sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

sys/alq.h: Kernel only file, mark as such

The alq interfaces are 100% in-kernel, so make this whole file #ifdef
_KERNEL. There's no users of this in the tree outside of the kernel, nor
does it define anything that could be useful at peeking into the state
of alq.

Sponsored by: Netflix

sys/sys: further 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.

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

- Rework the underlying ALQ storage to be a circular buffer, which amongst other
things allows variable length messages to be easily supported.

- Extend KPI with alq_writen() and alq_getn() to support variable length
messages, which is enabled at ALQ creation time depending on the
arguments passed to alq_open(). Also add variants of alq_open() and
alq_post() that accept a flags argument. The KPI is still fully
backwards compatible and shouldn't require any change in ALQ consumers
unless they wish to utilise the new features.

- Introduce the ALQ_NOACTIVATE and ALQ_ORDERED flags to allow ALQ consumers
to have more control over IO scheduling and resource acquisition
respectively.

- Strengthen invariants checking.

- Document ALQ changes in ALQ(9) man page.

Sponsored by: FreeBSD Foundation
Reviewed by: gnn, jeff, rpaulo, rwatson
MFC after: 1 month

- Import the HEAD csup code which is the basis for the cvsmode work.

Modify the alq(9) alq_open() API to accept a file creation mode, rather
than defaulting the cmode argument to vn_open() to 0. Supply a default
argument of ALQ_DEFAULT_CMODE (0600) in current callers.

Discussed with/pointed out by: hmp
Reveiwed by: jeff, hmp
MFC after: 3 days

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

Add an explicit credential argument to alq_open() to allow the caller to
specify what credential to use when authorizing vn_open() and later
write operations, rather than curthread->td_ucred.

When writing KTR traces to an ALQ, specify the credential of the thread
generating the sysctl request.

Obtained from: TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories

- Export the alq daemon thread pointer.
- Don't log ktr events from the alq daemon.

- Correct the name in the header guards.

Spotted by: rwatson

- Add an asynchronous fixed length record logging mechanism called
ALQ (Asynch. Logging Queues). ALQ supports many seperate queues with
different record and buffer sizes. It opens and logs to any vnode so
it can be used with character devices as well as regular files.

Reviewed in part by: phk, jake, markm