For each message in the list, test to see if the downstream queue is full with the canputnext(9F) function (line 21). If it is not full, use copyb to copy a header message block, and dupmsg(9F) to duplicate the data to be retransmitted. If either operation fails, reschedule a timeout at the next valid interval.

Update the new header block with the correct destination address (line 34), link the message to it (line 35), and send it downstream (line 36). At the end of the list, reschedule this routine.

1 struct retrans { 2 mblk_t *r_mp; 3 int r_address; 4 queue_t *r_outq; 5 struct retrans *r_next; 6 }; 7 8 struct protoheader { ... 9 int h_address; ... 10 }; 11 12 mblk_t *header; 13 14 void 15 retransmit(struct retrans *ret) 16 { 17 mblk_t *bp, *mp; 18 struct protoheader *php; 19 20 while (ret) { 21 if (!canputnext(ret->r_outq)) { /* no room */ 22 ret = ret->r_next; 23 continue; 24 } 25 bp = copyb(header); /* copy header msg. block */ 26 if (bp == NULL) 27 break; 28 mp = dupmsg(ret->r_mp); /* duplicate data */ 29 if (mp == NULL) { /* if unsuccessful */ 30 freeb(bp); /* free the block */ 31 break; 32 } 33 php = (struct protoheader *)bp->b_rptr; 34 php->h_address = ret->r_address; /* new header */ 35 bp->bp_cont = mp; /* link the message */ 36 putnext(ret->r_outq, bp); /* send downstream */ 37 ret = ret->r_next; 38 } 39 /* reschedule */ 40 (void) timeout(retransmit, (caddr_t)ret, RETRANS_TIME); 41 }