On 21/07/2021 18:19, Michael S. Tsirkin wrote: > On Wed, Jul 21, 2021 at 06:09:05PM +0200, Laurent Vivier wrote: >> The intend of failover is to allow to migrate a VM with a VFIO >> networking card without disrupting the network operation by switching >> to a virtio-net device during the migration. >> >> This simple change allows to test failover with a simulated device >> like e1000e rather than a vfio device, even if it's useless in real >> life it can help to debug failover. >> >> This is interesting to developers that want to test failover on >> a system with no vfio device. Moreover it simplifies host networking >> configuration as we can use the same bridge for virtio-net and >> the other failover networking device. >> >> Without this change the migration of a system configured with failover >> fails with: >> >> ... >> -device virtio-net-pci,id=virtionet0,failover=on,... \ >> -device e1000,failover_pair_id=virtionet0,... \ >> ... >> >> (qemu) migrate ... >> >> Unknown ramblock "0000:00:01.1:00.0/e1000e.rom", cannot accept migration >> error while loading state for instance 0x0 of device 'ram' >> load of migration failed: Invalid argument >> >> This happens because QEMU correctly unregisters the interface vmstate but >> not the ROM one. This patch fixes that. >> >> Signed-off-by: Laurent Vivier <lviv...@redhat.com> > > And does failover_replug_primary roll it all back then?
It seems not. To check I have started a migration, then I have canceled it, and I have started a migration to a file (migrate "exec:cat > mig") and I have analyzed the result with the script scripts/analyze-migration.py But: * with VFIO it's not a problem as we never migrate VFIO device itself, * with an emulated PCI device, it's only a problem if we disable failover after having canceled a first try (because if we keep failover we acts like for VFIO and we unplug the card and don't migrate vmstates). This means we need a scenario like that to hit the bug: - enable failover with an emulated PCI device - migrate to another machine - cancel/abort the migration before the end of the migration - unplug the virtio-net device to disable the failover behavior, - migrate the machine again with only the emulated PCI device but as I said previously failover with emulated PCI device is only for developers and test purpose and not to use in production... Thanks, Laurent