Re: [Qemu-block] [Qemu-devel] [PATCH] event_match: always match on None value

[John Snow]

On 5/27/19 9:24 AM, Max Reitz wrote:
> On 24.05.19 20:02, John Snow wrote:
>> Before, event_match didn't always recurse if the event value was not a
>> dictionary, and would instead check for equality immediately.
>>
>> By delaying equality checking to post-recursion, we can allow leaf
>> values like "5" to match "None" and take advantage of the generic
>> None-returns-True clause.
>>
>> This makes the matching a little more obviously consistent at the
>> expense of being able to check for explicit None values, which is
>> probably not that important given what this function is used for.
>>
>> Signed-off-by: John Snow <address@hidden>
>> ---
>>  python/qemu/__init__.py | 27 +++++++++++++++------------
>>  1 file changed, 15 insertions(+), 12 deletions(-)
>>
>> diff --git a/python/qemu/__init__.py b/python/qemu/__init__.py
>> index 98ed8a2e28..77d45f88fe 100644
>> --- a/python/qemu/__init__.py
>> +++ b/python/qemu/__init__.py
>> @@ -409,27 +409,30 @@ class QEMUMachine(object):
>>  
>>          The match criteria takes the form of a matching subdict. The event 
>> is
>>          checked to be a superset of the subdict, recursively, with matching
>> -        values whenever those values are not None.
>> +        values whenever the subdict values are not None.
>> +
>> +        This has a limitation that you cannot explicitly check for None 
>> values.
>>  
>>          Examples, with the subdict queries on the left:
>>           - None matches any object.
>>           - {"foo": None} matches {"foo": {"bar": 1}}
>> -         - {"foo": {"baz": None}} does not match {"foo": {"bar": 1}}
>> -         - {"foo": {"baz": 2}} matches {"foo": {"bar": 1, "baz": 2}}
>> +         - {"foo": None} matches {"foo": 5}
>> +         - {"foo": {"abc": None}} does not match {"foo": {"bar": 1}}
>> +         - {"foo": {"rab": 2}} matches {"foo": {"bar": 1, "rab": 2}}
>>          """
>>          if match is None:
>>              return True
>>  
>> -        for key in match:
>> -            if key in event:
>> -                if isinstance(event[key], dict):
>> -                    if not QEMUMachine.event_match(event[key], match[key]):
>> -                        return False
>> -                elif event[key] != match[key]:
>> +        try:
>> +            for key in match:
>> +                if key in event:
>> +                    return QEMUMachine.event_match(event[key], match[key])
> 
> With this change, we only check a single key that is both in @match and
> @event.  I think we want to keep the "if not -- return False" pattern,
> don’t we?
> 
> Max
> 

Whoops, way too fast on the send button. Sorry about that.