Re: [PATCH v7 04/12] vhost: Do not depend on !NULL VirtQueueElement on vhost_svq_flush

[Jason Wang]

On Fri, Aug 5, 2022 at 2:29 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> Since QEMU will be able to inject new elements on CVQ to restore the
> state, we need not to depend on a VirtQueueElement to know if a new
> element has been used by the device or not. Instead of check that, check
> if there are new elements only using used idx on vhost_svq_flush.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---

Acked-by: Jason Wang <jasowang@redhat.com>

> v6: Change less from the previous function
> ---
>  hw/virtio/vhost-shadow-virtqueue.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> index 1b49bf54f2..f863b08627 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -499,17 +499,20 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
>  size_t vhost_svq_poll(VhostShadowVirtqueue *svq)
>  {
>      int64_t start_us = g_get_monotonic_time();
> +    uint32_t len;
> +
>      do {
> -        uint32_t len;
> -        VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
> -        if (elem) {
> -            return len;
> +        if (vhost_svq_more_used(svq)) {
> +            break;
>          }
>
>          if (unlikely(g_get_monotonic_time() - start_us > 10e6)) {
>              return 0;
>          }
>      } while (true);
> +
> +    vhost_svq_get_buf(svq, &len);
> +    return len;
>  }
>
>  /**
> --
> 2.31.1
>