virtio: Migration helper function and macro

To make conversion of virtio devices to VMState simple
at first add a helper function for the simple virtio_save
case and a helper macro that defines the VMState structure.
These will probably go away or change as more of the virtio
code gets converted.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio.c

@@ -1464,6 +1464,12 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f)
     vmstate_save_state(f, &vmstate_virtio, vdev, NULL);
 }
 
+/* A wrapper for use as a VMState .put function */
+void virtio_vmstate_save(QEMUFile *f, void *opaque, size_t size)
+{
+    virtio_save(VIRTIO_DEVICE(opaque), f);
+}
+
 static int virtio_set_features_nocheck(VirtIODevice *vdev, uint64_t val)
 {
     VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);

include/hw/virtio/virtio.h

@@ -171,6 +171,26 @@ bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq);
 void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
 
 void virtio_save(VirtIODevice *vdev, QEMUFile *f);
+void virtio_vmstate_save(QEMUFile *f, void *opaque, size_t size);
+
+#define VMSTATE_VIRTIO_DEVICE(devname, v, getf, putf) \
+    static const VMStateDescription vmstate_virtio_ ## devname = { \
+        .name = "virtio-" #devname ,          \
+        .minimum_version_id = v,              \
+        .version_id = v,                      \
+        .fields = (VMStateField[]) {          \
+            {                                 \
+                .name = "virtio",             \
+                .info = &(const VMStateInfo) {\
+                        .name = "virtio",     \
+                        .get = getf,          \
+                        .put = putf,          \
+                    },                        \
+                .flags = VMS_SINGLE,          \
+            },                                \
+            VMSTATE_END_OF_LIST()             \
+        }                                     \
+    }
 
 int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id);