Re: [PATCH v2 14/21] hw/core/qdev-properties: allow qdev properties accept flags

[Zhao Liu <zhao1.liu@intel.com>]

> Not entirely true.
> 
> QAPI/QMP uses special feature flag @deprecated, i.e. a boolean.
> 
> We cannot emit a "user facing message": QMP cannot transport warnings.
> We could at best log one, in the hope that the user finds it.  But we
> don't.
> 
> Instead the deprecation note is in the documentation.
> 
> The deprecation flag is visible in QAPI/QMP introspection.  Management
> application developers need this; see Peter Krempa's reply.
> 
> QEMU can be configured to reject input that makes use of deprecated
> stuff, and to hide deprecated stuff in output.  This is intended for
> "testing the future".

I think a way is to add 'deprecated' flag (bool) in ObjectPropertyInfo,
just like CpuDefinitionInfo did. Then only when property has a
deprecation_note string, the 'deprecated' flag will be set for QAPI/QMP
query.

> >> Yes, rich deprecation hint is better. I think this still depends on
> >> USER_SET - distinguish internal/external or not :-(.
> >> 
> >> Since when we mark a property as deprecated, its code remains in the
> >> code tree, and internal calls should not trigger warnings. Deprecation
> >> hints are intended to reminder external users.
> >
> > This depends on where you put the deprecation check. IIUC, all the user
> > facing codepaths for setting properties end up calling through
> > object_set_properties_from_qdict, but internal codepaths don't use that.
> 
> This may well be true (I didn't check), but how can we ensure it remains
> true?

Perhaps this interface requires documentation - and strongly caution that
it *should not* be used for internal calls. Might this help prevent
potential misuse?

Thanks,
Zhao