From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44230) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bheet-0000s4-BW for qemu-devel@nongnu.org; Wed, 07 Sep 2016 11:21:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bheer-0003QI-0j for qemu-devel@nongnu.org; Wed, 07 Sep 2016 11:21:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47412) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bheeq-0003QE-R0 for qemu-devel@nongnu.org; Wed, 07 Sep 2016 11:21:00 -0400 From: Ladi Prosek Date: Wed, 7 Sep 2016 17:20:48 +0200 Message-Id: <1473261649-31465-3-git-send-email-lprosek@redhat.com> In-Reply-To: <1473261649-31465-1-git-send-email-lprosek@redhat.com> References: <1473261649-31465-1-git-send-email-lprosek@redhat.com> Subject: [Qemu-devel] [PATCH 2/3] virtio: add virtqueue_rewind() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: mst@redhat.com, rkagan@virtuozzo.com, stefanha@redhat.com, lprosek@redhat.com From: Stefan Hajnoczi 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 --- hw/virtio/virtio.c | 22 ++++++++++++++++++++++ include/hw/virtio/virtio.h | 1 + 2 files changed, 23 insertions(+) diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 74c085c..3de6029 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) { 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); -- 2.5.5