On Wed, 20 Jan 2021 11:18:01 -0500 Eduardo Habkost <ehabk...@redhat.com> wrote:
> On Wed, Jan 20, 2021 at 10:17:36AM +0000, David Edmondson wrote: > > On Wednesday, 2021-01-20 at 10:08:03 GMT, Daniel P. Berrangé wrote: > > > > > On Tue, Jan 19, 2021 at 11:30:52AM -0500, Eduardo Habkost wrote: > > >> 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? > > > > > > Where are you expecting warnings ? I don't see any when launching QEMU > > > > qemu-system-x86_64 -display none -cpu Westmere,-vmx,+vmx > > > > Warnings because the result of this is "-vmx". > > > > > IMHO just leave the parsing unchanged, deprecate it, and then delete > > > the code. We don't need to "improve" usability semantics of something > > > that we want to delete anyway. > > > > /me nods. > > I agree, but I guess we need to convince Paolo: > https://lore.kernel.org/qemu-devel/1990888058.22417362.1465939000140.javamail.zim...@redhat.com/ that's ancient :) He recently started this revolution himself :) https://www.mail-archive.com/qemu-devel@nongnu.org/msg757280.html That's why I have -cpu +/-foo deprecation on my not too far away TODO list.