1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Mini klogd implementation for busybox
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4 | *
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5 | * Copyright (C) 2001 by Gennady Feldman <gfeldman@gena01.com>.
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6 | * Changes: Made this a standalone busybox module which uses standalone
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7 | * syslog() client interface.
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8 | *
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9 | * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
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10 | *
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11 | * Copyright (C) 2000 by Karl M. Hegbloom <karlheg@debian.org>
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12 | *
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13 | * "circular buffer" Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
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14 | *
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15 | * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
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16 | *
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17 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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18 | */
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19 | //config:config KLOGD
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20 | //config: bool "klogd"
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21 | //config: default y
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22 | //config: help
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23 | //config: klogd is a utility which intercepts and logs all
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24 | //config: messages from the Linux kernel and sends the messages
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25 | //config: out to the 'syslogd' utility so they can be logged. If
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26 | //config: you wish to record the messages produced by the kernel,
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27 | //config: you should enable this option.
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28 | //config:
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29 | //config:comment "klogd should not be used together with syslog to kernel printk buffer"
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30 | //config: depends on KLOGD && FEATURE_KMSG_SYSLOG
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31 | //config:
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32 | //config:config FEATURE_KLOGD_KLOGCTL
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33 | //config: bool "Use the klogctl() interface"
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34 | //config: default y
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35 | //config: depends on KLOGD
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36 | //config: select PLATFORM_LINUX
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37 | //config: help
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38 | //config: The klogd applet supports two interfaces for reading
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39 | //config: kernel messages. Linux provides the klogctl() interface
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40 | //config: which allows reading messages from the kernel ring buffer
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41 | //config: independently from the file system.
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42 | //config:
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43 | //config: If you answer 'N' here, klogd will use the more portable
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44 | //config: approach of reading them from /proc or a device node.
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45 | //config: However, this method requires the file to be available.
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46 | //config:
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47 | //config: If in doubt, say 'Y'.
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48 |
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49 | //applet:IF_KLOGD(APPLET(klogd, BB_DIR_SBIN, BB_SUID_DROP))
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50 |
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51 | //kbuild:lib-$(CONFIG_KLOGD) += klogd.o
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52 |
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53 | //usage:#define klogd_trivial_usage
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54 | //usage: "[-c N] [-n]"
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55 | //usage:#define klogd_full_usage "\n\n"
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56 | //usage: "Kernel logger\n"
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57 | //usage: "\n -c N Print to console messages more urgent than prio N (1-8)"
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58 | //usage: "\n -n Run in foreground"
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59 |
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60 | #include "libbb.h"
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61 | #include "common_bufsiz.h"
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62 | #include <syslog.h>
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63 |
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64 |
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65 | /* The Linux-specific klogctl(3) interface does not rely on the filesystem and
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66 | * allows us to change the console loglevel. Alternatively, we read the
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67 | * messages from _PATH_KLOG. */
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68 |
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69 | #if ENABLE_FEATURE_KLOGD_KLOGCTL
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70 |
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71 | # include <sys/klog.h>
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72 |
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73 | static void klogd_open(void)
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74 | {
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75 | /* "Open the log. Currently a NOP" */
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76 | klogctl(1, NULL, 0);
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77 | }
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78 |
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79 | static void klogd_setloglevel(int lvl)
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80 | {
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81 | /* "printk() prints a message on the console only if it has a loglevel
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82 | * less than console_loglevel". Here we set console_loglevel = lvl. */
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83 | klogctl(8, NULL, lvl);
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84 | }
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85 |
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86 | static int klogd_read(char *bufp, int len)
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87 | {
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88 | return klogctl(2, bufp, len);
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89 | }
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90 | # define READ_ERROR "klogctl(2) error"
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91 |
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92 | static void klogd_close(void)
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93 | {
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94 | /* FYI: cmd 7 is equivalent to setting console_loglevel to 7
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95 | * via klogctl(8, NULL, 7). */
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96 | klogctl(7, NULL, 0); /* "7 -- Enable printk's to console" */
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97 | klogctl(0, NULL, 0); /* "0 -- Close the log. Currently a NOP" */
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98 | }
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99 |
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100 | #else
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101 |
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102 | # ifndef _PATH_KLOG
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103 | # ifdef __GNU__
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104 | # define _PATH_KLOG "/dev/klog"
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105 | # else
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106 | # error "your system's _PATH_KLOG is unknown"
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107 | # endif
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108 | # endif
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109 | # define PATH_PRINTK "/proc/sys/kernel/printk"
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110 |
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111 | enum { klogfd = 3 };
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112 |
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113 | static void klogd_open(void)
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114 | {
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115 | int fd = xopen(_PATH_KLOG, O_RDONLY);
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116 | xmove_fd(fd, klogfd);
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117 | }
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118 |
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119 | static void klogd_setloglevel(int lvl)
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120 | {
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121 | FILE *fp = fopen_or_warn(PATH_PRINTK, "w");
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122 | if (fp) {
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123 | /* This changes only first value:
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124 | * "messages with a higher priority than this
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125 | * [that is, with numerically lower value]
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126 | * will be printed to the console".
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127 | * The other three values in this pseudo-file aren't changed.
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128 | */
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129 | fprintf(fp, "%u\n", lvl);
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130 | fclose(fp);
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131 | }
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132 | }
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133 |
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134 | static int klogd_read(char *bufp, int len)
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135 | {
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136 | return read(klogfd, bufp, len);
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137 | }
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138 | # define READ_ERROR "read error"
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139 |
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140 | static void klogd_close(void)
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141 | {
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142 | klogd_setloglevel(7);
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143 | if (ENABLE_FEATURE_CLEAN_UP)
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144 | close(klogfd);
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145 | }
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146 |
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147 | #endif
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148 |
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149 | #define log_buffer bb_common_bufsiz1
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150 | enum {
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151 | KLOGD_LOGBUF_SIZE = COMMON_BUFSIZE,
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152 | OPT_LEVEL = (1 << 0),
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153 | OPT_FOREGROUND = (1 << 1),
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154 | };
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155 |
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156 | /* TODO: glibc openlog(LOG_KERN) reverts to LOG_USER instead,
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157 | * because that's how they interpret word "default"
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158 | * in the openlog() manpage:
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159 | * LOG_USER (default)
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160 | * generic user-level messages
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161 | * and the fact that LOG_KERN is a constant 0.
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162 | * glibc interprets it as "0 in openlog() call means 'use default'".
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163 | * I think it means "if openlog wasn't called before syslog() is called,
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164 | * use default".
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165 | * Convincing glibc maintainers otherwise is, as usual, nearly impossible.
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166 | * Should we open-code syslog() here to use correct facility?
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167 | */
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168 |
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169 | int klogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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170 | int klogd_main(int argc UNUSED_PARAM, char **argv)
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171 | {
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172 | int i = 0;
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173 | char *opt_c;
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174 | int opt;
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175 | int used;
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176 |
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177 | setup_common_bufsiz();
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178 |
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179 | opt = getopt32(argv, "c:n", &opt_c);
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180 | if (opt & OPT_LEVEL) {
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181 | /* Valid levels are between 1 and 8 */
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182 | i = xatou_range(opt_c, 1, 8);
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183 | }
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184 | if (!(opt & OPT_FOREGROUND)) {
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185 | bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
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186 | }
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187 |
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188 | logmode = LOGMODE_SYSLOG;
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189 |
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190 | /* klogd_open() before openlog(), since it might use fixed fd 3,
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191 | * and openlog() also may use the same fd 3 if we swap them:
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192 | */
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193 | klogd_open();
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194 | openlog("kernel", 0, LOG_KERN);
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195 | /*
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196 | * glibc problem: for some reason, glibc changes LOG_KERN to LOG_USER
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197 | * above. The logic behind this is that standard
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198 | * http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html
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199 | * says the following about openlog and syslog:
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200 | * "LOG_USER
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201 | * Messages generated by arbitrary processes.
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202 | * This is the default facility identifier if none is specified."
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203 | *
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204 | * I believe glibc misinterpreted this text as "if openlog's
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205 | * third parameter is 0 (=LOG_KERN), treat it as LOG_USER".
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206 | * Whereas it was meant to say "if *syslog* is called with facility
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207 | * 0 in its 1st parameter without prior call to openlog, then perform
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208 | * implicit openlog(LOG_USER)".
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209 | *
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210 | * As a result of this, eh, feature, standard klogd was forced
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211 | * to open-code its own openlog and syslog implementation (!).
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212 | *
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213 | * Note that prohibiting openlog(LOG_KERN) on libc level does not
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214 | * add any security: any process can open a socket to "/dev/log"
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215 | * and write a string "<0>Voila, a LOG_KERN + LOG_EMERG message"
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216 | *
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217 | * Google code search tells me there is no widespread use of
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218 | * openlog("foo", 0, 0), thus fixing glibc won't break userspace.
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219 | *
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220 | * The bug against glibc was filed:
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221 | * bugzilla.redhat.com/show_bug.cgi?id=547000
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222 | */
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223 |
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224 | if (i)
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225 | klogd_setloglevel(i);
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226 |
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227 | signal(SIGHUP, SIG_IGN);
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228 | /* We want klogd_read to not be restarted, thus _norestart: */
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229 | bb_signals_recursive_norestart(BB_FATAL_SIGS, record_signo);
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230 |
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231 | syslog(LOG_NOTICE, "klogd started: %s", bb_banner);
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232 |
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233 | write_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");
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234 |
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235 | used = 0;
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236 | while (!bb_got_signal) {
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237 | int n;
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238 | int priority;
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239 | char *start;
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240 |
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241 | /* "2 -- Read from the log." */
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242 | start = log_buffer + used;
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243 | n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
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244 | if (n < 0) {
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245 | if (errno == EINTR)
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246 | continue;
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247 | bb_perror_msg(READ_ERROR);
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248 | break;
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249 | }
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250 | start[n] = '\0';
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251 |
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252 | /* Process each newline-terminated line in the buffer */
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253 | start = log_buffer;
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254 | while (1) {
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255 | char *newline = strchrnul(start, '\n');
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256 |
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257 | if (*newline == '\0') {
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258 | /* This line is incomplete */
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259 |
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260 | /* move it to the front of the buffer */
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261 | overlapping_strcpy(log_buffer, start);
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262 | used = newline - start;
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263 | if (used < KLOGD_LOGBUF_SIZE-1) {
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264 | /* buffer isn't full */
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265 | break;
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266 | }
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267 | /* buffer is full, log it anyway */
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268 | used = 0;
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269 | newline = NULL;
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270 | } else {
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271 | *newline++ = '\0';
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272 | }
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273 |
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274 | /* Extract the priority */
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275 | priority = LOG_INFO;
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276 | if (*start == '<') {
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277 | start++;
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278 | if (*start)
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279 | priority = strtoul(start, &start, 10);
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280 | if (*start == '>')
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281 | start++;
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282 | }
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283 | /* Log (only non-empty lines) */
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284 | if (*start)
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285 | syslog(priority, "%s", start);
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286 |
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287 | if (!newline)
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288 | break;
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289 | start = newline;
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290 | }
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291 | }
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292 |
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293 | klogd_close();
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294 | syslog(LOG_NOTICE, "klogd: exiting");
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295 | remove_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");
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296 | if (bb_got_signal)
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297 | kill_myself_with_sig(bb_got_signal);
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298 | return EXIT_FAILURE;
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299 | }
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