virtio: add virtio_detach_element()

During device reset or similar situations a VirtQueueElement needs to be
freed without pushing it onto the used ring or rewinding the virtqueue.
Extract a new function to do this.

Later patches add virtio_detach_element() calls to existing device so
that scatter-gather lists are unmapped and vq->inuse goes back to zero
during device reset.  Currently some devices don't bother and simply
call g_free(elem) which is not a clean way to throw away a
VirtQueueElement.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Ladi Prosek <lprosek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 888c8debe6..e25ec4f0b5 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -155,6 +155,8 @@ void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_num);
 void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len);
 void virtqueue_flush(VirtQueue *vq, unsigned int count);
+void virtqueue_detach_element(VirtQueue *vq, const VirtQueueElement *elem,
+                              unsigned int len);
 void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
                        unsigned int len);
 bool virtqueue_rewind(VirtQueue *vq, unsigned int num);