Re: qom device lifecycle interaction with hotplug/hotunplug ?

[Damien Hedde <damien.hedde@greensocs.com>]

On 11/29/19 1:45 PM, Peter Maydell wrote:
> On Fri, 29 Nov 2019 at 12:26, Igor Mammedov <imammedo@redhat.com> wrote:
>> But from the my very limited understanding, on real hardware,
>> once device is uplugged it's gone (finalized) from machine
>> perspective, so it's unclear to my why someone would use
>> realize->unrealize->realize hotplug scenario.
> 
> Well, on real hardware 'unplug' is different from 'unrealize'.
> So I think for QEMU if we wanted to allow this sort of 'unplug
> and replug the same device' we should do it by:
> 
>  instance_init -> realize -> plug -> unplug -> plug -> unplug ->
>    unrealize -> finalize
> 
> So unrealize/finalize is when the device is actually destroyed,
> and if you're going to replug the device you don't destroy it
> on unplug.
> 

Hello everybody,

What I was initially wondering (or afraid of) when this question/problem
comes to me is;
Are there some cases where QEMU does the following (in the context of an
hotplugged device):

instance_init -> realize (and plug) -> unrealize -> change some
properties -> realize
with no unplug / plug in between

because I have the impression, the realize was here to allow setting
properties. But it may be pure nonsense as I do not know well the
underlying mechanisms there.

Regards,
--
Damien