From 6b2d5dafa9847ce29e5cddeb369b35db5ce076b1 Mon Sep 17 00:00:00 2001 From: Ladi Prosek Date: Thu, 10 Nov 2016 23:00:50 +0100 Subject: [PATCH 7/8] virtio: add virtqueue_rewind() RH-Author: Ladi Prosek Message-id: <1478797251-10302-1-git-send-email-lprosek@redhat.com> Patchwork-id: 72818 O-Subject: [PATCH v2 7/6] virtio: add virtqueue_rewind() Bugzilla: 1377968 RH-Acked-by: Paolo Bonzini RH-Acked-by: Michael S. Tsirkin RH-Acked-by: Miroslav Rezanina 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 Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin (cherry picked from commit 297a75e6c55d91db2704a3d6e4029d99c7df51fd) Signed-off-by: Ladi Prosek Signed-off-by: Miroslav Rezanina --- 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 cdb21b1..fe6b032 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -259,6 +259,28 @@ 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 de32425..d9bfe4c 100644 --- a/include/hw/virtio/virtio.h +++ b/include/hw/virtio/virtio.h @@ -167,6 +167,7 @@ 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); -- 1.8.3.1