Re: [RFC] virtio-blk PCI backend

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Tuesday 20 November 2007, Avi Kivity wrote:
> 
> >
> > Sorry for being late in this thread.
> > We (s390) will need a hypercall as we do not have port I/O. I think it should be
> > possible to default to hypercall on s390 and use pio everywhere else.
> >   
> 
> Or be generic: advertise the methods available according to host 
> (kvm/x86, qemu/x86, kvm/s390) and let the guest pick.

Not sure if I'm following the reasoning here. Shouldn't the method be
inherent to the virtio bus driver?

When you use a PCI based virtio bus, the natural choice would be PIO
in some way, but you could also have a different virtio implementation
on PCI that uses hcalls. This choice is completely up to virtio-pci.

On s390, you have a different virtio backend altogether, so you always
use DIAG or hcall instead of whatever virtio-pci does.

The virtio-blk and other high-level drivers don't need to care about
what transport the bus uses in the first place.

	Arnd <><

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