sys: Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

sysent: Get rid of bogus sys/sysent.h include.

Where appropriate hide sysent.h under proper condition.

MFC after: 2 weeks

kern_fflock: Fix a typo in a source code comment

- s/foward/forward/

MFC after: 3 days

Mark more nodes as CTLFLAG_MPSAFE or CTLFLAG_NEEDGIANT (17 of many)

r357614 added CTLFLAG_NEEDGIANT to make it easier to find nodes that are
still not MPSAFE (or already are but aren’t properly marked).
Use it in preparation for a general review of all nodes.

This is non-functional change that adds annotations to SYSCTL_NODE and
SYSCTL_PROC nodes using one of the soon-to-be-required flags.

Mark all obvious cases as MPSAFE. All entries that haven't been marked
as MPSAFE before are by default marked as NEEDGIANT

Approved by: kib (mentor, blanket)
Commented by: kib, gallatin, melifaro
Differential Revision: https://reviews.freebsd.org/D23718

sys/kern: adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

kernel: use our nitems() macro when it is available through param.h.

No functional change, only trivial cases are done in this sweep,

Discussed in: freebsd-current

The SYSCTL data pointers can come from userspace and must not be
directly accessed. Although this will work on some platforms, it can
throw an exception if the pointer is invalid and then panic the kernel.

Add a missing SYSCTL_IN() of "SCTP_BASE_STATS" structure.

MFC after: 3 days
Sponsored by: Mellanox Technologies

Revise the sysctl handling code and restructure the hierarchy of sysctls
introduced when feed-forward clock support is enabled in the kernel:

- Rename the "choice" variable to "available".

- Streamline the implementation of the "active" variable's sysctl handler
function.

- Create a kern.sysclock sysctl node for general sysclock related configuration
options. Place the "available" and "active" variables under this node.

- Create a kern.sysclock.ffclock sysctl node for feed-forward clock specific
configuration options. Place the "version" and "ffcounter_bypass" variables
under this node.

- Tweak some of the description strings.

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

Make sysclock_active publicly available to external consumers.

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)

Export the "ffclock" feature for kernels compiled with feed-forward clock
support.

Suggested by: netchild
Reviewed by: netchild

- Add the ffclock_getcounter(), ffclock_getestimate() and ffclock_setestimate()
system calls to provide feed-forward clock management capabilities to
userspace processes. ffclock_getcounter() returns the current value of the
kernel's feed-forward clock counter. ffclock_getestimate() returns the current
feed-forward clock parameter estimates and ffclock_setestimate() updates the
feed-forward clock parameter estimates.

- Document the syscalls in the ffclock.2 man page.

- Regenerate the script-derived syscall related files.

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/

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

- Provide a sysctl interface to change the active system clock at runtime.

- Wrap [get]{bin,nano,micro}[up]time() functions of sys/time.h to allow
requesting time from either the feedback or the feed-forward clock. If a
feedback (e.g. ntpd) and feed-forward (e.g. radclock) daemon are both running
on the system, both kernel clocks are updated but only one serves time.

- Add similar wrappers for the feed-forward difference 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/

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

Provide high-level functions to access the feed-forward absolute and difference
clocks. Each routine can output an upper bound on the absolute time or time
interval requested. Different flavours of absolute time can be requested, for
example with or without leap seconds, monotonic or not, etc.

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/

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