内核扩展概念的引入

代码说明：

Introduction to Kernel Extension Concepts 1:Hello Kernel: Creating a Kernel Extension With Xcode 2:Hello I/O Kit: Creating a Device Driver With Xcode 3:Hello Debugger: Debugging a Device Driver With GDB 4:Packaging Your KEXT for Distribution and Installation 5:Loading Kernel Extensions at Boot Time 6:Kernel Extension Dependencies 7：Kernel Extension Ownership and Permissions