> perl -d  snapper.pl -X x /home
Loading DB routines from perl5db.pl version 1.37
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Enter h or 'h h' for help, or 'man perldebug' for more help.
main::(snapper.pl:5):   our $VERSION = '0.0.2';
  DB<1>  b Lvm::Snapshot_Ops::lvm_BaseDiff_Lvh_4_Base_opt_mp
  DB<2> c
Lvm::Snapshot_Ops::lvm_BaseDiff_Lvh_4_Base_opt_mp(snapper.pl:832):
832:                    my $lvm = shift;
  DB<2> s
Lvm::Snapshot_Ops::lvm_BaseDiff_Lvh_4_Base_opt_mp(snapper.pl:833):
833:                    my ($base_lvh, $lv_mp) = @_;
  DB<2> s
Lvm::Snapshot_Ops::lvm_BaseDiff_Lvh_4_Base_opt_mp(snapper.pl:834):
834:                    my $diff_dev = pathcat("/dev", 
835:                                                                            $base_lvh->vg_name, $base_lvh->lv_name . ".diff");
  DB<2> n
Lvm::Snapshot_Ops::lvm_BaseDiff_Lvh_4_Base_opt_mp(snapper.pl:837):
------------
#### here is where I have the problem the return from the 'by_mp'  -- you'll see $lv_mp."diff" a bit below....

837:                    my $bdiff_lvh = (@_ && $lvm->by_mp($lv_mp . ".diff")) or
838:                            $lvm->by_devpath(
839:                            pathcat("/dev", $base_lvh->vg_name, $base_lvh->lv_name . ".diff"));
  DB<2> s
Lvm::Maps::by_mp(/home/law/bin/lib/Lvm_Utils.pm:793):
793:            sub by_mp(;$) { my $map = shift; my $c = ref $map || $map;
  DB<2> s
Lvm::Maps::by_mp(/home/law/bin/lib/Lvm_Utils.pm:793):
793:            sub by_mp(;$) { my $map = shift; my $c = ref $map || $map;
  DB<2> s
Lvm::Maps::by_mp(/home/law/bin/lib/Lvm_Utils.pm:794):
794:                    bless $map = $map->new(), $c unless ref $map;
  DB<2> s
Lvm::Maps::by_mp(/home/law/bin/lib/Lvm_Utils.pm:795):
795:                    my $arg = $_[0];
  DB<2> s
Lvm::Maps::by_mp(/home/law/bin/lib/Lvm_Utils.pm:796):
796:                    $map->_init_by_mp unless $map->{_by_mp};
  DB<2> p $arg
/home.diff
-----
^^Above^^ is the string I passed in... so then I 'r'eturn from the routine and see:

  DB<3> r
scalar context return from Lvm::Maps::by_mp: '_chunksize' => undef
'_d_type' => undef
'_fs_perms' => undef
'_fs_type' => Fs::Xfs=HASH(0x2198c08)
   'mount_ops' => 'nodiratime,noatime,swalloc'
   'name' => 'xfs'
   'snapshot_ops' => 'nouuid,norecovery,ro'
'_fs_type_name' => 'xfs'
'cfg' => undef
'fs_mp' => undef
'lv_attr' => '-wc-ao---'
'lv_kernel_major' => 254
'lv_kernel_minor' => 9
'lv_name' => 'Home.diff'
'lv_path' => '/dev/HnS/Home.diff'
'lv_size' => 549755813888
'origin' => ''
'vg_extent_size' => 4194304
'vg_name' => 'HnS'
Lvm::Snapshot_Ops::lvm_BaseDiff_Lvh_4_Base_opt_mp(snapper.pl:840):
840:                    die P "Can't find \"diff\" dir for vol %s by mount or device path", $lv_mp
841:                            unless ref $bdiff_lvh;