On Wed, Mar 20, 2019 at 07:46:33AM +0100, Markus Armbruster wrote: > We're going in circles. Igor keeps telling you QEMU needs to shed dead > weight, badly. In Igor's words: > > We really need to figure out how to introduce breaking change on > management (CLI) side* in QEMU and make it digestible for libvirt > and others. > (* at least for new machine types). > > You keep telling us QEMU can't ever deprecate stuff libvirt uses, > because libvirt promised forward and backward compatibility forever. Note that libvirt didn't want to promise compatibility with live migration from new -> old libvirt. We did break this a few times in the past, and we received very clear feedback that users/mgmt apps don't want their live migration to be broken in this way. > I'm with Igor on this one. I'm all for QEMU going the extra mile to > help libvirt, simply because that helps a very large fraction of our > users. I'm now asking libvirt to extend the courtesy back to QEMU. This isn't about helping libvirt - this is about helping the users of libvirt & QEMU, who *want* this back compatibility to be able to live migrate their VMs in both directions. Any time libvirt has had problems in this area we get bug reports requiring us to fix it. This is why we don't want to do a change which would knowingly create a problem which will result in more bugs being reported against libvirt/QEMU > Please sit down and think earnestly about how to best soften the > compatibility promise you made so you can cope with changes we feel QEMU > has to make. Please don't blame libvirt for giving users the live migration compatibility we have been asked to provide to them. QEMU can change its impl, but users none the less expect live migration to remain compatible for their VMs. I did think initially we could do this by assocating the changed syntax with the machine type, until I was reminded that this does not work for the backwards compatibility direction, which users and mgmt apps have required libvirt to support. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
