[RFC PATCH 1/1] qemu: Introduce VIRTIO_NET_F_BACKUP feature bit to virtio_net

[Sridhar Samudrala <sridhar.samudrala@intel.com>]

This feature bit can be used by hypervisor to indicate virtio_net device to
act as a backup for another device with the same MAC address.
    
Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index cd63659140..fa47e723b9 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -2193,6 +2193,8 @@ static Property virtio_net_properties[] = {
                      true),
     DEFINE_PROP_INT32("speed", VirtIONet, net_conf.speed, SPEED_UNKNOWN),
     DEFINE_PROP_STRING("duplex", VirtIONet, net_conf.duplex_str),
+    DEFINE_PROP_BIT64("backup", VirtIONet, host_features,
+                    VIRTIO_NET_F_BACKUP, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/include/standard-headers/linux/virtio_net.h b/include/standard-headers/linux/virtio_net.h
index 17c8531a22..6afca6dcaf 100644
--- a/include/standard-headers/linux/virtio_net.h
+++ b/include/standard-headers/linux/virtio_net.h
@@ -57,6 +57,9 @@
 					 * Steering */
 #define VIRTIO_NET_F_CTRL_MAC_ADDR 23	/* Set MAC address */
 
+#define VIRTIO_NET_F_BACKUP	  62   /* Act as backup for another device
+					* with the same MAC.
+					*/
 #define VIRTIO_NET_F_SPEED_DUPLEX 63   /* Device set linkspeed and duplex */
 
 #ifndef VIRTIO_NET_NO_LEGACY