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/

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

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

Drop "All rights reserved" from all my stuff. This includes
Foundation copyrights, approved by emaste@. It does not include
files which carry other people's copyrights; if you're one
of those people, feel free to make similar change.

Reviewed by: emaste, imp, gbe (manpages)
Differential Revision: https://reviews.freebsd.org/D26980

Replace hand-rolled unrefs if > 1 with refcount_release_if_not_last

Sponsored by: The FreeBSD Foundation

call racct_proc_ucred_changed() under the proc lock

The lock is required to ensure that the switch to the new credentials
and the transfer of the process's accounting data from the old
credentials to the new ones is done atomically. Otherwise, some updates
may be applied to the new credentials and then additionally transferred
from the old credentials if the updates happen after proc_set_cred() and
before racct_proc_ucred_changed().

The problem is especially pronounced for RACCT_RSS because
- there is a strict accounting for this resource (it's reclaimable)
- it's updated asynchronously by the vm daemon
- it's updated by setting an absolute value instead of applying a delta

I had to remove a call to rctl_proc_ucred_changed() from
racct_proc_ucred_changed() and make all callers of latter call the
former as well. The reason is that rctl_proc_ucred_changed, as it is
implemented now, cannot be called while holding the proc lock, so the
lock is dropped after calling racct_proc_ucred_changed. Additionally,
I've added calls to crhold / crfree around the rctl call, because
without the proc lock there is no gurantee that the new credentials,
owned by the process, will stay stable. That does not eliminate a
possibility that the credentials passed to the rctl will get stale.
Ideally, rctl_proc_ucred_changed should be able to work under the proc
lock.

Many thanks to kib for pointing out the above problems.

PR: 222027
Discussed with: kib
No comment: trasz
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D15048

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.

Fixup r325264, take #2

whack an unused variable

Fixup r325264

Accidentally committed an incomplete diff.

Save on loginclass list locking by checking if caller already uses the struct

Speed up rctl operation with large rulesets, by holding the lock
during iteration instead of relocking it for each traversed rule.

Reviewed by: mjg@
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D4110

cred: add proc_set_cred helper

The goal here is to provide one place altering process credentials.

This eases debugging and opens up posibilities to do additional work when such
an action is performed.

Simplify sys_getloginclass.

Just use current thread credentials as they have the same accuracy as the
ones obtained from proc..

Change loginclass mutex to an rwlock.

While here reduce nesting in loginclass_free.

Submitted by: Tiwei Bie <btw mail.ustc.edu.cn>
X-Additional: JuniorJobs project
MFC after: 2 weeks

Initialize loginclass mutex using MTX_SYSINIT instead of using SI_SUB_CPU.

Suggested by: rwatson@
MFC after: 1 month
Sponsored by: The FreeBSD Foundation

In order to maximize the re-usability of kernel code in user space this
patch modifies makesyscalls.sh to prefix all of the non-compatibility
calls (e.g. not linux_, freebsd32_) with sys_ and updates the kernel
entry points and all places in the code that use them. It also
fixes an additional name space collision between the kernel function
psignal and the libc function of the same name by renaming the kernel
psignal kern_psignal(). By introducing this change now we will ease future
MFCs that change syscalls.

Reviewed by: rwatson
Approved by: re (bz)

Add racct. It's an API to keep per-process, per-jail, per-loginclass
and per-loginclass resource accounting information, to be used by the new
resource limits code. It's connected to the build, but the code that
actually calls the new functions will come later.

Sponsored by: The FreeBSD Foundation
Reviewed by: kib (earlier version)

Add two new system calls, setloginclass(2) and getloginclass(2). This makes
it possible for the kernel to track login class the process is assigned to,
which is required for RCTL. This change also make setusercontext(3) call
setloginclass(2) and makes it possible to retrieve current login class using
id(1).

Reviewed by: kib (as part of a larger patch)