Finally document the option to avoid zombie creation

through ignoring SIGCHLD.

lib/libc/gen/signal.3

@@ -32,7 +32,7 @@
 .\"     @(#)signal.3	8.3 (Berkeley) 4/19/94
 .\" $FreeBSD$
 .\"
-.Dd April 19, 1994
+.Dd June 7, 2004
 .Dt SIGNAL 3
 .Os
 .Sh NAME
@@ -204,6 +204,22 @@ to the
 function;
 ignored signals remain ignored.
 .Pp
+If a process explicitly specifies
+.Dv SIG_IGN
+as the action for the signal
+.Dv SIGCHLD ,
+the system will not create zombie processes when children
+of the calling process exit.
+As a consequence, the system will discard the exit status
+from the child processes.
+If the calling process subsequently issues a call to
+.Xr wait 2
+or equivalent, it will block until all of the calling process's
+children terminate, and then return a value of \-1 with
+.Va errno
+set to
+.Er ECHILD .
+.Pp
 See
 .Xr sigaction 2
 for a list of functions
@@ -239,6 +255,7 @@ or
 .Xr sigaltstack 2 ,
 .Xr sigprocmask 2 ,
 .Xr sigsuspend 2 ,
+.Xr wait 2 ,
 .Xr fpsetmask 3 ,
 .Xr setjmp 3 ,
 .Xr siginterrupt 3 ,
@@ -248,3 +265,7 @@ This
 .Fn signal
 facility appeared in
 .Bx 4.0 .
+The option to avoid the creation of child zombies through ignoring
+.Dv SIGCHLD
+appeared in
+.Fx 5.0 .

lib/libc/sys/sigaction.2

@@ -32,7 +32,7 @@
 .\"	From: @(#)sigaction.2	8.2 (Berkeley) 4/3/94
 .\" $FreeBSD$
 .\"
-.Dd April 3, 1994
+.Dd June 7, 2004
 .Dt SIGACTION 2
 .Os
 .Sh NAME
@@ -201,6 +201,12 @@ a
 (or equivalent), it blocks until all of the calling process's child
 processes terminate, and then returns a value of -1 with errno set to
 .Er ECHILD .
+The same effect of avoiding zombie creation can also be achieved by setting
+.Fa sa_handler
+for
+.Dv SIGCHLD
+to
+.Dv SIG_IGN .
 .It Dv SA_ONSTACK
 If this bit is set, the system will deliver the signal to the process
 on a
@@ -601,6 +607,10 @@ and
 .\" and
 .\" SA_SIGINFO
 flags are featuring options commonly found in other operating systems.
+The flags are approved by
+.St -susv2 ,
+along with the option to avoid zombie creation by ignoring
+.Dv SIGCHLD .
 .Sh SEE ALSO
 .Xr kill 1 ,
 .Xr kill 2 ,

lib/libc/sys/wait.2

@@ -274,6 +274,14 @@ will fail and return immediately if:
 .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