Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add proper prerequisites for even two more headers.

Spotted by: http://hacks.owlfolio.org/header-survey/

/* -> /*- for license, minor formatting changes

Removed unused forward struct declaration.

Hide the private parts of timecounter from a couple of places that don't
really need to know the gory details.

Remove __P

Update to the 2001-04-02 version of the nanokernel code from Dave Mills.

Update the NTP kernel PLL code to the 2000-08-29 version of Dave Mills
nanokernel.

The FreeBSD private mode hardpps Type 2 PLL has been removed.

Change #ifdef KERNEL to #ifdef _KERNEL in the public headers. "KERNEL"
is an application space macro and the applications are supposed to be free
to use it as they please (but cannot). This is consistant with the other
BSD's who made this change quite some time ago. More commits to come.

Update to the latest nanokernel from Dave Mills.

Update to latest version from Dave Mills. Mostly textual.

Make even more of the PPSAPI implementations generic.

FLL support in hardpps()

Various magic shuffles and improved comments

Style fixes from Bruce.

Integrate the new "nanokernel" PLL from Dave Mills.

This code is backwards compatible with the older "microkernel" PLL, but
allows ntpd v4 to use nanosecond resolution. Many other improvements.

PPS_SYNC and hardpps() are NOT supported yet.

Introduce std_pps_ioctl() to automagically DTRT.

Add scaling capability to timex.offset, ntpd-4.0.73 will support this.

Replace TOD clock code with more systematic approach.

Highlights:
* Simple model for underlying hardware.
* Hardware basis for timekeeping can be changed on the fly.
* Only one hardware clock responsible for TOD keeping.
* Provides a real nanotime() function.
* Time granularity: .232E-18 seconds.
* Frequency granularity: .238E-12 s/s
* Frequency adjustment is continuous in time.
* Less overhead for frequency adjustment.
* Improves xntpd performance.

Reviewed by: bde, bde, bde

Make POWERFAIL_NMI, PPS_SYNC and NATM new style options.

This also fixes a couple of defunct options; submitted by bde.

Move almost all the ntp related stuff from kern_clock.c to
kern_ntptime.c. The only bit left over is that which is executed
in all calls to hardclock(). Various cleanups and staticizing
along the road.

Update our kernel ntp code to the latest from David Mills. The main change
is the addition of the FLL code, which is used by the latest versions of
xntpd. The kernel PPS code is also updated, although I can't test that yet.

Redo Kernel NTP PLL support, kernel side.

This code is mostly taken from the 1.1 port (which was in turn taken from
Dave Mills's kern.tar.Z example). A few significant differences:

1) ntp_gettime() is now a MIB variable rather than a system call. A few
fiddles are done in libc to make it behave the same.

2) mono_time does not participate in the PLL adjustments.

3) A new interface has been defined (in <machine/clock.h>) for doing
possibly machine-dependent things around the time of the clock update.
This is used in Pentium kernels to disable interrupts, set `time', and
reset the CPU cycle counter as quickly as possible to avoid jitter in
microtime(). Measurements show an apparent resolution of a bit more than
8.14usec, which is reasonable given system-call overhead.

Add timex.h for xntpd. The system calls will have to wait for tomorrow,
when I'm less sleepy.
Submitted by: jkh