内核辅助接口

1:内核常用的辅助接口函数的介绍（struct list_head）
链表是一种常用的组织有序数据的数据结构，它通过指针将一系列数据节点连接成一条数据链，是线性

表的一种重要实现方式。相对于数组，链表具有更好的动态性，建立链表时无需预先知道数据总量，可

以随机分配空间，可以高效地在链表中的任意位置实时插入或删除数据。

1:链表的原型//声明，基本添加，删除，查找等操作。
struct list_head{
struct list_head *next;
struct list_head *prev;
}

#define LIST_HEAD_INIT(name) {&(name),&(name)}
#define LIST_HEAD(name) struct list_head name=LIST_HEAD_INIT(name)
所以我们要声明一个链表的时候，则使用
LIST_HEAD(mylist);//声明并定义了一个链表mylist；
同时也可以采用下面的方式；
struct list_head mylist;//先声明
INIT_LIST_HEAD(&mylist);//再初始化


在linux的内核链表中，需要用链表组织起来的数据通常会包含一个struct list_head成员；
例如：
struct data{
struct list_head list;
 
……
void datas；
}；

struct data mydata0={……};
struct data mydata1={……};
通过list_head，将他们连在一起，形成链表；
删除操作：static inline void list_del(struct list_head *entry);
插入操作：
static inline void list_add(struct list_head *new, struct list_head *head);
static inline void list_add_tail(struct list_head *new, struct list_head *head);

链表的遍历：
(1):list_entry(ptr,type,member);通过list_head的指针找到宿主体；
ptr指向该数据中list_head成员的指针；
type是数据项的类型（宿主体类型）；
member则是数据项类型定义中list_head成员的变量名；

example:
/*********************************************************************
 *               
 * Filename:      pfile.c
 * Version:       1.0
 * Description:   Demo for Linux LIST utility
 * Compilation:   gcc -D__KERNEL__ -I/usr/src/linux/include pfile.c
 * Status:        Stable
 * Author:        Yang Shazhou
 * Created at:    Thu Jul 15 13:50:33 2004
 * Modified at:   Thu Jul 15 14:39:03 2004
 * Modified by:   Yang Shazhou
 *
 *     Copyright (c) 2004 Yang Shazhou, All Rights Reserved.
 *    
 *     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., 59 Temple Place, Suite 330, Boston,
 *     MA 02111-1307 USA
 *    
 ********************************************************************/
#include
#include
#include
int main(int argc,char *argv[])
{
 LIST_HEAD(list);  //定义存放文件内容的链表
 FILE *fp;
 struct file_store {
  char c;
  struct list_head node;
 } *pstore;
 if(argc<2){
  printf("usage: pfile <[r]>\n");
  return -1;
 }
 if(!(fp=fopen(argv[1],"rb"))){
  printf("fopen(%s) error\n",argv[1]);
         return -1;
 }
 /* 读文件到链表 */
 while(1){
  if(!(pstore=(struct file_store *)malloc(sizeof(struct file_store))))
   break;
  pstore->c=fgetc(fp);
  printf("input %c\n " ,pstore->c) ;
  if(feof(fp)){
   free(pstore);
   break;
  }
  list_add_tail(&pstore->node,&list);   //将本字符插入链表中
 }
 fclose(fp);
 /* 遍历链表，输出链表中的节点个数，即文件字符数 */
 int count=0;
 struct list_head *p;
 list_for_each(p,&list){
  count++;
 }
 printf("%s has altogether %d character(s)\n",argv[1],count);
       
 /* 根据命令行参数正向/反向遍历链表，输出链表中存放的字符，同时释放各节点 */
 /*if(argc>2 && !strcasecmp(argv[2],"r")){
  struct list_head *p;
  list_for_each_entry_reverse(pstore,&list,node){  //反向遍历，没有保护
   p=pstore->node.next;
   list_del(&pstore->node);
   putchar(pstore->c);
   free(pstore);
   // 如果没有这一句，将报segmentation fault //
pstore=list_entry(p,struct file_store,node); //取数据项
  }
 }else */{
  struct file_store *pstorenode;
  struct list_head *p ,*n;
  int k = 0 ;
    // list_for_each_entry_safe(pstore,p,&list,node){  //正向遍历，有保护
    //  list_for_each(p,&list) {
   list_for_each_safe(p, n,&list) {
         pstorenode = list_entry(p ,struct file_store ,node)  ;
   putchar(pstorenode->c);
   //list_del_init(&(pstorenode->node));
   k++ ;
   if( k ==7) break ;
   free(pstorenode);
  }
 }
 return 0;
}

笔者尝试使用2.6.24的版本测试上述代码，测试无法通过；直接采用低版本的list文件
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H

#include
#include "linux/poison.h"

#ifndef __KERNEL__
/**
 * 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) );})
#endif /* __KERNEL__ */

/*
 * 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_LIST
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;
}
#else
extern 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.
 */
#ifndef CONFIG_DEBUG_LIST
static inline void list_add(struct list_head *new, struct list_head *head)
{
    __list_add(new, head, head->next);
}
#else
extern void list_add(struct list_head *new, struct list_head *head);
#endif

/**
 * 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);
}


/**
 * 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)

/*
 * 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_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_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_LIST
static inline void list_del(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
//    entry->next = LIST_POISON1;
//    entry->prev = LIST_POISON2;
entry->next = entry;
entry->prev = entry;
}
#else
extern void list_del(struct list_head *entry);
#endif

/**
 * 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)
{
    return head->next == head;
}

/**
 * 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; 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; pos != (head); \
            pos = 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);    \
          &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_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)

/*
 * 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;
}

#endif