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[Xen-devel] Basic xenstore questions (building a watchdog)

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Subject: [Xen-devel] Basic xenstore questions (building a watchdog)
From: Charles Duffy <cduffy@xxxxxxxxxxx>
Date: Thu, 12 Jan 2006 15:46:38 -0600
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I'm looking at building a xenstore-based watchdog, as described at http://lists.xensource.com/archives/html/xen-users/2005-07/msg00597.html

However, being somewhat new to xenstore, I'd appreciate some pointers.

- What portions of the xenstore namespace should I use? I'm looking for at least two settings writable by the DomUs: A flag to enable/disable the watchdog for a given domain (ideally, this would be specific to an individual run of the instance in question and not persisted across runs), and a counter via the modification of which the watchdog may be pet.

http://wiki.xensource.com/xenwiki/XenStoreReference indicates that /tool is likely an appropriate region (perhaps I should create /tool/watchdog/<vmid>/{enabled,counter}?), but this doesn't provide guidance as to how I can avoid persistance (if this is possible). Alternately, are vm GUIDs unique on a per-invocation basis? If so, /tool/watchdog/vmid/enabled could enable the watchdog only when it contains the current vm's GUID (preventing it from working across restarts). (Given some basic playing around with xenstore-list, xenstore-read and friends from within a DomU, however, it looks like I can't read contents of /vm from the DomU -- so am I actually able to find my own GUID such as to be able to use it in this way? For that matter, how can a DomU find its own vmid?)

- Are the xend.xenstore classes intended exclusively for xend's use, or is it acceptable for them to be used by 3rd-party software as well?

- Any example code I'd be well-advised to look at?


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