On Thu, Aug 27, 2015 at 01:50:10PM +0300, Michael S. Tsirkin wrote: > On Tue, Aug 25, 2015 at 05:21:16PM +0100, Daniel P. Berrange wrote: > > On Mon, Aug 24, 2015 at 11:54:48AM +0200, Markus Armbruster wrote: > > > John Snow <js...@redhat.com> writes: > > > > > > > On 08/19/2015 02:55 AM, Dr. David Alan Gilbert wrote: > > > >> * Eduardo Habkost (ehabk...@redhat.com) 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 > > The reason we are deleting them is because changes in behaviour are not > user visible implementation details, and live migration is unsupported. > > In other words 2.4 is identical to <2.3 in all respect except live > migration, which didn't work in <2.3 and works in 2.4, that's why > aliasing them is fine.
I don't know what you mean by "not user visible implementation details" and "identical in all respect", because I see lots of compat code that implement user-visible differences inside pc_compat_*(), PC_COMPAT_*, pc_q35_*_machine_options() for 2.3 and older. -- Eduardo
