Linux kernel 笔记 （62）——list_head

双向链表是Linux kernel中常用的数据结构，定义如下：

struct list_head {
    struct list_head *next, *prev;
};

#define LIST_HEAD_INIT(name) { &(name), &(name) }

#define LIST_HEAD(name) \
    struct list_head name = LIST_HEAD_INIT(name)

static inline void INIT_LIST_HEAD(struct list_head *list)
{
    list->next = list;
    list->prev = list;
}
...

下图选自plka：

从上图可以看出，定义链表需要一个头结点，通过头结点继而可以完成插入，删除元素等操作。来看一个例子（list.c）：

struct list_head {
        struct list_head *next, *prev;
};

#define LIST_HEAD_INIT(name) { &(name), &(name) }

#define LIST_HEAD(name) \
        struct list_head name = LIST_HEAD_INIT(name)


int main(void) {
        LIST_HEAD(dev_list);
        return 0;
}

检查gcc预处理的输出：

# gcc -E -P list.c
struct list_head {
 struct list_head *next, *prev;
};
int main(void) {
 struct list_head dev_list = { &(dev_list), &(dev_list) };
 return 0;
}

可以看到，头结点dev_list的prev和next都指向了自己。下面代码达到同样的效果：

struct list_head {
    struct list_head *next, *prev;
};

static inline void INIT_LIST_HEAD(struct list_head *list)
{
    list->next = list;
    list->prev = list;
}

int main(void) {
    struct list_head dev_list;
    INIT_LIST_HEAD(&dev_list);
    return 0;
}