Re: [Qemu-devel] [PATCH v7 0/9] Add limited support of VMware's hyper-call rpc

[Michael S. Tsirkin]

On Wed, Jun 17, 2015 at 07:14:24PM +0200, Paolo Bonzini wrote:
> 
> 
> On 17/06/2015 19:03, Don Slutz wrote:
> > On 06/17/15 12:29, Michael S. Tsirkin wrote:
> >> On Wed, Jun 17, 2015 at 06:17:19PM +0200, Paolo Bonzini wrote:
> >>>
> >>>
> >>> On 17/06/2015 16:29, Michael S. Tsirkin wrote:
> >>>> On Wed, Jun 17, 2015 at 04:27:13PM +0200, Paolo Bonzini wrote:
> >>>>>
> >>>>>
> >>>>> On 17/06/2015 16:18, Michael S. Tsirkin wrote:
> >>>>>>>> Yes, that's what was done for parallel and pcspk as well.  There's no
> >>>>>>>> infrastructure to avoid it.
> >>>>>>>>
> >>>>>>>> Paolo
> >>>>>> How do you mean? We have multiple ways to keep devices
> >>>>>> compatible with old versions.
> >>>>>> Set a new property to skip the extra stuff.
> >>>>>
> >>>>> Not if the device didn't have a vmstate at all, unfortunately.
> >>>>
> >>>> Skip creating the device completely for old machine types.
> >>>
> >>> Which device?  The vmstate is tied to the same device that has always
> >>> been created.
> >>
> >> Just disable the new functionality. Make it behave in
> >> a compatible way.
> >>
> >>>  we enable this thing by default (why do we?)
> >>
> >> Sigh. There is a very simple way to add a device in qemu: let user
> >> request it with -device.  If one does this, one gets to maintain the
> >> resulting mess without bothering with pc maintainers in any way.
> >>
> >> But of course, everyone implementing a new feature feels it's such a
> >> great thing, and completel zero risk, it must be part of the default
> >> machine. Guess what, one then gets to bother with versioning from day 0.
> >>
> >>>>>> this seems like a big deal ...
> >>>>>
> >>>>> The PC speaker device is also enabled by default.
> >>>>
> >>>> This is historical, isn't it?
> >>>
> >>> Yes, but it has broken 2.3->2.2 migration.
> >>>
> >>> Let's just stop fighting windmills.
> >>>
> >>> Paolo
> >>
> >> I don't see what you are saying. Suddenly guest visible
> >> changes within a machine type are ok?
> >>
> >> So we have a bug, need to fix it, preferably before piling up
> >> more features. The best way imho is for 2.4 to avoid
> >> this device unless requested explicitly.
> >>
> > 
> > My take on this is that Michael would like me to have a vmport_rpc=on
> > option, just like vmport=on (which already exists).  With a default of off.
> 
> It wouldn't be enough, because dc->vmsd would be non-NULL anyway.

For which device class?

> (But yes, that option would be a good thing anyway).
> 
> Paolo