Make nice(3) standards compliant; adapted from patch by Matthias Drochner

While I'm here correct the lies in the manual page.

2 files changed, 30 insertions, 10 deletions

diff --git a/lib/libc/gen/nice.3 b/lib/libc/gen/nice.3
index 8e4a5365a68..41bfa6e979f 100644
--- a/lib/libc/gen/nice.3
+++ b/lib/libc/gen/nice.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: nice.3,v 1.11 2001/05/05 23:12:07 millert Exp $
+.\"	$OpenBSD: nice.3,v 1.12 2002/06/03 22:32:04 millert Exp $
 .\"
 .\" Copyright (c) 1980, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -36,7 +36,7 @@
 .Os
 .Sh NAME
 .Nm nice
-.Nd set program scheduling priority
+.Nd change process scheduling priority
 .Sh SYNOPSIS
 .Fd #include <unistd.h>
 .Ft int
@@ -49,18 +49,35 @@ This interface is obsoleted by
 .Pp
 The
 .Fn nice
-function obtains the scheduling priority of the process
-from the system and sets it to the priority value specified in
-.Fa incr .
-The priority is a value in the range \-20 to 20.
+function adds the value specified in
+.Fa incr
+to the scheduling priority of the invoking process.
+.Pp
+.Fa incr
+is an integer such that the resulting scheduling priority
+is within the range \-20 to 20.
 The default priority is 0; lower priorities cause more favorable scheduling.
 Only the superuser may lower priorities.
 .Pp
 Children inherit the priority of their parent processes via
 .Xr fork 2 .
 .Sh RETURN VALUES
+On success,
+.Fn nice
+returns the new priority.
+On error, it returns -1.
+.Pp
+Since
+.Fn nice
+can legitimately return the value -1, it is necessary
+to clear the external variable
+.Va errno
+prior to the
+call, then check it afterward to determine
+if a -1 is an error or a legitimate value.
+.Sh ERRORS
 .Fn nice
-returns the same values as
+has the same failure conditions as
 .Xr setpriority 2 .
 .Sh SEE ALSO
 .Xr nice 1 ,
diff --git a/lib/libc/gen/nice.c b/lib/libc/gen/nice.c
index b6a95079fa6..6c312a1da29 100644
--- a/lib/libc/gen/nice.c
+++ b/lib/libc/gen/nice.c
@@ -32,7 +32,7 @@
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char rcsid[] = "$OpenBSD: nice.c,v 1.3 1998/05/06 23:11:43 deraadt Exp $";
+static char rcsid[] = "$OpenBSD: nice.c,v 1.4 2002/06/03 22:32:04 millert Exp $";
 #endif /* LIBC_SCCS and not lint */
 
 #include <sys/types.h>
@@ -42,7 +42,7 @@ static char rcsid[] = "$OpenBSD: nice.c,v 1.3 1998/05/06 23:11:43 deraadt Exp $"
 #include <unistd.h>
 
 /*
- * Backwards compatible nice.
+ * Backwards compatible nice().
  */
 int
 nice(incr)
@@ -54,5 +54,8 @@ nice(incr)
 	prio = getpriority(PRIO_PROCESS, 0);
 	if (prio == -1 && errno)
 		return (-1);
-	return (setpriority(PRIO_PROCESS, 0, prio + incr));
+	prio += incr;
+	if (setpriority(PRIO_PROCESS, 0, prio) != 0)
+		return (-1);
+	return (prio);
 }