macro

1 container_of(ptr, type, member)

地址为ptr的成员member对应的type类型的结构的地址。

即 type S;  有 &(s.member ) == ptr;

那么有ptr,如何获得S

S = container_of(ptr, type, member)

define container_of(ptr, type, member) ({              \
    const __typeof__( ((type *)0)->member ) *__mptr = (ptr);    \
    (type *)( (char *)__mptr - offsetof(type,member) );})

2. offset

man 3:    offsetof - offset of a structure member

3. offset

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