Read in from disk

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)