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

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.

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

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