Re: [PATCH v3] failover: unregister ROM on unplug

[Dr. David Alan Gilbert]

* Juan Quintela (quintela@redhat.com) wrote:
> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
> > * Laurent Vivier (lvivier@redhat.com) 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 <lvivier@redhat.com>
> >> ---
> >> 
> >> Notes:
> >>     v3:
> >>       remove useless space before comma
> >>     
> >>     v2:
> >>       reset has_rom to false
> >>       update commit log message
> >> 
> >>  hw/net/virtio-net.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >> 
> >> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> >> index 16d20cdee52a..c0c2ec1ebb98 100644
> >> --- a/hw/net/virtio-net.c
> >> +++ b/hw/net/virtio-net.c
> >> @@ -3256,6 +3256,10 @@ static void 
> >> virtio_net_handle_migration_primary(VirtIONet *n, MigrationState *s)
> >>      if (migration_in_setup(s) && !should_be_hidden) {
> >>          if (failover_unplug_primary(n, dev)) {
> >>              vmstate_unregister(VMSTATE_IF(dev), qdev_get_vmsd(dev), dev);
> >> +            if (PCI_DEVICE(dev)->has_rom) {
> >> +                PCI_DEVICE(dev)->has_rom = false;
> >> +                vmstate_unregister_ram(&PCI_DEVICE(dev)->rom, dev);
> >> +            }
> >
> > Not actually originated by your fix, but....
> >
> > Why doesn't failover_replug_primary re-add the vmstates?
> 
> Because we can't migrate until the "unplug" has happened.
> Yes, it is a mess.

But if the migrate fails, shouldn't it add it back?

Dave

> I think this is the saner patch that I can think of for that
> functionality.
> 
> What I wonder is why we register rom as ram, but I guess that the rom
> can be updated from userspace, or who knows.
> 
> Later, Juan.
> 
> > (I did wonder if passing rom-file="" to the e1000 would help in your
> > testing case, but it still creates the RAM image).
> >
> > Dave
> >
> >>              qapi_event_send_unplug_primary(dev->id);
> >>              qatomic_set(&n->failover_primary_hidden, true);
> >>          } else {
> >> -- 
> >> 2.31.1
> >> 
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK