 @@ -1,782 +1,783 @@
-.\"	$NetBSD: kqueue.2,v 1.52 2020/10/31 10:51:59 wiz Exp $
+.\"	$NetBSD: kqueue.2,v 1.53 2020/10/31 14:35:28 christos Exp $
 .\"
 .\" Copyright (c) 2000 Jonathan Lemon
 .\" All rights reserved.
 .\"
 .\" Copyright (c) 2001, 2002, 2003 The NetBSD Foundation, Inc.
 .\" All rights reserved.
 .\"
 .\" Portions of this documentation is derived from text contributed by
 .\" Luke Mewburn.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    notice, this list of conditions and the following disclaimer.
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
 .\"
 .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND
 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
 .\" $FreeBSD: src/lib/libc/sys/kqueue.2,v 1.22 2001/06/27 19:55:57 dd Exp $
 .\"
 .Dd October 30, 2020
 .Dt KQUEUE 2
 .Os
 .Sh NAME
 .Nm kqueue ,
 .Nm kqueue1 ,
 .Nm kevent ,
 .Nm EV_SET
 .Nd kernel event notification mechanism
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In sys/event.h
 .In sys/time.h
 .Ft int
 .Fn kqueue "void"
 .Ft int
 .Fn kqueue1 "int flags"
 .Ft int
 .Fn kevent "int kq" "const struct kevent *changelist" "size_t nchanges" "struct kevent *eventlist" "size_t nevents" "const struct timespec *timeout"
 .Fn EV_SET "&kev" ident filter flags fflags data udata
 .Sh DESCRIPTION
 The
 .Fn kqueue
 system call
 provides a generic method of notifying the user when an event
 happens or a condition holds, based on the results of small
 pieces of kernel code termed filters.
 A kevent is identified by the (ident, filter) pair; there may only
 be one unique kevent per kqueue.
 .Pp
 The filter is executed upon the initial registration of a kevent
 in order to detect whether a preexisting condition is present, and is also
 executed whenever an event is passed to the filter for evaluation.
 If the filter determines that the condition should be reported,
 then the kevent is placed on the kqueue for the user to retrieve.
 .Pp
 The filter is also run when the user attempts to retrieve the kevent
 from the kqueue.
 If the filter indicates that the condition that triggered
 the event no longer holds, the kevent is removed from the kqueue and
 is not returned.
 .Pp
 Multiple events which trigger the filter do not result in multiple
 kevents being placed on the kqueue; instead, the filter will aggregate
 the events into a single struct kevent.
 Calling
 .Xr close 2
 on a file descriptor will remove any kevents that reference the descriptor.
 .Pp
 The
 .Fn kqueue
 system call
 creates a new kernel event queue and returns a descriptor.
 .Pp
 The
 .Fn kqueue1
 system call also allows to set the following
 .Fa flags
 on the returned file descriptor:
 .Bl -column O_NONBLOCK -offset indent
 .It Dv O_CLOEXEC
 Set the close on exec property.
 .It Dv O_NONBLOCK
 Set non-blocking I/O.
 .It Dv O_NOSIGPIPE
 Return
 .Er EPIPE
 instead of raising
 .Dv SIGPIPE .
 .El
 .Pp
 The queue is not inherited by a child created with
 .Xr fork 2 .
 .\" However, if
 .\" .Xr rfork 2
 .\" is called without the
 .\" .Dv RFFDG
 .\" flag, then the descriptor table is shared,
 .\" which will allow sharing of the kqueue between two processes.
 .Pp
 The
 .Fn kevent
 system call
 is used to register events with the queue, and return any pending
 events to the user.
 The
 .Fa changelist
 argument
 is a pointer to an array of
 .Va kevent
 structures, as defined in
 .In sys/event.h .
 All changes contained in the
 .Fa changelist
 are applied before any pending events are read from the queue.
 The
 .Fa nchanges
 argument
 gives the size of
 .Fa changelist .
 The
 .Fa eventlist
 argument
 is a pointer to an array of kevent structures.
 The
 .Fa nevents
 argument
 determines the size of
 .Fa eventlist .
 When
 .Fa nevents
 is zero,
 .Fn kevent
 will return immediately even if there is a
 .Fa timeout
 specified unlike
 .Xr select 2 .
 If
 .Fa timeout
 is a
 .No non- Ns Dv NULL
 pointer, it specifies a maximum interval to wait
 for an event, which will be interpreted as a
 .Li struct timespec .
 If
 .Fa timeout
 is a
 .Dv NULL
 pointer,
 .Fn kevent
 waits indefinitely.
 To effect a poll, the
 .Fa timeout
 argument should be
 .No non- Ns Dv NULL ,
 pointing to a zero-valued
 .Xr timespec 3
 structure.
 The same array may be used for the
 .Fa changelist
 and
 .Fa eventlist .
 .Pp
 The
 .Fn EV_SET
 macro is provided for ease of initializing a kevent structure.
 This macro does not evaluate its parameters multiple times.
 .Pp
 The
 .Va kevent
 structure is defined as:
 .Bd -literal
 struct kevent {
 	uintptr_t ident;	/* identifier for this event */
 	uint32_t  filter;	/* filter for event */
 	uint32_t  flags;	/* action flags for kqueue */
 	uint32_t  fflags;	/* filter flag value */
 	int64_t   data;		/* filter data value */
 	void     *udata;	/* opaque user data identifier */
 };
 .Ed
 .Pp
 The fields of
 .Fa struct kevent
 are:
 .Bl -tag -width "Fa filter" -offset indent
 .It ident
 Value used to identify this event.
 The exact interpretation is determined by the attached filter,
 but often is a file descriptor.
 .It Fa filter
 Identifies the kernel filter used to process this event.
 There are pre-defined system filters (which are described below), and
 other filters may be added by kernel subsystems as necessary.
 .It Fa flags
 Actions to perform on the event.
 .It Fa fflags
 Filter-specific flags.
 .It Fa data
 Filter-specific data value.
 .It Fa udata
 Opaque user-defined value passed through the kernel unchanged.
 .El
 .Pp
 The
 .Va flags
 field can contain the following values:
 .Bl -tag -width XXXEV_ONESHOT -offset indent
 .It Dv EV_ADD
 Adds the event to the kqueue.
 Re-adding an existing event will modify the parameters of the original
 event, and not result in a duplicate entry.
 Adding an event automatically enables it,
 unless overridden by the EV_DISABLE flag.
 .It Dv EV_ENABLE
 Permit
 .Fn kevent
 to return the event if it is triggered.
 .It Dv EV_DISABLE
 Disable the event so
 .Fn kevent
 will not return it.
 The filter itself is not disabled.
 .It Dv EV_DISPATCH
 Disable the event source immediately after delivery of an event.
 See
 .Dv EV_DISABLE
 above.
 .It Dv EV_DELETE
 Removes the event from the kqueue.
 Events which are attached to file descriptors are automatically deleted
 on the last close of the descriptor.
 .It Dv EV_RECEIPT
 This flag is useful for making bulk changes to a kqueue without draining
 any pending events.
 When passed as input, it forces
 .Dv EV_ERROR
 to always be returned.
 When a filter is successfully added the
 .Va data
 field will be zero.
 Note that if this flag is encountered and there is no remaining space in
 .Fa eventlist
 to hold the
 .Dv EV_ERROR
 event, then subsequent changes will not get processed.
 .It Dv EV_ONESHOT
 Causes the event to return only the first occurrence of the filter
 being triggered.
 After the user retrieves the event from the kqueue, it is deleted.
 .It Dv EV_CLEAR
 After the event is retrieved by the user, its state is reset.
 This is useful for filters which report state transitions
 instead of the current state.
 Note that some filters may automatically set this flag internally.
 .It Dv EV_EOF
 Filters may set this flag to indicate filter-specific EOF condition.
 .It Dv EV_ERROR
 See
 .Sx RETURN VALUES
 below.
 .El
 .Ss Filters
 Filters are identified by a number.
 There are two types of filters; pre-defined filters which
 are described below, and third-party filters that may be added with
 .Xr kfilter_register 9
 by kernel sub-systems, third-party device drivers, or loadable
 kernel modules.
 .Pp
 As a third-party filter is referenced by a well-known name instead
 of a statically assigned number, two
 .Xr ioctl 2 Ns s
 are supported on the file descriptor returned by
 .Fn kqueue
 to map a filter name to a filter number, and vice-versa (passing
 arguments in a structure described below):
 .Bl -tag -width KFILTER_BYFILTER -offset indent
 .It Dv KFILTER_BYFILTER
 Map
 .Va filter
 to
 .Va name ,
 which is of size
 .Va len .
 .It Dv KFILTER_BYNAME
 Map
 .Va name
 to
 .Va filter .
 .Va len
 is ignored.
 .El
 .Pp
 The following structure is used to pass arguments in and out of the
 .Xr ioctl 2 :
 .Bd -literal -offset indent
 struct kfilter_mapping {
 	char	 *name;		/* name to lookup or return */
 	size_t	 len;		/* length of name */
 	uint32_t filter;	/* filter to lookup or return */
 };
 .Ed
 .Pp
 The predefined system filters are listed below.
 Arguments may be passed to and from the filter via the
 .Va fflags
 and
 .Va data
 fields in the kevent structure.
 .Pp
 The predefined system filters are:
 .Bl -tag -width EVFILT_SIGNAL
 .It Dv EVFILT_READ
 Takes a descriptor as the identifier, and returns whenever
 there is data available to read.
 The behavior of the filter is slightly different depending
 on the descriptor type.
 .Bl -tag -width 2n
 .It Sockets
 Sockets which have previously been passed to
 .Xr listen 2
 return when there is an incoming connection pending.
 .Va data
 contains the size of the listen backlog (i.e., the number of
 connections ready to be accepted with
 .Xr accept 2 . )
 .Pp
 Other socket descriptors return when there is data to be read,
 subject to the
 .Dv SO_RCVLOWAT
 value of the socket buffer.
 This may be overridden with a per-filter low water mark at the
 time the filter is added by setting the
 NOTE_LOWAT
 flag in
 .Va fflags ,
 and specifying the new low water mark in
 .Va data .
 On return,
 .Va data
 contains the number of bytes in the socket buffer.
 .Pp
 If the read direction of the socket has shutdown, then the filter
 also sets EV_EOF in
 .Va flags ,
 and returns the socket error (if any) in
 .Va fflags .
 It is possible for EOF to be returned (indicating the connection is gone)
 while there is still data pending in the socket buffer.
 .It Vnodes
 Returns when the file pointer is not at the end of file.
 .Va data
 contains the offset from current position to end of file,
 and may be negative.
 .\" .Pp
 .\" This behavior is different from
 .\" .Xr poll 2 ,
 .\" where read events are triggered for regular files unconditionally.
 .\" This event can be triggered unconditionally by setting the
 .\" .Dv NOTE_FILE_POLL
 .\" flag in
 .\" .Va fflags .
 .It "Fifos, Pipes"
 Returns when there is data to read;
 .Va data
 contains the number of bytes available.
 .Pp
 When the last writer disconnects, the filter will set EV_EOF in
 .Va flags .
 This may be cleared by passing in EV_CLEAR, at which point the
 filter will resume waiting for data to become available before
 returning.
 .It "BPF devices"
 Returns when the BPF buffer is full, the BPF timeout has expired, or
 when the BPF has
 .Dq immediate mode
 enabled and there is any data to read;
 .Va data
 contains the number of bytes available.
 .El
 .It Dv EVFILT_WRITE
 Takes a descriptor as the identifier, and returns whenever
 it is possible to write to the descriptor.
 For sockets, pipes, fifos, and ttys,
 .Va data
 will contain the amount of space remaining in the write buffer.
 The filter will set EV_EOF when the reader disconnects, and for
 the fifo case, this may be cleared by use of EV_CLEAR.
 Note that this filter is not supported for vnodes.
 .Pp
 For sockets, the low water mark and socket error handling is
 identical to the EVFILT_READ case.
 .It Dv EVFILT_AIO
 This is not implemented in
 .Nx .
 .ig
 The sigevent portion of the AIO request is filled in, with
 .Va sigev_notify_kqueue
 containing the descriptor of the kqueue that the event should
 be attached to,
 .Va sigev_value
 containing the udata value, and
 .Va sigev_notify
 set to SIGEV_EVENT.
 When the aio_* function is called, the event will be registered
 with the specified kqueue, and the
 .Va ident
 argument set to the
 .Fa struct aiocb
 returned by the aio_* function.
 The filter returns under the same conditions as aio_error.
 .Pp
 Alternatively, a kevent structure may be initialized, with
 .Va ident
 containing the descriptor of the kqueue, and the
 address of the kevent structure placed in the
 .Va aio_lio_opcode
 field of the AIO request.
 However, this approach will not work on
 architectures with 64-bit pointers, and should be considered deprecated.
 ..
 .It Dv EVFILT_VNODE
 Takes a file descriptor as the identifier and the events to watch for in
 .Va fflags ,
 and returns when one or more of the requested events occurs on the descriptor.
 The events to monitor are:
 .Bl -tag -width XXNOTE_RENAME
 .It Dv NOTE_DELETE
 .Xr unlink 2
 was called on the file referenced by the descriptor.
 .It Dv NOTE_WRITE
 A write occurred on the file referenced by the descriptor.
 .It Dv NOTE_EXTEND
 The file referenced by the descriptor was extended.
 .It Dv NOTE_ATTRIB
 The file referenced by the descriptor had its attributes changed.
 .It Dv NOTE_LINK
 The link count on the file changed.
 .It Dv NOTE_RENAME
 The file referenced by the descriptor was renamed.
 .It Dv NOTE_REVOKE
 Access to the file was revoked via
 .Xr revoke 2
 or the underlying file system was unmounted.
 .El
 .Pp
 On return,
 .Va fflags
 contains the events which triggered the filter.
 .It Dv EVFILT_PROC
 Takes the process ID to monitor as the identifier and the events to watch for
 in
 .Va fflags ,
 and returns when the process performs one or more of the requested events.
 If a process can normally see another process, it can attach an event to it.
 The events to monitor are:
 .Bl -tag -width XXNOTE_TRACKERR
 .It Dv NOTE_EXIT
 The process has exited.
 The exit code of the process is stored in
 .Va data .
 .It Dv NOTE_FORK
 The process has called
 .Xr fork 2 .
 .It Dv NOTE_EXEC
 The process has executed a new process via
 .Xr execve 2
 or similar call.
 .It Dv NOTE_TRACK
 Follow a process across
 .Xr fork 2
 calls.
 The parent process will return with NOTE_TRACK set in the
 .Va fflags
 field, while the child process will return with NOTE_CHILD set in
 .Va fflags
 and the parent PID in
 .Va data .
 .It Dv NOTE_TRACKERR
 This flag is returned if the system was unable to attach an event to
 the child process, usually due to resource limitations.
 .El
 .Pp
 On return,
 .Va fflags
 contains the events which triggered the filter.
 .It Dv EVFILT_SIGNAL
 Takes the signal number to monitor as the identifier and returns
 when the given signal is delivered to the current process.
 This coexists with the
 .Xr signal 3
 and
 .Xr sigaction 2
 facilities, and has a lower precedence.
 The filter will record
 all attempts to deliver a signal to a process, even if the signal has
 been marked as SIG_IGN.
 Event notification happens after normal signal delivery processing.
 .Va data
 returns the number of times the signal has occurred since the last call to
 .Fn kevent .
 This filter automatically sets the EV_CLEAR flag internally.
 .It Dv EVFILT_TIMER
 Establishes an arbitrary timer identified by
 .Va ident .
 When adding a timer,
 .Va data
 specifies the timeout period in milliseconds.
 The timer will be periodic unless EV_ONESHOT is specified.
 On return,
 .Va data
 contains the number of times the timeout has expired since the last call to
 .Fn kevent .
 This filter automatically sets the EV_CLEAR flag internally.
 .It Dv EVFILT_FS
 Establishes a file system monitor.
 Currently it only monitors file system mount and unmount actions.
 .It Dv EVFILT_USER
 Establishes a user event identified by
 .Va ident
 which is not associated with any kernel mechanism but is triggered by
 user level code.
 The lower 24 bits of the
 .Va fflags
 may be used for user defined flags and manipulated using the following:
 .Bl -tag -width "Dv NOTE_FFLAGSMASK"
 .It Dv NOTE_FFNOP
 Ignore the input
 .Va fflags .
 .It Dv NOTE_FFAND
 Bitwise AND
 .Va fflags .
 .It Dv NOTE_FFOR
 Bitwise OR
 .Va fflags .
 .It Dv NOTE_FFCOPY
 Copy
 .Va fflags .
 .It Dv NOTE_FFCTRLMASK
 Control mask for
 .Va fflags .
 .It Dv NOTE_FFLAGSMASK
 User defined flag mask for
 .Va fflags .
 .El
 .Pp
 A user event is triggered for output with the following:
 .Bl -tag -width "Dv NOTE_FFLAGSMASK"
 .It Dv NOTE_TRIGGER
 Cause the event to be triggered.
 .El
 .Pp
 On return,
 .Va fflags
 contains the users defined flags in the lower 24 bits.
 .El
 .Sh CANCELLATION BEHAVIOUR
 If
 .Fa nevents
 is non-zero, i.e., the function is potentially blocking, the call
 is a cancellation point.
 Otherwise, i.e., if
 .Fa nevents
 is zero, the call is not cancellable.
 Cancellation can only occur before any changes are made to the kqueue,
 or when the call was blocked and no changes to the queue were requested.
 .Sh RETURN VALUES
 The
 .Fn kqueue
 system call
 creates a new kernel event queue and returns a file descriptor.
 If there was an error creating the kernel event queue, a value of \-1 is
 returned and
 .Dv errno
 is set.
 .Pp
 The
 .Fn kevent
 system call
 returns the number of events placed in the
 .Fa eventlist ,
 up to the value given by
 .Fa nevents .
 If an error occurs while processing an element of the
 .Fa changelist
 and there is enough room in the
 .Fa eventlist ,
 then the event will be placed in the
 .Fa eventlist
 with
 .Dv EV_ERROR
 set in
 .Va flags
 and the system error in
 .Va data .
 Otherwise,
 .Dv \-1
 will be returned, and
 .Dv errno
 will be set to indicate the error condition.
 If the time limit expires, then
 .Fn kevent
 returns 0.
 .Sh EXAMPLES
 The following example program monitors a file (provided to it as the first
 argument) and prints information about some common events it receives
 notifications for:
 .Bd -literal -offset indent
 #include <sys/types.h>
 #include <sys/event.h>
 #include <sys/time.h>
 #include <stdio.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <fcntl.h>
 #include <err.h>
 int
 main(int argc, char *argv[])
+{
         int fd, kq, nev;
         struct kevent ev;
         static const struct timespec tout = { 1, 0 };
         if ((fd = open(argv[1], O_RDONLY)) == -1)
                 err(1, "Cannot open `%s'", argv[1]);
         if ((kq = kqueue()) == -1)
                 err(1, "Cannot create kqueue");
         EV_SET(&ev, fd, EVFILT_VNODE, EV_ADD | EV_ENABLE | EV_CLEAR,
             NOTE_DELETE|NOTE_WRITE|NOTE_EXTEND|NOTE_ATTRIB|NOTE_LINK|
             NOTE_RENAME|NOTE_REVOKE, 0, 0);
         if (kevent(kq, &ev, 1, NULL, 0, &tout) == -1)
                 err(1, "kevent");
         for (;;) {
                 nev = kevent(kq, NULL, 0, &ev, 1, &tout);
                 if (nev == -1)
                         err(1, "kevent");
                 if (nev == 0)
                         continue;
                 if (ev.fflags & NOTE_DELETE) {
                         printf("deleted ");
                         ev.fflags &= ~NOTE_DELETE;
+                }
                 if (ev.fflags & NOTE_WRITE) {
                         printf("written ");
                         ev.fflags &= ~NOTE_WRITE;
+                }
                 if (ev.fflags & NOTE_EXTEND) {
                         printf("extended ");
                         ev.fflags &= ~NOTE_EXTEND;
+                }
                 if (ev.fflags & NOTE_ATTRIB) {
                         printf("chmod/chown/utimes ");
                         ev.fflags &= ~NOTE_ATTRIB;
+                }
                 if (ev.fflags & NOTE_LINK) {
                         printf("hardlinked ");
                         ev.fflags &= ~NOTE_LINK;
+                }
                 if (ev.fflags & NOTE_RENAME) {
                         printf("renamed ");
                         ev.fflags &= ~NOTE_RENAME;
+                }
                 if (ev.fflags & NOTE_REVOKE) {
                         printf("revoked ");
                         ev.fflags &= ~NOTE_REVOKE;
+                }
                 printf("\\n");
                 if (ev.fflags)
                         warnx("unknown event 0x%x\\n", ev.fflags);
+        }
+}
 .Ed
 .Sh ERRORS
 The
 .Fn kqueue
 function fails if:
 .Bl -tag -width Er
 .It Bq Er EMFILE
 The per-process descriptor table is full.
 .It Bq Er ENFILE
 The system file table is full.
 .It Bq Er ENOMEM
 The kernel failed to allocate enough memory for the kernel queue.
 .El
 .Pp
 The
 .Fn kevent
 function fails if:
 .Bl -tag -width Er
 .It Bq Er EACCES
 The process does not have permission to register a filter.
 .It Bq Er EBADF
 The specified descriptor is invalid.
 .It Bq Er EFAULT
 There was an error reading or writing the
 .Va kevent
 structure.
 .It Bq Er EINTR
 A signal was delivered before the timeout expired and before any
 events were placed on the kqueue for return.
 All changes contained in the
 .Fa changelist
 are applied before returning this error.
 .It Bq Er EINVAL
 The specified time limit or filter is invalid.
 .It Bq Er ENOENT
 The event could not be found to be modified or deleted.
 .It Bq Er ENOMEM
 No memory was available to register the event.
 .It Bq Er EOPNOTSUPP
 This type of file descriptor is not supported for
 .Fn kevent
 operations.
 .It Bq Er ESRCH
 The specified process to attach to does not exist.
 .El
 .Sh SEE ALSO
 .\" .Xr aio_error 2 ,
 .\" .Xr aio_read 2 ,
 .\" .Xr aio_return 2 ,
 .Xr fork 2 ,
 .Xr ioctl 2 ,
 .Xr listen 2 ,
 .Xr poll 2 ,
 .Xr read 2 ,
 .Xr select 2 ,
 .Xr sigaction 2 ,
 .Xr unlink 2 ,
 .Xr write 2 ,
 .Xr signal 3 ,
 .Xr timespec 3 ,
 .Xr kfilter_register 9 ,
 .Xr knote 9
 .Rs
 .%A Jonathan Lemon
 .%T "Kqueue: A Generic and Scalable Event Notification Facility"
 .%I USENIX Association
 .%B Proceedings of the FREENIX Track: 2001 USENIX Annual Technical Conference
 .%D June 25-30, 2001
 .%U http://www.usenix.org/event/usenix01/freenix01/full_papers/lemon/lemon.pdf
 .Re
 .Sh HISTORY
 The
 .Fn kqueue
 and
 .Fn kevent
 functions first appeared in
 .Fx 4.1 ,
 and then in
 .Nx 2.0 .
 The
 .Fn kqueue1
 function first appeared in
 .Nx 6.0 .
 .Pp
 The
 .Fn EV_SET
 macro was protected from evaluating multiple times the first argument in
 .Nx 8.0 .
 .Pp
 The
 .Va udata
 type was changed from intptr_t to void * in
 .Nx 10.0 .