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virtio-balloon: return empty data when no stats are available

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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>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Ján Tomko 2014-05-21 11:03:47 +02:00 committed by Michael S. Tsirkin
parent 7c8b724826
commit 38dbd48b24
2 changed files with 5 additions and 7 deletions
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5
docs/virtio-balloon-stats.txt
View File

@ -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

7
hw/virtio/virtio-balloon.c
View File

@ -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);