virtio: generation counter support

Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-pci.c

@@ -977,7 +977,7 @@ static uint64_t virtio_pci_common_read(void *opaque, hwaddr addr,
         val = vdev->status;
         break;
     case VIRTIO_PCI_COMMON_CFGGENERATION:
-        val = 0; /* TODO */
+        val = vdev->generation;
         break;
     case VIRTIO_PCI_COMMON_Q_SELECT:
         val = vdev->queue_sel;

hw/virtio/virtio.c

@@ -930,6 +930,7 @@ void virtio_notify_config(VirtIODevice *vdev)
         return;
 
     vdev->isr |= 0x03;
+    vdev->generation++;
     virtio_notify_vector(vdev, vdev->config_vector);
 }
 

include/hw/virtio/virtio.h

@@ -78,6 +78,7 @@ struct VirtIODevice
     size_t config_len;
     void *config;
     uint16_t config_vector;
+    uint32_t generation;
     int nvectors;
     VirtQueue *vq;
     uint16_t device_id;