On Thu, Nov 2, 2017 at 4:34 PM, Daniel P. Berrange <berrange@xxxxxxxxxx> wrote: > > On Thu, Nov 02, 2017 at 04:14:06PM +0100, Christian Ehrhardt wrote: > > Ping - since there wasn't any reply so far - any best practices one could > > share? > > > > Let me add a TL;DR: > > - bump of ipxe rom versions change the size of virtio-net-pci.rom > > - that breaks on migration "Length mismatch" > > > > I'd guess the size of that rom has to be fixed up on the fly, but if that > > is really ok and how/where is the question. > > The actual ROM contents will be transferred in the migration stream, so > the fact that the target host has ROMs with different content is not > important. The key thing that matters is that QEMU the target host loads > the ROMs at the same location, so that when the ROM contents is overwritten > with data from the incoming migration scheme, it all ends up at the same > place as it was on the source. Thanks Daniel for your answer, although you try to kill my remaining hopes of a better solution :-) But if the actual ROM content is migrated over anyway "all I'd have to do" is to make clear that the newer system (qemu) knows that the incoming rom has a different size than it thinks. I thought that was what the machine types and their mechanisms were for, but so far I only scratched like 10% of those - maybe they don't cover these rom sizes? > > Getting this to happen requires pre-planning when building the ROMs. By > the time you hit the size change during migration it is too late and your > VM is basically doomed. When building you need to add padding. IIUC for > RHEL we artificially increased the size of the seabios and ipxe ROMs to > 256k. So when later RHEL updates ship new seabios/ipxe they still fit in > the 256k region previously allowed for. That would have been a good solution to this - if it was done in the past :-) If I end up forced to draw a line anyway, that is a good way to start over safe against further size changes. -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
