Re: [PATCH v3 05/15] qemu-iotests: delay QMP socket timers

From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
To: Max Reitz <mreitz@redhat.com>, qemu-block@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
	Eduardo Habkost <ehabkost@redhat.com>,
	qemu-devel@nongnu.org, Cleber Rosa <crosa@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>, John Snow <jsnow@redhat.com>
Subject: Re: [PATCH v3 05/15] qemu-iotests: delay QMP socket timers
Date: Fri, 30 Apr 2021 23:03:35 +0200	[thread overview]
Message-ID: <bb2c8f3c-f1cf-6213-b67d-7b1ff2102992@redhat.com> (raw)
In-Reply-To: <df1df43e-cfdc-ddeb-f7c1-f9399f252b35@redhat.com>

On 30/04/2021 13:59, Max Reitz wrote:
> On 14.04.21 19:03, Emanuele Giuseppe Esposito wrote:
>> Attaching a gdbserver implies that the qmp socket
>> should wait indefinitely for an answer from QEMU.
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>> ---
>>   python/qemu/machine.py        |  3 +++
>>   tests/qemu-iotests/iotests.py | 10 +++++++++-
>>   2 files changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/python/qemu/machine.py b/python/qemu/machine.py
>> index 12752142c9..d6142271c2 100644
>> --- a/python/qemu/machine.py
>> +++ b/python/qemu/machine.py
>> @@ -409,6 +409,9 @@ def _launch(self) -> None:
>>                                          stderr=subprocess.STDOUT,
>>                                          shell=False,
>>                                          close_fds=False)
>> +
>> +        if 'gdbserver' in self._wrapper:
>> +            self._qmp_timer = None
> 
> Why doesn’t __init__() evaluate this?  This here doesn’t feel like the 
> right place for it.  If we want to evaluate it here, self._qmp_timer 
> shouldn’t exist, and instead the timeout should be a _post_launch() 
> parameter.  (Which I would have nothing against, by the way.)

Uhm.. I got another comment in a previous version where for the "event" 
callbacks it was better a property than passing around a parameter. 
Which I honestly agree.

What should __init__() do? The check here is to see if the invocation 
has gdb (and a couple of patches ahead also valgrind), to remove the timer.
If I understand what you mean, you want something like
def __init__(self, timer):

But from my understanding, the class hierarchy is:
QEMUMachine: in machine.py
QEMUQtestMachine(QEMUMachine): in qtest.py
VM(qtest.QEMUQtestMachine): in iotests.py
VM() is then invoked in each test.

So this is not easily reachable by check.py, to pass the parameter into 
__init__

> 
> Also, mypy complains that this variable is a float, so iotest 297 (which 
> runs mypy) fails.

This and all mistakes of test 297 (mypy) is my fault: I did not have 
pylint-3 installed thus when testing it skipped the 297 test.

> 
>>           self._post_launch()
>>       def _early_cleanup(self) -> None:
>> diff --git a/tests/qemu-iotests/iotests.py 
>> b/tests/qemu-iotests/iotests.py
>> index 05d0dc0751..380527245e 100644
>> --- a/tests/qemu-iotests/iotests.py
>> +++ b/tests/qemu-iotests/iotests.py
>> @@ -478,7 +478,10 @@ def log(msg: Msg,
>>   class Timeout:
>>       def __init__(self, seconds, errmsg="Timeout"):
>> -        self.seconds = seconds
>> +        if qemu_gdb:
>> +            self.seconds = 3000
>> +        else:
>> +            self.seconds = seconds
> 
> We might as well completely disable the timeout then, that would be more 
> honest, I think.  (I.e. to make __enter__ and __exit__ no-ops.)
> 
>>           self.errmsg = errmsg
>>       def __enter__(self):
>>           signal.signal(signal.SIGALRM, self.timeout)
>> @@ -684,6 +687,11 @@ def qmp_to_opts(self, obj):
>>               output_list += [key + '=' + obj[key]]
>>           return ','.join(output_list)
>> +    def get_qmp_events(self, wait: bool = False) -> List[QMPMessage]:
>> +        if qemu_gdb:
>> +            wait = 0.0
> 
> First, this is a bool.  I can see that qmp.py expects a
> Union[bool, float], but machine.py expects just a bool.  (Also, mypy 
> complains that this specific `wait` here is a `bool`.  You can see that 
> by running iotest 297.)

I think here machine.py should reflect the qmp.py behavior and have an 
Union[bool, float] too.
> 
> Second, I don’t understand this.  If the caller wants to block waiting 
> on an event, then that should have nothing to do with whether we have 
> gdb running or not.  As far as I understand, setting wait to 0.0 is the 
> same as wait = False, i.e. we don’t block and just return None 
> immediately if there is no pending event.

You're right, this might not be needed here. The problem I had was that 
calling gdb and pausing at a breakpoint or something for a while would 
make the QMP socket timeout, thus aborting the whole test. In order to 
avoid that, I need to stop or delay timers.

I can't remember why I added this check here. At some point I am sure 
the test was failing because of socket timeout expiration, but I cannot 
reproduce the problem when commenting out this check above in 
get_qmp_events. The other check in patch 3 should be enough.

Emanuele
> 
> Max
> 
>> +        return super().get_qmp_events(wait=wait)
>> +
>>       def get_qmp_events_filtered(self, wait=60.0):
>>           result = []
>>           for ev in self.get_qmp_events(wait=wait):
>>
> 