59c0fd0e17
When the network configuration changes we should relearn everything there is to know about the configured DNS servers, because we might talk to the same addresses, but there might be different servers behind them.
283 lines
10 KiB
C
283 lines
10 KiB
C
/***
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This file is part of systemd.
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Copyright 2014 Tom Gundersen <teg@jklm.no>
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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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 License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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***/
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#include <resolv.h>
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#include "alloc-util.h"
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#include "dns-domain.h"
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#include "fd-util.h"
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#include "fileio-label.h"
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#include "fileio.h"
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#include "ordered-set.h"
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#include "resolved-conf.h"
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#include "resolved-dns-server.h"
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#include "resolved-resolv-conf.h"
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#include "string-util.h"
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#include "strv.h"
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int manager_read_resolv_conf(Manager *m) {
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_cleanup_fclose_ FILE *f = NULL;
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struct stat st, own;
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char line[LINE_MAX];
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usec_t t;
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int r;
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assert(m);
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/* Reads the system /etc/resolv.conf, if it exists and is not
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* symlinked to our own resolv.conf instance */
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if (!m->read_resolv_conf)
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return 0;
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r = stat("/etc/resolv.conf", &st);
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if (r < 0) {
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if (errno == ENOENT)
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return 0;
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r = log_warning_errno(errno, "Failed to stat /etc/resolv.conf: %m");
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goto clear;
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}
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/* Have we already seen the file? */
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t = timespec_load(&st.st_mtim);
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if (t == m->resolv_conf_mtime)
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return 0;
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/* Is it symlinked to our own file? */
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if (stat(PRIVATE_RESOLV_CONF, &own) >= 0 &&
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st.st_dev == own.st_dev &&
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st.st_ino == own.st_ino)
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return 0;
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f = fopen("/etc/resolv.conf", "re");
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if (!f) {
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if (errno == ENOENT)
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return 0;
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r = log_warning_errno(errno, "Failed to open /etc/resolv.conf: %m");
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goto clear;
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}
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if (fstat(fileno(f), &st) < 0) {
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r = log_error_errno(errno, "Failed to stat open file: %m");
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goto clear;
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}
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dns_server_mark_all(m->dns_servers);
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dns_search_domain_mark_all(m->search_domains);
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FOREACH_LINE(line, f, r = -errno; goto clear) {
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const char *a;
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char *l;
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l = strstrip(line);
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if (IN_SET(*l, '#', ';'))
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continue;
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a = first_word(l, "nameserver");
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if (a) {
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r = manager_parse_dns_server_string_and_warn(m, DNS_SERVER_SYSTEM, a);
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if (r < 0)
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log_warning_errno(r, "Failed to parse DNS server address '%s', ignoring.", a);
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continue;
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}
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a = first_word(l, "domain");
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if (!a) /* We treat "domain" lines, and "search" lines as equivalent, and add both to our list. */
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a = first_word(l, "search");
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if (a) {
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r = manager_parse_search_domains_and_warn(m, a);
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if (r < 0)
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log_warning_errno(r, "Failed to parse search domain string '%s', ignoring.", a);
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}
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}
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m->resolv_conf_mtime = t;
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/* Flush out all servers and search domains that are still
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* marked. Those are then ones that didn't appear in the new
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* /etc/resolv.conf */
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dns_server_unlink_marked(m->dns_servers);
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dns_search_domain_unlink_marked(m->search_domains);
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/* Whenever /etc/resolv.conf changes, start using the first
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* DNS server of it. This is useful to deal with broken
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* network managing implementations (like NetworkManager),
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* that when connecting to a VPN place both the VPN DNS
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* servers and the local ones in /etc/resolv.conf. Without
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* resetting the DNS server to use back to the first entry we
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* will continue to use the local one thus being unable to
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* resolve VPN domains. */
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manager_set_dns_server(m, m->dns_servers);
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/* Unconditionally flush the cache when /etc/resolv.conf is
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* modified, even if the data it contained was completely
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* identical to the previous version we used. We do this
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* because altering /etc/resolv.conf is typically done when
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* the network configuration changes, and that should be
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* enough to flush the global unicast DNS cache. */
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if (m->unicast_scope)
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dns_cache_flush(&m->unicast_scope->cache);
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/* If /etc/resolv.conf changed, make sure to forget everything we learned about the DNS servers. After all we
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* might now talk to a very different DNS server that just happens to have the same IP address as an old one
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* (think 192.168.1.1). */
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dns_server_reset_features_all(m->dns_servers);
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return 0;
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clear:
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dns_server_unlink_all(m->dns_servers);
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dns_search_domain_unlink_all(m->search_domains);
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return r;
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}
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static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
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assert(s);
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assert(f);
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assert(count);
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if (!dns_server_string(s)) {
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log_warning("Our of memory, or invalid DNS address. Ignoring server.");
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return;
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}
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/* Check if the DNS server is limited to particular domains;
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* resolv.conf does not have a syntax to express that, so it must not
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* appear as a global name server to avoid routing unrelated domains to
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* it (which is a privacy violation, will most probably fail anyway,
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* and adds unnecessary load) */
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if (dns_server_limited_domains(s)) {
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log_debug("DNS server %s has route-only domains, not using as global name server", dns_server_string(s));
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return;
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}
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if (*count == MAXNS)
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fputs_unlocked("# Too many DNS servers configured, the following entries may be ignored.\n", f);
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(*count)++;
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fprintf(f, "nameserver %s\n", dns_server_string(s));
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}
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static void write_resolv_conf_search(
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OrderedSet *domains,
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FILE *f) {
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unsigned length = 0, count = 0;
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Iterator i;
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char *domain;
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assert(domains);
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assert(f);
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fputs_unlocked("search", f);
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ORDERED_SET_FOREACH(domain, domains, i) {
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if (++count > MAXDNSRCH) {
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fputs_unlocked("\n# Too many search domains configured, remaining ones ignored.", f);
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break;
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}
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length += strlen(domain) + 1;
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if (length > 256) {
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fputs_unlocked("\n# Total length of all search domains is too long, remaining ones ignored.", f);
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break;
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}
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fputc_unlocked(' ', f);
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fputs_unlocked(domain, f);
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}
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fputs_unlocked("\n", f);
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}
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static int write_resolv_conf_contents(FILE *f, OrderedSet *dns, OrderedSet *domains) {
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Iterator i;
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fputs_unlocked("# This file is managed by man:systemd-resolved(8). Do not edit.\n#\n"
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"# This is a dynamic resolv.conf file for connecting local clients directly to\n"
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"# all known DNS servers.\n#\n"
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"# Third party programs must not access this file directly, but only through the\n"
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"# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,\n"
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"# replace this symlink by a static file or a different symlink.\n#\n"
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"# See man:systemd-resolved.service(8) for details about the supported modes of\n"
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"# operation for /etc/resolv.conf.\n\n", f);
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if (ordered_set_isempty(dns))
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fputs_unlocked("# No DNS servers known.\n", f);
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else {
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unsigned count = 0;
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DnsServer *s;
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ORDERED_SET_FOREACH(s, dns, i)
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write_resolv_conf_server(s, f, &count);
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}
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if (!ordered_set_isempty(domains))
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write_resolv_conf_search(domains, f);
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return fflush_and_check(f);
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}
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int manager_write_resolv_conf(Manager *m) {
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_cleanup_ordered_set_free_ OrderedSet *dns = NULL, *domains = NULL;
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_cleanup_free_ char *temp_path = NULL;
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_cleanup_fclose_ FILE *f = NULL;
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int r;
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assert(m);
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/* Read the system /etc/resolv.conf first */
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(void) manager_read_resolv_conf(m);
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/* Add the full list to a set, to filter out duplicates */
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r = manager_compile_dns_servers(m, &dns);
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if (r < 0)
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return log_warning_errno(r, "Failed to compile list of DNS servers: %m");
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r = manager_compile_search_domains(m, &domains, false);
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if (r < 0)
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return log_warning_errno(r, "Failed to compile list of search domains: %m");
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r = fopen_temporary_label(PRIVATE_RESOLV_CONF, PRIVATE_RESOLV_CONF, &f, &temp_path);
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if (r < 0)
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return log_warning_errno(r, "Failed to open private resolv.conf file for writing: %m");
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(void) fchmod(fileno(f), 0644);
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r = write_resolv_conf_contents(f, dns, domains);
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if (r < 0) {
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log_error_errno(r, "Failed to write private resolv.conf contents: %m");
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goto fail;
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}
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if (rename(temp_path, PRIVATE_RESOLV_CONF) < 0) {
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r = log_error_errno(errno, "Failed to move private resolv.conf file into place: %m");
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goto fail;
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}
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return 0;
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fail:
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(void) unlink(PRIVATE_RESOLV_CONF);
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(void) unlink(temp_path);
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return r;
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}
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