On Thu, 2018-02-01 at 13:52 +0000, Daniel P. Berrangé wrote: > > Note that I'm not advocating adding controllers or any other > > hardware to *existing* guests - that would clearly be a guest ABI > > breakage and thus Extremely Bad™. For newly-defined guests, however, > > none of the above applies AFAICT. > > There's no practical way to distinguish an existing guest from a > new guest being provisioned. With transient domains they are one & > the same. Even with persistent guests the distinction is far from > clear. We have VIR_DOMAIN_DEF_PARSE_ABI_UPDATE, which is only passed in when the guest is new - or the user has updated the XML themselves, in which case all bets are off when it comes to guest ABI stability anyway. There are cases, when importing an existing OS image as opposed to installing from scratch, where scenarios like the ones you described might show up, but again I don't think it's realistic to expect all guests to have the same exact hardware regardless of libvirt version as long as they share machine type. I don't think we want to paint ourselves in that corner. Plus, even if we did everything right in libvirt, guests defined at different times would end up having different ABI if QEMU has been upgraded in the meantime and thus uses a new default machine type. -- Andrea Bolognani / Red Hat / Virtualization -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
