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virtio: add virtio_detach_element()

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During device reset or similar situations a VirtQueueElement needs to be
freed without pushing it onto the used ring or rewinding the virtqueue.
Extract a new function to do this.

Later patches add virtio_detach_element() calls to existing device so
that scatter-gather lists are unmapped and vq->inuse goes back to zero
during device reset.  Currently some devices don't bother and simply
call g_free(elem) which is not a clean way to throw away a
VirtQueueElement.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Ladi Prosek <lprosek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2016-09-19 14:28:03 +01:00 committed by Michael S. Tsirkin
parent af78c91f57
commit 2640d2a5ff
2 changed files with 27 additions and 2 deletions
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27
hw/virtio/virtio.c
View File

@ -264,12 +264,35 @@ static void virtqueue_unmap_sg(VirtQueue *vq, const VirtQueueElement *elem,
0, elem->out_sg[i].iov_len);
}
/* virtqueue_detach_element:
* @vq: The #VirtQueue
* @elem: The #VirtQueueElement
* @len: number of bytes written
*
* Detach the element from the virtqueue. This function is suitable for device
* reset or other situations where a #VirtQueueElement is simply freed and will
* not be pushed or discarded.
*/
void virtqueue_detach_element(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len)
{
vq->inuse--;
virtqueue_unmap_sg(vq, elem, len);
}
/* virtqueue_discard:
* @vq: The #VirtQueue
* @elem: The #VirtQueueElement
* @len: number of bytes written
*
* Pretend the most recent element wasn't popped from the virtqueue. The next
* call to virtqueue_pop() will refetch the element.
*/
void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len)
{
vq->last_avail_idx--;
vq->inuse--;
virtqueue_unmap_sg(vq, elem, len);
virtqueue_detach_element(vq, elem, len);
}
/* virtqueue_rewind:

2
include/hw/virtio/virtio.h
View File

@ -155,6 +155,8 @@ void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_num);
void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len);
void virtqueue_flush(VirtQueue *vq, unsigned int count);
void virtqueue_detach_element(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len);
void virtqueue_discard(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len);
bool virtqueue_rewind(VirtQueue *vq, unsigned int num);