sub _Var ($$$;$) {                          # Wrkhorse code for manufctrd Vars
#note $p->obj, $vn=varname, $wa=wantarray val
    my ($__, $p, $vn, $wa)=@$_;
    $_=$__;                                  '$_'
    my $v   = $p->{$vn};                      # value
    my $rfv = ref $v;                         # type(ref) of var
   ......
      } elsif ($rfv == 'HASH') {             
        my $subvar=$arg;                 ## 1 var w/hash is is a key
        $p->{$vn}{$subvar}=$_[0] if @_;       ## another?  =>assign value
        return $p->{$vn}{$subvar};  <- returns has here.

##</code><code>##

  sub by_mp(;$) { my $map = shift; my $c = ref $map || $map;
   ...init...

    my $arg_lvh = $map->_by_mp($arg);

    if (ref $arg_lvh) {
      $arg_lvh->fs_mp($arg);
      return $arg_lvh;    #<----seems to return from here
    }

    my $devno = (stat $arg)[0];

    $arg_lvh = $map->by_devno($devno);
    return undef unless $arg_lvh;
    die P "by_mp: by_devno(%s) returned %s, of type \"%s\", not a ref\n",
          $devno, $arg_lvh, ref $arg_lvh unless ref $arg_lvh;
    $map->_by_mp($arg, $arg_lvh);
    $arg_lvh->fs_mp($arg);
    return $arg_lvh;
  }

##</code><code>##

  sub lvm_BaseDiff_Lvh_4_Base_opt_mp ($;$) {
    my $lvm = shift;
    my ($base_lvh, $lv_mp) = @_;
    my $diff_dev = pathcat("/dev", 
                  $base_lvh->vg_name, $base_lvh->lv_name . ".diff");
    #TPe "diff_dev=%s", $diff_dev;

# next is call to by_mp -- here is where I don't seem to be
#getting a reference back.


    my $bdiff_lvh = $lvm->by_mp($lv_mp.".diff") if @_;
    $bdiff_lvh = $lvm->by_devpath($diff_dev) unless ref $bdiff_lvh;
## commented version below was orig -- trying above -- 
## seems to work better, but seems a bit random...

    #my $bdiff_lvh = (@_ && $lvm->by_mp($lv_mp . ".diff") or
    #               $lvm->by_devpath($diff_dev));
    die P "Can't find \"diff\" dir for vol %s by mount or device path", $lv_mp
      unless ref $bdiff_lvh;
    $bdiff_lvh->fs_mp($lv_mp) unless $bdiff_lvh->fs_mp;
    $bdiff_lvh->fs_type_name($base_lvh->fs_type_name) 
      unless $bdiff_lvh->fs_type_name;