
                 * on the queue.
                 */

                usable = 0;
        } else {
                int usable_r = tcp->tcp_swnd;

                /*
                 * 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_rput_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;
                }

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

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

                /* 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;
        }

        /* use uintptr_t to suppress the gcc warning */
        local_time = (mblk_t *)(uintptr_t)prom_gettime();

        /*
         * "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))
                goto done;

        num_burst_seg = tcp->tcp_snd_burst;
        for (;;) {
                tcph_t          *tcph;
                mblk_t          *new_mp;

                if (num_burst_seg-- == 0)
                        goto done;

                len = mss;
                if (len > usable) {
                        len = usable;
                        if (len <= 0) {
                                /* Terminate the loop */
                                goto done;
                        }
                        /*
                         * 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 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);
                                }
                                goto done;
                        }
                }

                tcph = tcp->tcp_tcph;

                usable -= len;  /* Approximate - can be adjusted later */
                if (usable > 0)
                        tcph->th_flags[0] = TH_ACK;
                else
                        tcph->th_flags[0] = (TH_ACK | TH_PUSH);

                U32_TO_ABE32(snxt, tcph->th_seq);

                if (tcp->tcp_valid_bits) {
                        uchar_t         *prev_rptr = xmit_tail->b_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 {
                                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)
                                xmit_tail->b_prev = local_time;
                        else
                                xmit_tail->b_rptr = prev_rptr;

                        if (mp == NULL)
                                break;

                        mp1 = mp->b_cont;

                        snxt += len;
                        tcp->tcp_last_sent_len = (ushort_t)len;
                        while (mp1->b_cont) {
                                xmit_tail = xmit_tail->b_cont;
                                xmit_tail->b_prev = local_time;
                                mp1 = mp1->b_cont;
                        }
                        tail_unsent = xmit_tail->b_wptr - mp1->b_wptr;
                        BUMP_MIB(tcp_mib.tcpOutDataSegs);
                        UPDATE_MIB(tcp_mib.tcpOutDataBytes, len);
                        /* Dump the packet when debugging. */
                        TCP_DUMP_PACKET("tcp_wput_data (valid bits)", mp);
                        (void) ipv4_tcp_output(sock_id, mp);
                        freeb(mp);
                        continue;
                }

                snxt += len;    /* Adjust later if we don't send all of len */
                BUMP_MIB(tcp_mib.tcpOutDataSegs);
                UPDATE_MIB(tcp_mib.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;
                                len += tcp_hdr_len;
                                tcp->tcp_ipha->ip_len = htons(len);
                                mp = dupb(xmit_tail);
                                if (!mp)
                                        break;
                                mp->b_rptr = rptr;
                                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);
                }

                tail_unsent -= len;
                tcp->tcp_last_sent_len = (ushort_t)len;

                len += tcp_hdr_len;
                if (tcp->tcp_ipversion == IPV4_VERSION)
                        tcp->tcp_ipha->ip_len = htons(len);

                xmit_tail->b_prev = local_time;

                mp = dupb(xmit_tail);
                if (mp == NULL)
                        goto out_of_mem;

                len = tcp_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) ||
                    rptr < mp->b_datap) {
                        /* NOTE: we assume allocb returns an OK_32PTR */

                must_alloc:;
                        mp1 = allocb(tcp->tcp_ip_hdr_len + TCP_MAX_HDR_LENGTH +
                            tcp_wroff_xtra, 0);
                        if (mp1 == NULL) {
                                freemsg(mp);
                                goto out_of_mem;
                        }
                        mp1->b_cont = mp;
                        mp = mp1;
                        /* Leave room for Link Level header */
                        len = tcp_hdr_len;
                        rptr = &mp->b_rptr[tcp_wroff_xtra];
                        mp->b_wptr = &rptr[len];
                }

                if (tcp->tcp_snd_ts_ok) {
                        /* use uintptr_t to suppress the gcc warning */
                        U32_TO_BE32((uint32_t)(uintptr_t)local_time,
                                (char *)tcph+TCP_MIN_HEADER_LENGTH+4);
                        U32_TO_BE32(tcp->tcp_ts_recent,
                            (char *)tcph+TCP_MIN_HEADER_LENGTH+8);
                } else {
                        assert(tcp->tcp_tcp_hdr_len == TCP_MIN_HEADER_LENGTH);
                }

                mp->b_rptr = rptr;

                /* Copy the template header. */
                dst = (ipaddr_t *)rptr;
                src = (ipaddr_t *)tcp->tcp_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];
                len = tcp->tcp_hdr_len;
                if (len -= 40) {
                        len >>= 2;
                        dst += 10;
                        src += 10;
                        do {
                                *dst++ = *src++;
                        } while (--len);
                }

                /*
                 * Set tcph to point to the header of the outgoing packet,
                 * not to the template header.
                 */
                tcph = (tcph_t *)(rptr + tcp->tcp_ip_hdr_len);

                /*
                 * 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) {
                        SET_ECT(tcp, rptr);

                        if (tcp->tcp_ecn_echo_on)
                                tcph->th_flags[0] |= TH_ECE;
                        if (tcp->tcp_cwr && !tcp->tcp_ecn_cwr_sent) {
                                tcph->th_flags[0] |= TH_CWR;
                                tcp->tcp_ecn_cwr_sent = B_TRUE;
                        }
                }

                /* Fill in SACK options */
                if (num_sack_blk > 0) {
                        uchar_t *wptr = rptr + tcp->tcp_hdr_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);
                        }
                        tcph->th_offset_and_rsrvd[0] += ((num_sack_blk * 2 + 1)
                            << 4);
                }

                if (tail_unsent) {
                        mp1 = mp->b_cont;
                        if (mp1 == NULL)
                                mp1 = mp;
                        /*
                         * If we're a little short, tack on more mblks
                         * as long as we don't need to split an mblk.
                         */
                        while (tail_unsent < 0 &&
                            tail_unsent + (int)(xmit_tail->b_cont->b_wptr -
                            xmit_tail->b_cont->b_rptr) <= 0) {
                                xmit_tail = xmit_tail->b_cont;
                                /* Stash for rtt use later */
                                xmit_tail->b_prev = local_time;
                                mp1->b_cont = dupb(xmit_tail);
                                mp1 = mp1->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);
                                if (mp1 == NULL) {
                                        freemsg(mp);
                                        goto out_of_mem;
                                }
                        }
                        /* Trim back any surplus on the last mblk */
                        if (tail_unsent > 0)
                                mp1->b_wptr -= tail_unsent;
                        if (tail_unsent < 0) {
                                uint32_t ip_len;

                                /*
                                 * We did not send everything we could in
                                 * order to preserve mblk boundaries.
                                 */
                                usable -= tail_unsent;
                                snxt += tail_unsent;
                                tcp->tcp_last_sent_len += tail_unsent;
                                UPDATE_MIB(tcp_mib.tcpOutDataBytes,
                                    tail_unsent);
                                /* Adjust the IP length field. */
                                ip_len = ntohs(((struct ip *)rptr)->ip_len) +
                                    tail_unsent;
                                ((struct ip *)rptr)->ip_len = htons(ip_len);
                                tail_unsent = 0;
                        }
                }

                if (mp == NULL)
                        goto out_of_mem;

                /*
                 * Performance hit!  We need to pullup the whole message
                 * in order to do checksum and for the MAC output routine.
                 */
                if (mp->b_cont != NULL) {
                        int mp_size;
#ifdef  DEBUG
                        printf("Multiple mblk %d\n", msgdsize(mp));
#endif
                        new_mp = allocb(msgdsize(mp) + tcp_wroff_xtra, 0);
                        new_mp->b_rptr += tcp_wroff_xtra;
                        new_mp->b_wptr = new_mp->b_rptr;
                        while (mp != NULL) {
                                mp_size = mp->b_wptr - mp->b_rptr;
                                bcopy(mp->b_rptr, new_mp->b_wptr, mp_size);
                                new_mp->b_wptr += mp_size;
                                mp = mp->b_cont;
                        }
                        freemsg(mp);
                        mp = new_mp;
                }
                tcp_set_cksum(mp);
                ((struct ip *)mp->b_rptr)->ip_ttl = (uint8_t)tcp_ipv4_ttl;
                TCP_DUMP_PACKET("tcp_wput_data", mp);
                (void) ipv4_tcp_output(sock_id, mp);
                freemsg(mp);
        }
out_of_mem:;
        /* Pretend that all we were trying to send really got sent */
        if (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);
                }
                /*
                 * Note that len is the amount we just sent but with a negative
                 * sign. We update tcp_unsent here since we may come back to
                 * tcp_wput_data from tcp_state_wait.
                 */
                len += tcp->tcp_unsent;
                tcp->tcp_unsent = len;

                /*
                 * Let's wait till all the segments have been acked, since we
                 * don't have a timer.
                 */
                (void) tcp_state_wait(sock_id, tcp, TCPS_ALL_ACKED);
                return;
        } 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 */
        len += tcp->tcp_unsent;
        tcp->tcp_unsent = len;

}

static void
tcp_time_wait_processing(tcp_t *tcp, mblk_t *mp,
    uint32_t seg_seq, uint32_t seg_ack, int seg_len, tcph_t *tcph,
    int sock_id)
{
        int32_t         bytes_acked;
        int32_t         gap;
        int32_t         rgap;
        tcp_opt_t       tcpopt;
        uint_t          flags;
        uint32_t        new_swnd = 0;

#ifdef DEBUG
        printf("Time wait processing called ###############3\n");
#endif

        /* Just make sure we send the right sock_id to tcp_clean_death */
        if ((sockets[sock_id].pcb == NULL) || (sockets[sock_id].pcb != tcp))
                sock_id = -1;

        flags = (unsigned int)tcph->th_flags[0] & 0xFF;
        new_swnd = BE16_TO_U16(tcph->th_win) <<
            ((tcph->th_flags[0] & TH_SYN) ? 0 : tcp->tcp_snd_ws);
        if (tcp->tcp_snd_ts_ok) {
                if (!tcp_paws_check(tcp, tcph, &tcpopt)) {
                        freemsg(mp);
                        tcp_xmit_ctl(NULL, tcp, NULL, tcp->tcp_snxt,
                            tcp->tcp_rnxt, TH_ACK, 0, -1);
                        return;
                }
        }
        gap = seg_seq - tcp->tcp_rnxt;
        rgap = tcp->tcp_rwnd - (gap + seg_len);
        if (gap < 0) {
                BUMP_MIB(tcp_mib.tcpInDataDupSegs);
                UPDATE_MIB(tcp_mib.tcpInDataDupBytes,
                    (seg_len > -gap ? -gap : seg_len));
                seg_len += gap;
                if (seg_len < 0 || (seg_len == 0 && !(flags & TH_FIN))) {
                        if (flags & TH_RST) {
                                freemsg(mp);
                                return;
                        }
                        if ((flags & TH_FIN) && seg_len == -1) {
                                /*
                                 * When TCP receives a duplicate FIN in
                                 * TIME_WAIT state, restart the 2 MSL timer.
                                 * See page 73 in RFC 793. Make sure this TCP
                                 * is already on the TIME_WAIT list. If not,
                                 * just restart the timer.
                                 */
                                tcp_time_wait_remove(tcp);
                                tcp_time_wait_append(tcp);
                                TCP_TIMER_RESTART(tcp, tcp_time_wait_interval);
                                tcp_xmit_ctl(NULL, tcp, NULL, tcp->tcp_snxt,
                                    tcp->tcp_rnxt, TH_ACK, 0, -1);
                                freemsg(mp);
                                return;
                        }
                        flags |=  TH_ACK_NEEDED;
                        seg_len = 0;
                        goto process_ack;
                }

                /* Fix seg_seq, and chew the gap off the front. */
                seg_seq = tcp->tcp_rnxt;
        }

        if ((flags & TH_SYN) && gap > 0 && rgap < 0) {
                /*
                 * Make sure that when we accept the connection, pick
                 * an ISS greater than (tcp_snxt + ISS_INCR/2) for the
                 * old connection.
                 *
                 * The next ISS generated is equal to tcp_iss_incr_extra
                 * + ISS_INCR/2 + other components depending on the
                 * value of tcp_strong_iss.  We pre-calculate the new
                 * ISS here and compare with tcp_snxt to determine if
                 * we need to make adjustment to tcp_iss_incr_extra.
                 *
                 * Note that since we are now in the global queue
                 * perimeter and need to do a lateral_put() to the
                 * listener queue, there can be other connection requests/
                 * attempts while the lateral_put() is going on.  That
                 * means what we calculate here may not be correct.  This
                 * is extremely difficult to solve unless TCP and IP
                 * modules are merged and there is no perimeter, but just
                 * locks.  The above calculation is ugly and is a
                 * waste of CPU cycles...
                 */
                uint32_t new_iss = tcp_iss_incr_extra;
                int32_t adj;

                /* Add time component and min random (i.e. 1). */
                new_iss += (prom_gettime() >> ISS_NSEC_SHT) + 1;
                if ((adj = (int32_t)(tcp->tcp_snxt - new_iss)) > 0) {
                        /*
                         * New ISS not guaranteed to be ISS_INCR/2
                         * ahead of the current tcp_snxt, so add the
                         * difference to tcp_iss_incr_extra.
                         */
                        tcp_iss_incr_extra += adj;
                }
                tcp_clean_death(sock_id, tcp, 0);

                /*
                 * This is a passive open.  Right now we do not
                 * do anything...
                 */
                freemsg(mp);
                return;
        }

        /*
         * rgap is the amount of stuff received out of window.  A negative
         * value is the amount out of window.
         */
        if (rgap < 0) {
                BUMP_MIB(tcp_mib.tcpInDataPastWinSegs);
                UPDATE_MIB(tcp_mib.tcpInDataPastWinBytes, -rgap);
                /* Fix seg_len and make sure there is something left. */
                seg_len += rgap;
                if (seg_len <= 0) {
                        if (flags & TH_RST) {
                                freemsg(mp);
                                return;
                        }
                        flags |=  TH_ACK_NEEDED;
                        seg_len = 0;
                        goto process_ack;
                }
        }
        /*
         * Check whether we can update tcp_ts_recent.  This test is
         * NOT the one in RFC 1323 3.4.  It is from Braden, 1993, "TCP
         * Extensions for High Performance: An Update", Internet Draft.
         */
        if (tcp->tcp_snd_ts_ok &&
            TSTMP_GEQ(tcpopt.tcp_opt_ts_val, tcp->tcp_ts_recent) &&
            SEQ_LEQ(seg_seq, tcp->tcp_rack)) {
                tcp->tcp_ts_recent = tcpopt.tcp_opt_ts_val;
                tcp->tcp_last_rcv_lbolt = prom_gettime();
        }

        if (seg_seq != tcp->tcp_rnxt && seg_len > 0) {
                /* Always ack out of order packets */
                flags |= TH_ACK_NEEDED;
                seg_len = 0;
        } else if (seg_len > 0) {
                BUMP_MIB(tcp_mib.tcpInDataInorderSegs);
                UPDATE_MIB(tcp_mib.tcpInDataInorderBytes, seg_len);
        }
        if (flags & TH_RST) {
                freemsg(mp);
                (void) tcp_clean_death(sock_id, tcp, 0);
                return;
        }
        if (flags & TH_SYN) {
                freemsg(mp);
                tcp_xmit_ctl("TH_SYN", tcp, NULL, seg_ack, seg_seq + 1,
                    TH_RST|TH_ACK, 0, -1);
                /*
                 * Do not delete the TCP structure if it is in
                 * TIME_WAIT state.  Refer to RFC 1122, 4.2.2.13.
                 */
                return;
        }
process_ack:
        if (flags & TH_ACK) {
                bytes_acked = (int)(seg_ack - tcp->tcp_suna);
                if (bytes_acked <= 0) {
                        if (bytes_acked == 0 && seg_len == 0 &&
                            new_swnd == tcp->tcp_swnd)
                                BUMP_MIB(tcp_mib.tcpInDupAck);
                } else {
                        /* Acks something not sent */
                        flags |= TH_ACK_NEEDED;
                }
        }
        freemsg(mp);
        if (flags & TH_ACK_NEEDED) {
                /*
                 * Time to send an ack for some reason.
                 */
                tcp_xmit_ctl(NULL, tcp, NULL, tcp->tcp_snxt,
                    tcp->tcp_rnxt, TH_ACK, 0, -1);
        }
}

static int
tcp_init_values(tcp_t *tcp, struct inetboot_socket *isp)
{
        int     err;

        tcp->tcp_family = AF_INET;
        tcp->tcp_ipversion = IPV4_VERSION;

        /*
         * Initialize tcp_rtt_sa and tcp_rtt_sd so that the calculated RTO
         * will be close to tcp_rexmit_interval_initial.  By doing this, we
         * allow the algorithm to adjust slowly to large fluctuations of RTT
         * during first few transmissions of a connection as seen in slow
         * links.
         */
        tcp->tcp_rtt_sa = tcp_rexmit_interval_initial << 2;
        tcp->tcp_rtt_sd = tcp_rexmit_interval_initial >> 1;
        tcp->tcp_rto = (tcp->tcp_rtt_sa >> 3) + tcp->tcp_rtt_sd +
            tcp_rexmit_interval_extra + (tcp->tcp_rtt_sa >> 5) +
            tcp_conn_grace_period;
        if (tcp->tcp_rto < tcp_rexmit_interval_min)
                tcp->tcp_rto = tcp_rexmit_interval_min;
        tcp->tcp_timer_backoff = 0;
        tcp->tcp_ms_we_have_waited = 0;
        tcp->tcp_last_recv_time = prom_gettime();
        tcp->tcp_cwnd_max = tcp_cwnd_max_;
        tcp->tcp_snd_burst = TCP_CWND_INFINITE;
        tcp->tcp_cwnd_ssthresh = TCP_MAX_LARGEWIN;
        /* For Ethernet, the mtu returned is actually 1550... */
        if (mac_get_type() == IFT_ETHER) {
                tcp->tcp_if_mtu = mac_get_mtu() - 50;
        } else {
                tcp->tcp_if_mtu = mac_get_mtu();
        }
        tcp->tcp_mss = tcp->tcp_if_mtu;

        tcp->tcp_first_timer_threshold = tcp_ip_notify_interval;
        tcp->tcp_first_ctimer_threshold = tcp_ip_notify_cinterval;
        tcp->tcp_second_timer_threshold = tcp_ip_abort_interval;
        /*
         * Fix it to tcp_ip_abort_linterval later if it turns out to be a
         * passive open.
         */
        tcp->tcp_second_ctimer_threshold = tcp_ip_abort_cinterval;

        tcp->tcp_naglim = tcp_naglim_def;

        /* NOTE:  ISS is now set in tcp_adapt_ire(). */

        /* Initialize the header template */
        if (tcp->tcp_ipversion == IPV4_VERSION) {
                err = tcp_header_init_ipv4(tcp);
        }
        if (err)
                return (err);

        /*
         * Init the window scale to the max so tcp_rwnd_set() won't pare
         * down tcp_rwnd. tcp_adapt_ire() will set the right value later.
         */
        tcp->tcp_rcv_ws = TCP_MAX_WINSHIFT;
        tcp->tcp_xmit_lowater = tcp_xmit_lowat;
        if (isp != NULL) {
                tcp->tcp_xmit_hiwater = isp->so_sndbuf;
                tcp->tcp_rwnd = isp->so_rcvbuf;
                tcp->tcp_rwnd_max = isp->so_rcvbuf;
        }
        tcp->tcp_state = TCPS_IDLE;
        return (0);
}

/*
 * Initialize the IPv4 header. Loses any record of any IP options.
 */
static int
tcp_header_init_ipv4(tcp_t *tcp)
{
        tcph_t          *tcph;

        /*
         * This is a simple initialization. If there's
         * already a template, it should never be too small,
         * so reuse it.  Otherwise, allocate space for the new one.
         */
        if (tcp->tcp_iphc != NULL) {
                assert(tcp->tcp_iphc_len >= TCP_MAX_COMBINED_HEADER_LENGTH);
                bzero(tcp->tcp_iphc, tcp->tcp_iphc_len);
        } else {
                tcp->tcp_iphc_len = TCP_MAX_COMBINED_HEADER_LENGTH;
                tcp->tcp_iphc = bkmem_zalloc(tcp->tcp_iphc_len);
                if (tcp->tcp_iphc == NULL) {
                        tcp->tcp_iphc_len = 0;
                        return (ENOMEM);
                }
        }
        tcp->tcp_ipha = (struct ip *)tcp->tcp_iphc;
        tcp->tcp_ipversion = IPV4_VERSION;

        /*
         * Note that it does not include TCP options yet.  It will
         * after the connection is established.
         */
        tcp->tcp_hdr_len = sizeof (struct ip) + sizeof (tcph_t);
        tcp->tcp_tcp_hdr_len = sizeof (tcph_t);
        tcp->tcp_ip_hdr_len = sizeof (struct ip);
        tcp->tcp_ipha->ip_v = IP_VERSION;
        /* We don't support IP options... */
        tcp->tcp_ipha->ip_hl = IP_SIMPLE_HDR_LENGTH_IN_WORDS;
        tcp->tcp_ipha->ip_p = IPPROTO_TCP;
        /* We are not supposed to do PMTU discovery... */
        tcp->tcp_ipha->ip_sum = 0;

        tcph = (tcph_t *)(tcp->tcp_iphc + sizeof (struct ip));
        tcp->tcp_tcph = tcph;
        tcph->th_offset_and_rsrvd[0] = (5 << 4);
        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.
 *
 * This function is called with or without a mp.
 */
static void
tcp_xmit_ctl(char *str, tcp_t *tcp, mblk_t *mp, uint32_t seq,
    uint32_t ack, int ctl, uint_t ip_hdr_len, int sock_id)
{
        uchar_t         *rptr;
        tcph_t          *tcph;
        struct ip       *iph = NULL;
        int             tcp_hdr_len;
        int             tcp_ip_hdr_len;

        tcp_hdr_len = tcp->tcp_hdr_len;
        tcp_ip_hdr_len = tcp->tcp_ip_hdr_len;

        if (mp) {
                assert(ip_hdr_len != 0);
                rptr = mp->b_rptr;
                tcph = (tcph_t *)(rptr + ip_hdr_len);
                /* Don't reply to a RST segment. */
                if (tcph->th_flags[0] & TH_RST) {
                        freeb(mp);
                        return;
                }
                freemsg(mp);
                rptr = NULL;
        } else {
                assert(ip_hdr_len == 0);
        }
        /* If a text string is passed in with the request, print it out. */
        if (str != NULL) {
                dprintf("tcp_xmit_ctl(%d): '%s', seq 0x%x, ack 0x%x, "
                    "ctl 0x%x\n", sock_id, str, seq, ack, ctl);
        }
        mp = allocb(tcp_ip_hdr_len + TCP_MAX_HDR_LENGTH + tcp_wroff_xtra, 0);
        if (mp == NULL) {
                dprintf("tcp_xmit_ctl(%d): Cannot allocate memory\n", sock_id);
                return;
        }
        rptr = &mp->b_rptr[tcp_wroff_xtra];
        mp->b_rptr = rptr;
        mp->b_wptr = &rptr[tcp_hdr_len];
        bcopy(tcp->tcp_iphc, rptr, tcp_hdr_len);

        iph = (struct ip *)rptr;
        iph->ip_len = htons(tcp_hdr_len);

        tcph = (tcph_t *)&rptr[tcp_ip_hdr_len];
        tcph->th_flags[0] = (uint8_t)ctl;
        if (ctl & TH_RST) {
                BUMP_MIB(tcp_mib.tcpOutRsts);
                BUMP_MIB(tcp_mib.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[tcp_hdr_len - TCPOPT_REAL_TS_LEN];
                        *(mp->b_wptr) = TCPOPT_EOL;
                        iph->ip_len = htons(tcp_hdr_len -
                            TCPOPT_REAL_TS_LEN);
                        tcph->th_offset_and_rsrvd[0] -= (3 << 4);
                }
        }
        if (ctl & TH_ACK) {
                uint32_t now = prom_gettime();

                if (tcp->tcp_snd_ts_ok) {
                        U32_TO_BE32(now,
                            (char *)tcph+TCP_MIN_HEADER_LENGTH+4);
                        U32_TO_BE32(tcp->tcp_ts_recent,
                            (char *)tcph+TCP_MIN_HEADER_LENGTH+8);
                }
                tcp->tcp_rack = ack;
                tcp->tcp_rack_cnt = 0;
                BUMP_MIB(tcp_mib.tcpOutAck);
        }
        BUMP_MIB(tcp_mib.tcpOutSegs);
        U32_TO_BE32(seq, tcph->th_seq);
        U32_TO_BE32(ack, tcph->th_ack);

        tcp_set_cksum(mp);
        iph->ip_ttl = (uint8_t)tcp_ipv4_ttl;
        TCP_DUMP_PACKET("tcp_xmit_ctl", mp);
        (void) ipv4_tcp_output(sock_id, mp);
        freeb(mp);
}

/* Generate an ACK-only (no data) segment for a TCP endpoint */
static mblk_t *
tcp_ack_mp(tcp_t *tcp)
{
        if (tcp->tcp_valid_bits) {
                /*
                 * For the complex case where we have to send some
                 * controls (FIN or SYN), let tcp_xmit_mp do it.
                 * When sending an ACK-only segment (no data)
                 * into a zero window, always set the seq number to
                 * suna, since snxt will be extended past the window.
                 * If we used snxt, the receiver might consider the ACK
                 * unacceptable.
                 */
                return (tcp_xmit_mp(tcp, NULL, 0, NULL, NULL,
                    (tcp->tcp_zero_win_probe) ?
                    tcp->tcp_suna :
                    tcp->tcp_snxt, B_FALSE, NULL, B_FALSE));
        } else {
                /* Generate a simple ACK */
                uchar_t *rptr;
                tcph_t  *tcph;
                mblk_t  *mp1;
                int32_t tcp_hdr_len;
                int32_t num_sack_blk = 0;
                int32_t sack_opt_len;

                /*
                 * Allocate space for TCP + IP headers
                 * and link-level header
                 */
                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;
                        tcp_hdr_len = tcp->tcp_hdr_len + sack_opt_len;
                } else {
                        tcp_hdr_len = tcp->tcp_hdr_len;
                }
                mp1 = allocb(tcp_hdr_len + tcp_wroff_xtra, 0);
                if (mp1 == NULL)
                        return (NULL);

                /* copy in prototype TCP + IP header */
                rptr = mp1->b_rptr + tcp_wroff_xtra;
                mp1->b_rptr = rptr;
                mp1->b_wptr = rptr + tcp_hdr_len;
                bcopy(tcp->tcp_iphc, rptr, tcp->tcp_hdr_len);

                tcph = (tcph_t *)&rptr[tcp->tcp_ip_hdr_len];

                /*
                 * Set the TCP sequence number.
                 * When sending an ACK-only segment (no data)
                 * into a zero window, always set the seq number to
                 * suna, since snxt will be extended past the window.
                 * If we used snxt, the receiver might consider the ACK
                 * unacceptable.
                 */
                U32_TO_ABE32((tcp->tcp_zero_win_probe) ?
                    tcp->tcp_suna : tcp->tcp_snxt, tcph->th_seq);

                /* Set up the TCP flag field. */
                tcph->th_flags[0] = (uchar_t)TH_ACK;
                if (tcp->tcp_ecn_echo_on)
                        tcph->th_flags[0] |= TH_ECE;

                tcp->tcp_rack = tcp->tcp_rnxt;
                tcp->tcp_rack_cnt = 0;

                /* fill in timestamp option if in use */
                if (tcp->tcp_snd_ts_ok) {
                        uint32_t llbolt = (uint32_t)prom_gettime();

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

                /* Fill in SACK options */
                if (num_sack_blk > 0) {
                        uchar_t *wptr = (uchar_t *)tcph + tcp->tcp_tcp_hdr_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);
                        }
                        tcph->th_offset_and_rsrvd[0] += ((num_sack_blk * 2 + 1)
                            << 4);
                }

                ((struct ip *)rptr)->ip_len = htons(tcp_hdr_len);
                tcp_set_cksum(mp1);
                ((struct ip *)rptr)->ip_ttl = (uint8_t)tcp_ipv4_ttl;
                return (mp1);
        }
}

/*
 * 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.
 */
static 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;
        mblk_t  *new_mp;
        uchar_t *rptr;
        tcph_t  *tcph;
        int32_t num_sack_blk = 0;
        int32_t sack_opt_len = 0;

        /* Allocate for our maximum TCP header + link-level */
        mp1 = allocb(tcp->tcp_ip_hdr_len + TCP_MAX_HDR_LENGTH +
            tcp_wroff_xtra, 0);
        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 == NULL) {
                        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;
        }

        rptr = mp1->b_rptr + tcp_wroff_xtra;
        mp1->b_rptr = rptr;
        mp1->b_wptr = rptr + tcp->tcp_hdr_len + sack_opt_len;
        bcopy(tcp->tcp_iphc, rptr, tcp->tcp_hdr_len);
        tcph = (tcph_t *)&rptr[tcp->tcp_ip_hdr_len];
        U32_TO_ABE32(seq, tcph->th_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) {
                        SET_ECT(tcp, rptr);
                        if (tcp->tcp_cwr && !tcp->tcp_ecn_cwr_sent) {
                                flags |= TH_CWR;
                                tcp->tcp_ecn_cwr_sent = B_TRUE;
                        }
                }
        }

        if (tcp->tcp_valid_bits) {
                uint32_t u1;

                if ((tcp->tcp_valid_bits & TCP_ISS_VALID) &&
                    seq == tcp->tcp_iss) {
                        uchar_t *wptr;

                        /*
                         * Tack on the MSS option.  It is always needed
                         * for both active and passive open.
                         */
                        wptr = mp1->b_wptr;
                        wptr[0] = TCPOPT_MAXSEG;
                        wptr[1] = TCPOPT_MAXSEG_LEN;
                        wptr += 2;
                        /*
                         * MSS option value should be interface MTU - MIN
                         * TCP/IP header.
                         */
                        u1 = tcp->tcp_if_mtu - IP_SIMPLE_HDR_LENGTH -
                            TCP_MIN_HEADER_LENGTH;
                        U16_TO_BE16(u1, wptr);
                        mp1->b_wptr = wptr + 2;
                        /* Update the offset to cover the additional word */
                        tcph->th_offset_and_rsrvd[0] += (1 << 4);

                        /*
                         * Note that the following way of filling in
                         * TCP options are not optimal.  Some NOPs can
                         * be saved.  But there is no need at this time
                         * to optimize it.  When it is needed, we will
                         * do it.
                         */
                        switch (tcp->tcp_state) {
                        case TCPS_SYN_SENT:
                                flags = TH_SYN;

                                if (tcp->tcp_snd_ws_ok) {
                                        wptr = mp1->b_wptr;
                                        wptr[0] =  TCPOPT_NOP;
                                        wptr[1] =  TCPOPT_WSCALE;
                                        wptr[2] =  TCPOPT_WS_LEN;
                                        wptr[3] = (uchar_t)tcp->tcp_rcv_ws;
                                        mp1->b_wptr += TCPOPT_REAL_WS_LEN;
                                        tcph->th_offset_and_rsrvd[0] +=
                                            (1 << 4);
                                }

                                if (tcp->tcp_snd_ts_ok) {
                                        uint32_t llbolt;

                                        llbolt = prom_gettime();
                                        wptr = mp1->b_wptr;
                                        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);
                                        mp1->b_wptr += TCPOPT_REAL_TS_LEN;
                                        tcph->th_offset_and_rsrvd[0] +=
                                            (3 << 4);
                                }

                                if (tcp->tcp_snd_sack_ok) {
                                        wptr = mp1->b_wptr;
                                        wptr[0] = TCPOPT_NOP;
                                        wptr[1] = TCPOPT_NOP;
                                        wptr[2] = TCPOPT_SACK_PERMITTED;
                                        wptr[3] = TCPOPT_SACK_OK_LEN;
                                        mp1->b_wptr += TCPOPT_REAL_SACK_OK_LEN;
                                        tcph->th_offset_and_rsrvd[0] +=
                                            (1 << 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;

                                if (tcp->tcp_snd_ws_ok) {
                                    wptr = mp1->b_wptr;
                                    wptr[0] =  TCPOPT_NOP;
                                    wptr[1] =  TCPOPT_WSCALE;
                                    wptr[2] =  TCPOPT_WS_LEN;
                                    wptr[3] = (uchar_t)tcp->tcp_rcv_ws;
                                    mp1->b_wptr += TCPOPT_REAL_WS_LEN;
                                    tcph->th_offset_and_rsrvd[0] += (1 << 4);
                                }

                                if (tcp->tcp_snd_sack_ok) {
                                        wptr = mp1->b_wptr;
                                        wptr[0] = TCPOPT_NOP;
                                        wptr[1] = TCPOPT_NOP;
                                        wptr[2] = TCPOPT_SACK_PERMITTED;
                                        wptr[3] = TCPOPT_SACK_OK_LEN;
                                        mp1->b_wptr += TCPOPT_REAL_SACK_OK_LEN;
                                        tcph->th_offset_and_rsrvd[0] +=
                                            (1 << 4);
                                }

                                /*
                                 * If the other side is ECN capable, reply
                                 * that we are also ECN capable.
                                 */
                                if (tcp->tcp_ecn_ok) {
                                        flags |= TH_ECE;
                                }
                                break;
                        default:
                                break;
                        }
                        /* allocb() of adequate mblk assures space */
                        assert((uintptr_t)(mp1->b_wptr -
                            mp1->b_rptr) <= (uintptr_t)INT_MAX);
                        if (flags & TH_SYN)
                                BUMP_MIB(tcp_mib.tcpOutControl);
                }
                if ((tcp->tcp_valid_bits & TCP_FSS_VALID) &&
                    (seq + data_length) == tcp->tcp_fss) {
                        if (!tcp->tcp_fin_acked) {
                                flags |= TH_FIN;
                                BUMP_MIB(tcp_mib.tcpOutControl);
                        }
                        if (!tcp->tcp_fin_sent) {
                                tcp->tcp_fin_sent = B_TRUE;
                                switch (tcp->tcp_state) {
                                case TCPS_SYN_RCVD:
                                case TCPS_ESTABLISHED:
                                        tcp->tcp_state = TCPS_FIN_WAIT_1;
                                        break;
                                case TCPS_CLOSE_WAIT:
                                        tcp->tcp_state = TCPS_LAST_ACK;
                                        break;
                                }
                                if (tcp->tcp_suna == tcp->tcp_snxt)
                                        TCP_TIMER_RESTART(tcp, tcp->tcp_rto);
                                tcp->tcp_snxt = tcp->tcp_fss + 1;
                        }
                }
        }
        tcph->th_flags[0] = (uchar_t)flags;
        tcp->tcp_rack = tcp->tcp_rnxt;
        tcp->tcp_rack_cnt = 0;

        if (tcp->tcp_snd_ts_ok) {
                if (tcp->tcp_state != TCPS_SYN_SENT) {
                        uint32_t llbolt = prom_gettime();

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

        if (num_sack_blk > 0) {
                uchar_t *wptr = (uchar_t *)tcph + tcp->tcp_tcp_hdr_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);
                }
                tcph->th_offset_and_rsrvd[0] += ((num_sack_blk * 2 + 1) << 4);
        }
        assert((uintptr_t)(mp1->b_wptr - rptr) <= (uintptr_t)INT_MAX);
        data_length += (int)(mp1->b_wptr - rptr);
        if (tcp->tcp_ipversion == IPV4_VERSION)
                ((struct ip *)rptr)->ip_len = htons(data_length);

        /*
         * Performance hit!  We need to pullup the whole message
         * in order to do checksum and for the MAC output routine.
         */
        if (mp1->b_cont != NULL) {
                int mp_size;
#ifdef DEBUG
                printf("Multiple mblk %d\n", msgdsize(mp1));
#endif
                mp2 = mp1;
                new_mp = allocb(msgdsize(mp1) + tcp_wroff_xtra, 0);
                new_mp->b_rptr += tcp_wroff_xtra;
                new_mp->b_wptr = new_mp->b_rptr;
                while (mp1 != NULL) {
                        mp_size = mp1->b_wptr - mp1->b_rptr;
                        bcopy(mp1->b_rptr, new_mp->b_wptr, mp_size);
                        new_mp->b_wptr += mp_size;
                        mp1 = mp1->b_cont;
                }
                freemsg(mp2);
                mp1 = new_mp;
        }
        tcp_set_cksum(mp1);
        /* Fill in the TTL field as it is 0 in the header template. */
        ((struct ip *)mp1->b_rptr)->ip_ttl = (uint8_t)tcp_ipv4_ttl;

        return (mp1);
}

/*
 * Generate a "no listener here" reset in response to the
 * connection request contained within 'mp'
 */
static void
tcp_xmit_listeners_reset(int sock_id, mblk_t *mp, uint_t ip_hdr_len)
{
        uchar_t         *rptr;
        uint32_t        seg_len;
        tcph_t          *tcph;
        uint32_t        seg_seq;
        uint32_t        seg_ack;
        uint_t          flags;

        rptr = mp->b_rptr;

        tcph = (tcph_t *)&rptr[ip_hdr_len];
        seg_seq = BE32_TO_U32(tcph->th_seq);
        seg_ack = BE32_TO_U32(tcph->th_ack);
        flags = tcph->th_flags[0];

        seg_len = msgdsize(mp) - (TCP_HDR_LENGTH(tcph) + ip_hdr_len);
        if (flags & TH_RST) {
                freeb(mp);
        } else if (flags & TH_ACK) {
                tcp_xmit_early_reset("no tcp, reset",
                    sock_id, mp, seg_ack, 0, TH_RST, ip_hdr_len);
        } else {
                if (flags & TH_SYN)
                        seg_len++;
                tcp_xmit_early_reset("no tcp, reset/ack", sock_id,
                    mp, 0, seg_seq + seg_len,
                    TH_RST | TH_ACK, ip_hdr_len);
        }
}

/* Non overlapping byte exchanger */
static void
tcp_xchg(uchar_t *a, uchar_t *b, int len)
{
        uchar_t uch;

        while (len-- > 0) {
                uch = a[len];
                a[len] = b[len];
                b[len] = uch;
        }
}

/*
 * Generate a reset based on an inbound packet for which there is no active
 * tcp state that we can find.
 */
static void
tcp_xmit_early_reset(char *str, int sock_id, mblk_t *mp, uint32_t seq,
    uint32_t ack, int ctl, uint_t ip_hdr_len)
{
        struct ip       *iph = NULL;
        ushort_t        len;
        tcph_t          *tcph;
        int             i;
        ipaddr_t        addr;
        mblk_t          *new_mp;

        if (str != NULL) {
                dprintf("tcp_xmit_early_reset: '%s', seq 0x%x, ack 0x%x, "
                    "flags 0x%x\n", str, seq, ack, ctl);
        }

        /*
         * We skip reversing source route here.
         * (for now we replace all IP options with EOL)
         */
        iph = (struct ip *)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 is not a limited broadcast
         * address. 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.
         */
        if (iph->ip_src.s_addr == INADDR_ANY ||
            iph->ip_src.s_addr == INADDR_BROADCAST) {
                freemsg(mp);
                return;
        }

        tcph = (tcph_t *)&mp->b_rptr[ip_hdr_len];
        if (tcph->th_flags[0] & TH_RST) {
                freemsg(mp);
                return;
        }
        /*
         * Now copy the original header to a new buffer.  The reason
         * for doing this is that we need to put extra room before
         * the header for the MAC layer address.  The original mblk
         * does not have this extra head room.
         */
        len = ip_hdr_len + sizeof (tcph_t);
        if ((new_mp = allocb(len + tcp_wroff_xtra, 0)) == NULL) {
                freemsg(mp);
                return;
        }
        new_mp->b_rptr += tcp_wroff_xtra;
        bcopy(mp->b_rptr, new_mp->b_rptr, len);
        new_mp->b_wptr = new_mp->b_rptr + len;
        freemsg(mp);
        mp = new_mp;
        iph = (struct ip *)mp->b_rptr;
        tcph = (tcph_t *)&mp->b_rptr[ip_hdr_len];

        tcph->th_offset_and_rsrvd[0] = (5 << 4);
        tcp_xchg(tcph->th_fport, tcph->th_lport, 2);
        U32_TO_BE32(ack, tcph->th_ack);
        U32_TO_BE32(seq, tcph->th_seq);
        U16_TO_BE16(0, tcph->th_win);
        bzero(tcph->th_sum, sizeof (int16_t));
        tcph->th_flags[0] = (uint8_t)ctl;
        if (ctl & TH_RST) {
                BUMP_MIB(tcp_mib.tcpOutRsts);
                BUMP_MIB(tcp_mib.tcpOutControl);
        }

        iph->ip_len = htons(len);
        /* Swap addresses */
        addr = iph->ip_src.s_addr;
        iph->ip_src = iph->ip_dst;
        iph->ip_dst.s_addr = addr;
        iph->ip_id = 0;
        iph->ip_ttl = 0;
        tcp_set_cksum(mp);
        iph->ip_ttl = (uint8_t)tcp_ipv4_ttl;

        /* Dump the packet when debugging. */
        TCP_DUMP_PACKET("tcp_xmit_early_reset", mp);
        (void) ipv4_tcp_output(sock_id, mp);
        freemsg(mp);
}

static void
tcp_set_cksum(mblk_t *mp)
{
        struct ip *iph;
        tcpha_t *tcph;
        int len;

        iph = (struct ip *)mp->b_rptr;
        tcph = (tcpha_t *)(iph + 1);
        len = ntohs(iph->ip_len);
        /*
         * Calculate the TCP checksum.  Need to include the psuedo header,
         * which is similar to the real IP header starting at the TTL field.
         */
        iph->ip_sum = htons(len - IP_SIMPLE_HDR_LENGTH);
        tcph->tha_sum = 0;
        tcph->tha_sum = tcp_cksum((uint16_t *)&(iph->ip_ttl),
            len - IP_SIMPLE_HDR_LENGTH + 12);
        iph->ip_sum = 0;
}

static uint16_t
tcp_cksum(uint16_t *buf, uint32_t len)
{
        /*
         * Compute Internet Checksum for "count" bytes
         * beginning at location "addr".
         */
        int32_t sum = 0;

        while (len > 1) {
                /*  This is the inner loop */
                sum += *buf++;
                len -= 2;
        }

        /*  Add left-over byte, if any */
        if (len > 0)
                sum += *(unsigned char *)buf * 256;

        /*  Fold 32-bit sum to 16 bits */
        while (sum >> 16)
                sum = (sum & 0xffff) + (sum >> 16);

        return ((uint16_t)~sum);
}

/*
 * Type three generator adapted from the random() function in 4.4 BSD:
 */

/*
 * Copyright (c) 1983, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* Type 3 -- x**31 + x**3 + 1 */
#define DEG_3           31
#define SEP_3           3


/* Protected by tcp_random_lock */
static int tcp_randtbl[DEG_3 + 1];

static int *tcp_random_fptr = &tcp_randtbl[SEP_3 + 1];
static int *tcp_random_rptr = &tcp_randtbl[1];

static int *tcp_random_state = &tcp_randtbl[1];
static int *tcp_random_end_ptr = &tcp_randtbl[DEG_3 + 1];

static void
tcp_random_init(void)
{
        int i;
        uint32_t hrt;
        uint32_t wallclock;
        uint32_t result;

        /*
         *
         * XXX We don't have high resolution time in standalone...  The
         * following is just some approximation on the comment below.
         *
         * Use high-res timer and current time for seed.  Gethrtime() returns
         * a longlong, which may contain resolution down to nanoseconds.
         * The current time will either be a 32-bit or a 64-bit quantity.
         * XOR the two together in a 64-bit result variable.
         * Convert the result to a 32-bit value by multiplying the high-order
         * 32-bits by the low-order 32-bits.
         *
         * XXX We don't have gethrtime() in prom and the wallclock....
         */

        hrt = prom_gettime();
        wallclock = (uint32_t)time(NULL);
        result = wallclock ^ hrt;
        tcp_random_state[0] = result;

        for (i = 1; i < DEG_3; i++)
                tcp_random_state[i] = 1103515245 * tcp_random_state[i - 1]
                        + 12345;
        tcp_random_fptr = &tcp_random_state[SEP_3];
        tcp_random_rptr = &tcp_random_state[0];
        for (i = 0; i < 10 * DEG_3; i++)
                (void) tcp_random();
}

/*
 * tcp_random: Return a random number in the range [1 - (128K + 1)].
 * This range is selected to be approximately centered on TCP_ISS / 2,
 * and easy to compute. We get this value by generating a 32-bit random
 * number, selecting out the high-order 17 bits, and then adding one so
 * that we never return zero.
 */
static int
tcp_random(void)
{
        int i;

        *tcp_random_fptr += *tcp_random_rptr;

        /*
         * The high-order bits are more random than the low-order bits,
         * so we select out the high-order 17 bits and add one so that
         * we never return zero.
         */
        i = ((*tcp_random_fptr >> 15) & 0x1ffff) + 1;
        if (++tcp_random_fptr >= tcp_random_end_ptr) {
                tcp_random_fptr = tcp_random_state;
                ++tcp_random_rptr;
        } else if (++tcp_random_rptr >= tcp_random_end_ptr)
                tcp_random_rptr = tcp_random_state;

        return (i);
}

/*
 * Generate ISS, taking into account NDD changes may happen halfway through.
 * (If the iss is not zero, set it.)
 */
static void
tcp_iss_init(tcp_t *tcp)
{
        tcp_iss_incr_extra += (ISS_INCR >> 1);
        tcp->tcp_iss = tcp_iss_incr_extra;
        tcp->tcp_iss += (prom_gettime() >> ISS_NSEC_SHT) + tcp_random();
        tcp->tcp_valid_bits = TCP_ISS_VALID;
        tcp->tcp_fss = tcp->tcp_iss - 1;
        tcp->tcp_suna = tcp->tcp_iss;
        tcp->tcp_snxt = tcp->tcp_iss + 1;
        tcp->tcp_rexmit_nxt = tcp->tcp_snxt;
        tcp->tcp_csuna = tcp->tcp_snxt;
}

/*
 * Diagnostic routine used to return a string associated with the tcp state.
 * Note that if the caller does not supply a buffer, it will use an internal
 * static string.  This means that if multiple threads call this function at
 * the same time, output can be corrupted...  Note also that this function
 * does not check the size of the supplied buffer.  The caller has to make
 * sure that it is big enough.
 */
static char *
tcp_display(tcp_t *tcp, char *sup_buf, char format)
{
        char            buf1[30];
        static char     priv_buf[INET_ADDRSTRLEN * 2 + 80];
        char            *buf;
        char            *cp;
        char            local_addrbuf[INET_ADDRSTRLEN];
        char            remote_addrbuf[INET_ADDRSTRLEN];
        struct in_addr  addr;

        if (sup_buf != NULL)
                buf = sup_buf;
        else
                buf = priv_buf;

        if (tcp == NULL)
                return ("NULL_TCP");
        switch (tcp->tcp_state) {
        case TCPS_CLOSED:
                cp = "TCP_CLOSED";
                break;
        case TCPS_IDLE:
                cp = "TCP_IDLE";
                break;
        case TCPS_BOUND:
                cp = "TCP_BOUND";
                break;
        case TCPS_LISTEN:
                cp = "TCP_LISTEN";
                break;
        case TCPS_SYN_SENT:
                cp = "TCP_SYN_SENT";
                break;
        case TCPS_SYN_RCVD:
                cp = "TCP_SYN_RCVD";
                break;
        case TCPS_ESTABLISHED:
                cp = "TCP_ESTABLISHED";
                break;
        case TCPS_CLOSE_WAIT:
                cp = "TCP_CLOSE_WAIT";
                break;
        case TCPS_FIN_WAIT_1:
                cp = "TCP_FIN_WAIT_1";
                break;
        case TCPS_CLOSING:
                cp = "TCP_CLOSING";
                break;
        case TCPS_LAST_ACK:
                cp = "TCP_LAST_ACK";
                break;
        case TCPS_FIN_WAIT_2:
                cp = "TCP_FIN_WAIT_2";
                break;
        case TCPS_TIME_WAIT:
                cp = "TCP_TIME_WAIT";
                break;
        default:
                (void) sprintf(buf1, "TCPUnkState(%d)", tcp->tcp_state);
                cp = buf1;
                break;
        }
        switch (format) {
        case DISP_ADDR_AND_PORT:
                /*
                 * Note that we use the remote address in the tcp_b
                 * structure.  This means that it will print out
                 * the real destination address, not the next hop's
                 * address if source routing is used.
                 */
                addr.s_addr = tcp->tcp_bound_source;
                bcopy(inet_ntoa(addr), local_addrbuf, sizeof (local_addrbuf));
                addr.s_addr = tcp->tcp_remote;
                bcopy(inet_ntoa(addr), remote_addrbuf, sizeof (remote_addrbuf));
                (void) snprintf(buf, sizeof (priv_buf), "[%s.%u, %s.%u] %s",
                    local_addrbuf, ntohs(tcp->tcp_lport), remote_addrbuf,
                    ntohs(tcp->tcp_fport), cp);
                break;
        case DISP_PORT_ONLY:
        default:
                (void) snprintf(buf, sizeof (priv_buf), "[%u, %u] %s",
                    ntohs(tcp->tcp_lport), ntohs(tcp->tcp_fport), cp);
                break;
        }

        return (buf);
}

/*
 * Add a new piece to the tcp reassembly queue.  If the gap at the beginning
 * is filled, return as much as we can.  The message passed in may be
 * multi-part, chained using b_cont.  "start" is the starting sequence
 * number for this piece.
 */
static mblk_t *
tcp_reass(tcp_t *tcp, mblk_t *mp, uint32_t start)
{
        uint32_t        end;
        mblk_t          *mp1;
        mblk_t          *mp2;
        mblk_t          *next_mp;
        uint32_t        u1;

        /* Walk through all the new pieces. */
        do {
                assert((uintptr_t)(mp->b_wptr - mp->b_rptr) <=
                    (uintptr_t)INT_MAX);
                end = start + (int)(mp->b_wptr - mp->b_rptr);
                next_mp = mp->b_cont;
                if (start == end) {
                        /* Empty.  Blast it. */
                        freeb(mp);
                        continue;
                }
                mp->b_cont = NULL;
                TCP_REASS_SET_SEQ(mp, start);
                TCP_REASS_SET_END(mp, end);
                mp1 = tcp->tcp_reass_tail;
                if (!mp1) {
                        tcp->tcp_reass_tail = mp;
                        tcp->tcp_reass_head = mp;
                        BUMP_MIB(tcp_mib.tcpInDataUnorderSegs);
                        UPDATE_MIB(tcp_mib.tcpInDataUnorderBytes, end - start);
                        continue;
                }
                /* New stuff completely beyond tail? */
                if (SEQ_GEQ(start, TCP_REASS_END(mp1))) {
                        /* Link it on end. */
                        mp1->b_cont = mp;
                        tcp->tcp_reass_tail = mp;
                        BUMP_MIB(tcp_mib.tcpInDataUnorderSegs);
                        UPDATE_MIB(tcp_mib.tcpInDataUnorderBytes, end - start);
                        continue;
                }
                mp1 = tcp->tcp_reass_head;
                u1 = TCP_REASS_SEQ(mp1);
                /* New stuff at the front? */
                if (SEQ_LT(start, u1)) {
                        /* Yes... Check for overlap. */
                        mp->b_cont = mp1;
                        tcp->tcp_reass_head = mp;
                        tcp_reass_elim_overlap(tcp, mp);
                        continue;
                }
                /*
                 * The new piece fits somewhere between the head and tail.
                 * We find our slot, where mp1 precedes us and mp2 trails.
                 */
                for (; (mp2 = mp1->b_cont) != NULL; mp1 = mp2) {
                        u1 = TCP_REASS_SEQ(mp2);
                        if (SEQ_LEQ(start, u1))
                                break;
                }
                /* Link ourselves in */
                mp->b_cont = mp2;
                mp1->b_cont = mp;

                /* Trim overlap with following mblk(s) first */
                tcp_reass_elim_overlap(tcp, mp);

                /* Trim overlap with preceding mblk */
                tcp_reass_elim_overlap(tcp, mp1);

        } while (start = end, mp = next_mp);
        mp1 = tcp->tcp_reass_head;
        /* Anything ready to go? */
        if (TCP_REASS_SEQ(mp1) != tcp->tcp_rnxt)
                return (NULL);
        /* Eat what we can off the queue */
        for (;;) {
                mp = mp1->b_cont;
                end = TCP_REASS_END(mp1);
                TCP_REASS_SET_SEQ(mp1, 0);
                TCP_REASS_SET_END(mp1, 0);
                if (!mp) {
                        tcp->tcp_reass_tail = NULL;
                        break;
                }
                if (end != TCP_REASS_SEQ(mp)) {
                        mp1->b_cont = NULL;
                        break;
                }
                mp1 = mp;
        }
        mp1 = tcp->tcp_reass_head;
        tcp->tcp_reass_head = mp;
        return (mp1);
}

/* Eliminate any overlap that mp may have over later mblks */
static void
tcp_reass_elim_overlap(tcp_t *tcp, mblk_t *mp)
{
        uint32_t        end;
        mblk_t          *mp1;
        uint32_t        u1;

        end = TCP_REASS_END(mp);
        while ((mp1 = mp->b_cont) != NULL) {
                u1 = TCP_REASS_SEQ(mp1);
                if (!SEQ_GT(end, u1))
                        break;
                if (!SEQ_GEQ(end, TCP_REASS_END(mp1))) {
                        mp->b_wptr -= end - u1;
                        TCP_REASS_SET_END(mp, u1);
                        BUMP_MIB(tcp_mib.tcpInDataPartDupSegs);
                        UPDATE_MIB(tcp_mib.tcpInDataPartDupBytes, end - u1);
                        break;
                }
                mp->b_cont = mp1->b_cont;
                freeb(mp1);
                BUMP_MIB(tcp_mib.tcpInDataDupSegs);
                UPDATE_MIB(tcp_mib.tcpInDataDupBytes, end - u1);
        }
        if (!mp1)
                tcp->tcp_reass_tail = mp;
}

/*
 * Remove a connection from the list of detached TIME_WAIT connections.
 */
static void
tcp_time_wait_remove(tcp_t *tcp)
{
        if (tcp->tcp_time_wait_expire == 0) {
                assert(tcp->tcp_time_wait_next == NULL);
                assert(tcp->tcp_time_wait_prev == NULL);
                return;
        }
        assert(tcp->tcp_state == TCPS_TIME_WAIT);
        if (tcp == tcp_time_wait_head) {
                assert(tcp->tcp_time_wait_prev == NULL);
                tcp_time_wait_head = tcp->tcp_time_wait_next;
                if (tcp_time_wait_head != NULL) {
                        tcp_time_wait_head->tcp_time_wait_prev = NULL;
                } else {
                        tcp_time_wait_tail = NULL;
                }
        } else if (tcp == tcp_time_wait_tail) {
                assert(tcp != tcp_time_wait_head);
                assert(tcp->tcp_time_wait_next == NULL);
                tcp_time_wait_tail = tcp->tcp_time_wait_prev;
                assert(tcp_time_wait_tail != NULL);
                tcp_time_wait_tail->tcp_time_wait_next = NULL;
        } else {
                assert(tcp->tcp_time_wait_prev->tcp_time_wait_next == tcp);
                assert(tcp->tcp_time_wait_next->tcp_time_wait_prev == tcp);
                tcp->tcp_time_wait_prev->tcp_time_wait_next =
                    tcp->tcp_time_wait_next;
                tcp->tcp_time_wait_next->tcp_time_wait_prev =
                    tcp->tcp_time_wait_prev;
        }
        tcp->tcp_time_wait_next = NULL;
        tcp->tcp_time_wait_prev = NULL;
        tcp->tcp_time_wait_expire = 0;
}

/*
 * Add a connection to the list of detached TIME_WAIT connections
 * and set its time to expire ...
 */
static void
tcp_time_wait_append(tcp_t *tcp)
{
        tcp->tcp_time_wait_expire = prom_gettime() + tcp_time_wait_interval;
        if (tcp->tcp_time_wait_expire == 0)
                tcp->tcp_time_wait_expire = 1;

        if (tcp_time_wait_head == NULL) {
                assert(tcp_time_wait_tail == NULL);
                tcp_time_wait_head = tcp;
        } else {
                assert(tcp_time_wait_tail != NULL);
                assert(tcp_time_wait_tail->tcp_state == TCPS_TIME_WAIT);
                tcp_time_wait_tail->tcp_time_wait_next = tcp;
                tcp->tcp_time_wait_prev = tcp_time_wait_tail;
        }
        tcp_time_wait_tail = tcp;

        /* for ndd stats about compression */
        tcp_cum_timewait++;
}

/*
 * Periodic qtimeout routine run on the default queue.
 * Performs 2 functions.
 *      1.  Does TIME_WAIT compression on all recently added tcps. List
 *          traversal is done backwards from the tail.
 *      2.  Blows away all tcps whose TIME_WAIT has expired. List traversal
 *          is done forwards from the head.
 */
void
tcp_time_wait_collector(void)
{
        tcp_t *tcp;
        uint32_t now;

        /*
         * In order to reap time waits reliably, we should use a
         * source of time that is not adjustable by the user
         */
        now = prom_gettime();
        while ((tcp = tcp_time_wait_head) != NULL) {
                /*
                 * Compare times using modular arithmetic, since
                 * lbolt can wrapover.
                 */
                if ((int32_t)(now - tcp->tcp_time_wait_expire) < 0) {
                        break;
                }
                /*
                 * Note that the err must be 0 as there is no socket
                 * associated with this TCP...
                 */
                (void) tcp_clean_death(-1, tcp, 0);
        }
        /* Schedule next run time. */
        tcp_time_wait_runtime = prom_gettime() + 10000;
}

void
tcp_time_wait_report(void)
{
        tcp_t *tcp;

        printf("Current time %u\n", prom_gettime());
        for (tcp = tcp_time_wait_head; tcp != NULL;
            tcp = tcp->tcp_time_wait_next) {
                printf("%s expires at %u\n", tcp_display(tcp, NULL,
                    DISP_ADDR_AND_PORT), tcp->tcp_time_wait_expire);
        }
}

/*
 * Send up all messages queued on tcp_rcv_list.
 * Have to set tcp_co_norm since we use putnext.
 */
static void
tcp_rcv_drain(int sock_id, tcp_t *tcp)
{
        mblk_t *mp;
        struct inetgram *in_gram;
        mblk_t *in_mp;
        int len;

        /* Don't drain if the app has not finished reading all the data. */
        if (sockets[sock_id].so_rcvbuf <= 0)
                return;

        /* We might have come here just to updated the rwnd */
        if (tcp->tcp_rcv_list == NULL)
                goto win_update;

        if ((in_gram = (struct inetgram *)bkmem_zalloc(
            sizeof (struct inetgram))) == NULL) {
                return;
        }
        if ((in_mp = allocb(tcp->tcp_rcv_cnt, 0)) == NULL) {
                bkmem_free((caddr_t)in_gram, sizeof (struct inetgram));
                return;
        }
        in_gram->igm_level = APP_LVL;
        in_gram->igm_mp = in_mp;
        in_gram->igm_id = 0;

        while ((mp = tcp->tcp_rcv_list) != NULL) {
                tcp->tcp_rcv_list = mp->b_cont;
                len = mp->b_wptr - mp->b_rptr;
                bcopy(mp->b_rptr, in_mp->b_wptr, len);
                in_mp->b_wptr += len;
                freeb(mp);
        }

        tcp->tcp_rcv_last_tail = NULL;
        tcp->tcp_rcv_cnt = 0;
        add_grams(&sockets[sock_id].inq, in_gram);

        /* This means that so_rcvbuf can be less than 0. */
        sockets[sock_id].so_rcvbuf -= in_mp->b_wptr - in_mp->b_rptr;
win_update:
        /*
         * Increase the receive window to max.  But we need to do receiver
         * SWS avoidance.  This means that we need to check the increase of
         * of receive window is at least 1 MSS.
         */
        if (sockets[sock_id].so_rcvbuf > 0 &&
            (tcp->tcp_rwnd_max - tcp->tcp_rwnd >= tcp->tcp_mss)) {
                tcp->tcp_rwnd = tcp->tcp_rwnd_max;
                U32_TO_ABE16(tcp->tcp_rwnd >> tcp->tcp_rcv_ws,
                    tcp->tcp_tcph->th_win);
        }
}

/*
 * Wrapper for recvfrom to call
 */
void
tcp_rcv_drain_sock(int sock_id)
{
        tcp_t *tcp;
        if ((tcp = sockets[sock_id].pcb) == NULL)
                return;
        tcp_rcv_drain(sock_id, tcp);
}

/*
 * If the inq == NULL and the tcp_rcv_list != NULL, we have data that
 * recvfrom could read. Place a magic message in the inq to let recvfrom
 * know that it needs to call tcp_rcv_drain_sock to pullup the data.
 */
static void
tcp_drain_needed(int sock_id, tcp_t *tcp)
{
        struct inetgram *in_gram;
#ifdef DEBUG
        printf("tcp_drain_needed: inq %x, tcp_rcv_list %x\n",
                sockets[sock_id].inq, tcp->tcp_rcv_list);
#endif
        if ((sockets[sock_id].inq != NULL) ||
                (tcp->tcp_rcv_list == NULL))
                return;

        if ((in_gram = (struct inetgram *)bkmem_zalloc(
                sizeof (struct inetgram))) == NULL)
                return;

        in_gram->igm_level = APP_LVL;
        in_gram->igm_mp = NULL;
        in_gram->igm_id = TCP_CALLB_MAGIC_ID;

        add_grams(&sockets[sock_id].inq, in_gram);
}

/*
 * Queue data on tcp_rcv_list which is a b_next chain.
 * Each element of the chain is a b_cont chain.
 *
 * M_DATA messages are added to the current element.
 * Other messages are added as new (b_next) elements.
 */
static void
tcp_rcv_enqueue(tcp_t *tcp, mblk_t *mp, uint_t seg_len)
{
        assert(seg_len == msgdsize(mp));
        if (tcp->tcp_rcv_list == NULL) {
                tcp->tcp_rcv_list = mp;
        } else {
                tcp->tcp_rcv_last_tail->b_cont = mp;
        }
        while (mp->b_cont)
                mp = mp->b_cont;
        tcp->tcp_rcv_last_tail = mp;
        tcp->tcp_rcv_cnt += seg_len;
        tcp->tcp_rwnd -= seg_len;
#ifdef DEBUG
        printf("tcp_rcv_enqueue rwnd %d\n", tcp->tcp_rwnd);
#endif
        U32_TO_ABE16(tcp->tcp_rwnd >> tcp->tcp_rcv_ws, tcp->tcp_tcph->th_win);
}

/* The minimum of smoothed mean deviation in RTO calculation. */
#define TCP_SD_MIN      400

/*
 * Set RTO for this connection.  The formula is from Jacobson and Karels'
 * "Congestion Avoidance and Control" in SIGCOMM '88.  The variable names
 * are the same as those in Appendix A.2 of that paper.
 *
 * m = new measurement
 * sa = smoothed RTT average (8 * average estimates).
 * sv = smoothed mean deviation (mdev) of RTT (4 * deviation estimates).
 */
static void
tcp_set_rto(tcp_t *tcp, int32_t rtt)
{
        int32_t m = rtt;
        uint32_t sa = tcp->tcp_rtt_sa;
        uint32_t sv = tcp->tcp_rtt_sd;
        uint32_t rto;

        BUMP_MIB(tcp_mib.tcpRttUpdate);
        tcp->tcp_rtt_update++;

        /* tcp_rtt_sa is not 0 means this is a new sample. */
        if (sa != 0) {
                /*
                 * Update average estimator:
                 *      new rtt = 7/8 old rtt + 1/8 Error
                 */

                /* m is now Error in estimate. */
                m -= sa >> 3;
                if ((int32_t)(sa += m) <= 0) {
                        /*
                         * Don't allow the smoothed average to be negative.
                         * We use 0 to denote reinitialization of the
                         * variables.
                         */
                        sa = 1;
                }

                /*
                 * Update deviation estimator:
                 *      new mdev = 3/4 old mdev + 1/4 (abs(Error) - old mdev)
                 */
                if (m < 0)
                        m = -m;
                m -= sv >> 2;
                sv += m;
        } else {
                /*
                 * This follows BSD's implementation.  So the reinitialized
                 * RTO is 3 * m.  We cannot go less than 2 because if the
                 * link is bandwidth dominated, doubling the window size
                 * during slow start means doubling the RTT.  We want to be
                 * more conservative when we reinitialize our estimates.  3
                 * is just a convenient number.
                 */
                sa = m << 3;
                sv = m << 1;
        }
        if (sv < TCP_SD_MIN) {
                /*
                 * We do not know that if sa captures the delay ACK
                 * effect as in a long train of segments, a receiver
                 * does not delay its ACKs.  So set the minimum of sv
                 * to be TCP_SD_MIN, which is default to 400 ms, twice
                 * of BSD DATO.  That means the minimum of mean
                 * deviation is 100 ms.
                 *
                 */
                sv = TCP_SD_MIN;
        }
        tcp->tcp_rtt_sa = sa;
        tcp->tcp_rtt_sd = sv;
        /*
         * RTO = average estimates (sa / 8) + 4 * deviation estimates (sv)
         *
         * Add tcp_rexmit_interval extra in case of extreme environment
         * where the algorithm fails to work.  The default value of
         * tcp_rexmit_interval_extra should be 0.
         *
         * As we use a finer grained clock than BSD and update
         * RTO for every ACKs, add in another .25 of RTT to the
         * deviation of RTO to accomodate burstiness of 1/4 of
         * window size.
         */
        rto = (sa >> 3) + sv + tcp_rexmit_interval_extra + (sa >> 5);

        if (rto > tcp_rexmit_interval_max) {
                tcp->tcp_rto = tcp_rexmit_interval_max;
        } else if (rto < tcp_rexmit_interval_min) {
                tcp->tcp_rto = tcp_rexmit_interval_min;
        } else {
                tcp->tcp_rto = rto;
        }

        /* Now, we can reset tcp_timer_backoff to use the new RTO... */
        tcp->tcp_timer_backoff = 0;
}

/*
 * Initiate closedown sequence on an active connection.
 * Return value zero for OK return, non-zero for error return.
 */
static int
tcp_xmit_end(tcp_t *tcp, int sock_id)
{
        mblk_t  *mp;

        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 != NULL) {
                        /* Dump the packet when debugging. */
                        TCP_DUMP_PACKET("tcp_xmit_end", mp);
                        (void) ipv4_tcp_output(sock_id, mp);
                        freeb(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 {
                tcp_wput_data(tcp, NULL, B_FALSE);
        }

        return (0);
}

int
tcp_opt_set(tcp_t *tcp, int level, int option, const void *optval,
    socklen_t optlen)
{
        switch (level) {
        case SOL_SOCKET: {
                switch (option) {
                case SO_RCVBUF:
                        if (optlen == sizeof (int)) {
                                int val = *(int *)optval;

                                if (val > tcp_max_buf) {
                                        errno = ENOBUFS;
                                        break;
                                }
                                /* Silently ignore zero */
                                if (val != 0) {
                                        val = MSS_ROUNDUP(val, tcp->tcp_mss);
                                        (void) tcp_rwnd_set(tcp, val);
                                }
                        } else {
                                errno = EINVAL;
                        }
                        break;
                case SO_SNDBUF:
                        if (optlen == sizeof (int)) {
                                tcp->tcp_xmit_hiwater = *(int *)optval;
                                if (tcp->tcp_xmit_hiwater > tcp_max_buf)
                                        tcp->tcp_xmit_hiwater = tcp_max_buf;
                        } else {
                                errno = EINVAL;
                        }
                        break;
                case SO_LINGER:
                        if (optlen == sizeof (struct linger)) {
                                struct linger *lgr = (struct linger *)optval;

                                if (lgr->l_onoff) {
                                        tcp->tcp_linger = 1;
                                        tcp->tcp_lingertime = lgr->l_linger;
                                } else {
                                        tcp->tcp_linger = 0;
                                        tcp->tcp_lingertime = 0;
                                }
                        } else {
                                errno = EINVAL;
                        }
                        break;
                default:
                        errno = ENOPROTOOPT;
                        break;
                }
                break;
        } /* case SOL_SOCKET */
        case IPPROTO_TCP: {
                switch (option) {
                default:
                        errno = ENOPROTOOPT;
                        break;
                }
                break;
        } /* case IPPROTO_TCP */
        case IPPROTO_IP: {
                switch (option) {
                default:
                        errno = ENOPROTOOPT;
                        break;
                }
                break;
        } /* case IPPROTO_IP */
        default:
                errno = ENOPROTOOPT;
                break;
        } /* switch (level) */

        if (errno != 0)
                return (-1);
        else
                return (0);
}