Hello Daniel,
On Tuesday 17 January 2012 22:24:11 Daniel P. Berrange wrote:
On Tue, Jan 17, 2012 at 05:02:14PM +0100, Philipp Hahn wrote:
> For PV, Xen implements the <clock offset='utc'> and <clock
> offset='localtime'> behaviour, while for HV it implements <clock
> offset='variable'>.
> This difference is important for domUs, which switch daylight saving on
> there own, since the state is kept inside the VM and must be in sync
> with the RTC provided by Xen.
What versions of Xen is that true for ? I didn't think that old
versions behaved this way for HVM. The libvirt Xen driver is still
intended to support the RHEL5 vintage Xen code (which is based on
3.0.3)
To me it looks like CentOS5 (since I don't have RHEL5) has the Xen-3.0.3
user-land XenD (rpm -q xen → xen-3.0.3-132.el5) but the Xen-3.1.2 hypervisor
(xm info → 3.1.2-.2-274.el5). Relevant for this change seems only the version
of XenD, which returns xendConfigVersion=2.
This is a version without "managed domain" support, which was added in the
3.1.x branch <
http://xenbits.xen.org/hg/xen-3.1-testing.hg/rev/7e431ea834a8>.
The generation bump to xendConfig_version=3 happend in 3.0.4 for "Live Cycle"
support <
http://xenbits.xen.org/hg/xen-3.0.4-testing.hg/rev/1c51c580dc05>.
The bump to 4 was in the 3.0.5 → 3.1.0 transition
<
http://xenbits.xen.org/hg/xen-3.1-testing.hg/rev/887fa548f650>
So for XenD version _ its _:
- < 3.1: "utc" or "localtime" (because there is no XenD keeping
track of the
modified rtc_timeoffset)
- >= 3.1: managed HV domains: "variable" (XenD keeps track)
- >= 3.1: managed PV domains: "utc" or "localtime" (they don't
have a RTC but
can access a PV-clock, which gets initialized to either "utc" or
"localtime".
As far as I know the offset can't be changed by the domU and is not visible
in any tool, only the "is_utc/localtime" flag is visible)
- >= 3.1: "xm" domains: same as with "managed domains". The
"variable" offset
is tracked by XenD and survives a "reboot", but as with other transient
domains, the information is lost after "destroy".
Patch will (hopefully) follow soon.
Sincerely
Philipp
--
Philipp Hahn Open Source Software Engineer hahn(a)univention.de
Univention GmbH Linux for Your Business fon: +49 421 22 232- 0
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