Linux内核中经常可见container_of的身影，它在实际驱动的编写中也是广泛应用。
container_of原理
作用：通过结构体的某个成员变量地址找到该结构体的首地址。
定义如下：
/**
* container_of - cast a member of a structure out to the containing structure
* @ptr: the pointer to the member.
* @type: the type of the container struct this is embedded in.
* @member: the name of the member within the struct.
*
*/
#define container_of(ptr, type, member) ({ \\
const typeof( ((type *)0)->member ) *__mptr = (ptr); \\
(type *)( (char *)__mptr - offsetof(type,member) );})
