Re: [PATCH 1/5] UML - Assign random MACs to interfaces if necessary

From: dhollis
Date: Wed Sep 27 2006 - 15:33:15 EST

Quoting Jeff Dike <jdike@xxxxxxxxxxx>:

Assign a random MAC to an ethernet interface if one was not provided on
the command line. This became pressing when distros started
bringing interfaces up before assigning IPs to them. The previous
pattern of assigning an IP then bringing it up allowed the MAC to be
generated from the first IP assigned. However, once the thing is
up, it's probably a bad idea to change the MAC, so the MAC stayed
initialized to fe:fd:0:0:0:0.

Now, if there is no MAC from the command line, one is generated. We
use the microseconds from gettimeofday (20 bits), plus the low 12
bits of the pid to seed the random number generator. random() is
called twice, with 16 bits of each result used. I didn't want to
have to try to fill in 32 bits optimally given an arbitrary
RAND_MAX, so I just assume that it is greater than 65536 and use 16
bits of each random() return.

There is also a bit of reformatting and whitespace cleanup here.

Signed-off-by: Jeff Dike <jdike@xxxxxxxxxxx>

Couldn't you use random_ether_addr() from linux/etherdevice.h?

static inline void random_ether_addr(u8 *addr)
get_random_bytes (addr, ETH_ALEN);
addr [0] &= 0xfe; /* clear multicast bit */
addr [0] |= 0x02; /* set local assignment bit (IEEE802) */

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