how does it pass in the rule sets

[bycn82]

On 4/21/14 22:34, Andrey V. Elsukov wrote:
> On 19.04.2014 11:45, bycn82 wrote:
>> Hi,
>> can someone help to explain how does the user land command `ipfw` pass
>> the rule set into the hook function in the kernel? I assume that it must
>> be hardcoded in somewhere, but I did not find it yet.
> ipfw(8) uses raw socket and setsockopt(2)/getsockopt(2) functions to
> interact with kernel. In particular, do_cmd() function from ipfw2.c does it.
>
Thanks very much,
Actually I saw the source already, the ipfw_ctl() method. I would like 
to call it as "an event handler"
But why it will triggered?  where are the code to register this method 
as listener?
Sorry for using Java terminologies ;)