GRE with key

[Cristian KLEIN]

Hello everybody,

I am new to FreeBSD kernel hacking, so please excuse my perhaps stupid
questions.

I would like to add key support to gre(4). I have already been able to
use gre(4) with a hardcoded key. The single thing remaining to do is to
transfer the key from ifconfig(8). The key is an uint32_t and I haven't
found a way to transfer it without modifying ifconfig(8).

My question is, which is the "BSD-style" to achieve the above? Solutions
I came up with are as follows:
1) Use SIOCSDRVSPEC / SIOCGDRVSPEC
2) Add SIOCSGREKEY / SIOCGGREKEY
3) [Probably to ugly to be mentioned, but requires fairy few
modifications.] Add a sysctl MIB which is read when calling "ifconfig
... create".

Another thing I wanted to ask is, which function of ifconfig(8) should I
modify to display the GRE key?

Thanks in advance.