'Convert an existing FSS volume to a Cinder volume.
We expect a volume id in the existing_ref that matches one in FSS.'

def manage_existing(self, volume, existing_ref):

    volume_metadata = {}
    self.proxy._get_existing_volume_ref_vid(existing_ref)
    self.proxy._manage_existing_volume(existing_ref['source-id'], volume)
    volume_metadata['FSS-vid'] = existing_ref['source-id']
    updates = {'metadata': volume_metadata}
    return updates
