resolv/res_init.c

   1 /*
   2  * Copyright (c) 1985, 1989, 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
  30 /*
  31  * Portions Copyright (c) 1993 by Digital Equipment Corporation.
  32  *
  33  * Permission to use, copy, modify, and distribute this software for any
  34  * purpose with or without fee is hereby granted, provided that the above
  35  * copyright notice and this permission notice appear in all copies, and that
  36  * the name of Digital Equipment Corporation not be used in advertising or
  37  * publicity pertaining to distribution of the document or software without
  38  * specific, written prior permission.
  39  *
  40  * THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
  41  * WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
  42  * OF MERCHANTABILITY AND FITNESS.   IN NO EVENT SHALL DIGITAL EQUIPMENT
  43  * CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  44  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  45  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  46  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  47  * SOFTWARE.
  48  */
  49
  50 /*
  51  * Portions Copyright (c) 1996-1999 by Internet Software Consortium.
  52  *
  53  * Permission to use, copy, modify, and distribute this software for any
  54  * purpose with or without fee is hereby granted, provided that the above
  55  * copyright notice and this permission notice appear in all copies.
  56  *
  57  * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
  58  * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
  59  * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
  60  * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  61  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  62  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  63  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  64  * SOFTWARE.
  65  */
  66
  67 #if defined(LIBC_SCCS) && !defined(lint)
  68 static const char sccsid[] = "@(#)res_init.c    8.1 (Berkeley) 6/7/93";
  69 static const char rcsid[] = "$BINDId: res_init.c,v 8.16 2000/05/09 07:10:12 vixie Exp $";
  70 #endif /* LIBC_SCCS and not lint */
  71
  72 #include <sys/types.h>
  73 #include <sys/param.h>
  74 #include <sys/socket.h>
  75 #include <sys/time.h>
  76
  77 #include <netinet/in.h>
  78 #include <arpa/inet.h>
  79 #include <arpa/nameser.h>
  80
  81 #include <ctype.h>
  82 #include <resolv.h>
  83 #include <stdio.h>
  84 #include <stdio_ext.h>
  85 #include <stdlib.h>
  86 #include <string.h>
  87 #include <unistd.h>
  88
  89 /* Options.  Should all be left alone. */
  90 #define RESOLVSORT
  91 #define RFC1535
  92 /* #undef DEBUG */
  93
  94 static void res_setoptions (res_state, const char *, const char *)
  95      internal_function;
  96
  97 #ifdef RESOLVSORT
  98 static const char sort_mask_chars[] = "/&";
  99 #define ISSORTMASK(ch) (strchr(sort_mask_chars, ch) != NULL)
 100 static u_int32_t net_mask __P((struct in_addr));
 101 #endif
 102
 103 #if !defined(isascii)   /* XXX - could be a function */
 104 # define isascii(c) (!(c & 0200))
 105 #endif
 106
 107 /*
 108  * Resolver state default settings.
 109  */
 110
 111 /*
 112  * Set up default settings.  If the configuration file exist, the values
 113  * there will have precedence.  Otherwise, the server address is set to
 114  * INADDR_ANY and the default domain name comes from the gethostname().
 115  *
 116  * An interrim version of this code (BIND 4.9, pre-4.4BSD) used 127.0.0.1
 117  * rather than INADDR_ANY ("0.0.0.0") as the default name server address
 118  * since it was noted that INADDR_ANY actually meant ``the first interface
 119  * you "ifconfig"'d at boot time'' and if this was a SLIP or PPP interface,
 120  * it had to be "up" in order for you to reach your own name server.  It
 121  * was later decided that since the recommended practice is to always
 122  * install local static routes through 127.0.0.1 for all your network
 123  * interfaces, that we could solve this problem without a code change.
 124  *
 125  * The configuration file should always be used, since it is the only way
 126  * to specify a default domain.  If you are running a server on your local
 127  * machine, you should say "nameserver 0.0.0.0" or "nameserver 127.0.0.1"
 128  * in the configuration file.
 129  *
 130  * Return 0 if completes successfully, -1 on error
 131  */
 132 int
 133 res_ninit(res_state statp) {
 134         extern int __res_vinit(res_state, int);
 135
 136         return (__res_vinit(statp, 0));
 137 }
 138 #ifdef _LIBC
 139 libc_hidden_def (__res_ninit)
 140 #endif
 141
 142 /* This function has to be reachable by res_data.c but not publically. */
 143 int
 144 __res_vinit(res_state statp, int preinit) {
 145         register FILE *fp;
 146         register char *cp, **pp;
 147         register int n;
 148         char buf[BUFSIZ];
 149         int nserv = 0;    /* number of nameserver records read from file */
 150 #ifdef _LIBC
 151         int nservall = 0; /* number of NS records read, nserv IPv4 only */
 152 #endif
 153         int haveenv = 0;
 154         int havesearch = 0;
 155 #ifdef RESOLVSORT
 156         int nsort = 0;
 157         char *net;
 158 #endif
 159 #ifndef RFC1535
 160         int dots;
 161 #endif
 162
 163         if (!preinit) {
 164                 statp->retrans = RES_TIMEOUT;
 165                 statp->retry = RES_DFLRETRY;
 166                 statp->options = RES_DEFAULT;
 167                 statp->id = res_randomid();
 168         }
 169
 170 #ifdef USELOOPBACK
 171         statp->nsaddr.sin_addr = inet_makeaddr(IN_LOOPBACKNET, 1);
 172 #else
 173         statp->nsaddr.sin_addr.s_addr = INADDR_ANY;
 174 #endif
 175         statp->nsaddr.sin_family = AF_INET;
 176         statp->nsaddr.sin_port = htons(NAMESERVER_PORT);
 177         statp->nscount = 1;
 178         statp->ndots = 1;
 179         statp->pfcode = 0;
 180         statp->_vcsock = -1;
 181         statp->_flags = 0;
 182         statp->qhook = NULL;
 183         statp->rhook = NULL;
 184         statp->_u._ext.nsinit = 0;
 185         statp->_u._ext.nscount = 0;
 186 #ifdef _LIBC
 187         statp->_u._ext.nscount6 = 0;
 188         for (n = 0; n < MAXNS; n++) {
 189                 statp->_u._ext.nsaddrs[n] = NULL;
 190                 statp->_u._ext.nsmap[n] = MAXNS;
 191         }
 192 #endif
 193
 194         /* Allow user to override the local domain definition */
 195         if ((cp = getenv("LOCALDOMAIN")) != NULL) {
 196                 (void)strncpy(statp->defdname, cp, sizeof(statp->defdname) - 1);
 197                 statp->defdname[sizeof(statp->defdname) - 1] = '\0';
 198                 haveenv++;
 199
 200                 /*
 201                  * Set search list to be blank-separated strings
 202                  * from rest of env value.  Permits users of LOCALDOMAIN
 203                  * to still have a search list, and anyone to set the
 204                  * one that they want to use as an individual (even more
 205                  * important now that the rfc1535 stuff restricts searches)
 206                  */
 207                 cp = statp->defdname;
 208                 pp = statp->dnsrch;
 209                 *pp++ = cp;
 210                 for (n = 0; *cp && pp < statp->dnsrch + MAXDNSRCH; cp++) {
 211                         if (*cp == '\n')        /* silly backwards compat */
 212                                 break;
 213                         else if (*cp == ' ' || *cp == '\t') {
 214                                 *cp = 0;
 215                                 n = 1;
 216                         } else if (n) {
 217                                 *pp++ = cp;
 218                                 n = 0;
 219                                 havesearch = 1;
 220                         }
 221                 }
 222                 /* null terminate last domain if there are excess */
 223                 while (*cp != '\0' && *cp != ' ' && *cp != '\t' && *cp != '\n')
 224                         cp++;
 225                 *cp = '\0';
 226                 *pp++ = 0;
 227         }
 228
 229 #define MATCH(line, name) \
 230         (!strncmp(line, name, sizeof(name) - 1) && \
 231         (line[sizeof(name) - 1] == ' ' || \
 232          line[sizeof(name) - 1] == '\t'))
 233
 234         if ((fp = fopen(_PATH_RESCONF, "r")) != NULL) {
 235                 /* No threads use this stream.  */
 236                 __fsetlocking (fp, FSETLOCKING_BYCALLER);
 237             /* read the config file */
 238             while (fgets_unlocked(buf, sizeof(buf), fp) != NULL) {
 239                 /* skip comments */
 240                 if (*buf == ';' || *buf == '#')
 241                         continue;
 242                 /* read default domain name */
 243                 if (MATCH(buf, "domain")) {
 244                     if (haveenv)        /* skip if have from environ */
 245                             continue;
 246                     cp = buf + sizeof("domain") - 1;
 247                     while (*cp == ' ' || *cp == '\t')
 248                             cp++;
 249                     if ((*cp == '\0') || (*cp == '\n'))
 250                             continue;
 251                     strncpy(statp->defdname, cp, sizeof(statp->defdname) - 1);
 252                     statp->defdname[sizeof(statp->defdname) - 1] = '\0';
 253                     if ((cp = strpbrk(statp->defdname, " \t\n")) != NULL)
 254                             *cp = '\0';
 255                     havesearch = 0;
 256                     continue;
 257                 }
 258                 /* set search list */
 259                 if (MATCH(buf, "search")) {
 260                     if (haveenv)        /* skip if have from environ */
 261                             continue;
 262                     cp = buf + sizeof("search") - 1;
 263                     while (*cp == ' ' || *cp == '\t')
 264                             cp++;
 265                     if ((*cp == '\0') || (*cp == '\n'))
 266                             continue;
 267                     strncpy(statp->defdname, cp, sizeof(statp->defdname) - 1);
 268                     statp->defdname[sizeof(statp->defdname) - 1] = '\0';
 269                     if ((cp = strchr(statp->defdname, '\n')) != NULL)
 270                             *cp = '\0';
 271                     /*
 272                      * Set search list to be blank-separated strings
 273                      * on rest of line.
 274                      */
 275                     cp = statp->defdname;
 276                     pp = statp->dnsrch;
 277                     *pp++ = cp;
 278                     for (n = 0; *cp && pp < statp->dnsrch + MAXDNSRCH; cp++) {
 279                             if (*cp == ' ' || *cp == '\t') {
 280                                     *cp = 0;
 281                                     n = 1;
 282                             } else if (n) {
 283                                     *pp++ = cp;
 284                                     n = 0;
 285                             }
 286                     }
 287                     /* null terminate last domain if there are excess */
 288                     while (*cp != '\0' && *cp != ' ' && *cp != '\t')
 289                             cp++;
 290                     *cp = '\0';
 291                     *pp++ = 0;
 292                     havesearch = 1;
 293                     continue;
 294                 }
 295                 /* read nameservers to query */
 296 #ifdef _LIBC
 297                 if (MATCH(buf, "nameserver") && nservall < MAXNS) {
 298 #else
 299                 if (MATCH(buf, "nameserver") && nserv < MAXNS) {
 300 #endif
 301                     struct in_addr a;
 302
 303                     cp = buf + sizeof("nameserver") - 1;
 304                     while (*cp == ' ' || *cp == '\t')
 305                         cp++;
 306                     if ((*cp != '\0') && (*cp != '\n')
 307                         && __inet_aton(cp, &a)) {
 308                         statp->nsaddr_list[nserv].sin_addr = a;
 309                         statp->nsaddr_list[nserv].sin_family = AF_INET;
 310                         statp->nsaddr_list[nserv].sin_port =
 311                                 htons(NAMESERVER_PORT);
 312                         nserv++;
 313 #ifdef _LIBC
 314                         nservall++;
 315                     } else {
 316                         struct in6_addr a6;
 317                         char *el;
 318
 319                         if ((el = strchr(cp, '\n')) != NULL)
 320                             *el = '\0';
 321                         if ((*cp != '\0') &&
 322                             (inet_pton(AF_INET6, cp, &a6) > 0)) {
 323                             struct sockaddr_in6 *sa6;
 324
 325                             sa6 = malloc(sizeof(*sa6));
 326                             if (sa6 != NULL) {
 327                                 sa6->sin6_addr = a6;
 328                                 sa6->sin6_family = AF_INET6;
 329                                 sa6->sin6_port = htons(NAMESERVER_PORT);
 330                                 statp->_u._ext.nsaddrs[nservall] = sa6;
 331                                 statp->_u._ext.nssocks[nservall] = -1;
 332                                 statp->_u._ext.nsmap[nservall] = MAXNS + 1;
 333                                 nservall++;
 334                             }
 335                         }
 336 #endif
 337                     }
 338                     continue;
 339                 }
 340 #ifdef RESOLVSORT
 341                 if (MATCH(buf, "sortlist")) {
 342                     struct in_addr a;
 343
 344                     cp = buf + sizeof("sortlist") - 1;
 345                     while (nsort < MAXRESOLVSORT) {
 346                         while (*cp == ' ' || *cp == '\t')
 347                             cp++;
 348                         if (*cp == '\0' || *cp == '\n' || *cp == ';')
 349                             break;
 350                         net = cp;
 351                         while (*cp && !ISSORTMASK(*cp) && *cp != ';' &&
 352                                isascii(*cp) && !isspace(*cp))
 353                                 cp++;
 354                         n = *cp;
 355                         *cp = 0;
 356                         if (__inet_aton(net, &a)) {
 357                             statp->sort_list[nsort].addr = a;
 358                             if (ISSORTMASK(n)) {
 359                                 *cp++ = n;
 360                                 net = cp;
 361                                 while (*cp && *cp != ';' &&
 362                                         isascii(*cp) && !isspace(*cp))
 363                                     cp++;
 364                                 n = *cp;
 365                                 *cp = 0;
 366                                 if (__inet_aton(net, &a)) {
 367                                     statp->sort_list[nsort].mask = a.s_addr;
 368                                 } else {
 369                                     statp->sort_list[nsort].mask =
 370                                         net_mask(statp->sort_list[nsort].addr);
 371                                 }
 372                             } else {
 373                                 statp->sort_list[nsort].mask =
 374                                     net_mask(statp->sort_list[nsort].addr);
 375                             }
 376                             nsort++;
 377                         }
 378                         *cp = n;
 379                     }
 380                     continue;
 381                 }
 382 #endif
 383                 if (MATCH(buf, "options")) {
 384                     res_setoptions(statp, buf + sizeof("options") - 1, "conf");
 385                     continue;
 386                 }
 387             }
 388             if (nserv > 1)
 389                 statp->nscount = nserv;
 390 #ifdef _LIBC
 391             if (nservall - nserv > 0)
 392                 statp->_u._ext.nscount6 = nservall - nserv;
 393 #endif
 394 #ifdef RESOLVSORT
 395             statp->nsort = nsort;
 396 #endif
 397             (void) fclose(fp);
 398         }
 399         if (statp->defdname[0] == 0 &&
 400             __gethostname(buf, sizeof(statp->defdname) - 1) == 0 &&
 401             (cp = strchr(buf, '.')) != NULL)
 402                 strcpy(statp->defdname, cp + 1);
 403
 404         /* find components of local domain that might be searched */
 405         if (havesearch == 0) {
 406                 pp = statp->dnsrch;
 407                 *pp++ = statp->defdname;
 408                 *pp = NULL;
 409
 410 #ifndef RFC1535
 411                 dots = 0;
 412                 for (cp = statp->defdname; *cp; cp++)
 413                         dots += (*cp == '.');
 414
 415                 cp = statp->defdname;
 416                 while (pp < statp->dnsrch + MAXDFLSRCH) {
 417                         if (dots < LOCALDOMAINPARTS)
 418                                 break;
 419                         cp = __rawmemchr(cp, '.') + 1;    /* we know there is one */
 420                         *pp++ = cp;
 421                         dots--;
 422                 }
 423                 *pp = NULL;
 424 #ifdef DEBUG
 425                 if (statp->options & RES_DEBUG) {
 426                         printf(";; res_init()... default dnsrch list:\n");
 427                         for (pp = statp->dnsrch; *pp; pp++)
 428                                 printf(";;\t%s\n", *pp);
 429                         printf(";;\t..END..\n");
 430                 }
 431 #endif
 432 #endif /* !RFC1535 */
 433         }
 434
 435         if ((cp = getenv("RES_OPTIONS")) != NULL)
 436                 res_setoptions(statp, cp, "env");
 437         statp->options |= RES_INIT;
 438         return (0);
 439 }
 440
 441 static void
 442 internal_function
 443 res_setoptions(res_state statp, const char *options, const char *source) {
 444         const char *cp = options;
 445         int i;
 446
 447 #ifdef DEBUG
 448         if (statp->options & RES_DEBUG)
 449                 printf(";; res_setoptions(\"%s\", \"%s\")...\n",
 450                        options, source);
 451 #endif
 452         while (*cp) {
 453                 /* skip leading and inner runs of spaces */
 454                 while (*cp == ' ' || *cp == '\t')
 455                         cp++;
 456                 /* search for and process individual options */
 457                 if (!strncmp(cp, "ndots:", sizeof("ndots:") - 1)) {
 458                         i = atoi(cp + sizeof("ndots:") - 1);
 459                         if (i <= RES_MAXNDOTS)
 460                                 statp->ndots = i;
 461                         else
 462                                 statp->ndots = RES_MAXNDOTS;
 463 #ifdef DEBUG
 464                         if (statp->options & RES_DEBUG)
 465                                 printf(";;\tndots=%d\n", statp->ndots);
 466 #endif
 467                 } else if (!strncmp(cp, "timeout:", sizeof("timeout:") - 1)) {
 468                         i = atoi(cp + sizeof("timeout:") - 1);
 469                         if (i <= RES_MAXRETRANS)
 470                                 statp->retrans = i;
 471                         else
 472                                 statp->retrans = RES_MAXRETRANS;
 473                 } else if (!strncmp(cp, "attempts:", sizeof("attempts:") - 1)){
 474                         i = atoi(cp + sizeof("attempts:") - 1);
 475                         if (i <= RES_MAXRETRY)
 476                                 statp->retry = i;
 477                         else
 478                                 statp->retry = RES_MAXRETRY;
 479                 } else if (!strncmp(cp, "debug", sizeof("debug") - 1)) {
 480 #ifdef DEBUG
 481                         if (!(statp->options & RES_DEBUG)) {
 482                                 printf(";; res_setoptions(\"%s\", \"%s\")..\n",
 483                                        options, source);
 484                                 statp->options |= RES_DEBUG;
 485                         }
 486                         printf(";;\tdebug\n");
 487 #endif
 488                 } else if (!strncmp(cp, "inet6", sizeof("inet6") - 1)) {
 489                         statp->options |= RES_USE_INET6;
 490                 } else if (!strncmp(cp, "rotate", sizeof("rotate") - 1)) {
 491                         statp->options |= RES_ROTATE;
 492                 } else if (!strncmp(cp, "no-check-names",
 493                                     sizeof("no-check-names") - 1)) {
 494                         statp->options |= RES_NOCHECKNAME;
 495                 } else {
 496                         /* XXX - print a warning here? */
 497                 }
 498                 /* skip to next run of spaces */
 499                 while (*cp && *cp != ' ' && *cp != '\t')
 500                         cp++;
 501         }
 502 }
 503
 504 #ifdef RESOLVSORT
 505 /* XXX - should really support CIDR which means explicit masks always. */
 506 static u_int32_t
 507 net_mask(in)            /* XXX - should really use system's version of this */
 508         struct in_addr in;
 509 {
 510         register u_int32_t i = ntohl(in.s_addr);
 511
 512         if (IN_CLASSA(i))
 513                 return (htonl(IN_CLASSA_NET));
 514         else if (IN_CLASSB(i))
 515                 return (htonl(IN_CLASSB_NET));
 516         return (htonl(IN_CLASSC_NET));
 517 }
 518 #endif
 519
 520 u_int
 521 res_randomid(void) {
 522         struct timeval now;
 523
 524         __gettimeofday(&now, NULL);
 525         return (0xffff & (now.tv_sec ^ now.tv_usec ^ __getpid()));
 526 }
 527 #ifdef _LIBC
 528 libc_hidden_def (__res_randomid)
 529 #endif
 530
 531
 532 /*
 533  * This routine is for closing the socket if a virtual circuit is used and
 534  * the program wants to close it.  This provides support for endhostent()
 535  * which expects to close the socket.
 536  *
 537  * This routine is not expected to be user visible.
 538  */
 539 void
 540 res_nclose(res_state statp) {
 541         int ns;
 542
 543         if (statp->_vcsock >= 0) {
 544                 (void) __close(statp->_vcsock);
 545                 statp->_vcsock = -1;
 546                 statp->_flags &= ~(RES_F_VC | RES_F_CONN);
 547         }
 548 #ifdef _LIBC
 549         for (ns = 0; ns < MAXNS; ns++)
 550 #else
 551         for (ns = 0; ns < statp->_u._ext.nscount; ns++)
 552 #endif
 553                 if (statp->_u._ext.nsaddrs[ns]
 554                     && statp->_u._ext.nssocks[ns] != -1) {
 555                         (void) __close(statp->_u._ext.nssocks[ns]);
 556                         statp->_u._ext.nssocks[ns] = -1;
 557                 }
 558         statp->_u._ext.nsinit = 0;
 559 }
 560 #ifdef _LIBC
 561 libc_hidden_def (__res_nclose)
 562 #endif
 563
 564 #ifdef _LIBC
 565 # ifdef _LIBC_REENTRANT
 566 /* This is called when a thread is exiting to free resources held in _res.  */
 567 static void __attribute__ ((section ("__libc_thread_freeres_fn")))
 568 res_thread_freeres (void)
 569 {
 570   if (_res.nscount == 0)
 571     /* Never called res_ninit.  */
 572     return;
 573
 574   __res_nclose (&_res);         /* Close any VC sockets.  */
 575
 576   for (int ns = 0; ns < MAXNS; ns++)
 577     if (_res._u._ext.nsaddrs[ns] != NULL)
 578       {
 579         free (_res._u._ext.nsaddrs[ns]);
 580         _res._u._ext.nsaddrs[ns] = NULL;
 581       }
 582 }
 583 text_set_element (__libc_thread_subfreeres, res_thread_freeres);
 584 text_set_element (__libc_subfreeres, res_thread_freeres);
 585 # endif
 586 #endif