include/linux/llist.h

   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/system.h>
  60 #include <asm/processor.h>
  61
  62 struct llist_head {
  63         struct llist_node *first;
  64 };
  65
  66 struct llist_node {
  67         struct llist_node *next;
  68 };
  69
  70 #define LLIST_HEAD_INIT(name)   { NULL }
  71 #define LLIST_HEAD(name)        struct llist_head name = LLIST_HEAD_INIT(name)
  72
  73 /**
  74  * init_llist_head - initialize lock-less list head
  75  * @head:       the head for your lock-less list
  76  */
  77 static inline void init_llist_head(struct llist_head *list)
  78 {
  79         list->first = NULL;
  80 }
  81
  82 /**
  83  * llist_entry - get the struct of this entry
  84  * @ptr:        the &struct llist_node pointer.
  85  * @type:       the type of the struct this is embedded in.
  86  * @member:     the name of the llist_node within the struct.
  87  */
  88 #define llist_entry(ptr, type, member)          \
  89         container_of(ptr, type, member)
  90
  91 /**
  92  * llist_for_each - iterate over some deleted entries of a lock-less list
  93  * @pos:        the &struct llist_node to use as a loop cursor
  94  * @node:       the first entry of deleted list entries
  95  *
  96  * In general, some entries of the lock-less list can be traversed
  97  * safely only after being deleted from list, so start with an entry
  98  * instead of list head.
  99  *
 100  * If being used on entries deleted from lock-less list directly, the
 101  * traverse order is from the newest to the oldest added entry.  If
 102  * you want to traverse from the oldest to the newest, you must
 103  * reverse the order by yourself before traversing.
 104  */
 105 #define llist_for_each(pos, node)                       \
 106         for ((pos) = (node); pos; (pos) = (pos)->next)
 107
 108 /**
 109  * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
 110  * @pos:        the type * to use as a loop cursor.
 111  * @node:       the fist entry of deleted list entries.
 112  * @member:     the name of the llist_node with the struct.
 113  *
 114  * In general, some entries of the lock-less list can be traversed
 115  * safely only after being removed from list, so start with an entry
 116  * instead of list head.
 117  *
 118  * If being used on entries deleted from lock-less list directly, the
 119  * traverse order is from the newest to the oldest added entry.  If
 120  * you want to traverse from the oldest to the newest, you must
 121  * reverse the order by yourself before traversing.
 122  */
 123 #define llist_for_each_entry(pos, node, member)                         \
 124         for ((pos) = llist_entry((node), typeof(*(pos)), member);       \
 125              &(pos)->member != NULL;                                    \
 126              (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
 127
 128 /**
 129  * llist_empty - tests whether a lock-less list is empty
 130  * @head:       the list to test
 131  *
 132  * Not guaranteed to be accurate or up to date.  Just a quick way to
 133  * test whether the list is empty without deleting something from the
 134  * list.
 135  */
 136 static inline bool llist_empty(const struct llist_head *head)
 137 {
 138         return ACCESS_ONCE(head->first) == NULL;
 139 }
 140
 141 /**
 142  * llist_add - add a new entry
 143  * @new:        new entry to be added
 144  * @head:       the head for your lock-less list
 145  */
 146 static inline void llist_add(struct llist_node *new, struct llist_head *head)
 147 {
 148         struct llist_node *entry, *old_entry;
 149
 150         entry = head->first;
 151         do {
 152                 old_entry = entry;
 153                 new->next = entry;
 154                 cpu_relax();
 155         } while ((entry = cmpxchg(&head->first, old_entry, new)) != old_entry);
 156 }
 157
 158 /**
 159  * llist_del_all - delete all entries from lock-less list
 160  * @head:       the head of lock-less list to delete all entries
 161  *
 162  * If list is empty, return NULL, otherwise, delete all entries and
 163  * return the pointer to the first entry.  The order of entries
 164  * deleted is from the newest to the oldest added one.
 165  */
 166 static inline struct llist_node *llist_del_all(struct llist_head *head)
 167 {
 168         return xchg(&head->first, NULL);
 169 }
 170 #endif /* LLIST_H */