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

[Markus Armbruster <armbru@redhat.com>]

BALATON Zoltan <balaton@eik.bme.hu> writes:

> On Thu, 6 Feb 2025, Akihiko Odaki wrote:
>> On 2025/02/06 18:48, Markus Armbruster wrote:
>>>>                                              This problem can be solved
>>>> using an existing mechanism, OnOffAuto, which differentiates the "auto"
>>>> state and explicit the "on" state.
>>>
>>> I guess you're proposing something like this:
>>>
>>> * auto: on if possible, else off
>>>
>>> * on: on if possible, else error
>>>
>>> * off: off (always possible)
>>>
>>> Which one is the default?
>>
>> I converted on to auto and off to false in a following patch.
>>
>>>> However, converting bool to OnOffAuto surfaces another problem: they
>>>> disagree how "on" and "off" should be written. Please note that the
>>>> disagreement already exists and so it is nice to solve anyway.
>>> 
>>> Yes, converting bool to OnOffAuto is an incompatible change.
>>
>> Not just about conversion, but this inconsistency require users to know whether a property is bool or OnOffAuto and change how the values are written in JSON accordingly. This somewhat hurts usability.
>
> Worse than that, the help text is also confusing.
> Excerpt from -device virtio-gpu,help
>
>   blob=<bool>            - on/off (default: false)
>   busnr=<busnr>
>   disable-legacy=<OnOffAuto> - on/off/auto (default: "auto")
>   disable-modern=<bool>  -  (default: false)
>   edid=<bool>            - on/off (default: true)
>   event_idx=<bool>       - on/off (default: true)
>
> For bools it says on/off yet expects true/false. Wasn't originally true/on/1 and false/off/0 accepted for bools? Where that got lost? I think getting back that behaviour would be easiest for users. Users don't care if OnOffAuto is an enum internally and can't (or don't want to) remember if bools are written on/off or true/false so accepting these as synonyms would help users.

The help text printed by -device is about usage of -device, not about
QMP.

There, the preferred syntax for bool values is on/off, but
yes/true/y/no/false/n are also accepted.  I think that's a disgusting
mess, but it's here to stay, so let's not argue this any further.

Instead of "(default: true)" we should have "(default: on)".

All of this is a digression from the topic at hand, which is QMP.