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chrt.c

/*
 * chrt.c - chrt
 * Command-line utility for manipulating a task's real-time attributes 
 *
 * Robert Love <rml@tech9.net>
 * 27-Apr-2002: initial version
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, v2, as
 * published by the Free Software Foundation
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * Copyright (C) 2004 Robert Love
 */

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <unistd.h>
#include <getopt.h>
#include <errno.h>

static void show_usage(const char *cmd)
{
      fprintf(stderr, "chrt version " VERSION "\n");
      fprintf(stderr, "usage: %s [options] [prio] [pid | cmd [args...]]\n",
                  cmd);
      fprintf(stderr, "manipulate real-time attributes of a process\n");
      fprintf(stderr, "  -f, --fifo                         "
                  "set policy to SCHED_FF\n");
      fprintf(stderr, "  -p, --pid                          "
                  "operate on existing given pid\n");
      fprintf(stderr, "  -m, --max                          "
                  "show min and max valid priorities\n");
      fprintf(stderr, "  -o, --other                        "
                  "set policy to SCHED_OTHER\n");
      fprintf(stderr, "  -r, --rr                           "
                  "set policy to SCHED_RR (default)\n");
      fprintf(stderr, "  -h, --help                         "
                  "display this help\n");
      fprintf(stderr, "  -v, --verbose                      "
                  "display status information\n");
      fprintf(stderr, "  -V, --version                      "
                  "output version information\n\n");
      fprintf(stderr, "You must give a priority if changing policy.\n\n");
      fprintf(stderr, "Report bugs and send patches to <rml@tech9.net>\n");
}

static void show_rt_info(const char *what, pid_t pid)
{
      struct sched_param sp;
      int policy;

      /* don't display "pid 0" as that is confusing */
      if (!pid)
            pid = getpid();

      policy = sched_getscheduler(pid);
      if (policy == -1) {
            perror("sched_getscheduler");
            fprintf(stderr, "failed to get pid %d's policy\n", pid);
            exit(1);
      }

      printf("pid %d's %s scheduling policy: ", pid, what);
      switch (policy) {
      case SCHED_OTHER:
            printf("SCHED_OTHER\n");
            break;
      case SCHED_FIFO:
            printf("SCHED_FIFO\n");
            break;
      case SCHED_RR:
            printf("SCHED_RR\n");
            break;
      default:
            printf("unknown\n");
      }

      if (sched_getparam(pid, &sp)) {
            perror("sched_getparam");
            fprintf(stderr, "failed to get pid %d's attributes\n", pid);
            exit(1);
      }

      printf("pid %d's %s scheduling priority: %d\n",
            pid, what, sp.sched_priority);
}

static void show_min_max(void)
{
      int max, min;

      max = sched_get_priority_max(SCHED_FIFO);
      min = sched_get_priority_min(SCHED_FIFO);
      if (max >= 0 && min >= 0)
            printf("SCHED_FIFO min/max priority\t: %d/%d\n", min, max);
      else
            printf("SCHED_FIFO not supported?\n");

      max = sched_get_priority_max(SCHED_RR);
      min = sched_get_priority_min(SCHED_RR);
      if (max >= 0 && min >= 0)
            printf("SCHED_RR min/max priority\t: %d/%d\n", min, max);
      else
            printf("SCHED_RR not supported?\n");

      max = sched_get_priority_max(SCHED_OTHER);
      min = sched_get_priority_min(SCHED_OTHER);
      if (max >= 0 && min >= 0)
            printf("SCHED_OTHER min/max priority\t: %d/%d\n", min, max);
      else
            printf("SCHED_OTHER not supported?\n");
}

int main(int argc, char *argv[])
{
      int i, policy = SCHED_RR, priority = 0, verbose = 0;
      struct sched_param sp;
      pid_t pid = 0;

      struct option longopts[] = {
            { "fifo",   0, NULL, 'f' },
            { "pid",    0, NULL, 'p' },
            { "help",   0, NULL, 'h' },
            { "max",        0, NULL, 'm' },
            { "other",  0, NULL, 'o' },
            { "rr",           0, NULL, 'r' },
            { "verbose",      0, NULL, 'v' },
            { "version",      0, NULL, 'V' },
            { NULL,           0, NULL, 0 }
      };

      while((i = getopt_long(argc, argv, "+fphmorvV", longopts, NULL)) != -1)
      {
            int ret = 1;

            switch (i) {
            case 'f':
                  policy = SCHED_FIFO;
                  break;
            case 'm':
                  show_min_max();
                  return 0;
            case 'o':
                  policy = SCHED_OTHER;
                  break;
            case 'p':
                  errno = 0;
                  pid = strtol(argv[argc - 1], NULL, 10);
                  if (errno) {
                        perror("strtol");
                        fprintf(stderr, "failed to parse pid!\n");
                        return 1;
                  }
                  break;
            case 'r':
                  policy = SCHED_RR;
                  break;
            case 'v':
                  verbose = 1;
                  break;
            case 'V':
                  printf("chrt version " VERSION "\n");
                  return 0;
            case 'h':
                  ret = 0;
            default:
                  show_usage(argv[0]);
                  return ret;
            }
            
      }

      if ((pid && argc - optind < 1) || (!pid && argc - optind < 2)) {
            show_usage(argv[0]);
            return 1;
      }

      if (pid && (verbose || argc - optind == 1)) {
            show_rt_info("current", pid);
            if (argc - optind == 1)
                  return 0;
      }

      errno = 0;
      priority = strtol(argv[optind], NULL, 10);
      if (errno) {
            perror("strtol");
            fprintf(stderr, "failed to parse priority!\n");
            return 1;
      }

      sp.sched_priority = priority;
      if (sched_setscheduler(pid, policy, &sp) == -1) {
            perror("sched_setscheduler");
            fprintf(stderr, "failed to set pid %d's policy\n", pid);
            return 1;
      }

      if (verbose)
            show_rt_info("new", pid);

      if (!pid) {
            argv += optind + 1;
            execvp(argv[0], argv);
            perror("execvp");
            fprintf(stderr, "failed to execute %s\n", argv[0]);
            return 1;
      }

      return 0;
}

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