netdev - Re: regression: UFO removal breaks kvm live migration

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Date:   Wed, 8 Nov 2017 16:49:57 +0900
From:   Jason Wang <jasowang@...hat.com>
To:     David Miller <davem@...emloft.net>, willemdebruijn.kernel@...il.com
Cc:     mkubecek@...e.cz, netdev@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Vlad Yasevic <vyasevic@...hat.com>
Subject: Re: regression: UFO removal breaks kvm live migration



On 2017年11月08日 15:26, David Miller wrote:
> From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
> Date: Wed, 8 Nov 2017 12:36:26 +0900
>
>> On Tue, Nov 7, 2017 at 5:02 PM, Michal Kubecek <mkubecek@...e.cz> wrote:
>>> I didn't have time to think it through yet but perhaps we could allow
>>> setting TUN_F_UFO and ignore its value.
>> If the feature is enabled guests may try to send UFO packets, which
>> the host is no longer able to fragment.
>>
>> virtio_net_hdr_to_skb will drop the packets immediately based on
>> gso_type and tun_get_user will return EINVAL.
>>
>> Still, perhaps that's preferable as migration will succeed and most
>> guests won't ever try to send those packets in the first place.
> However, this would create the situation where there is no way
> to properly probe for the actual presence of UFO support.

I think we should not have any assumption on how guest will use the 
feature. So I could not come a better than bring it back partially for 
TAP, looks like we only need segment them in tun_get_user().

Thanks