MFC r336457:

Make the definition of struct kevent in event.h match what the man page for kevent(2) says.

This is a trivial comment-only fix. The man page for kevent(2) gives
the definition of struct kevent, including a comment on each
field. The actual definition in sys/event.h omitted the comments on
some fields. Add the comments in. Not only does this make the man page
and include file agree, but the comments are useful in and of
themselves.

Sponsored by: Dell EMC

MFC r335765, r335776, r336186:

Remove potential identifier conflict in the EV_SET macro.

PR43905 pointed out a problem with the EV_SET macro if the passed
struct kevent pointer were specified with an expression with side
effects (e.g., "kevp++"). This was fixed in rS110241, but by using a
local block that defined an internal variable (named "kevp") to get
the pointer value once. This worked, but could cause issues if an
existing variable named "kevp" is in scope. To avoid that issue,
jilles@ pointed out that "C99 compound literals and designated
initializers allow doing this cleanly using a macro". This change
incorporates that suggestion, essentially verbatim from jilles@
comment on PR43905, except retaining the old definition for pre-C99 or
non-STDC (e.g., C++) compilers.

PR: 43905
Submitted by: Jilles Tjoelker (jilles@)
Reported by: Lamont Granquist <lamont@scriptkiddie.org>
Sponsored by: Dell EMC

MFC r311055:
Remove unneeded externs keywords. Reindent long lines.

Remove stray blank line added due to mismerge.

MFC r310554:
Some optimizations for kqueue timers.

MFC r298982:
Add EVFILT_VNODE open, read and close notifications.

MFC r298984:
Correct wording.

MFC r295012

kqueue EVFILT_PROC: avoid collision between NOTE_CHILD and NOTE_EXIT

NOTE_CHILD and NOTE_EXIT return something in kevent.data: the parent
pid (ppid) for NOTE_CHILD and the exit status for NOTE_EXIT.
Do not let the two events be combined, since one would overwrite
the other's data.

PR: 180385
Submitted by: David A. Bright <david_a_bright@dell.com>
Sponsored by: Dell Inc.

MFC r268843 (by bapt):
Extend kqueue's EVFILT_TIMER by adding precision unit flags support.

MFC r272528: Make kevent(2) periodic timer events more reliably periodic.

MFC r264146:
Fix a race between kqueue_register() and kqueue_scan() setting KN_INFLUX
flag while knlist is not locked, which caused lost notifications from
parallel knote().

MFC r268843 (by bapt):
Extend kqueue's EVFILT_TIMER by adding precision unit flags support.

MFC r272528: Make kevent(2) periodic timer events more reliably periodic.

MFC r264146:
Fix a race between kqueue_register() and kqueue_scan() setting KN_INFLUX
flag while knlist is not locked, which caused lost notifications from
parallel knote().