Re: [Qemu-devel] [PATCH 2/3] virtio-balloon: note optional features

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 06, 2012 at 01:22:06PM +0100, Paolo Bonzini wrote:
> It is not a problem if the destination does not have
> VIRTIO_BALLOON_F_MUST_TELL_HOST.  In that case, the guest
> will simply do useless virtqueue traffic, but the destination
> does not have a problem.
> (In fact, it _is_ a problem if the destination has
> VIRTIO_BALLOON_F_MUST_TELL_HOST but the source does not.
> The feature bit should have been backwards!  Luckily,
> our implementation is free from this problem).
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Can't we just add a flag to control this feature?

> ---
>  hw/virtio-balloon.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
> index 0ade8b0..d10df2e 100644
> --- a/hw/virtio-balloon.c
> +++ b/hw/virtio-balloon.c
> @@ -216,7 +216,7 @@ static int virtio_balloon_load(QEMUFile *f, void *opaque, int version_id)
>      if (version_id != 1)
>          return -EINVAL;
>  
> -    ret = virtio_load(&s->vdev, f, 0);
> +    ret = virtio_load(&s->vdev, f, VIRTIO_BALLOON_F_MUST_TELL_HOST);
>      if (ret) {
>          return ret;
>      }
> -- 
> 1.7.7.6
>