virtio-net: Add queues before loading them

Call virtio_net_set_multiqueue() to add queues before loading their
states. Otherwise the loaded queues will not have handlers and elements
in them will not be processed.

Cc: qemu-stable@nongnu.org
Fixes: 8c49756825da ("virtio-net: Add only one queue pair when realizing")
Reported-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/virtio-net.c

@@ -3064,6 +3064,15 @@ static void virtio_net_set_multiqueue(VirtIONet *n, int multiqueue)
     virtio_net_set_queue_pairs(n);
 }
 
+static int virtio_net_pre_load_queues(VirtIODevice *vdev)
+{
+    virtio_net_set_multiqueue(VIRTIO_NET(vdev),
+                              virtio_has_feature(vdev->guest_features, VIRTIO_NET_F_RSS) ||
+                              virtio_has_feature(vdev->guest_features, VIRTIO_NET_F_MQ));
+
+    return 0;
+}
+
 static int virtio_net_post_load_device(void *opaque, int version_id)
 {
     VirtIONet *n = opaque;
@@ -4073,6 +4082,7 @@ static void virtio_net_class_init(ObjectClass *klass, void *data)
     vdc->guest_notifier_mask = virtio_net_guest_notifier_mask;
     vdc->guest_notifier_pending = virtio_net_guest_notifier_pending;
     vdc->legacy_features |= (0x1 << VIRTIO_NET_F_GSO);
+    vdc->pre_load_queues = virtio_net_pre_load_queues;
     vdc->post_load = virtio_net_post_load_virtio;
     vdc->vmsd = &vmstate_virtio_net_device;
     vdc->primary_unplug_pending = primary_unplug_pending;

hw/virtio/virtio.c

@@ -3255,6 +3255,13 @@ virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
         config_len--;
     }
 
+    if (vdc->pre_load_queues) {
+        ret = vdc->pre_load_queues(vdev);
+        if (ret) {
+            return ret;
+        }
+    }
+
     num = qemu_get_be32(f);
 
     if (num > VIRTIO_QUEUE_MAX) {

include/hw/virtio/virtio.h

@@ -210,6 +210,8 @@ struct VirtioDeviceClass {
     void (*guest_notifier_mask)(VirtIODevice *vdev, int n, bool mask);
     int (*start_ioeventfd)(VirtIODevice *vdev);
     void (*stop_ioeventfd)(VirtIODevice *vdev);
+    /* Called before loading queues. Useful to add queues before loading. */
+    int (*pre_load_queues)(VirtIODevice *vdev);
     /* Saving and loading of a device; trying to deprecate save/load
      * use vmsd for new devices.
      */