text: /****************************************************************************
   * libs/libc/unistd/lib_getpriority.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 <nuttx/config.h>
  #include <sys/resource.h>
  
  #include <sched.h>
  #include <unistd.h>
  #include <errno.h>
  
  /****************************************************************************
   * Public Functions
   ****************************************************************************/
  
  /****************************************************************************
   * Name: getpriority
   *
   * Description:
   *   The getpriority() function shall obtain the nice value of a process,
   *   process group, or user.
   *
   * Input Parameters:
   *   which  - PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, ignored in current
   *            implementation.
   *   who    - Process id is interpreted relative to "which"
   *
   * Returned Value:
   *   Upon successful completion, getpriority() shall return an integer in
   *   the range -{NZERO} to {NZERO}-1. Otherwise, -1 shall be returned and
   *   errno set to indicate the error. The following errors may be
   *   reported:
   *
   *   - ESRCH: No process was located using the which and who values
   *            specified.
   *   - EINVAL: which was not one of PRIO_PROCESS, PRIO_PGRP, or
   *             PRIO_USER.
   *
   * Assumptions:
   *
   ****************************************************************************/
  
  int getpriority(int which, id_t who)
  {
    struct sched_param param;
    int ret;
  
    if (which > PRIO_USER || which < PRIO_PROCESS)
      {
        set_errno(EINVAL);
        return ERROR;
      }
  
    if (who == 0)
      {
        who = getpid();
      }
  
    ret = sched_getparam(who, &param);
    if (ret < 0)
      {
        return ret;
      }
  
    /* Since -1 is a legal return value, clear errno to avoid the chaos */
  
    set_errno(0);
  
    return NZERO - param.sched_priority;
  }
  