list.h在用户态下的应用

一、背景

list.h文件位于linux/include下，内核中链表的操作函数都在其中。它有许多关于链表的操作函数，所以我们可以尝试将list.h拉到用户态中来使用，这样，我们在用户态中若要用到链表就可以直接调用其中已经实现好的函数了。我这里将拉到用户态的经过“改造”后的list.h文件代码列出，然后举一个简单的例子来应用这个头文件。当然，list.h中的函数非常多，应用也应该很广泛，我这里只是简单的示例其中较简单的几个函数。

二、用户态下的list.h

/*
 * @file list.h
 * @author PF
 * @date 2017/05/1
 *
 * port from linux kernel list.h: https://github.com/torvalds/linux/raw/master/include/linux/list.h
 *
 * Here is a recipe to cook list.h for user space program.
 * 1. copy list.h from linux/include/list.h
 * 2. remove
 *     - #ifdef __KERNE__ and its #endif
 *     - all #include line
 *     - prefetch() and rcu related functions
 * 3. add macro offsetof() and container_of
 */

#ifndef LIST_H_
#define LIST_H_ (1)

// import from include/linux/types.h
struct list_head {
    struct list_head *next, *prev;
};

struct hlist_head {
    struct hlist_node *first;
};

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

// import from include/linux/poison.h

/*
 * Architectures might want to move the poison pointer offset
 * into some well-recognized area such as 0xdead000000000000,
 * that is also not mappable by user-space exploits:
 */
#ifdef CONFIG_ILLEGAL_POINTER_VALUE
# define POISON_POINTER_DELTA _AC(CONFIG_ILLEGAL_POINTER_VALUE, UL)
#else
# define POISON_POINTER_DELTA (0)
#endif

/*
 * These are non-NULL pointers that will result in page faults
 * under normal circumstances, used to verify that nobody uses
 * non-initialized list entries.
 */
#define LIST_POISON1  ((void *) 0x00100100 + POISON_POINTER_DELTA)
#define LIST_POISON2  ((void *) 0x00200200 + POISON_POINTER_DELTA)

// import from include/linux/stddef.h
#undef offsetof
#ifdef __compiler_offsetof
#define offsetof(TYPE,MEMBER) __compiler_offsetof(TYPE,MEMBER)
#else
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
#endif

// import from include/linux/kernel.h
/**
* 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) );})

/*
 * 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.
 */

#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.
 */
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_LIST

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

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

#else
extern void __list_del_entry(struct list_head *entry);
extern 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(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)

/*
 * 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 = 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_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;
}

/*
 * 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))

#endif // LIST_H_

三、一个简单的例子

#include <stdio.h>
#include <stdlib.h>
#include "list.h"

struct kool_list{
    int to;
    struct list_head list;
    int from;
};

int main(int argc, char **argv){

    struct kool_list *tmp;
    struct list_head *pos, *q;
    unsigned int i;

    struct kool_list mylist;
    INIT_LIST_HEAD(&mylist.list);

    for(i=5; i!=0; --i){
        tmp= (struct kool_list *)malloc(sizeof(struct kool_list));
        printf("enter to and from:");
        scanf("%d %d", &tmp->to, &tmp->from);
        list_add(&(tmp->list), &(mylist.list));
    }
    printf("\n");

    printf("traversing the list using list_for_each_entry()\n");
    list_for_each_entry(tmp, &mylist.list, list)
        printf("to= %d from= %d\n", tmp->to, tmp->from);
    printf("\n");

    printf("deleting the list using list_for_each_safe()\n");
    list_for_each_safe(pos, q, &mylist.list){
        tmp= list_entry(pos, struct kool_list, list);

    printf("freeing item to= %d from= %d\n", tmp->to, tmp->from);
        list_del(pos);
        free(tmp);
    }
    return 0;
}

这个例子中我使用了list.h作头文件，这样我就可以使用其中的函数了，先创建了一个结构体作为头结点，然后使用list_add函数添加了5个结点，再用三种遍历方式输出结果。从这个例子中也可以看出list_add添加结点的特点。

REF

http://blog.csdn.net/hty46565/article/details/71532022

https://www.cnblogs.com/hummersofdie/p/3727703.html