list_for_each_entry详解

这篇具有很好参考价值的文章主要介绍了list_for_each_entry详解。希望对大家有所帮助。如果存在错误或未考虑完全的地方,请大家不吝赐教,您也可以点击"举报违法"按钮提交疑问。

参考链接:
终于理解list_entry和list_for_each_entry
linux 内核代码中list_for_each_entry宏之我见
linux之list_for_each和list_for_each_entry函数
container_of的用法
用户态下的list.h

Linux内核中的许多链表操作,都是使用list_for_each_entry进行遍历,其定义在/usr/src/linux-2.6.32.9/include/linux/list.h路径,具体的宏定义如下所示:

list_for_each_entry

/**
 * list_for_each_entry    -    iterate over list of given type
 * @pos:    the type * to use as a loop cursor.
 * @head:    the head for your list.
 * @member:    the name of the list_struct within the struct.
 */
#define list_for_each_entry(pos, head, member)                \
    for (pos = list_entry((head)->next, typeof(*pos), member);    \
     prefetch(pos->member.next), &pos->member != (head);     \
     pos = list_entry(pos->member.next, typeof(*pos), member))

prefetch的作用是通知CPU即将使用该数据,需要提前加载到cache中,以提高代码效率

list_entry

/**
 * 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)

container_of

/**
 * 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) );})

containner_of的作用通过已知的数据结构成员指针ptr、数据结构type、以及ptr在数据结构中的成员名,获取到指向数据结构type的指针

工作原理:将0地址强制转换为数据结构type类型,使用临时变量__mptr指向结构体成员指针ptr

使用ptr指针减去成员在结构体中的偏移,__mptr指向的位置即为该数据结构的位置

示例:

struct person
{
  char* name;
  int age;
  int height;
  int weight;
  ...
};

person wang;

//目前可公开的情报:*ptr = &wang.age、type为person、member为age
//使用container_of即可获取到指向wang的指针
offsetof
#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)

offsetof的作用获取一个数据成员在该数据结构中的偏移量

工作原理:将0地址强制转换为Type*类型的指针,因此该数据结构的各个成员所在的位置,就是相对于0地址的偏移量,返回数据结构成员的地址就是成员的偏移量

list_for_each_entry作用

综上所述,我们可以了解到list_for_each_entry的作用:所有包含list_head的数据结构,均可使用此方法遍历链表;list_head结构体不包含数据部分,使用该函数进行遍历链表节点,然后在循环体中,对链表的数据部分进行读写操作,这就是list_for_each_entry的共通性

通过对链表中list成员的遍历,即可定位到链表的相关节点,进而访问链表节点中的数据部分

使用示例

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

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

typedef struct usrList
{ 
    int index;
    int data; 
    struct list_head_test list; 
}USR_LIST_TYPE; 

int main(int argc, char *argv[]) 
{ 
    USR_LIST_TYPE msg, *pmsg; 
    LIST_HEAD(msg_head);
    int *ptr = &msg.data;
    int i; /* insert the 10 msgs */ 
    for(i = 0; i < 10; i++)
    { 
        pmsg = (USR_LIST_TYPE *)malloc(sizeof(USR_LIST_TYPE)); 
        pmsg->index = i + 1; 
        pmsg->data = (i + 1)*10; 
        list_add_tail(&pmsg->list, &msg_head); 
    } 

    /* 根据list 遍历 整个链表,并打印信息 */ 
    list_for_each_entry(pmsg, &msg_head, list)
    { 
        printf("msg index:%d data:%d\n", pmsg->index, pmsg->data); 
    } 
    
    return 0;
}

用户态无法访问#include <linux/list.h>的头文件,因此将list.h的内容复制到自定义文件,以使用相关定义文章来源地址https://www.toymoban.com/news/detail-607434.html

/*
 * @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_


到了这里,关于list_for_each_entry详解的文章就介绍完了。如果您还想了解更多内容,请在右上角搜索TOY模板网以前的文章或继续浏览下面的相关文章,希望大家以后多多支持TOY模板网!

本文来自互联网用户投稿,该文观点仅代表作者本人,不代表本站立场。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如若转载,请注明出处: 如若内容造成侵权/违法违规/事实不符,请点击违法举报进行投诉反馈,一经查实,立即删除!

领支付宝红包 赞助服务器费用

相关文章

  • 深入理解 Java 循环结构:while、do while、for 和 for-each 循环

    循环可以执行一个代码块,只要达到指定的条件。循环很方便,因为它们节省时间,减少错误,并使代码更易读。 while 循环会循环执行一个代码块,只要指定的条件为真: 语法 在下面的示例中,只要变量(i)小于 5,循环中的代码将一遍又一遍地运行: 示例 注意:不要忘

    2024年02月19日
    浏览(38)
  • Terraform 系列-使用 for-each 对本地 json 进行迭代

    Terraform 系列文章 Grafana 系列文章 前文 Grafana 系列 - Grafana Terraform Provider 基础 介绍了使用 Grafana Terraform Provider 创建 Datasource. 现在有这么一个现实需求: 有大量的同类型 (type) 的 datasource 需要批量添加,而且这些 datasource 的基本信息是以 json 的格式已经存在。 需要对 json 进行

    2024年02月10日
    浏览(40)
  • react异常 Each child in a list should have a unique “key” prop

    react异常警告:Each child in a list should have a unique “key” prop 原因:Dom在渲染数组时,需要一个key,不然嵌套数组时会引起歧义 加了key为何还报Each child in a list should have a unique “key“ prop / 是Fragment的缩写形式,遍历使用时要加key,而缩写形式是不可以加key的,所以要这样写:

    2024年02月13日
    浏览(41)
  • 「SQL面试题库」 No_123 The Most Recent Orders for Each Product

    「SQL面试题库」是由 不是西红柿 发起,全员免费参与的SQL学习活动。我每天发布1道SQL面试真题,从简单到困难,涵盖所有SQL知识点,我敢保证只要做完这100道题,不仅能轻松搞定面试,代码能力和工作效率也会有明显提升。 1.1 活动流程 整理题目 :西红柿每天无论刮风下雨

    2024年02月15日
    浏览(36)
  • 【Linux】Shell脚本之流程控制语句 if判断、for循环、while循环、case循环判断 + 实战详解[⭐建议收藏!!⭐]

    👨‍🎓 博主简介   🏅云计算领域优质创作者   🏅华为云开发者社区专家博主   🏅阿里云开发者社区专家博主 💊 交流社区: 运维交流社区 欢迎大家的加入! 🐋 希望大家多多支持,我们一起进步!😄 🎉如果文章对你有帮助的话,欢迎 点赞 👍🏻 评论 💬 收藏

    2024年02月13日
    浏览(48)
  • mysql报错:Duplicate entry ‘...‘ for key ‘field‘

    错误信息 \\\"Duplicate entry \\\'...\\\' for key \\\'field\\\'\\\" 表示在数据库表中,你正在尝试插入一条数据的\\\'number\\\'字段的值已经存在。这通常是由于你设置了\\\'field\\\'字段为唯一键(UNIQUE KEY),而你又尝试插入一个已存在的值。 解决这个问题的方法有以下几种: 检查输入的数据 :确保你插入的数

    2024年02月06日
    浏览(42)
  • mysql 报错 Duplicate entry ‘xxx‘ for key ‘字段名‘

    有时候对表进行操作,例如加唯一键,或者插入数据(已经有唯一键),会报错 Duplicate entry...for key... 原因是primary key(主键)或unique key(唯一键)的值重复。 还有索引也会导致。 碰到这种情况,考虑是否需要主键或唯一键的约束,如果不需要,就直接删除约束。 在navica

    2024年02月12日
    浏览(54)
  • 报错Duplicate entry ‘值‘ for key ‘字段名‘的解决解决方法

    遇到这种问题, 是你的数据库表那个字段设置了唯一索引。所以这个字段新增的数据不能重复。具体可以打开表,然后点击表设置,具体教程可以看下文章最后 Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry \\\'测试\\\' for key \\\'teacher.uk_name\\\'     at

    2023年04月13日
    浏览(55)
  • 增加samba用户提示Failed to add entry for user

    这个问题我在CSDN上搜到了很多文章,而且都差不多,一开始并没有解决我的问题,不太理解怎么做,经过多次尝试,最后解决了。记录一下具体操作步骤。 第一个是要配置/etc/samba/smb.conf 文件,在文件最后,添加下图相应信息。其中path是我的共享文件夹路径。 windows是我取的

    2024年02月11日
    浏览(48)
  • Duplicate entry ‘XXX‘ for key ‘XXX.PRIMARY‘解决方案。

    今天在插入数据时,出现一个错误 网上查看说是主键冲突了,但是查看数据库并没有,把所有数据清空,或者把表删了之后,在重新建也还是报同样的错。 … … … 最后的结果方案: 方案一:设置主键自增,适合主键为int类型(我的主键是varchar) 方案二:把insert into 表名

    2024年02月01日
    浏览(51)

觉得文章有用就打赏一下文章作者

支付宝扫一扫打赏

博客赞助

微信扫一扫打赏

请作者喝杯咖啡吧~博客赞助

支付宝扫一扫领取红包,优惠每天领

二维码1

领取红包

二维码2

领红包