VOP_REQZCBUF
if (VOP_REQZCBUF(vp, UIO_READ, (xuio_t *)uiop, cr, &ct) == 0) {
if (!VOP_REQZCBUF(vp, UIO_READ, (xuio_t *)uiop, cs->cr, &ct)) {
error = VOP_REQZCBUF(vp, ioflag, xuio, cr, &smb_ct);