DT_EVTRING_SIZE
dtev = mallocarray(DT_EVTRING_SIZE, sizeof(*dtev), M_DEVBUF,
free(dtev, M_DEVBUF, DT_EVTRING_SIZE * sizeof(*dtev));
if (distance == 1 || distance == (1 - DT_EVTRING_SIZE)) {
dc->dc_cons = (dc->dc_cons + 1) % DT_EVTRING_SIZE;
count = DT_EVTRING_SIZE - prod;
prod = (prod + count) % DT_EVTRING_SIZE;