xenbus_grant_ring
error = xenbus_grant_ring(sc->xbd_dev,
error = xenbus_grant_ring(dev, virt_to_mfn(rxs),
error = xenbus_grant_ring(dev, virt_to_mfn(txs),
err = xenbus_grant_ring(pdev->xdev, virt_to_mfn(pdev->sh_info));
int xenbus_grant_ring(device_t dev, unsigned long ring_mfn, grant_ref_t *refp);