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e31b5cf393
https://bugzilla.redhat.com/show_bug.cgi?id=964177 Though both libvirt and QEMU's document say RTC_CHANGE returns the offset from the host UTC, qemu actually returns the offset from the specified date instead when specific date is provided (-rtc base=$date). It's not safe for qemu to fix it in code, it worked like that for 3 years, changing it now may break other QEMU use cases. What qemu tries to do is to fix the document: http://lists.gnu.org/archive/html/qemu-devel/2013-05/msg04782.html And in libvirt side, instead of replying on the value from qemu, this converts the offset returned from qemu to the offset from host UTC, by: /* * a: the offset from qemu RTC_CHANGE event * b: The specified date (-rtc base=$date) * c: the host date when libvirt gets the RTC_CHANGE event * offset: What libvirt will report */ offset = a + (b - c); The specified date (-rtc base=$date) is recorded in clock's def as an internal only member (may be useful to exposed outside?). Internal only XML tag "basetime" is introduced to not lose the guest's basetime after libvirt restarting/reloading: <clock offset='variable' adjustment='304' basis='utc' basetime='1370423588'/>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>