[Qemu-devel] Re: [PATCH 11/11] QMP: Command-line flag to enable control mode

[Jan Kiszka <jan.kiszka@siemens.com>]

Avi Kivity wrote:
> On 06/23/2009 01:11 PM, Jan Kiszka wrote:
>>> If we support multiple monitors, it might be desirable to allow the
>>> app owning the main 'control' monitor channel to be able to indicate
>>> that additional monitor channels are read-only. eg, so libvirt could
>>> allow the user to connect to the monitor to run 'info' commands for
>>> debug support without risk of having state changed behind its back
>>>      
>>
>> Couldn't libvirt deal with update given we provide them as events?
>> Otherwise, your suggestion makes sense, definitely as long as it would
>> wreck libvirt's internal house keeping or for commands that are not
>> synchronizable.
>>    
> 
> It would be a nightmare, consider both libvirt and a user hotplugging
> something into the same pci slot, or a user starting migration, or
> quitting, or ...

Migration, yes, but hot-plugging is resolvable - given config update events.

> 
> Having -monitor readonly makes sense.

But not for all features, only those libvirt is capable to handle (I
think there are quite a few qemu specifics libvirt does not bother
about) and only as long as there is no proper synchronization. Again,
migration and save/restore will continue to require exclusive access,
but the rest is just a question of proper synchronization IMHO.

See, I don't want to kill my management app just because I attached to a
guest via gdb and start injecting reconfiguration events for testing
purposes (e.g. attach/detach a USB device for which I develop a driver).

Jan

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