最近写东西老要用到链表和开链散列，又懒得自己写。于是想到Linux内核里有很完善的链表的实现可以利用，所以花了点时间将内核里的list和hlist的实现分离出来放在自己的代码树立用。
弄 完了又发现其实这个东西可以到处利用，这就又完善了一下。这里发给大家，抛砖引玉，也算是代码复用。大家有机会可以测试一下看还有什么问题没有。结构和原 理很简单，主要是移植性方面要考虑的比较多，一些多和硬件相关的地方我就写了宏直接跳过去没管了。经过我的测试目前还没有什么问题，C和C++都应该可以 用。见笑。
它的好处嘛，我认为有三点，一是空间利用比较精细，list和hlist也就一个指针空间的差别，看来内核中还是很注意空间节 省。二是比较灵活，只要你想链起来的结构，都能用。另外呢，它提供了很多好用的函数和宏，用法也很简单（上网一搜有很多分析的）。这些函数和宏里面有一些 在一般用户空间是没有多大意义的（比如_rcu类的函数主要是避免多CPU并行时互斥的，prefetch和rcu_dereference也是跟硬件有 关的），除非你在共享内存里并发操作，或者线程操作。大家也可以考虑在这方面完善一下。
由于文章长度有限制，所以下一篇是代码，我稍微做过一些修改，并加上了中文注释。
经过提醒，我还是把代码的许可证发上来一下好了：
/*
<list.h>
Copyright (C) 2007 Li Yi (pAnk7.yArdbird) <pank7yardbird (AT) gmail.com>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
代码还是太长，所以只好分两部分了……
这一部分是list的。
/*
* 描述: 双循环链表的实现，拷贝自Linux内核（2.6.20.1）。
* 稍作修改。头文件，使用时只需包含此头文件即可。
* 文件名: list.h
* 作者: pAnk7.yArdbird <pank7yardbird (AT) gmail.com>
* 日期 & 时间: Tue Nov 13 12:49:25 2007
*/
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H
#ifdef __cplusplus /* 使C++程序也能用。 */
extern "C" {
#endif
#if !defined(__cplusplus) && defined(WIN32)
#define inline
#endif
#define LIST_POISON1 ((void *) 0x00100100) /* 链表节点指针的特殊标志。 */
#define LIST_POISON2 ((void *) 0x00200200)
#ifndef NULL /* C语言中没有定义NULL。 */
#define NULL ((void *)0)
#endif /* NULL */
#ifndef offsetof /* 宏container_of需要使用。 */
#ifdef __compiler_offsetof /* 有的系统自带有此功能的宏。 */
#define offsetof(TYPE,MEMBER) __compiler_offsetof(TYPE,MEMBER)
#else
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif
#endif /* offsetof */
#define container_of(ptr, type, member) ({ \
const typeof( ((type *)0)->member ) *__mptr = (ptr); \
(type *)( (char *)__mptr - offsetof(type,member) );})
/* 并发互斥的处理，在用户空间的程序大多用不着。可考虑改善这里的功能。 */
#define smp_read_barrier_depends() do { } while(0)
#define rcu_dereference(p) ({ \
typeof(p) _________p1 = p; \
smp_read_barrier_depends(); \
(_________p1); \
})
/* 利用CPU的cache来提高效率。 */
static inline void prefetch(const void *x) { ; }
/*
* Simple doubly linked list implementation.
* 简单的双循环链表的实现。
*
* 当处理整个链表而不是单个节点的时候，有一些内部函数（“__xxx”）更有用，
* 因为有时候我们已经知道了前后节点，所以直接使用内部函数我们可以让写出
* 更好的代码。
*/
/*
* 在你需要链接起来的数据结构中加入一个此结构体（注意不能是list_head指针）
* 成员。你也可以加入多个此结构体的成员，从而可以让同一个数据结构可以加入多
* 个链表。
*/
typedef struct list_head {
struct list_head *next, *prev;
} list_head;
#define LIST_HEAD_INIT(name) { &(name), &(name) } /* 初始化。 */
/* 定义变量并初始化。 */
#define LIST_HEAD(name) \
struct list_head name = LIST_HEAD_INIT(name)
/* 初始化函数。 */
static inline void INIT_LIST_HEAD(struct list_head *list)
{
list->next = list;
list->prev = list;
}
/*
* 在两个已知的连续的节点中插入一个新的节点。
*
* 此函数仅作为链表内部操作使用，链表内部我们已经知道了前后节点。
*/
static inline void __list_add(struct list_head *newentry,
struct list_head *prev,
struct list_head *next)
{
next->prev = newentry;
newentry->next = next;
newentry->prev = prev;
prev->next = newentry;
}
/**
* 加入一个新的节点。
* @newentry: new entry to be added
* @head: list head to add it after
*
* 在指定链表头部后面加入一个新的节点。可以方便地用来实现栈。
*/
static inline void list_add(struct list_head *newentry, struct list_head *head)
{
__list_add(newentry, head, head->next);
}
/**
* 加入一个新的节点。
* @newentry: new entry to be added
* @head: list head to add it before
*
* 在指定链表头部前面加入一个新的节点（即加在尾部）。可以方便地用来实现队列。
*/
static inline void list_add_tail(struct list_head *newentry,
struct list_head *head)
{
__list_add(newentry, head->prev, head);
}
/*
* 在两个已知的连续的节点之间插入一个新的节点。由于我的修改此函数和之前的
* __list_add没有区别，但是为后续开发留下接口。
*
* 此函数仅作为链表的内部操作使用。
*/
static inline void __list_add_rcu(struct list_head * newentry,
struct list_head * prev,
struct list_head * next)
{
newentry->next = next;
newentry->prev = prev;
next->prev = newentry;
prev->next = newentry;
}
/**
* 在一个rcu保护下的链表中加入一个新的节点。与之前的list_add没有区别，
* 但是为后续开发留下接口。
* @newentry: new entry to be added
* @head: list head to add it after
*/
static inline void list_add_rcu(struct list_head *newentry,
struct list_head *head)
{
__list_add_rcu(newentry, head, head->next);
}
/**
* 在一个rcu保护下的链表中加入一个新的节点。与之前的list_add_tail没有区别，
* 但是为后续开发留下接口。
* @newentry: new entry to be added
* @head: list head to add it before
*/
static inline void list_add_tail_rcu(struct list_head *newentry,
struct list_head *head)
{
__list_add_rcu(newentry, head->prev, head);
}
/*
* 使前后节点相互指向对方，从而删掉一个节点。但是此节点的空间还得自己释放。
*
* 此函数仅作为链表的内部操作使用。
*/
static inline void __list_del(struct list_head * prev,
struct list_head * next)
{
next->prev = prev;
prev->next = next;
}
/**
* 从链表中删除一个节点。
* @entry: the element to delete from the list.
* 注意：调用此函数后list_empty并不返回真，节点处于一个未知状态。
*/
static inline void list_del(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->next = (list_head *)LIST_POISON1;
entry->prev = (list_head *)LIST_POISON2;
}
/**
* 从链表中删除一个节点，无需重新初始化。
* @entry: the element to delete from the list.
*/
static inline void list_del_rcu(struct list_head *entry)
{
__list_del(entry->prev, entry->next);
entry->prev = (list_head *)LIST_POISON2;
}
/**
* 用新的节点替换旧的节点。
* @old : the element to be replaced
* @newentry : the new element to insert
* Note: if 'old' was empty, it will be overwritten.
*/
static inline void list_replace(struct list_head *old,
struct list_head *newentry)
{
newentry->next = old->next;
newentry->next->prev = newentry;
newentry->prev = old->prev;
newentry->prev->next = newentry;
}
/* 用新的节点替换旧的节点，并将旧的节点初始化。 */
static inline void list_replace_init(struct list_head *old,
struct list_head *newentry)
{
list_replace(old, newentry);
INIT_LIST_HEAD(old);
}
/**
* list_replace_rcu - replace old entry by new one
* 用新的节点替换旧的节点。
* @old : the element to be replaced
* @newentry : the new element to insert
*
* The @old entry will be replaced with the @newentry entry atomically.
* Note: @old should not be empty.
*/
static inline void list_replace_rcu(struct list_head *old,
struct list_head *newentry)
{
newentry->next = old->next;
newentry->prev = old->prev;
newentry->next->prev = newentry;
newentry->prev->next = newentry;
old->prev = (list_head *)LIST_POISON2;
}
/**
* list_del_init - deletes entry from list and reinitialize it.
* 从链表中删除一个节点，并重新初始化该节点。
* @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
* 将一个节点从链表中删除，并加入到另外一个链表的头部（其实完全可以是同一个链表）。
* @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
* 将一个节点从链表中删除，并加入到另外一个链表的尾部（其实完全可以是同一个链表）。
*
* @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
* 测试一个节点是否是一个链表的最后一个节点。
* @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
* 测试一个链表是否为空。
* @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
* 测试一个链表是否为空，并且没有在被修改。
* @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);
}
/* 将两个链表合二为一。list的节点将被剔除。 */
static inline void __list_splice(struct list_head *list,
struct list_head *head)
{
struct list_head *first = list->next;
struct list_head *last = list->prev;
struct list_head *at = head->next;
first->prev = head;
head->next = first;
last->next = at;
at->prev = last;
}
/**
* list_splice - join two lists
* 将两个链表合二为一。list的节点将被剔除。
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list))
__list_splice(list, head);
}
/**
* list_splice_init - join two lists and reinitialise the emptied list.
* 将两个链表合二为一，并重新初始化空链表（list）。
* @list: the new list to add.
* @head: the place to add it in the first list.
*
* The list at @list is reinitialised
*/
static inline void list_splice_init(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list)) {
__list_splice(list, head);
INIT_LIST_HEAD(list);
}
}
/**
* list_entry - get the struct for this entry
* 返回节点所在的结构体的指针。
* @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)
/**
* list_for_each - iterate over a list
* 迭代一个链表。
* @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; prefetch(pos->next), pos != (head); \
pos = pos->next)
/**
* __list_for_each - iterate over a list
* 迭代一个链表。
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*
* This variant differs from list_for_each() in that it's the
* simplest possible list iteration code, no prefetching is done.
* Use this for code that knows the list to be very short (empty
* or 1 entry) most of the time.
* 此宏没有使用prefetch。
*/
#define __list_for_each(pos, head) \
for (pos = (head)->next; pos != (head); pos = pos->next)
/**
* list_for_each_prev - iterate over a list backwards
* 反向迭代一个链表。
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*/
#define list_for_each_prev(pos, head) \
for (pos = (head)->prev; prefetch(pos->prev), pos != (head); \
pos = pos->prev)
/**
* list_for_each_safe - iterate over a list safe against removal of list entry
* 安全地迭代一个链表，不能删除链表中的节点。
* @pos: the &struct list_head to use as a loop cursor.
* @n: another &struct list_head to use as temporary storage
* @head: the head for your list.
*/
#define list_for_each_safe(pos, n, head) \
for (pos = (head)->next, n = pos->next; pos != (head); \
pos = n, n = pos->next)
/**
* list_for_each_entry - iterate over list of given type
* 迭代一个链表，与list_for_each不同的地方在于此宏给出的是结构体指针。
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member); \
prefetch(pos->member.next), &pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_entry_reverse - iterate backwards over list of given type.
* 反向迭代一个链表。
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_reverse(pos, head, member) \
for (pos = list_entry((head)->prev, typeof(*pos), member); \
prefetch(pos->member.prev), &pos->member != (head); \
pos = list_entry(pos->member.prev, typeof(*pos), member))
/**
* list_prepare_entry - prepare a pos entry for use in
* list_for_each_entry_continue
* 为list_for_each_entry_continue准备一个节点。
* @pos: the type * to use as a start point
* @head: the head of the list
* @member: the name of the list_struct within the struct.
*
* Prepares a pos entry for use as a start point in
* list_for_each_entry_continue.
*/
#define list_prepare_entry(pos, head, member) \
((pos) ? : list_entry(head, typeof(*pos), member))
/**
* list_for_each_entry_continue - continue iteration over list of given type
* 从pos的下一个节点处开始继续迭代一个链表。
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* Continue to iterate over list of given type, continuing after
* the current position.
*/
#define list_for_each_entry_continue(pos, head, member) \
for (pos = list_entry(pos->member.next, typeof(*pos), member); \
prefetch(pos->member.next), &pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_entry_from - iterate over list of given type from the current
* point
* 从pos处开始继续迭代一个链表。
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* Iterate over list of given type, continuing from current position.
*/
#define list_for_each_entry_from(pos, head, member) \
for (; prefetch(pos->member.next), &pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_entry_safe - iterate over list of given type safe against
* removal of list entry
* 安全地迭代一个链表。使用结构体指针。
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*/
#define list_for_each_entry_safe(pos, n, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member), \
n = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.next, typeof(*n), member))
/**
* list_for_each_entry_safe_continue
* 顾名思义。
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* Iterate over list of given type, continuing after current point,
* safe against removal of list entry.
*/
#define list_for_each_entry_safe_continue(pos, n, head, member) \
for (pos = list_entry(pos->member.next, typeof(*pos), member), \
n = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.next, typeof(*n), member))
/**
* list_for_each_entry_safe_from
* 顾名思义。
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* Iterate over list of given type from current point, safe against
* removal of list entry.
*/
#define list_for_each_entry_safe_from(pos, n, head, member) \
for (n = list_entry(pos->member.next, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.next, typeof(*n), member))
/**
* list_for_each_entry_safe_reverse
* 顾名思义。
* @pos: the type * to use as a loop cursor.
* @n: another type * to use as temporary storage
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* Iterate backwards over list of given type, safe against removal
* of list entry.
*/
#define list_for_each_entry_safe_reverse(pos, n, head, member) \
for (pos = list_entry((head)->prev, typeof(*pos), member), \
n = list_entry(pos->member.prev, typeof(*pos), member); \
&pos->member != (head); \
pos = n, n = list_entry(n->member.prev, typeof(*n), member))
/**
* list_for_each_rcu - iterate over an rcu-protected list
* 顾名思义。
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*
* This list-traversal primitive may safely run concurrently with
* the _rcu list-mutation primitives such as list_add_rcu()
* as long as the traversal is guarded by rcu_read_lock().
*/
#define list_for_each_rcu(pos, head) \
for (pos = (head)->next; \
prefetch(rcu_dereference(pos)->next), pos != (head); \
pos = pos->next)
#define __list_for_each_rcu(pos, head) \
for (pos = (head)->next; \
rcu_dereference(pos) != (head); \
pos = pos->next)
/**
* list_for_each_safe_rcu
* 顾名思义。
* @pos: the &struct list_head to use as a loop cursor.
* @n: another &struct list_head to use as temporary storage
* @head: the head for your list.
*
* Iterate over an rcu-protected list, safe against removal of list entry.
*
* This list-traversal primitive may safely run concurrently with
* the _rcu list-mutation primitives such as list_add_rcu()
* as long as the traversal is guarded by rcu_read_lock().
*/
#define list_for_each_safe_rcu(pos, n, head) \
for (pos = (head)->next; \
n = rcu_dereference(pos)->next, pos != (head); \
pos = n)
/**
* list_for_each_entry_rcu - iterate over rcu list of given type
* 顾名思义。
* @pos: the type * to use as a loop cursor.
* @head: the head for your list.
* @member: the name of the list_struct within the struct.
*
* This list-traversal primitive may safely run concurrently with
* the _rcu list-mutation primitives such as list_add_rcu()
* as long as the traversal is guarded by rcu_read_lock().
*/
#define list_for_each_entry_rcu(pos, head, member) \
for (pos = list_entry((head)->next, typeof(*pos), member); \
prefetch(rcu_dereference(pos)->member.next), \
&pos->member != (head); \
pos = list_entry(pos->member.next, typeof(*pos), member))
/**
* list_for_each_continue_rcu
* 顾名思义。
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*
* Iterate over an rcu-protected list, continuing after current point.
*
* This list-traversal primitive may safely run concurrently with
* the _rcu list-mutation primitives such as list_add_rcu()
* as long as the traversal is guarded by rcu_read_lock().
*/
#define list_for_each_continue_rcu(pos, head) \
for ((pos) = (pos)->next; \
prefetch(rcu_dereference((pos))->next), (pos) != (head); \
(pos) = (pos)->next) |
