[PATCH -next 2/2] virtio_net: Read the advised MTU

[Aaron Conole]

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 <acon...@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