While learning about the kernel, I have come across various resources apart from main documentation.
- LDD3 book : https://lwn.net/Kernel/LDD3/
- Linux kernel development book (3rd edition)
- LKMPG : https://tldp.org/LDP/lkmpg/2.6/html/lkmpg.html#AEN121
- LKMPG latest version : https://github.com/sysprog21/lkmpg