/*
 * Moritz Orbach
 * Mo 21. Nov 00:21:03 CET 2011
 *
 * GPL
 * gcc -Wall procinfo.c -o procinfo
 *
 * How to get nice value (priority) scheduler and real time priority  of a 
 * process in C (like chrt -p PID from util-linux)
 *
 * Don't forget to look at threads! "H" in top or something like
 * for i in $(ps -eLf| awk '$10 ~ /^hydrogen$/ { print $4 }'); do echo $i; ./procinfo $i; echo;done
 *
 * man getpriority
 * http://oreilly.com/catalog/linuxkernel/chapter/ch10.html#40766
 * http://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_setschedprio.html
 * http://pubs.opengroup.org/onlinepubs/009695399/functions/setpriority.html
 */
#include <stdio.h>
#include <stdlib.h>
#include <error.h>
#include <errno.h>
#include <string.h>

/* getpriority */
#include <sys/time.h>
#include <sys/resource.h>

/* sched_getscheduler, sched_getparam */
#include <sched.h>

/* schedulers */
#include <linux/sched.h>

typedef struct scheduler_t {
	int index;
	char *name[128];
	/* int descht; */
} scheduler_t;

/* from linux/sched.h */
static scheduler_t schedulers[] = {
	{ SCHED_NORMAL,	{ "SCHED_NORMAL/SCHED_OTHER" } },
	{ SCHED_FIFO,	{ "SCHED_FIFO"   } },
	{ SCHED_RR,	{ "SCHED_RR"     } },
	{ SCHED_BATCH,	{ "SCHED_BATCH"  } },
	{ SCHED_IDLE,	{ "SCHED_IDLE"   } }
};


/*
 * string to int
 * returns
 *   0 if string is no number
 *   1 success
 */
int s2int(char *str, int *number)
{
	char *endptr;

	errno = 0;	/* To distinguish success/failure after call */
	*number = strtol(str, &endptr, 10);
	if (errno || *endptr != '\0') {
		if (errno) {
			perror("strtol");
		}
		return 0;
	}
	return 1;
}

void usage(void)
{
	printf("usage: procinfo PID\n");
}


/* 
 * nice value
 *
 * int getpriority(int which, int who);
 * int setpriority(int which, int who, int prio);
 */
int get_nice(pid_t pid, int *priority)
{

	errno = 0; /* so says the man page. Why? */
	*priority = getpriority(PRIO_PROCESS, pid);

	return errno == 0;
}


/*
 * int sched_getscheduler(pid_t pid);
 */
int get_schedpolicy(pid_t pid, int *algorithm)
{
	*algorithm = sched_getscheduler(pid);
	return *algorithm != -1;
}

/*
 * int sched_getparam(pid_t pid, struct sched_param *param);
 */
int get_schedparams(pid_t pid, int *priority)
{
	struct sched_param param;

	if (sched_getparam(pid, &param) != -1) {
		*priority = param.sched_priority;
		return 1;
	} else 
		return 0;
}


/*
 *
 */

int main(int argc, char *argv[])
{
	pid_t pid;

	if (argc != 2) {
		usage();
		return EXIT_FAILURE;
	}

	if (strcmp(argv[1], "-h") == 0) {
		usage();
		return EXIT_SUCCESS;
	}

	if (!s2int(argv[1], &pid)) {
		usage();
		return EXIT_FAILURE;
	}

	/* */
	int nice;
	if (get_nice(pid, &nice))
		printf("nice value\t: %d\n", nice);
	else {
		perror("getpriority");
		return EXIT_FAILURE;
	}


	/* */
	int scheduler;
	if (get_schedpolicy(pid, &scheduler))
		printf("scheduler\t: %s (%d)\n", *schedulers[scheduler].name, scheduler);
	else {
		perror("sched_getscheduler");
		return EXIT_FAILURE;
	}

	/* */
	int priority;
	if (get_schedparams(pid, &priority))
		printf("priority\t: %d\n", priority);
	else {
		perror("sched_getparam");
		return EXIT_FAILURE;
	}

	/*
	printf("Other threads of this process may have other values!\n");
	 */

	return EXIT_SUCCESS;
}