[Qemu-devel] Is it necessary to add a Monitor event of QEVENT_DEVICE_ADDED

[Qemu-devel] Is it necessary to add a Monitor event of QEVENT_DEVICE_ADDED

[xiexiangyou]

Hi all,

   As we know, when hot-add a device, we don't know whether the device is present in VM from outside(like libvirt).
However, unplugging device, when complete remove the device, Qemu will generate a Monitor event,QEVENT_DEVICE_DELETED.
Libvirt can receive the event and do something.
   So is it necessary to add a Monitor event of completing add device such as QEVENT_DEVICE_ADDED.

Regards,
-xie

Re: [Qemu-devel] Is it necessary to add a Monitor event of QEVENT_DEVICE_ADDED

[Michael S. Tsirkin]

On Thu, Apr 03, 2014 at 05:02:56PM +0800, xiexiangyou wrote:
> Hi all,
> 
>    As we know, when hot-add a device, we don't know whether the device is present in VM from outside(like libvirt).
> However, unplugging device, when complete remove the device, Qemu will generate a Monitor event,QEVENT_DEVICE_DELETED.
> Libvirt can receive the event and do something.
>    So is it necessary to add a Monitor event of completing add device such as QEVENT_DEVICE_ADDED.
> 
> Regards,
> -xie

I don't know.
We have QEVENT_DEVICE_DELETED so libvirt doesn't do things like reuse
the slot.  But what would be the point of QEVENT_DEVICE_ADDED?

-- 
MST

Re: [Qemu-devel] Is it necessary to add a Monitor event of QEVENT_DEVICE_ADDED

[Eric Blake]

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On 04/03/2014 03:02 AM, xiexiangyou wrote:
> Hi all,
> 
>    As we know, when hot-add a device, we don't know whether the device is present in VM from outside(like libvirt).
> However, unplugging device, when complete remove the device, Qemu will generate a Monitor event,QEVENT_DEVICE_DELETED.
> Libvirt can receive the event and do something.
>    So is it necessary to add a Monitor event of completing add device such as QEVENT_DEVICE_ADDED.

DEVICE_DELETED is important because the operation is still underway even
after the initial monitor command returns control to libvirt, because
there is guest interaction involved.  But for hotplug, the monitor
command doesn't return until the action is complete, and no guest
interaction is required to know that the action was completed; so I
don't see the use case for an event.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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