SA_REGISTRY
dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_REGISTRY);
dmu_tx_hold_zap(tx, sa->sa_master_obj, B_TRUE, SA_REGISTRY);
error = zap_lookup(os, sa_obj, SA_REGISTRY,
sa->sa_master_obj, SA_REGISTRY, tx);