EM_RING_HEAD
reg = oidp->oid_arg2 == EM_RING_HEAD ? E1000_TDH(txr->me) :
reg = oidp->oid_arg2 == EM_RING_HEAD ? E1000_RDH(rxr->me) :
CTLTYPE_UINT | CTLFLAG_RD, txr, EM_RING_HEAD,
CTLTYPE_UINT | CTLFLAG_RD, rxr, EM_RING_HEAD,