linux内核的链循环双链表简单使用

　　linux内核的循环双链表是非常经典的代码实现方式，个人总结如下：API多，像nginx（二者原理一致）、redis的链表在api数目上还差一点扩展性强，比如可以实现一个LRU、和线程池结合使用都可以，而redis的链表还差了点
　　demo代码如下：#include  #include  #include  #include ＂list.h＂  #define MAX_ELE_NUMS    (5)  struct Stu {     unsigned int ulId;     struct list_head stNode; };  struct StuList {     struct list_head stLi; };  // 打印单个Node信息 static DL_PrintNode(char *pcPrefix, struct Stu *pstStu) {     assert((NULL != pcPrefix) && (NULL != pstStu));     printf(＂%s, id: %u, addr: %p, node: %p ＂, pcPrefix, pstStu->ulId, pstStu, &(pstStu->stNode)); }  // 释放链表的所有数据 void DL_ClearStuLi(struct list_head *pstHead) {     assert(NULL != pstHead);     struct Stu *pstStu = NULL;     struct Stu *pstNextStu = NULL;     list_for_each_entry_safe(pstStu, pstNextStu, pstHead, stNode) {         list_del(&(pstStu->stNode));         DL_PrintNode(＂free＂, pstStu);         free((void *) pstStu);     } }  // 打印链表数据 void DL_PrintStuLi(struct list_head *pstHead, int lReverse) {     assert(NULL != pstHead);     struct Stu *pstStu = NULL;     struct Stu *pstNextStu = NULL;     if (lReverse) {         list_for_each_entry_safe_reverse(pstStu, pstNextStu, pstHead, stNode) {             DL_PrintNode(＂show backward＂, pstStu);         }     } else {         list_for_each_entry_safe(pstStu, pstNextStu, pstHead, stNode) {             DL_PrintNode(＂show forward＂, pstStu);         }     } }  // 批量添加至链表中 void DL_BatchAddStuLiNodes(struct list_head *pstHead, struct Stu **ppstStus, unsigned int ulNodeNum, int lAddTail) {     assert((NULL != pstHead) && (NULL != ppstStus));     struct Stu *pstStu = NULL;     if (lAddTail) {         for (unsigned int i = 0; i < ulNodeNum; ++i) {             pstStu = ppstStus[i];             list_add_tail(&(pstStu->stNode), pstHead);         }     } else {         for (unsigned int i = 0; i < ulNodeNum; ++i) {             pstStu = ppstStus[i];             list_add(&(pstStu->stNode), pstHead);         }     } }  void DL_BatchCreateNodes(struct Stu **ppstStus, unsigned int ulNodeNum, unsigned int ulStartId) {     assert(NULL != ppstStus);     for (unsigned int i = 0; i < ulNodeNum; ++i) {         ppstStus[i] = (struct Stu *) malloc(sizeof(struct Stu));         assert(NULL != ppstStus[i]);         ppstStus[i]->ulId = ulStartId;         DL_PrintNode(＂create＂, ppstStus[i]);         ulStartId++;     } }  // 从给定的元素开始遍历,包括给定的元素 void DL_IterateIncludeGivenEntry(struct list_head *pstHead, struct Stu *pstStu, int lReverse) {     assert((NULL != pstHead) && (NULL != pstStu));     struct Stu *pstNextStu = NULL;     if (lReverse) {         list_for_each_entry_from_reverse(pstStu, pstHead, stNode) {             DL_PrintNode(＂show backward＂, pstStu);         }     } else {         list_for_each_entry_safe_from(pstStu, pstNextStu, pstHead, stNode) {             DL_PrintNode(＂show forward＂, pstStu);         }     } }  // 从给定的元素开始遍历， void DL_IterateExcludeGivenEntry(struct list_head *pstHead, struct Stu *pstStu, int lReverse) {     assert((NULL != pstHead) && (NULL != pstStu));     struct Stu *pstNextStu = NULL;     if (lReverse) {         list_for_each_entry_continue_reverse(pstStu, pstHead, stNode) {             DL_PrintNode(＂show backward＂, pstStu);         }     } else {         list_for_each_entry_safe_continue(pstStu, pstNextStu, pstHead, stNode) {             DL_PrintNode(＂show forward＂, pstStu);         }     } }  void DL_CreateNoEmptyList(struct list_head *pstHead, unsigned int ulNodeNum) {     assert((NULL != pstHead) && (0 != ulNodeNum));     struct Stu **ppstStus = NULL;      ppstStus = (struct Stu **) malloc(sizeof(struct Stu *) * ulNodeNum);     assert(NULL != ppstStus);      INIT_LIST_HEAD(pstHead);     DL_BatchCreateNodes(ppstStus, ulNodeNum, 0);     DL_BatchAddStuLiNodes(pstHead, ppstStus, ulNodeNum, 1);     free((void *) ppstStus); }  /**********************************************************************************************************************/ void DL_IterateGivenPoint() {     // 分配空间     struct Stu *apstStus[MAX_ELE_NUMS] = {0};     DL_BatchCreateNodes(apstStus, MAX_ELE_NUMS, 0);      // 初始化链表     struct StuList stList = {0};     INIT_LIST_HEAD(&(stList.stLi));      // 链表尾部添加     DL_BatchAddStuLiNodes(&(stList.stLi), apstStus, MAX_ELE_NUMS, 1);      //DL_IterateIncludeGivenEntry(&(stList.stLi), apstStus[2], 1);     DL_IterateExcludeGivenEntry(&(stList.stLi), apstStus[2], 1);      // 释放链表所有数据     DL_ClearStuLi(&(stList.stLi)); }  // 简单使用 void DL_Basic() {     // 分配空间     struct Stu *apstStus[MAX_ELE_NUMS] = {0};     DL_BatchCreateNodes(apstStus, MAX_ELE_NUMS, 0);      // 初始化链表     struct StuList stList = {0};     INIT_LIST_HEAD(&(stList.stLi));      // 无数据，为空     printf(＂init, ＂            ＂list emtpy: %s＂            ＂ ＂,            list_empty(&(stList.stLi)) ? ＂yes＂ : ＂no＂);      // 链表尾部添加     DL_BatchAddStuLiNodes(&(stList.stLi), apstStus, MAX_ELE_NUMS, 1);      // 有数据不为空     printf(＂After Add, ＂            ＂list emtpy: %s＂            ＂ ＂,            list_empty(&(stList.stLi)) ? ＂yes＂ : ＂no＂);      struct Stu *pstStu = NULL;     struct list_head *pstNode = NULL;     struct list_head *pstNextNode = NULL;      // 打印所有的链表数据     DL_PrintStuLi(&(stList.stLi), 0);      // 释放链表所有数据     DL_ClearStuLi(&(stList.stLi)); }  void showBasicListInfo() {     struct Stu *apstStus[MAX_ELE_NUMS] = {0};     DL_BatchCreateNodes(apstStus, MAX_ELE_NUMS, 0);      // init list     struct StuList stList = {0};     INIT_LIST_HEAD(&(stList.stLi));      // no data, is empty     printf(＂init, ＂            ＂list emtpy: %s＂            ＂ ＂,            list_empty(&(stList.stLi)) ? ＂yes＂ : ＂no＂);      // add node to list tail     for (unsigned int i = 0; i < MAX_ELE_NUMS; ++i) {         list_add_tail(&(apstStus[i]->stNode), &(stList.stLi));         printf(＂list empty: %s, ＂                ＂list singular: %s, ＂                ＂list first: %s, ＂                ＂list last: %s, ＂                ＂entry is head: %s ＂                ＂ ＂,                list_empty(&(stList.stLi)) ? ＂yes＂ : ＂no＂,                list_is_singular(&(stList.stLi)) ? ＂yes＂ : ＂no＂,                list_is_first(&(apstStus[i]->stNode), &(stList.stLi)) ? ＂yes＂ : ＂no＂,                list_is_last(&(apstStus[i]->stNode), &(stList.stLi)) ? ＂yes＂ : ＂no＂,                list_entry_is_head(apstStus[i], &(stList.stLi), stNode) ? ＂yes＂ : ＂no＂         );     }      printf(＂list first: %u＂            ＂list last: %u＂            ＂ ＂,            list_first_entry_or_null(&(stList.stLi), struct Stu, stNode)->ulId,            list_last_entry(&(stList.stLi), struct Stu, stNode)->ulId     );     DL_PrintStuLi(&(stList.stLi), 0);     DL_ClearStuLi(&(stList.stLi)); }  struct InvalidStruct {     int ulInteger;     unsigned long long dulDoubleInteger;     char szName[20];     float fDataFloat; }; int main() {      showBasicListInfo();      return 0; }
　　为此，提取的代码如下，可直接复制粘贴供以后使用，由于代码中使用了new作为变量名，在C++中会报错，可以自行将new替换掉其他变量名即可。/* SPDX-License-Identifier: GPL-2.0 */ #ifndef _R2M_LIST_H_ #define _R2M_LIST_H_  #include   #ifndef offsetof #define offsetof(TYPE, MEMBER)	((size_t)&((TYPE *)0)->MEMBER) #endif  /**  * 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.  *  */ #ifndef container_of #define container_of(ptr, type, member) ({                         void *__mptr = (void *)(ptr);                              ((type *)(__mptr - offsetof(type, member))); }) #endif  #define POISON_POINTER_DELTA 0  /*  * 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 *) 0x100 + POISON_POINTER_DELTA) #define LIST_POISON2  ((void *) 0x122 + POISON_POINTER_DELTA)  /*  * Circular doubly linked list implementation.  *  * Some of the internal functions (＂__xxx＂) are useful when  * manipulating whole lists rather than single entries, as  * sometimes we already know the next/prev entries and we can  * generate better code by using them directly rather than  * using the generic single-entry routines.  */  struct list_head {     struct list_head *next, *prev; };  #define LIST_HEAD_INIT(name) { &(name), &(name) }  #define LIST_HEAD(name)  	struct list_head name = LIST_HEAD_INIT(name)  /**  * INIT_LIST_HEAD - Initialize a list_head structure  * @list: list_head structure to be initialized.  *  * Initializes the list_head to point to itself.  If it is a list header,  * the result is an empty list.  */ static inline void INIT_LIST_HEAD(struct list_head *list) {     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;     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.  */ 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; }  /*  * 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; }  static inline void __list_del_entry(struct list_head *entry) { 	if (!__list_del_entry_valid(entry)) 		return;  	__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(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; }  /**  * list_replace_init - replace old entry by new one and initialize the old 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_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 head->next == head; }  /**  * list_del_init_careful - deletes entry from list and reinitialize it.  * @entry: the element to delete from the list.  *  * This is the same as list_del_init(), except designed to be used  * together with list_empty_careful() in a way to guarantee ordering  * of other memory operations.  *  * Any memory operations done before a list_del_init_careful() are  * guaranteed to be visible after a list_empty_careful() test.  */ static inline void list_del_init_careful(struct list_head *entry) {     /* unsupported */ #if 0 	__list_del_entry(entry); 	entry->prev = entry; 	smp_store_release(&entry->next, entry); #endif }  /**  * 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) {     /* unsupported */ #if 0 	struct list_head *next = smp_load_acquire(&head->next); 	return (next == head) && (next == head->prev); #endif 	return 0; }  /**  * 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__ = 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.  */ #define list_for_each(pos, head)  	for (pos = (head)->next; pos != (head); pos = pos->next)  /**  * list_for_each_continue - continue iteration over a list  * @pos:	the &struct list_head to use as a loop cursor.  * @head:	the head for your list.  *  * Continue to iterate over a list, continuing after the current position.  */ #define list_for_each_continue(pos, head)  	for (pos = pos->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_entry_is_head - test if the entry points to the head of the list  * @pos:	the type * to cursor  * @head:	the head for your list.  * @member:	the name of the list_head within the struct.  */ #define list_entry_is_head(pos, head, member)				 	(&pos->member == (head))  /**  * 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);	 	     !list_entry_is_head(pos, head, member);			 	     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);		 	     !list_entry_is_head(pos, head, member); 			 	     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);			 	     !list_entry_is_head(pos, head, member);			 	     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);			 	     !list_entry_is_head(pos, head, member);			 	     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 (; !list_entry_is_head(pos, head, member);			 	     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 (; !list_entry_is_head(pos, head, member);			 	     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);			 	     !list_entry_is_head(pos, head, member); 			 	     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);				 	     !list_entry_is_head(pos, head, member);				 	     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);					 	     !list_entry_is_head(pos, head, member);				 	     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);			 	     !list_entry_is_head(pos, head, member); 			 	     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).  */  struct hlist_head {     struct hlist_node *first; };  struct hlist_node {     struct hlist_node *next, **pprev; };  #define HLIST_HEAD_INIT { .first = NULL } #define HLIST_HEAD(name) struct hlist_head name = {  .first = NULL } #define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL) static inline void INIT_HLIST_NODE(struct hlist_node *h) { 	h->next = NULL; 	h->pprev = NULL; }  /**  * hlist_unhashed - Has node been removed from list and reinitialized?  * @h: Node to be checked  *  * Not that not all removal functions will leave a node in unhashed  * state.  For example, hlist_nulls_del_init_rcu() does leave the  * node in unhashed state, but hlist_nulls_del() does not.  */ static inline int hlist_unhashed(const struct hlist_node *h) { 	return !h->pprev; }  /**  * hlist_unhashed_lockless - Version of hlist_unhashed for lockless use  * @h: Node to be checked  *  * This variant of hlist_unhashed() must be used in lockless contexts  * to avoid potential load-tearing.  The READ_ONCE() is paired with the  * various WRITE_ONCE() in hlist helpers that are defined below.  */ static inline int hlist_unhashed_lockless(const struct hlist_node *h) { 	return !h->pprev; }  /**  * hlist_empty - Is the specified hlist_head structure an empty hlist?  * @h: Structure to check.  */ 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; }  /**  * hlist_del - Delete the specified hlist_node from its list  * @n: Node to delete.  *  * Note that this function leaves the node in hashed state.  Use  * hlist_del_init() or similar instead to unhash @n.  */ static inline void hlist_del(struct hlist_node *n) { 	__hlist_del(n); 	n->next = LIST_POISON1; 	n->pprev = LIST_POISON2; }  /**  * hlist_del_init - Delete the specified hlist_node from its list and initialize  * @n: Node to delete.  *  * Note that this function leaves the node in unhashed state.  */ static inline void hlist_del_init(struct hlist_node *n) { 	if (!hlist_unhashed(n)) { 		__hlist_del(n); 		INIT_HLIST_NODE(n); 	} }  /**  * hlist_add_head - add a new entry at the beginning of the hlist  * @n: new entry to be added  * @h: hlist head to add it after  *  * Insert a new entry after the specified head.  * This is good for implementing stacks.  */ 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; }  /**  * hlist_add_before - add a new entry before the one specified  * @n: new entry to be added  * @next: hlist node to add it before, which must be non-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; }  /**  * hlist_add_behind - add a new entry after the one specified  * @n: new entry to be added  * @prev: hlist node to add it after, which must be non-NULL  */ 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; }  /**  * hlist_add_fake - create a fake hlist consisting of a single headless node  * @n: Node to make a fake list out of  *  * This makes @n appear to be its own predecessor on a headless hlist.  * The point of this is to allow things like hlist_del() to work correctly  * in cases where there is no list.  */ static inline void hlist_add_fake(struct hlist_node *n) { 	n->pprev = &n->next; }  /**  * hlist_fake: Is this node a fake hlist?  * @h: Node to check for being a self-referential fake hlist.  */ static inline bool hlist_fake(struct hlist_node *h) { 	return h->pprev == &h->next; }  /**  * hlist_is_singular_node - is node the only element of the specified hlist?  * @n: Node to check for singularity.  * @h: Header for potentially singular list.  *  * Check whether the node is the only node of the head without  * accessing head, thus avoiding unnecessary cache misses.  */ static inline bool hlist_is_singular_node(struct hlist_node *n, struct hlist_head *h) { 	return !n->next && n->pprev == &h->first; }  /**  * hlist_move_list - Move an hlist  * @old: hlist_head for old list.  * @new: hlist_head for new list.  *  * 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:		a &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