release/src/router/busybox/sysklogd/klogd.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini klogd implementation for busybox
   4  *
   5  * Copyright (C) 2001 by Gennady Feldman <gfeldman@gena01.com>.
   6  * Changes: Made this a standalone busybox module which uses standalone
   7  * syslog() client interface.
   8  *
   9  * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
  10  *
  11  * Copyright (C) 2000 by Karl M. Hegbloom <karlheg@debian.org>
  12  *
  13  * "circular buffer" Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
  14  *
  15  * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
  16  *
  17  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  18  */
  19 //config:config KLOGD
  20 //config:       bool "klogd"
  21 //config:       default y
  22 //config:       help
  23 //config:         klogd is a utility which intercepts and logs all
  24 //config:         messages from the Linux kernel and sends the messages
  25 //config:         out to the 'syslogd' utility so they can be logged. If
  26 //config:         you wish to record the messages produced by the kernel,
  27 //config:         you should enable this option.
  28 //config:
  29 //config:comment "klogd should not be used together with syslog to kernel printk buffer"
  30 //config:       depends on KLOGD && FEATURE_KMSG_SYSLOG
  31 //config:
  32 //config:config FEATURE_KLOGD_KLOGCTL
  33 //config:       bool "Use the klogctl() interface"
  34 //config:       default y
  35 //config:       depends on KLOGD
  36 //config:       select PLATFORM_LINUX
  37 //config:       help
  38 //config:         The klogd applet supports two interfaces for reading
  39 //config:         kernel messages. Linux provides the klogctl() interface
  40 //config:         which allows reading messages from the kernel ring buffer
  41 //config:         independently from the file system.
  42 //config:
  43 //config:         If you answer 'N' here, klogd will use the more portable
  44 //config:         approach of reading them from /proc or a device node.
  45 //config:         However, this method requires the file to be available.
  46 //config:
  47 //config:         If in doubt, say 'Y'.
  48
  49 //applet:IF_KLOGD(APPLET(klogd, BB_DIR_SBIN, BB_SUID_DROP))
  50
  51 //kbuild:lib-$(CONFIG_KLOGD) += klogd.o
  52
  53 //usage:#define klogd_trivial_usage
  54 //usage:       "[-c N] [-n]"
  55 //usage:#define klogd_full_usage "\n\n"
  56 //usage:       "Kernel logger\n"
  57 //usage:     "\n        -c N    Print to console messages more urgent than prio N (1-8)"
  58 //usage:     "\n        -n      Run in foreground"
  59
  60 #include "libbb.h"
  61 #include "common_bufsiz.h"
  62 #include <syslog.h>
  63
  64
  65 /* The Linux-specific klogctl(3) interface does not rely on the filesystem and
  66  * allows us to change the console loglevel. Alternatively, we read the
  67  * messages from _PATH_KLOG. */
  68
  69 #if ENABLE_FEATURE_KLOGD_KLOGCTL
  70
  71 # include <sys/klog.h>
  72
  73 static void klogd_open(void)
  74 {
  75         /* "Open the log. Currently a NOP" */
  76         klogctl(1, NULL, 0);
  77 }
  78
  79 static void klogd_setloglevel(int lvl)
  80 {
  81         /* "printk() prints a message on the console only if it has a loglevel
  82          * less than console_loglevel". Here we set console_loglevel = lvl. */
  83         klogctl(8, NULL, lvl);
  84 }
  85
  86 static int klogd_read(char *bufp, int len)
  87 {
  88         return klogctl(2, bufp, len);
  89 }
  90 # define READ_ERROR "klogctl(2) error"
  91
  92 static void klogd_close(void)
  93 {
  94         /* FYI: cmd 7 is equivalent to setting console_loglevel to 7
  95          * via klogctl(8, NULL, 7). */
  96         klogctl(7, NULL, 0); /* "7 -- Enable printk's to console" */
  97         klogctl(0, NULL, 0); /* "0 -- Close the log. Currently a NOP" */
  98 }
  99
 100 #else
 101
 102 # ifndef _PATH_KLOG
 103 #  ifdef __GNU__
 104 #   define _PATH_KLOG "/dev/klog"
 105 #  else
 106 #   error "your system's _PATH_KLOG is unknown"
 107 #  endif
 108 # endif
 109 # define PATH_PRINTK "/proc/sys/kernel/printk"
 110
 111 enum { klogfd = 3 };
 112
 113 static void klogd_open(void)
 114 {
 115         int fd = xopen(_PATH_KLOG, O_RDONLY);
 116         xmove_fd(fd, klogfd);
 117 }
 118
 119 static void klogd_setloglevel(int lvl)
 120 {
 121         FILE *fp = fopen_or_warn(PATH_PRINTK, "w");
 122         if (fp) {
 123                 /* This changes only first value:
 124                  * "messages with a higher priority than this
 125                  * [that is, with numerically lower value]
 126                  * will be printed to the console".
 127                  * The other three values in this pseudo-file aren't changed.
 128                  */
 129                 fprintf(fp, "%u\n", lvl);
 130                 fclose(fp);
 131         }
 132 }
 133
 134 static int klogd_read(char *bufp, int len)
 135 {
 136         return read(klogfd, bufp, len);
 137 }
 138 # define READ_ERROR "read error"
 139
 140 static void klogd_close(void)
 141 {
 142         klogd_setloglevel(7);
 143         if (ENABLE_FEATURE_CLEAN_UP)
 144                 close(klogfd);
 145 }
 146
 147 #endif
 148
 149 char log_buffer[6 * 1024 + 1];  /* Big enough to not lose msgs at bootup */
 150 enum {
 151         KLOGD_LOGBUF_SIZE = COMMON_BUFSIZE,
 152         OPT_LEVEL      = (1 << 0),
 153         OPT_FOREGROUND = (1 << 1),
 154 };
 155
 156 /* TODO: glibc openlog(LOG_KERN) reverts to LOG_USER instead,
 157  * because that's how they interpret word "default"
 158  * in the openlog() manpage:
 159  *      LOG_USER (default)
 160  *              generic user-level messages
 161  * and the fact that LOG_KERN is a constant 0.
 162  * glibc interprets it as "0 in openlog() call means 'use default'".
 163  * I think it means "if openlog wasn't called before syslog() is called,
 164  * use default".
 165  * Convincing glibc maintainers otherwise is, as usual, nearly impossible.
 166  * Should we open-code syslog() here to use correct facility?
 167  */
 168
 169 int klogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 170 int klogd_main(int argc UNUSED_PARAM, char **argv)
 171 {
 172         int i = 0;
 173         char *opt_c;
 174         int opt;
 175         int used;
 176         unsigned int cnt;
 177
 178         setup_common_bufsiz();
 179
 180         opt = getopt32(argv, "c:n", &opt_c);
 181         if (opt & OPT_LEVEL) {
 182                 /* Valid levels are between 1 and 8 */
 183                 i = xatou_range(opt_c, 1, 8);
 184         }
 185         if (!(opt & OPT_FOREGROUND)) {
 186                 bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
 187         }
 188
 189         logmode = LOGMODE_SYSLOG;
 190
 191         /* klogd_open() before openlog(), since it might use fixed fd 3,
 192          * and openlog() also may use the same fd 3 if we swap them:
 193          */
 194         klogd_open();
 195         openlog("kernel", 0, LOG_KERN);
 196         /*
 197          * glibc problem: for some reason, glibc changes LOG_KERN to LOG_USER
 198          * above. The logic behind this is that standard
 199          * http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html
 200          * says the following about openlog and syslog:
 201          * "LOG_USER
 202          *  Messages generated by arbitrary processes.
 203          *  This is the default facility identifier if none is specified."
 204          *
 205          * I believe glibc misinterpreted this text as "if openlog's
 206          * third parameter is 0 (=LOG_KERN), treat it as LOG_USER".
 207          * Whereas it was meant to say "if *syslog* is called with facility
 208          * 0 in its 1st parameter without prior call to openlog, then perform
 209          * implicit openlog(LOG_USER)".
 210          *
 211          * As a result of this, eh, feature, standard klogd was forced
 212          * to open-code its own openlog and syslog implementation (!).
 213          *
 214          * Note that prohibiting openlog(LOG_KERN) on libc level does not
 215          * add any security: any process can open a socket to "/dev/log"
 216          * and write a string "<0>Voila, a LOG_KERN + LOG_EMERG message"
 217          *
 218          * Google code search tells me there is no widespread use of
 219          * openlog("foo", 0, 0), thus fixing glibc won't break userspace.
 220          *
 221          * The bug against glibc was filed:
 222          * bugzilla.redhat.com/show_bug.cgi?id=547000
 223          */
 224
 225         if (i)
 226                 klogd_setloglevel(i);
 227
 228         signal(SIGHUP, SIG_IGN);
 229         /* We want klogd_read to not be restarted, thus _norestart: */
 230         bb_signals_recursive_norestart(BB_FATAL_SIGS, record_signo);
 231
 232         syslog(LOG_NOTICE, "klogd started: %s", bb_banner);
 233
 234         write_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");
 235
 236         used = 0;
 237         cnt = 0;
 238         while (!bb_got_signal) {
 239                 int n;
 240                 int priority;
 241                 char *start;
 242                 char *eor;
 243
 244                 /* "2 -- Read from the log." */
 245                 start = log_buffer + used;
 246                 n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
 247                 if (n < 0) {
 248                         if (errno == EINTR)
 249                                 continue;
 250                         bb_perror_msg(READ_ERROR);
 251                         break;
 252                 }
 253                 start[n] = '\0';
 254                 eor = &start[n];
 255
 256                 /* Process each newline-terminated line in the buffer */
 257                 start = log_buffer;
 258                 while (1) {
 259                         char *newline = strchrnul(start, '\n');
 260
 261                         if (*newline == '\0') {
 262                                 /* This line is incomplete */
 263
 264                                 /* move it to the front of the buffer */
 265                                 overlapping_strcpy(log_buffer, start);
 266                                 used = newline - start;
 267                                 if (used < KLOGD_LOGBUF_SIZE-1) {
 268                                         /* buffer isn't full */
 269                                         break;
 270                                 }
 271                                 /* buffer is full, log it anyway */
 272                                 used = 0;
 273                                 newline = NULL;
 274                         } else {
 275                                 *newline++ = '\0';
 276                         }
 277
 278                         /* Extract the priority */
 279                         priority = LOG_INFO;
 280                         if (*start == '<') {
 281                                 start++;
 282                                 if (*start)
 283                                         priority = strtoul(start, &start, 10);
 284                                 if (*start == '>')
 285                                         start++;
 286                         }
 287                         /* Log (only non-empty lines) */
 288                         if (*start) {
 289                                 syslog(priority, "%s", start);
 290                                 /* give syslog time to catch up */
 291                                 ++cnt;
 292                                 if ((cnt & 0x07) == 0 && (cnt < 300 || (eor - start) > 200))
 293                                         usleep(50 * 1000);
 294                         }
 295
 296                         if (!newline)
 297                                 break;
 298                         start = newline;
 299                 }
 300         }
 301
 302         klogd_close();
 303         syslog(LOG_NOTICE, "klogd: exiting");
 304         remove_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");
 305         if (bb_got_signal)
 306                 kill_myself_with_sig(bb_got_signal);
 307         return EXIT_FAILURE;
 308 }