DD_USED_REFRSRV
DD_USED_REFRSRV, DD_USED_HEAD, tx);
dsl_dir_diduse_space(ds->ds_dir, DD_USED_REFRSRV,
DD_USED_REFRSRV, DD_USED_HEAD, tx);
dsl_dir_diduse_space(origin_head->ds_dir, DD_USED_REFRSRV,
dsl_dir_diduse_space(ds->ds_dir, DD_USED_REFRSRV, delta, 0, 0, tx);
DD_USED_REFRSRV, -mrsdelta, 0, 0, tx);
return (dsl_dir_phys(dd)->dd_used_breakdown[DD_USED_REFRSRV]);