This patchset implements the XML described in
http://www.redhat.com/archives/libvir-list/2010-March/msg00304.html
(with one small change - the tickpolicy 'none' was changed to 'delay'
after a later discussion).
It also implements the qemu backend for those timer types that qemu supports.
One thing to point out to 'early adopters': qemu's driftfix option is
currently broken, so if you try to specify a tickpolicy=catchup in an
rtc timer, the domain will give an error on startup. A patch for that
has been posted by Zach Amsden to qemu-devel:
http://lists.gnu.org/archive/html/qemu-devel/2010-03/msg02036.html
Backends for other hypervisors have not been implemented. That is left
as an exercise for later ;-)