Handle a read reference for a vdev
#include <qvm/vio.h>
unsigned vio_read(struct vio_state *vsp,
unsigned cookie,
const struct qvm_state_block *vopnd,
const struct qvm_state_block *oopnd,
struct guest_cpu *gcp)
This function must be called by the vdev's vread() function, passing the parameters through.
(VIOREF_CLASS_*) indication of any further action that the reference requires the vdev to take.