subtype 'FilePath'
    => as 'Str'
    => where { m{^[\w/_.-]{1,80}\z} }
    => message { "I don't trust file name '$_'" };

has logfile => (
   traits  => [qw( Untaint )],
   is      => 'rw',
   isa     => 'FilePath',
   default => '/var/log/walrus.log',
);