From b7e90b290ab511dbbf1f1598e49092aaa73599e6 Mon Sep 17 00:00:00 2001
From: Kyle Evans <kevans@FreeBSD.org>
Date: Thu, 30 Sep 2021 13:19:05 -0500
Subject: [PATCH] kqueue: document how timers with low/past timeouts are
 handled

(cherry picked from commit 4b5554cebb66020f59dc869b835aebbd66e4bb8c)
---
 lib/libc/sys/kqueue.2 | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/libc/sys/kqueue.2 b/lib/libc/sys/kqueue.2
index ed737c626ef..ffcddc00303 100644
--- a/lib/libc/sys/kqueue.2
+++ b/lib/libc/sys/kqueue.2
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 7, 2021
+.Dd October 6, 2021
 .Dt KQUEUE 2
 .Os
 .Sh NAME
@@ -584,6 +584,12 @@ On return,
 .Va fflags
 contains the events which triggered the filter.
 .Pp
+Periodic timers with a specified timeout of 0 will be silently adjusted to
+timeout after 1 of the time units specified by the requested precision in
+.Va fflags .
+If an absolute time is specified that has already passed, then it is treated as
+if the current time were specified and the event will fire as soon as possible.
+.Pp
 If an existing timer is re-added, the existing timer will be
 effectively canceled (throwing away any undelivered record of previous
 timer expiration) and re-started using the new parameters contained in