Merge master.kernel.org:/pub/scm/linux/kernel/git/davej/cpufreq

[deliverable/linux.git] / include / linux / list.h

#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H

#ifdef __KERNEL__

#include <linux/stddef.h>
#include <linux/prefetch.h>
#include <asm/system.h>

/*
 * These are non-NULL pointers that will result in page faults
 * under normal circumstances, used to verify that nobody uses
 * non-initialized list entries.
 */
#define LIST_POISON1  ((void *) 0x00100100)
#define LIST_POISON2  ((void *) 0x00200200)

/*
 * 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.
 */

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)

static inline void INIT_LIST_HEAD(struct list_head *list)
{
        list->next = list;
        list->prev = list;
}

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

/**
 * 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);
}

/*
 * 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_rcu(struct list_head * new,
                struct list_head * prev, struct list_head * next)
{
        new->next = next;
        new->prev = prev;
        smp_wmb();
        next->prev = new;
        prev->next = new;
}

/**
 * list_add_rcu - add a new entry to rcu-protected list
 * @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.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_add_rcu()
 * or list_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 */
static inline void list_add_rcu(struct list_head *new, struct list_head *head)
{
        __list_add_rcu(new, head, head->next);
}

/**
 * list_add_tail_rcu - add a new entry to rcu-protected list
 * @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.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_add_tail_rcu()
 * or list_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 */
static inline void list_add_tail_rcu(struct list_head *new,
                                        struct list_head *head)
{
        __list_add_rcu(new, head->prev, head);
}

/*
 * Delete a list entry by making the prev/next entries
 * point to each other.
 *
 * This is only for internal list manipulation where we know
 * the prev/next entries already!
 */
static inline void __list_del(struct list_head * prev, struct list_head * next)
{
        next->prev = prev;
        prev->next = next;
}

/**
 * list_del - deletes entry from list.
 * @entry: the element to delete from the list.
 * Note: list_empty on entry does not return true after this, the entry is
 * in an undefined state.
 */
static inline void list_del(struct list_head *entry)
{
        __list_del(entry->prev, entry->next);
        entry->next = LIST_POISON1;
        entry->prev = LIST_POISON2;
}

/**
 * list_del_rcu - deletes entry from list without re-initialization
 * @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. It is useful for RCU based
 * lockfree traversal.
 *
 * In particular, it means that we can not poison the forward
 * pointers that may still be used for walking the list.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as list_del_rcu()
 * or list_add_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * list_for_each_entry_rcu().
 *
 * Note that the caller is not permitted to immediately free
 * the newly deleted entry.  Instead, either synchronize_rcu()
 * or call_rcu() must be used to defer freeing until an RCU
 * grace period has elapsed.
 */
static inline void list_del_rcu(struct list_head *entry)
{
        __list_del(entry->prev, entry->next);
        entry->prev = LIST_POISON2;
}

/*
 * list_replace_rcu - replace old entry by new one
 * @old : the element to be replaced
 * @new : the new element to insert
 *
 * The old entry will be replaced with the new entry atomically.
 */
static inline void list_replace_rcu(struct list_head *old,
                                struct list_head *new)
{
        new->next = old->next;
        new->prev = old->prev;
        smp_wmb();
        new->next->prev = new;
        new->prev->next = new;
        old->prev = LIST_POISON2;
}

/**
 * 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->prev, entry->next);
        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(list->prev, list->next);
        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(list->prev, list->next);
        list_add_tail(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 head->next == head;
}

/**
 * list_empty_careful - tests whether a list is
 * empty _and_ checks that no other CPU might be
 * in the process of still modifying either member
 *
 * 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.
 *
 * @head: the list to test.
 */
static inline int list_empty_careful(const struct list_head *head)
{
        struct list_head *next = head->next;
        return (next == head) && (next == head->prev);
}

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

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

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

/**
 * list_splice - join two lists
 * @list: the new list to add.
 * @head: the place to add it in the first list.
 */
static inline void list_splice(struct list_head *list, struct list_head *head)
{
        if (!list_empty(list))
                __list_splice(list, 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);
                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_struct within the struct.
 */
#define list_entry(ptr, type, member) \
        container_of(ptr, type, member)

/**
 * list_for_each        -       iterate over a list
 * @pos:        the &struct list_head to use as a loop counter.
 * @head:       the head for your list.
 */
#define list_for_each(pos, head) \
        for (pos = (head)->next; prefetch(pos->next), pos != (head); \
                pos = pos->next)

/**
 * __list_for_each      -       iterate over a list
 * @pos:        the &struct list_head to use as a loop counter.
 * @head:       the head for your list.
 *
 * This variant differs from list_for_each() in that it's the
 * simplest possible list iteration code, no prefetching is done.
 * Use this for code that knows the list to be very short (empty
 * or 1 entry) most of the time.
 */
#define __list_for_each(pos, head) \
        for (pos = (head)->next; pos != (head); pos = pos->next)

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

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

/**
 * list_prepare_entry - prepare a pos entry for use as a start point 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_struct within the struct.
 */
#define list_prepare_entry(pos, head, member) \
        ((pos) ? : list_entry(head, typeof(*pos), member))

/**
 * list_for_each_entry_continue -       iterate over list of given type
 *                      continuing after existing point
 * @pos:        the type * to use as a loop counter.
 * @head:       the head for your list.
 * @member:     the name of the list_struct within the struct.
 */
#define list_for_each_entry_continue(pos, head, member)                 \
        for (pos = list_entry(pos->member.next, typeof(*pos), member);  \
             prefetch(pos->member.next), &pos->member != (head);        \
             pos = list_entry(pos->member.next, typeof(*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 counter.
 * @n:          another type * to use as temporary storage
 * @head:       the head for your list.
 * @member:     the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe(pos, n, head, member)                  \
        for (pos = list_entry((head)->next, typeof(*pos), member),      \
                n = list_entry(pos->member.next, typeof(*pos), member); \
             &pos->member != (head);                                    \
             pos = n, n = list_entry(n->member.next, typeof(*n), member))

/**
 * list_for_each_entry_safe_continue -  iterate over list of given type
 *                      continuing after existing point safe against removal of list entry
 * @pos:        the type * to use as a loop counter.
 * @n:          another type * to use as temporary storage
 * @head:       the head for your list.
 * @member:     the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe_continue(pos, n, head, member)                 \
        for (pos = list_entry(pos->member.next, typeof(*pos), member),          \
                n = list_entry(pos->member.next, typeof(*pos), member);         \
             &pos->member != (head);                                            \
             pos = n, n = list_entry(n->member.next, typeof(*n), member))

/**
 * list_for_each_entry_safe_reverse - iterate backwards over list of given type safe against
 *                                    removal of list entry
 * @pos:        the type * to use as a loop counter.
 * @n:          another type * to use as temporary storage
 * @head:       the head for your list.
 * @member:     the name of the list_struct within the struct.
 */
#define list_for_each_entry_safe_reverse(pos, n, head, member)          \
        for (pos = list_entry((head)->prev, typeof(*pos), member),      \
                n = list_entry(pos->member.prev, typeof(*pos), member); \
             &pos->member != (head);                                    \
             pos = n, n = list_entry(n->member.prev, typeof(*n), member))

/**
 * list_for_each_rcu    -       iterate over an rcu-protected list
 * @pos:        the &struct list_head to use as a loop counter.
 * @head:       the head for your list.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as list_add_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define list_for_each_rcu(pos, head) \
        for (pos = (head)->next; \
                prefetch(rcu_dereference(pos)->next), pos != (head); \
                pos = pos->next)

#define __list_for_each_rcu(pos, head) \
        for (pos = (head)->next; \
                rcu_dereference(pos) != (head); \
                pos = pos->next)

/**
 * list_for_each_safe_rcu       -       iterate over an rcu-protected list safe
 *                                      against removal of list entry
 * @pos:        the &struct list_head to use as a loop counter.
 * @n:          another &struct list_head to use as temporary storage
 * @head:       the head for your list.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as list_add_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define list_for_each_safe_rcu(pos, n, head) \
        for (pos = (head)->next; \
                n = rcu_dereference(pos)->next, pos != (head); \
                pos = n)

/**
 * list_for_each_entry_rcu      -       iterate over rcu list of given type
 * @pos:        the type * to use as a loop counter.
 * @head:       the head for your list.
 * @member:     the name of the list_struct within the struct.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as list_add_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define list_for_each_entry_rcu(pos, head, member) \
        for (pos = list_entry((head)->next, typeof(*pos), member); \
                prefetch(rcu_dereference(pos)->member.next), \
                        &pos->member != (head); \
                pos = list_entry(pos->member.next, typeof(*pos), member))


/**
 * list_for_each_continue_rcu   -       iterate over an rcu-protected list
 *                      continuing after existing point.
 * @pos:        the &struct list_head to use as a loop counter.
 * @head:       the head for your list.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as list_add_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define list_for_each_continue_rcu(pos, head) \
        for ((pos) = (pos)->next; \
                prefetch(rcu_dereference((pos))->next), (pos) != (head); \
                (pos) = (pos)->next)

/*
 * 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;
}

static inline int hlist_unhashed(const struct hlist_node *h)
{
        return !h->pprev;
}

static inline int hlist_empty(const struct hlist_head *h)
{
        return !h->first;
}

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

static inline void hlist_del(struct hlist_node *n)
{
        __hlist_del(n);
        n->next = LIST_POISON1;
        n->pprev = LIST_POISON2;
}

/**
 * hlist_del_rcu - deletes entry from hash list without re-initialization
 * @n: the element to delete from the hash list.
 *
 * Note: list_unhashed() on entry does not return true after this,
 * the entry is in an undefined state. It is useful for RCU based
 * lockfree traversal.
 *
 * In particular, it means that we can not poison the forward
 * pointers that may still be used for walking the hash list.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry().
 */
static inline void hlist_del_rcu(struct hlist_node *n)
{
        __hlist_del(n);
        n->pprev = LIST_POISON2;
}

static inline void hlist_del_init(struct hlist_node *n)
{
        if (n->pprev)  {
                __hlist_del(n);
                INIT_HLIST_NODE(n);
        }
}

/*
 * hlist_replace_rcu - replace old entry by new one
 * @old : the element to be replaced
 * @new : the new element to insert
 *
 * The old entry will be replaced with the new entry atomically.
 */
static inline void hlist_replace_rcu(struct hlist_node *old,
                                        struct hlist_node *new)
{
        struct hlist_node *next = old->next;

        new->next = next;
        new->pprev = old->pprev;
        smp_wmb();
        if (next)
                new->next->pprev = &new->next;
        *new->pprev = new;
        old->pprev = LIST_POISON2;
}

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_head_rcu - adds the specified element to the specified hlist,
 * while permitting racing traversals.
 * @n: the element to add to the hash list.
 * @h: the list to add to.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 * problems on Alpha CPUs.  Regardless of the type of CPU, the
 * list-traversal primitive must be guarded by rcu_read_lock().
 */
static inline void hlist_add_head_rcu(struct hlist_node *n,
                                        struct hlist_head *h)
{
        struct hlist_node *first = h->first;
        n->next = first;
        n->pprev = &h->first;
        smp_wmb();
        if (first)
                first->pprev = &n->next;
        h->first = n;
}

/* next must be != NULL */
static inline void hlist_add_before(struct hlist_node *n,
                                        struct hlist_node *next)
{
        n->pprev = next->pprev;
        n->next = next;
        next->pprev = &n->next;
        *(n->pprev) = n;
}

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

        if(next->next)
                next->next->pprev  = &next->next;
}

/**
 * hlist_add_before_rcu - adds the specified element to the specified hlist
 * before the specified node while permitting racing traversals.
 * @n: the new element to add to the hash list.
 * @next: the existing element to add the new element before.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 * problems on Alpha CPUs.
 */
static inline void hlist_add_before_rcu(struct hlist_node *n,
                                        struct hlist_node *next)
{
        n->pprev = next->pprev;
        n->next = next;
        smp_wmb();
        next->pprev = &n->next;
        *(n->pprev) = n;
}

/**
 * hlist_add_after_rcu - adds the specified element to the specified hlist
 * after the specified node while permitting racing traversals.
 * @prev: the existing element to add the new element after.
 * @n: the new element to add to the hash list.
 *
 * The caller must take whatever precautions are necessary
 * (such as holding appropriate locks) to avoid racing
 * with another list-mutation primitive, such as hlist_add_head_rcu()
 * or hlist_del_rcu(), running on this same list.
 * However, it is perfectly legal to run concurrently with
 * the _rcu list-traversal primitives, such as
 * hlist_for_each_entry_rcu(), used to prevent memory-consistency
 * problems on Alpha CPUs.
 */
static inline void hlist_add_after_rcu(struct hlist_node *prev,
                                       struct hlist_node *n)
{
        n->next = prev->next;
        n->pprev = &prev->next;
        smp_wmb();
        prev->next = n;
        if (n->next)
                n->next->pprev = &n->next;
}

#define hlist_entry(ptr, type, member) container_of(ptr,type,member)

#define hlist_for_each(pos, head) \
        for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \
             pos = pos->next)

#define hlist_for_each_safe(pos, n, head) \
        for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \
             pos = n)

/**
 * hlist_for_each_entry - iterate over list of given type
 * @tpos:       the type * to use as a loop counter.
 * @pos:        the &struct hlist_node to use as a loop counter.
 * @head:       the head for your list.
 * @member:     the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry(tpos, pos, head, member)                    \
        for (pos = (head)->first;                                        \
             pos && ({ prefetch(pos->next); 1;}) &&                      \
                ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
             pos = pos->next)

/**
 * hlist_for_each_entry_continue - iterate over a hlist continuing after existing point
 * @tpos:       the type * to use as a loop counter.
 * @pos:        the &struct hlist_node to use as a loop counter.
 * @member:     the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_continue(tpos, pos, member)                 \
        for (pos = (pos)->next;                                          \
             pos && ({ prefetch(pos->next); 1;}) &&                      \
                ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
             pos = pos->next)

/**
 * hlist_for_each_entry_from - iterate over a hlist continuing from existing point
 * @tpos:       the type * to use as a loop counter.
 * @pos:        the &struct hlist_node to use as a loop counter.
 * @member:     the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_from(tpos, pos, member)                     \
        for (; pos && ({ prefetch(pos->next); 1;}) &&                    \
                ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
             pos = pos->next)

/**
 * hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry
 * @tpos:       the type * to use as a loop counter.
 * @pos:        the &struct hlist_node to use as a loop counter.
 * @n:          another &struct hlist_node to use as temporary storage
 * @head:       the head for your list.
 * @member:     the name of the hlist_node within the struct.
 */
#define hlist_for_each_entry_safe(tpos, pos, n, head, member)            \
        for (pos = (head)->first;                                        \
             pos && ({ n = pos->next; 1; }) &&                           \
                ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
             pos = n)

/**
 * hlist_for_each_entry_rcu - iterate over rcu list of given type
 * @tpos:       the type * to use as a loop counter.
 * @pos:        the &struct hlist_node to use as a loop counter.
 * @head:       the head for your list.
 * @member:     the name of the hlist_node within the struct.
 *
 * This list-traversal primitive may safely run concurrently with
 * the _rcu list-mutation primitives such as hlist_add_head_rcu()
 * as long as the traversal is guarded by rcu_read_lock().
 */
#define hlist_for_each_entry_rcu(tpos, pos, head, member)                \
        for (pos = (head)->first;                                        \
             rcu_dereference(pos) && ({ prefetch(pos->next); 1;}) &&     \
                ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
             pos = pos->next)

#else
#warning "don't include kernel headers in userspace"
#endif /* __KERNEL__ */
#endif