Re: [Qemu-devel] [PATCH v2] virtio-balloon: return empty data when no stats are available

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

On Wed, May 21, 2014 at 11:03:47AM +0200, Ján Tomko wrote:
> If the guest hasn't updated the stats yet, instead of returning
> an error, return '-1' for the stats and '0' as 'last-update'.
> 
> This lets applications ignore this without parsing the error message.
> 
> Related libvirt patch and discussion:
> https://www.redhat.com/archives/libvir-list/2014-May/msg00460.html
> 
> Tested against current upstream libvirt - stat reporting works and
> it no longer logs errors when the stats are queried on domain startup.
> (Note: libvirt doesn't use the last-update field for anything yet)
> 
> Signed-off-by: Ján Tomko <jtomko@redhat.com>


Applied, thanks!

> ---
> v1: https://lists.gnu.org/archive/html/qemu-devel/2014-05/msg03643.html
>   Reviewed-by: Eric Blake <eblake@redhat.com>
> v2:
>   rebased
>   added documentation changes
>   mentioned testing in the commit message
> 
>  docs/virtio-balloon-stats.txt | 5 +++--
>  hw/virtio/virtio-balloon.c    | 7 ++-----
>  2 files changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/docs/virtio-balloon-stats.txt b/docs/virtio-balloon-stats.txt
> index f74612f..edff5f2 100644
> --- a/docs/virtio-balloon-stats.txt
> +++ b/docs/virtio-balloon-stats.txt
> @@ -35,7 +35,8 @@ which will return a dictionary containing:
>  
>    o A key named last-update, which contains the last stats update
>      timestamp in seconds. Since this timestamp is generated by the host,
> -    a buggy guest can't influence its value
> +    a buggy guest can't influence its value. The value is 0 if the guest
> +    has not updated the stats (yet).
>  
>  It's also important to note the following:
>  
> @@ -49,7 +50,7 @@ It's also important to note the following:
>  
>   - Polling can be enabled even if the guest doesn't have stats support
>     or the balloon driver wasn't loaded in the guest. If this is the case
> -   and stats are queried, an error will be returned
> +   and stats are queried, last-update will be 0.
>  
>   - The polling timer is only re-armed when the guest responds to the
>     statistics request. This means that if a (buggy) guest doesn't ever
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index bf2b588..22cd52e 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -112,11 +112,6 @@ static void balloon_stats_get_all(Object *obj, struct Visitor *v,
>      VirtIOBalloon *s = opaque;
>      int i;
>  
> -    if (!s->stats_last_update) {
> -        error_setg(errp, "guest hasn't updated any stats yet");
> -        return;
> -    }
> -
>      visit_start_struct(v, NULL, "guest-stats", name, 0, &err);
>      if (err) {
>          goto out;
> @@ -378,6 +373,8 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>      s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>      s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
>  
> +    reset_stats(s);
> +
>      register_savevm(dev, "virtio-balloon", -1, 1,
>                      virtio_balloon_save, virtio_balloon_load, s);
>  
> -- 
> 1.8.3.2