code: def _report_disk_stats(self):
          
          stats = {
              'docker.data.used': None,
              'docker.data.total': None,
              'docker.data.free': None,
              'docker.metadata.used': None,
              'docker.metadata.total': None,
              'docker.metadata.free': None
              # these two are calculated by _calc_percent_disk_stats
              # 'docker.data.percent': None,
              # 'docker.metadata.percent': None
          }
          info = self.docker_util.client.info()
          driver_status = info.get('DriverStatus', [])
          if not driver_status:
              self.log.warning('Disk metrics collection is enabled but docker info did not'
                               ' report any. Your storage driver might not support them, skipping.')
              return
          for metric in driver_status:
              # only consider metrics about disk space
              if len(metric) == 2 and 'Space' in metric[0]:
                  # identify Data and Metadata metrics
                  mtype = 'data'
                  if 'Metadata' in metric[0]:
                      mtype = 'metadata'
  
                  if 'Used' in metric[0]:
                      stats['docker.{0}.used'.format(mtype)] = metric[1]
                  elif 'Space Total' in metric[0]:
                      stats['docker.{0}.total'.format(mtype)] = metric[1]
                  elif 'Space Available' in metric[0]:
                      stats['docker.{0}.free'.format(mtype)] = metric[1]
          stats = self._format_disk_metrics(stats)
          stats.update(self._calc_percent_disk_stats(stats))
          tags = self._get_tags()
          for name, val in stats.iteritems():
              if val is not None:
                  self.gauge(name, val, tags)
docs: Report metrics about the volume space usage