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Re: [Qemu-devel] [PATCH v3 21/22] virtio-pmem: hotplug support functions

From: David Gibson
Subject: Re: [Qemu-devel] [PATCH v3 21/22] virtio-pmem: hotplug support functions
Date: Tue, 25 Sep 2018 14:44:18 +1000
User-agent: Mutt/1.10.1 (2018-07-13)

On Mon, Sep 24, 2018 at 09:57:35AM +0200, David Hildenbrand wrote:
> On 24/09/2018 08:44, David Gibson wrote:
> > On Thu, Sep 20, 2018 at 12:32:42PM +0200, David Hildenbrand wrote:
> >> virtio-pmem devices will have to be hotplugged using the machine hotplug
> >> handler just like other memory devices. Therefore, all machines that
> >> want to support virtio-pmem will have to modify their machine hotplug
> >> handler.
> >>
> >> virtio-pmem devices are realized when their parent proxy device
> >> (virtio-pmem-pci) is realized. Therefore, they are attached to a bus
> >> without a hotplug handler. This makes things a lot easier, because
> >> without a hotplug handler, we can directly get control over the device
> >> in the machine hotplug handler (otherwise we would have to overwrite
> >> control and pass control to the bus hotplug handler from the machine
> >> hotplug handler).
> >>
> >> As we have to implement support for each machine we want to support,
> >> add a safety net ("pre_plugged") that catches if the pre_plug handler
> >> was not called - if trying to realize it with a machine that does not
> >> support it.
> >>
> >> Otherwise creating and realizing virtio-pmem-pci along with virtio-pmem
> >> would work, however the memory-device part would not properly get
> >> hotplugged.
> >>
> >> Signed-off-by: David Hildenbrand <address@hidden>
> > 
> > I'm thinking through how we'd make this work for pseries guests.
> > 
> > Am I right in thinking that the stuff here is purely for getting the
> > wiring correct on the qemu side.  On the guest side, the hotplug event
> > for the proxy device should be sufficient to trigger all the necessary
> > stuff.  Is that right?
> Yes, this is just wiring for to get the address assigned and the memory
> region properly registered in guest physical address space. The "real"
> hotplug ("notification") happens via the proxy device. Just like
> detection and hotplug of other virtio devices (e.g. virtio-balloon).

Ok, that should be easy then.

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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