sched/sched_setparam.c

/****************************************************************************
 * sched/sched_setparam.c
 *
 *   Copyright (C) 2007, 2009, 2013 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <sys/types.h>
#include <sched.h>
#include <errno.h>

#include <nuttx/arch.h>

#include "os_internal.h"

/****************************************************************************
 * Definitions
 ****************************************************************************/

/****************************************************************************
 * Private Type Declarations
 ****************************************************************************/

/****************************************************************************
 * Global Variables
 ****************************************************************************/

/****************************************************************************
 * Private Variables
 ****************************************************************************/

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name:  sched_setparam
 *
 * Description:
 *   This function sets the priority of a specified task.
 *
 *   NOTE: Setting a task's priority to the same value has a similar effect
 *   to sched_yield() -- The task will be moved to  after all other tasks
 *   with the same priority.
 *
 * Inputs:
 *   pid - the task ID of the task to reprioritize.  If pid is zero, the
 *      priority of the calling task is changed.
 *   param - A structure whose member sched_priority is the integer priority.
 *      The range of valid priority numbers is from SCHED_PRIORITY_MIN
 *      through SCHED_PRIORITY_MAX.
 *
 * Return Value:
 *   On success, sched_setparam() returns 0 (OK). On error, -1 (ERROR) is
 *   returned, and errno is set appropriately.
 *
 *  EINVAL The parameter 'param' is invalid or does not make sense for the
 *         current scheduling policy.
 *  EPERM  The calling task does not have appropriate privileges.
 *  ESRCH  The task whose ID is pid could not be found.
 *
 * Assumptions:
 *
 ****************************************************************************/

int sched_setparam(pid_t pid, const struct sched_param *param)
{
  FAR struct tcb_s *rtcb;
  FAR struct tcb_s *tcb;
  int ret;

  /* Verify that the requested priority is in the valid range */

  if (!param)
    {
      errno = EINVAL;
      return ERROR;
    }

  /* Prohibit modifications to the head of the ready-to-run task
   * list while adjusting the priority
   */

  sched_lock();

  /* Check if the task to reprioritize is the calling task */

  rtcb = (FAR struct tcb_s*)g_readytorun.head;
  if (pid == 0 || pid == rtcb->pid)
    {
      tcb = rtcb;
    }

  /* The pid is not the calling task, we will have to search for it */

  else
    {
      tcb = sched_gettcb(pid);
      if (!tcb)
        {
          /* No task with this pid was found */

          errno = ESRCH;
          sched_unlock();
          return ERROR;
        }
    }

 /* Then perform the reprioritization */

 ret = sched_reprioritize(tcb, param->sched_priority);
 sched_unlock();
 return ret;
}