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

[Max Reitz]

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

> +                else:
>                      return False
> -            else:
> -                return False
> -        return True
> +            return True
> +        except TypeError:
> +            # either match or event wasn't iterable (not a dict)
> +            return match == event
>  
>      def event_wait(self, name, timeout=60.0, match=None):
>          """
>

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