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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <f4b0cb70-7f86-f7cf-bb89-3a9f7ae15dc2@redhat.com>
Date: Mon, 6 Nov 2017 10:49:20 +0100
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Subject: Re: [Qemu-devel] kvm: virtio-net: saved image requires TUN_F_UFO
 support
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To: Stefan Priebe - Profihost AG <s.priebe@profihost.ag>, qemu-devel <qemu-devel@nongnu.org>

On 06/11/2017 10:48, Stefan Priebe - Profihost AG wrote:
> Hi Paolo,
> 
> Am 06.11.2017 um 10:40 schrieb Paolo Bonzini:
>> On 06/11/2017 10:38, Stefan Priebe - Profihost AG wrote:
>>> Hello,
>>>
>>> i've upgraded some servers from kernel 4.4 to 4.12 - both running Qemu
>>> 2.9.1.
>>>
>>> If i migrate a VM from a host running kernel 4.4 to a host running 4.12
>>> i get:
>>>
>>> kvm: virtio-net: saved image requires TUN_F_UFO support
>>> kvm: Failed to load virtio-net-device:tmp
>>> kvm: Failed to load virtio-net:virtio
>>> kvm: error while loading state for instance 0x0 of device
>>> '0000:00:12.0/virtio-net'
>>> kvm: load of migration failed: Invalid argument
>>>
>>>
>>> while migrating from 4.12 to 4.4 works fine.
>>>
>>> Can anybody help? Is this expected?
>>
>> Can you check why peer_has_ufo failed (in hw/net/virtio-net.c)?
> 
> May be - how can i archieve this? Patching the code is not a problem if
> you can give me a hint.
> 
>> Also, did this ioctl fail when the tap device was set up on the 4.12 destination?
>> int tap_probe_has_ufo(int fd)
>> {
>>     unsigned offload;
>>
>>     offload = TUN_F_CSUM | TUN_F_UFO;
>>
>>     if (ioctl(fd, TUNSETOFFLOAD, offload) < 0)
>>         return 0;
>>
>>     return 1;
>> }
> 
> Should there be any kernel output or how can i detect / check it?

For both, the simplest answer is probably just using printf.

Paolo