code: def _initBlockMajorMap(self):
          
          self._mapMajorDevclass = {}
          try:
              fp = open(devicesFile, 'r')
              data = fp.read()
              fp.close()
          except:
              raise IOError('Failed reading device information from file: %s'
                            % devicesFile)
          skip = True
          for line in data.splitlines():
              if skip:
                  if re.match('block.*:', line, re.IGNORECASE):
                      skip = False
              else:
                  mobj = re.match('\s*(\d+)\s+([\w\-]+)$', line)
                  if mobj:
                      major = int(mobj.group(1))
                      devtype = mobj.group(2)
                      self._mapMajorDevclass[major] = devtype
                      if devtype == 'device-mapper':
                          self._dmMajorNum = major
docs: Parses /proc/devices to initialize device class - major number map
          for block devices.