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

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

[Ján Tomko]

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>
---
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

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

[Eric Blake]

[-- Attachment #1: Type: text/plain, Size: 1080 bytes --]

On 05/21/2014 03:03 AM, 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>
> ---
> 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

Additional commit message and doc changes are good.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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

[Michael S. Tsirkin]

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