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

[Daniel P . Berrangé]

On Wed, Oct 18, 2023 at 02:02:08PM +0200, Markus Armbruster wrote:
> 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.

I guess we have different defintions of "for humans" in this context.
I consider QMP  data still relevant for humans, because humans are
reviewing patches to libvirt that add usage of QMP features, or
triaging bug reports that include examples of usage, and in both
cases it is pretty relevant to make unstable features stand out to
the human via the x- prefix IMHO.

With regards,
Daniel
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