From: Stefan Hajnoczi <stefa...@redhat.com>
virtqueue_discard() requires a VirtQueueElement but virtio-balloon does
not migrate its in-use element. Introduce a new function that is
similar to virtqueue_discard() but doesn't require a VirtQueueElement.
This will allow virtio-balloon to access element again after migration
with the usual proviso that the guest may have modified the vring since
last time.
Cc: Michael S. Tsirkin <m...@redhat.com>
Cc: Roman Kagan <rka...@virtuozzo.com>
Cc: Stefan Hajnoczi <stefa...@redhat.com>
Signed-off-by: Ladi Prosek <lpro...@redhat.com>
Reviewed-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
include/hw/virtio/virtio.h | 1 +
hw/virtio/virtio.c | 22 ++++++++++++++++++++++
2 files changed, 23 insertions(+)
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index d2490c1..f05559d 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);
+bool virtqueue_rewind(VirtQueue *vq, unsigned int num);
void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len, unsigned int idx);
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index e8a13a5..fcf3358 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -272,6 +272,28 @@ void virtqueue_discard(VirtQueue *vq, const
VirtQueueElement *elem,
virtqueue_unmap_sg(vq, elem, len);
}
+/* virtqueue_rewind:
+ * @vq: The #VirtQueue
+ * @num: Number of elements to push back
+ *
+ * Pretend that elements weren't popped from the virtqueue. The next
+ * virtqueue_pop() will refetch the oldest element.
+ *
+ * Use virtqueue_discard() instead if you have a VirtQueueElement.
+ *
+ * Returns: true on success, false if @num is greater than the number of in use
+ * elements.
+ */
+bool virtqueue_rewind(VirtQueue *vq, unsigned int num)
+{
+ if (num > vq->inuse) {
+ return false;
+ }
+ vq->last_avail_idx -= num;
+ vq->inuse -= num;
+ return true;
+}
+
void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len, unsigned int idx)
{
--
MST
