include/qemu/rcu_queue.h

   1 #ifndef QEMU_RCU_QUEUE_H
   2 #define QEMU_RCU_QUEUE_H
   3
   4 /*
   5  * rcu_queue.h
   6  *
   7  * RCU-friendly versions of the queue.h primitives.
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  *
  23  * Copyright (c) 2013 Mike D. Day, IBM Corporation.
  24  *
  25  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  26  */
  27
  28 #include "qemu/queue.h"
  29 #include "qemu/atomic.h"
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif
  34
  35
  36 /*
  37  * List access methods.
  38  */
  39 #define QLIST_EMPTY_RCU(head) (atomic_rcu_read(&(head)->lh_first) == NULL)
  40 #define QLIST_FIRST_RCU(head) (atomic_rcu_read(&(head)->lh_first))
  41 #define QLIST_NEXT_RCU(elm, field) (atomic_rcu_read(&(elm)->field.le_next))
  42
  43 /*
  44  * List functions.
  45  */
  46
  47
  48 /*
  49  *  The difference between atomic_read/set and atomic_rcu_read/set
  50  *  is in the including of a read/write memory barrier to the volatile
  51  *  access. atomic_rcu_* macros include the memory barrier, the
  52  *  plain atomic macros do not. Therefore, it should be correct to
  53  *  issue a series of reads or writes to the same element using only
  54  *  the atomic_* macro, until the last read or write, which should be
  55  *  atomic_rcu_* to introduce a read or write memory barrier as
  56  *  appropriate.
  57  */
  58
  59 /* Upon publication of the listelm->next value, list readers
  60  * will see the new node when following next pointers from
  61  * antecedent nodes, but may not see the new node when following
  62  * prev pointers from subsequent nodes until after the RCU grace
  63  * period expires.
  64  * see linux/include/rculist.h __list_add_rcu(new, prev, next)
  65  */
  66 #define QLIST_INSERT_AFTER_RCU(listelm, elm, field) do {    \
  67     (elm)->field.le_next = (listelm)->field.le_next;        \
  68     (elm)->field.le_prev = &(listelm)->field.le_next;       \
  69     atomic_rcu_set(&(listelm)->field.le_next, (elm));       \
  70     if ((elm)->field.le_next != NULL) {                     \
  71        (elm)->field.le_next->field.le_prev =                \
  72         &(elm)->field.le_next;                              \
  73     }                                                       \
  74 } while (/*CONSTCOND*/0)
  75
  76 /* Upon publication of the listelm->prev->next value, list
  77  * readers will see the new element when following prev pointers
  78  * from subsequent elements, but may not see the new element
  79  * when following next pointers from antecedent elements
  80  * until after the RCU grace period expires.
  81  */
  82 #define QLIST_INSERT_BEFORE_RCU(listelm, elm, field) do {   \
  83     (elm)->field.le_prev = (listelm)->field.le_prev;        \
  84     (elm)->field.le_next = (listelm);                       \
  85     atomic_rcu_set((listelm)->field.le_prev, (elm));        \
  86     (listelm)->field.le_prev = &(elm)->field.le_next;       \
  87 } while (/*CONSTCOND*/0)
  88
  89 /* Upon publication of the head->first value, list readers
  90  * will see the new element when following the head, but may
  91  * not see the new element when following prev pointers from
  92  * subsequent elements until after the RCU grace period has
  93  * expired.
  94  */
  95 #define QLIST_INSERT_HEAD_RCU(head, elm, field) do {    \
  96     (elm)->field.le_prev = &(head)->lh_first;           \
  97     (elm)->field.le_next = (head)->lh_first;            \
  98     atomic_rcu_set((&(head)->lh_first), (elm));         \
  99     if ((elm)->field.le_next != NULL) {                 \
 100        (elm)->field.le_next->field.le_prev =            \
 101         &(elm)->field.le_next;                          \
 102     }                                                   \
 103 } while (/*CONSTCOND*/0)
 104
 105
 106 /* prior to publication of the elm->prev->next value, some list
 107  * readers may still see the removed element when following
 108  * the antecedent's next pointer.
 109  */
 110 #define QLIST_REMOVE_RCU(elm, field) do {           \
 111     if ((elm)->field.le_next != NULL) {             \
 112        (elm)->field.le_next->field.le_prev =        \
 113         (elm)->field.le_prev;                       \
 114     }                                               \
 115     *(elm)->field.le_prev =  (elm)->field.le_next;  \
 116 } while (/*CONSTCOND*/0)
 117
 118 /* List traversal must occur within an RCU critical section.  */
 119 #define QLIST_FOREACH_RCU(var, head, field)                 \
 120         for ((var) = atomic_rcu_read(&(head)->lh_first);    \
 121                 (var);                                      \
 122                 (var) = atomic_rcu_read(&(var)->field.le_next))
 123
 124 /* List traversal must occur within an RCU critical section.  */
 125 #define QLIST_FOREACH_SAFE_RCU(var, head, field, next_var)           \
 126     for ((var) = (atomic_rcu_read(&(head)->lh_first));               \
 127       (var) &&                                                       \
 128           ((next_var) = atomic_rcu_read(&(var)->field.le_next), 1);  \
 129            (var) = (next_var))
 130
 131 #ifdef __cplusplus
 132 }
 133 #endif
 134 #endif /* QEMU_RCU_QUEUE_H */