Re: [Qemu-devel] [PATCH RFC v2 14/47] qapi-tests: New tests for union, alternate command arguments

[Markus Armbruster]

Eric Blake <address@hidden> writes:

> On 07/21/2015 06:43 AM, Eric Blake wrote:
>> On 07/01/2015 02:22 PM, Markus Armbruster wrote:
>>> A command's 'data' must be a struct type, given either as a
>>> dictionary, or as struct type name.
>>>
>>> Existing test case data-int.json covers simple type 'int'.  Add test
>>> cases for type names referring to union and alternate types.
>> 
>> We could probably relax things to allow a union (which is always a
>> dictionary on the wire), but I agree that allowing an alternate type is
>> not appropriate (the goal here is that we require a dictionary).  But
>> it's also easier to be conservative now and relax later.

Yes.

>>> +++ b/tests/qapi-schema/args-alternate.json
>>> @@ -0,0 +1,4 @@
>>> +# we do not allow alternate arguments
>>> +# TODO should we support this?
>> 
>> I see no reason to allow a non-dictionary in QMP, so this TODO could be
>> dropped.
>
> Or, to be clear, we document that arguments is always a dictionary, for:
> { "execute":"command", "arguments":{} }. Allowing an alternate would
> break that, so it is a different level of change to allow an alternate
> (change the QMP protocol) than what it would be to allow a union (the
> QMP protocol is unchanged).  Not that we can't do it if we ever have a
> reason, it's just that I don't see it being worth a TODO statement.

I'll drop it.

>>> +++ b/tests/qapi-schema/args-union.json
>>> @@ -0,0 +1,4 @@
>>> +# FIXME we should reject union arguments
>>> +# TODO should we support this?
>>> +{ 'union': 'Uni', 'data': { 'case1': 'int', 'case2': 'str' } }
>>> +{ 'command': 'oops', 'data': 'Uni' }
>> 
>> This, on the other hand, seems valid from the wire format (it will
>> always be a dictionary).  I guess the problem is that we generate a C
>> function signature based by calling out each member of the dictionary -
>> but how do you do that for a union?

Exactly: the problem is neither conceptual nor the wire API, it's the C
API we generate.

>>                                      So I see what you are doing:
>> marking that this test currently passes the parser, but then causes
>> problems for generating C code, so we should either reject it up front,
>> or fix the generator.  The FIXME documents what you will do later in the
>> series (reject it up front)

Yes, in PATCH 15.

>>                             and the TODO documents what we can do down
>> the road (fix the generator to allow it).

I figure we'd change the C API not to explode the data type into
multiple parameters.  We can consider that when we have a use for it.

> See also 32/47 - events have the same problem.

I'm afraid I don't see the connection to PATCH 32.

>> Reviewed-by: Eric Blake <address@hidden>

Thanks!