1、内核链表的定义在include/linux/list.h
struct list_head {
struct list_head *next, *prev;
};
容易看出，Linux内核链表为双向链表。
2、Linux链表与普通链表区别
我们通常定义的链表是在链表节点中嵌入元素,比如
struct MyList
{
int StudentID; /* 被嵌入的元素 */
struct MyList *prev;
struct MyList *next;
}
而LInux为了移植方便性和通用性，在元素结构体中嵌入链表节点
strcut MyList
{
int StudentID;
struct list_head head; /* 链表节点作为结构体元素 */
}
3、Linux内核链表中提供的操作链表函数
(1)初始化
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list; /* 下一个节点指向自己 */
list->prev = list; /* 前一个节点指向自己 */
}
(2)添加链表节点
/**
* list_add - add a new entry
* @new: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
static inline void list_add(struct list_head *new, struct list_head *head)
{
__list_add(new, head, head->next); /* 节点插入到head和head->next之间 */
}
而__list_add函数如下
static inline void __list_add(struct list_head *new,
struct list_head *prev, struct list_head *next)
{
next->prev = new;
new->next = next;
new->prev = prev;
prev->next = new;
}
(3)删除节点
方法一：
/**
* list_del - deletes entry from list.
* @entry: the element to delete from the list.
* Note: list_empty() on entry does not return true after this, the entry is
* in an undefined state.
*/
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = (void *)0xDEADBEEF; /* 将指针指向2个不可访问的位置 */
entry->prev = (void *)0xBEEFDEAD;
}
其中调用的__list_del函数如下，
static inline void __list_del(struct list_head *prev, struct list_head *next)
{
next->prev = prev; /* */
prev->next = next;
}
注意list_del函数中的最后两条语句，类似于free()的作用。
当用户打算访问地址0xDEADBEEF或0xBEEFDEAD时，将产生页中断。
方法二：
为了更安全的删除节点，可使用list_del_init
/**
* list_del_init - deletes entry from list and reinitialize it.
* @entry: the element to delete from the list.
*/
static inline void list_del_init(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
INIT_LIST_HEAD(entry);
}
(4)提取结构的数据信息
按通常的方式使用链表很容易获取数据信息，
但使用Linux内核链表要访问数据则比较困难，
关键是如何求取链表节点地址和数据地址的偏移量。
注意list_entry传递的参数！type指传递的是类型，不是变量。
/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_struct within the struct.
*/
#define list_entry(ptr, type, member) \
container_of(ptr, type, member)
container_of定义在include/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)); })
而其中，
[a]#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
[b]typeof()是gcc的扩展，和sizeof()类似