Linux kernel 笔记 （42）——container_of

container_of定义在<linux/kernel.h>中：

/**
 * 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) );})

它的功能是通过一个结构体成员的地址，得到结构体的地址。举例如下：

struct st_A
{
        int member_b;
        int member_c;
};

struct st_A a;

则container_of(&(a.member_c), struct st_A, member_c)会得到变量a的地址，也就是&a的值。