Document that wait3/waitpid can receive SIGCHILD when wpid does

not exist or is not a child of the calling process.
Document what happens when SIGCHLD is ignored or SA_NOCLDWAIT is
set in sa_flags (this part from FreeBSD).
OK guenther@

diff --git a/lib/libc/sys/wait.2 b/lib/libc/sys/wait.2
index f8b82b4..5ae9f42 100644 (file)
--- a/lib/libc/sys/wait.2
+++ b/lib/libc/sys/wait.2
@@ -1,4 +1,4 @@
-.\"    $OpenBSD: wait.2,v 1.29 2015/11/24 19:34:31 jmc Exp $
+.\"    $OpenBSD: wait.2,v 1.30 2017/05/01 00:08:31 millert Exp $
 .\"    $NetBSD: wait.2,v 1.6 1995/02/27 12:39:37 cgd Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993, 1994
@@ -30,7 +30,7 @@
 .\"
 .\"     @(#)wait.2     8.2 (Berkeley) 4/19/94
 .\"
-.Dd $Mdocdate: November 24 2015 $
+.Dd $Mdocdate: May 1 2017 $
 .Dt WAIT 2
 .Os
 .Sh NAME
@@ -261,11 +261,23 @@ is returned and
 .Va errno
 is set to indicate the error.
 .Sh ERRORS
-.Fn wait
+.Fn wait ,
+.Fn waitpid ,
+.Fn wait3 ,
+and
+.Fn wait4
 will fail and return immediately if:
 .Bl -tag -width Er
 .It Bq Er ECHILD
 The calling process has no existing unwaited-for child processes.
+.It Bq Er ECHILD
+No status from the terminated child process is available
+because the calling process has asked the system to discard
+such status by ignoring the signal
+.Dv SIGCHLD
+or setting the flag
+.Dv SA_NOCLDWAIT
+for that signal.
 .It Bq Er EFAULT
 The
 .Fa status
@@ -277,6 +289,17 @@ arguments point to an illegal address.
 The call was interrupted by a caught signal, or the signal did not have the
 .Dv SA_RESTART
 flag set.
+.El
+.Pp
+.Fn waitpid
+and
+.Fn wait4
+will fail and return immediately if:
+.Bl -tag -width Er
+.It Bq Er ECHILD
+The process specified by the
+.Ar wpid
+argument does not exist or is not a child of the calling process.
 .It Bq Er EINVAL
 Invalid or undefined flags were passed in the
 .Fa options