Re: [Qemu-devel] [PATCH v5 01/10] qemu.py: Pylint/style fixes

[Lukáš Doktor]

Dne 17.8.2017 v 07:24 Markus Armbruster napsal(a):
> Lukáš Doktor <address@hidden> writes:
> 
>> Dne 16.8.2017 v 18:58 Markus Armbruster napsal(a):
>>> Lukáš Doktor <address@hidden> writes:
>>>
>>>> Dne 15.8.2017 v 14:31 Markus Armbruster napsal(a):
>>>>> Lukáš Doktor <address@hidden> writes:
>>>>>
>>>>>> No actual code changes, just several pylint/style fixes and docstring
>>>>>> clarifications.
>>>>>>
>>>>>> Signed-off-by: Lukáš Doktor <address@hidden>
>>>>>> ---
>>>>>>  scripts/qemu.py | 76 
>>>>>> ++++++++++++++++++++++++++++++++++++++++-----------------
>>>>>>  1 file changed, 53 insertions(+), 23 deletions(-)
>>>>>>
>>>>>> diff --git a/scripts/qemu.py b/scripts/qemu.py
>>>>>> index 880e3e8..466aaab 100644
>>>>>> --- a/scripts/qemu.py
>>>>>> +++ b/scripts/qemu.py
>>>>>> @@ -23,8 +23,22 @@ import qmp.qmp
>>>>>>  class QEMUMachine(object):
>>>>>>      '''A QEMU VM'''
>>>>>>  
>>>>>> -    def __init__(self, binary, args=[], wrapper=[], name=None, 
>>>>>> test_dir="/var/tmp",
>>>>>> -                 monitor_address=None, socket_scm_helper=None, 
>>>>>> debug=False):
>>>>>> +    def __init__(self, binary, args=[], wrapper=[], name=None,
>>>>>> +                 test_dir="/var/tmp", monitor_address=None,
>>>>>> +                 socket_scm_helper=None, debug=False):
>>>>>> +        '''
>>>>>> +        Create a QEMUMachine object
>>>>>
>>>>> Initialize a QEMUMachine
>>>>>
>>>>> Rationale: it's __init__, not __create__, and "object" is redundant.
>>>>>
>>>>
>>>> sure
>>>>
>>>>>> +
>>>>>> +        @param binary: path to the qemu binary (str)
>>>>>
>>>>> Drop (str), because what else could it be?
>>>>
>>>> it could be shlex.split of arguments to be passed to process. Anyway no 
>>>> strong opinion here so I dropping it...
>>>>
>>>>>
>>>>>> +        @param args: initial list of extra arguments
>>>>>
>>>>> If this is the initial list, then what's the final list?
>>>>>
>>>>
>>>> It's the basic set of arguments which can be modified before the 
>>>> execution. Do you think it requires additional explanation, or would you 
>>>> like to improve it somehow?
>>>
>>> Can this list of extra arguments really be *modified*?  Adding more
>>> arguments doesn't count for me --- I'd consider them added to the
>>> "non-extra" arguments.
>>>
>>
>> Yes, one can remove, shuffle or modify it.
> 
> Bizarre :)
> 
> Who's "one"?
> 

The user, or some inherited classes (eg. iotest.py). Currently nobody does 
that, but one might...

>>> Drop "initial"?
>>
>> I can do that but it can give false impression that the args will be 
>> present. Anyway it's probably just a corner case so I'll drop it.
> 
> If it's intended to be modified, then keeping "initial" might be best.
> Your choice.
> 

OK, let's not over-complicate it and just say it's list of extra arguments.

>>>
>>>>>> +        @param wrapper: list of arguments used as prefix to qemu binary
>>>>>> +        @param name: name of this object (used for log/monitor/... file 
>>>>>> names)
>>>>> prefix for socket and log file names (default: qemu-PID)
>>>>>
>>>>
>>>> Sure, both make sense to me.
>>>>
>>>>>> +        @param test_dir: base location to put log/monitor/... files in
>>>>>
>>>>> where to create socket and log file
>>>>>
>>>>> Aside: test_dir is a lousy name.
>>>>
>>>> Agree but changing names is tricky as people might be using kwargs to set 
>>>> it. Anyway using your description here, keeping the possible rename for a 
>>>> separate patchset (if needed).
>>>
>>> I'm merely observing the lousiness of this name.  I'm not asking you to
>>> do anything about it :)
>>>
>>>>>> +        @param monitor_address: custom address for QMP monitor
>>>>>
>>>>> Yes, but what *is* a custom address?  Its user _base_args() appears to
>>>>> expect either a pair of strings (host, port) or a string filename.
>>>>>
>>>>
>>>> If you insist I can add something like "a tuple(host, port) or string to 
>>>> specify path", but I find it unnecessary detailed...
>>>
>>> I'm not the maintainer, I'm definitely not insisting on anything.
>>>
>>> If you're aiming for brevity, then drop "custom".
>>>
>>
>> OK, removing in v6
>>
>>>>>> +        @param socket_scm_helper: path to scm_helper binary (to forward 
>>>>>> fds)
>>>>>
>>>>> What is an scm_helper, and why would I want to use it?
>>>>>
>>>>
>>>> To forward a file descriptor. It's for example used in 
>>>> tests/qemu-iotests/045 or tests/qemu-iotests/147
>>>
>>> What about "socket_scm_helper: helper program, required for send_fd_scm()"?
>>>
>>>>>> +        @param debug: enable debug mode (forwarded to QMP helper and 
>>>>>> such)
>>>>>
>>>>> What is a QMP helper?  To what else is debug forwarded?
>>>>>
>>>>
>>>> Debug is set in `self._debug` and can be consumed by anyone who has access 
>>>> to this variable. Currently that is the QMP, but people can inherit and 
>>>> use that variable to adjust their behavior.
>>>
>>> Drop the parenthesis?
>>>
>>
>> OK
>>
>>>>>> +        @note: Qemu process is not started until launch() is used.
>>>>>
>>>>> until launch().
>>>>>
>>>>
>>>> OK
>>>
>>> One more thing: what the use of "@param"?
>>>
>>
>> The API documentation can be autogenerated by doxygen, it uses those 
>> keywords to make it easier to read (and to create links, warnings, ...)
> 
> "Can" or "could"?  As far as I can tell, we aren't actually using
> doxygen for anything, are we?  Just like we aren't actually using
> GTK-Doc.  Yet its comment rash^H^H^H^Hannotations can be found here and
> there, commonly mixed up with unannotated code, and often syntactically
> invalid.  No surprise, since they've never been processed by their
> intended consumer.
> 
> If we decide we want to generate documentation, we should pick *one*
> system and stick to it.  Having every deveoper sprinkle "his" code with
> the annotations he's used to from elsewhere will do us no good.
> 

I'm not aware of any official documentation (as those scripts are pretty much 
internal), anyway IDEs like them as well. I saw the docstring notation on other 
places (qmp.py, qtest.py so I went with that in this version.

PS: I'm used to sphinx notation (:param)

>>>>>> +        '''
>>>>>
>>>>> It's an improvement.
>>>>>
>>>>>>          if name is None:
>>>>>>              name = "qemu-%d" % os.getpid()
>>>>>>          if monitor_address is None:
>>>>>> @@ -33,12 +47,13 @@ class QEMUMachine(object):
>>>>>>          self._qemu_log_path = os.path.join(test_dir, name + ".log")
>>>>>>          self._popen = None
>>>>>>          self._binary = binary
>>>>>> -        self._args = list(args) # Force copy args in case we modify them
>>>>>> +        self._args = list(args)     # Force copy args in case we modify 
>>>>>> them
>>>>>>          self._wrapper = wrapper
>>>>>>          self._events = []
>>>>>>          self._iolog = None
>>>>>>          self._socket_scm_helper = socket_scm_helper
>>>>>>          self._debug = debug
>>>>>> +        self._qmp = None
>>>>>>  
>>>>>>      # This can be used to add an unused monitor instance.
>>>>>>      def add_monitor_telnet(self, ip, port):
>>>>>> @@ -64,16 +79,16 @@ class QEMUMachine(object):
>>>>>>          if self._socket_scm_helper is None:
>>>>>>              print >>sys.stderr, "No path to socket_scm_helper set"
>>>>>>              return -1
>>>>>> -        if os.path.exists(self._socket_scm_helper) == False:
>>>>>> +        if not os.path.exists(self._socket_scm_helper):
>>>>>>              print >>sys.stderr, "%s does not exist" % 
>>>>>> self._socket_scm_helper
>>>>>>              return -1
>>>>>>          fd_param = ["%s" % self._socket_scm_helper,
>>>>>>                      "%d" % self._qmp.get_sock_fd(),
>>>>>>                      "%s" % fd_file_path]
>>>>>>          devnull = open('/dev/null', 'rb')
>>>>>> -        p = subprocess.Popen(fd_param, stdin=devnull, stdout=sys.stdout,
>>>>>> -                             stderr=sys.stderr)
>>>>>> -        return p.wait()
>>>>>> +        proc = subprocess.Popen(fd_param, stdin=devnull, 
>>>>>> stdout=sys.stdout,
>>>>>> +                                stderr=sys.stderr)
>>>>>> +        return proc.wait()
>>>>>>  
>>>>>>      @staticmethod
>>>>>>      def _remove_if_exists(path):
>>>>>> @@ -99,8 +114,8 @@ class QEMUMachine(object):
>>>>>>          return self._popen.pid
>>>>>>  
>>>>>>      def _load_io_log(self):
>>>>>> -        with open(self._qemu_log_path, "r") as fh:
>>>>>> -            self._iolog = fh.read()
>>>>>> +        with open(self._qemu_log_path, "r") as iolog:
>>>>>> +            self._iolog = iolog.read()
>>>>>>  
>>>>>>      def _base_args(self):
>>>>>>          if isinstance(self._monitor_address, tuple):
>>>>>> @@ -114,8 +129,8 @@ class QEMUMachine(object):
>>>>>>                  '-display', 'none', '-vga', 'none']
>>>>>>  
>>>>>>      def _pre_launch(self):
>>>>>> -        self._qmp = qmp.qmp.QEMUMonitorProtocol(self._monitor_address, 
>>>>>> server=True,
>>>>>> -                                                debug=self._debug)
>>>>>> +        self._qmp = qmp.qmp.QEMUMonitorProtocol(self._monitor_address,
>>>>>> +                                                server=True, 
>>>>>> debug=self._debug)
>>>>>
>>>>> Recommend to break the line between the last two arguments.
>>>>>
>>>>
>>>> I'm not used to do that, but I can most certainly do that. Do you want me 
>>>> to change all places (eg. in the next chunk)
>>>
>>> PEP8 asks you to limit all lines to a maximum of 79 characters.  This
>>> one is right at the maximum.  Tolerable, but I prefer my lines a bit
>>> shorter.  Use your judgement.
>>>
>>
>> OK, I though you want to enforce the one-arg-per-line limit. I usually go 
>> with <=79 (+ '\n') so this is fine by me, but I'll put it into next line if 
>> that makes you happier.
> 
> Please wrap your lines in e-mail, too :)
> 

Oh, sorry, this is a tough one... I'll take a look at the options (thunderbird)

>>>>>>  
>>>>>>      def _post_launch(self):
>>>>>>          self._qmp.accept()
>>>>>> @@ -131,9 +146,11 @@ class QEMUMachine(object):
>>>>>>          qemulog = open(self._qemu_log_path, 'wb')
>>>>>>          try:
>>>>>>              self._pre_launch()
>>>>>> -            args = self._wrapper + [self._binary] + self._base_args() + 
>>>>>> self._args
>>>>>> +            args = (self._wrapper + [self._binary] + self._base_args() +
>>>>>> +                    self._args)
>>>>>>              self._popen = subprocess.Popen(args, stdin=devnull, 
>>>>>> stdout=qemulog,
>>>>>> -                                           stderr=subprocess.STDOUT, 
>>>>>> shell=False)
>>>>>> +                                           stderr=subprocess.STDOUT,
>>>>>> +                                           shell=False)
>>>>>>              self._post_launch()
>>>>>>          except:
>>>>>>              if self.is_running():
>>>>>> @@ -149,28 +166,34 @@ class QEMUMachine(object):
>>>>>>              try:
>>>>>>                  self._qmp.cmd('quit')
>>>>>>                  self._qmp.close()
>>>>>> -            except:
>>>>>> +            except:     # kill VM on any failure pylint: disable=W0702
>>>>>
>>>>> The bare except is almost certainly inappropriate.  Are you sure we
>>>>> should silence pylint?
>>>>>
>>>>> Note that there's another bare except in launch(), visible in the
>>>>> previous patch hunk.  I guess pylint is okay with that one because it
>>>>> re-throws the exception.
>>>>>
>>>>> In case we should silence pylint: what's the scope of this magic pylint
>>>>> comment?  Can we use the symbolic disable=bare-except?
>>>>>
>>>>
>>>> Yep, we can use symbolic name as well. Well more appropriate would be to 
>>>> catch `SystemExit` and `KeyboardInterrupt`, treat them and raise them and 
>>>> then ignore the rest of exceptions. I'll do that in the next version...
>>>>
>>>>>>                  self._popen.kill()
>>>>>>  
>>>>>>              exitcode = self._popen.wait()
>>>>>>              if exitcode < 0:
>>>>>> -                sys.stderr.write('qemu received signal %i: %s\n' % 
>>>>>> (-exitcode, ' '.join(self._args)))
>>>>>> +                sys.stderr.write('qemu received signal %i: %s\n'
>>>>>> +                                 % (-exitcode, ' '.join(self._args)))
>>>>>>              self._load_io_log()
>>>>>>              self._post_shutdown()
>>>>>>  
>>>>>>      underscore_to_dash = string.maketrans('_', '-')
>>>>>> +
>>>>>>      def qmp(self, cmd, conv_keys=True, **args):
>>>>>>          '''Invoke a QMP command and return the result dict'''
>>>>>
>>>>> Make that "and return the response", because that's how
>>>>> docs/interop/qmp-spec.txt calls the thing.
>>>>>
>>>>
>>>> Sure, no problem. I wanted to stress-out it's a dict and not encoded 
>>>> string, but it's probably given by the context.
>>>
>>> "return the response dict" would be fine with me.
>>>
>>
>> Yes, I like that.
>>
>>>>>>          qmp_args = dict()
>>>>>> -        for k in args.keys():
>>>>>> +        for key in args.keys():
>>>>>>              if conv_keys:
>>>>>> -                qmp_args[k.translate(self.underscore_to_dash)] = args[k]
>>>>>> +                qmp_args[key.translate(self.underscore_to_dash)] = 
>>>>>> args[key]
>>>>>>              else:
>>>>>> -                qmp_args[k] = args[k]
>>>>>> +                qmp_args[key] = args[key]
>>>>>>  
>>>>>>          return self._qmp.cmd(cmd, args=qmp_args)
>>>>>>  
>>>>>>      def command(self, cmd, conv_keys=True, **args):
>>>>>> +        '''
>>>>>> +        Invoke a QMP command and on success return result dict or on 
>>>>>> failure
>>>>>> +        raise exception with details.
>>>>>> +        '''
>>>>>
>>>>> I'm afraid "result dict" is wrong: it need not be a dict.  "on failure
>>>>> raise exception" adds precious little information, and "with details"
>>>>> adds none.
>>>>>
>>>>> Perhaps:
>>>>>
>>>>>            Invoke a QMP command.
>>>>>            On success return the return value.
>>>>>            On failure raise an exception.
>>>>>
>>>>
>>>> That is quite more verbose than I'd like and result in the same (for 
>>>> non-native speaker), but I have no strong opinion here so changing it to 
>>>> your version in v2.
>>>>
>>>>> The last sentence is too vague, but it's hard to do better because...
>>>>>
>>>>>>          reply = self.qmp(cmd, conv_keys, **args)
>>>>>>          if reply is None:
>>>>>>              raise Exception("Monitor is closed")
>>>>>
>>>>> ... we raise Exception!  This code is a *turd* (pardon my french), and
>>>>> PEP8 / pylint violations are the least of its problems.
>>>>>
>>>>
>>>> Yep, adding rework-exceptions to my TODO list (for a future patchset)
>>>>
>>>>>> @@ -193,15 +216,18 @@ class QEMUMachine(object):
>>>>>>          return events
>>>>>>  
>>>>>>      def event_wait(self, name, timeout=60.0, match=None):
>>>>>> -        # Test if 'match' is a recursive subset of 'event'
>>>>>> -        def event_match(event, match=None):
>>>>>> +        '''Wait for event in QMP, optionally filter results by match.'''
>>>>>
>>>>> What is match?
>>>>>
>>>>> name and timeout not worth mentioning?
>>>>>
>>>>
>>>> IMO this does not require full-blown documentation, it's not really a 
>>>> user-facing API and sometimes shorter is better. Anyway if you insist I 
>>>> can add full documentation of each parameter. I can even add `:type:` and 
>>>> `:returns:` and perhaps some `:warns:` and `:notes:` and I should descend 
>>>> and note all the possible `:raises:`.
>>>>
>>>> ... the point I'm trying to make is I don't think it's necessary to go 
>>>> that much into details. Anyway if you think the params are necessary to 
>>>> list, then I can do that.
>>>
>>> Use your judgement.  The more detailed comments you add, the more
>>> questions you'll get ;)
>>>
>>
>> Sure, I'll try to improve (but not too much) that in the v6.
>>
>>>>>> +        # Test if 'match' is a recursive subset of 'event'; skips branch
>>>>>> +        # processing on match's value `None`
>>>>>
>>>>> What's a "recursive subset"?  What's "branch processing"?
>>>>>
>>>>> There's an unusual set of quotes around `None`.
>>>>>
>>>>
>>>> Basically I was surprised why this function exists as one can directly 
>>>> compare dicts. It's because it works as the stock dict compare only on 
>>>> value "None" it breaks and assumes that "branch" matches. That's why I 
>>>> listed the example as I'm unsure how to explain it in a human language.
>>>>
>>>> As for the `None`, in sphinx/doxygen it becomes "block" so I'm used to 
>>>> these, anyway people use `'`s and `"`s here so I'll change it in next 
>>>> version to be consistent.
>>>
>>> According to git-grep, we're using neither sphinx nor doxygen right now.
>>>
>>
>> yep, as I said I'll change it for `"`.
> 
> I'd prefer plain None over "None", because the former is clearly the
> built-in constant None, while the latter looks like a string.
> 

Sure

>>>>>> +        #    {"foo": {"bar": 1} matches {"foo": None}
>>>>>
>>>>> Aha: None servers as wildcard.
>>>>
>>>> Exactly.
>>>>
>>>>>
>>>>>> +        def _event_match(event, match=None):
>>>>>
>>>>> Any particular reason for renaming this function?
>>>>>
>>>>
>>>> To emphasize it's internal, not a strong opinion but IMO looks better this 
>>>> way.
>>>
>>> It's a nested function, how could it *not* be internal?
>>>
>>
>> It is always internal for the computer, but humans sometimes need more 
>> pointers. I can drop this part if you really dislike that change but I'm 
>> used to this notation.
> 
> PEP8:
> 
>     Method Names and Instance Variables
> 
>     Use the function naming rules: lowercase with words separated by
>     underscores as necessary to improve readability.
> 
>     Use one leading underscore only for non-public methods and instance
>     variables.
> 
> A nested function is not a method or instance variable.
> 

OK, I'll keep the name and send v6 probably tomorrow.

Regards,
Lukáš

>>>>>>              if match is None:
>>>>>>                  return True
>>>>>>  
>>>>>>              for key in match:
>>>>>>                  if key in event:
>>>>>>                      if isinstance(event[key], dict):
>>>>>> -                        if not event_match(event[key], match[key]):
>>>>>> +                        if not _event_match(event[key], match[key]):
>>>>>>                              return False
>>>>>>                      elif event[key] != match[key]:
>>>>>>                          return False
>>>>>> @@ -212,18 +238,22 @@ class QEMUMachine(object):
>>>>>>  
>>>>>>          # Search cached events
>>>>>>          for event in self._events:
>>>>>> -            if (event['event'] == name) and event_match(event, match):
>>>>>> +            if (event['event'] == name) and _event_match(event, match):
>>>>>>                  self._events.remove(event)
>>>>>>                  return event
>>>>>>  
>>>>>>          # Poll for new events
>>>>>>          while True:
>>>>>>              event = self._qmp.pull_event(wait=timeout)
>>>>>> -            if (event['event'] == name) and event_match(event, match):
>>>>>> +            if (event['event'] == name) and _event_match(event, match):
>>>>>>                  return event
>>>>>>              self._events.append(event)
>>>>>>  
>>>>>>          return None
>>>>>>  
>>>>>>      def get_log(self):
>>>>>> +        '''
>>>>>> +        After self.shutdown or failed qemu execution this returns the 
>>>>>> output
>>>>>
>>>>> Comma after execution, please.
>>>>>
>>>>
>>>> OK
>>>>
>>>>>> +        of the qemu process.
>>>>>> +        '''
>>>>>>          return self._iolog
>>>>>
>>>>> I understand this code was factored out of qemu-iotests for use by
>>>>> qtest.py.  That's okay, but I'd rather not serve as its maintainer.
>>>>> -E2MUCH...
>>>>>
>>>>
>>>> Yep, anyway it contains several useful methods/helpers and fixing basic 
>>>> issues is the simplest way to get to know the code (and the submitting 
>>>> process). Thank you for your time.
>>>
>>> You're welcome!
>>>
>>
>> Thanks again,
>> Lukáš

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