/* GPL (includes a few bits from the linux kernel) */
/* gcc -lm loadavg.c */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/sysinfo.h> /* gets SI_LOAD_SHIFT 16 from linux/kernel.h */
#include <math.h>

#define HZ 100

/* linux-2.6.32.27/include/linux/sched.h */
#define FSHIFT		11		/* nr of bits of precision */
#define FIXED_1		(1<<FSHIFT)	/* 1.0 as fixed-point */
#define LOAD_FREQ	(5*HZ+1)	/* 5 sec intervals */
#define EXP_1		1884		/* 1/exp(5sec/1min) as fixed-point */
#define EXP_5		2014		/* 1/exp(5sec/5min) */
#define EXP_15		2037		/* 1/exp(5sec/15min) */

#define CALC_LOAD(load,exp,n) \
	load *= exp; \
	load += n*(FIXED_1-exp); \
	load >>= FSHIFT;

/* linux-2.6.32.27/kernel/sched.c */
static unsigned long
calc_load(unsigned long load, unsigned long exp, unsigned long active)
{
	load *= exp;
	load += active * (FIXED_1 - exp);
	return load >> FSHIFT;
}

/* fs/proc/loadavg.c */
#define LOAD_INT(x) ((x) >> FSHIFT)
#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)

/* end from kernel */


#define OUTSECS 5 /* length of rrd output interval */
#define OUTTICKS (100*OUTSECS) /* we assume HZ 100 regardless of actual value */

static int fakeload; /* first fakeload ticks per sec have load 1 */
static int intervals = 720; /* 1 hour at 5 sec intervals */
static int load_freq = 461; /* freq at which we probe */
static int printick; /* print each nth tick */
static unsigned long load, fload, pload; /* computed, fakeload, printload */
static long long nextmsec;
static double kload; /* kernel load */
static int basetime = 946684805; /* 1.1.2000 UTC + 5 sec, rrdtool refuses <1980 */
static int exp_1 = 1896; /* for 13 probes/min: 1896 2017 2038 */


int main (int argc, char **argv)
{
	struct timeval tv;
	int tick = 0, i,t,m,probesmin;

	while (--argc && '-' == **++argv)
		switch ((*argv)[1]) {
		case 'i': intervals = atoi((*argv)+2); break; /* -i1440 */
		case 'f': load_freq = atoi((*argv)+2); break; /* -f501 */
		case 'l': fakeload  = atoi((*argv)+2); break; /* -l30 */
		case 'p': printick  = atoi((*argv)+2); break; /* -p1 */
		case 'b': basetime  = atoi((*argv)+2); break; /* -b0 */
		case 'e': probesmin = atoi((*argv)+2); /* -e13 */
			exp_1  = round(FIXED_1 / exp(1./probesmin));
			fprintf(stderr, "EXP_1 %d %d %d\n",
				exp_1,
				(int)round(FIXED_1 / exp(1./5/probesmin)),
				(int)round(FIXED_1 / exp(1./15/probesmin)));
		}

	gettimeofday(&tv, 0);
	nextmsec = tv.tv_sec*1000 + tv.tv_usec/1000 + 1;
	if (!basetime) basetime = OUTSECS*(tv.tv_sec/OUTSECS);

	for (i=0; i<intervals; i++) {
		unsigned long sumload = 0;
		for (t=0; t<OUTTICKS; t++, tick++) {
			unsigned long curload, tickload;
			if (fakeload) { /* get cur and avg load for tick */
				curload = fakeload>(t%100) ? 1 : 0;
				tickload = 10*curload;
				if (!(tick % LOAD_FREQ)) {
					fload = calc_load(fload, EXP_1, curload*FIXED_1);
					kload = (double)fload/FIXED_1;
				}
			} else { /* take 10 msec probes */
				int runnable;
				double kl5, kl15;
				tickload = 0;
				for (m=10; m--; nextmsec++) {
					char buf[100];
					int f;
					long long udiff;
					gettimeofday(&tv, 0);
					udiff = nextmsec*1000 - tv.tv_sec*1000000 - tv.tv_usec;
					if (0 < udiff) usleep((__useconds_t)udiff);
					/* sysinfo has the loads but not runnable processes */
					f = open("/proc/loadavg", O_RDONLY);
					read(f, buf, sizeof buf);
					close(f);
					sscanf(buf, "%lf %lf %lf %d", &kload, &kl5, &kl15, &runnable);
					tickload += runnable - 1; /* do not count this process */
				}
				curload = runnable - 1;
			}
			sumload += tickload;
			if (!(tick % load_freq))
				load = calc_load(load, exp_1, curload*FIXED_1);
			if (printick && !(t % printick))
				fprintf(stderr, "%d\t%.3f\t%lu.%03lu\t%.2f\n",
					tick, tickload/10.,
					LOAD_INT(load), LOAD_INT(((load) & (FIXED_1-1)) * 1000),
					kload
					);
		}
		pload = load + FIXED_1/200; /* +0.5% as in fs/proc/loadavg.c get_avenrun */
		printf("update loadavg.rrd %d:%.3f:%lu.%02lu:%.2f\n",
			basetime + i*OUTSECS,
			sumload/(OUTSECS*1000.), /* real interval load on msec basis */
			LOAD_INT(pload), LOAD_FRAC(pload),
			kload
		);
	}	/* for intervals */
	return 0;
}