usleep(3): Note the historical rake that was stepped upon.

PR 58184

lib/libc/gen/usleep.3

@@ -1,4 +1,4 @@
-.\"	$NetBSD: usleep.3,v 1.21 2024/04/22 21:25:29 jdolecek Exp $
+.\"	$NetBSD: usleep.3,v 1.22 2024/05/15 13:12:04 riastradh Exp $
 .\"
 .\" Copyright (c) 1986, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -99,3 +99,17 @@ The
 .Fn usleep
 function appeared in
 .Bx 4.3 .
+.Sh CAVEATS
+In
+.St -p1003.1-2004 ,
+.Nm
+was limited to values of
+.Fa microseconds
+less than one million.
+Some implementations, including
+.Nx
+before 10.1, fail immediately with
+.Er EINVAL
+\(em and don't sleep at all \(em if
+.Fa microseconds
+is one million or greater.