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>
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