fd = open(argv[1], O_RDWR);
	if (fd == -1) {
		error_message(__FILE__, __LINE__, "'open' failed ");
		return 1;
	}
 
	// find out the size of the file in bytes
	// we need the size, because we cannot write past the end of the file
	// so, we need to make sure not to write at an offset larger than 'info.st_size'
	if (fstat(fd, &info) == -1) {
		error_message(__FILE__, __LINE__, "'fstat' failed ");
		return 1;
	}
 
	printf("The file has %ld bytes\n", info.st_size);
	if (info.st_size == 0) {
		fprintf(stderr, "We cannot map a file with size 0\n");
		return 0;
	}
 
 
	// TODO
	mapping = mmap(NULL, info.st_size, PROT_WRITE, MAP_PRIVATE, fd, 0);
	if (mapping == MAP_FAILED) {
		perror("mmap:");
		return -1;
	}
	else fprintf(stderr, "Successful mapping at the address %p\n", mapping);
 
	memcpy(mapping, "hello", 5);
 
	if (msync(mapping, info.st_size, MS_SYNC) == -1) {
		perror("msync:");
		return -1;
	}	
 
	// close the file
	if (close(fd) == -1) {
		error_message(__FILE__, __LINE__, "'close' failed ");
		return 1;
	}