[PATCH] ptp: Add vDSO-style vmclock support

[Michael S. Tsirkin]

On Thu, Jul 25, 2024 at 02:50:50PM +0100, David Woodhouse wrote:
> Even if the virtio-rtc specification were official today, and I was
> able to expose it via PCI, I probably wouldn't do it that way. There's
> just far more in virtio-rtc than we need; the simple shared memory
> region is perfectly sufficient for most needs, and especially ours.

I can't stop amazon from shipping whatever in its hypervisor,
I'd just like to understand this better, if there is a use-case
not addressed here then we can change virtio to address it.

The rtc driver patch posted is 900 lines, yours is 700 lines, does not
look like a big difference.  As for using a memory region, this is
valid, but maybe rtc should be changed to do exactly that?
E.g. we can easily add a capability describing such a region.
or put it in device config space.

I mean yes, we can build a new transport for each specific need but in
the end we'll get a ton of interfaces with unclear compatibility
requirements.  If effort is instead spent improving common interfaces,
we get consistency and everyone benefits. That's why I'm trying to
understand the need here.

-- 
MST