Subject: Re: dhcpd(8) _cannot_ be completely disabled on an interface
To: Michael Richardson <firstname.lastname@example.org>
From: Andrew Brown <email@example.com>
Date: 01/14/2002 04:04:04
> Andrew> does the interface pppoe0 get destroyed and created at each line drop,
> Andrew> or just go up and down? it's only destruction and creation that cause
> Andrew> the interface index to get bumped...
> Ah. I see.
> I'm still not clear why the 2 bytes here are so expensive, given typical
from the point of view of a struct ifnet, no, it might not make much
difference, however, from the point of view of the struct sockaddr_dl,
it makes a huge difference. that's very visible structure from
userland's point of view, and the two indices need to be the same
i can't see that it's really an issue that the numbers roll over. i
could just as easily cause a 32 bit counter to roll over as a 16 bit
counter. it would just take longer.
# time sh -c 'for i in $(jot 100); do ifconfig tun0 create ; ifconfig tun0 destroy ; done'
0.012u 0.043s 0:00.25 20.0% 0+0k 0+0io 0pf+0w
there. i just bumped it by 100 in a quarter of a second. by
extrapolation, that's 65536 in about three minutes. 32 bits would
take over four months at that rate, but i could easily write a c
program that just called SIOCIFCREATE and SIOCIFDESTROY repeatedly and
avoided the fork/exec/parse command line overhead, as well as all the
other associated system calls.
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