572 lines
14 KiB
C
572 lines
14 KiB
C
/* Copyright (C) 1993-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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/* This file provides a Linux /etc/host.conf compatible front end to
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the various name resolvers (/etc/hosts, named, NIS server, etc.).
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Though mostly compatibly, the following differences exist compared
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to the original implementation:
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- line comments can appear anywhere (not just at the beginning of
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a line)
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*/
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#include <assert.h>
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#include <errno.h>
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#include <ctype.h>
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#include <libintl.h>
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#include <memory.h>
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#include <stdio.h>
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#include <stdio_ext.h>
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#include <stdlib.h>
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#include <string.h>
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#include <net/if.h>
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#include <sys/ioctl.h>
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#include <unistd.h>
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#include <netinet/in.h>
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#include <libc-lock.h>
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#include "ifreq.h"
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#include "res_hconf.h"
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#include <wchar.h>
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#include <atomic.h>
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#if IS_IN (libc)
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# define fgets_unlocked __fgets_unlocked
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#endif
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#define _PATH_HOSTCONF "/etc/host.conf"
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/* Environment vars that all user to override default behavior: */
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#define ENV_HOSTCONF "RESOLV_HOST_CONF"
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#define ENV_TRIM_OVERR "RESOLV_OVERRIDE_TRIM_DOMAINS"
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#define ENV_TRIM_ADD "RESOLV_ADD_TRIM_DOMAINS"
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#define ENV_MULTI "RESOLV_MULTI"
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#define ENV_REORDER "RESOLV_REORDER"
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enum parse_cbs
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{
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CB_none,
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CB_arg_trimdomain_list,
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CB_arg_bool
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};
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static const struct cmd
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{
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const char name[11];
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uint8_t cb;
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unsigned int arg;
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} cmd[] =
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{
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{"order", CB_none, 0},
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{"trim", CB_arg_trimdomain_list, 0},
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{"multi", CB_arg_bool, HCONF_FLAG_MULTI},
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{"reorder", CB_arg_bool, HCONF_FLAG_REORDER}
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};
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/* Structure containing the state. */
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struct hconf _res_hconf;
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/* Skip white space. */
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static const char *
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skip_ws (const char *str)
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{
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while (isspace (*str)) ++str;
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return str;
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}
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/* Skip until whitespace, comma, end of line, or comment character. */
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static const char *
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skip_string (const char *str)
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{
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while (*str && !isspace (*str) && *str != '#' && *str != ',')
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++str;
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return str;
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}
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static const char *
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arg_trimdomain_list (const char *fname, int line_num, const char *args)
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{
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const char * start;
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size_t len;
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do
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{
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start = args;
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args = skip_string (args);
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len = args - start;
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if (_res_hconf.num_trimdomains >= TRIMDOMAINS_MAX)
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{
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char *buf;
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if (__asprintf (&buf, _("\
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%s: line %d: cannot specify more than %d trim domains"),
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fname, line_num, TRIMDOMAINS_MAX) < 0)
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return 0;
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__fxprintf (NULL, "%s", buf);
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free (buf);
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return 0;
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}
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_res_hconf.trimdomain[_res_hconf.num_trimdomains++] =
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__strndup (start, len);
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args = skip_ws (args);
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switch (*args)
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{
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case ',': case ';': case ':':
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args = skip_ws (++args);
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if (!*args || *args == '#')
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{
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char *buf;
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if (__asprintf (&buf, _("\
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%s: line %d: list delimiter not followed by domain"),
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fname, line_num) < 0)
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return 0;
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__fxprintf (NULL, "%s", buf);
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free (buf);
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return 0;
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}
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default:
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break;
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}
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}
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while (*args && *args != '#');
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return args;
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}
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static const char *
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arg_bool (const char *fname, int line_num, const char *args, unsigned flag)
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{
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if (__strncasecmp (args, "on", 2) == 0)
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{
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args += 2;
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_res_hconf.flags |= flag;
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}
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else if (__strncasecmp (args, "off", 3) == 0)
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{
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args += 3;
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_res_hconf.flags &= ~flag;
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}
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else
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{
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char *buf;
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if (__asprintf (&buf,
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_("%s: line %d: expected `on' or `off', found `%s'\n"),
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fname, line_num, args) < 0)
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return 0;
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__fxprintf (NULL, "%s", buf);
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free (buf);
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return 0;
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}
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return args;
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}
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static void
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parse_line (const char *fname, int line_num, const char *str)
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{
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const char *start;
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const struct cmd *c = 0;
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size_t len;
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size_t i;
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str = skip_ws (str);
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/* skip line comment and empty lines: */
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if (*str == '\0' || *str == '#') return;
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start = str;
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str = skip_string (str);
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len = str - start;
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for (i = 0; i < sizeof (cmd) / sizeof (cmd[0]); ++i)
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{
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if (__strncasecmp (start, cmd[i].name, len) == 0
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&& strlen (cmd[i].name) == len)
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{
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c = &cmd[i];
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break;
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}
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}
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if (c == NULL)
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{
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char *buf;
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if (__asprintf (&buf, _("%s: line %d: bad command `%s'\n"),
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fname, line_num, start) < 0)
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return;
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__fxprintf (NULL, "%s", buf);
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free (buf);
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return;
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}
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/* process args: */
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str = skip_ws (str);
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if (c->cb == CB_arg_trimdomain_list)
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str = arg_trimdomain_list (fname, line_num, str);
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else if (c->cb == CB_arg_bool)
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str = arg_bool (fname, line_num, str, c->arg);
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else
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/* Ignore the line. */
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return;
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if (!str)
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return;
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/* rest of line must contain white space or comment only: */
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while (*str)
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{
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if (!isspace (*str)) {
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if (*str != '#')
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{
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char *buf;
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if (__asprintf (&buf,
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_("%s: line %d: ignoring trailing garbage `%s'\n"),
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fname, line_num, str) < 0)
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break;
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__fxprintf (NULL, "%s", buf);
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free (buf);
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}
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break;
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}
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++str;
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}
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}
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static void
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do_init (void)
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{
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const char *hconf_name;
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int line_num = 0;
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char buf[256], *envval;
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FILE *fp;
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memset (&_res_hconf, '\0', sizeof (_res_hconf));
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hconf_name = getenv (ENV_HOSTCONF);
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if (hconf_name == NULL)
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hconf_name = _PATH_HOSTCONF;
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fp = fopen (hconf_name, "rce");
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if (fp)
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{
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/* No threads using this stream. */
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__fsetlocking (fp, FSETLOCKING_BYCALLER);
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while (fgets_unlocked (buf, sizeof (buf), fp))
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{
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++line_num;
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*__strchrnul (buf, '\n') = '\0';
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parse_line (hconf_name, line_num, buf);
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}
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fclose (fp);
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}
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envval = getenv (ENV_MULTI);
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if (envval)
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arg_bool (ENV_MULTI, 1, envval, HCONF_FLAG_MULTI);
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envval = getenv (ENV_REORDER);
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if (envval)
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arg_bool (ENV_REORDER, 1, envval, HCONF_FLAG_REORDER);
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envval = getenv (ENV_TRIM_ADD);
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if (envval)
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arg_trimdomain_list (ENV_TRIM_ADD, 1, envval);
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envval = getenv (ENV_TRIM_OVERR);
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if (envval)
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{
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_res_hconf.num_trimdomains = 0;
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arg_trimdomain_list (ENV_TRIM_OVERR, 1, envval);
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}
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/* See comments on the declaration of _res_hconf. */
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atomic_store_release (&_res_hconf.initialized, 1);
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}
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/* Initialize hconf datastructure by reading host.conf file and
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environment variables. */
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void
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_res_hconf_init (void)
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{
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__libc_once_define (static, once);
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__libc_once (once, do_init);
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}
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#if IS_IN (libc)
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# if defined SIOCGIFCONF && defined SIOCGIFNETMASK
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/* List of known interfaces. */
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libc_freeres_ptr (
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static struct netaddr
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{
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int addrtype;
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union
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{
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struct
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{
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uint32_t addr;
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uint32_t mask;
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} ipv4;
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} u;
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} *ifaddrs);
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# endif
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/* Reorder addresses returned in a hostent such that the first address
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is an address on the local subnet, if there is such an address.
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Otherwise, nothing is changed.
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Note that this function currently only handles IPv4 addresses. */
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void
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_res_hconf_reorder_addrs (struct hostent *hp)
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{
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#if defined SIOCGIFCONF && defined SIOCGIFNETMASK
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int i, j;
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/* Number of interfaces. Also serves as a flag for the
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double-checked locking idiom. */
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static int num_ifs = -1;
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/* Local copy of num_ifs, for non-atomic access. */
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int num_ifs_local;
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/* We need to protect the dynamic buffer handling. The lock is only
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acquired during initialization. Afterwards, a positive num_ifs
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value indicates completed initialization. */
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__libc_lock_define_initialized (static, lock);
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/* Only reorder if we're supposed to. */
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if ((_res_hconf.flags & HCONF_FLAG_REORDER) == 0)
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return;
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/* Can't deal with anything but IPv4 for now... */
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if (hp->h_addrtype != AF_INET)
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return;
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/* This load synchronizes with the release MO store in the
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initialization block below. */
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num_ifs_local = atomic_load_acquire (&num_ifs);
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if (num_ifs_local <= 0)
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{
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struct ifreq *ifr, *cur_ifr;
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int sd, num, i;
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/* Save errno. */
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int save = errno;
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/* Initialize interface table. */
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/* The SIOCGIFNETMASK ioctl will only work on an AF_INET socket. */
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sd = __socket (AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
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if (sd < 0)
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return;
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/* Get lock. */
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__libc_lock_lock (lock);
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/* Recheck, somebody else might have done the work by now. No
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ordering is required for the load because we have the lock,
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and num_ifs is only updated under the lock. Also see (3) in
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the analysis below. */
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num_ifs_local = atomic_load_relaxed (&num_ifs);
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if (num_ifs_local <= 0)
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{
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/* This is the only block which writes to num_ifs. It can
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be executed several times (sequentially) if
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initialization does not yield any interfaces, and num_ifs
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remains zero. However, once we stored a positive value
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in num_ifs below, this block cannot be entered again due
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to the condition above. */
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int new_num_ifs = 0;
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/* Get a list of interfaces. */
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__ifreq (&ifr, &num, sd);
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if (!ifr)
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goto cleanup;
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ifaddrs = malloc (num * sizeof (ifaddrs[0]));
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if (!ifaddrs)
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goto cleanup1;
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/* Copy usable interfaces in ifaddrs structure. */
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for (cur_ifr = ifr, i = 0; i < num;
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cur_ifr = __if_nextreq (cur_ifr), ++i)
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{
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union
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{
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struct sockaddr sa;
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struct sockaddr_in sin;
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} ss;
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if (cur_ifr->ifr_addr.sa_family != AF_INET)
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continue;
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ifaddrs[new_num_ifs].addrtype = AF_INET;
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ss.sa = cur_ifr->ifr_addr;
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ifaddrs[new_num_ifs].u.ipv4.addr = ss.sin.sin_addr.s_addr;
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if (__ioctl (sd, SIOCGIFNETMASK, cur_ifr) < 0)
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continue;
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ss.sa = cur_ifr->ifr_netmask;
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ifaddrs[new_num_ifs].u.ipv4.mask = ss.sin.sin_addr.s_addr;
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/* Now we're committed to this entry. */
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++new_num_ifs;
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}
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/* Just keep enough memory to hold all the interfaces we want. */
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ifaddrs = realloc (ifaddrs, new_num_ifs * sizeof (ifaddrs[0]));
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assert (ifaddrs != NULL);
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cleanup1:
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__if_freereq (ifr, num);
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cleanup:
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/* Release lock, preserve error value, and close socket. */
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errno = save;
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/* Advertise successful initialization if new_num_ifs is
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positive (and no updates to ifaddrs are permitted after
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that). Otherwise, num_ifs remains unchanged, at zero.
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This store synchronizes with the initial acquire MO
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load. */
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atomic_store_release (&num_ifs, new_num_ifs);
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/* Keep the local copy current, to save another load. */
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num_ifs_local = new_num_ifs;
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}
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__libc_lock_unlock (lock);
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__close (sd);
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}
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/* num_ifs_local cannot be negative because the if statement above
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covered this case. It can still be zero if we just performed
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initialization, but could not find any interfaces. */
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if (num_ifs_local == 0)
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return;
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/* The code below accesses ifaddrs, so we need to ensure that the
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initialization happens-before this point.
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The actual initialization is sequenced-before the release store
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to num_ifs, and sequenced-before the end of the critical section.
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This means there are three possible executions:
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(1) The thread that initialized the data also uses it, so
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sequenced-before is sufficient to ensure happens-before.
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(2) The release MO store of num_ifs synchronizes-with the acquire
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MO load, and the acquire MO load is sequenced before the use
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of the initialized data below.
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(3) We enter the critical section, and the relaxed MO load of
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num_ifs yields a positive value. The write to ifaddrs is
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sequenced-before leaving the critical section. Leaving the
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critical section happens-before we entered the critical
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section ourselves, which means that the write to ifaddrs
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happens-before this point.
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Consequently, all potential writes to ifaddrs (and the data it
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points to) happens-before this point. */
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/* Find an address for which we have a direct connection. */
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for (i = 0; hp->h_addr_list[i]; ++i)
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{
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struct in_addr *haddr = (struct in_addr *) hp->h_addr_list[i];
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for (j = 0; j < num_ifs_local; ++j)
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{
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uint32_t if_addr = ifaddrs[j].u.ipv4.addr;
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uint32_t if_netmask = ifaddrs[j].u.ipv4.mask;
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if (((haddr->s_addr ^ if_addr) & if_netmask) == 0)
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{
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void *tmp;
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tmp = hp->h_addr_list[i];
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hp->h_addr_list[i] = hp->h_addr_list[0];
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hp->h_addr_list[0] = tmp;
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return;
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}
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}
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}
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#endif /* defined(SIOCGIFCONF) && ... */
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}
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/* If HOSTNAME has a postfix matching any of the trimdomains, trim away
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that postfix. Notice that HOSTNAME is modified inplace. Also, the
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original code applied all trimdomains in order, meaning that the
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same domainname could be trimmed multiple times. I believe this
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was unintentional. */
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void
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_res_hconf_trim_domain (char *hostname)
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{
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size_t hostname_len, trim_len;
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int i;
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hostname_len = strlen (hostname);
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for (i = 0; i < _res_hconf.num_trimdomains; ++i)
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{
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const char *trim = _res_hconf.trimdomain[i];
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trim_len = strlen (trim);
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if (hostname_len > trim_len
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&& __strcasecmp (&hostname[hostname_len - trim_len], trim) == 0)
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{
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hostname[hostname_len - trim_len] = '\0';
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break;
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}
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}
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}
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/* Trim all hostnames/aliases in HP according to the trimdomain list.
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Notice that HP is modified inplace! */
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void
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_res_hconf_trim_domains (struct hostent *hp)
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{
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int i;
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if (_res_hconf.num_trimdomains == 0)
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return;
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_res_hconf_trim_domain (hp->h_name);
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for (i = 0; hp->h_aliases[i]; ++i)
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_res_hconf_trim_domain (hp->h_aliases[i]);
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}
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#endif
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