code: def _fetchDevAll(self, namestr, devlist, statsfunc):
          
          for dev in devlist:
              stats = statsfunc(dev)
              name = 'diskio_%s_requests' % namestr
              if self.hasGraph(name):
                  self.setGraphVal(name, dev + '_read', stats['rios'])
                  self.setGraphVal(name, dev + '_write', stats['wios'])
              name = 'diskio_%s_bytes' % namestr
              if self.hasGraph(name):
                  self.setGraphVal(name, dev + '_read', stats['rbytes'])
                  self.setGraphVal(name, dev + '_write', stats['wbytes'])
              name = 'diskio_%s_active' % namestr
              if self.hasGraph(name):
                  self.setGraphVal(name, dev, stats['ios_active'])
docs: Initialize I/O stats for devices.
          
          @param namestr:   Field name component indicating device type.
          @param devlist:   List of devices.
          @param statsfunc: Function for retrieving stats for device.