It provides fuzzer a reliable way to wait for a sequence of events
to complete for virtio-devices while not using a fixed timeout to
maintain the full speed of fuzzing.
Take virtio-block as an example, the 'queue event' with a valid
available queue setup can trigger a 'completion event'. This is a
meaningful virtio-block code path of processing guest inputs which is
our target for fuzzing virtio devices.
Signed-off-by: Bo Chen <chen.bo@intel.com>
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