[libvirt] Re: [Qemu-devel] [PATCH 1/6] Allow multiple monitor devices (v2)

Jan Kiszka jan.kiszka at siemens.com
Tue Apr 14 09:29:30 UTC 2009

Daniel P. Berrange wrote:
> On Tue, Apr 14, 2009 at 12:15:23PM +0300, Avi Kivity wrote:
>> Daniel P. Berrange wrote:
>>> Yes indeed its a little crazy :-)  As anthony mentioned if libvirt were 
>>> able to be notified of changes a user makes in the monitor, there's no 
>>> reason we could not allow end users to access the monitor of a VM 
>>> libvirt is managing. We just need to make sure libvirt doesn't miss
>>> changes like attaching or detaching block devices, etc, because that'll
>>> cause crash/data loss later when libvirt migrates or does save/restore,
>>> etc because it'll launch QEMU with wrong args
>> You still have an inherent race here.
>> user: plug in disk
>> libvirt: start migration, still without disk
>> qemu: libvirt, a disk has been plugged in.
> That is true, but we'd still be considering direct monitor access to
> be a 'expert' user mode of use. If they wish to shoot themselves in
> the foot by triggering a migration at same time they are hotplugging
> I'm fine if their whole leg gets blown away.  

...while there is also nothing that speaks against blocking any device
hot-plugging while migration is ongoing. Independent of if there is some
management app involved or the user himself plays with multiple monitors.


Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux

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