Re: [Qemu-devel] [PATCH 3/3] cirrus: mark as deprecated

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Fri, Oct 26, 2018 at 12:33:55PM +0530, P J P wrote:
> >   Hello Dan, all
> > 
> > +-- On Thu, 25 Oct 2018, Daniel P. Berrangé wrote --+
> > | On Thu, Oct 25, 2018 at 10:52:56AM +0200, Gerd Hoffmann wrote:
> > | > While being at it deprecate cirrus too.
> > | > 
> > | > Reason (short version): use stdvga instead.
> > | > Verbose version:
> > | >     https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful
> > | 
> > | 
> > | I don't debate the points in the blog post above that stdvga is a
> > | better choice, but I don't think that's enough to justify deprecating
> > | cirrus at this point in time, because when it then gets deleted it
> > | will break way too many existing deployments.
> > | 
> > | We need to socialize info in that blog post above more widely and
> > | especially ensure that apps are not using that by default. I don't
> > | see it being viable to formally deprecate it in QEMU any time soon
> > | though given existing usage.
> > 
> > To note, IMO there are other devices/sources in QEMU which are potential 
> > candidates for deprecation, similar to adlib etc. It'll help if we could 
> > device a process to deprecate/remove such code base. Other than maintenance it 
> > invariably also becomes source of security issues.
> > 
> > Ex.(similar to Fedora) we could announce such candidate on qemu-devel list and 
> > after review over a period of say a month, candidate will be
> > deprecated/expunged. (thinking aloud)
> 
> QEMU has a deprecation process:
> 
>   https://qemu.weilnetz.de/doc/qemu-doc.html#Deprecated-features
> 
> Most of the stuff deprecated is CLI args / monitor commands, etc where
> mgmt apps just adjust the way they are calling QEMU, so end user's VMs
> are largely not impacted.
> 
> Deprecating a device type that is widely used is not desirable because
> that will cause breakage of existing guests.  Distros are free to disable
> devices in their builds if they want to reduce the scope for CVEs in
> packages they maintain, but again they should think carefully about how
> many users they are going to break by doing so.

I'm a bit mixed here;  until recent guest kernels I've always treated
Cirrus as the 'safe' one that's likely to work on anything - so losing
it worries me.  Having said that, I understand why we want to deprecate
it;  but we should give a much longer deprecation warning - a few years?
I don't see any harm warning that it's deprecated and you really should
try not to use it.

Dave

> Regards,
> Daniel
> -- 
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--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK