sys: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

rangelock: add rangelock_cookie_assert

A future change to posixshm to add file sealing (in DIFF_21391[0] and child)
will move locking out of shm_dotruncate as kern_shm_open() will require the
lock to be held across the dotruncate until the seal is actually applied.
For this, the cookie is passed into shm_dotruncate_locked which asserts
RCA_WLOCKED.

[0] Name changed to protect the innocent, hopefully, from getting autoclosed
due to this reference...

Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D21628

Add non-blocking trylock variants for the rangelock functions.

A future patch that will add a Linux compatible copy_file_range(2) syscall
needs to be able to lock the byte ranges of two files concurrently.
To do this without a risk of deadlock, a non-blocking variant of
vn_rangelock_rlock() called vn_rangelock_tryrlock() was needed.
This patch adds this, along with vn_rangelock_trywlock(), in order to
do this.
The patch also adds a couple of comments, that I hope clarify how the
algorithm used in kern_rangelock.c works.

Reviewed by: kib, asomers (previous version)
Differential Revision: https://reviews.freebsd.org/D20645

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.

Change the queue of locks in kern_rangelock.c from holding lock requests in
the order that they arrive, to holding
(a) granted write lock requests, followed by
(b) granted read lock requests, followed by
(c) ungranted requests, in order of arrival.

This changes the stopping condition for iterating through granted locks to
see if a new request can be granted: When considering a read lock request,
we can stop iterating as soon as we see a read lock request, since anything
after that point is either a granted read lock request or a request which
has not yet been granted. (For write lock requests, we must still compare
against all granted lock requests.)

For workloads with R parallel reads and W parallel writes, this improves
the time spent from O((R+W)^2) to O(W*(R+W)); i.e., heavy parallel-read
workloads become significantly more scalable.

No statistically significant change in buildworld time has been measured,
but synthetic tests of parallel 'dd > /dev/null' and 'openssl enc >/dev/null'
with the input file cached yield dramatic (up to 10x) improvement with high
(up to 128 processes) levels of parallelism.

Reviewed by: kib

Add a rangelock implementation, intended to be used to range-locking
the i/o regions of the vnode data space. The implementation is quite
simple-minded, it uses the list of the lock requests, ordered by
arrival time. Each request may be for read or for write. The
implementation is fair FIFO.

MFC after: 2 month