最近编程总想着参考一些有名的开源代码是如何实现的，因为要写链表就看了下linux内核中对链表的实现。
链表是一种非常常见的数据结构，特别是在动态创建相应数据结构的情况下更是如此，然而在操作系统内核中，动态创建相应的数据结构尤为频繁。由于不带数据域所以Linux中的这种链表是通用的，在如何情况下，只要需要链表的数据结构包含它就行了。
链表只包含两个指针
struct list_head {
struct list_head *next, *prev;
};
数据结构如果需要链表只需要包含它就行
typedef struct s_DASTUC
{
int ds_stus;
int ds_type;
struct list_head ds_list;
int ds_count;
}
通过链表的地址获取链表所在的数据结构地址
#define list_entry(ptr, type, number) \
((type *)((char *)(ptr) - (unsigned long)(&((type *))->number)))
网上看到过有人说为什么不把链表放到数据结构首部，这样链表所在的地址就是数据结构的地址，何必实现list_entry(ptr, type, number)，不要去限制数据结构调用链表的写法。
详细的网上都有博客了，这里博主只是为了记下知识点而已，下面是从Linux源码List.h拿出来的部分实现：
#ifndef _MYLIST_H
#define _MYLIST_H #define LIST_POISON1 NULL
#define LIST_POISON2 NULL /*
* Simple doubly linked list implementation.
*
* Some of the internal functions ("__xxx") are useful when
* manipulating whole lists rather than single entries, as
* sometimes we already know the next/prev entries and we can
* generate better code by using them directly rather than
* using the generic single-entry routines.
*/ 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;
} /*
* Insert a new entry between two known consecutive entries.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
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 - 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);
} /**
* 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);
} /*
* Delete a list entry by making the prev/next entries
* point to each other.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
next->prev = prev;
prev->next = next;
} /**
* 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 = LIST_POISON1;
entry->prev = LIST_POISON2;
} /**
* list_replace - replace old entry by new one
* @old : the element to be replaced
* @new : the new element to insert
*
* If @old was empty, it will be overwritten.
*/
static inline void list_replace(struct list_head *old,
struct list_head *new)
{
new->next = old->next;
new->next->prev = new;
new->prev = old->prev;
new->prev->next = new;
} static inline void list_replace_init(struct list_head *old,
struct list_head *new)
{
list_replace(old, new);
INIT_LIST_HEAD(old);
} /**
* 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);
} /**
* list_move - delete from one list and add as another's head
* @list: the entry to move
* @head: the head that will precede our entry
*/
static inline void list_move(struct list_head *list, struct list_head *head)
{
__list_del(list->prev, list->next);
list_add(list, head);
} /**
* list_move_tail - delete from one list and add as another's tail
* @list: the entry to move
* @head: the head that will follow our entry
*/
static inline void list_move_tail(struct list_head *list,
struct list_head *head)
{
__list_del(list->prev, list->next);
list_add_tail(list, head);
} /**
* list_is_last - tests whether @list is the last entry in list @head
* @list: the entry to test
* @head: the head of the list
*/
static inline int list_is_last(const struct list_head *list,
const struct list_head *head)
{
return list->next == head;
} /**
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
static inline int list_empty(const struct list_head *head)
{
return head->next == head;
} /**
* list_empty_careful - tests whether a list is empty and not being modified
* @head: the list to test
*
* Description:
* tests whether a list is empty _and_ checks that no other CPU might be
* in the process of modifying either member (next or prev)
*
* NOTE: using list_empty_careful() without synchronization
* can only be safe if the only activity that can happen
* to the list entry is list_del_init(). Eg. it cannot be used
* if another CPU could re-list_add() it.
*/
static inline int list_empty_careful(const struct list_head *head)
{
struct list_head *next = head->next;
return (next == head) && (next == head->prev);
} #define __list_for_each(pos, head) \
for (pos = (head)->next; pos != (head); pos = pos->next) #define list_first_entry(ptr, type, member) \
list_entry((ptr)->next, type, member)
#define list_entry(ptr, type, number) \
((type *)((char *)(ptr) - (unsigned long)(&((type *))->number))) #endif