Re: [PATCH v2 5/9] qapi: Generalize struct member policy checking

[Philippe Mathieu-Daudé]

On 10/29/21 17:34, Markus Armbruster wrote:
> Eric Blake <eblake@redhat.com> writes:
> 
>> On Thu, Oct 28, 2021 at 12:25:16PM +0200, Markus Armbruster wrote:
>>> The generated visitor functions call visit_deprecated_accept() and
>>> visit_deprecated() when visiting a struct member with special feature
>>> flag 'deprecated'.  This makes the feature flag visible to the actual
>>> visitors.  I want to make feature flag 'unstable' visible there as
>>> well, so I can add policy for it.
>>>
>>> To let me make it visible, replace these functions by
>>> visit_policy_reject() and visit_policy_skip(), which take the member's
>>> special features as an argument.  Note that the new functions have the
>>> opposite sense, i.e. the return value flips.
>>>
>>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>>> ---
>>
>>> +++ b/qapi/qapi-forward-visitor.c
>>> @@ -246,25 +246,27 @@ static void forward_field_optional(Visitor *v, const 
>>> char *name, bool *present)
>>>      visit_optional(ffv->target, name, present);
>>>  }
>>>  
>>> -static bool forward_field_deprecated_accept(Visitor *v, const char *name,
>>> -                                            Error **errp)
>>> +static bool forward_field_policy_reject(Visitor *v, const char *name,
>>> +                                        unsigned special_features,
>>> +                                        Error **errp)
>>>  {
>>>      ForwardFieldVisitor *ffv = to_ffv(v);
>>>  
>>>      if (!forward_field_translate_name(ffv, &name, errp)) {
>>>          return false;
>>
>> Should this return value be flipped?
>>
>>>      }
>>> -    return visit_deprecated_accept(ffv->target, name, errp);
>>> +    return visit_policy_reject(ffv->target, name, special_features, errp);
>>>  }
>>>  
>>> -static bool forward_field_deprecated(Visitor *v, const char *name)
>>> +static bool forward_field_policy_skip(Visitor *v, const char *name,
>>> +                                      unsigned special_features)
>>>  {
>>>      ForwardFieldVisitor *ffv = to_ffv(v);
>>>  
>>>      if (!forward_field_translate_name(ffv, &name, NULL)) {
>>>          return false;
>>
>> and here too?
> 
> Good catch!

Ouch. I admit this patch logic is hard to review, but couldn't come
with a nice way to split it further.

> These functions are called indirectly like
> 
>     if (visit_policy_reject(v, "values", 1u << QAPI_DEPRECATED, errp)) {
>         return false;
>     }
>     if (!visit_policy_skip(v, "values", 1u << QAPI_DEPRECATED)) {
>         if (!visit_type_strList(v, "values", &obj->values, errp)) {
>             return false;
>         }
>     }
> 
> visit_policy_reject() must return true when it sets an error, or else we
> call visit_policy_skip() with @errp pointing to non-null.
> 
> Same argument for visit_policy_skip().
> 
>>>      }
>>> -    return visit_deprecated(ffv->target, name);
>>> +    return visit_policy_skip(ffv->target, name, special_features);
>>>  }
>>>  
>>
>> Otherwise, the rest of the logic changes for flipped sense look right.
>