/* 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 (5.5 kb)"
//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;
}