'Return size of volume to be managed by manage_existing.'

def manage_existing_get_size(self, volume, ref):

    volume_name = self._get_existing_volume_ref_name(ref)
    part_entry = self._get_latter_volume_dict(volume_name)
    if (part_entry is None):
        msg = _('Specified    logical    volume    does    not    exist.')
        LOG.error(msg)
        raise exception.ManageExistingInvalidReference(existing_ref=ref, reason=msg)
    (rc, map_info) = self._execute('ShowMap', ('part=%s' % part_entry['ID']))
    if (len(map_info) != 0):
        msg = _('The    specified    volume    is    mapped    to    a    host.')
        LOG.error(msg)
        raise exception.VolumeBackendAPIException(data=msg)
    return int(math.ceil(mi_to_gi(float(part_entry['Size']))))
