Dear Josh,
In message 55F91588.3040305@atmel.com you wrote:
In above commands, I have two duplicated eth addr: 92:33:16:3f:0a:56 d2:41:66:54:64:aa
Agreed. Randomness is really poor; for a sequence of 1000 invocations of gen_eth_addr in a shell loop I would only gt 124 different MAC addresses:
-> for i in {1..1000} ; do ./gen_eth_addr ; done >/tmp/0 -> sort -u /tmp/0 >/tmp/1 ; wc -l /tmp/[01] 1000 /tmp/0 124 /tmp/1
In a second run, even only 41 :-(
But without the getpid() part, it gets even worse - the same loop would produce only 15 different addresses!
Changing the '|' into a '+' would reliably generate 1000 different MAC addresses.
I understand your concern. My intention is make it harder to generate the duplicated result.
I understand this, and agree that we should implement such a fix.
Maybe we can ORing the MSB of time(0)? I'll investigate it little more.
The following patch appears to work fine for me. Maybe you can test it?
diff --git a/tools/gen_eth_addr.c b/tools/gen_eth_addr.c index bf9d935..834163a 100644 --- a/tools/gen_eth_addr.c +++ b/tools/gen_eth_addr.c @@ -15,7 +15,7 @@ main(int argc, char *argv[]) { unsigned long ethaddr_low, ethaddr_high;
- srand(time(0) | getpid()); + srand(time(0) + getpid());
/* * setting the 2nd LSB in the most significant byte of
Thanks.
Best regards,
Wolfgang Denk