Re: [PATCH v2 08/12] qapi: Make CpuModelExpansionInfo::deprecated-props optional and generic

[Markus Armbruster <armbru@redhat.com>]

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.

Let's add:

  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..e153291a7fc 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' : { 'type': ['str'] } },

[Copied from review of prior posts]

Make this

               '*deprecated-props' : ['str'] },

please.

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.

Philippe is happy to implement either variant.

>    'if': { 'any': [ 'TARGET_S390X',
>                     'TARGET_I386',
>                     'TARGET_ARM',

Note the patch doesn't touch any of the qmp_query_cpu_model_expansion().
The S390x version continues to set @deprecated_props always.  The others
continue not to set it.