sched_test.c

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <sys/types.h>
#include <sys/wait.h>

#define SCHED_LIFO 7
#define GET_CURRENT_POLICY 9999

#define error_exit(msg) \
	do { \
		perror(msg); \
		exit(-1); \
        } while(0);

static void usage(char *name)
{
	fprintf(stderr, "usage: %s [orflg] -- command line to run at chaild process\n", name);
	exit(-1);
}

static int get_policy(int argc, char **argv)
{
	int opt, policy;

	while ((opt = getopt(argc, argv, "orflg")) != -1) {
		switch (opt) {
			case 'o':
				policy = SCHED_OTHER;
				break;
			case 'r':
				policy = SCHED_RR;
				break;
			case 'f':
				policy = SCHED_FIFO;
				break;
			case 'l':
				policy = SCHED_LIFO;
				break;
			case 'g':
				policy = GET_CURRENT_POLICY;
				break;
			default:
				usage(argv[0]);
		}
	}

	return policy;
}

static int get_current_scheduler(pid_t pid)
{
	int ret = sched_getscheduler(pid);
	if (ret < 0)
		error_exit("sched_getscheduler");
	return ret;
}

static void show_current_policy(void)
{
	printf("current policy is %d\n", get_current_scheduler(getpid()));
	exit(0);
}

int main(int argc, char **argv)
{
	int policy = get_policy(argc, argv);

	if (policy == GET_CURRENT_POLICY)
		show_current_policy();

	pid_t pid;

	pid = fork();
	if (!pid) { // child
		pid_t my_pid = getpid();
		struct sched_param param = { 0 };
		if (policy != SCHED_OTHER)
			param.sched_priority = policy;

		printf("current schedulering policy is %d\n", get_current_scheduler(my_pid));
		int ret = sched_setscheduler(my_pid, policy, &param);
		if (ret)
			error_exit("sched_setscheduler");

		printf("schedulering policy set to %d\n", get_current_scheduler(my_pid));
		extern int optind;

		char **cmdline = argv + optind;

		ret = execve(cmdline[0], cmdline, NULL);
		if (ret)
			error_exit("execve");
	} else if (pid > 0) { // parent
		waitpid(pid, NULL, 0);
	} else {
		error_exit("fork");
	}

	return 0;
}