Re: qom device lifecycle interaction with hotplug/hotunplug ?

[Eduardo Habkost]

On Fri, Nov 29, 2019 at 12:45:09PM +0000, Peter Maydell wrote:
> On Fri, 29 Nov 2019 at 12:26, Igor Mammedov <address@hidden> 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.

So, to summarize the current issues:

1) realize triggers a plug operation implicitly.
2) unplug triggers unrealize implicitly.

Do you expect to see use cases that will require us to implement
realize-without-plug?

Similarly, do you expect use cases that will require us to
implement unplug-without-unrealize?

-- 
Eduardo