Re: [Qemu-devel] [PATCH] q35: Remove old machine versions

[Daniel P. Berrange]

On Mon, Aug 24, 2015 at 11:54:48AM +0200, Markus Armbruster wrote:
> John Snow <address@hidden> writes:
> 
> > On 08/19/2015 02:55 AM, Dr. David Alan Gilbert wrote:
> >> * Eduardo Habkost (address@hidden) wrote:
> >>> Migration with q35 was not possible before commit
> >>> 04329029a8c539eb5f75dcb6d8b016f0c53a031a, because q35 unconditionally 
> >>> creates
> >>> an ich9-ahci device, that was marked as unmigratable. So all q35 machines
> >>> before pc-q35-2.4 were unmigratable, and there's no point in keeping
> >>> compatibility code for them.
> >>>
> >>> Remove all old pc-q35 machine classes and keep only pc-q35-2.4.
> >> 
> >> But doesn't that mean that anyone who has a machine configured with one
> >> of those machine types will suddenly find it wont start?
> >> 
> >> Dave
> >> 
> >
> > To some extent, all versions of this board prior to 2.4 should be
> > considered unsupported and we should discourage their use anyway.
> >
> > If you really want, I suppose we could just alias them to 2.4 ...
> 
> I'd very much prefer an honest "won't start" over a silent change of the
> machine type.
> 
> If we really want to bend over backwards for existing uses of these
> machine types, we could make them error out with "use pc-q35-2.5
> instead".  Since I don't think they exist outside testing, I wouldn't
> bother.

Agreed, we should be reporting a hard error for any machine types we
have deleted. Or if we care about smooth upgrade path then we shouldn't
be deleting them in the first place. Silently changing the user's
requested machine type into a different machine type is violating
the semantics of stable machine types.

Regards,
Daniel
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