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Revision 973603a8

ID973603a813c5d60534b4fa0313f83be40e2b9c47

Added by Daniel P. Berrange almost 12 years ago

Add event notification for guest balloon changes

After setting a balloon target value, applications have to
continually poll 'query-balloon' to determine whether the
guest has reacted to this request. The virtio-balloon backend
knows exactly when the guest has reacted though, and thus it
is possible to emit a JSON event to tell the mgmt application
whenever the guest balloon changes.

This introduces a new 'qemu_balloon_changed()' API which is
to be called by balloon driver backends, whenever they have
a change in balloon value. This takes the 'actual' balloon
value, as would be found in the BalloonInfo struct.

The qemu_balloon_change API emits a JSON monitor event which
looks like:

{"timestamp": {"seconds": 1337162462, "microseconds": 814521},
   "event": "BALLOON_CHANGE", "data": {"actual": 944766976}}
  • balloon.c, balloon.h: Introduce qemu_balloon_changed() for
    emitting balloon change events on the monitor
  • hw/virtio-balloon.c: Invoke qemu_balloon_changed() whenever
    the guest changes the balloon actual value
  • monitor.c, monitor.h: Define QEVENT_BALLOON_CHANGE

Signed-off-by: Daniel P. Berrange <>
Acked-by: Amit Shah <>
Signed-off-by: Luiz Capitulino <>

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