合规部对于网站建设的意见/中国大数据平台官网
在Linux内核中，为了提供统一的链表操作，减少结构体的额外开支，内核提供了 list.h 文件，在源码中的路径为 include/linux/list.h。
list.h内嵌到不同的object中,配合container_of宏,为各种类型的object提供了"变身"的能力,程序中可以非常方便的根据list地址,将list_head对象强制cast为包含其的目标对象,过程有点类似于C++中的父类到子类的强制转化,这种转换当然是有前提的,对于CPP来说,由于转换后内存或扩张,你的对象得真的是一个子类对象才能保证转换的安全性,同样道理list_head也需要保证被转换的list真的在目标对象之中才可以.
READ_ONCE/WRITE_ONCE:
从linux 4.4版本开始,list的实现变得复杂了一些,主要是WRITE_ONCE/READ_ONCE的引入,将平凡的读取和写入操作变得麻烦了不少.
下载LINUX源码仓库,发现主要相关的提交有三个:1658d35ead5d8,1c97be677f72b,和d679ae94fdd5d.
上面的代码是初始化一个双向循环链表 ，将list中的两个指针 next 和 prev 都指向 自己，也就是 list , 那为什么不直接赋值呢？查以前版本的内核代码，发现 linux4.4 以下的版本都是直接赋值的，linux4.5以上的版本都进行了优化。
那我们进行思考以下两个问题：
1、内核出于什么原因进行优化呢？ 它和直接赋值有什么区别？
2、我们什么时候要使用 WRITE_ONCE/READ_ONCE？
先看看它的定义:
为什么要用READ_ONCE()和WRITE_ONCE()这两个宏呢？ 这里起到关键作用的就是 volatile ，它主要告诉编译器：
1、声明这个变量很重要，不要把它当成一个普通的变量，做出错误的优化。
2、保证 CPU 每次都从内存重新读取变量的值，而不是用寄存器中暂存的值。
因为在 多线程/多核 环境中，不会被当前线程修改的变量，可能会被其他的线程修改，从内存读才可靠。
还有一部分原因是，这两个宏可以作为标记，提醒编程人员这里面是一个多核/多线程共享的变量，必要的时候应该加互斥锁来保护。在多核多线程编程时，要注意共享变量的使用，要保证是 volatile的.
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _BR_LIST_H
#define _BR_LIST_H#define br_barrier() __asm__ __volatile__("": : :"memory")
#define br_smp_read_barrier_depends() do { } while (0)
#define BR_LIST_POISON1 ((void *) 0x100)
#define BR_LIST_POISON2 ((void *) 0x200)#define br_container_of(ptr, type, member) ({ \const typeof( ((type *)0)->member ) *__mptr = (ptr); \(type *)( (char *)__mptr - offsetof(type,member) );})#define __BR_READ_ONCE_SIZE \
({ \switch (size) { \case 1: *(__u8 *)res = *(volatile __u8 *)p; break; \case 2: *(__u16 *)res = *(volatile __u16 *)p; break; \case 4: *(__u32 *)res = *(volatile __u32 *)p; break; \case 8: *(__u64 *)res = *(volatile __u64 *)p; break; \default: \br_barrier(); \__builtin_memcpy((void *)res, (const void *)p, size); \br_barrier(); \} \
})static __always_inline
void __br_read_once_size(const volatile void *p, void *res, int size)
{__BR_READ_ONCE_SIZE;
}static __no_kasan_or_inline
void __br_read_once_size_nocheck(const volatile void *p, void *res, int size)
{__BR_READ_ONCE_SIZE;
}static __always_inline void __br_write_once_size(volatile void *p, void *res, int size)
{switch (size) {case 1: *(volatile __u8 *)p = *(__u8 *)res; break;case 2: *(volatile __u16 *)p = *(__u16 *)res; break;case 4: *(volatile __u32 *)p = *(__u32 *)res; break;case 8: *(volatile __u64 *)p = *(__u64 *)res; break;default:br_barrier();__builtin_memcpy((void *)p, (const void *)res, size);br_barrier();}
}#define __BR_READ_ONCE(x, check) \
({ \union { typeof(x) __val; char __c[1]; } __u; \if (check) \__br_read_once_size(&(x), __u.__c, sizeof(x)); \else \__br_read_once_size_nocheck(&(x), __u.__c, sizeof(x)); \br_smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \__u.__val; \
})#define BR_READ_ONCE(x) __BR_READ_ONCE(x, 1)
#define BR_WRITE_ONCE(x, val) \
({ \union { typeof(x) __val; char __c[1]; } __u = \{ .__val = (__force typeof(x)) (val) }; \__br_write_once_size(&(x), __u.__c, sizeof(x)); \__u.__val; \
})struct br_list_head {struct br_list_head *next, *prev;
};struct br_hlist_head {struct br_hlist_node *first;
};struct br_hlist_node {struct br_hlist_node *next, **pprev;
};/** 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 BR_LIST_HEAD_INIT(name) { &(name), &(name) }#define BR_LIST_HEAD(name) \struct br_list_head name = BR_LIST_HEAD_INIT(name)static inline void BR_INIT_LIST_HEAD(struct br_list_head *list)
{BR_WRITE_ONCE(list->next, list);list->prev = list;
}#ifdef CONFIG_DEBUG_LIST
extern bool __br_list_add_valid(struct br_list_head *new,struct br_list_head *prev,struct br_list_head *next);
extern bool __br_list_del_entry_valid(struct br_list_head *entry);
#else
static inline bool __br_list_add_valid(struct br_list_head *new,struct br_list_head *prev,struct br_list_head *next)
{return true;
}
static inline bool __br_list_del_entry_valid(struct br_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 __br_list_add(struct br_list_head *new,struct br_list_head *prev,struct br_list_head *next)
{if (!__br_list_add_valid(new, prev, next))return;next->prev = new;new->next = next;new->prev = prev;BR_WRITE_ONCE(prev->next, new);
}/*** br_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 br_list_add(struct br_list_head *new, struct br_list_head *head)
{__br_list_add(new, head, head->next);
}/*** br_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 br_list_add_tail(struct br_list_head *new, struct br_list_head *head)
{__br_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 __br_list_del(struct br_list_head * prev, struct br_list_head * next)
{next->prev = prev;BR_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* BR_WRITE_ONCE() overhead of a regular br_list_del_init(). The code that uses this* needs to check the node 'prev' pointer instead of calling br_list_empty().*/
static inline void __br_list_del_clearprev(struct br_list_head *entry)
{__br_list_del(entry->prev, entry->next);entry->prev = NULL;
}/*** br_list_del - deletes entry from list.* @entry: the element to delete from the list.* Note: br_list_empty() on entry does not return true after this, the entry is* in an undefined state.*/
static inline void __br_list_del_entry(struct br_list_head *entry)
{if (!__br_list_del_entry_valid(entry))return;__br_list_del(entry->prev, entry->next);
}static inline void br_list_del(struct br_list_head *entry)
{__br_list_del_entry(entry);entry->next = BR_LIST_POISON1;entry->prev = BR_LIST_POISON2;
}/*** br_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 br_list_replace(struct br_list_head *old,struct br_list_head *new)
{new->next = old->next;new->next->prev = new;new->prev = old->prev;new->prev->next = new;
}static inline void br_list_replace_init(struct br_list_head *old,struct br_list_head *new)
{br_list_replace(old, new);BR_INIT_LIST_HEAD(old);
}/*** br_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 br_list_swap(struct br_list_head *entry1,struct br_list_head *entry2)
{struct br_list_head *pos = entry2->prev;br_list_del(entry2);br_list_replace(entry1, entry2);if (pos == entry1)pos = entry2;br_list_add(entry1, pos);
}/*** br_list_del_init - deletes entry from list and reinitialize it.* @entry: the element to delete from the list.*/
static inline void br_list_del_init(struct br_list_head *entry)
{__br_list_del_entry(entry);BR_INIT_LIST_HEAD(entry);
}/*** br_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 br_list_move(struct br_list_head *list, struct br_list_head *head)
{__br_list_del_entry(list);br_list_add(list, head);
}/*** br_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 br_list_move_tail(struct br_list_head *list,struct br_list_head *head)
{__br_list_del_entry(list);br_list_add_tail(list, head);
}/*** br_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 br_list_bulk_move_tail(struct br_list_head *head,struct br_list_head *first,struct br_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;
}/*** br_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 br_list_is_first(const struct br_list_head *list,const struct br_list_head *head)
{return list->prev == head;
}/*** br_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 br_list_is_last(const struct br_list_head *list,const struct br_list_head *head)
{return list->next == head;
}/*** br_list_empty - tests whether a list is empty* @head: the list to test.*/
static inline int br_list_empty(const struct br_list_head *head)
{return BR_READ_ONCE(head->next) == head;
}/*** br_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 br_list_empty_careful() without synchronization* can only be safe if the only activity that can happen* to the list entry is br_list_del_init(). Eg. it cannot be used* if another CPU could re-br_list_add() it.*/
static inline int br_list_empty_careful(const struct br_list_head *head)
{struct br_list_head *next = head->next;return (next == head) && (next == head->prev);
}/*** br_list_rotate_left - rotate the list to the left* @head: the head of the list*/
static inline void br_list_rotate_left(struct br_list_head *head)
{struct br_list_head *first;if (!br_list_empty(head)) {first = head->next;br_list_move_tail(first, head);}
}/*** br_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 br_list_rotate_to_front(struct br_list_head *list,struct br_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.*/br_list_move_tail(head, list);
}/*** br_list_is_singular - tests whether a list has just one entry.* @head: the list to test.*/
static inline int br_list_is_singular(const struct br_list_head *head)
{return !br_list_empty(head) && (head->next == head->prev);
}static inline void __br_list_cut_position(struct br_list_head *list,struct br_list_head *head, struct br_list_head *entry)
{struct br_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;
}/*** br_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 br_list_cut_position(struct br_list_head *list,struct br_list_head *head, struct br_list_head *entry)
{if (br_list_empty(head))return;if (br_list_is_singular(head) &&(head->next != entry && head != entry))return;if (entry == head)BR_INIT_LIST_HEAD(list);else__br_list_cut_position(list, head, entry);
}/*** br_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 br_list_cut_before(struct br_list_head *list,struct br_list_head *head,struct br_list_head *entry)
{if (head->next == entry) {BR_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 __br_list_splice(const struct br_list_head *list,struct br_list_head *prev,struct br_list_head *next)
{struct br_list_head *first = list->next;struct br_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 br_list_splice(const struct br_list_head *list,struct br_list_head *head)
{if (!br_list_empty(list))__br_list_splice(list, head, head->next);
}/*** br_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 br_list_splice_tail(struct br_list_head *list,struct br_list_head *head)
{if (!br_list_empty(list))__br_list_splice(list, head->prev, head);
}/*** br_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 br_list_splice_init(struct br_list_head *list,struct br_list_head *head)
{if (!br_list_empty(list)) {__br_list_splice(list, head, head->next);BR_INIT_LIST_HEAD(list);}
}/*** br_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 br_list_splice_tail_init(struct br_list_head *list,struct br_list_head *head)
{if (!br_list_empty(list)) {__br_list_splice(list, head->prev, head);BR_INIT_LIST_HEAD(list);}
}/*** br_list_entry - get the struct for this entry* @ptr: the &struct br_list_head pointer.* @type: the type of the struct this is embedded in.* @member: the name of the br_list_head within the struct.*/
#define br_list_entry(ptr, type, member) \br_container_of(ptr, type, member)/*** br_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 br_list_head within the struct.** Note, that list is expected to be not empty.*/
#define br_list_first_entry(ptr, type, member) \br_list_entry((ptr)->next, type, member)/*** br_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 br_list_head within the struct.** Note, that list is expected to be not empty.*/
#define br_list_last_entry(ptr, type, member) \br_list_entry((ptr)->prev, type, member)/*** br_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 br_list_head within the struct.** Note that if the list is empty, it returns NULL.*/
#define br_list_first_entry_or_null(ptr, type, member) ({ \struct br_list_head *head__ = (ptr); \struct br_list_head *pos__ = BR_READ_ONCE(head__->next); \pos__ != head__ ? br_list_entry(pos__, type, member) : NULL; \
})/*** br_list_next_entry - get the next element in list* @pos: the type * to cursor* @member: the name of the br_list_head within the struct.*/
#define br_list_next_entry(pos, member) \br_list_entry((pos)->member.next, typeof(*(pos)), member)/*** br_list_prev_entry - get the prev element in list* @pos: the type * to cursor* @member: the name of the br_list_head within the struct.*/
#define br_list_prev_entry(pos, member) \br_list_entry((pos)->member.prev, typeof(*(pos)), member)/*** br_list_for_each - iterate over a list* @pos: the &struct br_list_head to use as a loop cursor.* @head: the head for your list.*/
#define br_list_for_each(pos, head) \for (pos = (head)->next; pos != (head); pos = pos->next)/*** br_list_for_each_prev - iterate over a list backwards* @pos: the &struct br_list_head to use as a loop cursor.* @head: the head for your list.*/
#define br_list_for_each_prev(pos, head) \for (pos = (head)->prev; pos != (head); pos = pos->prev)/*** br_list_for_each_safe - iterate over a list safe against removal of list entry* @pos: the &struct br_list_head to use as a loop cursor.* @n: another &struct br_list_head to use as temporary storage* @head: the head for your list.*/
#define br_list_for_each_safe(pos, n, head) \for (pos = (head)->next, n = pos->next; pos != (head); \pos = n, n = pos->next)/*** br_list_for_each_prev_safe - iterate over a list backwards safe against removal of list entry* @pos: the &struct br_list_head to use as a loop cursor.* @n: another &struct br_list_head to use as temporary storage* @head: the head for your list.*/
#define br_list_for_each_prev_safe(pos, n, head) \for (pos = (head)->prev, n = pos->prev; \pos != (head); \pos = n, n = pos->prev)/*** br_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 br_list_head within the struct.*/
#define br_list_entry_is_head(pos, head, member) \(&pos->member == (head))/*** br_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 br_list_head within the struct.*/
#define br_list_for_each_entry(pos, head, member) \for (pos = br_list_first_entry(head, typeof(*pos), member); \!br_list_entry_is_head(pos, head, member); \pos = br_list_next_entry(pos, member))/*** br_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 br_list_head within the struct.*/
#define br_list_for_each_entry_reverse(pos, head, member) \for (pos = br_list_last_entry(head, typeof(*pos), member); \!br_list_entry_is_head(pos, head, member); \pos = br_list_prev_entry(pos, member))/*** br_list_prepare_entry - prepare a pos entry for use in br_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 br_list_head within the struct.** Prepares a pos entry for use as a start point in br_list_for_each_entry_continue().*/
#define br_list_prepare_entry(pos, head, member) \((pos) ? : br_list_entry(head, typeof(*pos), member))/*** br_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 br_list_head within the struct.** Continue to iterate over list of given type, continuing after* the current position.*/
#define br_list_for_each_entry_continue(pos, head, member) \for (pos = br_list_next_entry(pos, member); \!br_list_entry_is_head(pos, head, member); \pos = br_list_next_entry(pos, member))/*** br_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 br_list_head within the struct.** Start to iterate over list of given type backwards, continuing after* the current position.*/
#define br_list_for_each_entry_continue_reverse(pos, head, member) \for (pos = br_list_prev_entry(pos, member); \!br_list_entry_is_head(pos, head, member); \pos = br_list_prev_entry(pos, member))/*** br_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 br_list_head within the struct.** Iterate over list of given type, continuing from current position.*/
#define br_list_for_each_entry_from(pos, head, member) \for (; !br_list_entry_is_head(pos, head, member); \pos = br_list_next_entry(pos, member))/*** br_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 br_list_head within the struct.** Iterate backwards over list of given type, continuing from current position.*/
#define br_list_for_each_entry_from_reverse(pos, head, member) \for (; !br_list_entry_is_head(pos, head, member); \pos = br_list_prev_entry(pos, member))/*** br_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 br_list_head within the struct.*/
#define br_list_for_each_entry_safe(pos, n, head, member) \for (pos = br_list_first_entry(head, typeof(*pos), member), \n = br_list_next_entry(pos, member); \!br_list_entry_is_head(pos, head, member); \pos = n, n = br_list_next_entry(n, member))/*** br_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 br_list_head within the struct.** Iterate over list of given type, continuing after current point,* safe against removal of list entry.*/
#define br_list_for_each_entry_safe_continue(pos, n, head, member) \for (pos = br_list_next_entry(pos, member), \n = br_list_next_entry(pos, member); \!br_list_entry_is_head(pos, head, member); \pos = n, n = br_list_next_entry(n, member))/*** br_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 br_list_head within the struct.** Iterate over list of given type from current point, safe against* removal of list entry.*/
#define br_list_for_each_entry_safe_from(pos, n, head, member) \for (n = br_list_next_entry(pos, member); \!br_list_entry_is_head(pos, head, member); \pos = n, n = br_list_next_entry(n, member))/*** br_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 br_list_head within the struct.** Iterate backwards over list of given type, safe against removal* of list entry.*/
#define br_list_for_each_entry_safe_reverse(pos, n, head, member) \for (pos = br_list_last_entry(head, typeof(*pos), member), \n = br_list_prev_entry(pos, member); \!br_list_entry_is_head(pos, head, member); \pos = n, n = br_list_prev_entry(n, member))/*** br_list_safe_reset_next - reset a stale br_list_for_each_entry_safe loop* @pos: the loop cursor used in the br_list_for_each_entry_safe loop* @n: temporary storage used in br_list_for_each_entry_safe* @member: the name of the br_list_head within the struct.** br_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 br_list_safe_reset_next is called after re-taking the lock and before* completing the current iteration of the loop body.*/
#define br_list_safe_reset_next(pos, n, member) \n = br_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 BR_HLIST_HEAD_INIT { .first = NULL }
#define BR_HLIST_HEAD(name) struct br_hlist_head name = { .first = NULL }
#define BR_INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)
static inline void BR_INIT_HLIST_NODE(struct br_hlist_node *h)
{h->next = NULL;h->pprev = NULL;
}static inline int br_hlist_unhashed(const struct br_hlist_node *h)
{return !h->pprev;
}static inline int br_hlist_empty(const struct br_hlist_head *h)
{return !BR_READ_ONCE(h->first);
}static inline void __br_hlist_del(struct br_hlist_node *n)
{struct br_hlist_node *next = n->next;struct br_hlist_node **pprev = n->pprev;BR_WRITE_ONCE(*pprev, next);if (next)next->pprev = pprev;
}static inline void br_hlist_del(struct br_hlist_node *n)
{__br_hlist_del(n);n->next = BR_LIST_POISON1;n->pprev = BR_LIST_POISON2;
}static inline void br_hlist_del_init(struct br_hlist_node *n)
{if (!br_hlist_unhashed(n)) {__br_hlist_del(n);BR_INIT_HLIST_NODE(n);}
}static inline void br_hlist_add_head(struct br_hlist_node *n, struct br_hlist_head *h)
{struct br_hlist_node *first = h->first;n->next = first;if (first)first->pprev = &n->next;BR_WRITE_ONCE(h->first, n);n->pprev = &h->first;
}/* next must be != NULL */
static inline void br_hlist_add_before(struct br_hlist_node *n,struct br_hlist_node *next)
{n->pprev = next->pprev;n->next = next;next->pprev = &n->next;BR_WRITE_ONCE(*(n->pprev), n);
}static inline void br_hlist_add_behind(struct br_hlist_node *n,struct br_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 br_hlist_del will work */
static inline void br_hlist_add_fake(struct br_hlist_node *n)
{n->pprev = &n->next;
}static inline bool br_hlist_fake(struct br_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
br_hlist_is_singular_node(struct br_hlist_node *n, struct br_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 br_hlist_move_list(struct br_hlist_head *old,struct br_hlist_head *new)
{new->first = old->first;if (new->first)new->first->pprev = &new->first;old->first = NULL;
}#define br_hlist_entry(ptr, type, member) br_container_of(ptr,type,member)#define br_hlist_for_each(pos, head) \for (pos = (head)->first; pos ; pos = pos->next)#define br_hlist_for_each_safe(pos, n, head) \for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \pos = n)#define br_hlist_entry_safe(ptr, type, member) \({ typeof(ptr) ____ptr = (ptr); \____ptr ? br_hlist_entry(____ptr, type, member) : NULL; \})/*** br_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 br_hlist_node within the struct.*/
#define br_hlist_for_each_entry(pos, head, member) \for (pos = br_hlist_entry_safe((head)->first, typeof(*(pos)), member);\pos; \pos = br_hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))/*** br_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 br_hlist_node within the struct.*/
#define br_hlist_for_each_entry_continue(pos, member) \for (pos = br_hlist_entry_safe((pos)->member.next, typeof(*(pos)), member);\pos; \pos = br_hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))/*** br_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 br_hlist_node within the struct.*/
#define br_hlist_for_each_entry_from(pos, member) \for (; pos; \pos = br_hlist_entry_safe((pos)->member.next, typeof(*(pos)), member))/*** br_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 br_hlist_node to use as temporary storage* @head: the head for your list.* @member: the name of the br_hlist_node within the struct.*/
#define br_hlist_for_each_entry_safe(pos, n, head, member) \for (pos = br_hlist_entry_safe((head)->first, typeof(*pos), member);\pos && ({ n = pos->member.next; 1; }); \pos = br_hlist_entry_safe(n, typeof(*pos), member))#endif