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virtio: Introduce virtqueue_drop_all procedure

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Add procedure for fast drop of queued packets, acting like
pop and push without mapping the buffers into memory.

Signed-off-by: Yuri Benditovich <yuri.benditovich@daynix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Yuri Benditovich 2016-12-13 10:12:07 +02:00 committed by Michael S. Tsirkin
parent aa94d52142
commit 54e17709ac
2 changed files with 39 additions and 0 deletions
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38
hw/virtio/virtio.c
View File

@ -783,6 +783,44 @@ err_undo_map:
return NULL;
}
/* virtqueue_drop_all:
* @vq: The #VirtQueue
* Drops all queued buffers and indicates them to the guest
* as if they are done. Useful when buffers can not be
* processed but must be returned to the guest.
*/
unsigned int virtqueue_drop_all(VirtQueue *vq)
{
unsigned int dropped = 0;
VirtQueueElement elem = {};
VirtIODevice *vdev = vq->vdev;
bool fEventIdx = virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
if (unlikely(vdev->broken)) {
return 0;
}
while (!virtio_queue_empty(vq) && vq->inuse < vq->vring.num) {
/* works similar to virtqueue_pop but does not map buffers
* and does not allocate any memory */
smp_rmb();
if (!virtqueue_get_head(vq, vq->last_avail_idx, &elem.index)) {
break;
}
vq->inuse++;
vq->last_avail_idx++;
if (fEventIdx) {
vring_set_avail_event(vq, vq->last_avail_idx);
}
/* immediately push the element, nothing to unmap
* as both in_num and out_num are set to 0 */
virtqueue_push(vq, &elem, 0);
dropped++;
}
return dropped;
}
/* Reading and writing a structure directly to QEMUFile is *awful*, but
* it is what QEMU has always done by mistake. We can change it sooner
* or later by bumping the version number of the affected vm states.

1
include/hw/virtio/virtio.h
View File

@ -173,6 +173,7 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
void virtqueue_map(VirtIODevice *vdev, VirtQueueElement *elem);
void *virtqueue_pop(VirtQueue *vq, size_t sz);
unsigned int virtqueue_drop_all(VirtQueue *vq);
void *qemu_get_virtqueue_element(VirtIODevice *vdev, QEMUFile *f, size_t sz);
void qemu_put_virtqueue_element(QEMUFile *f, VirtQueueElement *elem);
int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes,