Commit 297a75e6 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Michael S. Tsirkin
Browse files

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: default avatarLadi Prosek <lprosek@redhat.com>
Reviewed-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 104e70ca

hw/virtio/virtio.c

+22 −0
Original line number Diff line number Diff line
@@ -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)

{

include/hw/virtio/virtio.h

+1 −0
Original line number Diff line number Diff line
@@ -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);