source: MondoRescue/branches/3.3/mindi-busybox/sysklogd/klogd.c@ 3898

/* vi: set sw=4 ts=4: */
/*
 * Mini klogd implementation for busybox
 *
 * Copyright (C) 2001 by Gennady Feldman <gfeldman@gena01.com>.
 * Changes: Made this a standalone busybox module which uses standalone
 * syslog() client interface.
 *
 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 *
 * Copyright (C) 2000 by Karl M. Hegbloom <karlheg@debian.org>
 *
 * "circular buffer" Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
 *
 * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config KLOGD
//config:   bool "klogd"
//config:   default y
//config:   help
//config:     klogd is a utility which intercepts and logs all
//config:     messages from the Linux kernel and sends the messages
//config:     out to the 'syslogd' utility so they can be logged. If
//config:     you wish to record the messages produced by the kernel,
//config:     you should enable this option.
//config:
//config:comment "klogd should not be used together with syslog to kernel printk buffer"
//config:   depends on KLOGD && FEATURE_KMSG_SYSLOG
//config:
//config:config FEATURE_KLOGD_KLOGCTL
//config:   bool "Use the klogctl() interface"
//config:   default y
//config:   depends on KLOGD
//config:   select PLATFORM_LINUX
//config:   help
//config:     The klogd applet supports two interfaces for reading
//config:     kernel messages. Linux provides the klogctl() interface
//config:     which allows reading messages from the kernel ring buffer
//config:     independently from the file system.
//config:
//config:     If you answer 'N' here, klogd will use the more portable
//config:     approach of reading them from /proc or a device node.
//config:     However, this method requires the file to be available.
//config:
//config:     If in doubt, say 'Y'.

//applet:IF_KLOGD(APPLET(klogd, BB_DIR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_KLOGD) += klogd.o

//usage:#define klogd_trivial_usage
//usage:       "[-c N] [-n]"
//usage:#define klogd_full_usage "\n\n"
//usage:       "Kernel logger\n"
//usage:     "\n    -c N    Print to console messages more urgent than prio N (1-8)"
//usage:     "\n    -n  Run in foreground"

#include "libbb.h"
#include "common_bufsiz.h"
#include <syslog.h>


/* The Linux-specific klogctl(3) interface does not rely on the filesystem and
 * allows us to change the console loglevel. Alternatively, we read the
 * messages from _PATH_KLOG. */

#if ENABLE_FEATURE_KLOGD_KLOGCTL

# include <sys/klog.h>

static void klogd_open(void)
{
    /* "Open the log. Currently a NOP" */
    klogctl(1, NULL, 0);
}

static void klogd_setloglevel(int lvl)
{
    /* "printk() prints a message on the console only if it has a loglevel
     * less than console_loglevel". Here we set console_loglevel = lvl. */
    klogctl(8, NULL, lvl);
}

static int klogd_read(char *bufp, int len)
{
    return klogctl(2, bufp, len);
}
# define READ_ERROR "klogctl(2) error"

static void klogd_close(void)
{
    /* FYI: cmd 7 is equivalent to setting console_loglevel to 7
     * via klogctl(8, NULL, 7). */
    klogctl(7, NULL, 0); /* "7 -- Enable printk's to console" */
    klogctl(0, NULL, 0); /* "0 -- Close the log. Currently a NOP" */
}

#else

# ifndef _PATH_KLOG
#  ifdef __GNU__
#   define _PATH_KLOG "/dev/klog"
#  else
#   error "your system's _PATH_KLOG is unknown"
#  endif
# endif
# define PATH_PRINTK "/proc/sys/kernel/printk"

enum { klogfd = 3 };

static void klogd_open(void)
{
    int fd = xopen(_PATH_KLOG, O_RDONLY);
    xmove_fd(fd, klogfd);
}

static void klogd_setloglevel(int lvl)
{
    FILE *fp = fopen_or_warn(PATH_PRINTK, "w");
    if (fp) {
        /* This changes only first value:
         * "messages with a higher priority than this
         * [that is, with numerically lower value]
         * will be printed to the console".
         * The other three values in this pseudo-file aren't changed.
         */
        fprintf(fp, "%u\n", lvl);
        fclose(fp);
    }
}

static int klogd_read(char *bufp, int len)
{
    return read(klogfd, bufp, len);
}
# define READ_ERROR "read error"

static void klogd_close(void)
{
    klogd_setloglevel(7);
    if (ENABLE_FEATURE_CLEAN_UP)
        close(klogfd);
}

#endif

#define log_buffer bb_common_bufsiz1
enum {
    KLOGD_LOGBUF_SIZE = COMMON_BUFSIZE,
    OPT_LEVEL      = (1 << 0),
    OPT_FOREGROUND = (1 << 1),
};

/* TODO: glibc openlog(LOG_KERN) reverts to LOG_USER instead,
 * because that's how they interpret word "default"
 * in the openlog() manpage:
 *      LOG_USER (default)
 *              generic user-level messages
 * and the fact that LOG_KERN is a constant 0.
 * glibc interprets it as "0 in openlog() call means 'use default'".
 * I think it means "if openlog wasn't called before syslog() is called,
 * use default".
 * Convincing glibc maintainers otherwise is, as usual, nearly impossible.
 * Should we open-code syslog() here to use correct facility?
 */

int klogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int klogd_main(int argc UNUSED_PARAM, char **argv)
{
    int i = 0;
    char *opt_c;
    int opt;
    int used;

    setup_common_bufsiz();

    opt = getopt32(argv, "c:n", &opt_c);
    if (opt & OPT_LEVEL) {
        /* Valid levels are between 1 and 8 */
        i = xatou_range(opt_c, 1, 8);
    }
    if (!(opt & OPT_FOREGROUND)) {
        bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
    }

    logmode = LOGMODE_SYSLOG;

    /* klogd_open() before openlog(), since it might use fixed fd 3,
     * and openlog() also may use the same fd 3 if we swap them:
     */
    klogd_open();
    openlog("kernel", 0, LOG_KERN);
    /*
     * glibc problem: for some reason, glibc changes LOG_KERN to LOG_USER
     * above. The logic behind this is that standard
     * http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html
     * says the following about openlog and syslog:
     * "LOG_USER
     *  Messages generated by arbitrary processes.
     *  This is the default facility identifier if none is specified."
     *
     * I believe glibc misinterpreted this text as "if openlog's
     * third parameter is 0 (=LOG_KERN), treat it as LOG_USER".
     * Whereas it was meant to say "if *syslog* is called with facility
     * 0 in its 1st parameter without prior call to openlog, then perform
     * implicit openlog(LOG_USER)".
     *
     * As a result of this, eh, feature, standard klogd was forced
     * to open-code its own openlog and syslog implementation (!).
     *
     * Note that prohibiting openlog(LOG_KERN) on libc level does not
     * add any security: any process can open a socket to "/dev/log"
     * and write a string "<0>Voila, a LOG_KERN + LOG_EMERG message"
     *
     * Google code search tells me there is no widespread use of
     * openlog("foo", 0, 0), thus fixing glibc won't break userspace.
     *
     * The bug against glibc was filed:
     * bugzilla.redhat.com/show_bug.cgi?id=547000
     */

    if (i)
        klogd_setloglevel(i);

    signal(SIGHUP, SIG_IGN);
    /* We want klogd_read to not be restarted, thus _norestart: */
    bb_signals_recursive_norestart(BB_FATAL_SIGS, record_signo);

    syslog(LOG_NOTICE, "klogd started: %s", bb_banner);

    write_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");

    used = 0;
    while (!bb_got_signal) {
        int n;
        int priority;
        char *start;

        /* "2 -- Read from the log." */
        start = log_buffer + used;
        n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
        if (n < 0) {
            if (errno == EINTR)
                continue;
            bb_perror_msg(READ_ERROR);
            break;
        }
        start[n] = '\0';

        /* Process each newline-terminated line in the buffer */
        start = log_buffer;
        while (1) {
            char *newline = strchrnul(start, '\n');

            if (*newline == '\0') {
                /* This line is incomplete */

                /* move it to the front of the buffer */
                overlapping_strcpy(log_buffer, start);
                used = newline - start;
                if (used < KLOGD_LOGBUF_SIZE-1) {
                    /* buffer isn't full */
                    break;
                }
                /* buffer is full, log it anyway */
                used = 0;
                newline = NULL;
            } else {
                *newline++ = '\0';
            }

            /* Extract the priority */
            priority = LOG_INFO;
            if (*start == '<') {
                start++;
                if (*start)
                    priority = strtoul(start, &start, 10);
                if (*start == '>')
                    start++;
            }
            /* Log (only non-empty lines) */
            if (*start)
                syslog(priority, "%s", start);

            if (!newline)
                break;
            start = newline;
        }
    }

    klogd_close();
    syslog(LOG_NOTICE, "klogd: exiting");
    remove_pidfile(CONFIG_PID_FILE_PATH "/klogd.pid");
    if (bb_got_signal)
        kill_myself_with_sig(bb_got_signal);
    return EXIT_FAILURE;
}