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
  20 //usage:#define klogd_trivial_usage
  21 //usage:       "[-c N] [-n]"
  22 //usage:#define klogd_full_usage "\n\n"
  23 //usage:       "Kernel logger\n"
  24 //usage:     "\n        -c N    Print to console messages more urgent than prio N (1-8)"
  25 //usage:     "\n        -n      Run in foreground"
  26
  27 #include "libbb.h"
  28 #include <syslog.h>
  29
  30
  31 /* The Linux-specific klogctl(3) interface does not rely on the filesystem and
  32  * allows us to change the console loglevel. Alternatively, we read the
  33  * messages from _PATH_KLOG. */
  34
  35 #if ENABLE_FEATURE_KLOGD_KLOGCTL
  36
  37 # include <sys/klog.h>
  38
  39 static void klogd_open(void)
  40 {
  41         /* "Open the log. Currently a NOP" */
  42         klogctl(1, NULL, 0);
  43 }
  44
  45 static void klogd_setloglevel(int lvl)
  46 {
  47         /* "printk() prints a message on the console only if it has a loglevel
  48          * less than console_loglevel". Here we set console_loglevel = lvl. */
  49         klogctl(8, NULL, lvl);
  50 }
  51
  52 static int klogd_read(char *bufp, int len)
  53 {
  54         return klogctl(2, bufp, len);
  55 }
  56 # define READ_ERROR "klogctl(2) error"
  57
  58 static void klogd_close(void)
  59 {
  60         /* FYI: cmd 7 is equivalent to setting console_loglevel to 7
  61          * via klogctl(8, NULL, 7). */
  62         klogctl(7, NULL, 0); /* "7 -- Enable printk's to console" */
  63         klogctl(0, NULL, 0); /* "0 -- Close the log. Currently a NOP" */
  64 }
  65
  66 #else
  67
  68 # include <paths.h>
  69 # ifndef _PATH_KLOG
  70 #  ifdef __GNU__
  71 #   define _PATH_KLOG "/dev/klog"
  72 #  else
  73 #   error "your system's _PATH_KLOG is unknown"
  74 #  endif
  75 # endif
  76 # define PATH_PRINTK "/proc/sys/kernel/printk"
  77
  78 enum { klogfd = 3 };
  79
  80 static void klogd_open(void)
  81 {
  82         int fd = xopen(_PATH_KLOG, O_RDONLY);
  83         xmove_fd(fd, klogfd);
  84 }
  85
  86 static void klogd_setloglevel(int lvl)
  87 {
  88         FILE *fp = fopen_or_warn(PATH_PRINTK, "w");
  89         if (fp) {
  90                 /* This changes only first value:
  91                  * "messages with a higher priority than this
  92                  * [that is, with numerically lower value]
  93                  * will be printed to the console".
  94                  * The other three values in this pseudo-file aren't changed.
  95                  */
  96                 fprintf(fp, "%u\n", lvl);
  97                 fclose(fp);
  98         }
  99 }
 100
 101 static int klogd_read(char *bufp, int len)
 102 {
 103         return read(klogfd, bufp, len);
 104 }
 105 # define READ_ERROR "read error"
 106
 107 static void klogd_close(void)
 108 {
 109         klogd_setloglevel(7);
 110         if (ENABLE_FEATURE_CLEAN_UP)
 111                 close(klogfd);
 112 }
 113
 114 #endif
 115
 116 char log_buffer[6 * 1024 + 1];  /* Big enough to not lose msgs at bootup */
 117 enum {
 118         KLOGD_LOGBUF_SIZE = sizeof(log_buffer),
 119         OPT_LEVEL      = (1 << 0),
 120         OPT_FOREGROUND = (1 << 1),
 121 };
 122
 123 /* TODO: glibc openlog(LOG_KERN) reverts to LOG_USER instead,
 124  * because that's how they interpret word "default"
 125  * in the openlog() manpage:
 126  *      LOG_USER (default)
 127  *              generic user-level messages
 128  * and the fact that LOG_KERN is a constant 0.
 129  * glibc interprets it as "0 in openlog() call means 'use default'".
 130  * I think it means "if openlog wasn't called before syslog() is called,
 131  * use default".
 132  * Convincing glibc maintainers otherwise is, as usual, nearly impossible.
 133  * Should we open-code syslog() here to use correct facility?
 134  */
 135
 136 int klogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 137 int klogd_main(int argc UNUSED_PARAM, char **argv)
 138 {
 139         int i = 0;
 140         char *opt_c;
 141         int opt;
 142         int used;
 143         unsigned int cnt;
 144
 145         opt = getopt32(argv, "c:n", &opt_c);
 146         if (opt & OPT_LEVEL) {
 147                 /* Valid levels are between 1 and 8 */
 148                 i = xatou_range(opt_c, 1, 8);
 149         }
 150         if (!(opt & OPT_FOREGROUND)) {
 151                 bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
 152         }
 153
 154         logmode = LOGMODE_SYSLOG;
 155
 156         /* klogd_open() before openlog(), since it might use fixed fd 3,
 157          * and openlog() also may use the same fd 3 if we swap them:
 158          */
 159         klogd_open();
 160         openlog("kernel", 0, LOG_KERN);
 161         /*
 162          * glibc problem: for some reason, glibc changes LOG_KERN to LOG_USER
 163          * above. The logic behind this is that standard
 164          * http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html
 165          * says the following about openlog and syslog:
 166          * "LOG_USER
 167          *  Messages generated by arbitrary processes.
 168          *  This is the default facility identifier if none is specified."
 169          *
 170          * I believe glibc misinterpreted this text as "if openlog's
 171          * third parameter is 0 (=LOG_KERN), treat it as LOG_USER".
 172          * Whereas it was meant to say "if *syslog* is called with facility
 173          * 0 in its 1st parameter without prior call to openlog, then perform
 174          * implicit openlog(LOG_USER)".
 175          *
 176          * As a result of this, eh, feature, standard klogd was forced
 177          * to open-code its own openlog and syslog implementation (!).
 178          *
 179          * Note that prohibiting openlog(LOG_KERN) on libc level does not
 180          * add any security: any process can open a socket to "/dev/log"
 181          * and write a string "<0>Voila, a LOG_KERN + LOG_EMERG message"
 182          *
 183          * Google code search tells me there is no widespread use of
 184          * openlog("foo", 0, 0), thus fixing glibc won't break userspace.
 185          *
 186          * The bug against glibc was filed:
 187          * bugzilla.redhat.com/show_bug.cgi?id=547000
 188          */
 189
 190         if (i)
 191                 klogd_setloglevel(i);
 192
 193         signal(SIGHUP, SIG_IGN);
 194         /* We want klogd_read to not be restarted, thus _norestart: */
 195         bb_signals_recursive_norestart(BB_FATAL_SIGS, record_signo);
 196
 197         syslog(LOG_NOTICE, "klogd started: %s", bb_banner);
 198
 199         used = 0;
 200         cnt = 0;
 201         while (!bb_got_signal) {
 202                 int n;
 203                 int priority;
 204                 char *start;
 205                 char *eor;
 206
 207                 /* "2 -- Read from the log." */
 208                 start = log_buffer + used;
 209                 n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
 210                 if (n < 0) {
 211                         if (errno == EINTR)
 212                                 continue;
 213                         bb_perror_msg(READ_ERROR);
 214                         break;
 215                 }
 216                 start[n] = '\0';
 217                 eor = &start[n];
 218
 219                 /* Process each newline-terminated line in the buffer */
 220                 start = log_buffer;
 221                 while (1) {
 222                         char *newline = strchrnul(start, '\n');
 223
 224                         if (*newline == '\0') {
 225                                 /* This line is incomplete */
 226
 227                                 /* move it to the front of the buffer */
 228                                 overlapping_strcpy(log_buffer, start);
 229                                 used = newline - start;
 230                                 if (used < KLOGD_LOGBUF_SIZE-1) {
 231                                         /* buffer isn't full */
 232                                         break;
 233                                 }
 234                                 /* buffer is full, log it anyway */
 235                                 used = 0;
 236                                 newline = NULL;
 237                         } else {
 238                                 *newline++ = '\0';
 239                         }
 240
 241                         /* Extract the priority */
 242                         priority = LOG_INFO;
 243                         if (*start == '<') {
 244                                 start++;
 245                                 if (*start) {
 246                                         /* kernel never generates multi-digit prios */
 247                                         priority = (*start - '0');
 248                                         start++;
 249                                 }
 250                                 if (*start == '>')
 251                                         start++;
 252                         }
 253                         /* Log (only non-empty lines) */
 254                         if (*start) {
 255                                 syslog(priority, "%s", start);
 256                                 /* give syslog time to catch up */
 257                                 ++cnt;
 258                                 if ((cnt & 0x07) == 0 && (cnt < 300 || (eor - start) > 200))
 259                                         usleep(50 * 1000);
 260                         }
 261
 262                         if (!newline)
 263                                 break;
 264                         start = newline;
 265                 }
 266         }
 267
 268         klogd_close();
 269         syslog(LOG_NOTICE, "klogd: exiting");
 270         if (bb_got_signal)
 271                 kill_myself_with_sig(bb_got_signal);
 272         return EXIT_FAILURE;
 273 }