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 handler.  So code uses the list in NMI
  39  * handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG.
  40  */
  41
  42 struct llist_head {
  43         struct llist_node *first;
  44 };
  45
  46 struct llist_node {
  47         struct llist_node *next;
  48 };
  49
  50 #define LLIST_HEAD_INIT(name)   { NULL }
  51 #define LLIST_HEAD(name)        struct llist_head name = LLIST_HEAD_INIT(name)
  52
  53 /**
  54  * init_llist_head - initialize lock-less list head
  55  * @head:       the head for your lock-less list
  56  */
  57 static inline void init_llist_head(struct llist_head *list)
  58 {
  59         list->first = NULL;
  60 }
  61
  62 /**
  63  * llist_entry - get the struct of this entry
  64  * @ptr:        the &struct llist_node pointer.
  65  * @type:       the type of the struct this is embedded in.
  66  * @member:     the name of the llist_node within the struct.
  67  */
  68 #define llist_entry(ptr, type, member)          \
  69         container_of(ptr, type, member)
  70
  71 /**
  72  * llist_for_each - iterate over some deleted entries of a lock-less list
  73  * @pos:        the &struct llist_node to use as a loop cursor
  74  * @node:       the first entry of deleted list entries
  75  *
  76  * In general, some entries of the lock-less list can be traversed
  77  * safely only after being deleted from list, so start with an entry
  78  * instead of list head.
  79  *
  80  * If being used on entries deleted from lock-less list directly, the
  81  * traverse order is from the newest to the oldest added entry.  If
  82  * you want to traverse from the oldest to the newest, you must
  83  * reverse the order by yourself before traversing.
  84  */
  85 #define llist_for_each(pos, node)                       \
  86         for ((pos) = (node); pos; (pos) = (pos)->next)
  87
  88 /**
  89  * llist_for_each_entry - iterate over some deleted entries of lock-less list of given type
  90  * @pos:        the type * to use as a loop cursor.
  91  * @node:       the fist entry of deleted list entries.
  92  * @member:     the name of the llist_node with the struct.
  93  *
  94  * In general, some entries of the lock-less list can be traversed
  95  * safely only after being removed from list, so start with an entry
  96  * instead of list head.
  97  *
  98  * If being used on entries deleted from lock-less list directly, the
  99  * traverse order is from the newest to the oldest added entry.  If
 100  * you want to traverse from the oldest to the newest, you must
 101  * reverse the order by yourself before traversing.
 102  */
 103 #define llist_for_each_entry(pos, node, member)                         \
 104         for ((pos) = llist_entry((node), typeof(*(pos)), member);       \
 105              &(pos)->member != NULL;                                    \
 106              (pos) = llist_entry((pos)->member.next, typeof(*(pos)), member))
 107
 108 /**
 109  * llist_empty - tests whether a lock-less list is empty
 110  * @head:       the list to test
 111  *
 112  * Not guaranteed to be accurate or up to date.  Just a quick way to
 113  * test whether the list is empty without deleting something from the
 114  * list.
 115  */
 116 static inline int llist_empty(const struct llist_head *head)
 117 {
 118         return ACCESS_ONCE(head->first) == NULL;
 119 }
 120
 121 void llist_add(struct llist_node *new, struct llist_head *head);
 122 void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
 123                      struct llist_head *head);
 124 struct llist_node *llist_del_first(struct llist_head *head);
 125 struct llist_node *llist_del_all(struct llist_head *head);
 126 #endif /* LLIST_H */