1#ifndef LLIST_H 2#define LLIST_H 3/* 4 * Lock-less NULL terminated single linked list 5 * 6 * If there are multiple producers and multiple consumers, llist_add 7 * can be used in producers and llist_del_all can be used in 8 * consumers. They can work simultaneously without lock. But 9 * llist_del_first can not be used here. Because llist_del_first 10 * depends on list->first->next does not changed if list->first is not 11 * changed during its operation, but llist_del_first, llist_add, 12 * llist_add (or llist_del_all, llist_add, llist_add) sequence in 13 * another consumer may violate that. 14 * 15 * If there are multiple producers and one consumer, llist_add can be 16 * used in producers and llist_del_all or llist_del_first can be used 17 * in the consumer. 18 * 19 * This can be summarized as follow: 20 * 21 * | add | del_first | del_all 22 * add | - | - | - 23 * del_first | | L | L 24 * del_all | | | - 25 * 26 * Where "-" stands for no lock is needed, while "L" stands for lock 27 * is needed. 28 * 29 * The list entries deleted via llist_del_all can be traversed with 30 * traversing function such as llist_for_each etc. But the list 31 * entries can not be traversed safely before deleted from the list. 32 * The order of deleted entries is from the newest to the oldest added 33 * one. If you want to traverse from the oldest to the newest, you 34 * must reverse the order by yourself before traversing. 35 * 36 * The basic atomic operation of this list is cmpxchg on long. On 37 * architectures that don't have NMI-safe cmpxchg implementation, the 38 * list can NOT be used in NMI handlers. So code that uses the list in 39 * an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. 40 * 41 * Copyright 2010,2011 Intel Corp. 42 * Author: Huang Ying <ying.huang@intel.com> 43 * 44 * This program is free software; you can redistribute it and/or 45 * modify it under the terms of the GNU General Public License version 46 * 2 as published by the Free Software Foundation; 47 * 48 * This program is distributed in the hope that it will be useful, 49 * but WITHOUT ANY WARRANTY; without even the implied warranty of 50 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 51 * GNU General Public License for more details. 52 * 53 * You should have received a copy of the GNU General Public License 54 * along with this program; if not, write to the Free Software 55 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 56 */ 57 58#include <linux/kernel.h> 59#include <asm/cmpxchg.h> 60 61struct llist_head { 62 struct llist_node *first; 63}; 64 65struct llist_node { 66 struct llist_node *next; 67}; 68 69#define LLIST_HEAD_INIT(name) { NULL } 70#define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name) 71 72/** 73 * init_llist_head - initialize lock-less list head 74 * @head: the head for your lock-less list 75 */ 76static inline void init_llist_head(struct llist_head *list) 77{ 78 list->first = NULL; 79} 80 81/** 82 * llist_entry - get the struct of this entry 83 * @ptr: the &struct llist_node pointer. 84 * @type: the type of the struct this is embedded in. 85 * @member: the name of the llist_node within the struct. 86 */ 87#define llist_entry(ptr, type, member) \ 88 container_of(ptr, type, member) 89 90/** 91 * llist_for_each - iterate over some deleted entries of a lock-less list 92 * @pos: the &struct llist_node to use as a loop cursor 93 * @node: the first entry of deleted list entries 94 * 95 * In general, some entries of the lock-less list can be traversed 96 * safely only after being deleted from list, so start with an entry 97 * instead of list head. 98 * 99 * If being used on entries deleted from lock-less list directly, the 100 * traverse order is from the newest to the oldest added entry. If 101 * you want to traverse from the oldest to the newest, you must 102 * reverse the order by yourself before traversing. 103 */ 104#define llist_for_each(pos, node) \ 105 for ((pos) = (node); pos; (pos) = (pos)->next) 106 107/** 108 * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type 109 * @pos: the type * to use as a loop cursor. 110 * @node: the fist entry of deleted list entries. 111 * @member: the name of the llist_node with the struct. 112 * 113 * In general, some entries of the lock-less list can be traversed 114 * safely only after being removed from list, so start with an entry 115 * instead of list head. 116 * 117 * If being used on entries deleted from lock-less list directly, the 118 * traverse order is from the newest to the oldest added entry. If 119 * you want to traverse from the oldest to the newest, you must 120 * reverse the order by yourself before traversing. 121 */ 122#define llist_for_each_entry(pos, node, member) \ 123 for ((pos) = llist_entry((node), typeof(*(pos)), member); \ 124 &(pos)->member != NULL; \ 125 (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member)) 126 127/** 128 * llist_empty - tests whether a lock-less list is empty 129 * @head: the list to test 130 * 131 * Not guaranteed to be accurate or up to date. Just a quick way to 132 * test whether the list is empty without deleting something from the 133 * list. 134 */ 135static inline bool llist_empty(const struct llist_head *head) 136{ 137 return ACCESS_ONCE(head->first) == NULL; 138} 139 140static inline struct llist_node *llist_next(struct llist_node *node) 141{ 142 return node->next; 143} 144 145extern bool llist_add_batch(struct llist_node *new_first, 146 struct llist_node *new_last, 147 struct llist_head *head); 148/** 149 * llist_add - add a new entry 150 * @new: new entry to be added 151 * @head: the head for your lock-less list 152 * 153 * Returns true if the list was empty prior to adding this entry. 154 */ 155static inline bool llist_add(struct llist_node *new, struct llist_head *head) 156{ 157 return llist_add_batch(new, new, head); 158} 159 160/** 161 * llist_del_all - delete all entries from lock-less list 162 * @head: the head of lock-less list to delete all entries 163 * 164 * If list is empty, return NULL, otherwise, delete all entries and 165 * return the pointer to the first entry. The order of entries 166 * deleted is from the newest to the oldest added one. 167 */ 168static inline struct llist_node *llist_del_all(struct llist_head *head) 169{ 170 return xchg(&head->first, NULL); 171} 172 173extern struct llist_node *llist_del_first(struct llist_head *head); 174 175#endif /* LLIST_H */ 176