Linux内核链表(双向list)移植笔记

一、移植

1. 上层使用移植时最好移植tools/list.h，因为没有那么READ_ONCE/WRITE_ONCE.

2. 移植include/linux/lish.h后的list.h

/*
总结：
1. 一个entry同一时间只能添加到一个链表上，若在一个链表上，又添加到另一个链表上，有可能造成遍历时死循环。
2. entry没有必要进行初始化，但是head若不使用 INIT_LIST_HEAD() 进行初始化，使用时会产生段错误。
3. list_add()是头插法，最后插入的对象由head->next指向。
4. list_for_each()和list_for_each_entry()都是使用head->next进行正向遍历，前者返回list_add结构指针，后者返回执行链表上挂载成员的指针。
5. 带safe的只是多个一个备份，可以安全地删除取出来的元素。

*/


/* SPDX-License-Identifier: GPL-2.0 来自include/linux/list.h*/
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H

#include <stddef.h>
/*------------------I add--------------- */

#define WRITE_ONCE(var, val) (*((volatile typeof(val) *)(&(var))) = (val))
#define READ_ONCE(var) (*((volatile typeof(var) *)(&(var))))

struct list_head {
    struct list_head *next, *prev;
};

struct hlist_head {
    struct hlist_node *first;
};

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


typedef _Bool            bool;

enum {
    false    = 0,
    true    = 1
};

#define NULL ((void *)0)

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

/**
 * 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 offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER) //already defined in stddef.h
#define container_of(ptr, type, member) ({                      \
    const typeof( ((type *)0)->member ) *__mptr = (ptr);    \
    (type *)( (char *)__mptr - offsetof(type,member) );})

/*------------------end----------------- */


/*
 * 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)

/*head使用前必须要init，否则会段错误*/
static inline void INIT_LIST_HEAD(struct list_head *list)
{
    WRITE_ONCE(list->next, list);
    list->prev = list;
}

#ifdef CONFIG_DEBUG_LIST
extern bool __list_add_valid(struct list_head *new,
                  struct list_head *prev,
                  struct list_head *next);
extern bool __list_del_entry_valid(struct list_head *entry);
#else
static inline bool __list_add_valid(struct list_head *new,
                struct list_head *prev,
                struct list_head *next)
{
    return true;
}
static inline bool __list_del_entry_valid(struct list_head *entry)
{
    return true;
}
#endif

/*
 * 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,
                  struct list_head *prev,
                  struct list_head *next)
{
    if (!__list_add_valid(new, prev, next))
        return;

    next->prev = new;
    new->next = next;
    new->prev = prev;
    WRITE_ONCE(prev->next, new);
}

/**
 * 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.
 */
/*头插法，最后插入的元素被head->next指向*/
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.
 */
/*尾插法，最后一个插入的被head->prev指向*/
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!
 */
/*传入的参数是要被删除节点的前一个和后一个的list_head成员的地址*/
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
    next->prev = prev;
    WRITE_ONCE(prev->next, next);
}

/*
 * Delete a list entry and clear the 'prev' pointer.
 *
 * This is a special-purpose list clearing method used in the networking code
 * for lists allocated as per-cpu, where we don't want to incur the extra
 * WRITE_ONCE() overhead of a regular list_del_init(). The code that uses this
 * needs to check the node 'prev' pointer instead of calling list_empty().
 */
static inline void __list_del_clearprev(struct list_head *entry)
{
    __list_del(entry->prev, entry->next);
    entry->prev = NULL;
}

/**
 * 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_entry(struct list_head *entry)
{
    if (!__list_del_entry_valid(entry))
        return;

    __list_del(entry->prev, entry->next);
}

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

/**
 * 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;
}

/*删除后，被删除的节点的prev和next指针都指向自己*/
static inline void list_replace_init(struct list_head *old, struct list_head *new)
{
    list_replace(old, new);
    INIT_LIST_HEAD(old);
}

/**
 * list_swap - replace entry1 with entry2 and re-add entry1 at entry2's position
 * @entry1: the location to place entry2
 * @entry2: the location to place entry1
 */
static inline void list_swap(struct list_head *entry1,
                 struct list_head *entry2)
{
    struct list_head *pos = entry2->prev;

    list_del(entry2);
    list_replace(entry1, entry2);
    if (pos == entry1)
        pos = entry2;
    list_add(entry1, pos);
}

/**
 * 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_bulk_move_tail - move a subsection of a list to its tail
 * @head: the head that will follow our entry
 * @first: first entry to move
 * @last: last entry to move, can be the same as first
 *
 * Move all entries between @first and including @last before @head.
 * All three entries must belong to the same linked list.
 */
static inline void list_bulk_move_tail(struct list_head *head,
                       struct list_head *first,
                       struct list_head *last)
{
    first->prev->next = last->next;
    last->next->prev = first->prev;

    head->prev->next = first;
    first->prev = head->prev;

    last->next = head;
    head->prev = last;
}

/**
 * list_is_first -- tests whether @list is the first entry in list @head
 * @list: the entry to test
 * @head: the head of the list
 */
static inline int list_is_first(const struct list_head *list,
                    const struct list_head *head)
{
    return list->prev == 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 READ_ONCE(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_rotate_to_front() - Rotate list to specific item.
 * @list: The desired new front of the list.
 * @head: The head of the list.
 *
 * Rotates list so that @list becomes the new front of the list.
 */
static inline void list_rotate_to_front(struct list_head *list,
                    struct list_head *head)
{
    /*
     * Deletes the list head from the list denoted by @head and
     * places it as the tail of @list, this effectively rotates the
     * list so that @list is at the front.
     */
    list_move_tail(head, list);
}

/**
 * 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);
}

/**
 * list_cut_before - cut a list into two, before given entry
 * @list: a new list to add all removed entries
 * @head: a list with entries
 * @entry: an entry within head, could be the head itself
 *
 * This helper moves the initial part of @head, up to but
 * excluding @entry, from @head to @list.  You should pass
 * in @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.
 * If @entry == @head, all entries on @head are moved to
 * @list.
 */
static inline void list_cut_before(struct list_head *list,
                   struct list_head *head,
                   struct list_head *entry)
{
    if (head->next == entry) {
        INIT_LIST_HEAD(list);
        return;
    }
    list->next = head->next;
    list->next->prev = list;
    list->prev = entry->prev;
    list->prev->next = list;
    head->next = entry;
    entry->prev = head;
}

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) ({ \
    struct list_head *head__ = (ptr); \
    struct list_head *pos__ = READ_ONCE(head__->next); \
    pos__ != head__ ? list_entry(pos__, 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.
 */
/*返回的只是list_head类型的指针，非指向链表上成员的指针*/
#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.
 */
/*正序遍历，通过head->next成员进行遍历*/
#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_from_reverse - iterate backwards 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 backwards over list of given type, continuing from current position.
 */
#define list_for_each_entry_from_reverse(pos, head, member)        \
    for (; &pos->member != (head);                    \
         pos = list_prev_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 !READ_ONCE(h->first);
}

static inline void __hlist_del(struct hlist_node *n)
{
    struct hlist_node *next = n->next;
    struct hlist_node **pprev = n->pprev;

    WRITE_ONCE(*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;
    WRITE_ONCE(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;
    WRITE_ONCE(*(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))

#endif

 

二、实验

1. 测试代码

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

struct student_desc {
    int code;
    struct list_head entry;
    int age;
};

struct class_desc {
    char *c_name;
    struct list_head stus; //queue all students
    int category;
    int position;
};

#define STU_NUM 10
struct student_desc stu[STU_NUM];
struct class_desc cls1;


int class_init()
{
    int i;
    struct student_desc *s_pos;

    INIT_LIST_HEAD(&cls1.stus);

    for (i = 0; i < STU_NUM; i++) {
        stu[i].code = i;
        //list_add(&stu[i].entry, &cls1.stus);
        list_add_tail(&stu[i].entry, &cls1.stus);
    }

    //list_for_each_entry(s_pos, &cls1.stus, entry) {
    list_for_each_entry_reverse(s_pos, &cls1.stus, entry) {
        printf("student code is %d\n", s_pos->code);
    }
}

void main()
{
    class_init();
}

2. 在某个entry之前插入一个元素

list_add(&new_entry->list, &entry1->list);

3. 反向遍历

list_for_each_entry_reverse(pos, head, member);

pos 变量通过其 member 成员挂载在链表 head 上，返回指向pos类型的指针。

4. 此外，linux内核中还有 hlist (单向链表)，plist(带有优先级的双向链表，其实就是每个优先级节点上再挂一个链表)

5. 链表排序和merge功能

list_sort.c 中提供对链表进行sort和merge功能，相关函数 list_sort() merge_final() merge().

 

三、补充

1. list_for_each_entry_safe 解释

#define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos)            \
    list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)

cfs_rq 对应的结构通过其 leaf_cfs_rq_list 成员挂在到 rq->leaf_cfs_rq_list 链表上， 然后得到这个链表上挂载的所有结构。

2. list_for_each_entry(pos, head, member) 解释

pos 结构类型的变量通过其 member 成员挂在head链表中，得到链表上挂的所有pos结构的变量。退出条件是 &pos->member == head，否则永远不会退出。

3. 指向成员的成员也是可以的，如：item = list_entry(item->vb.queue.next, struct bttv_buffer, vb.queue); //media/pci/bt8xx/bttv-driver.c

4. 开发尽量使用userdebug版本，因为有些检查报错在user版本上不会出现。比如userdebug版本上有使能 CONFIG_DEBUG_LIST，此时 list_del() 一个还未初始化的节点或已经del过的节点会崩溃，而user版本没有使能 CONFIG_DEBUG_LIST 则不会报错。若逻辑必须涉及如此，可用 LIST_INIT()/list_del_init() 提前进行处理。

5. 常用操作

list_add(entry, head); //添加在列表头
list_add_tail(entry, head); //添加在列表尾
list_add(entry, waiter->list.prev); //添加在waiter的前面
list_add(entry, &waiter->list); //添加在waiter的后面
list_add(entry, waiter->list.next); //添加后waiter的后面的一个元素的后面