Root/lib/llist.c

1/*
2 * Lock-less NULL terminated single linked list
3 *
4 * The basic atomic operation of this list is cmpxchg on long. On
5 * architectures that don't have NMI-safe cmpxchg implementation, the
6 * list can NOT be used in NMI handlers. So code that uses the list in
7 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
8 *
9 * Copyright 2010,2011 Intel Corp.
10 * Author: Huang Ying <ying.huang@intel.com>
11 *
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License version
14 * 2 as published by the Free Software Foundation;
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU General Public License for more details.
20 *
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 */
25#include <linux/kernel.h>
26#include <linux/export.h>
27#include <linux/interrupt.h>
28#include <linux/llist.h>
29
30
31/**
32 * llist_add_batch - add several linked entries in batch
33 * @new_first: first entry in batch to be added
34 * @new_last: last entry in batch to be added
35 * @head: the head for your lock-less list
36 *
37 * Return whether list is empty before adding.
38 */
39bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
40             struct llist_head *head)
41{
42    struct llist_node *first;
43
44    do {
45        new_last->next = first = ACCESS_ONCE(head->first);
46    } while (cmpxchg(&head->first, first, new_first) != first);
47
48    return !first;
49}
50EXPORT_SYMBOL_GPL(llist_add_batch);
51
52/**
53 * llist_del_first - delete the first entry of lock-less list
54 * @head: the head for your lock-less list
55 *
56 * If list is empty, return NULL, otherwise, return the first entry
57 * deleted, this is the newest added one.
58 *
59 * Only one llist_del_first user can be used simultaneously with
60 * multiple llist_add users without lock. Because otherwise
61 * llist_del_first, llist_add, llist_add (or llist_del_all, llist_add,
62 * llist_add) sequence in another user may change @head->first->next,
63 * but keep @head->first. If multiple consumers are needed, please
64 * use llist_del_all or use lock between consumers.
65 */
66struct llist_node *llist_del_first(struct llist_head *head)
67{
68    struct llist_node *entry, *old_entry, *next;
69
70    entry = head->first;
71    for (;;) {
72        if (entry == NULL)
73            return NULL;
74        old_entry = entry;
75        next = entry->next;
76        entry = cmpxchg(&head->first, old_entry, next);
77        if (entry == old_entry)
78            break;
79    }
80
81    return entry;
82}
83EXPORT_SYMBOL_GPL(llist_del_first);
84
85/**
86 * llist_reverse_order - reverse order of a llist chain
87 * @head: first item of the list to be reversed
88 *
89 * Reverse the order of a chain of llist entries and return the
90 * new first entry.
91 */
92struct llist_node *llist_reverse_order(struct llist_node *head)
93{
94    struct llist_node *new_head = NULL;
95
96    while (head) {
97        struct llist_node *tmp = head;
98        head = head->next;
99        tmp->next = new_head;
100        new_head = tmp;
101    }
102
103    return new_head;
104}
105EXPORT_SYMBOL_GPL(llist_reverse_order);
106

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