[Qemu-devel] [PATCH 1/2] virtio: add virtqueue_rewind

[Roman Kagan <rkagan@virtuozzo.com>]

If the in-use elements aren't migrated (like is the case with
virtio-balloon stats vq), make virtqueue forget about them and pretend
they haven't been popped yet, to allow to start over on load.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Ladi Prosek <lprosek@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/virtio/virtio.c         | 6 ++++++
 include/hw/virtio/virtio.h | 1 +
 2 files changed, 7 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 74c085c..844d2a1 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -272,6 +272,12 @@ void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
     virtqueue_unmap_sg(vq, elem, len);
 }
 
+void virtqueue_rewind(VirtQueue *vq)
+{
+    vq->last_avail_idx -= vq->inuse;
+    vq->inuse = 0;
+}
+
 void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len, unsigned int idx)
 {
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index d2490c1..9f49fa4 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -154,6 +154,7 @@ void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
 void virtqueue_flush(VirtQueue *vq, unsigned int count);
 void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
                        unsigned int len);
+void virtqueue_rewind(VirtQueue *vq);
 void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len, unsigned int idx);
 
-- 
2.7.4