Content #
#define list_entry(ptr, type, member) \
container_of(ptr, type, member)
//container_of()宏的定义在kernel.h头文件中。
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
其中offsetof()宏是通过把0地址转换为type类型的指针，然后去获取该结构体中member成员的指针，也就是获取了member在type结构体中的偏移量。最后用指针ptr减去offset，就得到type结构体的真实地址了。
下面是遍历链表的一个例子。
//<drivers/block/osdblk.c>
static LIST_HEAD(osdblkdev_list);
struct osdblk_device {
int id; /* blkdev unique id */
int major; /* blkdev assigned major */
...
struct list_head node;
char osd_path[0]; /* OSD device path */
};
static ssize_t class_osdblk_list(struct class *c,
struct class_attribute *attr,
char *data)
{
int n = 0;
struct list_head *tmp;
list_for_each(tmp, &osdblkdev_list) {
struct osdblk_device *osdev;
osdev = list_entry(tmp, struct osdblk_device, node);
n += sprintf(data+n, "%d %d %llu %llu %s\n",
osdev->id,
osdev->major,
osdev->obj.partition,
osdev->obj.id,
osdev->osd_path);
}
return n;
}
From #
奔跑吧Linux内核——入门篇