netdev - Re: [PATCH] virtio_net: return error when there is no virtqueue or MQ isn't support

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Date:	Tue, 22 Apr 2014 11:53:34 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Amos Kong <akong@...hat.com>
CC:	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	mst@...hat.com
Subject: Re: [PATCH] virtio_net: return error when there is no virtqueue or
 MQ isn't support

On 04/22/2014 11:23 AM, Amos Kong wrote:
> On Tue, Apr 22, 2014 at 11:11:50AM +0800, Jason Wang wrote:
>> On 04/21/2014 11:11 PM, Amos Kong wrote:
>>> Currently ethtool returns zero if there is no virtqueue or MQ isn't
>>> support, we should return -ENOTSUPP to notice user.
>>>
>>> Signed-off-by: Amos Kong <akong@...hat.com>
>>> ---
>>>  drivers/net/virtio_net.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index 8a852b5..eaf8266 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -1053,7 +1053,7 @@ static int virtnet_set_queues(struct virtnet_info *vi, u16 queue_pairs)
>>>  	struct net_device *dev = vi->dev;
>>>  
>>>  	if (!vi->has_cvq || !virtio_has_feature(vi->vdev, VIRTIO_NET_F_MQ))
>>> -		return 0;
>>> +		return -ENOTSUPP;
>>>  
>>>  	s.virtqueue_pairs = queue_pairs;
>>>  	sg_init_one(&sg, &s, sizeof(s));
>> How about check the return value of virtnet_set_queues() in
>> virtnet_restore() also?
> If we migrate a guest from MQ supported side to MQ non-supported side,
> virtnet_restore() will not return error right now.
>
> If we return error when no vq or no mq support, and check return value
> of virtnet_set_queues() in virtnet_restore(), migration will fail. 
> Is it expected?
>
>

I think what you mean is restore not migration here. The point is not to
execute VIRTIO_NET_CTRL_MQ when multiqueue is not supported, so it's the
caller responsibility to pass a valid queue_pairs to
virtnet_set_queues(). This patch is not necessary, your last patch is
fine enough to solve the issue. Do you agree?

Thanks


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