code: def global_validate(self):
          
  
          raw_spec = (
              "[global]",
              "user = user(default=bbd)",
              "group = group(default=bbd)",
              "log_file = log(default=/var/log/blackbird/blackbird.log)",
              "log_level = log_level(default='info')",
              "log_format = log_format(default='ltsv')",
              "max_queue_length = integer(default=32767)",
              "lld_interval = integer(default=600)",
              "interval = integer(default=60)"
          )
  
          functions = {
              'user': is_user,
              'group': is_group,
              'dir': extend_is_dir,
              'log': is_log,
              'log_level': is_log_level,
              'log_format': is_log_format
          }
  
          validator = validate.Validator(functions=functions)
          spec = self._configobj_factory(infile=raw_spec,
                                         _inspec=True
                                         )
          self.config.configspec = spec
          result = self.config.validate(validator, preserve_errors=True)
          self._parse_result(result)
  
          self.config['global'].configspec = None
docs: Validate only global section.
          The options in global section
          is used by other private methods of ConfigReader.
          So, validate only global section at first.
          "raw_spec" is configspec for global section.
          "functions" is passed as an argument in "validate.Validator".
  
          about "functions"
              'name': <function object>
               'name':used in configspec.
               Same meaning as "string", "integer" and "float" in validate.py.
               <function object>: function which is determine by the 'name'.
  
          e.g: the contents of ConfigSpec File
              [hoge]
              ham = egg(default=fuga)
  
          Functions
              functions = {
                  'egg': is_egg
              }
  
          When validation, 'is_egg' function is called for ham option.