zap_lockdir_by_dnode
err = zap_lockdir_by_dnode(dn, tx, RW_WRITER, TRUE, TRUE, FTAG, &zap);
err = zap_lockdir_by_dnode(dn, tx, RW_WRITER, TRUE, FALSE, FTAG, &zap);
int err = zap_lockdir_by_dnode(dn, NULL, RW_READER, TRUE, FALSE,