container_of()宏

指针ptr指向结构体type中的成员member；通过指针ptr，返回结构体type的起始地址
          type
      |----------|
      |          |
      |          |
      |----------|
ptr-->| member --|
      |----------|
      |          |
      |          |
      |----------|
/**
* 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) );})

container_of宏，它的功能是得到包含某个结构成员的结构的指针:

 

其实现如下：

 

#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

#define container_of(ptr, type, member) ({                      /

        const typeof( ((type *)0)->member ) *__mptr = (ptr);    /

        (type *)( (char *)__mptr - offsetof(type,member) );})

 

    分析可知__mptr指向的是一个type结构里typeof(((type *)0)->member)类型member成员的指针，offsetof(type,member)是这个成员在结构中的偏移，单位是字节，所以为了计算type结构的起始地址，__mptr减去它自己的偏移。