vhost-net: Notify the backend about the host MTU

This patch provides a way for virtio-net to notify the
backend about the host MTU set by the user.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Aaron Conole <aconole@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/net/vhost_net.c

@@ -51,6 +51,7 @@ static const int kernel_feature_bits[] = {
     VIRTIO_RING_F_EVENT_IDX,
     VIRTIO_NET_F_MRG_RXBUF,
     VIRTIO_F_VERSION_1,
+    VIRTIO_NET_F_MTU,
     VHOST_INVALID_FEATURE_BIT
 };
 
@@ -74,6 +75,7 @@ static const int user_feature_bits[] = {
     VIRTIO_NET_F_HOST_ECN,
     VIRTIO_NET_F_HOST_UFO,
     VIRTIO_NET_F_MRG_RXBUF,
+    VIRTIO_NET_F_MTU,
 
     /* This bit implies RARP isn't sent by QEMU out of band */
     VIRTIO_NET_F_GUEST_ANNOUNCE,
@@ -435,6 +437,17 @@ int vhost_set_vring_enable(NetClientState *nc, int enable)
     return 0;
 }
 
+int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu)
+{
+    const VhostOps *vhost_ops = net->dev.vhost_ops;
+
+    if (!vhost_ops->vhost_net_set_mtu) {
+        return 0;
+    }
+
+    return vhost_ops->vhost_net_set_mtu(&net->dev, mtu);
+}
+
 #else
 uint64_t vhost_net_get_max_queues(VHostNetState *net)
 {
@@ -501,4 +514,9 @@ int vhost_set_vring_enable(NetClientState *nc, int enable)
 {
     return 0;
 }
+
+int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu)
+{
+    return 0;
+}
 #endif

include/net/vhost_net.h

@@ -35,4 +35,6 @@ int vhost_set_vring_enable(NetClientState * nc, int enable);
 
 uint64_t vhost_net_get_acked_features(VHostNetState *net);
 
+int vhost_net_set_mtu(struct vhost_net *net, uint16_t mtu);
+
 #endif