Re: [Alacrityvm-devel] [PATCH v3 3/6] vbus: add a "vbus-proxy" bus model for vbus_driver objects

[Stefan Hajnoczi]

On Wed, Aug 19, 2009 at 10:05 PM, Hollis Blanchard<hollisb@xxxxxxxxxx> wrote:
> On Wed, 2009-08-19 at 19:38 +0300, Avi Kivity wrote:
>> On 08/19/2009 07:29 PM, Ira W. Snyder wrote:
>> >>> That said, I'm not sure how qemu-system-ppc running on x86 could
>> >>> possibly communicate using virtio-net. This would mean the guest is an
>> >>> emulated big-endian PPC, while the host is a little-endian x86. I
>> >>> haven't actually tested this situation, so perhaps I am wrong.

Cross-platform virtio works when endianness is known in advance.  For
a hypervisor and a guest:
1. virtio-pci I/O registers use PCI endianness
2. vring uses guest endianness (hypervisor must byteswap)
3. guest memory buffers use guest endianness (hypervisor must byteswap)

I know of no existing way when endianness is not known in advance.
Perhaps a transport bit could be added to mark the endianness of the
guest/driver side.  This can be negotiated because virtio-pci has a
known endianness.  After negotiation, the host knows whether or not
byteswapping is necessary for structures in guest memory.

Stefan
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