The previous version did not ensure that the stopped/shutdown event was
handled before a new VM start. This can easily lead to problems like in
QubesOS/qubes-issues#3164.
This improved version now ensures that the stopped/shutdown events are
handled before a new VM start.
Additionally this version should be more robust against unreliable
events from libvirt. It handles missing, duplicated and delayed stopped
events.
Instead of one 'domain-shutdown' event there are now 'domain-stopped'
and 'domain-shutdown'. The later is generated after the former. This way
it's easy to run code after the VM is shutdown including the stop of
it's storage.
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