如何在用户空间使用container_of宏

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container_of(pointer,container_type,container_field);
这个宏需要一个container_field字段的指针，该字段包含在container_type类型的结构中，然后返回包含该字段的结构指针。
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但由于是在驱动中实现的这个宏，有没有办法在用户空间测试呢？
有的。我们可以将linux/kernel.h头文件包含进来，直接在用户空间测试这个宏的巧妙之处。

下面就是我的测试代码。

main.c文件

#include <linux/unistd.h>#include <linux/string.h>#include <linux/stdlib.h>#include <linux/kernel.h>struct cona_t{    int i;    int j;    int v;    char t[10];    unsigned short xy;};struct cona_t ct;unsigned short xy;int main(int argc,char * argv[]){    int xy;    struct cona_t * p;    memset(&ct,0,sizeof(struct cona_t));    ct.i = ct.j = ct.v = 10;    sprintf(ct.t,"%s","sdf");    ct.xy = 20;    p = container_of(&ct.xy,struct cona_t,xy);        printf("%s\n",p->t);    return 0;}

下面是Makefile文件
CC=gcc
TAR=main
SRC=main.c
KERNEL_INCLUDE ?= /lib/modules/$(shell uname -r)/build/include
all:
    $(CC) -D__KERNEL__ -o $(TAR) -I$(KERNEL_INCLUDE) $(SRC)

clean:

    rm -f $(TAR)

如果打开kernel.h文件，就会发现这个container_of这个宏定义如下：
#define container_of(ptr, type, member) ({            \
        const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
        (type *)( (char *)__mptr - offsetof(type,member) );})

offsetof又被如下定义：
#ifdef __KERNEL__
#undef offsetof
#ifdef __compiler_offsetof
#define offsetof(TYPE,MEMBER) __compiler_offsetof(TYPE,MEMBER)
#else
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif

那个__compiler_offsetof原型是__builtin_offsetof这个是GCC编译器所特有的。