+static int
+dsl_pool_txg_history_update(kstat_t *ksp, int rw)
+{
+ dsl_pool_t *dp = ksp->ks_private;
+ txg_history_t *th;
+ int i = 0;
+
+ if (rw == KSTAT_WRITE)
+ return (EACCES);
+
+ if (ksp->ks_data)
+ kmem_free(ksp->ks_data, ksp->ks_data_size);
+
+ mutex_enter(&dp->dp_lock);
+
+ ksp->ks_ndata = dp->dp_txg_history_size;
+ ksp->ks_data_size = dp->dp_txg_history_size * sizeof(kstat_txg_t);
+ if (ksp->ks_data_size > 0)
+ ksp->ks_data = kmem_alloc(ksp->ks_data_size, KM_PUSHPAGE);
+
+ /* Traversed oldest to youngest for the most readable kstat output */
+ for (th = list_tail(&dp->dp_txg_history); th != NULL;
+ th = list_prev(&dp->dp_txg_history, th)) {
+ mutex_enter(&th->th_lock);
+ ASSERT3S(i + sizeof(kstat_txg_t), <=, ksp->ks_data_size);
+ memcpy(ksp->ks_data + i, &th->th_kstat, sizeof(kstat_txg_t));
+ i += sizeof(kstat_txg_t);
+ mutex_exit(&th->th_lock);
+ }
+
+ mutex_exit(&dp->dp_lock);
+
+ return (0);
+}
+
+static void
+dsl_pool_txg_history_init(dsl_pool_t *dp, uint64_t txg)
+{
+ char name[KSTAT_STRLEN];
+
+ list_create(&dp->dp_txg_history, sizeof (txg_history_t),
+ offsetof(txg_history_t, th_link));
+ dsl_pool_txg_history_add(dp, txg);
+
+ (void) snprintf(name, KSTAT_STRLEN, "txgs-%s", spa_name(dp->dp_spa));
+ dp->dp_txg_kstat = kstat_create("zfs", 0, name, "misc",
+ KSTAT_TYPE_TXG, 0, KSTAT_FLAG_VIRTUAL);
+ if (dp->dp_txg_kstat) {
+ dp->dp_txg_kstat->ks_data = NULL;
+ dp->dp_txg_kstat->ks_private = dp;
+ dp->dp_txg_kstat->ks_update = dsl_pool_txg_history_update;
+ kstat_install(dp->dp_txg_kstat);
+ }
+}
+
+static void
+dsl_pool_txg_history_destroy(dsl_pool_t *dp)
+{
+ txg_history_t *th;
+
+ if (dp->dp_txg_kstat) {
+ if (dp->dp_txg_kstat->ks_data)
+ kmem_free(dp->dp_txg_kstat->ks_data,
+ dp->dp_txg_kstat->ks_data_size);
+
+ kstat_delete(dp->dp_txg_kstat);
+ }
+
+ mutex_enter(&dp->dp_lock);
+ while ((th = list_remove_head(&dp->dp_txg_history))) {
+ dp->dp_txg_history_size--;
+ mutex_destroy(&th->th_lock);
+ kmem_free(th, sizeof(txg_history_t));
+ }
+
+ ASSERT3U(dp->dp_txg_history_size, ==, 0);
+ list_destroy(&dp->dp_txg_history);
+ mutex_exit(&dp->dp_lock);
+}
+
+txg_history_t *
+dsl_pool_txg_history_add(dsl_pool_t *dp, uint64_t txg)
+{
+ txg_history_t *th, *rm;
+
+ th = kmem_zalloc(sizeof(txg_history_t), KM_SLEEP);
+ mutex_init(&th->th_lock, NULL, MUTEX_DEFAULT, NULL);
+ th->th_kstat.txg = txg;
+ th->th_kstat.state = TXG_STATE_OPEN;
+ th->th_kstat.birth = gethrtime();
+
+ mutex_enter(&dp->dp_lock);
+
+ list_insert_head(&dp->dp_txg_history, th);
+ dp->dp_txg_history_size++;
+
+ while (dp->dp_txg_history_size > zfs_txg_history) {
+ dp->dp_txg_history_size--;
+ rm = list_remove_tail(&dp->dp_txg_history);
+ mutex_destroy(&rm->th_lock);
+ kmem_free(rm, sizeof(txg_history_t));
+ }
+
+ mutex_exit(&dp->dp_lock);
+
+ return (th);
+}
+
+/*
+ * Traversed youngest to oldest because lookups are only done for open
+ * or syncing txgs which are guaranteed to be at the head of the list.
+ * The txg_history_t structure will be returned locked.
+ */
+txg_history_t *
+dsl_pool_txg_history_get(dsl_pool_t *dp, uint64_t txg)
+{
+ txg_history_t *th;
+
+ mutex_enter(&dp->dp_lock);
+ for (th = list_head(&dp->dp_txg_history); th != NULL;
+ th = list_next(&dp->dp_txg_history, th)) {
+ if (th->th_kstat.txg == txg) {
+ mutex_enter(&th->th_lock);
+ break;
+ }
+ }
+ mutex_exit(&dp->dp_lock);
+
+ return (th);
+}
+
+void
+dsl_pool_txg_history_put(txg_history_t *th)
+{
+ mutex_exit(&th->th_lock);
+}
+