Re: [Qemu-devel] [PATCH v5 18/21] iotests: add QMP event waiting queue

[Max Reitz <mreitz@redhat.com>]

On 09.04.2015 00:20, John Snow wrote:
> A filter is added to allow callers to request very specific
> events to be pulled from the event queue, while leaving undesired
> events still in the stream.
>
> This allows to poll for completion data for multiple asynchronous
> events in any arbitrary order.
>
> A new timeout context is added to the qmp pull_event method's
> wait parameter to allow tests to fail if they do not complete
> within some expected period of time.
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>   scripts/qmp/qmp.py            |  6 +++++-
>   tests/qemu-iotests/iotests.py | 38 ++++++++++++++++++++++++++++++++++++++
>   2 files changed, 43 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/qmp/qmp.py b/scripts/qmp/qmp.py
> index 20b6ec7..7f9ac1b 100644
> --- a/scripts/qmp/qmp.py
> +++ b/scripts/qmp/qmp.py
> @@ -140,7 +140,8 @@ class QEMUMonitorProtocol:
>           """
>           Get and delete the first available QMP event.
>   
> -        @param wait: block until an event is available (bool)
> +        @param wait: block until an event is available. If a float is provided,
> +                     use this as a timeout value. (bool, float)

Ouch... I guess it works, though...

>           """
>           self.__sock.setblocking(0)
>           try:
> @@ -151,7 +152,10 @@ class QEMUMonitorProtocol:
>                   pass
>           self.__sock.setblocking(1)
>           if not self.__events and wait:
> +            if isinstance(wait, float):
> +                self.__sock.settimeout(wait)
>               self.__json_read(only_event=True)
> +            self.__sock.settimeout(None)

If a timeout occurs, __json_read will do nothing and return (I guess...).

>           event = self.__events[0]

This will therefore probably return None...

>           del self.__events[0]

And I don't know what this will do. Will it be a no-op?

>           return event
> diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
> index 1402854..e93e623 100644
> --- a/tests/qemu-iotests/iotests.py
> +++ b/tests/qemu-iotests/iotests.py
> @@ -78,6 +78,23 @@ def create_image(name, size):
>           i = i + 512
>       file.close()
>   
> +# Test if 'match' is a recursive subset of 'event'
> +def event_match(event, match=None):
> +    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]):
> +                    return False
> +            elif event[key] != match[key]:
> +                return False
> +        else:
> +            return False
> +
> +    return True
> +
>   class VM(object):
>       '''A QEMU VM'''
>   
> @@ -92,6 +109,7 @@ class VM(object):
>                        '-machine', 'accel=qtest',
>                        '-display', 'none', '-vga', 'none']
>           self._num_drives = 0
> +        self._events = []
>   
>       # This can be used to add an unused monitor instance.
>       def add_monitor_telnet(self, ip, port):
> @@ -202,14 +220,34 @@ class VM(object):
>   
>       def get_qmp_event(self, wait=False):
>           '''Poll for one queued QMP events and return it'''
> +        if len(self._events) > 0:
> +            return self._events.pop(0)
>           return self._qmp.pull_event(wait=wait)
>   
>       def get_qmp_events(self, wait=False):
>           '''Poll for queued QMP events and return a list of dicts'''
>           events = self._qmp.get_events(wait=wait)
> +        events.extend(self._events)
> +        del self._events[:]
>           self._qmp.clear_events()
>           return events
>   
> +    def event_wait(self, name='BLOCK_JOB_COMPLETED', timeout=60.0, match=None):
> +        # Search cached events
> +        for event in self._events:
> +            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)

So if a timeout occurred, event will probably be None.

> +            if (event['event'] == name) and event_match(event, match):

And this (indexing event == None) will probably generate an exception. I 
guess it's one way to fail the test, but certainly not the best...

Max

> +                return event
> +            self._events.append(event)
> +
> +        return None
> +
>   index_re = re.compile(r'([^\[]+)\[([^\]]+)\]')
>   
>   class QMPTestCase(unittest.TestCase):