| 1 | /* $Id: HostDnsServiceLinux.cpp 98067 2023-01-12 23:04:34Z vboxsync $ */
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| 2 | /** @file
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| 3 | * Linux specific DNS information fetching.
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| 4 | */
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| 5 |
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| 6 | /*
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| 7 | * Copyright (C) 2013-2022 Oracle and/or its affiliates.
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| 8 | *
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| 9 | * This file is part of VirtualBox base platform packages, as
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| 10 | * available from https://www.virtualbox.org.
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| 11 | *
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| 12 | * This program is free software; you can redistribute it and/or
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| 13 | * modify it under the terms of the GNU General Public License
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| 14 | * as published by the Free Software Foundation, in version 3 of the
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| 15 | * License.
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| 16 | *
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| 17 | * This program is distributed in the hope that it will be useful, but
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| 18 | * WITHOUT ANY WARRANTY; without even the implied warranty of
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| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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| 20 | * General Public License for more details.
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| 21 | *
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| 22 | * You should have received a copy of the GNU General Public License
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| 23 | * along with this program; if not, see <https://www.gnu.org/licenses>.
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| 24 | *
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| 25 | * SPDX-License-Identifier: GPL-3.0-only
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| 26 | */
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| 27 |
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| 28 | #include <iprt/assert.h>
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| 29 | #include <iprt/errcore.h>
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| 30 | #include <iprt/initterm.h>
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| 31 | #include <iprt/file.h>
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| 32 | #include <iprt/log.h>
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| 33 | #include <iprt/stream.h>
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| 34 | #include <iprt/string.h>
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| 35 | #include <iprt/semaphore.h>
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| 36 | #include <iprt/thread.h>
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| 37 |
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| 38 | #include <errno.h>
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| 39 | #include <poll.h>
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| 40 | #include <string.h>
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| 41 | #include <unistd.h>
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| 42 |
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| 43 | #include <fcntl.h>
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| 44 |
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| 45 | #include <linux/limits.h>
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| 46 |
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| 47 | /* Workaround for <sys/cdef.h> defining __flexarr to [] which beats us in
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| 48 | * struct inotify_event (char name __flexarr). */
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| 49 | #include <sys/cdefs.h>
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| 50 | #undef __flexarr
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| 51 | #define __flexarr [0]
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| 52 | #include <sys/inotify.h>
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| 53 | #include <sys/types.h>
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| 54 | #include <sys/socket.h>
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| 55 |
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| 56 | #include <iprt/sanitized/string>
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| 57 | #include <vector>
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| 58 | #include "../HostDnsService.h"
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| 59 |
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| 60 |
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| 61 | static int g_DnsMonitorStop[2];
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| 62 |
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| 63 | static const std::string g_EtcFolder = "/etc";
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| 64 | static const std::string g_ResolvConf = "resolv.conf";
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| 65 | static const std::string g_ResolvConfFullPath = "/etc/resolv.conf";
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| 66 |
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| 67 | class FileDescriptor
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| 68 | {
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| 69 | public:
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| 70 | FileDescriptor(int d = -1)
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| 71 | : fd(d)
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| 72 | {}
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| 73 |
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| 74 | virtual ~FileDescriptor() {
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| 75 | if (fd != -1)
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| 76 | close(fd);
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| 77 | }
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| 78 |
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| 79 | int fileDescriptor() const {return fd;}
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| 80 |
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| 81 | protected:
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| 82 | int fd;
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| 83 | };
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| 84 |
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| 85 |
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| 86 | class AutoNotify : public FileDescriptor
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| 87 | {
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| 88 | public:
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| 89 | AutoNotify()
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| 90 | {
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| 91 | FileDescriptor::fd = inotify_init();
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| 92 | AssertReturnVoid(FileDescriptor::fd != -1);
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| 93 | }
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| 94 | };
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| 95 |
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| 96 | struct InotifyEventWithName
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| 97 | {
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| 98 | struct inotify_event e;
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| 99 | char name[NAME_MAX];
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| 100 | };
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| 101 |
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| 102 | HostDnsServiceLinux::~HostDnsServiceLinux()
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| 103 | {
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| 104 | }
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| 105 |
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| 106 | HRESULT HostDnsServiceLinux::init(HostDnsMonitorProxy *pProxy)
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| 107 | {
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| 108 | return HostDnsServiceResolvConf::init(pProxy, "/etc/resolv.conf");
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| 109 | }
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| 110 |
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| 111 | int HostDnsServiceLinux::monitorThreadShutdown(RTMSINTERVAL uTimeoutMs)
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| 112 | {
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| 113 | RT_NOREF(uTimeoutMs);
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| 114 |
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| 115 | send(g_DnsMonitorStop[0], "", 1, 0);
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| 116 |
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| 117 | /** @todo r=andy Do we have to wait for something here? Can this fail? */
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| 118 | return VINF_SUCCESS;
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| 119 | }
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| 120 |
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| 121 | int HostDnsServiceLinux::monitorThreadProc(void)
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| 122 | {
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| 123 | /*
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| 124 | * inotify initialization
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| 125 | *
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| 126 | * Note! Ignoring failures here is safe, because poll will ignore entires
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| 127 | * with negative fd values.
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| 128 | */
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| 129 | AutoNotify a;
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| 130 | int wd[2];
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| 131 | wd[0] = inotify_add_watch(a.fileDescriptor(),
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| 132 | g_ResolvConfFullPath.c_str(), IN_CLOSE_WRITE | IN_DELETE_SELF);
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| 133 |
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| 134 | /* If /etc/resolv.conf exists we want to listen for movements: because
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| 135 | # mv /etc/resolv.conf ...
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| 136 | won't arm IN_DELETE_SELF on wd[0] instead it will fire IN_MOVE_FROM on wd[1].
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| 137 |
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| 138 | Because on some distributions /etc/resolv.conf is a symlink, wd[0] can't detect
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| 139 | deletion, it's recognizible on directory level (wd[1]) only. */
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| 140 | wd[1] = inotify_add_watch(a.fileDescriptor(), g_EtcFolder.c_str(),
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| 141 | wd[0] == -1 ? IN_MOVED_TO | IN_CREATE : IN_MOVED_FROM | IN_DELETE);
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| 142 |
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| 143 | /*
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| 144 | * Create a socket pair for signalling shutdown via (see monitorThreadShutdown).
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| 145 | */
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| 146 | int rc = socketpair(AF_LOCAL, SOCK_DGRAM, 0, g_DnsMonitorStop);
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| 147 | AssertMsgReturn(rc == 0, ("socketpair: failed (%d: %s)\n", errno, strerror(errno)), E_FAIL);
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| 148 |
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| 149 | /* automatic cleanup tricks */
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| 150 | FileDescriptor stopper0(g_DnsMonitorStop[0]);
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| 151 | FileDescriptor stopper1(g_DnsMonitorStop[1]);
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| 152 |
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| 153 | /*
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| 154 | * poll initialization:
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| 155 | */
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| 156 | pollfd polls[2];
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| 157 | RT_ZERO(polls);
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| 158 |
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| 159 | polls[0].fd = a.fileDescriptor();
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| 160 | polls[0].events = POLLIN;
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| 161 |
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| 162 | polls[1].fd = g_DnsMonitorStop[1];
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| 163 | polls[1].events = POLLIN;
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| 164 |
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| 165 | onMonitorThreadInitDone();
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| 166 |
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| 167 | /*
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| 168 | * The monitoring loop.
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| 169 | */
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| 170 | for (;;)
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| 171 | {
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| 172 | rc = poll(polls, RT_ELEMENTS(polls), -1 /*infinite timeout*/);
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| 173 | if (rc == -1)
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| 174 | continue;
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| 175 |
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| 176 | AssertMsgReturn( (polls[0].revents & (POLLERR | POLLNVAL)) == 0
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| 177 | && (polls[1].revents & (POLLERR | POLLNVAL)) == 0, ("Debug Me"), VERR_INTERNAL_ERROR);
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| 178 |
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| 179 | if (polls[1].revents & POLLIN)
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| 180 | return VINF_SUCCESS; /* time to shutdown */
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| 181 |
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| 182 | if (polls[0].revents & POLLIN)
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| 183 | {
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| 184 | /*
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| 185 | * Read the notification event.
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| 186 | */
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| 187 | /** @todo r=bird: This is buggy in that it somehow assumes we'll only get
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| 188 | * one event here. But since we're waiting on two different DELETE
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| 189 | * events for both a specific file and its parent directory, we're likely
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| 190 | * to get two DELETE events at the same time. */
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| 191 | struct InotifyEventWithName combo;
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| 192 | RT_ZERO(combo);
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| 193 | combo.e.wd = -42; /* avoid confusion on the offchance that wd[0] or wd[1] is zero. */
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| 194 |
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| 195 | ssize_t r = read(polls[0].fd, &combo, sizeof(combo));
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| 196 | RT_NOREF(r);
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| 197 |
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| 198 | if (combo.e.wd == wd[0])
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| 199 | {
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| 200 | if (combo.e.mask & IN_CLOSE_WRITE)
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| 201 | readResolvConf();
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| 202 | else if (combo.e.mask & IN_DELETE_SELF)
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| 203 | {
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| 204 | inotify_rm_watch(a.fileDescriptor(), wd[0]); /* removes file watcher */
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| 205 | int wd2 = inotify_add_watch(a.fileDescriptor(), g_EtcFolder.c_str(),
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| 206 | IN_MOVED_TO|IN_CREATE); /* alter folder watcher */
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| 207 | Assert(wd2 == wd[1]); RT_NOREF(wd2); /* ASSUMES wd[1] will be updated */
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| 208 | }
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| 209 | else if (combo.e.mask & IN_IGNORED)
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| 210 | wd[0] = -1; /* we want receive any events on this watch */
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| 211 | else
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| 212 | {
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| 213 | /*
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| 214 | * It shouldn't happen, in release we will just ignore in debug
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| 215 | * we will have to chance to look at into inotify_event
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| 216 | */
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| 217 | AssertMsgFailed(("Debug Me!!!"));
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| 218 | }
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| 219 | }
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| 220 | else if (combo.e.wd == wd[1])
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| 221 | {
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| 222 | if (combo.e.mask & (IN_DELETE | IN_MOVED_FROM))
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| 223 | {
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| 224 | if (g_ResolvConf == combo.e.name)
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| 225 | {
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| 226 | /*
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| 227 | * Our file has been moved or deleted so we should change watching mode.
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| 228 | */
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| 229 | inotify_rm_watch(a.fileDescriptor(), wd[0]);
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| 230 | wd[1] = inotify_add_watch(a.fileDescriptor(), g_EtcFolder.c_str(),
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| 231 | IN_MOVED_TO | IN_CREATE);
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| 232 | AssertMsg(wd[1] != -1,
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| 233 | ("It shouldn't happen, further investigation is needed\n"));
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| 234 | }
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| 235 | }
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| 236 | else
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| 237 | {
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| 238 | AssertMsg(combo.e.mask & (IN_MOVED_TO | IN_CREATE),
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| 239 | ("%RX32 event isn't expected, we are waiting for IN_MOVED|IN_CREATE\n", combo.e.mask));
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| 240 | if (g_ResolvConf == combo.e.name)
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| 241 | {
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| 242 | AssertMsg(wd[0] == -1, ("We haven't removed file watcher first\n"));
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| 243 |
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| 244 | /* alter folder watcher: */
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| 245 | wd[1] = inotify_add_watch(a.fileDescriptor(),
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| 246 | g_EtcFolder.c_str(),
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| 247 | IN_MOVED_FROM | IN_DELETE);
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| 248 | AssertMsg(wd[1] != -1, ("It shouldn't happen.\n"));
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| 249 |
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| 250 | wd[0] = inotify_add_watch(a.fileDescriptor(),
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| 251 | g_ResolvConfFullPath.c_str(),
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| 252 | IN_CLOSE_WRITE | IN_DELETE_SELF);
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| 253 | AssertMsg(wd[0] != -1, ("Adding watcher to file (%s) has been failed!\n",
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| 254 | g_ResolvConfFullPath.c_str()));
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| 255 |
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| 256 | /* Notify our listeners */
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| 257 | readResolvConf();
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| 258 | }
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| 259 | }
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| 260 | }
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| 261 | else
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| 262 | {
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| 263 | /* It shouldn't happen */
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| 264 | AssertMsgFailed(("Shouldn't happen! Please debug me!"));
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| 265 | }
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| 266 | }
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| 267 | }
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| 268 | }
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| 269 |
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