vio_dring_next
for (idx = dr->cons; idx != dr->prod; idx = vio_dring_next(dr, idx)) {
dr->cons = vio_dring_next(dr, idx);
dr->cons = vio_dring_next(dr, index);
dr->prod = vio_dring_next(dr, dr->prod);
dr->prod = vio_dring_next(dr, dr->prod);
: vio_dring_next(dr, end);
start = vio_dring_next(dr, start);
idx = vio_dring_next(dr, idx);
dr->cons = vio_dring_next(dr, end);
pkt->start_idx = vio_dring_next(dr,