Re: [Qemu-arm] [PATCH 06/10] target-i386: print obsolete warnings if +-features are used

[Paolo Bonzini]

On 07/06/2016 14:54, Igor Mammedov wrote:
> On Tue, 7 Jun 2016 14:36:51 +0200
> Paolo Bonzini <address@hidden> wrote:
> 
>> On 07/06/2016 14:32, Igor Mammedov wrote:
>>>>> Could you detect using +foo together with foo=off, and -foo together
>>>>> with foo=on?  Those are the really problematic cases, without them +foo
>>>>> and -foo can become synonyms for =on and =off.  
>>> That's (legacy)current semantic of -cpu +-foo where it overrides any foo=x,
>>> potentially it's possible to track foo=x locally in parser
>>> and then compare with +-foo both ways.
>>> But all we can do currently is to print warning about such use case.
>>>
>>> I think Eduardo's suggestion to just warn that +-foo is obsolete for now
>>> and drop support for it in several releases is sufficient(good) enough.  
>>
>> kvm-unit-tests and libvirt both use it, especially because =on and =off
>> are relatively new I think?  It seems like it's really widespread.
> 
> Yep, that's why it's not removed now.
> Looks like libvirt would be able to switch to foo=x syntax,
> I can take a look at kvm-unit-tests and make it use foo=x too.

And all tutorials, and all scripts.  It's really too hard.

I'd really prefer to make an incompatible change straight in 2.7 for the
case of mixed foo=x and [+-]foo.

Paolo