virtio-net: Add initial MTU advice feature

This commit adds the feature bit and associated mtu device entry for the
virtio network device.  When a virtio device comes up, it checks the
feature bit for the VIRTIO_NET_F_MTU feature.  If such feature bit is
enabled, the driver will read the advised MTU and use it as the initial
value.

Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
index ec32293a00db..1ab4ea6ec847 100644
--- a/include/uapi/linux/virtio_net.h
+++ b/include/uapi/linux/virtio_net.h
@@ -55,6 +55,7 @@
 #define VIRTIO_NET_F_MQ 22      /* Device supports Receive Flow
                                          * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23   /* Set MAC address */
+#define VIRTIO_NET_F_MTU 25     /* Initial MTU advice */
 
 #ifndef VIRTIO_NET_NO_LEGACY
 #define VIRTIO_NET_F_GSO        6       /* Host handles pkts w/ any GSO type */
@@ -73,6 +74,8 @@ struct virtio_net_config {
          * Legal values are between 1 and 0x8000
          */
         __u16 max_virtqueue_pairs;
+        /* Default maximum transmit unit advice */
+        __u16 mtu;
 } __attribute__((packed));
 
 /*