+static void
+spa_feature_stats_from_cache(spa_t *spa, nvlist_t *features)
+{
+ int i;
+
+ for (i = 0; i < SPA_FEATURES; i++) {
+ zfeature_info_t feature = spa_feature_table[i];
+ uint64_t refcount;
+
+ if (feature_get_refcount(spa, &feature, &refcount) != 0)
+ continue;
+
+ VERIFY0(nvlist_add_uint64(features, feature.fi_guid, refcount));
+ }
+}
+
+/*
+ * Store a list of pool features and their reference counts in the
+ * config.
+ *
+ * The first time this is called on a spa, allocate a new nvlist, fetch
+ * the pool features and reference counts from disk, then save the list
+ * in the spa. In subsequent calls on the same spa use the saved nvlist
+ * and refresh its values from the cached reference counts. This
+ * ensures we don't block here on I/O on a suspended pool so 'zpool
+ * clear' can resume the pool.
+ */
+static void
+spa_add_feature_stats(spa_t *spa, nvlist_t *config)
+{
+ nvlist_t *features;
+
+ ASSERT(spa_config_held(spa, SCL_CONFIG, RW_READER));
+
+ mutex_enter(&spa->spa_feat_stats_lock);
+ features = spa->spa_feat_stats;
+
+ if (features != NULL) {
+ spa_feature_stats_from_cache(spa, features);
+ } else {
+ VERIFY0(nvlist_alloc(&features, NV_UNIQUE_NAME, KM_SLEEP));
+ spa->spa_feat_stats = features;
+ spa_feature_stats_from_disk(spa, features);
+ }
+
+ VERIFY0(nvlist_add_nvlist(config, ZPOOL_CONFIG_FEATURE_STATS,
+ features));
+
+ mutex_exit(&spa->spa_feat_stats_lock);