1 /* 2 * Copyright (c) 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)queue.h 8.5 (Berkeley) 8/20/94 30 */ 31 32 #ifndef _SYS_QUEUE_H_ 33 #define _SYS_QUEUE_H_ 34 35 /* 36 * This file defines five types of data structures: singly-linked lists, 37 * lists, simple queues, tail queues, and circular queues. 38 * 39 * A singly-linked list is headed by a single forward pointer. The 40 * elements are singly linked for minimum space and pointer manipulation 41 * overhead at the expense of O(n) removal for arbitrary elements. New 42 * elements can be added to the list after an existing element or at the 43 * head of the list. Elements being removed from the head of the list 44 * should use the explicit macro for this purpose for optimum 45 * efficiency. A singly-linked list may only be traversed in the forward 46 * direction. Singly-linked lists are ideal for applications with large 47 * datasets and few or no removals or for implementing a LIFO queue. 48 * 49 * A list is headed by a single forward pointer (or an array of forward 50 * pointers for a hash table header). The elements are doubly linked 51 * so that an arbitrary element can be removed without a need to 52 * traverse the list. New elements can be added to the list before 53 * or after an existing element or at the head of the list. A list 54 * may only be traversed in the forward direction. 55 * 56 * A simple queue is headed by a pair of pointers, one the head of the 57 * list and the other to the tail of the list. The elements are singly 58 * linked to save space, so elements can only be removed from the 59 * head of the list. New elements can be added to the list after 60 * an existing element, at the head of the list, or at the end of the 61 * list. A simple queue may only be traversed in the forward direction. 62 * 63 * A tail queue is headed by a pair of pointers, one to the head of the 64 * list and the other to the tail of the list. The elements are doubly 65 * linked so that an arbitrary element can be removed without a need to 66 * traverse the list. New elements can be added to the list before or 67 * after an existing element, at the head of the list, or at the end of 68 * the list. A tail queue may be traversed in either direction. 69 * 70 * A circle queue is headed by a pair of pointers, one to the head of the 71 * list and the other to the tail of the list. The elements are doubly 72 * linked so that an arbitrary element can be removed without a need to 73 * traverse the list. New elements can be added to the list before or after 74 * an existing element, at the head of the list, or at the end of the list. 75 * A circle queue may be traversed in either direction, but has a more 76 * complex end of list detection. 77 * 78 * For details on the use of these macros, see the queue(3) manual page. 79 */ 80 81 /* 82 * List definitions. 83 */ 84 #define LIST_HEAD(name, type) \ 85 struct name { \ 86 struct type *lh_first; /* first element */ \ 87 } 88 89 #define LIST_HEAD_INITIALIZER(head) \ 90 { NULL } 91 92 #define LIST_ENTRY(type) \ 93 struct { \ 94 struct type *le_next; /* next element */ \ 95 struct type **le_prev; /* address of previous next element */ \ 96 } 97 98 /* 99 * List functions. 100 */ 101 #define LIST_INIT(head) do { \ 102 (head)->lh_first = NULL; \ 103 } while (/*CONSTCOND*/0) 104 105 #define LIST_INSERT_AFTER(listelm, elm, field) do { \ 106 if (((elm)->field.le_next = (listelm)->field.le_next) != NULL) \ 107 (listelm)->field.le_next->field.le_prev = \ 108 &(elm)->field.le_next; \ 109 (listelm)->field.le_next = (elm); \ 110 (elm)->field.le_prev = &(listelm)->field.le_next; \ 111 } while (/*CONSTCOND*/0) 112 113 #define LIST_INSERT_BEFORE(listelm, elm, field) do { \ 114 (elm)->field.le_prev = (listelm)->field.le_prev; \ 115 (elm)->field.le_next = (listelm); \ 116 *(listelm)->field.le_prev = (elm); \ 117 (listelm)->field.le_prev = &(elm)->field.le_next; \ 118 } while (/*CONSTCOND*/0) 119 120 #define LIST_INSERT_HEAD(head, elm, field) do { \ 121 if (((elm)->field.le_next = (head)->lh_first) != NULL) \ 122 (head)->lh_first->field.le_prev = &(elm)->field.le_next;\ 123 (head)->lh_first = (elm); \ 124 (elm)->field.le_prev = &(head)->lh_first; \ 125 } while (/*CONSTCOND*/0) 126 127 #define LIST_REMOVE(elm, field) do { \ 128 if ((elm)->field.le_next != NULL) \ 129 (elm)->field.le_next->field.le_prev = \ 130 (elm)->field.le_prev; \ 131 *(elm)->field.le_prev = (elm)->field.le_next; \ 132 } while (/*CONSTCOND*/0) 133 134 #define LIST_FOREACH(var, head, field) \ 135 for ((var) = ((head)->lh_first); \ 136 (var); \ 137 (var) = ((var)->field.le_next)) 138 139 /* 140 * List access methods. 141 */ 142 #define LIST_EMPTY(head) ((head)->lh_first == NULL) 143 #define LIST_FIRST(head) ((head)->lh_first) 144 #define LIST_NEXT(elm, field) ((elm)->field.le_next) 145 146 147 /* 148 * Singly-linked List definitions. 149 */ 150 #define SLIST_HEAD(name, type) \ 151 struct name { \ 152 struct type *slh_first; /* first element */ \ 153 } 154 155 #define SLIST_HEAD_INITIALIZER(head) \ 156 { NULL } 157 158 #define SLIST_ENTRY(type) \ 159 struct { \ 160 struct type *sle_next; /* next element */ \ 161 } 162 163 /* 164 * Singly-linked List functions. 165 */ 166 #define SLIST_INIT(head) do { \ 167 (head)->slh_first = NULL; \ 168 } while (/*CONSTCOND*/0) 169 170 #define SLIST_INSERT_AFTER(slistelm, elm, field) do { \ 171 (elm)->field.sle_next = (slistelm)->field.sle_next; \ 172 (slistelm)->field.sle_next = (elm); \ 173 } while (/*CONSTCOND*/0) 174 175 #define SLIST_INSERT_HEAD(head, elm, field) do { \ 176 (elm)->field.sle_next = (head)->slh_first; \ 177 (head)->slh_first = (elm); \ 178 } while (/*CONSTCOND*/0) 179 180 #define SLIST_REMOVE_HEAD(head, field) do { \ 181 (head)->slh_first = (head)->slh_first->field.sle_next; \ 182 } while (/*CONSTCOND*/0) 183 184 #define SLIST_REMOVE(head, elm, type, field) do { \ 185 if ((head)->slh_first == (elm)) { \ 186 SLIST_REMOVE_HEAD((head), field); \ 187 } \ 188 else { \ 189 struct type *curelm = (head)->slh_first; \ 190 while(curelm->field.sle_next != (elm)) \ 191 curelm = curelm->field.sle_next; \ 192 curelm->field.sle_next = \ 193 curelm->field.sle_next->field.sle_next; \ 194 } \ 195 } while (/*CONSTCOND*/0) 196 197 #define SLIST_FOREACH(var, head, field) \ 198 for((var) = (head)->slh_first; (var); (var) = (var)->field.sle_next) 199 200 /* 201 * Singly-linked List access methods. 202 */ 203 #define SLIST_EMPTY(head) ((head)->slh_first == NULL) 204 #define SLIST_FIRST(head) ((head)->slh_first) 205 #define SLIST_NEXT(elm, field) ((elm)->field.sle_next) 206 207 208 /* 209 * Singly-linked Tail queue declarations. 210 */ 211 #define STAILQ_HEAD(name, type) \ 212 struct name { \ 213 struct type *stqh_first; /* first element */ \ 214 struct type **stqh_last; /* addr of last next element */ \ 215 } 216 217 #define STAILQ_HEAD_INITIALIZER(head) \ 218 { NULL, &(head).stqh_first } 219 220 #define STAILQ_ENTRY(type) \ 221 struct { \ 222 struct type *stqe_next; /* next element */ \ 223 } 224 225 /* 226 * Singly-linked Tail queue functions. 227 */ 228 #define STAILQ_INIT(head) do { \ 229 (head)->stqh_first = NULL; \ 230 (head)->stqh_last = &(head)->stqh_first; \ 231 } while (/*CONSTCOND*/0) 232 233 #define STAILQ_INSERT_HEAD(head, elm, field) do { \ 234 if (((elm)->field.stqe_next = (head)->stqh_first) == NULL) \ 235 (head)->stqh_last = &(elm)->field.stqe_next; \ 236 (head)->stqh_first = (elm); \ 237 } while (/*CONSTCOND*/0) 238 239 #define STAILQ_INSERT_TAIL(head, elm, field) do { \ 240 (elm)->field.stqe_next = NULL; \ 241 *(head)->stqh_last = (elm); \ 242 (head)->stqh_last = &(elm)->field.stqe_next; \ 243 } while (/*CONSTCOND*/0) 244 245 #define STAILQ_INSERT_AFTER(head, listelm, elm, field) do { \ 246 if (((elm)->field.stqe_next = (listelm)->field.stqe_next) == NULL)\ 247 (head)->stqh_last = &(elm)->field.stqe_next; \ 248 (listelm)->field.stqe_next = (elm); \ 249 } while (/*CONSTCOND*/0) 250 251 #define STAILQ_REMOVE_HEAD(head, field) do { \ 252 if (((head)->stqh_first = (head)->stqh_first->field.stqe_next) == NULL) \ 253 (head)->stqh_last = &(head)->stqh_first; \ 254 } while (/*CONSTCOND*/0) 255 256 #define STAILQ_REMOVE(head, elm, type, field) do { \ 257 if ((head)->stqh_first == (elm)) { \ 258 STAILQ_REMOVE_HEAD((head), field); \ 259 } else { \ 260 struct type *curelm = (head)->stqh_first; \ 261 while (curelm->field.stqe_next != (elm)) \ 262 curelm = curelm->field.stqe_next; \ 263 if ((curelm->field.stqe_next = \ 264 curelm->field.stqe_next->field.stqe_next) == NULL) \ 265 (head)->stqh_last = &(curelm)->field.stqe_next; \ 266 } \ 267 } while (/*CONSTCOND*/0) 268 269 #define STAILQ_FOREACH(var, head, field) \ 270 for ((var) = ((head)->stqh_first); \ 271 (var); \ 272 (var) = ((var)->field.stqe_next)) 273 274 /* 275 * Singly-linked Tail queue access methods. 276 */ 277 #define STAILQ_EMPTY(head) ((head)->stqh_first == NULL) 278 #define STAILQ_FIRST(head) ((head)->stqh_first) 279 #define STAILQ_NEXT(elm, field) ((elm)->field.stqe_next) 280 281 282 /* 283 * Simple queue definitions. 284 */ 285 #define SIMPLEQ_HEAD(name, type) \ 286 struct name { \ 287 struct type *sqh_first; /* first element */ \ 288 struct type **sqh_last; /* addr of last next element */ \ 289 } 290 291 #define SIMPLEQ_HEAD_INITIALIZER(head) \ 292 { NULL, &(head).sqh_first } 293 294 #define SIMPLEQ_ENTRY(type) \ 295 struct { \ 296 struct type *sqe_next; /* next element */ \ 297 } 298 299 /* 300 * Simple queue functions. 301 */ 302 #define SIMPLEQ_INIT(head) do { \ 303 (head)->sqh_first = NULL; \ 304 (head)->sqh_last = &(head)->sqh_first; \ 305 } while (/*CONSTCOND*/0) 306 307 #define SIMPLEQ_INSERT_HEAD(head, elm, field) do { \ 308 if (((elm)->field.sqe_next = (head)->sqh_first) == NULL) \ 309 (head)->sqh_last = &(elm)->field.sqe_next; \ 310 (head)->sqh_first = (elm); \ 311 } while (/*CONSTCOND*/0) 312 313 #define SIMPLEQ_INSERT_TAIL(head, elm, field) do { \ 314 (elm)->field.sqe_next = NULL; \ 315 *(head)->sqh_last = (elm); \ 316 (head)->sqh_last = &(elm)->field.sqe_next; \ 317 } while (/*CONSTCOND*/0) 318 319 #define SIMPLEQ_INSERT_AFTER(head, listelm, elm, field) do { \ 320 if (((elm)->field.sqe_next = (listelm)->field.sqe_next) == NULL)\ 321 (head)->sqh_last = &(elm)->field.sqe_next; \ 322 (listelm)->field.sqe_next = (elm); \ 323 } while (/*CONSTCOND*/0) 324 325 #define SIMPLEQ_REMOVE_HEAD(head, field) do { \ 326 if (((head)->sqh_first = (head)->sqh_first->field.sqe_next) == NULL) \ 327 (head)->sqh_last = &(head)->sqh_first; \ 328 } while (/*CONSTCOND*/0) 329 330 #define SIMPLEQ_REMOVE(head, elm, type, field) do { \ 331 if ((head)->sqh_first == (elm)) { \ 332 SIMPLEQ_REMOVE_HEAD((head), field); \ 333 } else { \ 334 struct type *curelm = (head)->sqh_first; \ 335 while (curelm->field.sqe_next != (elm)) \ 336 curelm = curelm->field.sqe_next; \ 337 if ((curelm->field.sqe_next = \ 338 curelm->field.sqe_next->field.sqe_next) == NULL) \ 339 (head)->sqh_last = &(curelm)->field.sqe_next; \ 340 } \ 341 } while (/*CONSTCOND*/0) 342 343 #define SIMPLEQ_FOREACH(var, head, field) \ 344 for ((var) = ((head)->sqh_first); \ 345 (var); \ 346 (var) = ((var)->field.sqe_next)) 347 348 /* 349 * Simple queue access methods. 350 */ 351 #define SIMPLEQ_EMPTY(head) ((head)->sqh_first == NULL) 352 #define SIMPLEQ_FIRST(head) ((head)->sqh_first) 353 #define SIMPLEQ_NEXT(elm, field) ((elm)->field.sqe_next) 354 355 356 /* 357 * Tail queue definitions. 358 */ 359 #define _TAILQ_HEAD(name, type, qual) \ 360 struct name { \ 361 qual type *tqh_first; /* first element */ \ 362 qual type *qual *tqh_last; /* addr of last next element */ \ 363 } 364 #define TAILQ_HEAD(name, type) _TAILQ_HEAD(name, struct type,) 365 366 #define TAILQ_HEAD_INITIALIZER(head) \ 367 { NULL, &(head).tqh_first } 368 369 #define _TAILQ_ENTRY(type, qual) \ 370 struct { \ 371 qual type *tqe_next; /* next element */ \ 372 qual type *qual *tqe_prev; /* address of previous next element */\ 373 } 374 #define TAILQ_ENTRY(type) _TAILQ_ENTRY(struct type,) 375 376 /* 377 * Tail queue functions. 378 */ 379 #define TAILQ_INIT(head) do { \ 380 (head)->tqh_first = NULL; \ 381 (head)->tqh_last = &(head)->tqh_first; \ 382 } while (/*CONSTCOND*/0) 383 384 #define TAILQ_INSERT_HEAD(head, elm, field) do { \ 385 if (((elm)->field.tqe_next = (head)->tqh_first) != NULL) \ 386 (head)->tqh_first->field.tqe_prev = \ 387 &(elm)->field.tqe_next; \ 388 else \ 389 (head)->tqh_last = &(elm)->field.tqe_next; \ 390 (head)->tqh_first = (elm); \ 391 (elm)->field.tqe_prev = &(head)->tqh_first; \ 392 } while (/*CONSTCOND*/0) 393 394 #define TAILQ_INSERT_TAIL(head, elm, field) do { \ 395 (elm)->field.tqe_next = NULL; \ 396 (elm)->field.tqe_prev = (head)->tqh_last; \ 397 *(head)->tqh_last = (elm); \ 398 (head)->tqh_last = &(elm)->field.tqe_next; \ 399 } while (/*CONSTCOND*/0) 400 401 #define TAILQ_INSERT_AFTER(head, listelm, elm, field) do { \ 402 if (((elm)->field.tqe_next = (listelm)->field.tqe_next) != NULL)\ 403 (elm)->field.tqe_next->field.tqe_prev = \ 404 &(elm)->field.tqe_next; \ 405 else \ 406 (head)->tqh_last = &(elm)->field.tqe_next; \ 407 (listelm)->field.tqe_next = (elm); \ 408 (elm)->field.tqe_prev = &(listelm)->field.tqe_next; \ 409 } while (/*CONSTCOND*/0) 410 411 #define TAILQ_INSERT_BEFORE(listelm, elm, field) do { \ 412 (elm)->field.tqe_prev = (listelm)->field.tqe_prev; \ 413 (elm)->field.tqe_next = (listelm); \ 414 *(listelm)->field.tqe_prev = (elm); \ 415 (listelm)->field.tqe_prev = &(elm)->field.tqe_next; \ 416 } while (/*CONSTCOND*/0) 417 418 #define TAILQ_REMOVE(head, elm, field) do { \ 419 if (((elm)->field.tqe_next) != NULL) \ 420 (elm)->field.tqe_next->field.tqe_prev = \ 421 (elm)->field.tqe_prev; \ 422 else \ 423 (head)->tqh_last = (elm)->field.tqe_prev; \ 424 *(elm)->field.tqe_prev = (elm)->field.tqe_next; \ 425 } while (/*CONSTCOND*/0) 426 427 #define TAILQ_FOREACH(var, head, field) \ 428 for ((var) = ((head)->tqh_first); \ 429 (var); \ 430 (var) = ((var)->field.tqe_next)) 431 432 #define TAILQ_FOREACH_REVERSE(var, head, headname, field) \ 433 for ((var) = (*(((struct headname *)((head)->tqh_last))->tqh_last)); \ 434 (var); \ 435 (var) = (*(((struct headname *)((var)->field.tqe_prev))->tqh_last))) 436 437 /* 438 * Tail queue access methods. 439 */ 440 #define TAILQ_EMPTY(head) ((head)->tqh_first == NULL) 441 #define TAILQ_FIRST(head) ((head)->tqh_first) 442 #define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next) 443 444 #define TAILQ_LAST(head, headname) \ 445 (*(((struct headname *)((head)->tqh_last))->tqh_last)) 446 #define TAILQ_PREV(elm, headname, field) \ 447 (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last)) 448 449 450 /* 451 * Circular queue definitions. 452 */ 453 #define CIRCLEQ_HEAD(name, type) \ 454 struct name { \ 455 struct type *cqh_first; /* first element */ \ 456 struct type *cqh_last; /* last element */ \ 457 } 458 459 #define CIRCLEQ_HEAD_INITIALIZER(head) \ 460 { (void *)&head, (void *)&head } 461 462 #define CIRCLEQ_ENTRY(type) \ 463 struct { \ 464 struct type *cqe_next; /* next element */ \ 465 struct type *cqe_prev; /* previous element */ \ 466 } 467 468 /* 469 * Circular queue functions. 470 */ 471 #define CIRCLEQ_INIT(head) do { \ 472 (head)->cqh_first = (void *)(head); \ 473 (head)->cqh_last = (void *)(head); \ 474 } while (/*CONSTCOND*/0) 475 476 #define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do { \ 477 (elm)->field.cqe_next = (listelm)->field.cqe_next; \ 478 (elm)->field.cqe_prev = (listelm); \ 479 if ((listelm)->field.cqe_next == (void *)(head)) \ 480 (head)->cqh_last = (elm); \ 481 else \ 482 (listelm)->field.cqe_next->field.cqe_prev = (elm); \ 483 (listelm)->field.cqe_next = (elm); \ 484 } while (/*CONSTCOND*/0) 485 486 #define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do { \ 487 (elm)->field.cqe_next = (listelm); \ 488 (elm)->field.cqe_prev = (listelm)->field.cqe_prev; \ 489 if ((listelm)->field.cqe_prev == (void *)(head)) \ 490 (head)->cqh_first = (elm); \ 491 else \ 492 (listelm)->field.cqe_prev->field.cqe_next = (elm); \ 493 (listelm)->field.cqe_prev = (elm); \ 494 } while (/*CONSTCOND*/0) 495 496 #define CIRCLEQ_INSERT_HEAD(head, elm, field) do { \ 497 (elm)->field.cqe_next = (head)->cqh_first; \ 498 (elm)->field.cqe_prev = (void *)(head); \ 499 if ((head)->cqh_last == (void *)(head)) \ 500 (head)->cqh_last = (elm); \ 501 else \ 502 (head)->cqh_first->field.cqe_prev = (elm); \ 503 (head)->cqh_first = (elm); \ 504 } while (/*CONSTCOND*/0) 505 506 #define CIRCLEQ_INSERT_TAIL(head, elm, field) do { \ 507 (elm)->field.cqe_next = (void *)(head); \ 508 (elm)->field.cqe_prev = (head)->cqh_last; \ 509 if ((head)->cqh_first == (void *)(head)) \ 510 (head)->cqh_first = (elm); \ 511 else \ 512 (head)->cqh_last->field.cqe_next = (elm); \ 513 (head)->cqh_last = (elm); \ 514 } while (/*CONSTCOND*/0) 515 516 #define CIRCLEQ_REMOVE(head, elm, field) do { \ 517 if ((elm)->field.cqe_next == (void *)(head)) \ 518 (head)->cqh_last = (elm)->field.cqe_prev; \ 519 else \ 520 (elm)->field.cqe_next->field.cqe_prev = \ 521 (elm)->field.cqe_prev; \ 522 if ((elm)->field.cqe_prev == (void *)(head)) \ 523 (head)->cqh_first = (elm)->field.cqe_next; \ 524 else \ 525 (elm)->field.cqe_prev->field.cqe_next = \ 526 (elm)->field.cqe_next; \ 527 } while (/*CONSTCOND*/0) 528 529 #define CIRCLEQ_FOREACH(var, head, field) \ 530 for ((var) = ((head)->cqh_first); \ 531 (var) != (const void *)(head); \ 532 (var) = ((var)->field.cqe_next)) 533 534 #define CIRCLEQ_FOREACH_REVERSE(var, head, field) \ 535 for ((var) = ((head)->cqh_last); \ 536 (var) != (const void *)(head); \ 537 (var) = ((var)->field.cqe_prev)) 538 539 /* 540 * Circular queue access methods. 541 */ 542 #define CIRCLEQ_EMPTY(head) ((head)->cqh_first == (void *)(head)) 543 #define CIRCLEQ_FIRST(head) ((head)->cqh_first) 544 #define CIRCLEQ_LAST(head) ((head)->cqh_last) 545 #define CIRCLEQ_NEXT(elm, field) ((elm)->field.cqe_next) 546 #define CIRCLEQ_PREV(elm, field) ((elm)->field.cqe_prev) 547 548 #define CIRCLEQ_LOOP_NEXT(head, elm, field) \ 549 (((elm)->field.cqe_next == (void *)(head)) \ 550 ? ((head)->cqh_first) \ 551 : (elm->field.cqe_next)) 552 #define CIRCLEQ_LOOP_PREV(head, elm, field) \ 553 (((elm)->field.cqe_prev == (void *)(head)) \ 554 ? ((head)->cqh_last) \ 555 : (elm->field.cqe_prev)) 556 557 #endif /* sys/queue.h */ 558