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Subject: Re: [virtio] Groups - Action Item "Create text version of virtio 0.9.5 document" added

On Wed, 2013-07-31 at 15:51 +0100, Anthony Liguori wrote:
> > On Wed, 2013-07-31 at 14:25 +0100, Anthony Liguori wrote:
> >> I'm not sure where this discussion took place, but there is nothing in
> >> QEMU that requires a dummy device to be used.
> >
> > http://thread.gmane.org/gmane.linux.kernel.virtualization/20144
> N.B.  If you aren't discussing something on qemu-devel, then you aren't
> getting the full input of the community.

The discussion was more about virtio, not qemu. Nevertheless I blame
Peter :-)

> > It is very unsafe to "probe" memory mapped peripherals.
> It simply depends on the devices.

It depends on the architecture and interconnect more than on the device.
I'm not talking about potential dangerous side effects of reading a
device's register. I'm talking about generating a read transaction on a
address not known to the interconnect or - even worse - belonging to a
powered-down device. In such cases you can *completely* lock down the
system. It's not really relevant here - let's just agree that blind
reads are unsafe.

> > Maybe instead of
> > defining zero as a do-nothing-device we should simply make this value
> > reserved or illegal?
> Yes, I think that's a good idea.
> > This would make PCI situation clear (no device will
> > be ever allowed to have it) and mmio driver could "overload" its meaning
> > as "ignore".
> Agreed.

Cool, I'll proceed in this direction then and once we have a base to
work on will submit a patch adding the relevant position to the IDs
list. Then we can argue on the value and naming again :-)


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