Re: [PATCH v4 2/4] qdev-properties: Accept bool for OnOffAuto

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jan 08, 2025 at 03:17:51PM +0900, Akihiko Odaki wrote:
> Accept bool literals for OnOffAuto properties for consistency with bool
> properties. This enables users to set the "on" or "off" value in a
> uniform syntax without knowing whether the "auto" value is accepted.
> This behavior is especially useful when converting an existing bool
> property to OnOffAuto or vice versa.

Again, to repeat my previous feedback, OnOffAuto is a well defined
QAPI type - making it secretly accept other values/types behind
the scenes which are not visible in QAPI scheme is not acceptable.

Effectively this is a backdoor impl of a QAPI alternate

  { 'alternate': 'OnOffAutoOrBool',
    'data': {
      'o': 'OnOffAuto',
      'b': 'bool'
    }
  }

except this isn't permitted as the QAPI generator explicitly blocks
use of alternate when the two branches are 'bool' and 'enum'.

I'm assuming this is because in the QemuOpts scenario, it cannot
guess upfront whether the input is a bool or enum. This is unfortunate
though, because at the JSON visitor level it is unambiguous. 

I wonder if the QAPI generator could be relaxed in any viable way ?

> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  hw/core/qdev-properties.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
> index 434a76f5036e..0081d79f9b7b 100644
> --- a/hw/core/qdev-properties.c
> +++ b/hw/core/qdev-properties.c
> @@ -491,6 +491,21 @@ const PropertyInfo qdev_prop_string = {
>      .set   = set_string,
>  };
>  
> +static void set_on_off_auto(Object *obj, Visitor *v, const char *name,
> +                            void *opaque, Error **errp)
> +{
> +    Property *prop = opaque;
> +    int *ptr = object_field_prop_ptr(obj, prop);
> +    bool value;
> +
> +    if (visit_type_bool(v, name, &value, NULL)) {
> +        *ptr = value ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
> +        return;
> +    }
> +
> +    qdev_propinfo_set_enum(obj, v, name, opaque, errp);
> +}
> +
>  /* --- on/off/auto --- */
>  
>  const PropertyInfo qdev_prop_on_off_auto = {
> @@ -498,7 +513,7 @@ const PropertyInfo qdev_prop_on_off_auto = {
>      .description = "on/off/auto",
>      .enum_table = &OnOffAuto_lookup,
>      .get = qdev_propinfo_get_enum,
> -    .set = qdev_propinfo_set_enum,
> +    .set = set_on_off_auto,
>      .set_default_value = qdev_propinfo_set_default_value_enum,
>  };
>  
> 
> -- 
> 2.47.1
> 

With regards,
Daniel
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