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Re: [Xen-API] [ACS4.4, XenServer] Problem starting system VMs

On 01/05/14 11:35, Dave Scott wrote:
> Hi,
> I think I’ve tracked this down. I believe it’s a bug in the XenServer’s event 
> mechanism, specifically a bug where some shared state causes parallel calls 
> to event.from to interfere with each other. From CloudStack’s point of view 
> this manifests as
> * spurious SESSION_INVALID exceptions in waitForTask, which triggers cleanup 
> (Task.destroy), which prevents the VM.start from completing, leaving the VM 
> paused
> * empty lists of events being returned in non-timeout cases
> I’ve prototyped a fix together with a test case (which fails before and 
> passes after) and made a pull request containing both:
> https://github.com/xapi-project/xen-api/pull/1719

Pull request looks very nice. Your second bullet point was due to the
fact that the autogenerated code couldn't cope with the immutable
database being passed in, so we're generating the snapshots from the
live db. I believe this has now changed and we can associate a database
snapshot with a context, so we could make that problem go away
completely rather than looping until the problem doesn't happen :-)

I think the snapshots fix is a nice-to-have though, so if you could make
a PR for master rather than the clearwater branch, I'll merge.


> I’d appreciate review from xapi experts, particularly Jon Ludlam (cc:d). I’ve 
> also cc:d the main xapi development list.
> Cheers,
> Dave

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