setloadavg.c

#define _GNU_SOURCE
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>

void *worker(void *data) {
	int fd = open("/tmp/setloadavg", O_RDWR|O_CREAT|O_DIRECT);
	if (fd == -1) {
		perror("open");
		return NULL;
	}
	FILE *fp = fdopen(fd, "rb+");
	if (fp == NULL) {
		close(fd);
		perror("fdopen");
		return NULL;
	}

	char buf[256];
	char mybyte = rand() % 256;

	for (int i = 0; i < sizeof(buf); i++) {
		buf[i] = mybyte;
	}

	while (1) {
		fseek(fp, 0, SEEK_SET);
		fwrite(buf, 1, sizeof(buf), fp);
		fflush(fp);
	}

	return NULL;
}

int main(int argc, char *argv[]) {
	if (argc < 2) {
		printf("usage: %s <target>\n", argv[0]);
		return 1;
	}

	int target = atoi(argv[1]);
	printf("spinning up %i threads...\n", target);

	pthread_t *threads = (pthread_t *)malloc(sizeof(pthread_t) * target);
	for (int i = 0; i < target; i++) {
		pthread_create(&threads[i], NULL, worker, NULL);
	}
	for (int i = 0; i < target; i++) {
		pthread_join(threads[i], NULL);
	}
	return 0;
}