Extend kqueue interface with EVFILT_EXCEPT filter.

This filter, already implemented in macOS and Dragonfly BSD, returns
exceptional conditions like the reception of out-of-band data.

The functionnality is similar to poll(2)'s POLLPRI & POLLRDBAND and
it can be used by the kqfilter-based poll & select implementation.

ok millert@ on a previous version, ok visa@

1 files changed, 9 insertions, 2 deletions

diff --git a/lib/libc/sys/kqueue.2 b/lib/libc/sys/kqueue.2
index fd5cc41c248..66c92b166c7 100644
--- a/lib/libc/sys/kqueue.2
+++ b/lib/libc/sys/kqueue.2
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: kqueue.2,v 1.40 2020/05/31 03:49:44 visa Exp $
+.\"	$OpenBSD: kqueue.2,v 1.41 2020/06/22 13:14:32 mpi Exp $
 .\"
 .\" Copyright (c) 2000 Jonathan Lemon
 .\" All rights reserved.
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD: src/lib/libc/sys/kqueue.2,v 1.18 2001/02/14 08:48:35 guido Exp $
 .\"
-.Dd $Mdocdate: May 31 2020 $
+.Dd $Mdocdate: June 22 2020 $
 .Dt KQUEUE 2
 .Os
 .Sh NAME
@@ -310,6 +310,13 @@ enabled and there is any data to read;
 .Fa data
 contains the number of bytes available.
 .El
+.It Dv EVFILT_EXCEPT
+Takes a descriptor as the identifier, and returns whenever one of the
+specified exceptional conditions has occured on the descriptor.
+Conditions are specified in
+.Fa fflags .
+Currently, a filter can monitor the reception of out-of-band data with
+.Dv NOTE_OOB .
 .It Dv EVFILT_WRITE
 Takes a descriptor as the identifier, and returns whenever
 it is possible to write to the descriptor.