'Returns the EC specific filename for given timestamp.
:param timestamp: the object timestamp, an instance of
:class:`~swift.common.utils.Timestamp`
:param ext: an optional string representing a file extension to be
appended to the returned file name
:param frag_index: a fragment archive index, used with .data extension
only, must be a whole number.
:param ctype_timestamp: an optional content-type timestamp, an instance
of :class:`~swift.common.utils.Timestamp`
:param durable: if True then include a durable marker in data filename.
:returns: a file name
:raises DiskFileError: if ext==\'.data\' and the kwarg frag_index is not
a whole number'

def make_on_disk_filename(self, timestamp, ext=None, frag_index=None, ctype_timestamp=None, durable=False, *a, **kw):

    if (ext == '.data'):
        frag_index = self.validate_fragment_index(frag_index)
        rv = ((timestamp.internal + '#') + str(frag_index))
        if durable:
            rv += '#d'
        return ('%s%s' % (rv, ext))
    return super(ECDiskFileManager, self).make_on_disk_filename(timestamp, ext, ctype_timestamp, *a, **kw)
