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Re: [External] : Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+featu

From: Eduardo Habkost
Subject: Re: [External] : Re: [RFC PATCH 1/2] hw/i386: -cpu model,-feature,+feature should enable feature
Date: Tue, 19 Jan 2021 11:30:52 -0500

On Tue, Jan 19, 2021 at 04:27:56PM +0000, David Edmondson wrote:
> On Tuesday, 2021-01-19 at 10:20:56 -05, Eduardo Habkost wrote:
> > Hi,
> >
> > Thanks for the patch.  Getting rid of special -feature/+feature
> > behavior was in our TODO list for a long time.
> >
> > On Tue, Jan 19, 2021 at 02:22:06PM +0000, David Edmondson wrote:
> >> "Minus" features are applied after "plus" features, so ensure that a
> >> later "plus" feature causes an earlier "minus" feature to be removed.
> >> 
> >> This has no effect on the existing "-feature,feature=on" backward
> >> compatibility code (which warns and turns the feature off).
> >
> > If we are changing behavior, why not change behavior of
> > "-feature,feature=on" at the same time?  This would allow us to
> > get rid of plus_features/minus_features completely and just make
> > +feature/-feature synonyms to feature=on/feature=off.
> Okay, I'll do that.
> Given that there have been warnings associated with
> "-feature,feature=on" for a while, changing that behaviour seems
> acceptable.
> Would the same be true for changing "-feature,+feature"? (i.e. what this
> patch does) Really: can this just be changed, or does there have to be
> some period where the behaviour stays the same with a warning?

I actually expected warnings to be triggered when using
"-feature,+feature" as well.  If we were not generating warnings
for that case, it will need more careful evaluation, just to be
sure it's safe.  Igor, do you remember the details here?


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