Re: [libvirt] [Xen-devel] [BUG, PATCH-RFC] libvirt localtime and rtc_timeoffset handling in xen-sexpr/sxpr/sxp

[Philipp Hahn <hahn@univention.de>]

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Hello Ian,

Am Mittwoch 11 Januar 2012 12:54:04 schrieb Ian Campbell:
> On Wed, 2012-01-11 at 10:20 +0000, Philipp Hahn wrote:
> > I'm currently tracking a problem in libvirt regarding Xens handling of
> > localtime and rtc_timeoffset. My current understanding (Xen-3.4.3 and
> > Xen-4.1.2 under Linux) of Xend (the depcrecated Python one still used by
> > libvirt) is as this:
> > - for HV domains, the RTC gets setup to either UTC or localtime depending
> > on "/domain/image/hvm/localtime" ± "/domain/image/hvm/rtc_offset".
>
> Are those xenstore paths or a reference to a config file/sxp var?

Those are XenStore paths.

> I don't see the string "rtc_offset" anywhere under tools in
> xen-unstable.

I missed the "time", it's "rtc_timeoffset". Best search for RegExp 
rtc.timeoffset, since so you'll find 'rtc/timeoffset' as well.

...
> They get PV time direct from the hypervisor which exposes the
> hypervisor's wallclock to guests via the shared info. It is always UTC.
> See
> http://xenbits.xen.org/docs/unstable/hypercall/include,public,xen.h.html#St
>ruct_shared_info in particular the wc_* fields.

Yes, I figured that out as well, but thanks for the link.

> Classic-Xen kernels by default will take wallclock time from the shared
> info for each gettimeofday but can be configured to be free-running
> (that is the "independent_wallclock" mode).

A lot of documentation still talks about /proc/xen/independent_wallclock, 
which doesn't exist in 2.6.32 any more. I wish they would mention the Xen 
version and Linux kerbel version they were using ...

Thank you for your fast feedback.

Sincerely
Philipp Hahn
-- 
Philipp Hahn           Open Source Software Engineer      hahn@univention.de
Univention GmbH        Linux for Your Business        fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/

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