kcmp(2): implement for generic file types

Reviewed by: brooks, markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D43518

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spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD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

struct kinfo_file changes needed for lsof to work using only usermode APIs`

Add kf_pipe_buffer_[in/out/size] fields to kf_pipe, and populate them.

Add a kf_kqueue struct to the kf_un union, to allow querying kqueue state,
and populate it.

Populate the kf_sock_rcv_sb_state and kf_sock_snd_sb_state fields in
kf_sock for INET/INET6 sockets, and populate all other fields for all
transport layer protocols, not just TCP.

Bump __FreeBSD_version.

Differential revision: https://reviews.freebsd.org/D34184
Reviewed by: jhb, kib, se
MFC after: 1 week

vfs: remove thread argument from VOP_STAT

and fo_stat.

Drop "All rights reserved" from my copyright statements.

Add email and fixup years while here.

Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D30912
MFC after: 2 weeks

Fix copyright, remove "all rights reserved".

The eventfd code was written by me, rdivacky@ copyrigth applicable only
to epoll part of the Linuxulator code. Roman is ok to retire his copyright
from sys/kern/sys_eventfd.c and 'All rights reserved.' lines from
sys/compat/linux/linux_event.[c|h] and sys/kern/sys_eventfd.c files.

Reviewed by: kib, emaste
Approved by: rdivacky
Differential Revision: https://reviews.freebsd.org/D30677
MFC after: 2 weeks

Expose eventfd in the native API/ABI using a new __specialfd syscall

eventfd is a Linux system call that produces special file descriptors
for event notification. When porting Linux software, it is currently
usually emulated by epoll-shim on top of kqueues. Unfortunately, kqueues
are not passable between processes. And, as noted by the author of
epoll-shim, even if they were, the library state would also have to be
passed somehow. This came up when debugging strange HW video decode
failures in Firefox. A native implementation would avoid these problems
and help with porting Linux software.

Since we now already have an eventfd implementation in the kernel (for
the Linuxulator), it's pretty easy to expose it natively, which is what
this patch does.

Submitted by: greg@unrelenting.technology
Reviewed by: markj (previous version)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D26668