#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>

int main(int argc, char** argv) {
	if (geteuid() != 0) {
		fprintf(stderr, "run me as root!\n");
		return 1;
	}

	argc--; // argv[0] is the program name
	if (argc == 0) {
		fprintf(stderr, "usage: %s /dev/lork\n", argv[0]);
		return 1;
	}

	char* dev = argv[1];
	const char* input = "test";
	int fd;
	ssize_t bytes;

	fd = open(dev, O_RDWR);
	if (-1 == fd) {
		fprintf(stderr, "open() failed with code %d\n", errno);
		return 1;
	}

	bytes = write(fd, input, strlen(input));
	if (-1 == bytes) {
		fprintf(stderr, "write() failed with code %d\n", errno);
		return 1;
	}
	fprintf(stderr, "input \"%s\" to %s (%ld bytes succesful)\n", input, dev, bytes);

	char buf[80];
	bytes = read(fd, buf, 80);
	if (-1 == bytes) {
		fprintf(stderr, "read() failed with code %d\n", errno);
		return 1;
	}
	fprintf(stderr, "output from %s: (%ld bytes)\n", dev, bytes);
	if (bytes > 0) {
		if (bytes < 80) buf[bytes] = '\0'; // null terminate string for printf
		printf("%s\n", buf);
	}

	if (-1 == close(fd)) {
		fprintf(stderr, "close() failed with code %d\n", errno);
		return 1;
	}

	return 0;
}