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xen-devel
Re: [Xen-devel] Xen watchdog?
> I took a brief look at it. It was kind of big, with no great justification.
> I would have written a simple little user daemon for kicking the watchdog
> directly, rather than add extra stuff in our Linux kernel. But perhaps the
> latter is the 'proper' way? If so, the driver probably needs review on
> lkml.
It's the Linux Way - a userspace app wouldn't work, since it wouldn't be able
to export the /dev/watchdog device node that HA infrastructure needs.
To be honest, IIRC, it seemed to me like most watchdog drivers in Linux could
share more common code and then all be a decent bit smaller - something I
could look at if the Linux folks are interested but wasn't on my todo list at
the time.
A fair bit of the bulk in the rest of the code was in making the dom0 tools be
a bit more aware of the watchdog state. This was needed to support features
such as the "watchdog initiated reboot" flag, but isn't strictly needed for
basic functionality. I can trim this bit out, at least for an initial merge,
but there may be other stuff it'd be helpful to hook in here.
> Either way, I think the hypervisor interface should support multiple
> entities per guest trying to set up a watchdog timer. Even if just so that
> entities that lose the race get -EBUSY. This would make it safer to use
> without a single controlling entity in the guest kernel.
Hmmm. I could do something like that, certainly. The model I was following
was that of hardware - I'm not sure what a physical watchdog card would do
with multiple controlling entities but I doubt it'd be pretty. As we're in
the hypervisor, we've got more smarts available to us though, so a bit of
opaque state to identify a "watchdog handle" should be trivial to add. I
wonder if there are any potential users this sort of behaviour, though -
maybe Richard would comment here?
The only significant feature I'd want to add before merge is support for
suspend / resume - that should be fairly simple to add, though.
Cheers,
Mark
--
Dave: Just a question. What use is a unicyle with no seat? And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!
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