# Re: \[PATCH -next 2/2\] virtio\_net: Read the advised MTU

- List: netdev
- 1 message, 1 author
- Page: https://ratatoskr.run/netdev/2016/06/4763513/t

## Re: \[PATCH -next 2/2\] virtio\_net: Read the advised MTU

- From: Aaron Conole \<aconole@redhat.com\>
- Date: 2016-06-02 17:10:30 
- Message: https://ratatoskr.run/netdev/2016/06/4763513.md

```text
"Michael S. Tsirkin" [ref] writes:

> On Thu, Jun 02, 2016 at 11:43:31AM -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 a warning and I don't think it's needed.
> Patch is ok commit log isn't.

Okay, I'll fix it when I submit v2.

>> Signed-off-by: Aaron Conole <aconole@redhat.com>
>> ---
>>  drivers/net/virtio_net.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>> 
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index e0638e5..ef5ee01 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1896,6 +1896,12 @@ 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)) {
>> +		dev->mtu = virtio_cread16(vdev,
>> +					  offsetof(struct virtio_net_config,
>> +						   mtu));
>> +	}
>> +
>>  	if (vi->any_header_sg)
>>  		dev->needed_headroom = vi->hdr_len;
>>  
>> @@ -2067,6 +2073,7 @@ 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 = {
>> -- 
>> 2.5.5
```