hv_get_ring_buffer
void *ring_buffer = hv_get_ring_buffer(ring_info);
desc = hv_get_ring_buffer(outring_info) + old_write;
desc = (struct vmpacket_descriptor *)(hv_get_ring_buffer(rbi) + rbi->priv_read_index);
prefetch(hv_get_ring_buffer(rbi) + rbi->priv_read_index);