Re: [PATCH 4/4] qapi: introduce CONFIG_READ event

[Markus Armbruster]

Daniel P. Berrangé <berrange@redhat.com> writes:

> On Wed, Oct 18, 2023 at 06:51:41AM -0400, Michael S. Tsirkin wrote:
>> On Wed, Oct 18, 2023 at 12:36:10PM +0200, Markus Armbruster wrote:
>> > > x- seems safer for management tool that doesn't know about "unstable" 
>> > > properties..
>> > 
>> > Easy, traditional, and unreliable :)
>> 
>> > > But on the other hand, changing from x- to no-prefix is already
>> > > done when the feature is stable, and thouse who use it already
>> > > use the latest version of interface, so, removing the prefix is
>> > > just extra work.
>> > 
>> > Exactly.
>> > 
>> 
>> I think "x-" is still better for command line use of properties - we
>> don't have an API to mark things unstable there, do we?
>
> Personally I like to see "x-" prefix present *everywhere* there is
> an unstable feature, and consider the need to rename when declaring
> it stable to be good thing as it sets an easily identifiable line
> in the sand and is self-evident to outside observers.
>
> The self-documenting nature of the "x-" prefer is what makes it most
> compelling to me. A patch submission, or command line invokation or
> an example QMP command, or a bug report, that exhibit an 'x-' prefix
> are an immediate red flag to anyone who sees them.

Except when it isn't, like in "x-origin".

> If someone sees a QMP comamnd / a typical giant QEMU command line,
> they are never going to go look at the QAPI schema to check whether
> any feature used had an 'unstable' marker. The 'unstable' marker
> might as well not exist in most cases.
>
> IOW, having the 'unstable' flag in the QAPI schema is great for machine
> introspection, but it isn't a substitute for having an 'x-' prefix used
> for the benefit of humans IMHO.

I'm not sure there's disagreement.  Quoting myself:

    The "x-" can remind humans "this is unstable" better than a feature
    flag can (for machines, it's the other way round).

CLI and HMP are for humans.  We continue to use "x-" there.

QMP is for machines.  The feature flag is the sole source of truth.
Additional use of "x-" is fine, but not required.