docs: def _read(self):
          '''
          Read in from disk
          '''
          if msgpack is None:
              log.error('Cache cannot be read from the disk: msgpack is missing')
          elif not os.path.exists(self._path):
              log.debug('Cache path does not exist for reading: %s', self._path)
          else:
              try:
                  with salt.utils.files.fopen(self._path, 'rb') as fp_:
                      cache = salt.utils.data.decode(msgpack.load(fp_, encoding=__salt_system_encoding__))
                  if "CacheDisk_cachetime" in cache:  # new format
                      self._dict = cache["CacheDisk_data"]
                      self._key_cache_time = cache["CacheDisk_cachetime"]
                  else:  # old format
                      self._dict = cache
                      timestamp = os.path.getmtime(self._path)
                      for key in self._dict:
                          self._key_cache_time[key] = timestamp
                  if log.isEnabledFor(logging.DEBUG):
                      log.debug('Disk cache retrieved: %s', cache)
              except (IOError, OSError) as err:
                  log.error('Error while reading disk cache from %s: %s', self._path, err)