vdev_probe
ret = vdev_probe(vdev_read, vdev_write, (void *)(uintptr_t)fd, &spa);
extern zio_t *vdev_probe(vdev_t *vd, zio_t *pio);
(error = zio_wait(vdev_probe(vd, NULL))) != 0) {
VERIFY(vdev_probe(vd, zio) == NULL);