Re: [Xen-devel] yanked share problem

[Anthony Liguori <aliguori@xxxxxxxxxx>]

M.A. Williamson wrote:

> > Yes, that's the desired way in most cases, as long as domain crash 
> > event can be notified to xenstore and then watches upon specific node 
> > can work for this purpose. Normal shutdown command issued from user 
> > can follow this process due to driver code aware to send traffic on 
> > xenbus. But abnormal crash may not go to such branch. Maybe we need a 
> > heartbeat check between xenstore and hooked domains? ;-)
>
> When a domain dies (for any reason), a VIRQ_DOM_EXC will be sent to 
> dom0, telling it that something "exceptional" (like being shutdown, or 
> crashing) has happened to a domain. This causes some entity (currently 
> still Xend, AFAIK) to go check the state of all the domains - the 
> store will get updated appropriately as a result of this.
Actually, now the VIRQ_DOM_EXC is delivered to xenstored which results 
in watches on @releaseDomain to be triggered.  Xend set watches on 
@releaseDomain and does the appropriate action.
> This should work even for crashes - in the current world, this 
> mechanism also ensures it's possible to restart domains, clean up 
> their devices, etc if they die unexpectedly.
If you're really concerned about the backend freeing it's resources, the 
most reliable approach (albiet somewhat hacky) is to have the backend 
periodically make a getdomaininfo() call and check to see if shutdown, 
crashed, or dying bits are set and cleanup automatically.
> So watching the store ought to be fine in all cases, so long as dom0 
> stays up (which is another problem ;-)
Until we can kexec() dom0 in place :-)

Regards,

Anthony Liguori

> Cheers,
> Mark
>
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