re-queue delay line in ip_dummynet.c

[Liu, Huan (Huan)]

I'd like to give a pipe random delay time and re-queue packets in delay-line
according to their output_time, However I always get fatal error when
packets go through pipe. I guess the code get match condition when re-queue
the delay line while other process may be sending a packet and delete it
from delay line at same time.

Here is what I modified in ip_dummynet.c

float mydelay;   /*cast integer random() to float*/
/* added for re-queue delay chain in move_pkt*/
struct dn_pkt *mypkt, *prepkt;

static void
move_pkt(struct dn_pkt *pkt, struct dn_flow_queue *q,
        struct dn_pipe *p, int len)
{
    q->head = DN_NEXT(pkt) ;
    q->len-- ;
    q->len_bytes -= len ;

/* example, delay 9010ms, will delay random interval range 0~10ms*/
    if(p->delay >= 9000) {
        mydelay = random();
        pkt->output_time = curr_time +
(int)((mydelay/0x7fffffff)*(p->delay-9000));
    }
    else
        pkt->output_time = curr_time + p->delay;

    if (p->head == NULL) {
        p->head = pkt;
        p->tail = pkt;
    }
    else {
        mypkt = p->head;
        prepkt = NULL;
        while(mypkt != NULL) {
                if(pkt->output_time < mypkt->output_time) {
                        if(prepkt == NULL) {
                                DN_NEXT(pkt) = mypkt;
                                p->head = pkt;
                        } else {
                                DN_NEXT(pkt) = mypkt;
                                DN_NEXT(prepkt) = pkt;
                        }
                /*      printf("no problem in move_pkt, re-chain delay line.
\n"); */
                        break;
                }
                prepkt = mypkt;
                mypkt = DN_NEXT(prepkt);
        }

        if(mypkt == NULL) {
                DN_NEXT(p->tail) = pkt;
                p->tail = pkt;
        }
    }
    DN_NEXT(p->tail) = NULL;
}


I set 
ipfw add 500 pipe 1 icmp from 135.254.62.218 to 135.254.61.230
ipfw add 501 pipe 2 icmp from 135.254.62.230 to 135.254.61.218
ipfw pipe 1 config delay 9020ms
ipfw pipe 2 config delay 9020ms

Then I ping 135.254.62.218 from 135.254.61.230, the icmp will go through
this freeBSD machine, after a well, the machine got page fault error and
reboot.

Any comment will be appreciated, I'd like to know if it's possible to
re-queue delay-line. No problem found if only giving each packet a random
delay time without re-queue delay line.

Thanks.

Huan Liu