vring_total_read_len
extern size_t vring_total_read_len(struct virtual_ring *);
size = vring_total_read_len(&pvc->tx_ring[0]);
size += vring_total_read_len(&pvc->tx_ring[1]);
return (vring_total_read_len(&pvc->rx_ring[1]));
data.val = vring_total_read_len(&pvc->tx_ring[1]);
if (total > vring_total_read_len(pvr))