Re: [PATCH 2/3] hw/9pfs/virtio: disable hotpluggable property of virtio-9p device

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Jul 17, 2026 at 04:05:42PM +0200, Christian Schoenebeck wrote:
> On Monday, 13 July 2026 09:49:35 CEST Igor Mammedov wrote:
> > On Fri, 10 Jul 2026 15:40:04 +0100
> > 
> > Daniel P. Berrangé <berrange@redhat.com> wrote:
> > > On Fri, Jul 10, 2026 at 04:31:51PM +0200, Christian Schoenebeck wrote:
> > > > On Friday, 10 July 2026 14:51:49 CEST Igor Mammedov wrote:
> > > > > On Fri, 10 Jul 2026 12:49:06 +0200
> > > > > 
> > > > > Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:
> > > > > > On Friday, 10 July 2026 12:23:45 CEST Igor Mammedov wrote:
> > > > [...]
> > > > 
> > > > > note: I'm looking from pov of hotpluggable PCI device and generic
> > > > > hotplug
> > > > > infra, only.
> > > > 
> > > > That's okay, but so far I don't see the relevance for this particular 9p
> > > > device.
> > > > 
> > > > > it's not guest users directly, it's how hotplug flow works for various
> > > > > guest OSes:
> > > > > 
> > > > > 1. host plugs device in (-device or device_add)
> > > > > 2. guest OS get's notified one way or another and does what ever guest
> > > > > side
> > > > > 
> > > > >    init needed (incl. mounting share in 9pfs case)
> > > > 
> > > > That's not affected by this patch, right?
> > > > 
> > > > > opposite flow:
> > > > > 1. host does device_del (basically notify guest to remove device)
> > > > > 2. guest OS frees resources and tells qemu to delete device
> > > > > 3. qemu process remove event (which incl. unrealize as part of
> > > > > destroying
> > > > > device)
> > > > 
> > > > And that's not affected by this patch either, right?
> > 
> > the patch would break unplug flow by effectively removing 'eject' knob
> > from guest side, which is part of unplug flow.
> 
> These are two different things: device_del would not be affected by this. 
> 
> 1. Ejecting the device from host side e.g. via QMP would still work.
> 
> vs.
> 
> 2. Ejecting from guest side OTOH would be disabled.
> 
> It is also different from regular block devices where you have convenient ways
> to eject a block device on guest OSes. For a virtio-9p device it is not that
> easy.

Igor can correct me if I'm wrong, but IIUC there's no distinction
to those 2 scenarios from the guest POV.

A "device_del" in QMP does not actually delete a device from the
QEMU POV.  Rather it triggers an ACPI notification to the geust
OS, that the operator wants to unplug the device.  The guest OS
then honours (or not) that by initiating a guest side "eject".
IOW disabling guest initiated eject would break device_del too
AFAIK.

With regards,
Daniel
-- 
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