source: MondoRescue/branches/3.3/mindi-busybox/sysklogd/syslogd.c@ 3865

/* vi: set sw=4 ts=4: */
/*
 * Mini syslogd implementation for busybox
 *
 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 *
 * Copyright (C) 2000 by Karl M. Hegbloom <karlheg@debian.org>
 *
 * "circular buffer" Copyright (C) 2001 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 SYSLOGD
//config:   bool "syslogd"
//config:   default y
//config:   help
//config:     The syslogd utility is used to record logs of all the
//config:     significant events that occur on a system. Every
//config:     message that is logged records the date and time of the
//config:     event, and will generally also record the name of the
//config:     application that generated the message. When used in
//config:     conjunction with klogd, messages from the Linux kernel
//config:     can also be recorded. This is terribly useful,
//config:     especially for finding what happened when something goes
//config:     wrong. And something almost always will go wrong if
//config:     you wait long enough....
//config:
//config:config FEATURE_ROTATE_LOGFILE
//config:   bool "Rotate message files"
//config:   default y
//config:   depends on SYSLOGD
//config:   help
//config:     This enables syslogd to rotate the message files
//config:     on his own. No need to use an external rotate script.
//config:
//config:config FEATURE_REMOTE_LOG
//config:   bool "Remote Log support"
//config:   default y
//config:   depends on SYSLOGD
//config:   help
//config:     When you enable this feature, the syslogd utility can
//config:     be used to send system log messages to another system
//config:     connected via a network. This allows the remote
//config:     machine to log all the system messages, which can be
//config:     terribly useful for reducing the number of serial
//config:     cables you use. It can also be a very good security
//config:     measure to prevent system logs from being tampered with
//config:     by an intruder.
//config:
//config:config FEATURE_SYSLOGD_DUP
//config:   bool "Support -D (drop dups) option"
//config:   default y
//config:   depends on SYSLOGD
//config:   help
//config:     Option -D instructs syslogd to drop consecutive messages
//config:     which are totally the same.
//config:
//config:config FEATURE_SYSLOGD_CFG
//config:   bool "Support syslog.conf"
//config:   default y
//config:   depends on SYSLOGD
//config:   help
//config:     Supports restricted syslogd config. See docs/syslog.conf.txt
//config:
//config:config FEATURE_SYSLOGD_READ_BUFFER_SIZE
//config:   int "Read buffer size in bytes"
//config:   default 256
//config:   range 256 20000
//config:   depends on SYSLOGD
//config:   help
//config:     This option sets the size of the syslog read buffer.
//config:     Actual memory usage increases around five times the
//config:     change done here.
//config:
//config:config FEATURE_IPC_SYSLOG
//config:   bool "Circular Buffer support"
//config:   default y
//config:   depends on SYSLOGD
//config:   help
//config:     When you enable this feature, the syslogd utility will
//config:     use a circular buffer to record system log messages.
//config:     When the buffer is filled it will continue to overwrite
//config:     the oldest messages. This can be very useful for
//config:     systems with little or no permanent storage, since
//config:     otherwise system logs can eventually fill up your
//config:     entire filesystem, which may cause your system to
//config:     break badly.
//config:
//config:config FEATURE_IPC_SYSLOG_BUFFER_SIZE
//config:   int "Circular buffer size in Kbytes (minimum 4KB)"
//config:   default 16
//config:   range 4 2147483647
//config:   depends on FEATURE_IPC_SYSLOG
//config:   help
//config:     This option sets the size of the circular buffer
//config:     used to record system log messages.
//config:
//config:config FEATURE_KMSG_SYSLOG
//config:   bool "Linux kernel printk buffer support"
//config:   default y
//config:   depends on SYSLOGD
//config:   select PLATFORM_LINUX
//config:   help
//config:     When you enable this feature, the syslogd utility will
//config:     write system log message to the Linux kernel's printk buffer.
//config:     This can be used as a smaller alternative to the syslogd IPC
//config:     support, as klogd and logread aren't needed.
//config:
//config:     NOTICE: Syslog facilities in log entries needs kernel 3.5+.

//applet:IF_SYSLOGD(APPLET(syslogd, BB_DIR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_SYSLOGD) += syslogd_and_logger.o

//usage:#define syslogd_trivial_usage
//usage:       "[OPTIONS]"
//usage:#define syslogd_full_usage "\n\n"
//usage:       "System logging utility\n"
//usage:    IF_NOT_FEATURE_SYSLOGD_CFG(
//usage:       "(this version of syslogd ignores /etc/syslog.conf)\n"
//usage:    )
//usage:     "\n    -n      Run in foreground"
//usage:    IF_FEATURE_REMOTE_LOG(
//usage:     "\n    -R HOST[:PORT]  Log to HOST:PORT (default PORT:514)"
//usage:     "\n    -L      Log locally and via network (default is network only if -R)"
//usage:    )
//usage:    IF_FEATURE_IPC_SYSLOG(
/* NB: -Csize shouldn't have space (because size is optional) */
//usage:     "\n    -C[size_kb] Log to shared mem buffer (use logread to read it)"
//usage:    )
//usage:    IF_FEATURE_KMSG_SYSLOG(
//usage:     "\n    -K      Log to kernel printk buffer (use dmesg to read it)"
//usage:    )
//usage:     "\n    -O FILE     Log to FILE (default: /var/log/messages, stdout if -)"
//usage:    IF_FEATURE_ROTATE_LOGFILE(
//usage:     "\n    -s SIZE     Max size (KB) before rotation (default:200KB, 0=off)"
//usage:     "\n    -b N        N rotated logs to keep (default:1, max=99, 0=purge)"
//usage:    )
//usage:     "\n    -l N        Log only messages more urgent than prio N (1-8)"
//usage:     "\n    -S      Smaller output"
//usage:    IF_FEATURE_SYSLOGD_DUP(
//usage:     "\n    -D      Drop duplicates"
//usage:    )
//usage:    IF_FEATURE_SYSLOGD_CFG(
//usage:     "\n    -f FILE     Use FILE as config (default:/etc/syslog.conf)"
//usage:    )
/* //usage:  "\n    -m MIN      Minutes between MARK lines (default:20, 0=off)" */
//usage:
//usage:#define syslogd_example_usage
//usage:       "$ syslogd -R masterlog:514\n"
//usage:       "$ syslogd -R 192.168.1.1:601\n"

/*
 * Done in syslogd_and_logger.c:
#include "libbb.h"
#define SYSLOG_NAMES
#define SYSLOG_NAMES_CONST
#include <syslog.h>
*/
#ifndef _PATH_LOG
#define _PATH_LOG   "/dev/log"
#endif

#include <sys/un.h>
#include <sys/uio.h>

#if ENABLE_FEATURE_REMOTE_LOG
#include <netinet/in.h>
#endif

#if ENABLE_FEATURE_IPC_SYSLOG
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#endif


#define DEBUG 0

/* MARK code is not very useful, is bloat, and broken:
 * can deadlock if alarmed to make MARK while writing to IPC buffer
 * (semaphores are down but do_mark routine tries to down them again) */
#undef SYSLOGD_MARK

/* Write locking does not seem to be useful either */
#undef SYSLOGD_WRLOCK

enum {
    MAX_READ = CONFIG_FEATURE_SYSLOGD_READ_BUFFER_SIZE,
    DNS_WAIT_SEC = 2 * 60,
};

/* Semaphore operation structures */
struct shbuf_ds {
    int32_t size;   /* size of data - 1 */
    int32_t tail;   /* end of message list */
    char data[1];   /* data/messages */
};

#if ENABLE_FEATURE_REMOTE_LOG
typedef struct {
    int remoteFD;
    unsigned last_dns_resolve;
    len_and_sockaddr *remoteAddr;
    const char *remoteHostname;
} remoteHost_t;
#endif

typedef struct logFile_t {
    const char *path;
    int fd;
    time_t last_log_time;
#if ENABLE_FEATURE_ROTATE_LOGFILE
    unsigned size;
    uint8_t isRegular;
#endif
} logFile_t;

#if ENABLE_FEATURE_SYSLOGD_CFG
typedef struct logRule_t {
    uint8_t enabled_facility_priomap[LOG_NFACILITIES];
    struct logFile_t *file;
    struct logRule_t *next;
} logRule_t;
#endif

/* Allows us to have smaller initializer. Ugly. */
#define GLOBALS \
    logFile_t logFile;                      \
    /* interval between marks in seconds */ \
    /*int markInterval;*/                   \
    /* level of messages to be logged */    \
    int logLevel;                           \
IF_FEATURE_ROTATE_LOGFILE( \
    /* max size of file before rotation */  \
    unsigned logFileSize;                   \
    /* number of rotated message files */   \
    unsigned logFileRotate;                 \
) \
IF_FEATURE_IPC_SYSLOG( \
    int shmid; /* ipc shared memory id */   \
    int s_semid; /* ipc semaphore id */     \
    int shm_size;                           \
    struct sembuf SMwup[1];                 \
    struct sembuf SMwdn[3];                 \
) \
IF_FEATURE_SYSLOGD_CFG( \
    logRule_t *log_rules; \
) \
IF_FEATURE_KMSG_SYSLOG( \
    int kmsgfd; \
    int primask; \
)

struct init_globals {
    GLOBALS
};

struct globals {
    GLOBALS

#if ENABLE_FEATURE_REMOTE_LOG
    llist_t *remoteHosts;
#endif
#if ENABLE_FEATURE_IPC_SYSLOG
    struct shbuf_ds *shbuf;
#endif
    /* localhost's name. We print only first 64 chars */
    char *hostname;

    /* We recv into recvbuf... */
    char recvbuf[MAX_READ * (1 + ENABLE_FEATURE_SYSLOGD_DUP)];
    /* ...then copy to parsebuf, escaping control chars */
    /* (can grow x2 max) */
    char parsebuf[MAX_READ*2];
    /* ...then sprintf into printbuf, adding timestamp (15 chars),
     * host (64), fac.prio (20) to the message */
    /* (growth by: 15 + 64 + 20 + delims = ~110) */
    char printbuf[MAX_READ*2 + 128];
};

static const struct init_globals init_data = {
    .logFile = {
        .path = "/var/log/messages",
        .fd = -1,
    },
#ifdef SYSLOGD_MARK
    .markInterval = 20 * 60,
#endif
    .logLevel = 8,
#if ENABLE_FEATURE_ROTATE_LOGFILE
    .logFileSize = 200 * 1024,
    .logFileRotate = 1,
#endif
#if ENABLE_FEATURE_IPC_SYSLOG
    .shmid = -1,
    .s_semid = -1,
    .shm_size = ((CONFIG_FEATURE_IPC_SYSLOG_BUFFER_SIZE)*1024), /* default shm size */
    .SMwup = { {1, -1, IPC_NOWAIT} },
    .SMwdn = { {0, 0}, {1, 0}, {1, +1} },
#endif
};

#define G (*ptr_to_globals)
#define INIT_G() do { \
    SET_PTR_TO_GLOBALS(memcpy(xzalloc(sizeof(G)), &init_data, sizeof(init_data))); \
} while (0)


/* Options */
enum {
    OPTBIT_mark = 0, // -m
    OPTBIT_nofork, // -n
    OPTBIT_outfile, // -O
    OPTBIT_loglevel, // -l
    OPTBIT_small, // -S
    IF_FEATURE_ROTATE_LOGFILE(OPTBIT_filesize   ,)  // -s
    IF_FEATURE_ROTATE_LOGFILE(OPTBIT_rotatecnt  ,)  // -b
    IF_FEATURE_REMOTE_LOG(    OPTBIT_remotelog  ,)  // -R
    IF_FEATURE_REMOTE_LOG(    OPTBIT_locallog   ,)  // -L
    IF_FEATURE_IPC_SYSLOG(    OPTBIT_circularlog,)  // -C
    IF_FEATURE_SYSLOGD_DUP(   OPTBIT_dup        ,)  // -D
    IF_FEATURE_SYSLOGD_CFG(   OPTBIT_cfg        ,)  // -f
    IF_FEATURE_KMSG_SYSLOG(   OPTBIT_kmsg       ,)  // -K

    OPT_mark        = 1 << OPTBIT_mark    ,
    OPT_nofork      = 1 << OPTBIT_nofork  ,
    OPT_outfile     = 1 << OPTBIT_outfile ,
    OPT_loglevel    = 1 << OPTBIT_loglevel,
    OPT_small       = 1 << OPTBIT_small   ,
    OPT_filesize    = IF_FEATURE_ROTATE_LOGFILE((1 << OPTBIT_filesize   )) + 0,
    OPT_rotatecnt   = IF_FEATURE_ROTATE_LOGFILE((1 << OPTBIT_rotatecnt  )) + 0,
    OPT_remotelog   = IF_FEATURE_REMOTE_LOG(    (1 << OPTBIT_remotelog  )) + 0,
    OPT_locallog    = IF_FEATURE_REMOTE_LOG(    (1 << OPTBIT_locallog   )) + 0,
    OPT_circularlog = IF_FEATURE_IPC_SYSLOG(    (1 << OPTBIT_circularlog)) + 0,
    OPT_dup         = IF_FEATURE_SYSLOGD_DUP(   (1 << OPTBIT_dup        )) + 0,
    OPT_cfg         = IF_FEATURE_SYSLOGD_CFG(   (1 << OPTBIT_cfg        )) + 0,
    OPT_kmsg        = IF_FEATURE_KMSG_SYSLOG(   (1 << OPTBIT_kmsg       )) + 0,
};
#define OPTION_STR "m:nO:l:S" \
    IF_FEATURE_ROTATE_LOGFILE("s:" ) \
    IF_FEATURE_ROTATE_LOGFILE("b:" ) \
    IF_FEATURE_REMOTE_LOG(    "R:" ) \
    IF_FEATURE_REMOTE_LOG(    "L"  ) \
    IF_FEATURE_IPC_SYSLOG(    "C::") \
    IF_FEATURE_SYSLOGD_DUP(   "D"  ) \
    IF_FEATURE_SYSLOGD_CFG(   "f:" ) \
    IF_FEATURE_KMSG_SYSLOG(   "K"  )
#define OPTION_DECL *opt_m, *opt_l \
    IF_FEATURE_ROTATE_LOGFILE(,*opt_s) \
    IF_FEATURE_ROTATE_LOGFILE(,*opt_b) \
    IF_FEATURE_IPC_SYSLOG(    ,*opt_C = NULL) \
    IF_FEATURE_SYSLOGD_CFG(   ,*opt_f = NULL)
#define OPTION_PARAM &opt_m, &(G.logFile.path), &opt_l \
    IF_FEATURE_ROTATE_LOGFILE(,&opt_s) \
    IF_FEATURE_ROTATE_LOGFILE(,&opt_b) \
    IF_FEATURE_REMOTE_LOG(    ,&remoteAddrList) \
    IF_FEATURE_IPC_SYSLOG(    ,&opt_C) \
    IF_FEATURE_SYSLOGD_CFG(   ,&opt_f)


#if ENABLE_FEATURE_SYSLOGD_CFG
static const CODE* find_by_name(char *name, const CODE* c_set)
{
    for (; c_set->c_name; c_set++) {
        if (strcmp(name, c_set->c_name) == 0)
            return c_set;
    }
    return NULL;
}
#endif
static const CODE* find_by_val(int val, const CODE* c_set)
{
    for (; c_set->c_name; c_set++) {
        if (c_set->c_val == val)
            return c_set;
    }
    return NULL;
}

#if ENABLE_FEATURE_SYSLOGD_CFG
static void parse_syslogdcfg(const char *file)
{
    char *t;
    logRule_t **pp_rule;
    /* tok[0] set of selectors */
    /* tok[1] file name */
    /* tok[2] has to be NULL */
    char *tok[3];
    parser_t *parser;

    parser = config_open2(file ? file : "/etc/syslog.conf",
                file ? xfopen_for_read : fopen_for_read);
    if (!parser)
        /* didn't find default /etc/syslog.conf */
        /* proceed as if we built busybox without config support */
        return;

    /* use ptr to ptr to avoid checking whether head was initialized */
    pp_rule = &G.log_rules;
    /* iterate through lines of config, skipping comments */
    while (config_read(parser, tok, 3, 2, "# \t", PARSE_NORMAL | PARSE_MIN_DIE)) {
        char *cur_selector;
        logRule_t *cur_rule;

        /* unexpected trailing token? */
        if (tok[2])
            goto cfgerr;

        cur_rule = *pp_rule = xzalloc(sizeof(*cur_rule));

        cur_selector = tok[0];
        /* iterate through selectors: "kern.info;kern.!err;..." */
        do {
            const CODE *code;
            char *next_selector;
            uint8_t negated_prio; /* "kern.!err" */
            uint8_t single_prio;  /* "kern.=err" */
            uint32_t facmap; /* bitmap of enabled facilities */
            uint8_t primap;  /* bitmap of enabled priorities */
            unsigned i;

            next_selector = strchr(cur_selector, ';');
            if (next_selector)
                *next_selector++ = '\0';

            t = strchr(cur_selector, '.');
            if (!t)
                goto cfgerr;
            *t++ = '\0'; /* separate facility from priority */

            negated_prio = 0;
            single_prio = 0;
            if (*t == '!') {
                negated_prio = 1;
                ++t;
            }
            if (*t == '=') {
                single_prio = 1;
                ++t;
            }

            /* parse priority */
            if (*t == '*')
                primap = 0xff; /* all 8 log levels enabled */
            else {
                uint8_t priority;
                code = find_by_name(t, prioritynames);
                if (!code)
                    goto cfgerr;
                primap = 0;
                priority = code->c_val;
                if (priority == INTERNAL_NOPRI) {
                    /* ensure we take "enabled_facility_priomap[fac] &= 0" branch below */
                    negated_prio = 1;
                } else {
                    priority = 1 << priority;
                    do {
                        primap |= priority;
                        if (single_prio)
                            break;
                        priority >>= 1;
                    } while (priority);
                    if (negated_prio)
                        primap = ~primap;
                }
            }

            /* parse facility */
            if (*cur_selector == '*')
                facmap = (1<<LOG_NFACILITIES) - 1;
            else {
                char *next_facility;
                facmap = 0;
                t = cur_selector;
                /* iterate through facilities: "kern,daemon.<priospec>" */
                do {
                    next_facility = strchr(t, ',');
                    if (next_facility)
                        *next_facility++ = '\0';
                    code = find_by_name(t, facilitynames);
                    if (!code)
                        goto cfgerr;
                    /* "mark" is not a real facility, skip it */
                    if (code->c_val != INTERNAL_MARK)
                        facmap |= 1<<(LOG_FAC(code->c_val));
                    t = next_facility;
                } while (t);
            }

            /* merge result with previous selectors */
            for (i = 0; i < LOG_NFACILITIES; ++i) {
                if (!(facmap & (1<<i)))
                    continue;
                if (negated_prio)
                    cur_rule->enabled_facility_priomap[i] &= primap;
                else
                    cur_rule->enabled_facility_priomap[i] |= primap;
            }

            cur_selector = next_selector;
        } while (cur_selector);

        /* check whether current file name was mentioned in previous rules or
         * as global logfile (G.logFile).
         */
        if (strcmp(G.logFile.path, tok[1]) == 0) {
            cur_rule->file = &G.logFile;
            goto found;
        }
        /* temporarily use cur_rule as iterator, but *pp_rule still points
         * to currently processing rule entry.
         * NOTE: *pp_rule points to the current (and last in the list) rule.
         */
        for (cur_rule = G.log_rules; cur_rule != *pp_rule; cur_rule = cur_rule->next) {
            if (strcmp(cur_rule->file->path, tok[1]) == 0) {
                /* found - reuse the same file structure */
                (*pp_rule)->file = cur_rule->file;
                cur_rule = *pp_rule;
                goto found;
            }
        }
        cur_rule->file = xzalloc(sizeof(*cur_rule->file));
        cur_rule->file->fd = -1;
        cur_rule->file->path = xstrdup(tok[1]);
 found:
        pp_rule = &cur_rule->next;
    }
    config_close(parser);
    return;

 cfgerr:
    bb_error_msg_and_die("error in '%s' at line %d",
            file ? file : "/etc/syslog.conf",
            parser->lineno);
}
#endif

/* circular buffer variables/structures */
#if ENABLE_FEATURE_IPC_SYSLOG

#if CONFIG_FEATURE_IPC_SYSLOG_BUFFER_SIZE < 4
#error Sorry, you must set the syslogd buffer size to at least 4KB.
#error Please check CONFIG_FEATURE_IPC_SYSLOG_BUFFER_SIZE
#endif

/* our shared key (syslogd.c and logread.c must be in sync) */
enum { KEY_ID = 0x414e4547 }; /* "GENA" */

static void ipcsyslog_cleanup(void)
{
    if (G.shmid != -1) {
        shmdt(G.shbuf);
    }
    if (G.shmid != -1) {
        shmctl(G.shmid, IPC_RMID, NULL);
    }
    if (G.s_semid != -1) {
        semctl(G.s_semid, 0, IPC_RMID, 0);
    }
}

static void ipcsyslog_init(void)
{
    if (DEBUG)
        printf("shmget(%x, %d,...)\n", (int)KEY_ID, G.shm_size);

    G.shmid = shmget(KEY_ID, G.shm_size, IPC_CREAT | 0644);
    if (G.shmid == -1) {
        bb_perror_msg_and_die("shmget");
    }

    G.shbuf = shmat(G.shmid, NULL, 0);
    if (G.shbuf == (void*) -1L) { /* shmat has bizarre error return */
        bb_perror_msg_and_die("shmat");
    }

    memset(G.shbuf, 0, G.shm_size);
    G.shbuf->size = G.shm_size - offsetof(struct shbuf_ds, data) - 1;
    /*G.shbuf->tail = 0;*/

    /* we'll trust the OS to set initial semval to 0 (let's hope) */
    G.s_semid = semget(KEY_ID, 2, IPC_CREAT | IPC_EXCL | 1023);
    if (G.s_semid == -1) {
        if (errno == EEXIST) {
            G.s_semid = semget(KEY_ID, 2, 0);
            if (G.s_semid != -1)
                return;
        }
        bb_perror_msg_and_die("semget");
    }
}

/* Write message to shared mem buffer */
static void log_to_shmem(const char *msg)
{
    int old_tail, new_tail;
    int len;

    if (semop(G.s_semid, G.SMwdn, 3) == -1) {
        bb_perror_msg_and_die("SMwdn");
    }

    /* Circular Buffer Algorithm:
     * --------------------------
     * tail == position where to store next syslog message.
     * tail's max value is (shbuf->size - 1)
     * Last byte of buffer is never used and remains NUL.
     */
    len = strlen(msg) + 1; /* length with NUL included */
 again:
    old_tail = G.shbuf->tail;
    new_tail = old_tail + len;
    if (new_tail < G.shbuf->size) {
        /* store message, set new tail */
        memcpy(G.shbuf->data + old_tail, msg, len);
        G.shbuf->tail = new_tail;
    } else {
        /* k == available buffer space ahead of old tail */
        int k = G.shbuf->size - old_tail;
        /* copy what fits to the end of buffer, and repeat */
        memcpy(G.shbuf->data + old_tail, msg, k);
        msg += k;
        len -= k;
        G.shbuf->tail = 0;
        goto again;
    }
    if (semop(G.s_semid, G.SMwup, 1) == -1) {
        bb_perror_msg_and_die("SMwup");
    }
    if (DEBUG)
        printf("tail:%d\n", G.shbuf->tail);
}
#else
static void ipcsyslog_cleanup(void) {}
static void ipcsyslog_init(void) {}
void log_to_shmem(const char *msg);
#endif /* FEATURE_IPC_SYSLOG */

#if ENABLE_FEATURE_KMSG_SYSLOG
static void kmsg_init(void)
{
    G.kmsgfd = xopen("/dev/kmsg", O_WRONLY);

    /*
     * kernel < 3.5 expects single char printk KERN_* priority prefix,
     * from 3.5 onwards the full syslog facility/priority format is supported
     */
    if (get_linux_version_code() < KERNEL_VERSION(3,5,0))
        G.primask = LOG_PRIMASK;
    else
        G.primask = -1;
}

static void kmsg_cleanup(void)
{
    if (ENABLE_FEATURE_CLEAN_UP)
        close(G.kmsgfd);
}

/* Write message to /dev/kmsg */
static void log_to_kmsg(int pri, const char *msg)
{
    /*
     * kernel < 3.5 expects single char printk KERN_* priority prefix,
     * from 3.5 onwards the full syslog facility/priority format is supported
     */
    pri &= G.primask;

    full_write(G.kmsgfd, G.printbuf, sprintf(G.printbuf, "<%d>%s\n", pri, msg));
}
#else
static void kmsg_init(void) {}
static void kmsg_cleanup(void) {}
static void log_to_kmsg(int pri UNUSED_PARAM, const char *msg UNUSED_PARAM) {}
#endif /* FEATURE_KMSG_SYSLOG */

/* Print a message to the log file. */
static void log_locally(time_t now, char *msg, logFile_t *log_file)
{
#ifdef SYSLOGD_WRLOCK
    struct flock fl;
#endif
    int len = strlen(msg);

    /* fd can't be 0 (we connect fd 0 to /dev/log socket) */
    /* fd is 1 if "-O -" is in use */
    if (log_file->fd > 1) {
        /* Reopen log files every second. This allows admin
         * to delete the files and not worry about restarting us.
         * This costs almost nothing since it happens
         * _at most_ once a second for each file, and happens
         * only when each file is actually written.
         */
        if (!now)
            now = time(NULL);
        if (log_file->last_log_time != now) {
            log_file->last_log_time = now;
            close(log_file->fd);
            goto reopen;
        }
    }
    else if (log_file->fd == 1) {
        /* We are logging to stdout: do nothing */
    }
    else {
        if (LONE_DASH(log_file->path)) {
            log_file->fd = 1;
            /* log_file->isRegular = 0; - already is */
        } else {
 reopen:
            log_file->fd = open(log_file->path, O_WRONLY | O_CREAT
                    | O_NOCTTY | O_APPEND | O_NONBLOCK,
                    0666);
            if (log_file->fd < 0) {
                /* cannot open logfile? - print to /dev/console then */
                int fd = device_open(DEV_CONSOLE, O_WRONLY | O_NOCTTY | O_NONBLOCK);
                if (fd < 0)
                    fd = 2; /* then stderr, dammit */
                full_write(fd, msg, len);
                if (fd != 2)
                    close(fd);
                return;
            }
#if ENABLE_FEATURE_ROTATE_LOGFILE
            {
                struct stat statf;
                log_file->isRegular = (fstat(log_file->fd, &statf) == 0 && S_ISREG(statf.st_mode));
                /* bug (mostly harmless): can wrap around if file > 4gb */
                log_file->size = statf.st_size;
            }
#endif
        }
    }

#ifdef SYSLOGD_WRLOCK
    fl.l_whence = SEEK_SET;
    fl.l_start = 0;
    fl.l_len = 1;
    fl.l_type = F_WRLCK;
    fcntl(log_file->fd, F_SETLKW, &fl);
#endif

#if ENABLE_FEATURE_ROTATE_LOGFILE
    if (G.logFileSize && log_file->isRegular && log_file->size > G.logFileSize) {
        if (G.logFileRotate) { /* always 0..99 */
            int i = strlen(log_file->path) + 3 + 1;
            char oldFile[i];
            char newFile[i];
            i = G.logFileRotate - 1;
            /* rename: f.8 -> f.9; f.7 -> f.8; ... */
            while (1) {
                sprintf(newFile, "%s.%d", log_file->path, i);
                if (i == 0) break;
                sprintf(oldFile, "%s.%d", log_file->path, --i);
                /* ignore errors - file might be missing */
                rename(oldFile, newFile);
            }
            /* newFile == "f.0" now */
            rename(log_file->path, newFile);
        }

        /* We may or may not have just renamed the file away;
         * if we didn't rename because we aren't keeping any backlog,
         * then it's time to clobber the file. If we did rename it...,
         * incredibly, if F and F.0 are hardlinks, POSIX _demands_
         * that rename returns 0 but does not remove F!!!
         * (hardlinked F/F.0 pair was observed after
         * power failure during rename()).
         * So ensure old file is gone in any case:
         */
        unlink(log_file->path);
#ifdef SYSLOGD_WRLOCK
        fl.l_type = F_UNLCK;
        fcntl(log_file->fd, F_SETLKW, &fl);
#endif
        close(log_file->fd);
        goto reopen;
    }
/* TODO: what to do on write errors ("disk full")? */
    len = full_write(log_file->fd, msg, len);
    if (len > 0)
        log_file->size += len;
#else
    full_write(log_file->fd, msg, len);
#endif

#ifdef SYSLOGD_WRLOCK
    fl.l_type = F_UNLCK;
    fcntl(log_file->fd, F_SETLKW, &fl);
#endif
}

static void parse_fac_prio_20(int pri, char *res20)
{
    const CODE *c_pri, *c_fac;

    c_fac = find_by_val(LOG_FAC(pri) << 3, facilitynames);
    if (c_fac) {
        c_pri = find_by_val(LOG_PRI(pri), prioritynames);
        if (c_pri) {
            snprintf(res20, 20, "%s.%s", c_fac->c_name, c_pri->c_name);
            return;
        }
    }
    snprintf(res20, 20, "<%d>", pri);
}

/* len parameter is used only for "is there a timestamp?" check.
 * NB: some callers cheat and supply len==0 when they know
 * that there is no timestamp, short-circuiting the test. */
static void timestamp_and_log(int pri, char *msg, int len)
{
    char *timestamp;
    time_t now;

    /* Jan 18 00:11:22 msg... */
    /* 01234567890123456 */
    if (len < 16 || msg[3] != ' ' || msg[6] != ' '
     || msg[9] != ':' || msg[12] != ':' || msg[15] != ' '
    ) {
        time(&now);
        timestamp = ctime(&now) + 4; /* skip day of week */
    } else {
        now = 0;
        timestamp = msg;
        msg += 16;
    }
    timestamp[15] = '\0';

    if (option_mask32 & OPT_kmsg) {
        log_to_kmsg(pri, msg);
        return;
    }

    if (option_mask32 & OPT_small)
        sprintf(G.printbuf, "%s %s\n", timestamp, msg);
    else {
        char res[20];
        parse_fac_prio_20(pri, res);
        sprintf(G.printbuf, "%s %.64s %s %s\n", timestamp, G.hostname, res, msg);
    }

    /* Log message locally (to file or shared mem) */
#if ENABLE_FEATURE_SYSLOGD_CFG
    {
        bool match = 0;
        logRule_t *rule;
        uint8_t facility = LOG_FAC(pri);
        uint8_t prio_bit = 1 << LOG_PRI(pri);

        for (rule = G.log_rules; rule; rule = rule->next) {
            if (rule->enabled_facility_priomap[facility] & prio_bit) {
                log_locally(now, G.printbuf, rule->file);
                match = 1;
            }
        }
        if (match)
            return;
    }
#endif
    if (LOG_PRI(pri) < G.logLevel) {
#if ENABLE_FEATURE_IPC_SYSLOG
        if ((option_mask32 & OPT_circularlog) && G.shbuf) {
            log_to_shmem(G.printbuf);
            return;
        }
#endif
        log_locally(now, G.printbuf, &G.logFile);
    }
}

static void timestamp_and_log_internal(const char *msg)
{
    /* -L, or no -R */
    if (ENABLE_FEATURE_REMOTE_LOG && !(option_mask32 & OPT_locallog))
        return;
    timestamp_and_log(LOG_SYSLOG | LOG_INFO, (char*)msg, 0);
}

/* tmpbuf[len] is a NUL byte (set by caller), but there can be other,
 * embedded NULs. Split messages on each of these NULs, parse prio,
 * escape control chars and log each locally. */
static void split_escape_and_log(char *tmpbuf, int len)
{
    char *p = tmpbuf;

    tmpbuf += len;
    while (p < tmpbuf) {
        char c;
        char *q = G.parsebuf;
        int pri = (LOG_USER | LOG_NOTICE);

        if (*p == '<') {
            /* Parse the magic priority number */
            pri = bb_strtou(p + 1, &p, 10);
            if (*p == '>')
                p++;
            if (pri & ~(LOG_FACMASK | LOG_PRIMASK))
                pri = (LOG_USER | LOG_NOTICE);
        }

        while ((c = *p++)) {
            if (c == '\n')
                c = ' ';
            if (!(c & ~0x1f) && c != '\t') {
                *q++ = '^';
                c += '@'; /* ^@, ^A, ^B... */
            }
            *q++ = c;
        }
        *q = '\0';

        /* Now log it */
        timestamp_and_log(pri, G.parsebuf, q - G.parsebuf);
    }
}

#ifdef SYSLOGD_MARK
static void do_mark(int sig)
{
    if (G.markInterval) {
        timestamp_and_log_internal("-- MARK --");
        alarm(G.markInterval);
    }
}
#endif

/* Don't inline: prevent struct sockaddr_un to take up space on stack
 * permanently */
static NOINLINE int create_socket(void)
{
    struct sockaddr_un sunx;
    int sock_fd;
    char *dev_log_name;

    memset(&sunx, 0, sizeof(sunx));
    sunx.sun_family = AF_UNIX;

    /* Unlink old /dev/log or object it points to. */
    /* (if it exists, bind will fail) */
    strcpy(sunx.sun_path, _PATH_LOG);
    dev_log_name = xmalloc_follow_symlinks(_PATH_LOG);
    if (dev_log_name) {
        safe_strncpy(sunx.sun_path, dev_log_name, sizeof(sunx.sun_path));
        free(dev_log_name);
    }
    unlink(sunx.sun_path);

    sock_fd = xsocket(AF_UNIX, SOCK_DGRAM, 0);
    xbind(sock_fd, (struct sockaddr *) &sunx, sizeof(sunx));
    chmod(_PATH_LOG, 0666);

    return sock_fd;
}

#if ENABLE_FEATURE_REMOTE_LOG
static int try_to_resolve_remote(remoteHost_t *rh)
{
    if (!rh->remoteAddr) {
        unsigned now = monotonic_sec();

        /* Don't resolve name too often - DNS timeouts can be big */
        if ((now - rh->last_dns_resolve) < DNS_WAIT_SEC)
            return -1;
        rh->last_dns_resolve = now;
        rh->remoteAddr = host2sockaddr(rh->remoteHostname, 514);
        if (!rh->remoteAddr)
            return -1;
    }
    return xsocket(rh->remoteAddr->u.sa.sa_family, SOCK_DGRAM, 0);
}
#endif

static void do_syslogd(void) NORETURN;
static void do_syslogd(void)
{
#if ENABLE_FEATURE_REMOTE_LOG
    llist_t *item;
#endif
#if ENABLE_FEATURE_SYSLOGD_DUP
    int last_sz = -1;
    char *last_buf;
    char *recvbuf = G.recvbuf;
#else
#define recvbuf (G.recvbuf)
#endif

    /* Set up signal handlers (so that they interrupt read()) */
    signal_no_SA_RESTART_empty_mask(SIGTERM, record_signo);
    signal_no_SA_RESTART_empty_mask(SIGINT, record_signo);
    //signal_no_SA_RESTART_empty_mask(SIGQUIT, record_signo);
    signal(SIGHUP, SIG_IGN);
#ifdef SYSLOGD_MARK
    signal(SIGALRM, do_mark);
    alarm(G.markInterval);
#endif
    xmove_fd(create_socket(), STDIN_FILENO);

    if (option_mask32 & OPT_circularlog)
        ipcsyslog_init();

    if (option_mask32 & OPT_kmsg)
        kmsg_init();

    timestamp_and_log_internal("syslogd started: BusyBox v" BB_VER);

    while (!bb_got_signal) {
        ssize_t sz;

#if ENABLE_FEATURE_SYSLOGD_DUP
        last_buf = recvbuf;
        if (recvbuf == G.recvbuf)
            recvbuf = G.recvbuf + MAX_READ;
        else
            recvbuf = G.recvbuf;
#endif
 read_again:
        sz = read(STDIN_FILENO, recvbuf, MAX_READ - 1);
        if (sz < 0) {
            if (!bb_got_signal)
                bb_perror_msg("read from %s", _PATH_LOG);
            break;
        }

        /* Drop trailing '\n' and NULs (typically there is one NUL) */
        while (1) {
            if (sz == 0)
                goto read_again;
            /* man 3 syslog says: "A trailing newline is added when needed".
             * However, neither glibc nor uclibc do this:
             * syslog(prio, "test")   sends "test\0" to /dev/log,
             * syslog(prio, "test\n") sends "test\n\0".
             * IOW: newline is passed verbatim!
             * I take it to mean that it's syslogd's job
             * to make those look identical in the log files. */
            if (recvbuf[sz-1] != '\0' && recvbuf[sz-1] != '\n')
                break;
            sz--;
        }
#if ENABLE_FEATURE_SYSLOGD_DUP
        if ((option_mask32 & OPT_dup) && (sz == last_sz))
            if (memcmp(last_buf, recvbuf, sz) == 0)
                continue;
        last_sz = sz;
#endif
#if ENABLE_FEATURE_REMOTE_LOG
        /* Stock syslogd sends it '\n'-terminated
         * over network, mimic that */
        recvbuf[sz] = '\n';

        /* We are not modifying log messages in any way before send */
        /* Remote site cannot trust _us_ anyway and need to do validation again */
        for (item = G.remoteHosts; item != NULL; item = item->link) {
            remoteHost_t *rh = (remoteHost_t *)item->data;

            if (rh->remoteFD == -1) {
                rh->remoteFD = try_to_resolve_remote(rh);
                if (rh->remoteFD == -1)
                    continue;
            }

            /* Send message to remote logger.
             * On some errors, close and set remoteFD to -1
             * so that DNS resolution is retried.
             */
            if (sendto(rh->remoteFD, recvbuf, sz+1,
                    MSG_DONTWAIT | MSG_NOSIGNAL,
                    &(rh->remoteAddr->u.sa), rh->remoteAddr->len) == -1
            ) {
                switch (errno) {
                case ECONNRESET:
                case ENOTCONN: /* paranoia */
                case EPIPE:
                    close(rh->remoteFD);
                    rh->remoteFD = -1;
                    free(rh->remoteAddr);
                    rh->remoteAddr = NULL;
                }
            }
        }
#endif
        if (!ENABLE_FEATURE_REMOTE_LOG || (option_mask32 & OPT_locallog)) {
            recvbuf[sz] = '\0'; /* ensure it *is* NUL terminated */
            split_escape_and_log(recvbuf, sz);
        }
    } /* while (!bb_got_signal) */

    timestamp_and_log_internal("syslogd exiting");
    remove_pidfile(CONFIG_PID_FILE_PATH "/syslogd.pid");
    ipcsyslog_cleanup();
    if (option_mask32 & OPT_kmsg)
        kmsg_cleanup();
    kill_myself_with_sig(bb_got_signal);
#undef recvbuf
}

int syslogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int syslogd_main(int argc UNUSED_PARAM, char **argv)
{
    int opts;
    char OPTION_DECL;
#if ENABLE_FEATURE_REMOTE_LOG
    llist_t *remoteAddrList = NULL;
#endif

    INIT_G();

    /* No non-option params, -R can occur multiple times */
    opt_complementary = "=0" IF_FEATURE_REMOTE_LOG(":R::");
    opts = getopt32(argv, OPTION_STR, OPTION_PARAM);
#if ENABLE_FEATURE_REMOTE_LOG
    while (remoteAddrList) {
        remoteHost_t *rh = xzalloc(sizeof(*rh));
        rh->remoteHostname = llist_pop(&remoteAddrList);
        rh->remoteFD = -1;
        rh->last_dns_resolve = monotonic_sec() - DNS_WAIT_SEC - 1;
        llist_add_to(&G.remoteHosts, rh);
    }
#endif

#ifdef SYSLOGD_MARK
    if (opts & OPT_mark) // -m
        G.markInterval = xatou_range(opt_m, 0, INT_MAX/60) * 60;
#endif
    //if (opts & OPT_nofork) // -n
    //if (opts & OPT_outfile) // -O
    if (opts & OPT_loglevel) // -l
        G.logLevel = xatou_range(opt_l, 1, 8);
    //if (opts & OPT_small) // -S
#if ENABLE_FEATURE_ROTATE_LOGFILE
    if (opts & OPT_filesize) // -s
        G.logFileSize = xatou_range(opt_s, 0, INT_MAX/1024) * 1024;
    if (opts & OPT_rotatecnt) // -b
        G.logFileRotate = xatou_range(opt_b, 0, 99);
#endif
#if ENABLE_FEATURE_IPC_SYSLOG
    if (opt_C) // -Cn
        G.shm_size = xatoul_range(opt_C, 4, INT_MAX/1024) * 1024;
#endif
    /* If they have not specified remote logging, then log locally */
    if (ENABLE_FEATURE_REMOTE_LOG && !(opts & OPT_remotelog)) // -R
        option_mask32 |= OPT_locallog;
#if ENABLE_FEATURE_SYSLOGD_CFG
    parse_syslogdcfg(opt_f);
#endif

    /* Store away localhost's name before the fork */
    G.hostname = safe_gethostname();
    *strchrnul(G.hostname, '.') = '\0';

    if (!(opts & OPT_nofork)) {
        bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
    }

    //umask(0); - why??
    write_pidfile(CONFIG_PID_FILE_PATH "/syslogd.pid");

    do_syslogd();
    /* return EXIT_SUCCESS; */
}

/* Clean up. Needed because we are included from syslogd_and_logger.c */
#undef DEBUG
#undef SYSLOGD_MARK
#undef SYSLOGD_WRLOCK
#undef G
#undef GLOBALS
#undef INIT_G
#undef OPTION_STR
#undef OPTION_DECL
#undef OPTION_PARAM