Re: [PATCH v4 08/15] qapi: Make CpuModelExpansionInfo::deprecated-props optional and generic

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 5/27/25 4:32 AM, Markus Armbruster wrote:
> Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:
> 
>> From: Philippe Mathieu-Daudé <philmd@linaro.org>
>>
>> We'd like to have some unified QAPI schema. Having a structure field
>> conditional to a target being built in is not very practical.
>>
>> While @deprecated-props is only used by s390x target, it is generic
>> enough and could be used by other targets (assuming we expand
>> CpuModelExpansionType enum values).
>>
>> Let's always include this field, regardless of the target, but make it
>> optional. This is not a compatibility break only because the field
>> remains present always on S390x.
>>
>> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>> ---
>>   qapi/machine-target.json | 7 +++----
>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
>> index 426ce4ee82d..d8dbda4b508 100644
>> --- a/qapi/machine-target.json
>> +++ b/qapi/machine-target.json
>> @@ -244,19 +244,18 @@
>>   #
>>   # @model: the expanded CpuModelInfo.
>>   #
>> -# @deprecated-props: a list of properties that are flagged as
>> +# @deprecated-props: an optional list of properties that are flagged as
>>   #     deprecated by the CPU vendor.  The list depends on the
>>   #     CpuModelExpansionType: "static" properties are a subset of the
>>   #     enabled-properties for the expanded model; "full" properties are
>>   #     a set of properties that are deprecated across all models for
>> -#     the architecture.  (since: 9.1).
>> +#     the architecture.  (since: 10.1 -- since 9.1 on s390x --).
>>   #
>>   # Since: 2.8
>>   ##
>>   { 'struct': 'CpuModelExpansionInfo',
>>     'data': { 'model': 'CpuModelInfo',
>> -            'deprecated-props' : { 'type': ['str'],
>> -                                   'if': 'TARGET_S390X' } },
>> +            '*deprecated-props' : ['str'] },
>>     'if': { 'any': [ 'TARGET_S390X',
>>                      'TARGET_I386',
>>                      'TARGET_ARM',
> 
> [Copied from review of prior posts]
> 
> When I see "optional array", I wonder about the difference between
> "absent" and "present and empty".  The doc comment doesn't quite explain
> it.  I figure "present and empty" means empty, while "absent" means we
> don't know / not implemented.
> 
> Is the difference useful?
> 
> Daniel doubts it is.
> 
> [end of copy]
> 
> Let's take with this patch as is.  If we prefer to remove the
> difference, we can do so on top.
> 

I didn't answer to this question because I have no opinion on it.
If I have to pick an answer, following Daniel, I doubt the difference is 
useful also, as it's not changing anything for s390, which is the only 
producer for this entry.

Thanks,
Pierrick