On Wed, Nov 25, 2009 at 02:59:58PM +0100, Gerd Hoffmann wrote: > On 11/25/09 14:40, Michael S. Tsirkin wrote: > >>> We could add a DeviceState->savevm field and make that available as >>> property for devices which need to support multiple versions. Then you >>> we can use the compat properties to switch back to the older format with >>> -M pc-0.10. > >> I'm confused sorry. Of course when you want to migrate to qemu 0.10 >> you must have a compatible machine. And savevm format has nothing >> to do with it IMO, so MSI is orthogonal to this discussion. >> It just shows that it was smart not to save MSI state when >> MSI is not present (/me pats self on the back). >> >> In this thread we were discussing changes like pvclock bug, >> where we change savevm format without changing the machine, >> or almost without changing the machine. > > If 0.12 has this fixed (and thus a new version) and 0.11 hasn't, then > you'll want -M pc-0.11 use the old (buggy) savevm version. You have to > stay bug compatible otherwise you can't migrate to the old buggy version > because the old qemu can't handle the new format. > > Could be implemented via DeviceState->savevm as outlined above. > > cheers, > Gerd
There might be many reasons to use -M pc-0.11. Migrating to old qemu is only one of them. We should not force old savevm bugs on all users that use -M pc-0.11. In partucular, I think with time (years) we might drop support for old savevm bugs, but I see no reason not to support old machines indefinitely. -- MST
