docs: def check_removable(dev, opts):
      ''' Removable drives can be identified under /sys. '''
      try:  # get parent device from sys filesystem, look from right.  :-/
          parent = os.readlink(f'/sys/class/block/{dev}').rsplit("/", 2)[1]
          with open(f'/sys/block/{parent}/removable') as f:
              return f.read() == '1\n'
  
      except IndexError as err:
          if opts.debug:
              print('ERROR: parent block device not found.', err)
      except IOError as err:
          if opts.debug:
              print('ERROR:', err)