Re: [Qemu-devel] [PATCH 0/3] add hotplug opt-out option for devices.

[Gerd Hoffmann <kraxel@redhat.com>]

> I understand why you're adding this but this is one of those horrible
> abuses of qdev that we really need to avoid.
>
> There are two valid reasons why hotplug is not possible:
>
> 1) Hotplugging is not supported by the *slot*.  This is something that
> needs to be exposes through ACPI. This is not a qdev property, but a
> property of a PCI slot.

Well, yea, right.  Sort of.  The ACPI thing applies to some of the slots 
only.  But, yes, strictly speaking this is a slot not a device property 
in the case of PCI.  Problem is qemu doesn't really has an idea what a 
pci slot is ...

> It's very important that we do this correctly
> because Windows puts a little icon in the systray that advertises
> quick-removal of devices in slots that support hotplug.

Indeed.

> 2) The PCI device is soldered to the MB or is otherwise not part of a
> PCI slot. Again, this is part of the ACPI definition.

(3) The qemu emulation can't handle hot-unplug.

> Since the PIIX3 lives in slot 1, our ACPI tables should not advertise
> slot 0 or slot 1 as supporting hotplug.

They do currently.  Should be easily fixable.

> Hotplug information has no business being part of the core qdev
> structures. Hotplug is a PCI concept and the information needs to live
> at the PCI layer to be meaningfully.

Wrong.  PCI certainly isn't the only bus which supports hotplug.  It 
*does* make sense to handle generic hotplug stuff at qdev level.

> An ideal interface would explicitly allow a user to mark a series of PCI
> slots as no supporting hotplug. It would be convenient in order to
> ensure that your virtio-net wasn't accidentally ejected by a click-happy
> Windows user.

Indeed.  That one is a bit harder I suspect.  Can this be done without 
generating acpi tables dynamically?

cheers,
   Gerd