블록킹 read 와 논 블록킹 read 질문이요

int main(void)
{
	int i;
	int key_fd;
	int key_value[2];
 
	/*Open device */
	key_fd = open("/dev/key", O_RDONLY);
	if (key_fd < 0) {
		perror("APP: open device key");
		exit(1);
	}
 
	for (;;) {
		int ret;
 
		/* start to read */
		ret = read(key_fd, key_value, sizeof key_value);
		if (ret == sizeof key_value) {
			for (i = 0; i < 2; i++) {
				if (key_value[i]) {	/* if pressed */
					if(key_value[i] == 1)
						printf("APP: Left key pressed\n");
					if(key_value[i] == 2)
						printf("APP: Right key pressed\n");
				}
			}
		} else {
			/* let system get its breath back */
			printf("...\n");
			sleep(1);
		}
	}
 
	close(key_fd);
	return 0;
}