libc/sched: Implement nice API

Specified here:
https://pubs.opengroup.org/onlinepubs/007904875/functions/nice.html

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: Ib25be28c8dc1c9288e8c78ad756c91ec6ef325a7

include/unistd.h

@@ -301,6 +301,8 @@ void    _exit(int status) noreturn_function;
 unsigned int sleep(unsigned int seconds);
 int     usleep(useconds_t usec);
 int     pause(void);
+int     nice(int inc);
+
 int     daemon(int nochdir, int noclose);
 
 /* File descriptor operations */

libs/libc/unistd/Make.defs

@@ -23,15 +23,12 @@
 CSRCS += lib_access.c lib_daemon.c lib_swab.c lib_pathconf.c lib_sysconf.c
 CSRCS += lib_getopt_common.c lib_getopt.c lib_getopt_long.c
 CSRCS += lib_getopt_longonly.c lib_getoptvars.c lib_getoptargp.c
-CSRCS += lib_getopterrp.c
-CSRCS += lib_getoptindp.c lib_getoptoptp.c
-CSRCS += lib_alarm.c lib_fstatvfs.c lib_statvfs.c lib_sleep.c
+CSRCS += lib_getopterrp.c lib_getoptindp.c lib_getoptoptp.c
+CSRCS += lib_alarm.c lib_fstatvfs.c lib_statvfs.c lib_sleep.c lib_nice.c
 CSRCS += lib_usleep.c lib_seteuid.c lib_setegid.c lib_geteuid.c lib_getegid.c
-CSRCS += lib_setreuid.c lib_setregid.c
-CSRCS += lib_getrusage.c lib_utimes.c
-CSRCS += lib_setrlimit.c lib_getrlimit.c
-CSRCS += lib_setpriority.c lib_getpriority.c
-CSRCS += lib_futimes.c lib_futimens.c
+CSRCS += lib_setreuid.c lib_setregid.c lib_getrusage.c lib_utimes.c
+CSRCS += lib_setrlimit.c lib_getrlimit.c lib_setpriority.c lib_getpriority.c
+CSRCS += lib_futimes.c lib_futimens.c lib_gethostname.c lib_sethostname.c
 
 ifneq ($(CONFIG_SCHED_USER_IDENTITY),y)
 CSRCS += lib_setuid.c lib_setgid.c lib_getuid.c lib_getgid.c
@@ -53,8 +50,6 @@ ifeq ($(CONFIG_PIPES),y)
 CSRCS += lib_pipe.c lib_pipe2.c
 endif
 
-CSRCS += lib_gethostname.c lib_sethostname.c
-
 # Add the unistd directory to the build
 
 DEPPATH += --dep-path unistd

libs/libc/unistd/lib_nice.c

@@ -0,0 +1,63 @@
+/****************************************************************************
+ * libs/libc/unistd/lib_nice.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <sys/resource.h>
+#include <unistd.h>
+#include <errno.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: nice
+ *
+ * Description:
+ *  The nice() function shall add the value of incr to the nice value of the
+ *  calling process. A process' nice value is a non-negative number for which
+ *  a more positive value shall result in less favorable scheduling.
+ *
+ ****************************************************************************/
+
+int nice(int inc)
+{
+  int prio;
+  int ret;
+
+  set_errno(0);
+  ret = getpriority(PRIO_PROCESS, 0);
+  if (get_errno() != 0)
+    {
+      return ret;
+    }
+
+  prio = ret + inc;
+  ret = setpriority(PRIO_PROCESS, 0, prio);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
+  return prio;
+}