Request for Help

[Mery'em βЄL]

HI,I'm a student preparing a Master degree , my project subject is the implementation of a   statefull ARP , I actually  did several research to find a novel solution to defend and interrupt ARP attacks .I'm trynig to understand the kernel modules in linux  so than i can implement my solution , i have some difficulties to figure out the general functionment  of the Sk_buff specially , for exemple What does define COMMENT_ONLY (in the module if_arp.f )mean?  if you could please ( with all of my respect) help me with some ideas and explanations about this subject .please allow Mr Bruce the expression of my most respectful salutations