http://www.crashcourse.ca/introduction-linux-kernel-programming/lesson-17-your-first-character-device-driver

http://www.tldp.org/LDP/lkmpg/2.4/html/x579.html

http://derekmolloy.ie/writing-a-linux-kernel-module-part-1-introduction/

Kernel export a symbol: http://tuxthink.blogspot.it/2011/07/exporting-symbols-from-module.html

Sharing semaphores between kernel and user spaces: http://stackoverflow.com/questions/17391276/shared-semaphore-between-user-and-kernel-spaces

Kernel space semaphores: http://www.makelinux.net/ldd3/chp-5-sect-3