Subject: Re: [PATCH] virtio_net: zero is an invald queue_pairs number

From: Amos Kong <[email-masked]>
Date: Mon, 21 Apr 2014 23:03:46 +0800

On Mon, Apr 21, 2014 at 02:45:25PM +0800, Jason Wang wrote:
> On 04/21/2014 02:32 PM, Jason Wang wrote:
> > On 04/18/2014 01:45 PM, Amos Kong wrote:
> >> Execute "ethtool -L eth0 combined 0" in guest, if multiqueue
> >> is enabled, virtnet_send_command() will return -EINVAL error,
> >> there is a validation in QEMU.
> >>
> >> But if multiqueue is disabled, virtnet_set_queues() will just
> >> return zero (success). We should return error for this situation.
> >>
> >> Signed-off-by: Amos Kong <[email-masked]>
> >> ---
> >>  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 7b68746..8a852b5 100644
> >> --- a/drivers/net/virtio_net.c
> >> +++ b/drivers/net/virtio_net.c
> >> @@ -1285,7 +1285,7 @@ static int virtnet_set_channels(struct net_device *dev,
> >>  	if (channels->rx_count || channels->tx_count || channels->other_count)
> >>  		return -EINVAL;
> >>  
> >> -	if (queue_pairs > vi->max_queue_pairs)
> >> +	if (queue_pairs > vi->max_queue_pairs || queue_pairs == 0)
> >>  		return -EINVAL;
> >>  
> >>  	get_online_cpus();
> > Acked-by:  Jason Wang <[email-masked]>
> 
> Looking at virtnet_set_queues(), it will return success even if no cvq
> and no mq support. This is wrong. We need return error in this case.
> We'd better fix it and check the its return value in virtnet_restore().
> 
> With this fix, there's no need for us to check queue_pairs against zero
> like what this patch does.
 
As we talked in IRC, the problem I tried to fix is actually caused by
that we don't return error when MQ isn't support. I will post another
patch to fix it.

However, this fix is also useful, it will catch the error early.

-- 
			Amos.