A kernel module is practically a driver that can be loaded/unloaded in the kernel on demand.

jvns wrote a kernel module that prints hello world to the kernel log each time a packet is processed by the kernel.

Some good starting points:

• Kernel Newbies → go here after going through jvns’s post AND after experimenting yourself.
• How to Write Your Own Linux Kernel Module with a Simple Example
• GitHub - jvns/kernel-module-fun: Some fun things you can do with kernel modules (all “bad ideas”) → kernel module examples

I should probably make a linux VM (in kvm) for kernel module development.