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Re: [Qemu-devel] [PATCH v5 2/5] arm: qmp: add query-gic-capabilities int

From: Markus Armbruster
Subject: Re: [Qemu-devel] [PATCH v5 2/5] arm: qmp: add query-gic-capabilities interface
Date: Wed, 23 Mar 2016 15:06:35 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Peter Xu <address@hidden> writes:

> On Wed, Mar 23, 2016 at 10:52:29AM +0100, Markus Armbruster wrote:
>> The rule against returning non-dictionaries exists to avoid interfaces
>> that cannot evolve.  With a dictionary, you can evolve by adding
>> members.
>> The rule does *not* forbid returning lists of dictionaries.  When a
>> command fundamentally returns a list of things, being able to evolve the
>> things suffices.
> Ok.
>> query-gic-capabilities looks like it fundamentally returns a list of
>> capabilities.  Returning ['GICCapability'] is just fine then.
> I have posted v6 just as Eric has suggested. At least one advantage
> is that it is easier to be extended (if needed) in the future, also
> to follow the more-generic format to use dicts rather than
> arrays. If you would not mind, I'll keep the dict interface there.

Returning such a list of a structured type is a well-established
convention by now --- qmp-introspect.c shows 28 commands doing it, most
of them named query-FOO.  I'd rather not start a different convention
now, just because we got temporarily confused about our own rules.  So,
unless there's something about query-gic-capabilities that makes it more
likely to need extension outside its list element type, let's stick to
returning the list.


> [...]
>> In either case, drop the change to returns_whitelist.
> Yep. Dropped in v6.
> Thanks.
> -- peterx

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