"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
> On Tue, Mar 15, 2016 at 05:04:13PM -0400, 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.
>
> I don't see this as an error. Device might at best give a hint,
> user/network admin always knows best.
>
>>
>> Signed-off-by: Aaron Conole <aconole@xxxxxxxxxx>
>> ---
>> v2:
>> * Whitespace cleanup in the last hunk
>> * Code style change around the pr_warn
>> * Additional test for mtu change before printing warning
>>
>> drivers/net/virtio_net.c | 12 ++++++++++++
>> 1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 767ab11..429fe01 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -146,6 +146,7 @@ struct virtnet_info {
>> virtio_net_ctrl_ack ctrl_status;
>> u8 ctrl_promisc;
>> u8 ctrl_allmulti;
>> + bool negotiated_mtu;
>> };
>>
>> struct padded_vnet_hdr {
>> @@ -1390,8 +1391,11 @@ 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) && (dev->mtu != new_mtu))
>> + pr_warn("changing mtu while the advised mtu bit exists.");
>
> I don't really see why are we warning here. Just drop this chunk,
> as well as the flag in struct virtnet_info.
Okay. I was warning because the user is changing this after telling to
use something different - but if you don't think it's an error, I will
drop it.
Thanks so much for the review, Michael!
-Aaron
>> dev->mtu = new_mtu;
>> return 0;
>> }
>> @@ -1836,6 +1840,13 @@ static int virtnet_probe(struct virtio_device *vdev)
>> if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
>> vi->has_cvq = true;
>>
>> + if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) {
>> + vi->negotiated_mtu = true;
>> + dev->mtu = virtio_cread16(vdev,
>> + offsetof(struct virtio_net_config,
>> + mtu));
>> + }
>> +
>> if (vi->any_header_sg)
>> dev->needed_headroom = vi->hdr_len;
>>
>> @@ -2019,6 +2030,7 @@ static unsigned int features[] = {
>> VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ,
>> VIRTIO_NET_F_CTRL_MAC_ADDR,
>> VIRTIO_F_ANY_LAYOUT,
>> + VIRTIO_NET_F_MTU,
>> };
>>
>> static struct virtio_driver virtio_net_driver = {
>> --
>> 2.5.0
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