[U-Boot] [PATCH v3 02/21] net: Move MAC-seeded rand out of bootp.c

[Joe Hershberger]

Hi Michael,

On Tue, May 29, 2012 at 1:23 PM, Michael Walle <michael at walle.cc> wrote:
> Hi Joe,
>
> Am Dienstag 29 Mai 2012, 20:08:26 schrieb Joe Hershberger:
>> If you can verify that the functionality of the
>> CONFIG_BOOTP_RANDOM_DELAY and CONFIG_CMD_LINK_LOCAL are uneffected,
>> then I'm OK with it.
>>
>> One thing to note is that the link-local implementation needs to use a
>> MAC seeded random number.  That means we can't have other things
>> coming in and seeding it with a time.  It is nice that it is separate
>> for that reason.  Can you solve that and integrate it with your PRNG?
>
> I'm in a hurry, short answer for now:
> I thought of sth like this:
>
> static inline void srand_mac(void)
> {
>        unsigned char enetaddr[6];
>        unsigned int seed;
>
>        /* get our mac */
>        eth_getenv_enetaddr("ethaddr", enetaddr);
>
>        seed = enetaddr[5];
>        seed |= enetaddr[4] << 8;
>        seed |= enetaddr[3] << 16;
>        seed |= enetaddr[2] << 24;
>
>        srand(seed);
> }

I'm not sure why you are only seeding with the last 4 bytes of the
MAC.  The original algorithm used all 6 (in its way).  You also
haven't addressed the issue of isolating the link-local algorithm from
other non-MAC-seeded random numbers.  The most naive way around it
would be to rename the rand() in net to rand_mac() or something like
that and not attempt to combine them.

-Joe