[libvirt] RFC: Domain events add DEFINED and UNDEFINED events

[Daniel P. Berrange]

On Fri, Nov 07, 2008 at 07:12:46AM -0500, Ben Guthro wrote:
> I think this sounds reasonable.
> 
> Let me see if I understand the state machine for a newly created persistent domain:
> DEFINED->ADDED->STARTED->STOPPED

Actually, swap ADDED & DEFINED, and for completeness, if I
add in an virDomainUndefine, you'd get

 ADDED->DEFINED->STARTED->STOPPED->UNDEFINED->REMOVED

> 
> Starting, then stopping a previously defined persistent domain would just emit 
> STARTED->STOPPED
> 
> and a transient domain would be:
> ADDED->STARTED->STOPPED->REMOVED

Yes, that's one possible path. If you were to define a config
for an existing transient domain though you could end up with

  ADDED->STARTED->DEFINED->STOPPED->UNDEFINED->REMOVED

> Will it be an issue for domains that only support a 
> subset of these events (like xen)

I think it is inevitable that this happens, so we likely
want some way to inform the application what events are
available for the driver.

> Yesterday, I began looking into creating a xen driver patch for emitting the DEFINED/UNDEFINED events via inotify.
> It looks like the easiest way to do this right now is to create yet another Xen sub-driver.
> I don't expect this to take an extremely long time, as this tutorial from IBM makes it fairly straightforward to understand:
> http://www-128.ibm.com/developerworks/linux/library/l-inotify.html

The experimental user mode linux driver has some iNotify code in
it too if you want another point of reference. See the
umlInotifyEvent() method umlStartup() where I register for the
events

http://www.redhat.com/archives/libvir-list/2008-October/msg00355.html

Daniel
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