llist.h

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#ifndef LLIST_H
#define LLIST_H
/*
 * Lock-less NULL terminated single linked list
 *
 * If there are multiple producers and multiple consumers, llist_add
 * can be used in producers and llist_del_all can be used in
 * consumers.  They can work simultaneously without lock.  But
 * llist_del_first can not be used here.  Because llist_del_first
 * depends on list->first->next does not changed if list->first is not
 * changed during its operation, but llist_del_first, llist_add,
 * llist_add (or llist_del_all, llist_add, llist_add) sequence in
 * another consumer may violate that.
 *
 * If there are multiple producers and one consumer, llist_add can be
 * used in producers and llist_del_all or llist_del_first can be used
 * in the consumer.
 *
 * This can be summarized as follow:
 *
 *           |   add    | del_first |  del_all
 * add       |    -     |     -     |     -
 * del_first |          |     L     |     L
 * del_all   |          |           |     -
 *
 * Where "-" stands for no lock is needed, while "L" stands for lock
 * is needed.
 *
 * The list entries deleted via llist_del_all can be traversed with
 * traversing function such as llist_for_each etc.  But the list
 * entries can not be traversed safely before deleted from the list.
 * The order of deleted entries is from the newest to the oldest added
 * one.  If you want to traverse from the oldest to the newest, you
 * must reverse the order by yourself before traversing.
 *
 * The basic atomic operation of this list is cmpxchg on long.  On
 * architectures that don't have NMI-safe cmpxchg implementation, the
 * list can NOT be used in NMI handlers.  So code that uses the list in
 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
 *
 * Copyright 2010,2011 Intel Corp.
 *   Author: Huang Ying <[email protected]>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation;
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/kernel.h>
#include <asm/cmpxchg.h>

struct llist_head {
    struct llist_node *first;
};

struct llist_node {
    struct llist_node *next;
};

#define LLIST_HEAD_INIT(name)   { NULL }
#define LLIST_HEAD(name)    struct llist_head name = LLIST_HEAD_INIT(name)

static inline void init_llist_head(struct llist_head *list)
{
    list->first = NULL;
}

#define llist_entry(ptr, type, member)      \
    container_of(ptr, type, member)

#define llist_for_each(pos, node)           \
    for ((pos) = (node); pos; (pos) = (pos)->next)

#define llist_for_each_entry(pos, node, member)             \
    for ((pos) = llist_entry((node), typeof(*(pos)), member);   \
         &(pos)->member != NULL;                    \
         (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))

static inline bool llist_empty(const struct llist_head *head)
{
    return ACCESS_ONCE(head->first) == NULL;
}

static inline struct llist_node *llist_next(struct llist_node *node)
{
    return node->next;
}

static inline bool llist_add(struct llist_node *new, struct llist_head *head)
{
    struct llist_node *entry, *old_entry;

    entry = head->first;
    for (;;) {
        old_entry = entry;
        new->next = entry;
        entry = cmpxchg(&head->first, old_entry, new);
        if (entry == old_entry)
            break;
    }

    return old_entry == NULL;
}

static inline struct llist_node *llist_del_all(struct llist_head *head)
{
    return xchg(&head->first, NULL);
}

extern bool llist_add_batch(struct llist_node *new_first,
                struct llist_node *new_last,
                struct llist_head *head);
extern struct llist_node *llist_del_first(struct llist_head *head);

#endif /* LLIST_H */