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[unix-history] / usr / src / sys / netinet / tcp_input.c
/* tcp_input.c 1.49 82/01/17 */
#include "../h/param.h"
#include "../h/systm.h"
#include "../h/mbuf.h"
#include "../h/protosw.h"
#include "../h/socket.h"
#include "../h/socketvar.h"
#include "../net/in.h"
#include "../net/in_pcb.h"
#include "../net/in_systm.h"
#include "../net/if.h"
#include "../net/ip.h"
#include "../net/ip_var.h"
#include "../net/tcp.h"
#include "../net/tcp_fsm.h"
#include "../net/tcp_seq.h"
#include "../net/tcp_timer.h"
#include "../net/tcp_var.h"
#include "../net/tcpip.h"
#include "../net/tcp_debug.h"
#include "../errno.h"
int tcpprintfs = 0;
int tcpcksum = 1;
struct sockaddr_in tcp_in = { AF_INET };
struct tcpiphdr tcp_saveti;
extern tcpnodelack;
struct tcpcb *tcp_newtcpcb();
/*
* TCP input routine, follows pages 65-76 of the
* protocol specification dated September, 1981 very closely.
*/
tcp_input(m0)
struct mbuf *m0;
{
register struct tcpiphdr *ti;
struct inpcb *inp;
register struct mbuf *m;
struct mbuf *om = 0;
int len, tlen, off;
register struct tcpcb *tp = 0;
register int tiflags;
struct socket *so;
int todrop, acked;
short ostate;
COUNT(TCP_INPUT);
/*
* Get IP and TCP header together in first mbuf.
* Note: IP leaves IP header in first mbuf.
*/
m = m0;
ti = mtod(m, struct tcpiphdr *);
if (((struct ip *)ti)->ip_hl > (sizeof (struct ip) >> 2))
ip_stripoptions((struct ip *)ti, (struct mbuf *)0);
if (m->m_off > MMAXOFF || m->m_len < sizeof (struct tcpiphdr)) {
if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
tcpstat.tcps_hdrops++;
return;
}
ti = mtod(m, struct tcpiphdr *);
}
/*
* Checksum extended TCP header and data.
*/
tlen = ((struct ip *)ti)->ip_len;
len = sizeof (struct ip) + tlen;
if (tcpcksum) {
ti->ti_next = ti->ti_prev = 0;
ti->ti_x1 = 0;
ti->ti_len = (u_short)tlen;
#if vax
ti->ti_len = htons(ti->ti_len);
#endif
if (ti->ti_sum = in_cksum(m, len)) {
tcpstat.tcps_badsum++;
printf("tcp cksum %x\n", ti->ti_sum);
goto drop;
}
}
/*
* Check that TCP offset makes sense,
* pull out TCP options and adjust length.
*/
off = ti->ti_off << 2;
if (off < sizeof (struct tcphdr) || off > tlen) {
tcpstat.tcps_badoff++;
goto drop;
}
ti->ti_len = tlen - off;
if (off > sizeof (struct tcphdr)) {
if ((m = m_pullup(m, sizeof (struct ip) + off)) == 0) {
tcpstat.tcps_hdrops++;
goto drop;
}
ti = mtod(m, struct tcpiphdr *);
om = m_get(M_DONTWAIT);
if (om == 0)
goto drop;
om->m_off = MMINOFF;
om->m_len = off - sizeof (struct tcphdr);
{ caddr_t op = mtod(m, caddr_t) + sizeof (struct tcpiphdr);
bcopy(op, mtod(om, caddr_t), om->m_len);
m->m_len -= om->m_len;
bcopy(op+om->m_len, op, m->m_len-sizeof (struct tcpiphdr));
}
}
tiflags = ti->ti_flags;
#if vax
/*
* Convert TCP protocol specific fields to host format.
*/
ti->ti_seq = ntohl(ti->ti_seq);
ti->ti_ack = ntohl(ti->ti_ack);
ti->ti_win = ntohs(ti->ti_win);
ti->ti_urp = ntohs(ti->ti_urp);
#endif
/*
* Locate pcb for segment.
*/
inp = in_pcblookup
(&tcb, ti->ti_src, ti->ti_sport, ti->ti_dst, ti->ti_dport);
/*
* If the state is CLOSED (i.e., TCB does not exist) then
* all data in the incoming segment is discarded.
*/
if (inp == 0)
goto dropwithreset;
tp = intotcpcb(inp);
if (tp == 0)
goto dropwithreset;
so = inp->inp_socket;
if (so->so_options & SO_DEBUG) {
ostate = tp->t_state;
tcp_saveti = *ti;
}
/*
* Segment received on connection.
* Reset idle time and keep-alive timer.
*/
tp->t_idle = 0;
tp->t_timer[TCPT_KEEP] = TCPTV_KEEP;
/*
* Process options.
*/
if (om) {
tcp_dooptions(tp, om);
om = 0;
}
/*
* Calculate amount of space in receive window,
* and then do TCP input processing.
*/
tp->rcv_wnd = sbspace(&so->so_rcv);
if (tp->rcv_wnd < 0)
tp->rcv_wnd = 0;
switch (tp->t_state) {
/*
* If the state is LISTEN then ignore segment if it contains an RST.
* If the segment contains an ACK then it is bad and send a RST.
* If it does not contain a SYN then it is not interesting; drop it.
* Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
* tp->iss, and send a segment:
* <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
* Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
* Fill in remote peer address fields if not previously specified.
* Enter SYN_RECEIVED state, and process any other fields of this
* segment in this state.
*/
case TCPS_LISTEN:
if (tiflags & TH_RST)
goto drop;
if (tiflags & TH_ACK)
goto dropwithreset;
if ((tiflags & TH_SYN) == 0)
goto drop;
tcp_in.sin_addr = ti->ti_src;
tcp_in.sin_port = ti->ti_sport;
if (in_pcbconnect(inp, (struct sockaddr *)&tcp_in))
goto drop;
tp->t_template = tcp_template(tp);
if (tp->t_template == 0) {
in_pcbdisconnect(inp);
goto drop;
}
tp->iss = tcp_iss; tcp_iss += TCP_ISSINCR/2;
tp->irs = ti->ti_seq;
tcp_sendseqinit(tp);
tcp_rcvseqinit(tp);
tp->t_state = TCPS_SYN_RECEIVED;
tp->t_timer[TCPT_KEEP] = TCPTV_KEEP;
goto trimthenstep6;
/*
* If the state is SYN_SENT:
* if seg contains an ACK, but not for our SYN, drop the input.
* if seg contains a RST, then drop the connection.
* if seg does not contain SYN, then drop it.
* Otherwise this is an acceptable SYN segment
* initialize tp->rcv_nxt and tp->irs
* if seg contains ack then advance tp->snd_una
* if SYN has been acked change to ESTABLISHED else SYN_RCVD state
* arrange for segment to be acked (eventually)
* continue processing rest of data/controls, beginning with URG
*/
case TCPS_SYN_SENT:
if ((tiflags & TH_ACK) &&
/* this should be SEQ_LT; is SEQ_LEQ for BBN vax TCP only */
(SEQ_LT(ti->ti_ack, tp->iss) ||
SEQ_GT(ti->ti_ack, tp->snd_max)))
goto dropwithreset;
if (tiflags & TH_RST) {
if (tiflags & TH_ACK)
tcp_drop(tp, ECONNREFUSED);
goto drop;
}
if ((tiflags & TH_SYN) == 0)
goto drop;
tp->snd_una = ti->ti_ack;
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
tp->t_timer[TCPT_REXMT] = 0;
tp->irs = ti->ti_seq;
tcp_rcvseqinit(tp);
tp->t_flags |= TF_ACKNOW;
if (SEQ_GT(tp->snd_una, tp->iss)) {
if (so->so_options & SO_ACCEPTCONN)
so->so_state |= SS_CONNAWAITING;
soisconnected(so);
tp->t_state = TCPS_ESTABLISHED;
(void) tcp_reass(tp, (struct tcpiphdr *)0);
} else
tp->t_state = TCPS_SYN_RECEIVED;
goto trimthenstep6;
trimthenstep6:
/*
* Advance ti->ti_seq to correspond to first data byte.
* If data, trim to stay within window,
* dropping FIN if necessary.
*/
ti->ti_seq++;
if (ti->ti_len > tp->rcv_wnd) {
todrop = ti->ti_len - tp->rcv_wnd;
m_adj(m, -todrop);
ti->ti_len = tp->rcv_wnd;
ti->ti_flags &= ~TH_FIN;
}
tp->snd_wl1 = ti->ti_seq - 1;
goto step6;
}
/*
* States other than LISTEN or SYN_SENT.
* First check that at least some bytes of segment are within
* receive window.
*/
if (tp->rcv_wnd == 0) {
/*
* If window is closed can only take segments at
* window edge, and have to drop data and PUSH from
* incoming segments.
*/
if (tp->rcv_nxt != ti->ti_seq)
goto dropafterack;
if (ti->ti_len > 0) {
ti->ti_len = 0;
ti->ti_flags &= ~(TH_PUSH|TH_FIN);
}
} else {
/*
* If segment begins before rcv_nxt, drop leading
* data (and SYN); if nothing left, just ack.
*/
if (SEQ_GT(tp->rcv_nxt, ti->ti_seq)) {
todrop = tp->rcv_nxt - ti->ti_seq;
if (tiflags & TH_SYN) {
tiflags &= ~TH_SYN;
ti->ti_seq++;
if (ti->ti_urp > 1)
ti->ti_urp--;
else
tiflags &= ~TH_URG;
todrop--;
}
if (todrop > ti->ti_len)
goto dropafterack;
m_adj(m, todrop);
ti->ti_seq += todrop;
ti->ti_len -= todrop;
if (ti->ti_urp > todrop)
ti->ti_urp -= todrop;
else {
tiflags &= ~TH_URG;
/* ti->ti_flags &= ~TH_URG; */
/* ti->ti_urp = 0; */
}
/* tiflags &= ~TH_SYN; */
/* ti->ti_flags &= ~TH_SYN; */
}
/*
* If segment ends after window, drop trailing data
* (and PUSH and FIN); if nothing left, just ACK.
*/
if (SEQ_GT(ti->ti_seq+ti->ti_len, tp->rcv_nxt+tp->rcv_wnd)) {
todrop =
ti->ti_seq+ti->ti_len - (tp->rcv_nxt+tp->rcv_wnd);
if (todrop > ti->ti_len)
goto dropafterack;
m_adj(m, -todrop);
ti->ti_len -= todrop;
ti->ti_flags &= ~(TH_PUSH|TH_FIN);
}
}
/*
* If the RST bit is set examine the state:
* SYN_RECEIVED STATE:
* If passive open, return to LISTEN state.
* If active open, inform user that connection was refused.
* ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
* Inform user that connection was reset, and close tcb.
* CLOSING, LAST_ACK, TIME_WAIT STATES
* Close the tcb.
*/
if (tiflags&TH_RST) switch (tp->t_state) {
case TCPS_SYN_RECEIVED:
if (inp->inp_socket->so_options & SO_ACCEPTCONN) {
/* a miniature tcp_close, but invisible to user */
(void) m_free(dtom(tp->t_template));
(void) m_free(dtom(tp));
inp->inp_ppcb = 0;
tp = tcp_newtcpcb(inp);
tp->t_state = TCPS_LISTEN;
goto drop;
}
tcp_drop(tp, ECONNREFUSED);
goto drop;
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
tcp_drop(tp, ECONNRESET);
goto drop;
case TCPS_CLOSING:
case TCPS_LAST_ACK:
case TCPS_TIME_WAIT:
tcp_close(tp);
goto drop;
}
/*
* If a SYN is in the window, then this is an
* error and we send an RST and drop the connection.
*/
if (tiflags & TH_SYN) {
tcp_drop(tp, ECONNRESET);
goto dropwithreset;
}
/*
* If the ACK bit is off we drop the segment and return.
*/
if ((tiflags & TH_ACK) == 0)
goto drop;
/*
* Ack processing.
*/
switch (tp->t_state) {
/*
* In SYN_RECEIVED state if the ack ACKs our SYN then enter
* ESTABLISHED state and continue processing, othewise
* send an RST.
*/
case TCPS_SYN_RECEIVED:
if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
SEQ_GT(ti->ti_ack, tp->snd_max))
goto dropwithreset;
tp->snd_una++; /* SYN acked */
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
tp->t_timer[TCPT_REXMT] = 0;
if (so->so_options & SO_ACCEPTCONN)
so->so_state |= SS_CONNAWAITING;
soisconnected(so);
tp->t_state = TCPS_ESTABLISHED;
(void) tcp_reass(tp, (struct tcpiphdr *)0);
tp->snd_wl1 = ti->ti_seq - 1;
/* fall into ... */
/*
* In ESTABLISHED state: drop duplicate ACKs; ACK out of range
* ACKs. If the ack is in the range
* tp->snd_una < ti->ti_ack <= tp->snd_max
* then advance tp->snd_una to ti->ti_ack and drop
* data from the retransmission queue. If this ACK reflects
* more up to date window information we update our window information.
*/
case TCPS_ESTABLISHED:
case TCPS_FIN_WAIT_1:
case TCPS_FIN_WAIT_2:
case TCPS_CLOSE_WAIT:
case TCPS_CLOSING:
case TCPS_LAST_ACK:
case TCPS_TIME_WAIT:
#define ourfinisacked (acked > 0)
if (SEQ_LEQ(ti->ti_ack, tp->snd_una))
break;
if (SEQ_GT(ti->ti_ack, tp->snd_max))
goto dropafterack;
acked = ti->ti_ack - tp->snd_una;
if (ti->ti_ack == tp->snd_max)
tp->t_timer[TCPT_REXMT] = 0;
else {
TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX);
tp->t_rtt = 0;
tp->t_rxtshift = 0;
}
if (acked > so->so_snd.sb_cc) {
sbdrop(&so->so_snd, so->so_snd.sb_cc);
tp->snd_wnd -= so->so_snd.sb_cc;
} else {
sbdrop(&so->so_snd.sb_cc, acked);
tp->snd_wnd -= acked;
acked = 0;
}
if (so->so_snd.sb_flags & SB_WAIT)
sowwakeup(so);
tp->snd_una = ti->ti_ack;
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
/*
* If transmit timer is running and timed sequence
* number was acked, update smoothed round trip time.
*/
if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq)) {
if (tp->t_srtt == 0)
tp->t_srtt = tp->t_rtt;
else
tp->t_srtt =
tcp_alpha * tp->t_srtt +
(1 - tcp_alpha) * tp->t_rtt;
tp->t_rtt = 0;
}
switch (tp->t_state) {
/*
* In FIN_WAIT_1 STATE in addition to the processing
* for the ESTABLISHED state if our FIN is now acknowledged
* then enter FIN_WAIT_2.
*/
case TCPS_FIN_WAIT_1:
if (ourfinisacked)
tp->t_state = TCPS_FIN_WAIT_2;
break;
/*
* In CLOSING STATE in addition to the processing for
* the ESTABLISHED state if the ACK acknowledges our FIN
* then enter the TIME-WAIT state, otherwise ignore
* the segment.
*/
case TCPS_CLOSING:
if (ourfinisacked) {
tp->t_state = TCPS_TIME_WAIT;
tcp_canceltimers(tp);
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
soisdisconnected(so);
}
break;
/*
* The only thing that can arrive in LAST_ACK state
* is an acknowledgment of our FIN. If our FIN is now
* acknowledged, delete the TCB, enter the closed state
* and return.
*/
case TCPS_LAST_ACK:
if (ourfinisacked)
tcp_close(tp);
goto drop;
/*
* In TIME_WAIT state the only thing that should arrive
* is a retransmission of the remote FIN. Acknowledge
* it and restart the finack timer.
*/
case TCPS_TIME_WAIT:
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
goto dropafterack;
}
#undef ourfinisacked
}
step6:
/*
* Update window information.
*/
if (SEQ_LT(tp->snd_wl1, ti->ti_seq) || tp->snd_wl1 == ti->ti_seq &&
(SEQ_LT(tp->snd_wl2, ti->ti_ack) ||
tp->snd_wl2 == ti->ti_ack && ti->ti_win > tp->snd_wnd)) {
/*
printf("wl1 %x seq %x wl2 %x ack %x win %x wnd %x\n", tp->snd_wl1, ti->ti_seq, tp->snd_wl2, ti->ti_ack, ti->ti_win, tp->snd_wnd);
*/
tp->snd_wnd = ti->ti_win;
tp->snd_wl1 = ti->ti_seq;
tp->snd_wl2 = ti->ti_ack;
if (tp->snd_wnd > 0)
tp->t_timer[TCPT_PERSIST] = 0;
}
/*
* If an URG bit is set and in the segment and is greater than the
* current known urgent pointer, then mark the data stream.
* If the TCP is not doing out-of-band data, then indicate
* urgent to the user. This should not happen
* in CLOSE_WAIT, CLOSING, LAST-ACK or TIME_WAIT STATES since
* a FIN has been received from the remote side. In these states
* we ignore the URG.
*/
if ((tiflags & TH_URG) && TCPS_HAVERCVDFIN(tp->t_state) == 0 &&
SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) {
tp->rcv_up = ti->ti_seq + ti->ti_urp;
so->so_oobmark = so->so_rcv.sb_cc +
(tp->rcv_up - tp->rcv_nxt) - 1;
if (so->so_oobmark == 0)
so->so_state |= SS_RCVATMARK;
#ifdef TCPTRUEOOB
if ((tp->t_flags & TF_DOOOB) == 0)
#endif
{
sohasoutofband(so);
tp->t_oobflags |= TCPOOB_HAVEDATA;
}
}
/*
* Process the segment text, merging it into the TCP sequencing queue,
* and arranging for acknowledgment of receipt if necessary.
* This process logically involves adjusting tp->rcv_wnd as data
* is presented to the user (this happens in tcp_usrreq.c,
* case PRU_RCVD). If a FIN has already been received on this
* connection then we just ignore the text.
*/
if ((ti->ti_len || (tiflags&TH_FIN)) &&
TCPS_HAVERCVDFIN(tp->t_state) == 0) {
off += sizeof (struct ip); /* drop IP header */
m->m_off += off;
m->m_len -= off;
tiflags = tcp_reass(tp, ti);
if (tcpnodelack == 0)
tp->t_flags |= TF_DELACK;
else
tp->t_flags |= TF_ACKNOW;
} else {
m_freem(m);
tiflags &= ~TH_FIN;
}
/*
* If FIN is received ACK the FIN and let the user know
* that the connection is closing.
*/
if (tiflags & TH_FIN) {
if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
socantrcvmore(so);
tp->t_flags |= TF_ACKNOW;
tp->rcv_nxt++;
}
switch (tp->t_state) {
/*
* In SYN_RECEIVED and ESTABLISHED STATES
* enter the CLOSE_WAIT state.
*/
case TCPS_SYN_RECEIVED:
case TCPS_ESTABLISHED:
tp->t_state = TCPS_CLOSE_WAIT;
break;
/*
* If still in FIN_WAIT_1 STATE FIN has not been acked so
* enter the CLOSING state.
*/
case TCPS_FIN_WAIT_1:
tp->t_state = TCPS_CLOSING;
break;
/*
* In FIN_WAIT_2 state enter the TIME_WAIT state,
* starting the time-wait timer, turning off the other
* standard timers.
*/
case TCPS_FIN_WAIT_2:
tp->t_state = TCPS_TIME_WAIT;
tcp_canceltimers(tp);
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
soisdisconnected(so);
break;
/*
* In TIME_WAIT state restart the 2 MSL time_wait timer.
*/
case TCPS_TIME_WAIT:
tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
break;
}
}
if (so->so_options & SO_DEBUG)
tcp_trace(TA_INPUT, ostate, tp, &tcp_saveti, 0);
/*
* Return any desired output.
*/
tcp_output(tp);
return;
dropafterack:
/*
* Generate an ACK dropping incoming segment.
* Make ACK reflect our state.
*/
if (tiflags & TH_RST)
goto drop;
tcp_respond(tp, ti, tp->rcv_nxt, tp->snd_nxt, TH_ACK);
return;
dropwithreset:
if (om)
m_free(om);
/*
* Generate a RST, dropping incoming segment.
* Make ACK acceptable to originator of segment.
*/
if (tiflags & TH_RST)
goto drop;
if (tiflags & TH_ACK)
tcp_respond(tp, ti, (tcp_seq)0, ti->ti_ack, TH_RST);
else {
if (tiflags & TH_SYN)
ti->ti_len++;
tcp_respond(tp, ti, ti->ti_seq+ti->ti_len, (tcp_seq)0, TH_RST|TH_ACK);
}
return;
drop:
/*
* Drop space held by incoming segment and return.
*/
m_freem(m);
return;
}
tcp_dooptions(tp, om)
struct tcpcb *tp;
struct mbuf *om;
{
register u_char *cp;
int opt, optlen, cnt;
cp = mtod(om, u_char *);
cnt = om->m_len;
for (; cnt > 0; cnt -= optlen, cp += optlen) {
opt = cp[0];
if (opt == TCPOPT_EOL)
break;
if (opt == TCPOPT_NOP)
optlen = 1;
else
optlen = cp[1];
switch (opt) {
default:
break;
case TCPOPT_MAXSEG:
if (optlen != 4)
continue;
tp->t_maxseg = *(u_short *)(cp + 2);
#if vax
tp->t_maxseg = ntohs(tp->t_maxseg);
#endif
break;
#ifdef TCPTRUEOOB
case TCPOPT_WILLOOB:
tp->t_flags |= TF_DOOOB;
printf("tp %x dooob\n", tp);
break;
case TCPOPT_OOBDATA: {
int seq;
if (optlen != 4)
continue;
seq = cp[2];
if (seq < tp->t_iobseq)
seq += 256;
printf("oobdata cp[2] %d iobseq %d seq %d\n", cp[2], tp->t_iobseq, seq);
if (seq - tp->t_iobseq > 128) {
printf("bad seq\n");
tp->t_oobflags |= TCPOOB_OWEACK;
break;
}
tp->t_iobseq = cp[2];
tp->t_iobc = cp[3];
printf("take oob data %x input iobseq now %x\n", tp->t_iobc, tp->t_iobseq);
sohasoutofband(tp->t_inpcb->inp_socket);
break;
}
case TCPOPT_OOBACK: {
int seq;
if (optlen != 4)
continue;
if (tp->t_oobseq != cp[2]) {
printf("wrong ack\n");
break;
}
printf("take oob ack %x and cancel rexmt\n", cp[2]);
tp->t_oobflags &= ~TCPOOB_NEEDACK;
tp->t_timer[TCPT_OOBREXMT] = 0;
break;
}
#endif TCPTRUEOOB
}
}
m_free(om);
}
/*
* Insert segment ti into reassembly queue of tcp with
* control block tp. Return TH_FIN if reassembly now includes
* a segment with FIN.
*/
tcp_reass(tp, ti)
register struct tcpcb *tp;
register struct tcpiphdr *ti;
{
register struct tcpiphdr *q;
struct socket *so = tp->t_inpcb->inp_socket;
struct mbuf *m;
int flags;
COUNT(TCP_REASS);
/*
* Call with ti==0 after become established to
* force pre-ESTABLISHED data up to user socket.
*/
if (ti == 0)
goto present;
/*
* Find a segment which begins after this one does.
*/
for (q = tp->seg_next; q != (struct tcpiphdr *)tp;
q = (struct tcpiphdr *)q->ti_next)
if (SEQ_GT(q->ti_seq, ti->ti_seq))
break;
/*
* If there is a preceding segment, it may provide some of
* our data already. If so, drop the data from the incoming
* segment. If it provides all of our data, drop us.
*/
if ((struct tcpiphdr *)q->ti_prev != (struct tcpiphdr *)tp) {
register int i;
q = (struct tcpiphdr *)(q->ti_prev);
/* conversion to int (in i) handles seq wraparound */
i = q->ti_seq + q->ti_len - ti->ti_seq;
if (i > 0) {
if (i >= ti->ti_len)
goto drop;
m_adj(dtom(tp), i);
ti->ti_len -= i;
ti->ti_seq += i;
}
q = (struct tcpiphdr *)(q->ti_next);
}
/*
* While we overlap succeeding segments trim them or,
* if they are completely covered, dequeue them.
*/
while (q != (struct tcpiphdr *)tp &&
SEQ_GT(ti->ti_seq + ti->ti_len, q->ti_seq)) {
register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq;
if (i < q->ti_len) {
q->ti_len -= i;
m_adj(dtom(q), i);
break;
}
q = (struct tcpiphdr *)q->ti_next;
m_freem(dtom(q->ti_prev));
remque(q->ti_prev);
}
/*
* Stick new segment in its place.
*/
insque(ti, q->ti_prev);
present:
/*
* Present data to user, advancing rcv_nxt through
* completed sequence space.
*/
if (TCPS_HAVERCVDSYN(tp->t_state) == 0)
return (0);
ti = tp->seg_next;
if (ti == (struct tcpiphdr *)tp || ti->ti_seq != tp->rcv_nxt)
return (0);
if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len)
return (0);
do {
tp->rcv_nxt += ti->ti_len;
flags = ti->ti_flags & TH_FIN;
remque(ti);
m = dtom(ti);
ti = (struct tcpiphdr *)ti->ti_next;
if (so->so_state & SS_CANTRCVMORE)
(void) m_freem(m);
else
sbappend(&so->so_rcv, m);
} while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt);
sorwakeup(so);
return (flags);
drop:
m_freem(dtom(ti));
return (0);
}
Continuous source code history from original PDP-7 UNIX to FreeBSD 2, the first fully unencumbered FreeBSD release.