if (!ibuf || !buf) {

    perror("malloc");

    exit(1);

  }

  if ((f = fopen(argv[2], "rb"))==NULL) {

    perror(argv[2]);

    exit(1);

  }

  if (fseek(f, offset, SEEK_SET)==-1) {

    perror("fseek");

    exit(1);

  }

  if (fread(ibuf, 1, length, f)!=length) {

    perror("fread");

    exit(1);

  }