localize header files

[unix-history] / usr / src / sys / netinet / tcp_output.c

diff --git a/usr/src/sys/netinet/tcp_output.c b/usr/src/sys/netinet/tcp_output.c
index 9f82abf..b166b98 100644 (file)
--- a/usr/src/sys/netinet/tcp_output.c
+++ b/usr/src/sys/netinet/tcp_output.c
@@ -1,350 +1,341 @@
-/* tcp_output.c 4.4 81/10/31 */
+/*     tcp_output.c    4.46    82/10/09        */

 
 #include "../h/param.h"
 #include "../h/systm.h"
 #include "../h/mbuf.h"
 
 #include "../h/param.h"
 #include "../h/systm.h"
 #include "../h/mbuf.h"

+#include "../h/protosw.h"

 #include "../h/socket.h"
 #include "../h/socket.h"

-#include "../inet/inet.h"
-#include "../inet/inet_host.h"
-#include "../inet/inet_systm.h"
-#include "../inet/imp.h"
-#include "../inet/ip.h"
-#include "../inet/tcp.h"
-#include "../inet/tcp_fsm.h"
+#include "../h/socketvar.h"
+#include "../netinet/in.h"
+#include "../net/route.h"
+#include "../netinet/in_pcb.h"
+#include "../netinet/in_systm.h"
+#include "../netinet/ip.h"
+#include "../netinet/ip_var.h"
+#include "../netinet/tcp.h"
+#define        TCPOUTFLAGS
+#include "../netinet/tcp_fsm.h"
+#include "../netinet/tcp_seq.h"
+#include "../netinet/tcp_timer.h"
+#include "../netinet/tcp_var.h"
+#include "../netinet/tcpip.h"
+#include "../netinet/tcp_debug.h"
+#include <errno.h>
+
+char *tcpstates[]; /* XXX */

 
 /*
 
 /*

- * Special routines to send control messages.
+ * Initial options.

  */
  */

-tcp_sndctl(tp)
-       struct tcb *tp;
-{
-COUNT(TCP_SNDCTL);
-
-        if (tcp_send(tp))
-               return (1);
-       tcp_sndnull(tp);
-       return(0);
-}
+u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };

 
 

-tcp_sndwin(tp)
-       struct tcb *tp;
+/*
+ * Tcp output routine: figure out what should be sent and send it.
+ */
+tcp_output(tp)
+       register struct tcpcb *tp;

 {
 {

-       int ihave, hehas;
-COUNT(TCP_SNDWIN);
+       register struct socket *so = tp->t_inpcb->inp_socket;
+       register int len;
+       struct mbuf *m0;
+       int off, flags, win, error;
+       register struct mbuf *m;
+       register struct tcpiphdr *ti;
+       u_char *opt;
+       unsigned optlen = 0;
+       int sendalot;

 
 

-       if (tp->rcv_adv) {
-               ihave = tp->t_ucb->uc_rhiwat -
-                   (tp->t_ucb->uc_rcc + tp->seqcnt);
-               hehas = tp->rcv_adv - tp->rcv_nxt;
-               if ((100*(ihave-hehas)/tp->t_ucb->uc_rhiwat) < 35)
-                       return;
-       }
-        if (tcp_send(tp))
-               return (1);
-       tcp_sndnull(tp);
-       return (0);
-}

 
 

-tcp_sndnull(tp)
-       register struct tcb *tp;
-{
-COUNT(TCP_SNDNULL);
+       /*
+        * Determine length of data that should be transmitted,
+        * and flags that will be used.
+        * If there is some data or critical controls (SYN, RST)
+        * to send, then transmit; otherwise, investigate further.
+        */
+again:
+       sendalot = 0;
+       off = tp->snd_nxt - tp->snd_una;
+       len = MIN(so->so_snd.sb_cc, tp->snd_wnd+tp->t_force) - off;
+       if (len < 0)
+               return (0);     /* ??? */       /* past FIN */
+       if (len > tp->t_maxseg) {
+               len = tp->t_maxseg;
+               sendalot = 1;
+       }

 
 

-       tcp_output(tp, 0, 0, (struct mbuf *)0);
-        tp->tc_flags &= ~TC_ACK_DUE;
-}
+       flags = tcp_outflags[tp->t_state];
+       if (tp->snd_nxt + len < tp->snd_una + so->so_snd.sb_cc)
+               flags &= ~TH_FIN;
+       if (flags & (TH_SYN|TH_RST|TH_FIN))
+               goto send;
+       if (SEQ_GT(tp->snd_up, tp->snd_una))
+               goto send;

 
 

-tcp_sndrst(tp, n)
-       register struct tcb *tp;
-       register struct th *n;
-{
-COUNT(TCP_SNDRST);
+       /*
+        * Sender silly window avoidance.  If can send all data,
+        * a maximum segment, at least 1/4 of window do it,
+        * or are forced, do it; otherwise don't bother.
+        */
+       if (len) {
+               if (len == tp->t_maxseg || off+len >= so->so_snd.sb_cc)
+                       goto send;
+               if (len * 4 >= tp->snd_wnd)             /* a lot */
+                       goto send;
+               if (tp->t_force)
+                       goto send;
+       }

 
 

-        /* don't send a reset in response to a reset */
-       if (n->th_flags&TH_RST)
-               return;
-       tp->tc_flags |= TC_SND_RST;
-       if (n->th_flags&TH_ACK)
-               tp->snd_nxt = n->t_ackno;
-       tp->tc_flags &= ~TC_SYN_RCVD;
-       tcp_sndnull(tp);
-       tp->tc_flags &= ~TC_SND_RST;
-}
+       /*
+        * Send if we owe peer an ACK.
+        */
+       if (tp->t_flags&TF_ACKNOW)
+               goto send;

 
 

-/*
- * Tcp segment output routine.
- */
-tcp_send(tp)
-       register struct tcb *tp;
-{
-       register struct ucb *up;
-       register unsigned long last, wind;
-       struct mbuf *m;
-       int flags = 0, forced, sent;
-       struct mbuf *tcp_sndcopy();
-       int len;

 
 

-COUNT(TCP_SEND);
-       up = tp->t_ucb;
-       tp->snd_lst = tp->snd_nxt;
-       forced = 0;
-       m = NULL;
-       if (tp->snd_nxt == tp->iss) {
-               flags |= TH_SYN;
-               tp->snd_lst++;
-       }
-       last = tp->snd_off;
-       for (m = up->uc_sbuf; m != NULL; m = m->m_next)
-               last += m->m_len;
-       if (tp->snd_nxt > last) {
-               if ((tp->tc_flags&TC_SND_FIN) &&
-                   (tp->seq_fin == tp->iss || tp->snd_nxt <= tp->seq_fin)) {
+       /*
+        * Calculate available window in i, and also amount
+        * of window known to peer (as advertised window less
+        * next expected input.)  If this is 35% or more of the
+        * maximum possible window, then want to send a segment to peer.
+        */
+       win = sbspace(&so->so_rcv);
+       if (win > 0 &&
+           ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35))
+               goto send;

 
 

-                       flags |= TH_FIN;
-                       tp->seq_fin = tp->snd_lst++;
-               }
-       } else {
-               if (tp->tc_flags&TC_SYN_ACKED) {
-                       wind = tp->snd_una + tp->snd_wnd;
-                       tp->snd_lst = min(last, wind);
-                       if ((len = tp->snd_lst - tp->snd_nxt) > 1024)
-                               tp->snd_lst -= len - 1024;
-                       if (tp->snd_lst >= wind)
-                               tp->t_persist = T_PERS;
-               }
-               if ((tp->tc_flags&TC_FORCE_ONE) && (tp->snd_lst == wind)) {
-                       tp->snd_lst = tp->snd_nxt + 1;
-                       forced = 1;
-               }
-               m = tcp_sndcopy(tp, max(tp->iss+1,tp->snd_nxt), tp->snd_lst);
-               if (tp->snd_end > tp->iss && tp->snd_end <= tp->snd_lst)
-                       flags |= TH_EOL;
-               if ((tp->tc_flags&TC_SND_FIN) && !forced &&
-                   tp->snd_lst == last &&
-                   (tp->seq_fin == tp->iss || tp->snd_nxt <= tp->seq_fin)) {
-                       flags |= TH_FIN;
-                       tp->seq_fin = tp->snd_lst++;
-               }
-       }
-       if (tp->snd_nxt >= tp->snd_lst)
-               return (0);
-       if (tp->tc_flags & TC_SND_URG)
-               flags |= TH_URG;
-       sent = tcp_output(tp, flags, tp->snd_lst - tp->snd_nxt, m);
-       if (!forced) {
-               tp->t_rexmt = tp->t_xmtime;
-               tp->t_rexmt_val = tp->snd_lst;
-               if ((tp->tc_flags&TC_REXMT) == 0) {
-                       tp->t_rexmttl = T_REXMTTL;
-                       tp->t_rtl_val = tp->snd_lst;
-               }
+       /*
+        * TCP window updates are not reliable, rather a polling protocol
+        * using ``persist'' packets is used to insure receipt of window
+        * updates.  The three ``states'' for the output side are:
+        *      idle                    not doing retransmits or persists
+        *      persisting              to move a zero window
+        *      (re)transmitting        and thereby not persisting
+        *
+        * tp->t_timer[TCPT_PERSIST]
+        *      is set when we are in persist state.
+        * tp->t_force
+        *      is set when we are called to send a persist packet.
+        * tp->t_timer[TCPT_REXMT]
+        *      is set when we are retransmitting
+        * The output side is idle when both timers are zero.
+        *
+        * If send window is closed, there is data to transmit, and no
+        * retransmit or persist is pending, then go to persist state,
+        * arranging to force out a byte to get more current window information
+        * if nothing happens soon.
+        */
+       if (tp->snd_wnd == 0 && so->so_snd.sb_cc &&
+           tp->t_timer[TCPT_REXMT] == 0 && tp->t_timer[TCPT_PERSIST] == 0) {
+               tp->t_rxtshift = 0;
+               tcp_setpersist(tp);

        }
        }

-       if (sent)
-               tp->snd_nxt = tp->snd_lst;
-       if ((tp->tc_flags&TC_SYN_ACKED) &&
-           tp->snd_una > tp->t_xmt_val) {
-               tp->t_xmt = 0;
-               tp->t_xmt_val = tp->snd_lst;
-       }
-       tp->tc_flags &= ~(TC_ACK_DUE|TC_REXMT|TC_FORCE_ONE);
-       tp->snd_hi = max(tp->snd_nxt, tp->snd_hi);
-       return (1);
-}

 
 

-/*
- * Create template to be used to send tcp packets on a connection.
- * Call after host entry created, allocates an mbuf and fills
- * in a skeletal tcp/ip header, minimizing the amount of work
- * necessary when the connection is used.
- */
-struct th *
-tcp_template(tp)
-       struct tcb *tp;
-{
-       register struct host *h = tp->t_ucb->uc_host;
-       register struct mbuf *m;
-       register struct th *n;
-       register struct ip *ip;
+       /*
+        * No reason to send a segment, just return.
+        */
+       return (0);

 
 

-       if (h == 0)
-               return (0);
-       m = m_get(1);
+send:
+       /*
+        * Grab a header mbuf, attaching a copy of data to
+        * be transmitted, and initialize the header from
+        * the template for sends on this connection.
+        */
+       MGET(m, 0);

        if (m == 0)
        if (m == 0)

-               return (0);
-       m->m_off = MMAXOFF - sizeof (struct th);
-       m->m_len = sizeof (struct th);
-       n = mtod(m, struct th *);
-       n->t_next = n->t_prev = 0;
-       n->t_x1 = 0;
-       n->t_pr = TCPROTO;
-       n->t_len = htons(sizeof (struct th) - sizeof (struct ip));
-       n->t_s.s_addr = n_lhost.s_addr;
-       n->t_d.s_addr = h->h_addr.s_addr;
-       n->t_src = htons(tp->t_lport);
-       n->t_dst = htons(tp->t_fport);
-       n->t_seq = 0;
-       n->t_ackno = 0;
-       n->t_x2 = 0;
-       n->t_off = 5;
-       n->th_flags = 0;
-       n->t_win = 0;
-       n->t_sum = 0;
-       n->t_urp = 0;
-       return (n);
-}
+               return (ENOBUFS);
+       m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
+       m->m_len = sizeof (struct tcpiphdr);
+       if (len) {
+               m->m_next = m_copy(so->so_snd.sb_mb, off, len);
+               if (m->m_next == 0)
+                       len = 0;
+       }
+       ti = mtod(m, struct tcpiphdr *);
+       if (tp->t_template == 0)
+               panic("tcp_output");
+       bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));

 
 

-tcp_output(tp, flags, len, dat)
-       register struct tcb *tp;
-       register int flags;
-       int len;
-       struct mbuf *dat;
-{
-       register struct mbuf *m;
-       register struct th *t;
-       register struct ip *ip;
-       int i;
-#ifdef TCPDEBUG
-       struct tcp_debug tdb;
+       /*
+        * Fill in fields, remembering maximum advertised
+        * window for use in delaying messages about window sizes.
+        */
+       ti->ti_seq = tp->snd_nxt;
+       ti->ti_ack = tp->rcv_nxt;
+#if vax
+       ti->ti_seq = htonl(ti->ti_seq);
+       ti->ti_ack = htonl(ti->ti_ack);

 #endif
 #endif

-COUNT(SEND_TCP);
-
-       if ((t = tp->t_ucb->uc_template) == 0)
-               return (0);
-       MGET(m, 0);
-       if (m == 0)
-               return (0);
-       m->m_off = MMAXOFF - sizeof(struct th);
-       m->m_len = sizeof (struct th);
-       m->m_next = dat;
-       if (flags & TH_SYN)
-               len--;
-       if (flags & TH_FIN)
-               len--;
-       bcopy((caddr_t)t, mtod(m, caddr_t), sizeof (struct th));
-       t = mtod(m, struct th *);
-       if (tp->tc_flags&TC_SND_RST) {
-               flags &= ~TH_SYN;
-               flags |= TH_RST;
+       /*
+        * Before ESTABLISHED, force sending of initial options
+        * unless TCP set to not do any options.
+        */
+       if (tp->t_state < TCPS_ESTABLISHED) {
+               if (tp->t_flags&TF_NOOPT)
+                       goto noopt;
+               opt = tcp_initopt;
+               optlen = sizeof (tcp_initopt);
+               *(u_short *)(opt + 2) = MIN(so->so_rcv.sb_hiwat / 2, 1024);
+#if vax
+               *(u_short *)(opt + 2) = htons(*(u_short *)(opt + 2));
+#endif
+       } else {
+               if (tp->t_tcpopt == 0)
+                       goto noopt;
+               opt = mtod(tp->t_tcpopt, u_char *);
+               optlen = tp->t_tcpopt->m_len;

        }
        }

-       if (tp->tc_flags&TC_SYN_RCVD)
-               flags |= TH_ACK;
-       t->th_flags = flags;
-       if (flags & TH_URG)
-               t->t_urp = htons(tp->snd_urp);
-       t->t_win =
-           tp->t_ucb->uc_rhiwat - (tp->t_ucb->uc_rcc + tp->seqcnt);
-       if (tp->rcv_nxt + t->t_win > tp->rcv_adv)
-               tp->rcv_adv = tp->rcv_nxt + t->t_win;
-       if (len)
-               t->t_len = htons(len + TCPSIZE);
-       t->t_win = htons(t->t_win);
-#ifdef TCPDEBUG
-       if ((tp->t_ucb->uc_flags & UDEBUG) || tcpconsdebug) {
-               t->t_seq = tp->snd_nxt;
-               t->t_ackno = tp->rcv_nxt;
-               tdb_setup(tp, t, INSEND, &tdb);
-               tdb_stuff(&tdb, -2);
+       if (opt) {
+               m0 = m->m_next;
+               m->m_next = m_get(M_DONTWAIT);
+               if (m->m_next == 0) {
+                       (void) m_free(m);
+                       m_freem(m0);
+                       return (ENOBUFS);
+               }
+               m->m_next->m_next = m0;
+               m0 = m->m_next;
+               m0->m_len = optlen;
+               bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen);
+               opt = (u_char *)(mtod(m0, caddr_t) + optlen);
+               while (m0->m_len & 0x3) {
+                       *opt++ = TCPOPT_EOL;
+                       m0->m_len++;
+               }
+               optlen = m0->m_len;
+               ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;

        }
        }

+noopt:
+       ti->ti_flags = flags;
+       win = sbspace(&so->so_rcv);
+       if (win < so->so_rcv.sb_hiwat / 4)      /* avoid silly window */
+               win = 0;
+       if (win > 0)
+#if vax
+               ti->ti_win = htons((u_short)win);
+#else
+               ti->ti_win = win;

 #endif
 #endif

-       t->t_seq = htonl(tp->snd_nxt);
-       t->t_ackno = htonl(tp->rcv_nxt);
-       t->t_sum = cksum(m, len + sizeof(struct th));
-       ip = (struct ip *)t;
-       ip->ip_v = IPVERSION;
-       ip->ip_hl = 5;
-       ip->ip_tos = 0;
-       ip->ip_len = len + sizeof(struct th);
-       ip->ip_id = ip_id++;
-       ip->ip_off = 0;
-       ip->ip_ttl = MAXTTL;
-       i = ip_send(ip);
-       return(i);
-}
+       if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
+               ti->ti_urp = tp->snd_up - tp->snd_nxt;
+#if vax
+               ti->ti_urp = htons(ti->ti_urp);
+#endif
+               ti->ti_flags |= TH_URG;
+       } else
+               /*
+                * If no urgent pointer to send, then we pull
+                * the urgent pointer to the left edge of the send window
+                * so that it doesn't drift into the send window on sequence
+                * number wraparound.
+                */
+               tp->snd_up = tp->snd_una;               /* drag it along */
+       /*
+        * If anything to send and we can send it all, set PUSH.
+        * (This will keep happy those implementations which only
+        * give data to the user when a buffer fills or a PUSH comes in.
+        */
+       if (len && off+len == so->so_snd.sb_cc)
+               ti->ti_flags |= TH_PUSH;

 
 

-firstempty(tp)
-       register struct tcb *tp;
-{
-       register struct th *p, *q;
-COUNT(FIRSTEMPTY);
+       /*
+        * Put TCP length in extended header, and then
+        * checksum extended header and data.
+        */
+       if (len + optlen) {
+               ti->ti_len = sizeof (struct tcphdr) + optlen + len;
+#if vax
+               ti->ti_len = htons((u_short)ti->ti_len);
+#endif
+       }
+       ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len);

 
 

-       if ((p = tp->t_rcv_next) == (struct th *)tp || tp->rcv_nxt < p->t_seq)
-               return (tp->rcv_nxt);
-       while ((q = p->t_next) != (struct th *)tp &&
-           (t_end(p) + 1) == q->t_seq)
-               p = q;
-       return (t_end(p) + 1);
-}
+       /*
+        * In transmit state, time the transmission and arrange for
+        * the retransmit.  In persist state, reset persist time for
+        * next persist.
+        */
+       if (tp->t_force == 0) {
+               /*
+                * Advance snd_nxt over sequence space of this segment.
+                */
+               if (flags & (TH_SYN|TH_FIN))
+                       tp->snd_nxt++;
+               tp->snd_nxt += len;
+               if (SEQ_GT(tp->snd_nxt, tp->snd_max))
+                       tp->snd_max = tp->snd_nxt;

 
 

-struct mbuf *
-tcp_sndcopy(tp, start, end)
-       struct tcb *tp;
-       u_long start, end;
-{
-       register struct mbuf *m, *n, **np;
-       u_long off;
-       register int len;
-       int adj;
-       struct mbuf *top, *p;
-COUNT(SND_COPY);
+               /*
+                * Time this transmission if not a retransmission and
+                * not currently timing anything.
+                */
+               if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) {
+                       tp->t_rtt = 1;
+                       tp->t_rtseq = tp->snd_nxt - len;
+               }

 
 

-       if (start >= end)    
-               return(NULL);
-       off = tp->snd_off;
-       m = tp->t_ucb->uc_sbuf;
-       while (m != NULL && start >= (off + m->m_len)) {
-               off += m->m_len;
-               m = m->m_next;
-       }
-       np = &top;
-       top = 0;
-       adj = start - off;
-       len = end - start;
-       while (m && len > 0) {
-               MGET(n, 1);
-               *np = n;
-               if (n == 0)
-                       goto nospace;
-               n->m_len = MIN(len, m->m_len - adj);
-               if (m->m_off > MMAXOFF) {
-                       p = mtod(m, struct mbuf *);
-                       n->m_off = ((int)p - (int)n) + adj;
-                       mprefcnt[mtopf(p)]++;
-               } else {
-                       n->m_off = MMINOFF;
-                       bcopy(mtod(m, caddr_t)+adj, mtod(n, caddr_t),
-                           n->m_len);
+               /*
+                * Set retransmit timer if not currently set.
+                * Initial value for retransmit timer to tcp_beta*tp->t_srtt.
+                * Initialize shift counter which is used for exponential
+                * backoff of retransmit time.
+                */
+               if (tp->t_timer[TCPT_REXMT] == 0 &&
+                   tp->snd_nxt != tp->snd_una) {
+                       TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
+                           tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX);
+                       tp->t_rtt = 0;
+                       tp->t_rxtshift = 0;

                }
                }

-               len -= n->m_len;
-               adj = 0;
-               m = m->m_next;
-               /* SHOULD TRY PACKING INTO SMALL MBUFS HERE */
-               np = &n->m_next;
+               tp->t_timer[TCPT_PERSIST] = 0;
+       } else {
+               if (SEQ_GT(tp->snd_una+1, tp->snd_max))
+                       tp->snd_max = tp->snd_una+1;

        }
        }

-       /* SHOULD NEVER RUN OUT OF m WHEN LEN */
-       if (len)
-               printf("snd_copy: m %x len %d\n", m, len);
-       return (top);
-nospace:
-       printf("snd_copy: no space\n");
-       m_freem(top);
-       return (0);
-}

 
 

-tcp_enq(p, prev)
-       register struct th *p;
-       register struct th *prev;
-{
+       /*
+        * Trace.
+        */
+       if (so->so_options & SO_DEBUG)
+               tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);
+
+       /*
+        * Fill in IP length and desired time to live and
+        * send to IP level.
+        */
+       ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
+       ((struct ip *)ti)->ip_ttl = TCP_TTL;
+       if (error = ip_output(m, tp->t_ipopt, (so->so_options & SO_DONTROUTE) ?
+           &routetoif : &tp->t_inpcb->inp_route, 0))
+               return (error);

 
 

-       p->t_prev = prev;
-       p->t_next = prev->t_next;
-       prev->t_next->t_prev = p;
-       prev->t_next = p;
+       /*
+        * Data sent (as far as we can tell).
+        * If this advertises a larger window than any other segment,
+        * then remember the size of the advertised window.
+        * Drop send for purpose of ACK requirements.
+        */
+       if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
+               tp->rcv_adv = tp->rcv_nxt + win;
+       tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
+       if (sendalot && tp->t_force == 0)
+               goto again;
+       return (0);

 }
 }

- 
-tcp_deq(p)
-       register struct th *p;
+
+tcp_setpersist(tp)
+       register struct tcpcb *tp;

 {
 
 {
 

-       p->t_prev->t_next = p->t_next;
-       p->t_next->t_prev = p->t_prev;
+       if (tp->t_timer[TCPT_REXMT])
+               panic("tcp_output REXMT");
+       /*
+        * Start/restart persistance timer.
+        */
+       TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
+           ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift,
+           TCPTV_PERSMIN, TCPTV_MAX);
+       tp->t_rxtshift++;
+       if (tp->t_rxtshift >= TCP_MAXRXTSHIFT)
+               tp->t_rxtshift = 0;

 }
 }