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authorStefan Hajnoczi <stefanha@redhat.com>2016-09-07 17:20:48 +0200
committerMichael S. Tsirkin <mst@redhat.com>2016-09-09 20:58:34 +0300
commit297a75e6c55d91db2704a3d6e4029d99c7df51fd (patch)
tree43f752f0502cecc089680c1a08dc6b5cb6c3da9c /hw
parent104e70cae78bd4afd95d948c6aff188f10508a9c (diff)
virtio: add virtqueue_rewind()
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 <mst@redhat.com> Cc: Roman Kagan <rkagan@virtuozzo.com> Cc: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Ladi Prosek <lprosek@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Diffstat (limited to 'hw')
-rw-r--r--hw/virtio/virtio.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index e8a13a50bf..fcf3358d6c 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)
{