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(struct list_head *new, struct list_head *head)
// new 的节点被插入到 head（head为任意链表头） 的后面
/** * 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; }
list_add_tail(struct list_head *new, struct list_head *head)
new 的节点插入到 head 的前面
/** * list_add_tail - add a new entry * @new: new entry to be added * @head: list head to add it before * * Insert a new entry before the specified head. * This is useful for implementing queues. */ static inline void list_add_tail(struct list_head *new, struct list_head *head) { __list_add(new, head->prev, head); }
(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(ptr, type, member) // list_head的指针 ， 外部结构的数据类型（struct statu），成员名
//返回指向 data 的指针
/** * 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)); })
（5）链表的遍历
/** * list_for_each - iterate over a list * @pos: the &struct list_head to use as a loop cursor. * @head: the head for your list. */ #define list_for_each(pos, head) for (pos = (head)->next; pos != (head); pos = pos->next)
举一个栗子：
struct list_head *entry; struct list_head dev; //链表头 list_for_each(entry, dev) { card = list_entry(entry, struct list_head, card); if(card->dev_midi == minor) break; }