LXR qemu/include/qemu/rcu

   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
  32extern "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 */
 135