udv_attach
sc->sc_uobj = udv_attach(dev, VM_PROT_READ|VM_PROT_WRITE, 0,
uobj = udv_attach(vp->v_rdev,
struct uvm_object *udv_attach(dev_t, vm_prot_t, voff_t, vsize_t);
uobj = udv_attach(dev, prot, off, len);