Function vdev_uberblock_load

freebsd/contrib/openzfs/module/zfs/vdev_label.c:1511–1555

* Reads the 'best' uberblock from disk along with its associated * configuration. First, we read the uberblock array of each label of each * vdev, keeping track of the uberblock with the highest txg in each array. * Then, we read the configuration from the same vdev as the best uberblock. */

 * Then, we read the configuration from the same vdev as the best uberblock.
 */
void
vdev_uberblock_load(vdev_t *rvd, uberblock_t *ub, nvlist_t **config)
{
	zio_t *zio;
	spa_t *spa = rvd->vdev_spa;
	struct ubl_cbdata cb;
	int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL |
	    ZIO_FLAG_SPECULATIVE | ZIO_FLAG_TRYHARD;

	ASSERT(ub);
	ASSERT(config);

	bzero(ub, sizeof (uberblock_t));
	*config = NULL;

	cb.ubl_ubbest = ub;
	cb.ubl_vd = NULL;

	spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
	zio = zio_root(spa, NULL, &cb, flags);
	vdev_uberblock_load_impl(zio, rvd, flags, &cb);
	(void) zio_wait(zio);

	/*
	 * It's possible that the best uberblock was discovered on a label
	 * that has a configuration which was written in a future txg.
	 * Search all labels on this vdev to find the configuration that
	 * matches the txg for our uberblock.
	 */
	if (cb.ubl_vd != NULL) {
		vdev_dbgmsg(cb.ubl_vd, "best uberblock found for spa %s. "
		    "txg %llu", spa->spa_name, (u_longlong_t)ub->ub_txg);

		*config = vdev_label_read_config(cb.ubl_vd, ub->ub_txg);
		if (*config == NULL && spa->spa_extreme_rewind) {
			vdev_dbgmsg(cb.ubl_vd, "failed to read label config. "
			    "Trying again without txg restrictions.");
			*config = vdev_label_read_config(cb.ubl_vd, UINT64_MAX);
		}
		if (*config == NULL) {
			vdev_dbgmsg(cb.ubl_vd, "failed to read label config");
		}
	}
	spa_config_exit(spa, SCL_ALL, FTAG);
}

/*
 * For use when a leaf vdev is expanded.