code: func (c *buddyinfoCollector) Update(ch chan<- prometheus.Metric) error {
  	buddyInfo, err := c.fs.NewBuddyInfo()
  	if err != nil {
  		return fmt.Errorf("couldn't get buddyinfo: %s", err)
  	}
  
  	log.Debugf("Set node_buddy: %#v", buddyInfo)
  	for _, entry := range buddyInfo {
  		for size, value := range entry.Sizes {
  			ch <- prometheus.MustNewConstMetric(
  				c.desc,
  				prometheus.GaugeValue, value,
  				entry.Node, entry.Zone, strconv.Itoa(size),
  			)
  		}
  	}
  	return nil
  }
docs: // Update calls (*buddyinfoCollector).getBuddyInfo to get the platform specific
  // buddyinfo metrics.