Thread (8 messages) 8 messages, 4 authors, 2010-09-06

Re: Using virtio as a physical (wire-level) transport

From: Rusty Russell <hidden>
Date: 2010-08-16 00:19:47

On Sat, 14 Aug 2010 09:04:19 pm Alexander Graf wrote:
Am 06.08.2010 um 11:34 schrieb "Ira W. Snyder" [off-list ref]:
quoted
This problem is not limited to my new use of virtio. Virtio is
completely useless in a relatively common virtualization scenario:
x86 host with qemu-ppc guest. Or any other big endian guest system.
This one actually works because we know that we're building for a BE guest.
But I agree that it's a mess and clearly a very incorrect design decision.
Yes, since you need to know the guest's endian to virtualize it, the
correct interpretation of the virtio ring seemed the least problem.  Perhaps
I went overboard in simplification here, but it seemed pure legacy.

If we did a virtio2, as has been suggested, it would be possible to address
this.  You could of course do a hack where you detect the ring endianness
the first time they use it (based on avail.flags, avail.index and the
descriptor it would be quite reliable in practice).

Cheers,
Rusty.
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