[fedora-virt] 'eject' on a KVM guest

[Daniel P. Berrange]

On Mon, Oct 19, 2009 at 02:49:52PM +0100, Matthew Booth wrote:
> On 19/10/09 14:38, Daniel P. Berrange wrote:
> >On Mon, Oct 19, 2009 at 09:35:04AM -0400, Cole Robinson wrote:
> >>On 10/19/2009 05:47 AM, Matthew Booth wrote:
> >>>What does the eject (to eject a CD) command do to a KVM guest? It
> >>>succeeds, and the result is that the device can no longer be mounted.
> >>>However, looking at the domain XML reveals it hasn't disconnected the
> >>>backing file.
> >>>
> >>>Matt
> >>
> >>It should be the equivalent of ejecting a CD or floppy on a physical
> >>machine.
> >>
> >>If you do this through libvirt (with the attach-device command and
> >>suitable XML string), then the change should be reflected in the XML.
> >>
> >>If you managed to send a monitor command to the KVM guest that didn't go
> >>through libvirt, the change wouldn't be reflected in the domain XML for
> >>the majority of operations (media eject included).
> >
> >I think the problem Matt sees is from running 'eject' inside the guest.
> >libvirt will not see that, because KVM has no way to notify us that the
> >guest ejected the media.
> 
> That's it. Re-reading, that wasn't clear from my original question.
> 
> >Fortunately, the new KVM monitor control protocol includes support for
> >this notification, so we'll be able to address this limitation in the
> >future.
> 
> Sounds good. Any idea what the timeframe might be for that?

When QEMU developers agree on the implementation of the new protocol...

> 
> To put this in context, I was trying to think of an existing way a guest 
> can modify its environment. I was thinking that if you configured a boot 
> order of cdrom, hd, and attached a custom LiveCD, the LiveCD could do 
> its thing and then eject itself, booting from hd next time with no 
> administrative intervention. Could that ever work?

Yes, that kind of thing is supposed to work.


Daniel
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