>The way to do this would be the same as other tools, such as telnet, get
>done - compile in the INET6 support from the start.  So long as all the
>IPv6 headers were available, only the code which sets up the pfil hook
>for IPv6 would need to be conditionally compiled for a kernel with or
>without IPv6.  Basically, when compiled with IPv6 support, in6_addr is
>used to store both IPv6 and IPv4 addresses and is used in structs passed
>between userland and the kernel in place of in_addr (size differences).

	Please clarify: kernel API is the same for IPv4-only kernel
	and IPv4/v6 kernel?  or will they change the size?
	If the API is kept same regardless from "options INET6" it should
	be okay.  (always use 16bytes, or use sockaddr/sockaddr_storage
	- sockaddr comes with indication of address family so it is better
	than passing in{,6}_addr) 

itojun