vdev_alloc_common
extern vdev_t *vdev_alloc_common(spa_t *spa, uint_t id, uint64_t guid,
mvd = vdev_alloc_common(spa, cvd->vdev_id, 0, ops);
vd = vdev_alloc_common(spa, id, guid, ops);
vd = vdev_alloc_common(spa, id, 0, &vdev_hole_ops);