From 297a75e6c55d91db2704a3d6e4029d99c7df51fd Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 7 Sep 2016 17:20:48 +0200 Subject: 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 Cc: Roman Kagan Cc: Stefan Hajnoczi Signed-off-by: Ladi Prosek Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- hw/virtio/virtio.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'hw') 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) { -- cgit v1.2.3