Quelle list.h Sprache: C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H

#include <linux/container_of.h>
#include <linux/types.h>
#include <linux/stddef.h>
#include <linux/poison.h>
#include <linux/const.h>

#include <asm/barrier.h>

/*
* 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.
*/

#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)
{
WRITE_ONCE(list->next, list);
WRITE_ONCE(list->prev, list);
}

#ifdef CONFIG_LIST_HARDENED

#ifdef CONFIG_DEBUG_LIST
# define __list_valid_slowpath
#else
# define __list_valid_slowpath __cold __preserve_most
#endif

/*
* Performs the full set of list corruption checks before __list_add().
* On list corruption reports a warning, and returns false.
*/
bool __list_valid_slowpath __list_add_valid_or_report(struct list_head *new,
            struct list_head *prev,
            struct list_head *next);

/*
* Performs list corruption checks before __list_add(). Returns false if a
* corruption is detected, true otherwise.
*
* With CONFIG_LIST_HARDENED only, performs minimal list integrity checking
* inline to catch non-faulting corruptions, and only if a corruption is
* detected calls the reporting function __list_add_valid_or_report().
*/
static __always_inline bool __list_add_valid(struct list_head *new,
          struct list_head *prev,
          struct list_head *next)
{
bool ret = true;

if (!IS_ENABLED(CONFIG_DEBUG_LIST)) {
  /*
* With the hardening version, elide checking if next and prev
* are NULL, since the immediate dereference of them below would
* result in a fault if NULL.
*
* With the reduced set of checks, we can afford to inline the
* checks, which also gives the compiler a chance to elide some
* of them completely if they can be proven at compile-time. If
* one of the pre-conditions does not hold, the slow-path will
* show a report which pre-condition failed.
*/
  if (likely(next->prev == prev && prev->next == next && new != prev && new != next))
   return true;
  ret = false;
}

ret &= __list_add_valid_or_report(new, prev, next);
return ret;
}

/*
* Performs the full set of list corruption checks before __list_del_entry().
* On list corruption reports a warning, and returns false.
*/
bool __list_valid_slowpath __list_del_entry_valid_or_report(struct list_head *entry);

/*
* Performs list corruption checks before __list_del_entry(). Returns false if a
* corruption is detected, true otherwise.
*
* With CONFIG_LIST_HARDENED only, performs minimal list integrity checking
* inline to catch non-faulting corruptions, and only if a corruption is
* detected calls the reporting function __list_del_entry_valid_or_report().
*/
static __always_inline bool __list_del_entry_valid(struct list_head *entry)
{
bool ret = true;

if (!IS_ENABLED(CONFIG_DEBUG_LIST)) {
  struct list_head *prev = entry->prev;
  struct list_head *next = entry->next;

  /*
* With the hardening version, elide checking if next and prev
* are NULL, LIST_POISON1 or LIST_POISON2, since the immediate
* dereference of them below would result in a fault.
*/
  if (likely(prev->next == entry && next->prev == entry))
   return true;
  ret = false;
}

ret &= __list_del_entry_valid_or_report(entry);
return ret;
}
#else
static inline bool __list_add_valid(struct list_head *new,
    struct list_head *prev,
    struct list_head *next)
{
return true;
}
static inline bool __list_del_entry_valid(struct list_head *entry)
{
return true;
}
#endif

/*
* Insert a new entry between two known consecutive entries.
*
* This is only for internal list manipulation where we know
* the prev/next entries already!
*/
static inline void __list_add(struct list_head *new,
         struct list_head *prev,
         struct list_head *next)
{
if (!__list_add_valid(new, prev, next))
  return;

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

/**
* list_add - add a new entry
* @new: new entry to be added
* @head: list head to add it after
*
* Insert a new entry after the specified head.
* This is good for implementing stacks.
*/
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;
WRITE_ONCE(prev->next, next);
}

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

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_is_head - tests whether @list is the list @head
* @list: the entry to test
* @head: the head of the list
*/
static inline int list_is_head(const struct list_head *list, const struct list_head *head)
{
return list == head;
}

/**
* list_empty - tests whether a list is empty
* @head: the list to test.
*/
static inline int list_empty(const struct list_head *head)
{
return READ_ONCE(head->next) == head;
}

/**
* list_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)
{
__list_del_entry(entry);
WRITE_ONCE(entry->prev, entry);
smp_store_release(&entry->next, entry);
}

/**
* 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 = smp_load_acquire(&head->next);
return list_is_head(next, head) && (next == READ_ONCE(head->prev));
}

/**
* list_rotate_left - rotate the list to the left
* @head: the head of the list
*/
static inline void list_rotate_left(struct list_head *head)
{
struct list_head *first;

if (!list_empty(head)) {
  first = head->next;
  list_move_tail(first, head);
}
}

/**
* list_rotate_to_front() - Rotate list to specific item.
* @list: The desired new front of the list.
* @head: The head of the list.
*
* Rotates list so that @list becomes the new front of the list.
*/
static inline void list_rotate_to_front(struct list_head *list,
     struct list_head *head)
{
/*
* Deletes the list head from the list denoted by @head and
* places it as the tail of @list, this effectively rotates the
* list so that @list is at the front.
*/
list_move_tail(head, list);
}

/**
* list_is_singular - tests whether a list has just one entry.
* @head: the list to test.
*/
static inline int list_is_singular(const struct list_head *head)
{
return !list_empty(head) && (head->next == head->prev);
}

static inline void __list_cut_position(struct list_head *list,
  struct list_head *head, struct list_head *entry)
{
struct list_head *new_first = entry->next;
list->next = head->next;
list->next->prev = list;
list->prev = entry;
entry->next = list;
head->next = new_first;
new_first->prev = head;
}

/**
* list_cut_position - cut a list into two
* @list: a new list to add all removed entries
* @head: a list with entries
* @entry: an entry within head, could be the head itself
* and if so we won't cut the list
*
* This helper moves the initial part of @head, up to and
* including @entry, from @head to @list. You should
* pass on @entry an element you know is on @head. @list
* should be an empty list or a list you do not care about
* losing its data.
*
*/
static inline void list_cut_position(struct list_head *list,
  struct list_head *head, struct list_head *entry)
{
if (list_empty(head))
  return;
if (list_is_singular(head) && !list_is_head(entry, head) && (entry != head->next))
  return;
if (list_is_head(entry, head))
  INIT_LIST_HEAD(list);
else
  __list_cut_position(list, head, entry);
}

/**
* list_cut_before - cut a list into two, before given entry
* @list: a new list to add all removed entries
* @head: a list with entries
* @entry: an entry within head, could be the head itself
*
* This helper moves the initial part of @head, up to but
* excluding @entry, from @head to @list.  You should pass
* in @entry an element you know is on @head.  @list should
* be an empty list or a list you do not care about losing
* its data.
* If @entry == @head, all entries on @head are moved to
* @list.
*/
static inline void list_cut_before(struct list_head *list,
       struct list_head *head,
       struct list_head *entry)
{
if (head->next == entry) {
  INIT_LIST_HEAD(list);
  return;
}
list->next = head->next;
list->next->prev = list;
list->prev = entry->prev;
list->prev->next = list;
head->next = entry;
entry->prev = head;
}

static inline void __list_splice(const struct list_head *list,
     struct list_head *prev,
     struct list_head *next)
{
struct list_head *first = list->next;
struct list_head *last = list->prev;

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

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

/**
* list_splice - join two lists, this is designed for stacks
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice(const struct list_head *list,
    struct list_head *head)
{
if (!list_empty(list))
  __list_splice(list, head, head->next);
}

/**
* list_splice_tail - join two lists, each list being a queue
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
static inline void list_splice_tail(struct list_head *list,
    struct list_head *head)
{
if (!list_empty(list))
  __list_splice(list, head->prev, head);
}

/**
* list_splice_init - join two lists and reinitialise the emptied list.
* @list: the new list to add.
* @head: the place to add it in the first list.
*
* The list at @list is reinitialised
*/
static inline void list_splice_init(struct list_head *list,
        struct list_head *head)
{
if (!list_empty(list)) {
  __list_splice(list, head, head->next);
  INIT_LIST_HEAD(list);
}
}

/**
* list_splice_tail_init - join two lists and reinitialise the emptied list
* @list: the new list to add.
* @head: the place to add it in the first list.
*
* Each of the lists is a queue.
* The list at @list is reinitialised
*/
static inline void list_splice_tail_init(struct list_head *list,
      struct list_head *head)
{
if (!list_empty(list)) {
  __list_splice(list, head->prev, head);
  INIT_LIST_HEAD(list);
}
}

/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_head within the struct.
*/
#define list_entry(ptr, type, member) \
container_of(ptr, type, member)

/**
* list_first_entry - get the first element from a list
* @ptr: the list head to take the element from.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_head within the struct.
*
* Note, that list is expected to be not empty.
*/
#define list_first_entry(ptr, type, member) \
list_entry((ptr)->next, type, member)

/**
* list_last_entry - get the last element from a list
* @ptr: the list head to take the element from.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_head within the struct.
*
* Note, that list is expected to be not empty.
*/
#define list_last_entry(ptr, type, member) \
list_entry((ptr)->prev, type, member)

/**
* list_first_entry_or_null - get the first element from a list
* @ptr: the list head to take the element from.
* @type: the type of the struct this is embedded in.
* @member: the name of the list_head within the struct.
*
* Note that if the list is empty, it returns NULL.
*/
#define list_first_entry_or_null(ptr, type, member) ({ \
struct list_head *head__ = (ptr); \
struct list_head *pos__ = READ_ONCE(head__->next); \
pos__ != head__ ? list_entry(pos__, type, member) : NULL; \
})

/**
* list_next_entry - get the next element in list
* @pos: the type * to cursor
* @member: the name of the list_head within the struct.
*/
#define list_next_entry(pos, member) \
list_entry((pos)->member.next, typeof(*(pos)), member)

/**
* list_next_entry_circular - get the next element in list
* @pos: the type * to cursor.
* @head: the list head to take the element from.
* @member: the name of the list_head within the struct.
*
* Wraparound if pos is the last element (return the first element).
* Note, that list is expected to be not empty.
*/
#define list_next_entry_circular(pos, head, member) \
(list_is_last(&(pos)->member, head) ? \
list_first_entry(head, typeof(*(pos)), member) : list_next_entry(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_prev_entry_circular - get the prev element in list
* @pos: the type * to cursor.
* @head: the list head to take the element from.
* @member: the name of the list_head within the struct.
*
* Wraparound if pos is the first element (return the last element).
* Note, that list is expected to be not empty.
*/
#define list_prev_entry_circular(pos, head, member) \
(list_is_first(&(pos)->member, head) ? \
list_last_entry(head, typeof(*(pos)), member) : list_prev_entry(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; !list_is_head(pos, (head)); pos = pos->next)

/**
* list_for_each_rcu - Iterate over a list in an RCU-safe fashion
* @pos: the &struct list_head to use as a loop cursor.
* @head: the head for your list.
*/
#define list_for_each_rcu(pos, head)    \
for (pos = rcu_dereference((head)->next); \
      !list_is_head(pos, (head)); \
      pos = rcu_dereference(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; !list_is_head(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; !list_is_head(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; \
      !list_is_head(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; \
      !list_is_head(pos, (head)); \
      pos = n, n = pos->prev)

/**
* list_count_nodes - count nodes in the list
* @head: the head for your list.
*/
static inline size_t list_count_nodes(struct list_head *head)
{
struct list_head *pos;
size_t count = 0;

list_for_each(pos, head)
  count++;

return count;
}

/**
* 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)    \
list_is_head(&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).
*/

#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 !READ_ONCE(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 !READ_ONCE(h->first);
}

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

WRITE_ONCE(*pprev, next);
if (next)
  WRITE_ONCE(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;
WRITE_ONCE(n->next, first);
if (first)
  WRITE_ONCE(first->pprev, &n->next);
WRITE_ONCE(h->first, n);
WRITE_ONCE(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)
{
WRITE_ONCE(n->pprev, next->pprev);
WRITE_ONCE(n->next, next);
WRITE_ONCE(next->pprev, &n->next);
WRITE_ONCE(*(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)
{
WRITE_ONCE(n->next, prev->next);
WRITE_ONCE(prev->next, n);
WRITE_ONCE(n->pprev, &prev->next);

if (n->next)
  WRITE_ONCE(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;
}

/**
* hlist_splice_init() - move all entries from one list to another
* @from: hlist_head from which entries will be moved
* @last: last entry on the @from list
* @to:   hlist_head to which entries will be moved
*
* @to can be empty, @from must contain at least @last.
*/
static inline void hlist_splice_init(struct hlist_head *from,
         struct hlist_node *last,
         struct hlist_head *to)
{
if (to->first)
  to->first->pprev = &last->next;
last->next = to->first;
to->first = from->first;
from->first->pprev = &to->first;
from->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))

/**
* hlist_count_nodes - count nodes in the hlist
* @head: the head for your hlist.
*/
static inline size_t hlist_count_nodes(struct hlist_head *head)
{
struct hlist_node *pos;
size_t count = 0;

hlist_for_each(pos, head)
  count++;

return count;
}

#endif

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