Xen devel - Jun 2007 - [RFC] Xen paravirtual watchdog device [0/4]

Hi all,

As I''ve previously mentioned, I''ve been tinkering with a
Xen-based virtual
watchdog device and I think it''s about time I put out some patches for 
discussion.  The principle of the watchdog device is to provide a simple, 
high-assurance watchdog to domains running on Xen.  The goal is to give 
better assurance than an in-kernel software watchdog.

The patches were developed for 2.6.16.33, but I''ve done what fixups I
could
see were necessary to make them apply against tip but I still need to test it 
works there correctly.  I''m primarily just putting these out here for
people
to eyeball and argue about, but if you do try them out please let me know how 
you get on.

Under Linux, a watchdog daemon is typically run in userspace.  This talks to 
the watchdog device driver through /dev/watchdog, which is responsible for 
resetting the timeout on the watchdog device whenever the daemon kicks it.  
The reliance on the userspace daemon ensures that scheduling, etc, is still 
occurring correctly in the system, and makes it easy for different 
functionality to be implemented on top of the basic watchdog feature.

The XenLinux watchdog driver sets up the in-Xen watchdog for the current 
domain using a simple hypercall interface.  The watchdog timer is implemented 
within Xen itself, isolating it from any guest bugs that might take out a 
normal software watchdog.  Standard interfaces to userspace are supported so 
that any watchdog-aware software should be able to interact with it without 
modification.

The patchset also includes some watchdog-awareness enhancements for the dom0 
toolset (more of these are possible in the future).

Comments, questions, abuse, anyone?

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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Add Kconfig configuration option for watchdog.

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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XenLinux driver for Xen virtual watchdog device.

This is based on the Linux softdog driver, but features slightly more 
functionality and omits all the internal timer logic since it has moved to 
Xen.

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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Tools support for the virtual watchdog device.

Currently, this is used to support some extra status information for the 
guest, which may be useful in some circumstances.  The tools could usefully 
be extended to have more interaction with the watchdog for management 
purposes.

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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Xen virtual watchdog - hypervisor code.

A Xen-internal software watchdog service for paravirt domains including dom0 
and driver domains.  Ideally dom0 would use a hardware watchdog device, but 
this is still a higher assurance design than a kernel-based software 
watchdog.

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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And as if that description wasn''t enough, for your pleasure and
enjoyment I
present ... the actual patch!

On Friday 01 June 2007, Mark Williamson wrote:
> Xen virtual watchdog - hypervisor code.
>
> A Xen-internal software watchdog service for paravirt domains including
> dom0 and driver domains.  Ideally dom0 would use a hardware watchdog
> device, but this is still a higher assurance design than a kernel-based
> software watchdog.
>
> 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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On Fri, 1 Jun 2007, Mark Williamson wrote:
> The XenLinux watchdog driver sets up the in-Xen watchdog for the current 
> domain using a simple hypercall interface.  The watchdog timer is 
> implemented within Xen itself, isolating it from any guest bugs that 
> might take out a normal software watchdog.  Standard interfaces to 
> userspace are supported so that any watchdog-aware software should be 
> able to interact with it without modification.
Sounds like an excellent idea! I really need a box running unstable so I 
can test this (and other things) out! :)

------------------------------------------------------------------------
| nate carlson | natecars@natecarlson.com | http://www.natecarlson.com |
|       depriving some poor village of its idiot since 1981            |
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