Linux Virtualization - Oct 2016 - [PATCH] virtio-net: Update the mtu code to match virtio spec

From: Aaron Conole <aconole at bytheb.org>

The virtio committee recently ratified a change, VIRTIO-152, which
defines the mtu field to be 'max' MTU, not simply desired MTU.

This commit brings the virtio-net device in compliance with VIRTIO-152.

Additionally, drop the max_mtu branch - it cannot be taken since the u16
returned by virtio_cread16 will never exceed the initial value of
max_mtu.

Cc: "Michael S. Tsirkin" <mst at redhat.com>
Cc: Jarod Wilson <jarod at redhat.com>
Signed-off-by: Aaron Conole <aconole at redhat.com>
---
 drivers/net/virtio_net.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 720809f..2cafd12 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1870,10 +1870,12 @@ static int virtnet_probe(struct virtio_device *vdev)
 		mtu = virtio_cread16(vdev,
 				     offsetof(struct virtio_net_config,
 					      mtu));
-		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
+		if (mtu < dev->min_mtu) {
 			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
-		else
+		} else {
 			dev->mtu = mtu;
+			dev->max_mtu = mtu;
+		}
 	}
 
 	if (vi->any_header_sg)
-- 
2.7.4

On Tue, Oct 25, 2016 at 12:35:35PM -0400, Aaron Conole
wrote:
> From: Aaron Conole <aconole at bytheb.org>
> 
> The virtio committee recently ratified a change, VIRTIO-152, which
> defines the mtu field to be 'max' MTU, not simply desired MTU.
> 
> This commit brings the virtio-net device in compliance with VIRTIO-152.
> 
> Additionally, drop the max_mtu branch - it cannot be taken since the u16
> returned by virtio_cread16 will never exceed the initial value of
> max_mtu.
> 
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Cc: Jarod Wilson <jarod at redhat.com>
> Signed-off-by: Aaron Conole <aconole at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
> ---
>  drivers/net/virtio_net.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 720809f..2cafd12 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1870,10 +1870,12 @@ static int virtnet_probe(struct virtio_device
*vdev)
>  		mtu = virtio_cread16(vdev,
>  				     offsetof(struct virtio_net_config,
>  					      mtu));
> -		if (mtu < dev->min_mtu || mtu > dev->max_mtu)
> +		if (mtu < dev->min_mtu) {
>  			__virtio_clear_bit(vdev, VIRTIO_NET_F_MTU);
> -		else
> +		} else {
>  			dev->mtu = mtu;
> +			dev->max_mtu = mtu;
> +		}
>  	}
>  
>  	if (vi->any_header_sg)
> -- 
> 2.7.4

On Tue, Oct 25, 2016 at 12:35:35PM -0400, Aaron Conole
wrote:
> From: Aaron Conole <aconole at bytheb.org>
> 
> The virtio committee recently ratified a change, VIRTIO-152, which
> defines the mtu field to be 'max' MTU, not simply desired MTU.
> 
> This commit brings the virtio-net device in compliance with VIRTIO-152.
> 
> Additionally, drop the max_mtu branch - it cannot be taken since the u16
> returned by virtio_cread16 will never exceed the initial value of
> max_mtu.
> 
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Cc: Jarod Wilson <jarod at redhat.com>
> Signed-off-by: Aaron Conole <aconole at redhat.com>
Worksforme.

Acked-by: Jarod Wilson <jarod at redhat.com>

-- 
Jarod Wilson
jarod at redhat.com

> From: Aaron Conole <aconole at bytheb.org>
>
> The virtio committee recently ratified a change, VIRTIO-152, which
> defines the mtu field to be 'max' MTU, not simply desired MTU.
>
> This commit brings the virtio-net device in compliance with VIRTIO-152.
>
> Additionally, drop the max_mtu branch - it cannot be taken since the u16
> returned by virtio_cread16 will never exceed the initial value of
> max_mtu.
>
> Cc: "Michael S. Tsirkin" <mst at redhat.com>
> Cc: Jarod Wilson <jarod at redhat.com>
> Signed-off-by: Aaron Conole <aconole at redhat.com>
> ---
Sorry about the subject line, David.  This is targetted at net-next, and
it appears my from was mangled.  Would you like me to resubmit with
these details corrected?

-Aaron

Aaron Conole <aconole at redhat.com> writes:
>> From: Aaron Conole <aconole at bytheb.org>
>>
>> The virtio committee recently ratified a change, VIRTIO-152, which
>> defines the mtu field to be 'max' MTU, not simply desired MTU.
>>
>> This commit brings the virtio-net device in compliance with VIRTIO-152.
>>
>> Additionally, drop the max_mtu branch - it cannot be taken since the
u16
>> returned by virtio_cread16 will never exceed the initial value of
>> max_mtu.
>>
>> Cc: "Michael S. Tsirkin" <mst at redhat.com>
>> Cc: Jarod Wilson <jarod at redhat.com>
>> Signed-off-by: Aaron Conole <aconole at redhat.com>
>> ---
>
> Sorry about the subject line, David.  This is targetted at net-next, and
> it appears my from was mangled.  Would you like me to resubmit with
> these details corrected?
I answered my own question.  Sorry for the noise.