Linux Virtualization - Aug 2013 - [PATCH] virtio-net: Set RXCSUM feature if GUEST_CSUM is available

If the VIRTIO_NET_F_GUEST_CSUM virtio feature is available, the guest
does not have to calculate the checksums on all received packets. This
is pretty much the same feature as RX checksum offloading on real
network cards, so the virtio-net driver should report this by setting
the NETIF_F_RXCSUM flag. When the user now runs "ethtool -k", he or
she
can see whether the virtio-net interface has to calculate RX checksums
or not.

Signed-off-by: Thomas Huth <thuth at linux.vnet.ibm.com>
---
 drivers/net/virtio_net.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f216002..defec2b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1538,6 +1538,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 			dev->features |= dev->hw_features & (NETIF_F_ALL_TSO|NETIF_F_UFO);
 		/* (!csum && gso) case will be fixed by register_netdev() */
 	}
+	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_CSUM))
+		dev->features |= NETIF_F_RXCSUM;
 
 	dev->vlan_features = dev->features;
 
-- 
1.8.1.4

From: Thomas Huth <thuth at linux.vnet.ibm.com>
Date: Tue, 27 Aug 2013 17:09:02 +0200
> If the VIRTIO_NET_F_GUEST_CSUM virtio feature is available, the guest
> does not have to calculate the checksums on all received packets. This
> is pretty much the same feature as RX checksum offloading on real
> network cards, so the virtio-net driver should report this by setting
> the NETIF_F_RXCSUM flag. When the user now runs "ethtool -k", he
or she
> can see whether the virtio-net interface has to calculate RX checksums
> or not.
> 
> Signed-off-by: Thomas Huth <thuth at linux.vnet.ibm.com>
Can one of the virtio_net folks please review this?

Thanks.

David Miller <davem at davemloft.net> writes:
> From: Thomas Huth <thuth at linux.vnet.ibm.com>
> Date: Tue, 27 Aug 2013 17:09:02 +0200
>
>> If the VIRTIO_NET_F_GUEST_CSUM virtio feature is available, the guest
>> does not have to calculate the checksums on all received packets. This
>> is pretty much the same feature as RX checksum offloading on real
>> network cards, so the virtio-net driver should report this by setting
>> the NETIF_F_RXCSUM flag. When the user now runs "ethtool -k",
he or she
>> can see whether the virtio-net interface has to calculate RX checksums
>> or not.
>> 
>> Signed-off-by: Thomas Huth <thuth at linux.vnet.ibm.com>
>
> Can one of the virtio_net folks please review this?
Hmm, so NETIF_F_RXCSUM only exists for ethtool's benefit.  Weird.

But this patch is correct:

Acked-by: Rusty Russell <rusty at rustcorp.com.au>

Thanks,
Rusty.