+/*
+ * 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.
+ */
+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)
+ *config = vdev_label_read_config(cb.ubl_vd, ub->ub_txg);
+ spa_config_exit(spa, SCL_ALL, FTAG);