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

[Juan Quintela <quintela@redhat.com>]

"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.

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
>>