virtio: introduce qemu_get/put_virtqueue_element

Move allocation to virtio functions also when loading/saving a
VirtQueueElement.  This will also let the load/save functions
keep backwards compatibility when the VirtQueueElement layout
is changed.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index bf70b52..c427698 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -808,8 +808,7 @@
 
     while (req) {
         qemu_put_sbyte(f, 1);
-        qemu_put_buffer(f, (unsigned char *)&req->elem,
-                        sizeof(VirtQueueElement));
+        qemu_put_virtqueue_element(f, &req->elem);
         req = req->next;
     }
     qemu_put_sbyte(f, 0);
@@ -832,14 +831,11 @@
     VirtIOBlock *s = VIRTIO_BLK(vdev);
 
     while (qemu_get_sbyte(f)) {
-        VirtIOBlockReq *req = g_new(VirtIOBlockReq, 1);
+        VirtIOBlockReq *req;
+        req = qemu_get_virtqueue_element(f, sizeof(VirtIOBlockReq));
         virtio_blk_init_request(s, req);
-        qemu_get_buffer(f, (unsigned char *)&req->elem,
-                        sizeof(VirtQueueElement));
         req->next = s->rq;
         s->rq = req;
-
-        virtqueue_map(&req->elem);
     }
 
     return 0;