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I have begun the jounery of understanding Linux module development. Currently I am using the following reference to build my knowledge:

The Linux Kernel Module Programming Guide (2.6) by Peter Jay Salzman

The reason I am looking at developing a kernel module is to utilize the Netfilter framework. The Netfilter framework is used for filtering packets within the kernel. The user-space program IPTABLES uses the Netfilter framework for creating packet filters, which allow you to create Linux Firewalls. What I am trying to do is develop a module for application layer filtering. The framework is documented in a HOWTO titled, Netfilter Hacking HOWTO. Its a little dated, but should be enough to point me in the right direction.