[PATCH v3] failover: unregister ROM on unplug

[Laurent Vivier <lvivier@redhat.com>]

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);
+            }
             qapi_event_send_unplug_primary(dev->id);
             qatomic_set(&n->failover_primary_hidden, true);
         } else {
-- 
2.31.1