[parted-devel] generate_random_id() fix

[H. Peter Anvin]

Jim Meyering wrote:
> 
> 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?

I would avoid using the UUID, since the UUID is not guaranteed to be
random in any way -- in fact, even for a "random" UUID there are at
least 6 bits which are fixed.

I don't know exactly what uuid_generate() does, so it's hard to say
exactly if this is a problem or not.  At the very least I would XOR the
different words of the UUID together.

	-hpa