zap_deref_leaf
rc = zap_deref_leaf(&z, hash, &zl);
err = zap_deref_leaf(zap, zc->zc_hash, NULL, RW_READER,
err = zap_deref_leaf(zap, hash, tx, RW_WRITER, &l);
err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, NULL, RW_READER, &l);
err = zap_deref_leaf(zap, zn->zn_hash, tx, RW_WRITER, &l);
err = zap_deref_leaf(zap, zn->zn_hash, tx, RW_WRITER, &l);
err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, NULL, RW_READER, &l);
err = zap_deref_leaf(zn->zn_zap, zn->zn_hash, tx, RW_WRITER, &l);