/*- * Copyright (c) 2020 SAULX * Copyright (c) 2015 Olli Vanhoja * 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 * SPDX-License-Identifier: BSD-3-Clause */ #ifndef _SYS_QUEUE_H_ #define _SYS_QUEUE_H_ /* * 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 + + + + * */ #ifdef QUEUE_MACRO_DEBUG /* Store the last 2 places the queue element or head was altered */ struct qm_trace { unsigned long lastline; unsigned long prevline; const char * lastfile; const char * prevfile; }; #define TRACEBUF struct qm_trace trace; #define TRACEBUF_INITIALIZER { __FILE__, __LINE__, NULL, 0 } , #define TRASHIT(x) do {(x) = (void *)-1;} while (0) #define QMD_SAVELINK(name, link) void **name = (void *)&(link) #define QMD_TRACE_HEAD(head) do { \ (head)->trace.prevline = (head)->trace.lastline; \ (head)->trace.prevfile = (head)->trace.lastfile; \ (head)->trace.lastline = __LINE__; \ (head)->trace.lastfile = __FILE__; \ } while (0) #define QMD_TRACE_ELEM(elem) do { \ (elem)->trace.prevline = (elem)->trace.lastline; \ (elem)->trace.prevfile = (elem)->trace.lastfile; \ (elem)->trace.lastline = __LINE__; \ (elem)->trace.lastfile = __FILE__; \ } while (0) #else #define QMD_TRACE_ELEM(elem) #define QMD_TRACE_HEAD(head) #define QMD_SAVELINK(name, link) #define TRACEBUF #define TRACEBUF_INITIALIZER #define TRASHIT(x) #endif /* QUEUE_MACRO_DEBUG */ /* * Singly-linked List declarations. */ #define SLIST_HEAD(name, type) \ struct name { \ struct type *slh_first; /* first element */ \ } #define SLIST_HEAD_INITIALIZER(head) \ { NULL } #define SLIST_ENTRY(type) \ struct { \ struct type *sle_next; /* next element */ \ } /* * Singly-linked List functions. */ #define SLIST_EMPTY(head) ((head)->slh_first == NULL) #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)) != NULL; \ (varp) = &SLIST_NEXT((var), field)) #define SLIST_INIT(head) do { \ SLIST_FIRST((head)) = NULL; \ } 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) \ { NULL, &(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 == NULL) #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)) = NULL; \ (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)) == NULL)\ (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))) == NULL) \ (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) = NULL; \ *(head)->stqh_last = (elm); \ (head)->stqh_last = &STAILQ_NEXT((elm), field); \ } while (0) #define STAILQ_LAST(head, type, field) \ (STAILQ_EMPTY((head)) ? NULL : \ 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)) == NULL) \ (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)) == NULL) \ (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) \ { NULL } #define LIST_ENTRY(type) \ struct { \ struct type *le_next; /* next element */ \ struct type **le_prev; /* address of previous next element */ \ } /* * List functions. */ #define LIST_EMPTY(head) ((head)->lh_first == NULL) #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)) = NULL; \ } while (0) #define LIST_INSERT_AFTER(listelm, elm, field) do { \ if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\ 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 { \ (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 { \ if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL) \ 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)) ? NULL : \ 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); \ if (LIST_NEXT((elm), field) != NULL) \ 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))) != NULL) \ swap_tmp->field.le_prev = &LIST_FIRST((head1)); \ if ((swap_tmp = LIST_FIRST((head2))) != NULL) \ 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) \ { NULL, &(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 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 == NULL) #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)) = NULL; \ (head)->tqh_last = &TAILQ_FIRST((head)); \ QMD_TRACE_HEAD(head); \ } while (0) #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do { \ if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\ 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 { \ (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 { \ if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL) \ 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 { \ TAILQ_NEXT((elm), field) = NULL; \ (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); \ if ((TAILQ_NEXT((elm), field)) != NULL) \ 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) != NULL) \ swap_first->field.tqe_prev = &(head1)->tqh_first; \ else \ (head1)->tqh_last = &(head1)->tqh_first; \ if ((swap_first = (head2)->tqh_first) != NULL) \ swap_first->field.tqe_prev = &(head2)->tqh_first; \ else \ (head2)->tqh_last = &(head2)->tqh_first; \ } while (0) #endif /* !_SYS_QUEUE_H_ */