Introduce the new "fromclock" public wrapper API which allows consumers to select which system clock to obtain time from, independent of the current default system clock. In the brave new multi sysclock world, both feedback and feed-forward system clocks can be maintained and used concurrently, so this API provides a minimalist first step for interested consumers to exercise control over their choice of system clock.
Introduce the new "fromclock" public wrapper API which allows consumers to
select which system clock to obtain time from, independent of the current
default system clock. In the brave new multi sysclock world, both feedback and
feed-forward system clocks can be maintained and used concurrently, so this API
provides a minimalist first step for interested consumers to exercise control
over their choice of system clock.

Committed on behalf of Julien Ridoux and Darryl Veitch from the University of
Melbourne, Australia, as part of the FreeBSD Foundation funded "Feed-Forward
Clock Synchronization Algorithms" project.

For more information, see http://www.synclab.org/radclock/

Discussed with:	Julien Ridoux (jridoux at unimelb edu au)
Submitted by:	Julien Ridoux (jridoux at unimelb edu au)

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