hd_input.c

早期freebsd实现

	/* 
	 *  This section tests the IFRAME for proper sequence. That is, it's
	 *  sequence number N(S) MUST be equal to V(S).
	 */

	if (ns != hdp->hd_vr) {
		hdp->hd_invalid_ns++;
		if (pf || (hdp->hd_condition & REJ_CONDITION) == 0) {
			hdp->hd_condition |= REJ_CONDITION;
			/*
			 * Flush the transmit queue. This is ugly but we
			 * have no choice.  A reject response must be
			 * immediately sent to the DCE.  Failure to do so
			 * may result in another out of sequence iframe
			 * arriving (and thus sending another reject)
			 * before the first reject is transmitted. This
			 * will cause the DCE to receive two or more
			 * rejects back to back, which must never happen.
			 */
			hd_flush (hdp->hd_ifp);
			hd_writeinternal (hdp, REJ, pf);
		}
		return (queued);
	}
	hdp->hd_condition &= ~REJ_CONDITION;

	/* 
	 *  This section finally tests the IFRAME's sequence number against
	 *  the window size (K)  and the sequence number of the  last frame
	 *  we have acknowledged.  If the IFRAME is completely correct then 
	 *  it is queued for the packet level.
	 */

	if (ns != (hdp -> hd_lasttxnr + hdp -> hd_xcp -> xc_lwsize) % MODULUS) {
		hdp -> hd_vr = (hdp -> hd_vr + 1) % MODULUS;
		if (pf == 1) {
			/* Must generate a RR or RNR with final bit on. */
			hd_writeinternal (hdp, RR, POLLON);
		} else
			/*    
			 *  Hopefully we can piggyback the RR, if not we will generate
			 *  a RR when T3 timer expires.
			 */
			if (hdp -> hd_rrtimer == 0)
				hdp->hd_rrtimer = hd_t3;

		/* Forward iframe to packet level of X.25. */
		fbuf -> m_data += HDHEADERLN;
		fbuf -> m_len -= HDHEADERLN;
		fbuf -> m_pkthdr.len -= HDHEADERLN;
		fbuf -> m_pkthdr.rcvif = (struct ifnet *)hdp -> hd_pkp;
#ifdef BSD4_3
		fbuf->m_act = 0;	/* probably not necessary */
#else
		{
			register struct mbuf *m;
			
			for (m = fbuf; m -> m_next; m = m -> m_next)
				m -> m_act = (struct mbuf *) 0;
			m -> m_act = (struct mbuf *) 1;
		}
#endif
		pk_input (fbuf);
		queued = TRUE;
		hd_start (hdp);
	} else {
		/* 
		 *  Here if the remote station has transmitted more iframes then
		 *  the number which have been acknowledged plus K. 
		 */
		hdp->hd_invalid_ns++;
		frame_reject (hdp, W, frame);
	}
	return (queued);
}

/* 
 *  This routine is used to determine if a value (the middle parameter)
 *  is between two other values. The low value is  the first  parameter
 *  the high value is the last parameter. The routine checks the middle
 *  value to see if it is within the range of the first and last values.
 *  The reason we need this routine is the values are modulo some  base
 *  hence a simple test for greater or less than is not sufficient.
 */

bool
range_check (rear, value, front)
int     rear,
        value,
        front;
{
	register bool result = FALSE;

	if (front > rear)
		result = (rear <= value) && (value <= front);
	else
		result = (rear <= value) || (value <= front);

	return (result);
}

/* 
 *  This routine handles all the frame reject conditions which can
 *  arise as a result  of secondary  processing.  The frame reject
 *  condition Y (frame length error) are handled elsewhere.
 */

static
frame_reject (hdp, rejectcode, frame)
struct hdcb *hdp;
struct Hdlc_iframe *frame;
{
	register struct Frmr_frame *frmr = &hd_frmr;

	frmr -> frmr_control = ((struct Hdlc_frame *) frame) -> control;

	frmr -> frmr_ns = frame -> ns;
	frmr -> frmr_f1_0 = 0;
	frmr -> frmr_nr = frame -> nr;
	frmr -> frmr_f2_0 = 0;

	frmr -> frmr_0000 = 0;
	frmr -> frmr_w = frmr -> frmr_x = frmr -> frmr_y =
		frmr -> frmr_z = 0;
	switch (rejectcode) {
	case Z: 
		frmr -> frmr_z = 1;/* invalid N(R). */
		break;

	case Y: 
		frmr -> frmr_y = 1;/* iframe length error. */
		break;

	case X: 
		frmr -> frmr_x = 1;/* invalid information field. */
		frmr -> frmr_w = 1;
		break;

	case W: 
		frmr -> frmr_w = 1;/* invalid N(S). */
	}

	hd_writeinternal (hdp, FRMR, POLLOFF);

	hdp->hd_state = WAIT_SABM;
	SET_TIMER (hdp);
}

/* 
 *  This procedure is invoked when ever we receive a supervisor
 *  frame such as RR, RNR and REJ. All processing for these
 *  frames is done here.
 */

process_sframe (hdp, frame, frametype)
register struct hdcb *hdp;
register struct Hdlc_sframe *frame;
int frametype;
{
	register int nr = frame -> nr, pf = frame -> pf, pollbit = 0;

	if (valid_nr (hdp, nr, pf) == TRUE) {
		switch (frametype) {
		case RR: 
			hdp->hd_condition &= ~REMOTE_RNR_CONDITION;
			break;

		case RNR: 
			hdp->hd_condition |= REMOTE_RNR_CONDITION;
			hdp->hd_retxcnt = 0;
			break;

		case REJ: 
			hdp->hd_condition &= ~REMOTE_RNR_CONDITION;
			rej_routine (hdp, nr);
		}

		if (pf == 1) {
			hdp->hd_retxcnt = 0;
			hdp->hd_condition &= ~TIMER_RECOVERY_CONDITION;

			if (frametype == RR && hdp->hd_lastrxnr == hdp->hd_vs
				&& hdp->hd_timer == 0 && hdp->hd_txq.head == 0)
				hd_writeinternal(hdp, RR, pf);
			else
			/* If any iframes have been queued because of the
			   timer condition, transmit then now. */
			if (hdp->hd_condition & REMOTE_RNR_CONDITION) {
				/* Remote is busy or timer condition, so only
				   send one. */
				if (hdp->hd_vs != hdp->hd_retxqi)
					hd_send_iframe (hdp, hdp->hd_retxq[hdp->hd_vs], pollbit);
			}
			else	/* Flush the retransmit list first. */
				while (hdp->hd_vs != hdp->hd_retxqi)
					hd_send_iframe (hdp, hdp->hd_retxq[hdp->hd_vs], POLLOFF);
		}

		hd_start (hdp);
	} else
		frame_reject (hdp, Z, (struct Hdlc_iframe *)frame);	/* Invalid N(R). */
}

/* 
 *  This routine tests the validity of the N(R) which we have received.
 *  If it is ok,  then all the  iframes which it acknowledges  (if any)
 *  will be freed.
 */

bool
valid_nr (hdp, nr, finalbit)
register struct hdcb *hdp;
register int finalbit;
{
	/* Make sure it really does acknowledge something. */
	if (hdp->hd_lastrxnr == nr)
		return (TRUE);

	/* 
	 *  This section validates the frame's  N(R) value.  It's N(R) value
	 *  must be  in syncronization  with  our V(S)  value and  our "last
	 *  received nr" variable. If it is correct then we are able to send
	 *  more IFRAME's, else frame reject condition is entered.
	 */

	if (range_check (hdp->hd_lastrxnr, nr, hdp->hd_vs) == FALSE) {
		if ((hdp->hd_condition & TIMER_RECOVERY_CONDITION) &&
				range_check (hdp->hd_vs, nr, hdp->hd_xx) == TRUE)
			hdp->hd_vs = nr;

		else {
			hdp->hd_invalid_nr++;
			return (FALSE);
		}
	}

	/* 
	 *  If we get to here, we do have a valid frame  but it might be out
	 *  of sequence.  However, we should  still accept the receive state
	 *  number N(R) since it has already passed our previous test and it
	 *  does acknowledge frames which we are sending.
	 */

	KILL_TIMER (hdp);
	free_iframes (hdp, &nr, finalbit);/* Free all acknowledged iframes */
	if (nr != hdp->hd_vs)
		SET_TIMER (hdp);

	return (TRUE);
}

/* 
 *  This routine determines how many iframes need to be retransmitted.
 *  It then resets the Send State Variable V(S) to accomplish this.
 */

static
rej_routine (hdp, rejnr)
register struct hdcb *hdp;
register int rejnr;
{
	register int anchor;

	/*
	 * Flush the output queue.  Any iframes queued for
	 * transmission will be out of sequence.
	 */

	hd_flush (hdp->hd_ifp);

	/* 
	 *  Determine how many frames should be re-transmitted. In the case 
	 *  of a normal REJ this  should be 1 to K.  In the case of a timer
	 *  recovery REJ (ie. a REJ with the Final Bit on) this could be 0. 
	 */

	anchor = hdp->hd_vs;
	if (hdp->hd_condition & TIMER_RECOVERY_CONDITION)
		anchor = hdp->hd_xx;

	anchor = (anchor - rejnr + 8) % MODULUS;

	if (anchor > 0) {

		/* There is at least one iframe to retransmit. */
		KILL_TIMER (hdp);
		hdp->hd_vs = rejnr;

		while (hdp->hd_vs != hdp->hd_retxqi)
			hd_send_iframe (hdp, hdp->hd_retxq[hdp->hd_vs], POLLOFF);

	}
	hd_start (hdp);
}

/* 
 *  This routine frees iframes from the retransmit queue. It is called
 *  when a previously written iframe is acknowledged.
 */

static
free_iframes (hdp, nr, finalbit)
register struct hdcb *hdp;
int *nr;
register int finalbit;

{
	register int    i, k;

	/* 
	 *  We  need to do the  following  because  of a  funny quirk  in  the 
	 *  protocol.  This case  occures  when  in Timer  recovery  condition 
	 *  we get  a  N(R)  which  acknowledges all  the outstanding  iframes
	 *  but with  the Final Bit off. In this case we need to save the last
	 *  iframe for possible retransmission even though it has already been 
	 *  acknowledged!
	 */

	if ((hdp->hd_condition & TIMER_RECOVERY_CONDITION) && *nr == hdp->hd_xx && finalbit == 0) {
		*nr = (*nr - 1 + 8) % MODULUS;
/*		printf ("QUIRK\n"); */
	}

	k = (*nr - hdp->hd_lastrxnr + 8) % MODULUS;

	/* Loop here freeing all acknowledged iframes. */
	for (i = 0; i < k; ++i) {
		m_freem (hdp->hd_retxq[hdp->hd_lastrxnr]);
		hdp->hd_retxq[hdp->hd_lastrxnr] = 0;
		hdp->hd_lastrxnr = (hdp->hd_lastrxnr + 1) % MODULUS;
	}

}