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 01:03:00PM -0400, 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.
> 
> I have no problem adding it.
> 
>    -Don Slutz

I'd prefer -device instead. This way we don't need to deal
with it in PC code at all.

-- 
MST