Function vdev_remove_parent

freebsd/contrib/openzfs/module/zfs/vdev.c:1234–1284

* Remove a 1-way mirror/replacing vdev from the tree. */

 * Remove a 1-way mirror/replacing vdev from the tree.
 */
void
vdev_remove_parent(vdev_t *cvd)
{
	vdev_t *mvd = cvd->vdev_parent;
	vdev_t *pvd = mvd->vdev_parent;

	ASSERT(spa_config_held(cvd->vdev_spa, SCL_ALL, RW_WRITER) == SCL_ALL);

	ASSERT(mvd->vdev_children == 1);
	ASSERT(mvd->vdev_ops == &vdev_mirror_ops ||
	    mvd->vdev_ops == &vdev_replacing_ops ||
	    mvd->vdev_ops == &vdev_spare_ops);
	cvd->vdev_ashift = mvd->vdev_ashift;
	cvd->vdev_logical_ashift = mvd->vdev_logical_ashift;
	cvd->vdev_physical_ashift = mvd->vdev_physical_ashift;
	vdev_remove_child(mvd, cvd);
	vdev_remove_child(pvd, mvd);

	/*
	 * If cvd will replace mvd as a top-level vdev, preserve mvd's guid.
	 * Otherwise, we could have detached an offline device, and when we
	 * go to import the pool we'll think we have two top-level vdevs,
	 * instead of a different version of the same top-level vdev.
	 */
	if (mvd->vdev_top == mvd) {
		uint64_t guid_delta = mvd->vdev_guid - cvd->vdev_guid;
		cvd->vdev_orig_guid = cvd->vdev_guid;
		cvd->vdev_guid += guid_delta;
		cvd->vdev_guid_sum += guid_delta;

		/*
		 * If pool not set for autoexpand, we need to also preserve
		 * mvd's asize to prevent automatic expansion of cvd.
		 * Otherwise if we are adjusting the mirror by attaching and
		 * detaching children of non-uniform sizes, the mirror could
		 * autoexpand, unexpectedly requiring larger devices to
		 * re-establish the mirror.
		 */
		if (!cvd->vdev_spa->spa_autoexpand)
			cvd->vdev_asize = mvd->vdev_asize;
	}
	cvd->vdev_id = mvd->vdev_id;
	vdev_add_child(pvd, cvd);
	vdev_top_update(cvd->vdev_top, cvd->vdev_top);

	if (cvd == cvd->vdev_top)
		vdev_top_transfer(mvd, cvd);

	ASSERT(mvd->vdev_children == 0);
	vdev_free(mvd);
}

static void
vdev_metaslab_group_create(vdev_t *vd)