MFC r279154,r279397:

r279154 (by jilles):

nice(): Correct return value and [EPERM] error.

PR:		189821
Obtained from:	NetBSD
Relnotes:	yes

r279397 (by jilles):

nice(): Put back old return value, keeping [EPERM] error.

Commit r279154 changed the API and ABI significantly, and {NZERO} is still
wrong.

Also, preserve errno on success instead of setting it to 0.

PR:		189821
Relnotes:	yes

2 files changed, 43 insertions, 9 deletions

diff --git a/lib/libc/gen/nice.3 b/lib/libc/gen/nice.3
index 9c39b78..8ce13af 100644
--- a/lib/libc/gen/nice.3
+++ b/lib/libc/gen/nice.3
@@ -28,7 +28,7 @@
 .\"     @(#)nice.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd June 4, 1993
+.Dd February 28, 2015
 .Dt NICE 3
 .Os
 .Sh NAME
@@ -48,20 +48,48 @@ 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 .
+function adds
+.Fa incr
+to the scheduling priority of the process.
 The priority is a value in the range -20 to 20.
 The default priority is 0; lower priorities cause more favorable scheduling.
 Only the super-user may lower priorities.
 .Pp
 Children inherit the priority of their parent processes via
 .Xr fork 2 .
+.Sh RETURN VALUES
+Upon successful completion,
+.Fn nice
+returns 0, and
+.Va errno
+is unchanged.
+Otherwise, \-1 is returned, the process' nice value is not changed, and
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+The
+.Fn nice
+function will fail if:
+.Bl -tag -width Er
+.It Bq Er EPERM
+The
+.Fa incr
+argument is negative and the caller does not have appropriate privileges.
+.El
 .Sh SEE ALSO
 .Xr nice 1 ,
 .Xr fork 2 ,
 .Xr setpriority 2 ,
 .Xr renice 8
+.Sh STANDARDS
+The
+.Fn nice
+function conforms to
+.St -p1003.1-2008
+except for the return value.
+This implementation returns 0 upon successful completion but 
+the standard requires returning the new nice value,
+which could be \-1.
 .Sh HISTORY
 A
 .Fn nice
diff --git a/lib/libc/gen/nice.c b/lib/libc/gen/nice.c
index e8375e8..ba9524b 100644
--- a/lib/libc/gen/nice.c
+++ b/lib/libc/gen/nice.c
@@ -43,14 +43,20 @@ __FBSDID("$FreeBSD$");
  * Backwards compatible nice.
  */
 int
-nice(incr)
-	int incr;
+nice(int incr)
 {
-	int prio;
+	int saverrno, prio;
 
+	saverrno = errno;
 	errno = 0;
 	prio = getpriority(PRIO_PROCESS, 0);
-	if (prio == -1 && errno)
+	if (prio == -1 && errno != 0)
 		return (-1);
-	return (setpriority(PRIO_PROCESS, 0, prio + incr));
+	if (setpriority(PRIO_PROCESS, 0, prio + incr) == -1) {
+		if (errno == EACCES)
+			errno = EPERM;
+		return (-1);
+	}
+	errno = saverrno;
+	return (0);
 }