virtio-net: unbreak the minix guest

Multiqueue patchset conditionally add control vq only when guest negotiate the
feature. Though the spec is not clear on this but it breaks the minix guest
since it will identify the ctrl vq even if it does not support it. Though this
behavior seems a violation on the spec "If the VIRTIO_NET_F_CTRL_VQ feature bit
is negotiated, identify the control virtqueue.", to keep the backward
compatibility, always add the ctrl vq at end of the queues.

Reported-by: Aurelien Jarno <aurelien@aurel32.net>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-id: 1366874663-2566-1-git-send-email-jasowang@redhat.com
Cc: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

hw/net/virtio-net.c

@@ -309,7 +309,7 @@ static void virtio_net_set_queues(VirtIONet *n)
     }
 }
 
-static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue, int ctrl);
+static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue);
 
 static uint32_t virtio_net_get_features(VirtIODevice *vdev, uint32_t features)
 {
@@ -364,8 +364,7 @@ static void virtio_net_set_features(VirtIODevice *vdev, uint32_t features)
     VirtIONet *n = VIRTIO_NET(vdev);
     int i;
 
-    virtio_net_set_multiqueue(n, !!(features & (1 << VIRTIO_NET_F_MQ)),
-                              !!(features & (1 << VIRTIO_NET_F_CTRL_VQ)));
+    virtio_net_set_multiqueue(n, !!(features & (1 << VIRTIO_NET_F_MQ)));
 
     virtio_net_set_mrg_rx_bufs(n, !!(features & (1 << VIRTIO_NET_F_MRG_RXBUF)));
 
@@ -1038,7 +1037,7 @@ static void virtio_net_tx_bh(void *opaque)
     }
 }
 
-static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue, int ctrl)
+static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
     int i, max = multiqueue ? n->max_queues : 1;
@@ -1067,9 +1066,11 @@ static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue, int ctrl)
         n->vqs[i].n = n;
     }
 
-    if (ctrl) {
-        n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);
-    }
+    /* Note: Minux Guests (version 3.2.1) use ctrl vq but don't ack
+     * VIRTIO_NET_F_CTRL_VQ. Create ctrl vq unconditionally to avoid
+     * breaking them.
+     */
+    n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);
 
     virtio_net_set_queues(n);
 }