lapb.c

ppp协议实现源代码

	    buffer_release(buffer);
	else {
	    ls->rxq[woffs].buffer = buffer;
	    ls->rxq[woffs].length = count;
	    ls->rhead = nr;
	    if (ls->rcvnonempty != NULL &&
		woffs == ls->rtail)
		(*ls->rcvnonempty)(ls->userstate);
	}
	return;
    } else {
	/* Error; bad address. */
	buffer_release(buffer);
	return;
    }

    /* Next, extract the command/response code and sequence. */
    DBG(("process input on %p\n",ls));
    ns = nr = 0;	/* quiet down compiler */
    crcode = buffer[1];
    ilen = 2;
    if (IS_U_TYPE(crcode)) {
	pfbit = (crcode & 0x10)>>4;
    } else switch (ls->mode) {
    case MODE_BASIC:
	ns = (crcode & 0x0E)>>1;
	pfbit = (crcode & 0x10)>>4;
	nr = (crcode & 0xE0)>>5;
	break;
    case MODE_EXTENDED:
	if (count < 3) {
	    errbits = 3;
	    goto frmr_handler;
	}
	ns = (crcode & 0xFE)>>1;
	pfbit = buffer[2] & 1;
	nr = (buffer[2] & 0xFE)>>1;
	ilen = 3;
	break;
    case MODE_SUPER:
	if (count < 5) {
	    errbits = 3;
	    goto frmr_handler;
	}
	ns = ((crcode & 0xFE)>>1) | (buffer[2]<<7);
	pfbit = buffer[3] & 1;
	nr = ((buffer[3] & 0xFE)>>1) | (buffer[4]<<7);
	ilen = 5;
	break;
    default:
	/* This can't happen. */
	buffer_release(buffer);
	return;
    }
    if (IS_I_TYPE(crcode))
	crcode &= ITYPE_MASK;
    else if (IS_S_TYPE(crcode))
	crcode &= STYPE_MASK;
     else
	crcode &= UTYPE_MASK;

    /* Switch out on type of received frame. */
    DBG(("code %d, nr %d, ns %d\n",crcode,nr,ns));
    errbits = 0;
    switch (crcode) {
    case CRI_I:
	DBG(("received I frame\n"));
	/* Still setting up; silent discard. */
	if (ls->phase == phInitial)
	    break;
	if (!iscmd) {
	    errbits = 1;
	    break;
	}
	handle_nr(ls,nr);
	/*
	 * Note:  LAP-B assumes that packets cannot be reordered on the
	 * link.  For that reason, it is safe to assume that a sequence
	 * number error implies a lost packet.
	 */
	if (INWINDOW(ns,ls->vr,ls->rxqsize,ls->rxkval)) {
	    DBG(("inside window; vr is %d\n",ls->vr));

	    /* Get non-negative window offset. */
	    woffs = (ls->rtail+ns-ls->vr+ls->rxkval+1) % (ls->rxkval+1);

	    if (ls->rxq[woffs].buffer != NULL) {
		/* Discard duplicate buffer. */
		DBG(("duplicate buffer; discarding.\n"));
		break;
	    }
	    ls->rxq[woffs].buffer = buffer+ilen;
	    ls->rxq[woffs].length = count-ilen;

	    /* Check for sequence number error. */
	    if (woffs != ls->rhead) {
		DBG(("queue offset %d not equal to head %d; need reject.\n",
		     woffs,ls->rhead));
		need_transmit(ls,STF_NEEDREJ);
	    }

	    if (++woffs > ls->rxkval)
		woffs = 0;

	    if (ls->rhead >= ls->rtail) {
		if (woffs > ls->rhead || woffs < ls->rtail)
		    ls->rhead = woffs;
	    } else {
		if (woffs > ls->rhead && woffs < ls->rtail)
		    ls->rhead = woffs;
	    }

	    /* While in sequence, send data to application */
	    if (ls->rcvnonempty != NULL &&
		ls->rxq[ls->rtail].buffer != NULL)
		(*ls->rcvnonempty)(ls->userstate);

	    /* Don't free queued packets. */
	    buffer = NULL;
	} else {
	    DBG(("outside window; vr is %d\n",ls->vr));
	}
	if (pfbit) {
	    need_transmit(ls,STF_NEEDSTATUS | STF_PFBIT);
	}
	break;

    case CRS_RR:
    case CRS_RNR:
	if (crcode == CRS_RR)
	    DBG(("received RR frame\n"));
	else
	    DBG(("received RNR frame\n"));
	/* Still setting up; silent discard. */
	if (ls->phase == phInitial)
	    break;
	if (count != ilen) {
	    errbits = 3;
	    break;
	}
	if (crcode == CRS_RR)
	    ls->flags |= LBF_PEERREADY;
	else
	    ls->flags &= ~LBF_PEERREADY;
	handle_nr(ls,nr);
	if (iscmd && pfbit) {
	    need_transmit(ls,STF_NEEDSTATUS | STF_PFBIT);
	}
	break;

    case CRS_REJ:
	DBG(("received REJ frame\n"));
	/* Still setting up; silent discard. */
	if (ls->phase == phInitial)
	    break;
	if (ls->mode == MODE_EXTENDED || (ls->flags & LBF_RXSREJ)) {
	    errbits = 1;
	    break;
	}
	if (count != ilen) {
	    errbits = 3;
	    break;
	}
	ls->flags |= LBF_PEERREADY;
	handle_nr(ls,nr);
	if (iscmd && pfbit)
	    need_transmit(ls,STF_NEEDSTATUS | STF_PFBIT);
	/* Drop back to sequence N(R) and try again on all. */
	DBG(("reject marking retransmit %d to %d\n",nr,ls->vs));
	mark_retransmit(ls,nr,ls->vs);
	break;

    case CRS_SREJ:
	DBG(("received SREJ frame\n"));
	/* Still setting up; silent discard. */
	if (ls->phase == phInitial)
	    break;
	if (ls->mode == MODE_BASIC || iscmd || !(ls->flags & LBF_RXSREJ)) {
	    errbits = 1;
	    break;
	}
	if (pfbit)
	    handle_nr(ls,nr);
	/* Drop back to sequence N(R) and try again on some. */
	mark_retransmit(ls,nr,nr);
	bp = buffer+ilen;
	count -= ilen;
	while (count > 0) {
	    nr = *bp++;
	    count--;
	    if (ls->mode == MODE_SUPER) {
		if (--count < 0)
		    break;
		nr |= *bp++ << 8;
	    }
	    if ((nr & 1) && count > 0) {
		woffs = *bp++;
		if (ls->mode == MODE_SUPER) {
		    if (--count < 0)	/* XXX */
			break;
		    woffs |= *bp++ << 8;
		}
		mark_retransmit(ls,nr>>1,woffs>>1);
	    } else {
		nr >>= 1;
		mark_retransmit(ls,nr,nr);
	    }
	}
	break;

    case CRU_SABM:
	DBG(("received SABM frame\n"));
	if (ls->flags & LBF_PERMISSIVE)
	    ls->mode = MODE_BASIC;
	if (ls->mode != MODE_BASIC || !iscmd) {
	    errbits = 1;
	    break;
	}
	if (count != 2) {
	    errbits = 3;
	    break;
	}
    enter_data_phase:
	DBG(("received entering data phase\n"));
	if (ls->statflag & STF_T1RUNNING) {
	    ls->t2ctr = 0;
	    ls->statflag &= ~STF_T1RUNNING;
	    untimeout(t1handler,(void *)ls);
	}
	ls->flags |= LBF_PEERREADY;
	ls->vr = ls->vs = 0;
	free_all_packets(ls);
	ls->phase = phData;
	ls->statflag &= ~STF_UAFBIT;
	need_transmit(ls,STF_NEEDUA | (pfbit ? STF_UAFBIT : 0));
	if (ls->xmthasroom != NULL)
	    (*ls->xmthasroom)(ls->userstate);
	break;

    case CRU_SABME:
	DBG(("received SABME frame\n"));
	if (ls->flags & LBF_PERMISSIVE)
	    ls->mode = MODE_EXTENDED;
	if (ls->mode != MODE_EXTENDED || !iscmd) {
	    errbits = 1;
	    break;
	}
	if (count != 2) {
	    errbits = 3;
	    break;
	}
	goto enter_data_phase;

    case CRU_SM:
	DBG(("received SM frame\n"));
	if (ls->flags & LBF_PERMISSIVE)
	    ls->mode = MODE_SUPER;
	ilen = (count > 6) ? 6 : count;	/* FRMR generation */
	if (ls->mode != MODE_SUPER || !iscmd) {
	    errbits = 1;
	    break;
	}
	/* Should have one address byte and 5 Set Mode bytes */
	if (count != 6 || buffer[2] != 0 || buffer[3] != 0x40 ||
	    buffer[4] != 0x80 || buffer[5] != 0x20) {
	    errbits = 3;
	    break;
	}
	goto enter_data_phase;

    case CRU_DISC:
	DBG(("received DISC frame\n"));
	if (!iscmd) {
	    errbits = 1;
	    break;
	}
	if (count != 2) {
	    errbits = 3;
	    break;
	}
	ls->phase = phDisconnected;
	ls->statflag &= ~STF_UAFBIT;
	need_transmit(ls,STF_NEEDUA | (pfbit ? STF_UAFBIT : 0));
	break;

    case CRU_DM:
	DBG(("received DM frame\n"));
	if (iscmd) {
	    errbits = 1;
	    break;
	}
	if (count != 2) {
	    errbits = 3;
	    break;
	}
	if (ls->phase != phInitial)
	    ls->phase = phDisconnected;
	break;

    case CRU_UA:
	DBG(("received UA frame\n"));
	if (iscmd) {
	    errbits = 1;
	    break;
	}
	if (count != 2) {
	    errbits = 3;
	    break;
	}
	if (ls->phase == phDisconnecting)
	    ls->phase = phDisconnected;
	ls->flags |= LBF_PEERREADY;
	break;

    case CRU_FRMR:
	DBG(("received FRMR frame\n"));
	/* Still setting up; silent discard. */
	if (ls->phase == phInitial)
	    break;
	if (iscmd) {
	    /* Rejecting a rejection seems like a bad idea. */
	    /* errbits = 1; */
	    break;
	}
	break;

    default:
	DBG(("received bad frame\n"));
	/* Error; bad code. */
	errbits = 1;
	break;
    }

frmr_handler:
    if (errbits && !(ls->txpend.qflags & QF_SENDING)) {
	/*
	 * We don't assume here that the input buffer is big
	 * enough to hold this error frame.  It probably is
	 * (and certainly is with the example AHDLC code),
	 * but better safe than sorry.
	 */
	DBG(("Generating FRMR in response\n"));
	bp = (octet *)buffer_fetch(11);
	if (bp != NULL) {
	    bp[0] = ls->cmdaddr ^ ls->crabit;
	    bp[1] = CRU_FRMR;
	    bp[3] = bp[4] = bp[5] = 0;
	    memcpy(bp+2,buffer+1,ilen-1);
	    switch (ls->mode) {
	    case MODE_BASIC:
		bp[3] = (ls->vs<<1) | (iscmd?0:0x10) | (ls->vr<<5);
		bp[4] = errbits;
		ilen = 5;
		break;
	    case MODE_EXTENDED:
		bp[4] = ls->vs<<1;
		bp[5] = (iscmd?0:1) | (ls->vr<<1);
		bp[6] = errbits;
		ilen = 7;
		break;
	    case MODE_SUPER:
		bp[6] = ls->vs<<1;
		bp[7] = ls->vs>>7;
		bp[8] = (iscmd?0:1) | (ls->vr<<1);
		bp[9] = ls->vr>>1;
		bp[10] = errbits;
		ilen = 11;
		break;
	    }
	    ls->txpend.qflags = QF_SEND;
	    ls->txpend.length = ilen;
	    if (ls->txpend.buffer != NULL)
		buffer_release(ls->txpend.buffer);
	    ls->txpend.buffer = bp;
	}
    }
    if (buffer != NULL)
	buffer_release(buffer);
}

/*
 * This creates a SABM, SABME, or SM message as appropriate for the
 * configured mode.
 */
static octet *
make_set_mode(struct lapb_state *ls, int *lengthp)
{
    octet *bp,ctl;
    int len;

    len = 0;
    bp = (octet *)buffer_fetch(6);
    if (bp != NULL) {
	bp[0] = ls->cmdaddr;
	/* 2.4.4.1 -- DTE sets P bit in set-mode command */
	ctl = (ls->flags & LBF_ISDTE) ? 0x10 : 0;
	switch (ls->mode) {
	case MODE_BASIC:
	    bp[1] = CRU_SABM | ctl;
	    len = 2;
	    break;
	case MODE_EXTENDED:
	    bp[1] = CRU_SABME | ctl;
	    len = 2;
	    break;
	case MODE_SUPER:
	    bp[1] = CRU_SM | ctl;
	    bp[2] = 0;
	    bp[3] = 0x40;
	    bp[4] = 0x80;
	    bp[5] = 0x20;
	    len = 6;
	    break;
	default:
	    /* This can't happen. */
	    buffer_release(bp);
	    bp = NULL;
	}
    }
    *lengthp = len;
    return bp;
}

/*
 * This creates a Receive Ready or Receive Not Ready message as
 * appropriate for the current state and mode.
 */
static octet *
make_status(struct lapb_state *ls, int *lengthp)
{
    octet *bp,ctl;
    int len;

    if ((bp = (octet *)buffer_fetch(5)) == NULL)
	return NULL;
    bp[0] = ls->cmdaddr ^ (0 ? 0 : ls->crabit);
    ctl = ALLSET(ls->flags,LBF_IMREADY|LBF_USERREADY) ? CRS_RR : CRS_RNR;
    switch (ls->mode) {
    case MODE_BASIC:
	bp[1] = ctl | (ls->statflag & STF_PFBIT ? 0x10 : 0) | (ls->vr<<5);
	len = 2;
	break;
    case MODE_EXTENDED:
	bp[1] = ctl;
	bp[2] = (ls->statflag & STF_PFBIT ? 1 : 0) | (ls->vr<<1);
	len = 3;
	break;
    case MODE_SUPER:
	bp[1] = ctl;
	bp[2] = 0;
	bp[3] = (ls->statflag & STF_PFBIT ? 1 : 0) | (ls->vr<<1);
	bp[4] = ls->vr>>7;
	len = 5;
	break;
    default:
	/* This can't happen. */
	buffer_release(bp);
	return NULL;
    }
    *lengthp = len;
    return bp;
}

/*
 * Generate an unnumbered acknowledgement response.  This is used as a
 * reply to a received SABM/SABME/SM frame.
 */
static octet *
make_ua(struct lapb_state *ls, int *lengthp)
{
    octet *bp;

    if ((bp = (octet *)buffer_fetch(2)) == NULL)
	return NULL;
    bp[0] = ls->cmdaddr ^ ls->crabit;
    bp[1] = CRU_UA | ((ls->statflag & STF_UAFBIT) ? 0x10 : 0);
    *lengthp = 2;
    return bp;
}

/*
 * Generate a disconnect mode response.
 */
static octet *
make_dm(struct lapb_state *ls, int *lengthp)
{
    octet *bp;

    if ((bp = (octet *)buffer_fetch(2)) == NULL)
	return NULL;
    bp[0] = ls->cmdaddr ^ ls->crabit;
    bp[1] = CRU_DM;
    *lengthp = 2;
    return bp;
}

/*
 * Generate a disconnect command.
 */
static octet *
make_disc(struct lapb_state *ls, int *lengthp)
{
    octet *bp;

    if ((bp = (octet *)buffer_fetch(2)) == NULL)
	return NULL;
    bp[0] = ls->cmdaddr;
    bp[1] = CRU_DISC | 0x10;
    *lengthp = 2;
    return bp;
}

/*
 * Make a reject or selective reject command frame as appropriate.
 */