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 * 4. 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 * $FreeBSD$ 31 */ 32 33 #ifndef XEN__SYS_QUEUE_H_ 34 #define XEN__SYS_QUEUE_H_ 35 36 /* #include <sys/cdefs.h> */ 37 38 /* 39 * This file defines four types of data structures: singly-linked lists, 40 * singly-linked tail queues, lists and tail queues. 41 * 42 * A singly-linked list is headed by a single forward pointer. The elements 43 * are singly linked for minimum space and pointer manipulation overhead at 44 * the expense of O(n) removal for arbitrary elements. New elements can be 45 * added to the list after an existing element or at the head of the list. 46 * Elements being removed from the head of the list should use the explicit 47 * macro for this purpose for optimum efficiency. A singly-linked list may 48 * only be traversed in the forward direction. Singly-linked lists are ideal 49 * for applications with large datasets and few or no removals or for 50 * implementing a LIFO queue. 51 * 52 * A singly-linked tail queue is headed by a pair of pointers, one to the 53 * head of the list and the other to the tail of the list. The elements are 54 * singly linked for minimum space and pointer manipulation overhead at the 55 * expense of O(n) removal for arbitrary elements. New elements can be added 56 * to the list after an existing element, at the head of the list, or at the 57 * end of the list. Elements being removed from the head of the tail queue 58 * should use the explicit macro for this purpose for optimum efficiency. 59 * A singly-linked tail queue may only be traversed in the forward direction. 60 * Singly-linked tail queues are ideal for applications with large datasets 61 * and few or no removals or for implementing a FIFO queue. 62 * 63 * A list is headed by a single forward pointer (or an array of forward 64 * pointers for a hash table header). The elements are doubly linked 65 * 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 67 * or after an existing element or at the head of the list. A list 68 * may only be traversed in the forward direction. 69 * 70 * A tail 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 74 * after an existing element, at the head of the list, or at the end of 75 * the list. A tail queue may be traversed in either direction. 76 * 77 * For details on the use of these macros, see the queue(3) manual page. 78 * 79 * 80 * XEN_SLIST XEN_LIST XEN_STAILQ XEN_TAILQ 81 * _HEAD + + + + 82 * _HEAD_INITIALIZER + + + + 83 * _ENTRY + + + + 84 * _INIT + + + + 85 * _EMPTY + + + + 86 * _FIRST + + + + 87 * _NEXT + + + + 88 * _PREV - - - + 89 * _LAST - - + + 90 * _FOREACH + + + + 91 * _FOREACH_SAFE + + + + 92 * _FOREACH_REVERSE - - - + 93 * _FOREACH_REVERSE_SAFE - - - + 94 * _INSERT_HEAD + + + + 95 * _INSERT_BEFORE - + - + 96 * _INSERT_AFTER + + + + 97 * _INSERT_TAIL - - + + 98 * _CONCAT - - + + 99 * _REMOVE_AFTER + - + - 100 * _REMOVE_HEAD + - + - 101 * _REMOVE + + + + 102 * _SWAP + + + + 103 * 104 */ 105 106 /* 107 * Singly-linked List declarations. 108 */ 109 #define XEN_SLIST_HEAD(name, type) \ 110 struct name { \ 111 type *slh_first; /* first element */ \ 112 } 113 114 #define XEN_SLIST_HEAD_INITIALIZER(head) \ 115 { 0 } 116 117 #define XEN_SLIST_ENTRY(type) \ 118 struct { \ 119 type *sle_next; /* next element */ \ 120 } 121 122 /* 123 * Singly-linked List functions. 124 */ 125 #define XEN_SLIST_EMPTY(head) ((head)->slh_first == 0) 126 127 #define XEN_SLIST_FIRST(head) ((head)->slh_first) 128 129 #define XEN_SLIST_FOREACH(var, head, field) \ 130 for ((var) = XEN_SLIST_FIRST((head)); \ 131 (var); \ 132 (var) = XEN_SLIST_NEXT((var), field)) 133 134 #define XEN_SLIST_FOREACH_SAFE(var, head, field, tvar) \ 135 for ((var) = XEN_SLIST_FIRST((head)); \ 136 (var) && ((tvar) = XEN_SLIST_NEXT((var), field), 1); \ 137 (var) = (tvar)) 138 139 #define XEN_SLIST_FOREACH_PREVPTR(var, varp, head, field) \ 140 for ((varp) = &XEN_SLIST_FIRST((head)); \ 141 ((var) = *(varp)) != 0; \ 142 (varp) = &XEN_SLIST_NEXT((var), field)) 143 144 #define XEN_SLIST_INIT(head) do { \ 145 XEN_SLIST_FIRST((head)) = 0; \ 146 } while (0) 147 148 #define XEN_SLIST_INSERT_AFTER(slistelm, elm, field) do { \ 149 XEN_SLIST_NEXT((elm), field) = XEN_SLIST_NEXT((slistelm), field);\ 150 XEN_SLIST_NEXT((slistelm), field) = (elm); \ 151 } while (0) 152 153 #define XEN_SLIST_INSERT_HEAD(head, elm, field) do { \ 154 XEN_SLIST_NEXT((elm), field) = XEN_SLIST_FIRST((head)); \ 155 XEN_SLIST_FIRST((head)) = (elm); \ 156 } while (0) 157 158 #define XEN_SLIST_NEXT(elm, field) ((elm)->field.sle_next) 159 160 #define XEN_SLIST_REMOVE(head, elm, type, field) do { \ 161 if (XEN_SLIST_FIRST((head)) == (elm)) { \ 162 XEN_SLIST_REMOVE_HEAD((head), field); \ 163 } \ 164 else { \ 165 type *curelm = XEN_SLIST_FIRST((head)); \ 166 while (XEN_SLIST_NEXT(curelm, field) != (elm)) \ 167 curelm = XEN_SLIST_NEXT(curelm, field); \ 168 XEN_SLIST_REMOVE_AFTER(curelm, field); \ 169 } \ 170 } while (0) 171 172 #define XEN_SLIST_REMOVE_AFTER(elm, field) do { \ 173 XEN_SLIST_NEXT(elm, field) = \ 174 XEN_SLIST_NEXT(XEN_SLIST_NEXT(elm, field), field); \ 175 } while (0) 176 177 #define XEN_SLIST_REMOVE_HEAD(head, field) do { \ 178 XEN_SLIST_FIRST((head)) = XEN_SLIST_NEXT(XEN_SLIST_FIRST((head)), field);\ 179 } while (0) 180 181 #define XEN_SLIST_SWAP(head1, head2, type) do { \ 182 type *swap_first = XEN_SLIST_FIRST(head1); \ 183 XEN_SLIST_FIRST(head1) = XEN_SLIST_FIRST(head2); \ 184 XEN_SLIST_FIRST(head2) = swap_first; \ 185 } while (0) 186 187 /* 188 * Singly-linked Tail queue declarations. 189 */ 190 #define XEN_STAILQ_HEAD(name, type) \ 191 struct name { \ 192 type *stqh_first;/* first element */ \ 193 type **stqh_last;/* addr of last next element */ \ 194 } 195 196 #define XEN_STAILQ_HEAD_INITIALIZER(head) \ 197 { 0, &(head).stqh_first } 198 199 #define XEN_STAILQ_ENTRY(type) \ 200 struct { \ 201 type *stqe_next; /* next element */ \ 202 } 203 204 /* 205 * Singly-linked Tail queue functions. 206 */ 207 #define XEN_STAILQ_CONCAT(head1, head2) do { \ 208 if (!XEN_STAILQ_EMPTY((head2))) { \ 209 *(head1)->stqh_last = (head2)->stqh_first; \ 210 (head1)->stqh_last = (head2)->stqh_last; \ 211 XEN_STAILQ_INIT((head2)); \ 212 } \ 213 } while (0) 214 215 #define XEN_STAILQ_EMPTY(head) ((head)->stqh_first == 0) 216 217 #define XEN_STAILQ_FIRST(head) ((head)->stqh_first) 218 219 #define XEN_STAILQ_FOREACH(var, head, field) \ 220 for((var) = XEN_STAILQ_FIRST((head)); \ 221 (var); \ 222 (var) = XEN_STAILQ_NEXT((var), field)) 223 224 225 #define XEN_STAILQ_FOREACH_SAFE(var, head, field, tvar) \ 226 for ((var) = XEN_STAILQ_FIRST((head)); \ 227 (var) && ((tvar) = XEN_STAILQ_NEXT((var), field), 1); \ 228 (var) = (tvar)) 229 230 #define XEN_STAILQ_INIT(head) do { \ 231 XEN_STAILQ_FIRST((head)) = 0; \ 232 (head)->stqh_last = &XEN_STAILQ_FIRST((head)); \ 233 } while (0) 234 235 #define XEN_STAILQ_INSERT_AFTER(head, tqelm, elm, field) do { \ 236 if ((XEN_STAILQ_NEXT((elm), field) = XEN_STAILQ_NEXT((tqelm), field)) == 0)\ 237 (head)->stqh_last = &XEN_STAILQ_NEXT((elm), field); \ 238 XEN_STAILQ_NEXT((tqelm), field) = (elm); \ 239 } while (0) 240 241 #define XEN_STAILQ_INSERT_HEAD(head, elm, field) do { \ 242 if ((XEN_STAILQ_NEXT((elm), field) = XEN_STAILQ_FIRST((head))) == 0)\ 243 (head)->stqh_last = &XEN_STAILQ_NEXT((elm), field); \ 244 XEN_STAILQ_FIRST((head)) = (elm); \ 245 } while (0) 246 247 #define XEN_STAILQ_INSERT_TAIL(head, elm, field) do { \ 248 XEN_STAILQ_NEXT((elm), field) = 0; \ 249 *(head)->stqh_last = (elm); \ 250 (head)->stqh_last = &XEN_STAILQ_NEXT((elm), field); \ 251 } while (0) 252 253 #define XEN_STAILQ_LAST(head, type, field) \ 254 (XEN_STAILQ_EMPTY((head)) ? \ 255 0 : \ 256 ((type *)(void *) \ 257 ((char *)((head)->stqh_last) - offsetof(type, field)))) 258 259 #define XEN_STAILQ_NEXT(elm, field) ((elm)->field.stqe_next) 260 261 #define XEN_STAILQ_REMOVE(head, elm, type, field) do { \ 262 if (XEN_STAILQ_FIRST((head)) == (elm)) { \ 263 XEN_STAILQ_REMOVE_HEAD((head), field); \ 264 } \ 265 else { \ 266 type *curelm = XEN_STAILQ_FIRST((head)); \ 267 while (XEN_STAILQ_NEXT(curelm, field) != (elm)) \ 268 curelm = XEN_STAILQ_NEXT(curelm, field); \ 269 XEN_STAILQ_REMOVE_AFTER(head, curelm, field); \ 270 } \ 271 } while (0) 272 273 #define XEN_STAILQ_REMOVE_AFTER(head, elm, field) do { \ 274 if ((XEN_STAILQ_NEXT(elm, field) = \ 275 XEN_STAILQ_NEXT(XEN_STAILQ_NEXT(elm, field), field)) == 0) \ 276 (head)->stqh_last = &XEN_STAILQ_NEXT((elm), field); \ 277 } while (0) 278 279 #define XEN_STAILQ_REMOVE_HEAD(head, field) do { \ 280 if ((XEN_STAILQ_FIRST((head)) = \ 281 XEN_STAILQ_NEXT(XEN_STAILQ_FIRST((head)), field)) == 0) \ 282 (head)->stqh_last = &XEN_STAILQ_FIRST((head)); \ 283 } while (0) 284 285 #define XEN_STAILQ_SWAP(head1, head2, type) do { \ 286 type *swap_first = XEN_STAILQ_FIRST(head1); \ 287 type **swap_last = (head1)->stqh_last; \ 288 XEN_STAILQ_FIRST(head1) = XEN_STAILQ_FIRST(head2); \ 289 (head1)->stqh_last = (head2)->stqh_last; \ 290 XEN_STAILQ_FIRST(head2) = swap_first; \ 291 (head2)->stqh_last = swap_last; \ 292 if (XEN_STAILQ_EMPTY(head1)) \ 293 (head1)->stqh_last = &XEN_STAILQ_FIRST(head1); \ 294 if (XEN_STAILQ_EMPTY(head2)) \ 295 (head2)->stqh_last = &XEN_STAILQ_FIRST(head2); \ 296 } while (0) 297 298 299 /* 300 * List declarations. 301 */ 302 #define XEN_LIST_HEAD(name, type) \ 303 struct name { \ 304 type *lh_first; /* first element */ \ 305 } 306 307 #define XEN_LIST_HEAD_INITIALIZER(head) \ 308 { 0 } 309 310 #define XEN_LIST_ENTRY(type) \ 311 struct { \ 312 type *le_next; /* next element */ \ 313 type **le_prev; /* address of previous next element */ \ 314 } 315 316 /* 317 * List functions. 318 */ 319 320 #define XEN_LIST_EMPTY(head) ((head)->lh_first == 0) 321 322 #define XEN_LIST_FIRST(head) ((head)->lh_first) 323 324 #define XEN_LIST_FOREACH(var, head, field) \ 325 for ((var) = XEN_LIST_FIRST((head)); \ 326 (var); \ 327 (var) = XEN_LIST_NEXT((var), field)) 328 329 #define XEN_LIST_FOREACH_SAFE(var, head, field, tvar) \ 330 for ((var) = XEN_LIST_FIRST((head)); \ 331 (var) && ((tvar) = XEN_LIST_NEXT((var), field), 1); \ 332 (var) = (tvar)) 333 334 #define XEN_LIST_INIT(head) do { \ 335 XEN_LIST_FIRST((head)) = 0; \ 336 } while (0) 337 338 #define XEN_LIST_INSERT_AFTER(listelm, elm, field) do { \ 339 if ((XEN_LIST_NEXT((elm), field) = XEN_LIST_NEXT((listelm), field)) != 0)\ 340 XEN_LIST_NEXT((listelm), field)->field.le_prev = \ 341 &XEN_LIST_NEXT((elm), field); \ 342 XEN_LIST_NEXT((listelm), field) = (elm); \ 343 (elm)->field.le_prev = &XEN_LIST_NEXT((listelm), field); \ 344 } while (0) 345 346 #define XEN_LIST_INSERT_BEFORE(listelm, elm, field) do { \ 347 (elm)->field.le_prev = (listelm)->field.le_prev; \ 348 XEN_LIST_NEXT((elm), field) = (listelm); \ 349 *(listelm)->field.le_prev = (elm); \ 350 (listelm)->field.le_prev = &XEN_LIST_NEXT((elm), field); \ 351 } while (0) 352 353 #define XEN_LIST_INSERT_HEAD(head, elm, field) do { \ 354 if ((XEN_LIST_NEXT((elm), field) = XEN_LIST_FIRST((head))) != 0)\ 355 XEN_LIST_FIRST((head))->field.le_prev = &XEN_LIST_NEXT((elm), field);\ 356 XEN_LIST_FIRST((head)) = (elm); \ 357 (elm)->field.le_prev = &XEN_LIST_FIRST((head)); \ 358 } while (0) 359 360 #define XEN_LIST_NEXT(elm, field) ((elm)->field.le_next) 361 362 #define XEN_LIST_REMOVE(elm, field) do { \ 363 if (XEN_LIST_NEXT((elm), field) != 0) \ 364 XEN_LIST_NEXT((elm), field)->field.le_prev = \ 365 (elm)->field.le_prev; \ 366 *(elm)->field.le_prev = XEN_LIST_NEXT((elm), field); \ 367 } while (0) 368 369 #define XEN_LIST_SWAP(head1, head2, type, field) do { \ 370 type *swap_tmp = XEN_LIST_FIRST((head1)); \ 371 XEN_LIST_FIRST((head1)) = XEN_LIST_FIRST((head2)); \ 372 XEN_LIST_FIRST((head2)) = swap_tmp; \ 373 if ((swap_tmp = XEN_LIST_FIRST((head1))) != 0) \ 374 swap_tmp->field.le_prev = &XEN_LIST_FIRST((head1)); \ 375 if ((swap_tmp = XEN_LIST_FIRST((head2))) != 0) \ 376 swap_tmp->field.le_prev = &XEN_LIST_FIRST((head2)); \ 377 } while (0) 378 379 /* 380 * Tail queue declarations. 381 */ 382 #define XEN_TAILQ_HEAD(name, type) \ 383 struct name { \ 384 type *tqh_first; /* first element */ \ 385 type **tqh_last; /* addr of last next element */ \ 386 } 387 388 #define XEN_TAILQ_HEAD_INITIALIZER(head) \ 389 { 0, &(head).tqh_first } 390 391 #define XEN_TAILQ_ENTRY(type) \ 392 struct { \ 393 type *tqe_next; /* next element */ \ 394 type **tqe_prev; /* address of previous next element */ \ 395 } 396 397 /* 398 * Tail queue functions. 399 */ 400 401 #define XEN_TAILQ_CONCAT(head1, head2, field) do { \ 402 if (!XEN_TAILQ_EMPTY(head2)) { \ 403 *(head1)->tqh_last = (head2)->tqh_first; \ 404 (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last; \ 405 (head1)->tqh_last = (head2)->tqh_last; \ 406 XEN_TAILQ_INIT((head2)); \ 407 } \ 408 } while (0) 409 410 #define XEN_TAILQ_EMPTY(head) ((head)->tqh_first == 0) 411 412 #define XEN_TAILQ_FIRST(head) ((head)->tqh_first) 413 414 #define XEN_TAILQ_FOREACH(var, head, field) \ 415 for ((var) = XEN_TAILQ_FIRST((head)); \ 416 (var); \ 417 (var) = XEN_TAILQ_NEXT((var), field)) 418 419 #define XEN_TAILQ_FOREACH_SAFE(var, head, field, tvar) \ 420 for ((var) = XEN_TAILQ_FIRST((head)); \ 421 (var) && ((tvar) = XEN_TAILQ_NEXT((var), field), 1); \ 422 (var) = (tvar)) 423 424 #define XEN_TAILQ_FOREACH_REVERSE(var, head, headname, field) \ 425 for ((var) = XEN_TAILQ_LAST((head), headname); \ 426 (var); \ 427 (var) = XEN_TAILQ_PREV((var), headname, field)) 428 429 #define XEN_TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar) \ 430 for ((var) = XEN_TAILQ_LAST((head), headname); \ 431 (var) && ((tvar) = XEN_TAILQ_PREV((var), headname, field), 1);\ 432 (var) = (tvar)) 433 434 #define XEN_TAILQ_INIT(head) do { \ 435 XEN_TAILQ_FIRST((head)) = 0; \ 436 (head)->tqh_last = &XEN_TAILQ_FIRST((head)); \ 437 } while (0) 438 439 #define XEN_TAILQ_INSERT_AFTER(head, listelm, elm, field) do { \ 440 if ((XEN_TAILQ_NEXT((elm), field) = XEN_TAILQ_NEXT((listelm), field)) != 0)\ 441 XEN_TAILQ_NEXT((elm), field)->field.tqe_prev = \ 442 &XEN_TAILQ_NEXT((elm), field); \ 443 else { \ 444 (head)->tqh_last = &XEN_TAILQ_NEXT((elm), field); \ 445 } \ 446 XEN_TAILQ_NEXT((listelm), field) = (elm); \ 447 (elm)->field.tqe_prev = &XEN_TAILQ_NEXT((listelm), field); \ 448 } while (0) 449 450 #define XEN_TAILQ_INSERT_BEFORE(listelm, elm, field) do { \ 451 (elm)->field.tqe_prev = (listelm)->field.tqe_prev; \ 452 XEN_TAILQ_NEXT((elm), field) = (listelm); \ 453 *(listelm)->field.tqe_prev = (elm); \ 454 (listelm)->field.tqe_prev = &XEN_TAILQ_NEXT((elm), field); \ 455 } while (0) 456 457 #define XEN_TAILQ_INSERT_HEAD(head, elm, field) do { \ 458 if ((XEN_TAILQ_NEXT((elm), field) = XEN_TAILQ_FIRST((head))) != 0)\ 459 XEN_TAILQ_FIRST((head))->field.tqe_prev = \ 460 &XEN_TAILQ_NEXT((elm), field); \ 461 else \ 462 (head)->tqh_last = &XEN_TAILQ_NEXT((elm), field); \ 463 XEN_TAILQ_FIRST((head)) = (elm); \ 464 (elm)->field.tqe_prev = &XEN_TAILQ_FIRST((head)); \ 465 } while (0) 466 467 #define XEN_TAILQ_INSERT_TAIL(head, elm, field) do { \ 468 XEN_TAILQ_NEXT((elm), field) = 0; \ 469 (elm)->field.tqe_prev = (head)->tqh_last; \ 470 *(head)->tqh_last = (elm); \ 471 (head)->tqh_last = &XEN_TAILQ_NEXT((elm), field); \ 472 } while (0) 473 474 #define XEN_TAILQ_LAST(head, headname) \ 475 (*(((struct headname *)((head)->tqh_last))->tqh_last)) 476 477 #define XEN_TAILQ_NEXT(elm, field) ((elm)->field.tqe_next) 478 479 #define XEN_TAILQ_PREV(elm, headname, field) \ 480 (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last)) 481 482 #define XEN_TAILQ_REMOVE(head, elm, field) do { \ 483 if ((XEN_TAILQ_NEXT((elm), field)) != 0) \ 484 XEN_TAILQ_NEXT((elm), field)->field.tqe_prev = \ 485 (elm)->field.tqe_prev; \ 486 else { \ 487 (head)->tqh_last = (elm)->field.tqe_prev; \ 488 } \ 489 *(elm)->field.tqe_prev = XEN_TAILQ_NEXT((elm), field); \ 490 } while (0) 491 492 #define XEN_TAILQ_SWAP(head1, head2, type, field) do { \ 493 type *swap_first = (head1)->tqh_first; \ 494 type **swap_last = (head1)->tqh_last; \ 495 (head1)->tqh_first = (head2)->tqh_first; \ 496 (head1)->tqh_last = (head2)->tqh_last; \ 497 (head2)->tqh_first = swap_first; \ 498 (head2)->tqh_last = swap_last; \ 499 if ((swap_first = (head1)->tqh_first) != 0) \ 500 swap_first->field.tqe_prev = &(head1)->tqh_first; \ 501 else \ 502 (head1)->tqh_last = &(head1)->tqh_first; \ 503 if ((swap_first = (head2)->tqh_first) != 0) \ 504 swap_first->field.tqe_prev = &(head2)->tqh_first; \ 505 else \ 506 (head2)->tqh_last = &(head2)->tqh_first; \ 507 } while (0) 508 509 #endif /* !XEN__SYS_QUEUE_H_ */ 510