netdev - Re: [RFC -next 2/2] virtio_net: Read and use the advised MTU

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Message-ID: <56E1C372.60204@cogentembedded.com>
Date:	Thu, 10 Mar 2016 21:56:50 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Aaron Conole <aconole@...hat.com>, netdev@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...hat.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC -next 2/2] virtio_net: Read and use the advised MTU

Hello.

On 03/10/2016 05:28 PM, Aaron Conole wrote:

> This patch checks the feature bit for the VIRTIO_NET_F_MTU feature. If it
> exists, read the advised MTU and use it.
>
> No proper error handling is provided for the case where a user changes the
> negotiated MTU. A future commit will add proper error handling. Instead, a
> warning is emitted if the guest changes the device MTU after previously being
> given advice.
>
> Signed-off-by: Aaron Conole <aconole@...hat.com>
> ---
>   drivers/net/virtio_net.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 767ab11..7175563 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
[...]
> @@ -1390,8 +1391,12 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>
>   static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
>   {
> +	struct virtnet_info *vi = netdev_priv(dev);
>   	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
>   		return -EINVAL;
> +	if (vi->negotiated_mtu == true) {
> +		pr_warn("changing mtu from negotiated mtu.");
> +	}

    {} not needed, see Documentation/CodingStyle.

[...]

MBR, Sergei