header file related question

[vxp]

hi,

i realize it's most likely a stupid question, but try not to be too hard
on me please - i'm trying to learn :)

i'm experimenting with the kernel's source, and i'm not quite sure how to
find what all the header files are that i need, for the stuff i'd like to
do.. how do i track down what header files i need to #include in my stuff?

for instance, i'm trying to modify icmp_input() (found in
/sys/netinet/ip_icmp.c) and load the new function via a kernel module.

so, i copied all the #include's from /sys/netinet/ip_icmp.c and only have
the icmp_input() function (unmodified right now, from the form i found
it), the header files from the original ip_icmp, and a main() that
simply returns 0. doesn't want to compile, with errors about header files
such as:
---------------
In file included from icmp.c:37:
/usr/include/netinet/in_var.h:50: error: field `ia_ifa' has incomplete
type
In file included from /usr/include/netinet/in_var.h:238,
                 from icmp.c:37:
/usr/include/netinet6/in6_var.h:103: error: field `ia_ifa' has incomplete
type
---------------
i realize that it's most likely because i didn't #include something else i
need..  but how come /sys/netinet/ip_icmp.c compiles, then?  because this
file is basically that, with all functions but icmp_input removed, and a
main() that does nothing..

so.. sorry for the long post.
but please tell me how do i find out what header files i need ? :)

thanks.

Val