Amador Pahim <apa...@redhat.com> writes:
> On Fri, Aug 18, 2017 at 4:01 PM, Markus Armbruster <arm...@redhat.com> wrote:
>> Amador Pahim <apa...@redhat.com> writes:
>>
>>> On Tue, Aug 15, 2017 at 10:57 AM, Markus Armbruster <arm...@redhat.com>
>>> wrote:
>>>> Amador Pahim <apa...@redhat.com> writes:
>>>>
>>>>> When launching a VM, if an exception happens and the VM is not
>>>>> initiated, it is useful to see the qemu command line that was executed
>>>>> and the output of that command.
>>>>>
>>>>> Before this patch:
>>>>>
>>>>> >>> import qemu
>>>>> >>> vm = qemu.QEMUMachine('qemu-system-aarch64', debug=True)
>>>>> >>> vm.launch()
>>>>> Traceback (most recent call last):
>>>>> File "<stdin>", line 1, in <module>
>>>>> File "qemu.py", line 175, in launch
>>>>> self._launch()
>>>>> File "qemu.py", line 189, in _launch
>>>>> self._post_launch()
>>>>> File "qemu.py", line 154, in _post_launch
>>>>> self._qmp.accept()
>>>>> File "qmp/qmp.py", line 145, in accept
>>>>> self.__sock, _ = self.__sock.accept()
>>>>> File "/usr/lib64/python2.7/socket.py", line 206, in accept
>>>>> sock, addr = self._sock.accept()
>>>>> socket.timeout: timed out
>>>>> >>>
>>>>>
>>>>> After this patch:
>>>>>
>>>>> >>> import qemu
>>>>> >>> vm = qemu.QEMUMachine('qemu-system-aarch64', debug=True)
>>>>> >>> vm.launch()
>>>>> DEBUG:qemu:Error launching VM. Command: 'qemu-system-aarch64
>>>>> -chardev socket,id=mon,path=/var/tmp/qemu-5298-monitor.sock
>>>>> -mon chardev=mon,mode=control -display none -vga none'.
>>>>> Output: 'qemu-system-aarch64: No machine specified, and there
>>>>> is no default\nUse -machine help to list supported machines\n'.
>>>>> Traceback (most recent call last):
>>>>> File "<stdin>", line 1, in <module>
>>>>> File "qemu.py", line 175, in launch
>>>>> self._launch()
>>>>> File "qemu.py", line 189, in _launch
>>>>> self._post_launch()
>>>>> File "qemu.py", line 154, in _post_launch
>>>>> self._qmp.accept()
>>>>> File "qmp/qmp.py", line 145, in accept
>>>>> self.__sock, _ = self.__sock.accept()
>>>>> File "/usr/lib64/python2.7/socket.py", line 206, in accept
>>>>> sock, addr = self._sock.accept()
>>>>> socket.timeout: timed out
>>>>> >>>
>>>>>
>>>>> Signed-off-by: Amador Pahim <apa...@redhat.com>
>>>>> ---
>>>>> scripts/qemu.py | 12 +++++++++++-
>>>>> 1 file changed, 11 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/scripts/qemu.py b/scripts/qemu.py
>>>>> index e9a3a96d13..43fd0b072c 100644
>>>>> --- a/scripts/qemu.py
>>>>> +++ b/scripts/qemu.py
>>>>> @@ -158,7 +158,10 @@ class QEMUMachine(object):
>>>>> self._remove_if_exists(self._created_files.pop())
>>>>>
>>>>> def launch(self):
>>>>> - '''Launch the VM and establish a QMP connection'''
>>>>> + '''
>>>>> + Try to launch the VM and make sure we cleanup and expose the
>>>>> + command line/output in case of exception.
>>>>> + '''
>>>>>
>>>>> if self.is_running():
>>>>> raise QEMULaunchError('VM already running.')
>>>>> @@ -169,6 +172,7 @@ class QEMUMachine(object):
>>>>> 'before launching again.')
>>>>>
>>>>> try:
>>>>> + self._iolog = None
>>>>> self._qemu_full_args = None
>>>>> self._qemu_full_args = (self._wrapper + [self._binary] +
>>>>> self._base_args() + self._args)
>>>>> @@ -176,9 +180,15 @@ class QEMUMachine(object):
>>>>> self._pending_shutdown = True
>>>>> except:
>>>>> self.shutdown()
>>>>> + LOG.debug('Error launching VM.%s%s',
>>>>> + ' Command: %r.' % ' '.join(self._qemu_full_args)
>>>>> + if self._qemu_full_args else '',
>>>>> + ' Output: %r.' % self._iolog
>>>>> + if self._iolog else '')
>>>>
>>>> This nested interpolation is too ugly to live :)
>>>
>>> I find it beautiful :)
>>> Killing it anyway.
>>>
>>>>
>>>> Nesting is easy to avoid:
>>>>
>>>> LOG.debug('Error launching VM\n. ' Command: %r. Output: %r.'
>>>> % (' '.join(self._qemu_full_args)
>>>> if self._qemu_full_args else '',
>>>> self._iolog
>>>> if self._iolog else ''))
>>>
>>> In this case we will have the strings "Command: " and "Output:" even
>>> with no content to expose.
>>
>> No command should not happen.
>
> It can happen, if we fail before the self._qemu_full_args become ready
> (i.e. if self._base_args() fails).
If we fail before we even have a command line, it's not really an "Error
launching VM", it's more like "can't figure out how to launch the VM".
I suspect the root of the problem is an overly large try block. Which
also has a catch-all except to further enhance that delicious code
smell.
I fear we have bigger fish to fry than careless error reporting.
Debating it to the n-th degree is no use; do what you think is best.
[...]
