[parted-devel] generate_random_id() fix

[Jim Meyering]

"H. Peter Anvin" <hpa at zytor.com> wrote:
> The existing generate_random_id() in libparted only produces numbers in
> the range 0..999999, less than 20 bits.  This patch tries to get a
> random number from /dev/urandom if available, and otherwise produces a
> 32-bit value from gettimeofday().
...
> -static inline uint32_t generate_random_id (void)
> +static uint32_t
> +generate_random_id (void)
>  {
> +	int fd;
>  	struct timeval tv;
>  	int rc;
> +	uint32_t v;
> +
> +	fd = open("/dev/urandom", O_RDONLY);

Thanks for the patch.
It's definitely an improvement.

However, since there's already code to generate a 32-bit
serial number in fs/fat/fat.c:

  /* hack: use the ext2 uuid library to generate a reasonably random (hopefully
   * with /dev/random) number.  Unfortunately, we can only use 4 bytes of it
   */
  static uint32_t
  _gen_new_serial_number ()
  {
          uuid_t		uuid;

          uuid_generate (uuid);
          return * (uint32_t*) &uuid [0];
  }

I'm thinking about using something like this from both places:

  static uint32_t
  _gen_new_serial_number (void)
  {
    static uuid_t uuid;
    static unsigned int i = 0;
    unsigned int n = sizeof uuid / sizeof (uint32_t);

    if (i % n == 0)
      {
        uuid_generate (uuid);
        i = 0;
      }

    return ((uint32_t *)uuid)[i++];
  }

What do you think?