链表（list）使用注意

如下代码是linux上的链表接口源码，使用的这个链表（list）源码，可以方便快捷的建立链表队列，但使用时需要注意的坑有：
 1、不支持，多对多，否则在add的时候，因为要加入链表的对象只有一块list_head内存，如果将它多次添加到其他链表，那么只有最后一个有效，前面的均无效。
 2、如果链表节点的内存是动态申请的，在遍历链表的循环中，取得链表数据后要释放节点资源，必须使用list_for_each_entry_safe，不能使用list_for_each_entry
    否则将有访问异常风险，原因是：_safe才会将下一个节点先保存起来，当取得链表数据,释放完节点资源后，才能保证能查找到该节点后面的节点。

#ifndef _LINUX_LIST_H_
#define _LINUX_LIST_H_ 

#ifdef __cplusplus
extern "C" {
#endif

#include <stdbool.h>

#define offset_of(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER) 

#define container_of(ptr, type, member) ({
    const __typeof__( ((type *)0)->member ) *__mptr = (ptr); 
    (type *)( (char *)__mptr - offset_of(type,member) ); })

#define LIST_POISON1  ((void *) 0x00100100) 
#define LIST_POISON2  ((void *) 0x00200200) 

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_entry, 
       struct list_head *prev, 
       struct list_head *next) 
{ 
    next->prev = new_entry; 
    new_entry->next = next; 
    new_entry->prev = prev; 
    prev->next = new_entry;
} 

/** 
 * list_add - add a new entry 
 * @new_entry: 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_entry, struct list_head *head) 
{ 
    __list_add(new_entry, head, head->next); 
} 

/** 
 * list_add_tail - add a new entry 
 * @new_entry: 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_entry, struct list_head *head) 
{ 
    __list_add(new_entry, 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; 
} 

static inline void __list_del_entry(struct list_head *entry)
{
    __list_del(entry->prev, entry->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 = (struct list_head *)LIST_POISON1; 
    entry->prev = (struct list_head *)LIST_POISON2; 
}

/**
 * list_replace - replace old entry by new one
 * @old : the element to be replaced
 * @new_entry : 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_entry)
{
    new_entry->next = old->next;
    new_entry->next->prev = new_entry;
    new_entry->prev = old->prev;
    new_entry->prev->next = new_entry;
}

static inline void list_replace_init(struct list_head *old,
                    struct list_head *new_entry)
{
    list_replace(old, new_entry);
    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(entry);
    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_entry(list);
    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_entry(list);
    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_rotate_left - rotate the list to the left
 * @head: the head of the list
 */
static inline void list_rotate_left(struct list_head *head)
{
    struct list_head *first;

    if (!list_empty(head)) {
        first = head->next;
        list_move_tail(first, head);
    }
}

/**
 * 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_head 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_head 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_last_entry - get the last 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_head within the struct.
 *
 * Note, that list is expected to be not empty.
 */
#define list_last_entry(ptr, type, member) 
    list_entry((ptr)->prev, type, member)

/**
 * list_first_entry_or_null - 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_head within the struct.
 *
 * Note that if the list is empty, it returns NULL.
 */
#define list_first_entry_or_null(ptr, type, member) 
    (!list_empty(ptr) ? list_first_entry(ptr, type, member) : NULL)

/**
 * list_next_entry - get the next element in list
 * @pos:    the type * to cursor
 * @member:    the name of the list_head within the struct.
 */
#define list_next_entry(pos, member) 
    list_entry((pos)->member.next, __typeof__(*(pos)), member)

/**
 * list_prev_entry - get the prev element in list
 * @pos:    the type * to cursor
 * @member:    the name of the list_head within the struct.
 */
#define list_prev_entry(pos, member) 
    list_entry((pos)->member.prev, __typeof__(*(pos)), 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_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_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; 
         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_head within the struct.
 */
#define list_for_each_entry(pos, head, member) 
    for (pos = list_first_entry(head, __typeof__(*pos), member); 
         &pos->member != (head);                    
         pos = list_next_entry(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_head within the struct.
 */
#define list_for_each_entry_reverse(pos, head, member) 
    for (pos = list_last_entry(head, __typeof__(*pos), member); 
         &pos->member != (head); 
         pos = list_prev_entry(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_head 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_head 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_next_entry(pos, member); 
         &pos->member != (head); 
         pos = list_next_entry(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_head 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_prev_entry(pos, member); 
         &pos->member != (head); 
         pos = list_prev_entry(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_head within the struct.
 *
 * Iterate over list of given type, continuing from current position.
 */
#define list_for_each_entry_from(pos, head, member) 
    for (; &pos->member != (head); 
         pos = list_next_entry(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_head within the struct.
 */
#define list_for_each_entry_safe(pos, n, head, member) 
    for (pos = list_first_entry(head, __typeof__(*pos), member), 
            n = list_next_entry(pos, member); 
         &pos->member != (head); 
         pos = n, n = list_next_entry(n, member))

/**
 * list_for_each_entry_safe_continue - continue list iteration safe against removal
 * @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_head 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_next_entry(pos, member), 
        n = list_next_entry(pos, member); 
         &pos->member != (head); 
         pos = n, n = list_next_entry(n, member))
    
/**
 * list_for_each_entry_safe_from - iterate over list from current point safe against removal
 * @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_head 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_next_entry(pos, member); 
         &pos->member != (head); 
         pos = n, n = list_next_entry(n, member))

/**
 * list_for_each_entry_safe_reverse - iterate backwards over list safe against removal
 * @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_head 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_last_entry(head, __typeof__(*pos), member), 
        n = list_prev_entry(pos, member); 
         &pos->member != (head); 
         pos = n, n = list_prev_entry(n, member))

/**
 * list_safe_reset_next - reset a stale list_for_each_entry_safe loop
 * @pos:    the loop cursor used in the list_for_each_entry_safe loop
 * @n:        temporary storage used in list_for_each_entry_safe
 * @member: the name of the list_head within the struct.
 *
 * list_safe_reset_next is not safe to use in general if the list may be
 * modified concurrently (eg. the lock is dropped in the loop body). An
 * exception to this is if the cursor element (pos) is pinned in the list,
 * and list_safe_reset_next is called after re-taking the lock and before
 * completing the current iteration of the loop body.
 */
#define list_safe_reset_next(pos, n, member)                
    n = list_next_entry(pos, member)

//HASH LIST 
struct hlist_head { 
    struct hlist_node *first; 
}; 

struct hlist_node { 
    struct hlist_node *next, **pprev; 
}; 

/*
 * 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).
 */
#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 = (struct hlist_node *)LIST_POISON1; 
    n->pprev = (struct hlist_node **)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_behind(struct hlist_node *n,
                    struct hlist_node *prev)
{
    n->next = prev->next;
    prev->next = n;
    n->pprev = &prev->next;

    if (n->next)
        n->next->pprev = &n->next;
}

/* after that we'll appear to be on some hlist and hlist_del will work */
static inline void hlist_add_fake(struct hlist_node *n)
{
    n->pprev = &n->next;
}

static inline bool hlist_fake(struct hlist_node *h)
{
    return h->pprev == &h->next;
}

/*
 * Check whether the node is the only node of the head without
 * accessing head:
 */
static inline bool hlist_is_singular_node(struct hlist_node *n, 
                                        struct hlist_head *h)
{
    return !n->next && n->pprev == &h->first;
}

/*
 * 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 ; pos = pos->next)

#define hlist_for_each_safe(pos, n, head) 
    for (pos = (head)->first; pos && ({ n = pos->next; 1; }); 
         pos = n)

#define hlist_entry_safe(ptr, type, member) 
    ({ __typeof__(ptr) ____ptr = (ptr); 
       ____ptr ? hlist_entry(____ptr, type, member) : NULL; 
    })

/**
 * hlist_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 hlist_node within the struct.
 */
#define hlist_for_each_entry(pos, head, member) 
    for (pos = hlist_entry_safe((head)->first, __typeof__(*(pos)), member);
         pos; 
         pos = hlist_entry_safe((pos)->member.next, __typeof__(*(pos)), member))

/**
 * hlist_for_each_entry_continue - iterate over a hlist continuing after current point
 * @pos:    the type * to use as a loop cursor.
 * @member: the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_continue(pos, member) 
    for (pos = hlist_entry_safe((pos)->member.next, __typeof__(*(pos)), member); 
         pos; 
         pos = hlist_entry_safe((pos)->member.next, __typeof__(*(pos)), member))

/**
 * hlist_for_each_entry_from - iterate over a hlist continuing from current point
 * @pos:    the type * to use as a loop cursor.
 * @member:    the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_from(pos, member) 
    for (; pos; 
         pos = hlist_entry_safe((pos)->member.next, __typeof__(*(pos)), member))

/**
 * hlist_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 &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(pos, n, head, member) 
    for (pos = hlist_entry_safe((head)->first, __typeof__(*pos), member); 
         pos && ({ n = pos->member.next; 1; });    
         pos = hlist_entry_safe(n, __typeof__(*pos), member))

#ifdef __cplusplus
} /* extern "C" */
#endif

#endif