From: Stefan Hajnoczi <stefa...@redhat.com>
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 <stefa...@redhat.com>
Acked-by: Greg Kurz <gr...@kaod.org>
Reviewed-by: Ladi Prosek <lpro...@redhat.com>
Reviewed-by: Michael S. Tsirkin <m...@redhat.com>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
include/hw/virtio/virtio.h | 2 ++
hw/virtio/virtio.c | 27 +++++++++++++++++++++++++--
2 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 888c8de..e25ec4f 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -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);
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 18ce333..46f79c9 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -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:
--
MST
