tcp_reass.c

一款类linux的操作系统源码

/*
 *  Roadrunner/pk
 *    Copyright (C) 1989-2002  Cornfed Systems, Inc.
 *
 *  The Roadrunner/pk operating system is free software; you can
 *  redistribute and/or modify it under the terms of the GNU General
 *  Public License, version 2, as published by the Free Software
 *  Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public
 *  License along with this program; if not, write to the Free
 *  Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 *  MA 02111-1307 USA
 *
 *  More information about the Roadrunner/pk operating system of
 *  which this file is a part is available on the World-Wide Web
 *  at: http://www.cornfed.com.
 *
 */

#include <net/ether.h>
#include <net/tcp.h>
#if _DEBUG_TCP
#include <stdio.h>
#endif
#include <stdlib.h>
#include <sys/intr.h>

int
tcp_reass(buf_t b, tcb_t tcb)
{
    buf_t p, q;
    etherhdr_t eh, qeh;
    iphdr_t ih, qih;
    tcphdr_t th, qth;
    int len, segcnt = 0;

    eh = (etherhdr_t) bstart(b);
    ih = (iphdr_t) eh->data;
    th = (tcphdr_t) (eh->data + IP_HLEN(ih));
    len = ih->len - IP_HLEN(ih) - TCP_HLEN(th);

    disable;

    /*
     * Find reassembly queue position for new segment.  q points to the
     * segment in the queue that should succeed the new segment or NULL
     * if the new segment belongs at the end of the queue.
     */
    for (q = tcb->reass.h; q != NULL; q = q->next) {
	qeh = (etherhdr_t) bstart(q);
	qih = (iphdr_t) qeh->data;
	qth = (tcphdr_t) (qeh->data + IP_HLEN(qih));
	if (SEQ_GT(qth->seq, th->seq))
	    break;
    }
    /*
     * p points to the segment that should precede the new segment or
     * NULL if the new segment belongs at the front of the queue.
     */
    if (q == NULL)
	p = tcb->reass.t;
    else
	p = q->prev;

    /* Trim data from preceding segment if it overlaps the new segment */
    if (p != NULL) {
	etherhdr_t peh = (etherhdr_t) bstart(p);
	iphdr_t pih = (iphdr_t) peh->data;
	tcphdr_t pth = (tcphdr_t) (peh->data + IP_HLEN(pih));
	int n, plen;

	/* Conversion to integer type in n handles sequence wraparound */
	plen = pih->len - IP_HLEN(pih) - TCP_HLEN(pth);
	n = pth->seq + plen - th->seq;
	if (n > 0) {
	    if (n >= len) {
#if _DEBUG_TCP
		kprintf("tcp_reass: preceding segment covers new segment\n");
#endif
		enable;
		return (-1);
	    }
	    pih->len -= n;
	}
    }
    /* Trim data from new segment if it overlaps the succeeding segment */
    if (q != NULL) {
	int n;

	/* Conversion to integer type in n handles sequence wraparound */
	n = th->seq + len - qth->seq;
	if (n > 0)
	    ih->len -= n;
    }
    /* Insert new segment in queue */
    b->prev = p;
    b->next = q;

    if (p == NULL)
	tcb->reass.h = b;
    else
	p->next = b;

    if (q == NULL)
	tcb->reass.t = b;
    else
	q->prev = b;

#if _DEBUG_TCP
    tcp_dump_reass("tcp_reass: new segment inserted", tcb->reass.h);
#endif
    /*
     * Present data to user advancing tcb->rcv_nxt through the completed
     * sequence space
     */
    if (TCPS_HAVERCVDSYN(tcb->state)) {
	int qlen;

	for (q = tcb->reass.h; q != NULL; q = tcb->reass.h) {
	    qeh = (etherhdr_t) bstart(q);
	    qih = (iphdr_t) qeh->data;
	    qth = (tcphdr_t) (qeh->data + IP_HLEN(qih));
	    qlen = qih->len - IP_HLEN(qih) - TCP_HLEN(qth);
	    if (qth->seq != tcb->rcv_nxt)
		break;

	    /* Remove segment from head of reassembly queue */
	    tcb->reass.h = q->next;
	    if (q->next == NULL)
		tcb->reass.t = NULL;
	    else {
		q->next->prev = NULL;
		q->next = NULL;
	    }
	    /* Place segment in socket receive queue */
	    bstart(q) = (char *) qth + TCP_HLEN(qth);
	    blen(q) = qlen;
	    tcb->rcv_nxt += qlen;
	    tcb->socket->rcv_cc += qlen;
	    benq(q, &(tcb->socket->rcvq));
	    segcnt++;
	}
	if (segcnt > 0) {
	    proc_t proc;

	    /* Restart waiting receivers */
	    for (;;) {
		proc = remfirstq(&(tcb->socket->rcvr));
		if (proc == NULL)
		    break;
		proc->state = PS_READY;
		insq(proc, &ready);
	    }
	}
    }
#if _DEBUG_TCP
    tcp_dump_reass("tcp_reass: after segments presented to user",
		   tcb->reass.h);
#endif
    enable;
    return segcnt;
}