ref: a3f2d6d23ed1be69fee607bdedadc0438fd01305
dir: /sys/src/cmd/ext4srv/include/queue.h/
/*-
* 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.
* 4. 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
* $FreeBSD$
*/
#pragma once
/*
* This file defines four types of data structures: singly-linked lists,
* singly-linked tail queues, lists 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 singly-linked 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
* 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, at the head of the list, or at the
* end of the list. Elements being removed from the head of the tail queue
* should use the explicit macro for this purpose for optimum efficiency.
* A singly-linked tail queue may only be traversed in the forward direction.
* Singly-linked tail queues are ideal for applications with large datasets
* and few or no removals or for implementing a FIFO 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 be traversed in either 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.
*
*
* SLIST LIST STAILQ TAILQ
* _HEAD + + + +
* _HEAD_INITIALIZER + + + +
* _ENTRY + + + +
* _INIT + + + +
* _EMPTY + + + +
* _FIRST + + + +
* _NEXT + + + +
* _PREV - + - +
* _LAST - - + +
* _FOREACH + + + +
* _FOREACH_FROM + + + +
* _FOREACH_SAFE + + + +
* _FOREACH_FROM_SAFE + + + +
* _FOREACH_REVERSE - - - +
* _FOREACH_REVERSE_FROM - - - +
* _FOREACH_REVERSE_SAFE - - - +
* _FOREACH_REVERSE_FROM_SAFE - - - +
* _INSERT_HEAD + + + +
* _INSERT_BEFORE - + - +
* _INSERT_AFTER + + + +
* _INSERT_TAIL - - + +
* _CONCAT - - + +
* _REMOVE_AFTER + - + -
* _REMOVE_HEAD + - + -
* _REMOVE + + + +
* _SWAP + + + +
*
*/
#define QMD_TRACE_ELEM(elem)
#define QMD_TRACE_HEAD(head)
#define QMD_SAVELINK(name, link)
#define TRACEBUF
#define TRACEBUF_INITIALIZER
#define TRASHIT(x)
/*
* Singly-linked List declarations.
*/
#define SLIST_HEAD(name, type) \
struct name { \
struct type *slh_first; /* first element */ \
}
#define SLIST_HEAD_INITIALIZER(head) \
{ nil }
#define SLIST_ENTRY(type) \
struct { \
struct type *sle_next; /* next element */ \
}
/*
* Singly-linked List functions.
*/
#define SLIST_EMPTY(head) ((head)->slh_first == nil)
#define SLIST_FIRST(head) ((head)->slh_first)
#define SLIST_FOREACH(var, head, field) \
for ((var) = SLIST_FIRST((head)); \
(var); \
(var) = SLIST_NEXT((var), field))
#define SLIST_FOREACH_FROM(var, head, field) \
for ((var) = ((var) ? (var) : SLIST_FIRST((head))); \
(var); \
(var) = SLIST_NEXT((var), field))
#define SLIST_FOREACH_SAFE(var, head, field, tvar) \
for ((var) = SLIST_FIRST((head)); \
(var) && ((tvar) = SLIST_NEXT((var), field), 1); \
(var) = (tvar))
#define SLIST_FOREACH_FROM_SAFE(var, head, field, tvar) \
for ((var) = ((var) ? (var) : SLIST_FIRST((head))); \
(var) && ((tvar) = SLIST_NEXT((var), field), 1); \
(var) = (tvar))
#define SLIST_FOREACH_PREVPTR(var, varp, head, field) \
for ((varp) = &SLIST_FIRST((head)); \
((var) = *(varp)) != nil; \
(varp) = &SLIST_NEXT((var), field))
#define SLIST_INIT(head) do { \
SLIST_FIRST((head)) = nil; \
} while (0)
#define SLIST_INSERT_AFTER(slistelm, elm, field) do { \
SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field); \
SLIST_NEXT((slistelm), field) = (elm); \
} while (0)
#define SLIST_INSERT_HEAD(head, elm, field) do { \
SLIST_NEXT((elm), field) = SLIST_FIRST((head)); \
SLIST_FIRST((head)) = (elm); \
} while (0)
#define SLIST_NEXT(elm, field) ((elm)->field.sle_next)
#define SLIST_REMOVE(head, elm, type, field) do { \
QMD_SAVELINK(oldnext, (elm)->field.sle_next); \
if (SLIST_FIRST((head)) == (elm)) { \
SLIST_REMOVE_HEAD((head), field); \
} \
else { \
struct type *curelm = SLIST_FIRST((head)); \
while (SLIST_NEXT(curelm, field) != (elm)) \
curelm = SLIST_NEXT(curelm, field); \
SLIST_REMOVE_AFTER(curelm, field); \
} \
TRASHIT(*oldnext); \
} while (0)
#define SLIST_REMOVE_AFTER(elm, field) do { \
SLIST_NEXT(elm, field) = \
SLIST_NEXT(SLIST_NEXT(elm, field), field); \
} while (0)
#define SLIST_REMOVE_HEAD(head, field) do { \
SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field); \
} while (0)
#define SLIST_SWAP(head1, head2, type) do { \
struct type *swap_first = SLIST_FIRST(head1); \
SLIST_FIRST(head1) = SLIST_FIRST(head2); \
SLIST_FIRST(head2) = swap_first; \
} while (0)
/*
* Singly-linked Tail queue declarations.
*/
#define STAILQ_HEAD(name, type) \
struct name { \
struct type *stqh_first;/* first element */ \
struct type **stqh_last;/* addr of last next element */ \
}
#define STAILQ_HEAD_INITIALIZER(head) \
{ nil, &(head).stqh_first }
#define STAILQ_ENTRY(type) \
struct { \
struct type *stqe_next; /* next element */ \
}
/*
* Singly-linked Tail queue functions.
*/
#define STAILQ_CONCAT(head1, head2) do { \
if (!STAILQ_EMPTY((head2))) { \
*(head1)->stqh_last = (head2)->stqh_first; \
(head1)->stqh_last = (head2)->stqh_last; \
STAILQ_INIT((head2)); \
} \
} while (0)
#define STAILQ_EMPTY(head) ((head)->stqh_first == nil)
#define STAILQ_FIRST(head) ((head)->stqh_first)
#define STAILQ_FOREACH(var, head, field) \
for((var) = STAILQ_FIRST((head)); \
(var); \
(var) = STAILQ_NEXT((var), field))
#define STAILQ_FOREACH_FROM(var, head, field) \
for ((var) = ((var) ? (var) : STAILQ_FIRST((head))); \
(var); \
(var) = STAILQ_NEXT((var), field))
#define STAILQ_FOREACH_SAFE(var, head, field, tvar) \
for ((var) = STAILQ_FIRST((head)); \
(var) && ((tvar) = STAILQ_NEXT((var), field), 1); \
(var) = (tvar))
#define STAILQ_FOREACH_FROM_SAFE(var, head, field, tvar) \
for ((var) = ((var) ? (var) : STAILQ_FIRST((head))); \
(var) && ((tvar) = STAILQ_NEXT((var), field), 1); \
(var) = (tvar))
#define STAILQ_INIT(head) do { \
STAILQ_FIRST((head)) = nil; \
(head)->stqh_last = &STAILQ_FIRST((head)); \
} while (0)
#define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do { \
if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == nil)\
(head)->stqh_last = &STAILQ_NEXT((elm), field); \
STAILQ_NEXT((tqelm), field) = (elm); \
} while (0)
#define STAILQ_INSERT_HEAD(head, elm, field) do { \
if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == nil) \
(head)->stqh_last = &STAILQ_NEXT((elm), field); \
STAILQ_FIRST((head)) = (elm); \
} while (0)
#define STAILQ_INSERT_TAIL(head, elm, field) do { \
STAILQ_NEXT((elm), field) = nil; \
*(head)->stqh_last = (elm); \
(head)->stqh_last = &STAILQ_NEXT((elm), field); \
} while (0)
#define STAILQ_LAST(head, type, field) \
(STAILQ_EMPTY((head)) ? nil : \
__containerof((head)->stqh_last, struct type, field.stqe_next))
#define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next)
#define STAILQ_REMOVE(head, elm, type, field) do { \
QMD_SAVELINK(oldnext, (elm)->field.stqe_next); \
if (STAILQ_FIRST((head)) == (elm)) { \
STAILQ_REMOVE_HEAD((head), field); \
} \
else { \
struct type *curelm = STAILQ_FIRST((head)); \
while (STAILQ_NEXT(curelm, field) != (elm)) \
curelm = STAILQ_NEXT(curelm, field); \
STAILQ_REMOVE_AFTER(head, curelm, field); \
} \
TRASHIT(*oldnext); \
} while (0)
#define STAILQ_REMOVE_AFTER(head, elm, field) do { \
if ((STAILQ_NEXT(elm, field) = \
STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == nil) \
(head)->stqh_last = &STAILQ_NEXT((elm), field); \
} while (0)
#define STAILQ_REMOVE_HEAD(head, field) do { \
if ((STAILQ_FIRST((head)) = \
STAILQ_NEXT(STAILQ_FIRST((head)), field)) == nil) \
(head)->stqh_last = &STAILQ_FIRST((head)); \
} while (0)
#define STAILQ_SWAP(head1, head2, type) do { \
struct type *swap_first = STAILQ_FIRST(head1); \
struct type **swap_last = (head1)->stqh_last; \
STAILQ_FIRST(head1) = STAILQ_FIRST(head2); \
(head1)->stqh_last = (head2)->stqh_last; \
STAILQ_FIRST(head2) = swap_first; \
(head2)->stqh_last = swap_last; \
if (STAILQ_EMPTY(head1)) \
(head1)->stqh_last = &STAILQ_FIRST(head1); \
if (STAILQ_EMPTY(head2)) \
(head2)->stqh_last = &STAILQ_FIRST(head2); \
} while (0)
/*
* List declarations.
*/
#define LIST_HEAD(name, type) \
struct name { \
struct type *lh_first; /* first element */ \
}
#define LIST_HEAD_INITIALIZER(head) \
{ nil }
#define LIST_ENTRY(type) \
struct { \
struct type *le_next; /* next element */ \
struct type **le_prev; /* address of previous next element */ \
}
/*
* List functions.
*/
#define QMD_LIST_CHECK_HEAD(head, field)
#define QMD_LIST_CHECK_NEXT(elm, field)
#define QMD_LIST_CHECK_PREV(elm, field)
#define LIST_EMPTY(head) ((head)->lh_first == nil)
#define LIST_FIRST(head) ((head)->lh_first)
#define LIST_FOREACH(var, head, field) \
for ((var) = LIST_FIRST((head)); \
(var); \
(var) = LIST_NEXT((var), field))
#define LIST_FOREACH_FROM(var, head, field) \
for ((var) = ((var) ? (var) : LIST_FIRST((head))); \
(var); \
(var) = LIST_NEXT((var), field))
#define LIST_FOREACH_SAFE(var, head, field, tvar) \
for ((var) = LIST_FIRST((head)); \
(var) && ((tvar) = LIST_NEXT((var), field), 1); \
(var) = (tvar))
#define LIST_FOREACH_FROM_SAFE(var, head, field, tvar) \
for ((var) = ((var) ? (var) : LIST_FIRST((head))); \
(var) && ((tvar) = LIST_NEXT((var), field), 1); \
(var) = (tvar))
#define LIST_INIT(head) do { \
LIST_FIRST((head)) = nil; \
} while (0)
#define LIST_INSERT_AFTER(listelm, elm, field) do { \
QMD_LIST_CHECK_NEXT(listelm, field); \
if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != nil)\
LIST_NEXT((listelm), field)->field.le_prev = \
&LIST_NEXT((elm), field); \
LIST_NEXT((listelm), field) = (elm); \
(elm)->field.le_prev = &LIST_NEXT((listelm), field); \
} while (0)
#define LIST_INSERT_BEFORE(listelm, elm, field) do { \
QMD_LIST_CHECK_PREV(listelm, field); \
(elm)->field.le_prev = (listelm)->field.le_prev; \
LIST_NEXT((elm), field) = (listelm); \
*(listelm)->field.le_prev = (elm); \
(listelm)->field.le_prev = &LIST_NEXT((elm), field); \
} while (0)
#define LIST_INSERT_HEAD(head, elm, field) do { \
QMD_LIST_CHECK_HEAD((head), field); \
if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != nil) \
LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
LIST_FIRST((head)) = (elm); \
(elm)->field.le_prev = &LIST_FIRST((head)); \
} while (0)
#define LIST_NEXT(elm, field) ((elm)->field.le_next)
#define LIST_PREV(elm, head, type, field) \
((elm)->field.le_prev == &LIST_FIRST((head)) ? nil : \
__containerof((elm)->field.le_prev, struct type, field.le_next))
#define LIST_REMOVE(elm, field) do { \
QMD_SAVELINK(oldnext, (elm)->field.le_next); \
QMD_SAVELINK(oldprev, (elm)->field.le_prev); \
QMD_LIST_CHECK_NEXT(elm, field); \
QMD_LIST_CHECK_PREV(elm, field); \
if (LIST_NEXT((elm), field) != nil) \
LIST_NEXT((elm), field)->field.le_prev = \
(elm)->field.le_prev; \
*(elm)->field.le_prev = LIST_NEXT((elm), field); \
TRASHIT(*oldnext); \
TRASHIT(*oldprev); \
} while (0)
#define LIST_SWAP(head1, head2, type, field) do { \
struct type *swap_tmp = LIST_FIRST((head1)); \
LIST_FIRST((head1)) = LIST_FIRST((head2)); \
LIST_FIRST((head2)) = swap_tmp; \
if ((swap_tmp = LIST_FIRST((head1))) != nil) \
swap_tmp->field.le_prev = &LIST_FIRST((head1)); \
if ((swap_tmp = LIST_FIRST((head2))) != nil) \
swap_tmp->field.le_prev = &LIST_FIRST((head2)); \
} while (0)
/*
* Tail queue declarations.
*/
#define TAILQ_HEAD(name, type) \
struct name { \
struct type *tqh_first; /* first element */ \
struct type **tqh_last; /* addr of last next element */ \
TRACEBUF \
}
#define TAILQ_HEAD_INITIALIZER(head) \
{ nil, &(head).tqh_first, TRACEBUF_INITIALIZER }
#define TAILQ_ENTRY(type) \
struct { \
struct type *tqe_next; /* next element */ \
struct type **tqe_prev; /* address of previous next element */ \
TRACEBUF \
}
/*
* Tail queue functions.
*/
#define QMD_TAILQ_CHECK_HEAD(head, field)
#define QMD_TAILQ_CHECK_TAIL(head, headname)
#define QMD_TAILQ_CHECK_NEXT(elm, field)
#define QMD_TAILQ_CHECK_PREV(elm, field)
#define TAILQ_CONCAT(head1, head2, field) do { \
if (!TAILQ_EMPTY(head2)) { \
*(head1)->tqh_last = (head2)->tqh_first; \
(head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \
(head1)->tqh_last = (head2)->tqh_last; \
TAILQ_INIT((head2)); \
QMD_TRACE_HEAD(head1); \
QMD_TRACE_HEAD(head2); \
} \
} while (0)
#define TAILQ_EMPTY(head) ((head)->tqh_first == nil)
#define TAILQ_FIRST(head) ((head)->tqh_first)
#define TAILQ_FOREACH(var, head, field) \
for ((var) = TAILQ_FIRST((head)); \
(var); \
(var) = TAILQ_NEXT((var), field))
#define TAILQ_FOREACH_FROM(var, head, field) \
for ((var) = ((var) ? (var) : TAILQ_FIRST((head))); \
(var); \
(var) = TAILQ_NEXT((var), field))
#define TAILQ_FOREACH_SAFE(var, head, field, tvar) \
for ((var) = TAILQ_FIRST((head)); \
(var) && ((tvar) = TAILQ_NEXT((var), field), 1); \
(var) = (tvar))
#define TAILQ_FOREACH_FROM_SAFE(var, head, field, tvar) \
for ((var) = ((var) ? (var) : TAILQ_FIRST((head))); \
(var) && ((tvar) = TAILQ_NEXT((var), field), 1); \
(var) = (tvar))
#define TAILQ_FOREACH_REVERSE(var, head, headname, field) \
for ((var) = TAILQ_LAST((head), headname); \
(var); \
(var) = TAILQ_PREV((var), headname, field))
#define TAILQ_FOREACH_REVERSE_FROM(var, head, headname, field) \
for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname)); \
(var); \
(var) = TAILQ_PREV((var), headname, field))
#define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar) \
for ((var) = TAILQ_LAST((head), headname); \
(var) && ((tvar) = TAILQ_PREV((var), headname, field), 1); \
(var) = (tvar))
#define TAILQ_FOREACH_REVERSE_FROM_SAFE(var, head, headname, field, tvar) \
for ((var) = ((var) ? (var) : TAILQ_LAST((head), headname)); \
(var) && ((tvar) = TAILQ_PREV((var), headname, field), 1); \
(var) = (tvar))
#define TAILQ_INIT(head) do { \
TAILQ_FIRST((head)) = nil; \
(head)->tqh_last = &TAILQ_FIRST((head)); \
QMD_TRACE_HEAD(head); \
} while (0)
#define TAILQ_INSERT_AFTER(head, listelm, elm, field) do { \
QMD_TAILQ_CHECK_NEXT(listelm, field); \
if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != nil)\
TAILQ_NEXT((elm), field)->field.tqe_prev = \
&TAILQ_NEXT((elm), field); \
else { \
(head)->tqh_last = &TAILQ_NEXT((elm), field); \
QMD_TRACE_HEAD(head); \
} \
TAILQ_NEXT((listelm), field) = (elm); \
(elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field); \
QMD_TRACE_ELEM(&(elm)->field); \
QMD_TRACE_ELEM(&(listelm)->field); \
} while (0)
#define TAILQ_INSERT_BEFORE(listelm, elm, field) do { \
QMD_TAILQ_CHECK_PREV(listelm, field); \
(elm)->field.tqe_prev = (listelm)->field.tqe_prev; \
TAILQ_NEXT((elm), field) = (listelm); \
*(listelm)->field.tqe_prev = (elm); \
(listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field); \
QMD_TRACE_ELEM(&(elm)->field); \
QMD_TRACE_ELEM(&(listelm)->field); \
} while (0)
#define TAILQ_INSERT_HEAD(head, elm, field) do { \
QMD_TAILQ_CHECK_HEAD(head, field); \
if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != nil) \
TAILQ_FIRST((head))->field.tqe_prev = \
&TAILQ_NEXT((elm), field); \
else \
(head)->tqh_last = &TAILQ_NEXT((elm), field); \
TAILQ_FIRST((head)) = (elm); \
(elm)->field.tqe_prev = &TAILQ_FIRST((head)); \
QMD_TRACE_HEAD(head); \
QMD_TRACE_ELEM(&(elm)->field); \
} while (0)
#define TAILQ_INSERT_TAIL(head, elm, field) do { \
QMD_TAILQ_CHECK_TAIL(head, field); \
TAILQ_NEXT((elm), field) = nil; \
(elm)->field.tqe_prev = (head)->tqh_last; \
*(head)->tqh_last = (elm); \
(head)->tqh_last = &TAILQ_NEXT((elm), field); \
QMD_TRACE_HEAD(head); \
QMD_TRACE_ELEM(&(elm)->field); \
} while (0)
#define TAILQ_LAST(head, headname) \
(*(((struct headname *)((head)->tqh_last))->tqh_last))
#define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
#define TAILQ_PREV(elm, headname, field) \
(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
#define TAILQ_REMOVE(head, elm, field) do { \
QMD_SAVELINK(oldnext, (elm)->field.tqe_next); \
QMD_SAVELINK(oldprev, (elm)->field.tqe_prev); \
QMD_TAILQ_CHECK_NEXT(elm, field); \
QMD_TAILQ_CHECK_PREV(elm, field); \
if ((TAILQ_NEXT((elm), field)) != nil) \
TAILQ_NEXT((elm), field)->field.tqe_prev = \
(elm)->field.tqe_prev; \
else { \
(head)->tqh_last = (elm)->field.tqe_prev; \
QMD_TRACE_HEAD(head); \
} \
*(elm)->field.tqe_prev = TAILQ_NEXT((elm), field); \
TRASHIT(*oldnext); \
TRASHIT(*oldprev); \
QMD_TRACE_ELEM(&(elm)->field); \
} while (0)
#define TAILQ_SWAP(head1, head2, type, field) do { \
struct type *swap_first = (head1)->tqh_first; \
struct type **swap_last = (head1)->tqh_last; \
(head1)->tqh_first = (head2)->tqh_first; \
(head1)->tqh_last = (head2)->tqh_last; \
(head2)->tqh_first = swap_first; \
(head2)->tqh_last = swap_last; \
if ((swap_first = (head1)->tqh_first) != nil) \
swap_first->field.tqe_prev = &(head1)->tqh_first; \
else \
(head1)->tqh_last = &(head1)->tqh_first; \
if ((swap_first = (head2)->tqh_first) != nil) \
swap_first->field.tqe_prev = &(head2)->tqh_first; \
else \
(head2)->tqh_last = &(head2)->tqh_first; \
} while (0)