timecounting: add gettime(9), getuptime(9)

time_second and time_uptime are used widely in the tree.  This is a
problem on 32-bit platforms because time_t is 64-bit, so there is a
potential split-read whenever they are used at or below IPL_CLOCK.

Here are two replacement interfaces: gettime(9) and getuptime(9).
The "get" prefix signifies that they do not read the hardware
timecounter, i.e. they are fast and low-res.  The lack of a unit
(e.g. micro, nano) signifies that they yield a plain time_t.

As an optimization on LP64 platforms we can just return time_second or
time_uptime, as a single read is atomic.  On 32-bit platforms we need
to do the lockless read loop and get the values from the timecounter.

In a subsequent diff these will be substituted for time_second and
time_uptime almost everywhere in the kernel.

With input from visa@ and dlg@.

ok kettenis@

0 files changed, 0 insertions, 0 deletions