text: /*      $NetBSD: queue.h,v 1.52 2009/04/20 09:56:08 mschuett Exp $ */
  
  /*
   * QEMU version: Copy from netbsd, removed debug code, removed some of
   * the implementations.  Left in singly-linked lists, lists, simple
   * queues, and tail queues.
   */
  
  /*
   * Copyright (c) 1991, 1993
   *      The Regents of the University of California.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   *      @(#)queue.h     8.5 (Berkeley) 8/20/94
   */
  
  #ifndef QEMU_SYS_QUEUE_H
  #define QEMU_SYS_QUEUE_H
  
  /*
   * This file defines four types of data structures: singly-linked lists,
   * lists, simple queues, and tail queues.
   *
   * A singly-linked list is headed by a single forward pointer. The
   * elements are singly linked for minimum space and pointer manipulation
   * overhead at the expense of O(n) removal for arbitrary elements. New
   * elements can be added to the list after an existing element or at the
   * head of the list.  Elements being removed from the head of the list
   * should use the explicit macro for this purpose for optimum
   * efficiency. A singly-linked list may only be traversed in the forward
   * direction.  Singly-linked lists are ideal for applications with large
   * datasets and few or no removals or for implementing a LIFO queue.
   *
   * A list is headed by a single forward pointer (or an array of forward
   * pointers for a hash table header). The elements are doubly linked
   * so that an arbitrary element can be removed without a need to
   * traverse the list. New elements can be added to the list before
   * or after an existing element or at the head of the list. A list
   * may only be traversed in the forward direction.
   *
   * A simple queue is headed by a pair of pointers, one the head of the
   * list and the other to the tail of the list. The elements are singly
   * linked to save space, so elements can only be removed from the
   * head of the list. New elements can be added to the list after
   * an existing element, at the head of the list, or at the end of the
   * list. A simple queue may only be traversed in the forward direction.
   *
   * A tail queue is headed by a pair of pointers, one to the head of the
   * list and the other to the tail of the list. The elements are doubly
   * linked so that an arbitrary element can be removed without a need to
   * traverse the list. New elements can be added to the list before or
   * after an existing element, at the head of the list, or at the end of
   * the list. A tail queue may be traversed in either direction.
   *
   * For details on the use of these macros, see the queue(3) manual page.
   */
  
  #include "qemu/atomic.h" /* for smp_wmb() */
  
  /*
   * List definitions.
   */
  #define QLIST_HEAD(name, type)                                          \
  struct name {                                                           \
          struct type *lh_first;  /* first element */                     \
  }
  
  #define QLIST_HEAD_INITIALIZER(head)                                    \
          { NULL }
  
  #define QLIST_ENTRY(type)                                               \
  struct {                                                                \
          struct type *le_next;   /* next element */                      \
          struct type **le_prev;  /* address of previous next element */  \
  }
  
  /*
   * List functions.
   */
  #define QLIST_INIT(head) do {                                           \
          (head)->lh_first = NULL;                                        \
  } while (/*CONSTCOND*/0)
  
  #define QLIST_SWAP(dstlist, srclist, field) do {                        \
          void *tmplist;                                                  \
          tmplist = (srclist)->lh_first;                                  \
          (srclist)->lh_first = (dstlist)->lh_first;                      \
          if ((srclist)->lh_first != NULL) {                              \
              (srclist)->lh_first->field.le_prev = &(srclist)->lh_first;  \
          }                                                               \
          (dstlist)->lh_first = tmplist;                                  \
          if ((dstlist)->lh_first != NULL) {                              \
              (dstlist)->lh_first->field.le_prev = &(dstlist)->lh_first;  \
          }                                                               \
  } while (/*CONSTCOND*/0)
  
  #define QLIST_INSERT_AFTER(listelm, elm, field) do {                    \
          if (((elm)->field.le_next = (listelm)->field.le_next) != NULL)  \
                  (listelm)->field.le_next->field.le_prev =               \
                      &(elm)->field.le_next;                              \
          (listelm)->field.le_next = (elm);                               \
          (elm)->field.le_prev = &(listelm)->field.le_next;               \
  } while (/*CONSTCOND*/0)
  
  #define QLIST_INSERT_BEFORE(listelm, elm, field) do {                   \
          (elm)->field.le_prev = (listelm)->field.le_prev;                \
          (elm)->field.le_next = (listelm);                               \
          *(listelm)->field.le_prev = (elm);                              \
          (listelm)->field.le_prev = &(elm)->field.le_next;               \
  } while (/*CONSTCOND*/0)
  
  #define QLIST_INSERT_HEAD(head, elm, field) do {                        \
          if (((elm)->field.le_next = (head)->lh_first) != NULL)          \
                  (head)->lh_first->field.le_prev = &(elm)->field.le_next;\
          (head)->lh_first = (elm);                                       \
          (elm)->field.le_prev = &(head)->lh_first;                       \
  } while (/*CONSTCOND*/0)
  
  #define QLIST_REMOVE(elm, field) do {                                   \
          if ((elm)->field.le_next != NULL)                               \
                  (elm)->field.le_next->field.le_prev =                   \
                      (elm)->field.le_prev;                               \
          *(elm)->field.le_prev = (elm)->field.le_next;                   \
  } while (/*CONSTCOND*/0)
  
  #define QLIST_FOREACH(var, head, field)                                 \
          for ((var) = ((head)->lh_first);                                \
                  (var);                                                  \
                  (var) = ((var)->field.le_next))
  
  #define QLIST_FOREACH_SAFE(var, head, field, next_var)                  \
          for ((var) = ((head)->lh_first);                                \
                  (var) && ((next_var) = ((var)->field.le_next), 1);      \
                  (var) = (next_var))
  
  /*
   * List access methods.
   */
  #define QLIST_EMPTY(head)                ((head)->lh_first == NULL)
  #define QLIST_FIRST(head)                ((head)->lh_first)
  #define QLIST_NEXT(elm, field)           ((elm)->field.le_next)
  
  
  /*
   * Singly-linked List definitions.
   */
  #define QSLIST_HEAD(name, type)                                          \
  struct name {                                                           \
          struct type *slh_first; /* first element */                     \
  }
  
  #define QSLIST_HEAD_INITIALIZER(head)                                    \
          { NULL }
  
  #define QSLIST_ENTRY(type)                                               \
  struct {                                                                \
          struct type *sle_next;  /* next element */                      \
  }
  
  /*
   * Singly-linked List functions.
   */
  #define QSLIST_INIT(head) do {                                           \
          (head)->slh_first = NULL;                                       \
  } while (/*CONSTCOND*/0)
  
  #define QSLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
          (elm)->field.sle_next = (slistelm)->field.sle_next;             \
          (slistelm)->field.sle_next = (elm);                             \
  } while (/*CONSTCOND*/0)
  
  #define QSLIST_INSERT_HEAD(head, elm, field) do {                        \
          (elm)->field.sle_next = (head)->slh_first;                       \
          (head)->slh_first = (elm);                                       \
  } while (/*CONSTCOND*/0)
  
  #define QSLIST_INSERT_HEAD_ATOMIC(head, elm, field) do {                     \
          typeof(elm) save_sle_next;                                           \
          do {                                                                 \
              save_sle_next = (elm)->field.sle_next = (head)->slh_first;       \
          } while (atomic_cmpxchg(&(head)->slh_first, save_sle_next, (elm)) != \
                   save_sle_next);                                             \
  } while (/*CONSTCOND*/0)
  
  #define QSLIST_MOVE_ATOMIC(dest, src) do {                               \
          (dest)->slh_first = atomic_xchg(&(src)->slh_first, NULL);        \
  } while (/*CONSTCOND*/0)
  
  #define QSLIST_REMOVE_HEAD(head, field) do {                             \
          (head)->slh_first = (head)->slh_first->field.sle_next;          \
  } while (/*CONSTCOND*/0)
  
  #define QSLIST_REMOVE_AFTER(slistelm, field) do {                        \
          (slistelm)->field.sle_next =                                    \
              QSLIST_NEXT(QSLIST_NEXT((slistelm), field), field);           \
  } while (/*CONSTCOND*/0)
  
  #define QSLIST_FOREACH(var, head, field)                                 \
          for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next)
  
  #define QSLIST_FOREACH_SAFE(var, head, field, tvar)                      \
          for ((var) = QSLIST_FIRST((head));                               \
              (var) && ((tvar) = QSLIST_NEXT((var), field), 1);            \
              (var) = (tvar))
  
  /*
   * Singly-linked List access methods.
   */
  #define QSLIST_EMPTY(head)       ((head)->slh_first == NULL)
  #define QSLIST_FIRST(head)       ((head)->slh_first)
  #define QSLIST_NEXT(elm, field)  ((elm)->field.sle_next)
  
  
  /*
   * Simple queue definitions.
   */
  #define QSIMPLEQ_HEAD(name, type)                                       \
  struct name {                                                           \
      struct type *sqh_first;    /* first element */                      \
      struct type **sqh_last;    /* addr of last next element */          \
  }
  
  #define QSIMPLEQ_HEAD_INITIALIZER(head)                                 \
      { NULL, &(head).sqh_first }
  
  #define QSIMPLEQ_ENTRY(type)                                            \
  struct {                                                                \
      struct type *sqe_next;    /* next element */                        \
  }
  
  /*
   * Simple queue functions.
   */
  #define QSIMPLEQ_INIT(head) do {                                        \
      (head)->sqh_first = NULL;                                           \
      (head)->sqh_last = &(head)->sqh_first;                              \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_INSERT_HEAD(head, elm, field) do {                     \
      if (((elm)->field.sqe_next = (head)->sqh_first) == NULL)            \
          (head)->sqh_last = &(elm)->field.sqe_next;                      \
      (head)->sqh_first = (elm);                                          \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_INSERT_TAIL(head, elm, field) do {                     \
      (elm)->field.sqe_next = NULL;                                       \
      *(head)->sqh_last = (elm);                                          \
      (head)->sqh_last = &(elm)->field.sqe_next;                          \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do {           \
      if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)    \
          (head)->sqh_last = &(elm)->field.sqe_next;                      \
      (listelm)->field.sqe_next = (elm);                                  \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_REMOVE_HEAD(head, field) do {                          \
      if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL)\
          (head)->sqh_last = &(head)->sqh_first;                          \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_SPLIT_AFTER(head, elm, field, removed) do {            \
      QSIMPLEQ_INIT(removed);                                             \
      if (((removed)->sqh_first = (head)->sqh_first) != NULL) {           \
          if (((head)->sqh_first = (elm)->field.sqe_next) == NULL) {      \
              (head)->sqh_last = &(head)->sqh_first;                      \
          }                                                               \
          (removed)->sqh_last = &(elm)->field.sqe_next;                   \
          (elm)->field.sqe_next = NULL;                                   \
      }                                                                   \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_REMOVE(head, elm, type, field) do {                    \
      if ((head)->sqh_first == (elm)) {                                   \
          QSIMPLEQ_REMOVE_HEAD((head), field);                            \
      } else {                                                            \
          struct type *curelm = (head)->sqh_first;                        \
          while (curelm->field.sqe_next != (elm))                         \
              curelm = curelm->field.sqe_next;                            \
          if ((curelm->field.sqe_next =                                   \
              curelm->field.sqe_next->field.sqe_next) == NULL)            \
                  (head)->sqh_last = &(curelm)->field.sqe_next;           \
      }                                                                   \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_FOREACH(var, head, field)                              \
      for ((var) = ((head)->sqh_first);                                   \
          (var);                                                          \
          (var) = ((var)->field.sqe_next))
  
  #define QSIMPLEQ_FOREACH_SAFE(var, head, field, next)                   \
      for ((var) = ((head)->sqh_first);                                   \
          (var) && ((next = ((var)->field.sqe_next)), 1);                 \
          (var) = (next))
  
  #define QSIMPLEQ_CONCAT(head1, head2) do {                              \
      if (!QSIMPLEQ_EMPTY((head2))) {                                     \
          *(head1)->sqh_last = (head2)->sqh_first;                        \
          (head1)->sqh_last = (head2)->sqh_last;                          \
          QSIMPLEQ_INIT((head2));                                         \
      }                                                                   \
  } while (/*CONSTCOND*/0)
  
  #define QSIMPLEQ_LAST(head, type, field)                                \
      (QSIMPLEQ_EMPTY((head)) ?                                           \
          NULL :                                                          \
              ((struct type *)(void *)                                    \
          ((char *)((head)->sqh_last) - offsetof(struct type, field))))
  
  /*
   * Simple queue access methods.
   */
  #define QSIMPLEQ_EMPTY(head)        ((head)->sqh_first == NULL)
  #define QSIMPLEQ_FIRST(head)        ((head)->sqh_first)
  #define QSIMPLEQ_NEXT(elm, field)   ((elm)->field.sqe_next)
  
  
  /*
   * Tail queue definitions.
   */
  #define Q_TAILQ_HEAD(name, type, qual)                                  \
  struct name {                                                           \
          qual type *tqh_first;           /* first element */             \
          qual type *qual *tqh_last;      /* addr of last next element */ \
  }
  #define QTAILQ_HEAD(name, type)  Q_TAILQ_HEAD(name, struct type,)
  
  #define QTAILQ_HEAD_INITIALIZER(head)                                   \
          { NULL, &(head).tqh_first }
  
  #define Q_TAILQ_ENTRY(type, qual)                                       \
  struct {                                                                \
          qual type *tqe_next;            /* next element */              \
          qual type *qual *tqe_prev;      /* address of previous next element */\
  }
  #define QTAILQ_ENTRY(type)       Q_TAILQ_ENTRY(struct type,)
  
  /*
   * Tail queue functions.
   */
  #define QTAILQ_INIT(head) do {                                          \
          (head)->tqh_first = NULL;                                       \
          (head)->tqh_last = &(head)->tqh_first;                          \
  } while (/*CONSTCOND*/0)
  
  #define QTAILQ_INSERT_HEAD(head, elm, field) do {                       \
          if (((elm)->field.tqe_next = (head)->tqh_first) != NULL)        \
                  (head)->tqh_first->field.tqe_prev =                     \
                      &(elm)->field.tqe_next;                             \
          else                                                            \
                  (head)->tqh_last = &(elm)->field.tqe_next;              \
          (head)->tqh_first = (elm);                                      \
          (elm)->field.tqe_prev = &(head)->tqh_first;                     \
  } while (/*CONSTCOND*/0)
  
  #define QTAILQ_INSERT_TAIL(head, elm, field) do {                       \
          (elm)->field.tqe_next = NULL;                                   \
          (elm)->field.tqe_prev = (head)->tqh_last;                       \
          *(head)->tqh_last = (elm);                                      \
          (head)->tqh_last = &(elm)->field.tqe_next;                      \
  } while (/*CONSTCOND*/0)
  
  #define QTAILQ_INSERT_AFTER(head, listelm, elm, field) do {             \
          if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\
                  (elm)->field.tqe_next->field.tqe_prev =                 \
                      &(elm)->field.tqe_next;                             \
          else                                                            \
                  (head)->tqh_last = &(elm)->field.tqe_next;              \
          (listelm)->field.tqe_next = (elm);                              \
          (elm)->field.tqe_prev = &(listelm)->field.tqe_next;             \
  } while (/*CONSTCOND*/0)
  
  #define QTAILQ_INSERT_BEFORE(listelm, elm, field) do {                  \
          (elm)->field.tqe_prev = (listelm)->field.tqe_prev;              \
          (elm)->field.tqe_next = (listelm);                              \
          *(listelm)->field.tqe_prev = (elm);                             \
          (listelm)->field.tqe_prev = &(elm)->field.tqe_next;             \
  } while (/*CONSTCOND*/0)
  
  #define QTAILQ_REMOVE(head, elm, field) do {                            \
          if (((elm)->field.tqe_next) != NULL)                            \
                  (elm)->field.tqe_next->field.tqe_prev =                 \
                      (elm)->field.tqe_prev;                              \
          else                                                            \
                  (head)->tqh_last = (elm)->field.tqe_prev;               \
          *(elm)->field.tqe_prev = (elm)->field.tqe_next;                 \
          (elm)->field.tqe_prev = NULL;                                   \
  } while (/*CONSTCOND*/0)
  
  #define QTAILQ_FOREACH(var, head, field)                                \
          for ((var) = ((head)->tqh_first);                               \
                  (var);                                                  \
                  (var) = ((var)->field.tqe_next))
  
  #define QTAILQ_FOREACH_SAFE(var, head, field, next_var)                 \
          for ((var) = ((head)->tqh_first);                               \
                  (var) && ((next_var) = ((var)->field.tqe_next), 1);     \
                  (var) = (next_var))
  
  #define QTAILQ_FOREACH_REVERSE(var, head, headname, field)              \
          for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last));    \
                  (var);                                                  \
                  (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last)))
  
  /*
   * Tail queue access methods.
   */
  #define QTAILQ_EMPTY(head)               ((head)->tqh_first == NULL)
  #define QTAILQ_FIRST(head)               ((head)->tqh_first)
  #define QTAILQ_NEXT(elm, field)          ((elm)->field.tqe_next)
  #define QTAILQ_IN_USE(elm, field)        ((elm)->field.tqe_prev != NULL)
  
  #define QTAILQ_LAST(head, headname) \
          (*(((struct headname *)((head)->tqh_last))->tqh_last))
  #define QTAILQ_PREV(elm, headname, field) \
          (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  
  #define field_at_offset(base, offset, type)                                    \
          ((type) (((char *) (base)) + (offset)))
  
  typedef struct DUMMY_Q_ENTRY DUMMY_Q_ENTRY;
  typedef struct DUMMY_Q DUMMY_Q;
  
  struct DUMMY_Q_ENTRY {
          QTAILQ_ENTRY(DUMMY_Q_ENTRY) next;
  };
  
  struct DUMMY_Q {
          QTAILQ_HEAD(DUMMY_Q_HEAD, DUMMY_Q_ENTRY) head;
  };
  
  #define dummy_q ((DUMMY_Q *) 0)
  #define dummy_qe ((DUMMY_Q_ENTRY *) 0)
  
  /*
   * Offsets of layout of a tail queue head.
   */
  #define QTAILQ_FIRST_OFFSET (offsetof(typeof(dummy_q->head), tqh_first))
  #define QTAILQ_LAST_OFFSET  (offsetof(typeof(dummy_q->head), tqh_last))
  /*
   * Raw access of elements of a tail queue
   */
  #define QTAILQ_RAW_FIRST(head)                                                 \
          (*field_at_offset(head, QTAILQ_FIRST_OFFSET, void **))
  #define QTAILQ_RAW_TQH_LAST(head)                                              \
          (*field_at_offset(head, QTAILQ_LAST_OFFSET, void ***))
  
  /*
   * Offsets of layout of a tail queue element.
   */
  #define QTAILQ_NEXT_OFFSET (offsetof(typeof(dummy_qe->next), tqe_next))
  #define QTAILQ_PREV_OFFSET (offsetof(typeof(dummy_qe->next), tqe_prev))
  
  /*
   * Raw access of elements of a tail entry
   */
  #define QTAILQ_RAW_NEXT(elm, entry)                                            \
          (*field_at_offset(elm, entry + QTAILQ_NEXT_OFFSET, void **))
  #define QTAILQ_RAW_TQE_PREV(elm, entry)                                        \
          (*field_at_offset(elm, entry + QTAILQ_PREV_OFFSET, void ***))
  /*
   * Tail queue tranversal using pointer arithmetic.
   */
  #define QTAILQ_RAW_FOREACH(elm, head, entry)                                   \
          for ((elm) = QTAILQ_RAW_FIRST(head);                                   \
               (elm);                                                            \
               (elm) = QTAILQ_RAW_NEXT(elm, entry))
  /*
   * Tail queue insertion using pointer arithmetic.
   */
  #define QTAILQ_RAW_INSERT_TAIL(head, elm, entry) do {                          \
          QTAILQ_RAW_NEXT(elm, entry) = NULL;                                    \
          QTAILQ_RAW_TQE_PREV(elm, entry) = QTAILQ_RAW_TQH_LAST(head);           \
          *QTAILQ_RAW_TQH_LAST(head) = (elm);                                    \
          QTAILQ_RAW_TQH_LAST(head) = &QTAILQ_RAW_NEXT(elm, entry);              \
  } while (/*CONSTCOND*/0)
  
  #endif /* QEMU_SYS_QUEUE_H */
  