Linux2.6.32内核笔记（5）在应用程序中移植使用内核链表

    摘要：将内核链表移植到应用程序中，实现创建，添加节点，遍历，删除的操作。

    

    首先复习一下内核链表中经常使用的几个函数，在/include/linux/list.h中。

    

    创建链表：

<span style="font-size:18px;">INIT_LIST_HEAD（）staticinline void INIT_LIST_HEAD(struct list_head *list){    list->next = list;    list->prev = list;}</span>

    插入节点：

<span style="font-size:18px;">list_add（）在链表头插入list_add_tail()在链表尾插入staticinline void list_add(struct list_head *new, struct list_head *head){    __list_add(new, head, head->next);}staticinline void list_add_tail(struct list_head *new, struct list_head *head){    __list_add(new, head->prev, head);}</span>   

    删除节点：

<span style="font-size:18px;">list_del()staticinline void list_del(struct list_head *entry){    __list_del(entry->prev, entry->next);    entry->next = LIST_POISON1;    entry->prev = LIST_POISON2;}</span>

    遍历链表：

<span style="font-size:18px;">list_for_each()#definelist_for_each(pos, head) \for(pos = (head)->next; prefetch(pos->next), pos != (head); \      pos = pos->next)</span> 

    取出节点：

<span style="font-size:18px;">list_entry()#definelist_entry(ptr, type, member) \container_of(ptr,type, member)</span>   

    移植过程中用到的其他函数：

    1.malloc

    函数原型：extern void *malloc(unsigned int num_bytes);

   功能：分配字节长度为num_bytes内存，如果成功则返回指向内存起始地址的指针，否则返回null。

    说明：这里声明为void *表示未确定类型的指针，这样使用的时候就可以强制转换为其他我们需要的任何类型的指针。

    2.memset

    函数原型：void *memset(void *s,int ch,seze_t n);

    功能：将s指向的某一块内存中的前n个字节的内容全部填充为ch。一般用来对新申请的内存做初始化工作，ch一般都是填充0。我们在使用较大的结构体和数组的时候，都会使用其对分配到的内存清零。

    3.sprintf

    函数原型：int sprintf(char *buffer,const char *format，[arugument]…);

    功能：把格式化的数据写入某个字符串中，返回值是字符串的长度。

    移植步骤：

    1.创建list.h

    因为我们要写成一个app，里面用到很多内核链表的函数，都在list.h里面声明的，一开始这里我就偷懒把内核里面的list.h拷贝一份，放到我当前的工作目录下，命名为list.h，后来编译的时候提示找不到list.h里面加进去的那三个头文件，于是我又把position.h,这三个头文件注释掉了，但是提示LIST_POSITION1和LIST_POSITION2没有定义还有别的错误，于是利用grep查找，到源码目录下，把这部分拷贝到我们的list.h前面部分里面来就可以了。完整的list.c附在最后。

<span style="font-size:18px;">#ifndef _LINUX_LIST_H#define _LINUX_LIST_H  #include <linux/stddef.h> #ifndef ARCH_HAS_PREFETCH#define ARCH_HAS_PREFETCHstatic inline void prefetch(const void *x){;}#endif #define LIST_POISON1 ((void *) 0x0) #define LIST_POISON2 ((void *) 0x0) #define container_of(ptr ,type,member)({              \   const typeof( ((type *)0)->member ) *__mptr = (ptr);     \   (type *)( (char *)__mptr - offsetof(type,member) );})</span>

    2.创建listapp.c添加头文件

    这里我命名为listapp.c，因为我们要用到很多头文件，这里都添加进去，我添加的如下;

<span style="font-size:18px;">#include"list.h"//内核链表操作函数#include<malloc.h>//使用malloc分配内存#include<stdio.h>//sprintf和printf#include<string.h>//memset</span><span style="font-size:14px; font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">                </span>

   

     3.创建球员信息结构体

<span style="font-size:18px;">    structmember{    charname[10];    intnum;    intscore;    intassists;    structlist_head list;};</span>

    4.main函数

    主要思想是创建链表，分配内存，插入节点，遍历输出，删除节点。

    编译成功后运行出现如下信息;

   

    可以看到我们的链表操作是成功了，输出信息也与期望值一样，但是最后free的时候出现了core dump，这个问题查了下有几种解释，这里大概是数组操作越界，或者我们修改了mem区的指针信息，导致free释放内存的时候，释放到别的地方去了，这里不做深究了，留待之后结局。

    最后附上list.h和listapp.c的代码，结束，如有不正确的地方还请指出，大家共同进步。

    

list.h如下

<span style="font-size:14px;">#ifndef _LINUX_LIST_H#define _LINUX_LIST_H#include <linux/stddef.h>#ifndef ARCH_HAS_PREFETCH#define ARCH_HAS_PREFETCHstatic inline void prefetch(const void *x) {;}#endif#define LIST_POISON1 ((void *) 0x0)  #define LIST_POISON2 ((void *) 0x0)#define container_of(ptr ,type,member) ({              \    const typeof( ((type *)0)->member ) *__mptr = (ptr);     \    (type *)( (char *)__mptr - offsetof(type,member) );})/* * 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! */#ifndef CONFIG_DEBUG_LISTstatic 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;}#elseextern void __list_add(struct list_head *new,      struct list_head *prev,      struct list_head *next);#endif/** * 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. */#ifndef CONFIG_DEBUG_LISTstatic inline void list_del(struct list_head *entry){__list_del(entry->prev, entry->next);entry->next = LIST_POISON1;entry->prev = LIST_POISON2;}#elseextern void list_del(struct list_head *entry);#endif/** * 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);}/** * list_is_singular - tests whether a list has just one entry. * @head: the list to test. */static inline int list_is_singular(const struct list_head *head){return !list_empty(head) && (head->next == head->prev);}static inline void __list_cut_position(struct list_head *list,struct list_head *head, struct list_head *entry){struct list_head *new_first = entry->next;list->next = head->next;list->next->prev = list;list->prev = entry;entry->next = list;head->next = new_first;new_first->prev = head;}/** * list_cut_position - cut a list into two * @list: a new list to add all removed entries * @head: a list with entries * @entry: an entry within head, could be the head itself *and if so we won't cut the list * * This helper moves the initial part of @head, up to and * including @entry, from @head to @list. You should * pass on @entry an element you know is on @head. @list * should be an empty list or a list you do not care about * losing its data. * */static inline void list_cut_position(struct list_head *list,struct list_head *head, struct list_head *entry){if (list_empty(head))return;if (list_is_singular(head) &&(head->next != entry && head != entry))return;if (entry == head)INIT_LIST_HEAD(list);else__list_cut_position(list, head, entry);}static inline void __list_splice(const struct list_head *list, struct list_head *prev, struct list_head *next){struct list_head *first = list->next;struct list_head *last = list->prev;first->prev = prev;prev->next = first;last->next = next;next->prev = last;}/** * list_splice - join two lists, this is designed for stacks * @list: the new list to add. * @head: the place to add it in the first list. */static inline void list_splice(const struct list_head *list,struct list_head *head){if (!list_empty(list))__list_splice(list, head, head->next);}/** * list_splice_tail - join two lists, each list being a queue * @list: the new list to add. * @head: the place to add it in the first list. */static inline void list_splice_tail(struct list_head *list,struct list_head *head){if (!list_empty(list))__list_splice(list, head->prev, head);}/** * list_splice_init - join two lists and reinitialise the emptied 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, head->next);INIT_LIST_HEAD(list);}}/** * list_splice_tail_init - join two lists and reinitialise the emptied list * @list: the new list to add. * @head: the place to add it in the first list. * * Each of the lists is a queue. * The list at @list is reinitialised */static inline void list_splice_tail_init(struct list_head *list, struct list_head *head){if (!list_empty(list)) {__list_splice(list, head->prev, head);INIT_LIST_HEAD(list);}}/** * 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)/** * list_first_entry - get the first element from a list * @ptr:the list head to take the element from. * @type:the type of the struct this is embedded in. * @member:the name of the list_struct within the struct. * * Note, that list is expected to be not empty. */#define list_first_entry(ptr, type, member) \list_entry((ptr)->next, type, member)/** * 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; prefetch(pos->next), pos != (head); \        pos = pos->next)/** * __list_for_each-iterate over a list * @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. */#define __list_for_each(pos, head) \for (pos = (head)->next; pos != (head); pos = pos->next)/** * list_for_each_prev-iterate over a list backwards * @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 * @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_prev_safe - iterate over a list backwards safe against removal of list entry * @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_prev_safe(pos, n, head) \for (pos = (head)->prev, n = pos->prev; \     prefetch(pos->prev), pos != (head); \     pos = n, n = pos->prev)/** * list_for_each_entry-iterate over list of given type * @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. * @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() * @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 * @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_continue_reverse - iterate backwards from the given point * @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. * * Start to iterate over list of given type backwards, continuing after * the current position. */#define list_for_each_entry_continue_reverse(pos, head, member)\for (pos = list_entry(pos->member.prev, typeof(*pos), member);\     prefetch(pos->member.prev), &pos->member != (head);\     pos = list_entry(pos->member.prev, typeof(*pos), member))/** * list_for_each_entry_from - iterate over list of given type from the current point * @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 * @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 * @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 * @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 * @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))/* * Double linked lists with a single pointer list head. * Mostly useful for hash tables where the two pointer list head is * too wasteful. * You lose the ability to access the tail in O(1). */struct hlist_head {struct hlist_node *first;};struct hlist_node {struct hlist_node *next, **pprev;};#define HLIST_HEAD_INIT { .first = NULL }#define HLIST_HEAD(name) struct hlist_head name = {  .first = NULL }#define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)static inline void INIT_HLIST_NODE(struct hlist_node *h){h->next = NULL;h->pprev = NULL;}static inline int hlist_unhashed(const struct hlist_node *h){return !h->pprev;}static inline int hlist_empty(const struct hlist_head *h){return !h->first;}static inline void __hlist_del(struct hlist_node *n){struct hlist_node *next = n->next;struct hlist_node **pprev = n->pprev;*pprev = next;if (next)next->pprev = pprev;}static inline void hlist_del(struct hlist_node *n){__hlist_del(n);n->next = LIST_POISON1;n->pprev = LIST_POISON2;}static inline void hlist_del_init(struct hlist_node *n){if (!hlist_unhashed(n)) {__hlist_del(n);INIT_HLIST_NODE(n);}}static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h){struct hlist_node *first = h->first;n->next = first;if (first)first->pprev = &n->next;h->first = n;n->pprev = &h->first;}/* next must be != NULL */static inline void hlist_add_before(struct hlist_node *n,struct hlist_node *next){n->pprev = next->pprev;n->next = next;next->pprev = &n->next;*(n->pprev) = n;}static inline void hlist_add_after(struct hlist_node *n,struct hlist_node *next){next->next = n->next;n->next = next;next->pprev = &n->next;if(next->next)next->next->pprev  = &next->next;}/* * Move a list from one list head to another. Fixup the pprev * reference of the first entry if it exists. */static inline void hlist_move_list(struct hlist_head *old,   struct hlist_head *new){new->first = old->first;if (new->first)new->first->pprev = &new->first;old->first = NULL;}#define hlist_entry(ptr, type, member) container_of(ptr,type,member)#define hlist_for_each(pos, head) \for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \     pos = pos->next)#define hlist_for_each_safe(pos, n, head) \for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \     pos = n)/** * hlist_for_each_entry- iterate over list of given type * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @head:the head for your list. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry(tpos, pos, head, member) \for (pos = (head)->first; \     pos && ({ prefetch(pos->next); 1;}) && \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = pos->next)/** * hlist_for_each_entry_continue - iterate over a hlist continuing after current point * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry_continue(tpos, pos, member) \for (pos = (pos)->next; \     pos && ({ prefetch(pos->next); 1;}) && \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = pos->next)/** * hlist_for_each_entry_from - iterate over a hlist continuing from current point * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry_from(tpos, pos, member) \for (; pos && ({ prefetch(pos->next); 1;}) && \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = pos->next)/** * hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry * @tpos:the type * to use as a loop cursor. * @pos:the &struct hlist_node to use as a loop cursor. * @n:another &struct hlist_node to use as temporary storage * @head:the head for your list. * @member:the name of the hlist_node within the struct. */#define hlist_for_each_entry_safe(tpos, pos, n, head, member)  \for (pos = (head)->first; \     pos && ({ n = pos->next; 1; }) &&  \({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \     pos = n)#endif</span>

listapp.c如下

<span style="font-size:14px;">#include"list.h"//内核链表操作函数#include<malloc.h>//使用malloc分配内存#include<stdio.h>//sprintf和printf#include<string.h>//memsetstruct member{char name[100];int num;int score;struct list_head list;};struct list_head *pos;//遍历指针的pos，不断地指向链表中节点的指针域，需要是list_head指针类型struct list_head member_list;//名为menber_list的链表struct member *tmp;//存放遍历结果，为struct member类型struct member *pmember;//member的成员int main(void){unsigned int i = 0;            //循环变量的声明INIT_LIST_HEAD(&member_list); //创建一个链表头，使其前向和后继指针都指向自己，传入参数必须为指针类型，所以取地址pmember=malloc(sizeof(struct member)*4);memset(pmember,0,sizeof(struct member)*4);//为member成员分配内存，这里分配四个成员，并且对分配到的内存清零/*给球员成员命名，编号，进球数*/sprintf(pmember[1].name,"player %s","xu");sprintf(pmember[2].name,"player %s","zeng");sprintf(pmember[3].name,"player %s","le");sprintf(pmember[4].name,"player %s","suo");pmember[1].num=9;pmember[2].num=21;pmember[3].num=10;pmember[4].num=66;pmember[1].score=2;pmember[2].score=0;pmember[3].score=1;pmember[4].score=5;/*插入节点，list_add第一个参数是成员内部list的指针，第二个是刚才创建的链表头，这样就插入进去了*/for(i=0;i<4;i++){list_add(&(pmember[i+1].list),&member_list);printf("###num %d player add sucess!###\n",i+1);}/*遍历链表，并开始输出球员信息*/printf("###start list_for_each player information###\n");list_for_each(pos,&member_list){tmp=list_entry(pos,struct member,list);//第一个参数为pos，第二个要给进去我们定义的球员信息结构体，最后是结构内部的list名printf("play %d name %s score %d\n",tmp->num,tmp->name,tmp->score);}/*最后删除节点*/for(i=0;i<4;i++){list_del(&(pmember[i+1].list));printf("### num %d has deleted###\n",i+1);}/*释放分配得内存*/free(pmember);}</span>