/* vi: set sw=4 ts=4: */
/*
 * run as root, but NOT setuid root
 *
 * Copyright 1994 Matthew Dillon (dillon@apollo.west.oic.com)
 * (version 2.3.2)
 * Vladimir Oleynik <dzo@simtreas.ru> (C) 2002
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
//config:config CROND
//config:       bool "crond (14 kb)"
//config:       default y
//config:       select FEATURE_SYSLOG
//config:       help
//config:       Crond is a background daemon that parses individual crontab
//config:       files and executes commands on behalf of the users in question.
//config:       This is a port of dcron from slackware. It uses files of the
//config:       format /var/spool/cron/crontabs/<username> files, for example:
//config:               $ cat /var/spool/cron/crontabs/root
//config:               # Run daily cron jobs at 4:40 every day:
//config:               40 4 * * * /etc/cron/daily > /dev/null 2>&1
//config:
//config:config FEATURE_CROND_D
//config:       bool "Support -d (redirect output to stderr)"
//config:       depends on CROND
//config:       default y
//config:       help
//config:       -d N sets loglevel (0:most verbose) and directs all output to stderr.
//config:
//config:config FEATURE_CROND_CALL_SENDMAIL
//config:       bool "Report command output via email (using sendmail)"
//config:       default y
//config:       depends on CROND
//config:       help
//config:       Command output will be sent to corresponding user via email.
//config:
//config:config FEATURE_CROND_SPECIAL_TIMES
//config:       bool "Support special times (@reboot, @daily, etc) in crontabs"
//config:       default y
//config:       depends on CROND
//config:       help
//config:       string        meaning
//config:       ------        -------
//config:       @reboot       Run once, at startup
//config:       @yearly       Run once a year:  "0 0 1 1 *"
//config:       @annually     Same as @yearly:  "0 0 1 1 *"
//config:       @monthly      Run once a month: "0 0 1 * *"
//config:       @weekly       Run once a week:  "0 0 * * 0"
//config:       @daily        Run once a day:   "0 0 * * *"
//config:       @midnight     Same as @daily:   "0 0 * * *"
//config:       @hourly       Run once an hour: "0 * * * *"
//config:
//config:config FEATURE_CROND_DIR
//config:       string "crond spool directory"
//config:       default "/var/spool/cron"
//config:       depends on CROND || CRONTAB
//config:       help
//config:       Location of crond spool.

//applet:IF_CROND(APPLET(crond, BB_DIR_USR_SBIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_CROND) += crond.o

//usage:#define crond_trivial_usage
//usage:       "[-fbS] [-l N] " IF_FEATURE_CROND_D("[-d N] ") "[-L LOGFILE] [-c DIR]"
//usage:#define crond_full_usage "\n\n"
//usage:       "        -f      Foreground"
//usage:     "\n        -b      Background (default)"
//usage:     "\n        -S      Log to syslog (default)"
//usage:     "\n        -l N    Set log level. Most verbose 0, default 8"
//usage:        IF_FEATURE_CROND_D(
//usage:     "\n        -d N    Set log level, log to stderr"
//usage:        )
//usage:     "\n        -L FILE Log to FILE"
//usage:     "\n        -c DIR  Cron dir. Default:"CONFIG_FEATURE_CROND_DIR"/crontabs"

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

#if 0
/* If libc tracks and reuses setenv()-allocated memory, ok to set this to 0 */
/* Neither glibc nor uclibc do that! */
# define SETENV_LEAKS 0
#else
# define SETENV_LEAKS 1
#endif


#define CRON_DIR        CONFIG_FEATURE_CROND_DIR
#define CRONTABS        CONFIG_FEATURE_CROND_DIR "/crontabs"
#define CRON_REBOOT     CONFIG_PID_FILE_PATH "/crond.reboot"
#ifndef SENDMAIL
# define SENDMAIL       "sendmail"
#endif
#ifndef SENDMAIL_ARGS
# define SENDMAIL_ARGS  "-ti"
#endif
#ifndef CRONUPDATE
# define CRONUPDATE     "cron.update"
#endif
#ifndef MAXLINES
# define MAXLINES       256  /* max lines in non-root crontabs */
#endif


typedef struct CronFile {
        struct CronFile *cf_next;
        struct CronLine *cf_lines;
        char *cf_username;
        smallint cf_wants_starting;     /* bool: one or more jobs ready */
        smallint cf_has_running;        /* bool: one or more jobs running */
        smallint cf_deleted;            /* marked for deletion (but still has running jobs) */
} CronFile;

typedef struct CronLine {
        struct CronLine *cl_next;
        char *cl_cmd;                   /* shell command */
        pid_t cl_pid;                   /* >0:running, <0:needs to be started in this minute, 0:dormant */
#define START_ME_REBOOT -2
#define START_ME_NORMAL -1
#if ENABLE_FEATURE_CROND_CALL_SENDMAIL
        int cl_empty_mail_size;         /* size of mail header only, 0 if no mailfile */
        char *cl_mailto;                /* whom to mail results, may be NULL */
#endif
        char *cl_shell;
        /* ordered by size, not in natural order. makes code smaller: */
        char cl_Dow[7];                 /* 0-6, beginning sunday */
        char cl_Mons[12];               /* 0-11 */
        char cl_Hrs[24];                /* 0-23 */
        char cl_Days[32];               /* 1-31 */
        char cl_Mins[60];               /* 0-59 */
} CronLine;


#define DAEMON_UID 0


enum {
        OPT_l = (1 << 0),
        OPT_L = (1 << 1),
        OPT_f = (1 << 2),
        OPT_b = (1 << 3),
        OPT_S = (1 << 4),
        OPT_c = (1 << 5),
        OPT_d = (1 << 6) * ENABLE_FEATURE_CROND_D,
};

struct globals {
        unsigned log_level; /* = 8; */
        time_t crontab_dir_mtime;
        const char *log_filename;
        const char *crontab_dir_name; /* = CRONTABS; */
        CronFile *cron_files;
        char *default_shell;
#if SETENV_LEAKS
        char *env_var_user;
        char *env_var_home;
        char *env_var_shell;
        char *env_var_logname;
#endif
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { \
        setup_common_bufsiz(); \
        G.log_level = 8; \
        G.crontab_dir_name = CRONTABS; \
} while (0)

/* Log levels:
 * 0 is the most verbose, default 8.
 * For some reason, in fact only 5, 7 and 8 are used.
 */
static void crondlog(unsigned level, const char *msg, va_list va)
{
        if (level >= G.log_level) {
                /*
                 * We are called only for info meesages.
                 * Warnings/errors use plain bb_[p]error_msg's, which
                 * need not touch syslog_level
                 * (they are ok with LOG_ERR default).
                 */
                bb_vinfo_msg(msg, va);
        }
}

static void log5(const char *msg, ...)
{
        va_list va;
        va_start(va, msg);
        crondlog(4, msg, va);
        va_end(va);
}

static void log7(const char *msg, ...)
{
        va_list va;
        va_start(va, msg);
        crondlog(7, msg, va);
        va_end(va);
}

static void log8(const char *msg, ...)
{
        va_list va;
        va_start(va, msg);
        crondlog(8, msg, va);
        va_end(va);
}


static const char DowAry[] ALIGN1 =
        "sun""mon""tue""wed""thu""fri""sat"
;

static const char MonAry[] ALIGN1 =
        "jan""feb""mar""apr""may""jun""jul""aug""sep""oct""nov""dec"
;

static void ParseField(char *user, char *ary, int modvalue, int off,
                                const char *names, char *ptr)
/* 'names' is a pointer to a set of 3-char abbreviations */
{
        char *base = ptr;
        int n1 = -1;
        int n2 = -1;

        // this can't happen due to config_read()
        /*if (base == NULL)
                return;*/

        while (1) {
                int skip = 0;

                /* Handle numeric digit or symbol or '*' */
                if (*ptr == '*') {
                        n1 = 0;  /* everything will be filled */
                        n2 = modvalue - 1;
                        skip = 1;
                        ++ptr;
                } else if (isdigit(*ptr)) {
                        char *endp;
                        if (n1 < 0) {
                                n1 = strtol(ptr, &endp, 10) + off;
                        } else {
                                n2 = strtol(ptr, &endp, 10) + off;
                        }
                        ptr = endp; /* gcc likes temp var for &endp */
                        skip = 1;
                } else if (names) {
                        int i;

                        for (i = 0; names[i]; i += 3) {
                                /* was using strncmp before... */
                                if (strncasecmp(ptr, &names[i], 3) == 0) {
                                        ptr += 3;
                                        if (n1 < 0) {
                                                n1 = i / 3;
                                        } else {
                                                n2 = i / 3;
                                        }
                                        skip = 1;
                                        break;
                                }
                        }
                }

                /* handle optional range '-' */
                if (skip == 0) {
                        goto err;
                }
                if (*ptr == '-' && n2 < 0) {
                        ++ptr;
                        continue;
                }

                /*
                 * collapse single-value ranges, handle skipmark, and fill
                 * in the character array appropriately.
                 */
                if (n2 < 0) {
                        n2 = n1;
                }
                if (*ptr == '/') {
                        char *endp;
                        skip = strtol(ptr + 1, &endp, 10);
                        ptr = endp; /* gcc likes temp var for &endp */
                }

                /*
                 * fill array, using a failsafe is the easiest way to prevent
                 * an endless loop
                 */
                {
                        int s0 = 1;
                        int failsafe = 1024;

                        --n1;
                        do {
                                n1 = (n1 + 1) % modvalue;

                                if (--s0 == 0) {
                                        ary[n1 % modvalue] = 1;
                                        s0 = skip;
                                }
                                if (--failsafe == 0) {
                                        goto err;
                                }
                        } while (n1 != n2);
                }
                if (*ptr != ',') {
                        break;
                }
                ++ptr;
                n1 = -1;
                n2 = -1;
        }

        if (*ptr) {
 err:
                bb_error_msg("user %s: parse error at %s", user, base);
                return;
        }

        /* can't use log5 (it inserts newlines), open-coding it */
        if (G.log_level <= 5 && logmode != LOGMODE_SYSLOG) {
                int i;
                for (i = 0; i < modvalue; ++i)
                        fprintf(stderr, "%d", (unsigned char)ary[i]);
                bb_putchar_stderr('\n');
        }
}

static void FixDayDow(CronLine *line)
{
        unsigned i;
        int weekUsed = 0;
        int daysUsed = 0;

        for (i = 0; i < ARRAY_SIZE(line->cl_Dow); ++i) {
                if (line->cl_Dow[i] == 0) {
                        weekUsed = 1;
                        break;
                }
        }
        for (i = 0; i < ARRAY_SIZE(line->cl_Days); ++i) {
                if (line->cl_Days[i] == 0) {
                        daysUsed = 1;
                        break;
                }
        }
        if (weekUsed != daysUsed) {
                if (weekUsed)
                        memset(line->cl_Days, 0, sizeof(line->cl_Days));
                else /* daysUsed */
                        memset(line->cl_Dow, 0, sizeof(line->cl_Dow));
        }
}

/*
 * delete_cronfile() - delete user database
 *
 * Note: multiple entries for same user may exist if we were unable to
 * completely delete a database due to running processes.
 */
//FIXME: we will start a new job even if the old job is running
//if crontab was reloaded: crond thinks that "new" job is different from "old"
//even if they are in fact completely the same. Example
//Crontab was:
// 0-59 * * * * job1
// 0-59 * * * * long_running_job2
//User edits crontab to:
// 0-59 * * * * job1_updated
// 0-59 * * * * long_running_job2
//Bug: crond can now start another long_running_job2 even if old one
//is still running.
//OTOH most other versions of cron do not wait for job termination anyway,
//they end up with multiple copies of jobs if they don't terminate soon enough.
static void delete_cronfile(const char *userName)
{
        CronFile **pfile = &G.cron_files;
        CronFile *file;

        while ((file = *pfile) != NULL) {
                if (strcmp(userName, file->cf_username) == 0) {
                        CronLine **pline = &file->cf_lines;
                        CronLine *line;

                        file->cf_has_running = 0;
                        file->cf_deleted = 1;

                        while ((line = *pline) != NULL) {
                                if (line->cl_pid > 0) {
                                        file->cf_has_running = 1;
                                        pline = &line->cl_next;
                                } else {
                                        *pline = line->cl_next;
                                        free(line->cl_cmd);
                                        free(line);
                                }
                        }
                        if (file->cf_has_running == 0) {
                                *pfile = file->cf_next;
                                free(file->cf_username);
                                free(file);
                                continue;
                        }
                }
                pfile = &file->cf_next;
        }
}

static void load_crontab(const char *fileName)
{
        struct parser_t *parser;
        struct stat sbuf;
        int maxLines;
        char *tokens[6];
#if ENABLE_FEATURE_CROND_CALL_SENDMAIL
        char *mailTo = NULL;
#endif
        char *shell = NULL;

        delete_cronfile(fileName);

        if (!getpwnam(fileName)) {
                log7("ignoring file '%s' (no such user)", fileName);
                return;
        }

        parser = config_open(fileName);
        if (!parser)
                return;

        maxLines = (strcmp(fileName, "root") == 0) ? 65535 : MAXLINES;

        if (fstat(fileno(parser->fp), &sbuf) == 0 && sbuf.st_uid == DAEMON_UID) {
                CronFile *file = xzalloc(sizeof(CronFile));
                CronLine **pline;
                int n;

                file->cf_username = xstrdup(fileName);
                pline = &file->cf_lines;

                while (1) {
                        CronLine *line;

                        if (!--maxLines) {
                                bb_error_msg("user %s: too many lines", fileName);
                                break;
                        }

                        n = config_read(parser, tokens, 6, 1, "# \t", PARSE_NORMAL | PARSE_KEEP_COPY);
                        if (!n)
                                break;

                        log5("user:%s entry:%s", fileName, parser->data);

                        /* check if line is setting MAILTO= */
                        if (is_prefixed_with(tokens[0], "MAILTO=")) {
#if ENABLE_FEATURE_CROND_CALL_SENDMAIL
                                free(mailTo);
                                mailTo = (tokens[0][7]) ? xstrdup(&tokens[0][7]) : NULL;
#endif /* otherwise just ignore such lines */
                                continue;
                        }
                        if (is_prefixed_with(tokens[0], "SHELL=")) {
                                free(shell);
                                shell = xstrdup(&tokens[0][6]);
                                continue;
                        }
//TODO: handle HOME= too? "man crontab" says:
//name = value
//
//where the spaces around the equal-sign (=) are optional, and any subsequent
//non-leading spaces in value will be part of the value assigned to name.
//The value string may be placed in quotes (single or double, but matching)
//to preserve leading or trailing blanks.
//
//Several environment variables are set up automatically by the cron(8) daemon.
//SHELL is set to /bin/sh, and LOGNAME and HOME are set from the /etc/passwd
//line of the crontab's owner. HOME and SHELL may be overridden by settings
//in the crontab; LOGNAME may not.

#if ENABLE_FEATURE_CROND_SPECIAL_TIMES
                        if (tokens[0][0] == '@') {
                                /*
                                 * "@daily /a/script/to/run PARAM1 PARAM2..."
                                 */
                                typedef struct SpecialEntry {
                                        const char *name;
                                        const char tokens[8];
                                } SpecialEntry;
                                static const SpecialEntry SpecAry[] ALIGN8 = {
                                        /*              hour  day   month weekday */
                                        { "yearly",     "0\0" "1\0" "1\0" "*" },
                                        { "annually",   "0\0" "1\0" "1\0" "*" },
                                        { "monthly",    "0\0" "1\0" "*\0" "*" },
                                        { "weekly",     "0\0" "*\0" "*\0" "0" },
                                        { "daily",      "0\0" "*\0" "*\0" "*" },
                                        { "midnight",   "0\0" "*\0" "*\0" "*" },
                                        { "hourly",     "*\0" "*\0" "*\0" "*" },
                                        { "reboot",     ""                    },
                                };
                                const SpecialEntry *e = SpecAry;

                                if (n < 2)
                                        continue;
                                for (;;) {
                                        if (strcmp(e->name, tokens[0] + 1) == 0) {
                                                /*
                                                 * tokens[1] is only the first word of command,
                                                 * can'r use it.
                                                 * find the entire command in unmodified string:
                                                 */
                                                tokens[5] = skip_whitespace(
                                                        skip_non_whitespace(
                                                        skip_whitespace(parser->data)));
                                                if (e->tokens[0]) {
                                                        char *et = (char*)e->tokens;
                                                        /* minute is "0" for all specials */
                                                        tokens[0] = (char*)"0";
                                                        tokens[1] = et;
                                                        tokens[2] = et + 2;
                                                        tokens[3] = et + 4;
                                                        tokens[4] = et + 6;
                                                }
                                                goto got_it;
                                        }
                                        if (!e->tokens[0])
                                                break;
                                        e++;
                                }
                                continue; /* bad line (unrecognized '@foo') */
                        }
#endif
                        /* check if a minimum of tokens is specified */
                        if (n < 6)
                                continue;
 IF_FEATURE_CROND_SPECIAL_TIMES(
  got_it:
 )
                        *pline = line = xzalloc(sizeof(*line));
#if ENABLE_FEATURE_CROND_SPECIAL_TIMES
                        if (tokens[0][0] == '@') { /* "@reboot" line */
                                file->cf_wants_starting = 1;
                                line->cl_pid = START_ME_REBOOT; /* wants to start */
                                /* line->cl_Mins/Hrs/etc stay zero: never match any time */
                        } else
#endif
                        {
                                /* parse date ranges */
                                ParseField(file->cf_username, line->cl_Mins, 60, 0, NULL, tokens[0]);
                                ParseField(file->cf_username, line->cl_Hrs, 24, 0, NULL, tokens[1]);
                                ParseField(file->cf_username, line->cl_Days, 32, 0, NULL, tokens[2]);
                                ParseField(file->cf_username, line->cl_Mons, 12, -1, MonAry, tokens[3]);
                                ParseField(file->cf_username, line->cl_Dow, 7, 0, DowAry, tokens[4]);
                                /*
                                 * fix days and dow - if one is not "*" and the other
                                 * is "*", the other is set to 0, and vise-versa
                                 */
                                FixDayDow(line);
                        }
#if ENABLE_FEATURE_CROND_CALL_SENDMAIL
                        /* copy mailto (can be NULL) */
                        line->cl_mailto = xstrdup(mailTo);
#endif
                        line->cl_shell = xstrdup(shell);
                        /* copy command */
                        line->cl_cmd = xstrdup(tokens[5]);
                        pline = &line->cl_next;
//bb_error_msg("M[%s]F[%s][%s][%s][%s][%s][%s]", mailTo, tokens[0], tokens[1], tokens[2], tokens[3], tokens[4], tokens[5]);
                }
                *pline = NULL;

                file->cf_next = G.cron_files;
                G.cron_files = file;
        }
        config_close(parser);
#if ENABLE_FEATURE_CROND_CALL_SENDMAIL
        free(mailTo);
#endif
        free(shell);
}

static void process_cron_update_file(void)
{
        FILE *fi;
        char buf[256];

        fi = fopen_for_read(CRONUPDATE);
        if (fi != NULL) {
                unlink(CRONUPDATE);
                while (fgets(buf, sizeof(buf), fi) != NULL) {
                        /* use first word only */
                        skip_non_whitespace(buf)[0] = '\0';
                        load_crontab(buf);
                }
                fclose(fi);
        }
}

static void rescan_crontab_dir(void)
{
        CronFile *file;

        /* Delete all files until we only have ones with running jobs (or none) */
 again:
        for (file = G.cron_files; file; file = file->cf_next) {
                if (!file->cf_deleted) {
                        delete_cronfile(file->cf_username);
                        goto again;
                }
        }

        /* Remove cron update file */
        unlink(CRONUPDATE);
        /* Re-chdir, in case directory was renamed & deleted */
        xchdir(G.crontab_dir_name);

        /* Scan directory and add associated users */
        {
                DIR *dir = opendir(".");
                struct dirent *den;

                /* xopendir exists, but "can't open '.'" is not informative */
                if (!dir)
                        bb_error_msg_and_die("can't open '%s'", G.crontab_dir_name);
                while ((den = readdir(dir)) != NULL) {
                        if (strchr(den->d_name, '.') != NULL) {
                                continue;
                        }
                        load_crontab(den->d_name);
                }
                closedir(dir);
        }
}

#if SETENV_LEAKS
/* We set environment *before* vfork (because we want to use vfork),
 * so we cannot use setenv() - repeated calls to setenv() may leak memory!
 * Using putenv(), and freeing memory after unsetenv() won't leak */
static void safe_setenv(char **pvar_val, const char *var, const char *val)
{
        char *var_val = *pvar_val;

        if (var_val) {
                bb_unsetenv_and_free(var_val);
        }
        *pvar_val = xasprintf("%s=%s", var, val);
        putenv(*pvar_val);
}
#endif

static void set_env_vars(struct passwd *pas, const char *shell)
{
        /* POSIX requires crond to set up at least HOME, LOGNAME, PATH, SHELL.
         * We assume crond inherited suitable PATH.
         */
#if SETENV_LEAKS
        safe_setenv(&G.env_var_logname, "LOGNAME", pas->pw_name);
        safe_setenv(&G.env_var_user, "USER", pas->pw_name);
        safe_setenv(&G.env_var_home, "HOME", pas->pw_dir);
        safe_setenv(&G.env_var_shell, "SHELL", shell);
#else
        xsetenv("LOGNAME", pas->pw_name);
        xsetenv("USER", pas->pw_name);
        xsetenv("HOME", pas->pw_dir);
        xsetenv("SHELL", shell);
#endif
}

static void change_user(struct passwd *pas)
{
        /* careful: we're after vfork! */
        change_identity(pas); /* - initgroups, setgid, setuid */
        if (chdir(pas->pw_dir) < 0) {
                bb_error_msg("can't change directory to '%s'", pas->pw_dir);
                xchdir(CRON_DIR);
        }
}

// TODO: sendmail should be _run-time_ option, not compile-time!
#if ENABLE_FEATURE_CROND_CALL_SENDMAIL

static pid_t
fork_job(const char *user, int mailFd, CronLine *line, bool run_sendmail)
{
        struct passwd *pas;
        const char *shell, *prog;
        smallint sv_logmode;
        pid_t pid;

        /* prepare things before vfork */
        pas = getpwnam(user);
        if (!pas) {
                bb_error_msg("can't get uid for %s", user);
                goto err;
        }

        shell = line->cl_shell ? line->cl_shell : G.default_shell;
        prog = run_sendmail ? SENDMAIL : shell;

        set_env_vars(pas, shell);

        sv_logmode = logmode;
        pid = vfork();
        if (pid == 0) {
                /* CHILD */
                /* initgroups, setgid, setuid, and chdir to home or CRON_DIR */
                change_user(pas);
                log5("child running %s", prog);
                if (mailFd >= 0) {
                        xmove_fd(mailFd, run_sendmail ? 0 : 1);
                        dup2(1, 2);
                }
                /* crond 3.0pl1-100 puts tasks in separate process groups */
                bb_setpgrp();
                if (!run_sendmail)
                        execlp(prog, prog, "-c", line->cl_cmd, (char *) NULL);
                else
                        execlp(prog, prog, SENDMAIL_ARGS, (char *) NULL);
                /*
                 * I want this error message on stderr too,
                 * even if other messages go only to syslog:
                 */
                logmode |= LOGMODE_STDIO;
                bb_error_msg_and_die("can't execute '%s' for user %s", prog, user);
        }
        logmode = sv_logmode;

        if (pid < 0) {
                bb_simple_perror_msg("vfork");
 err:
                pid = 0;
        } /* else: PARENT, FORK SUCCESS */

        /*
         * Close the mail file descriptor.. we can't just leave it open in
         * a structure, closing it later, because we might run out of descriptors
         */
        if (mailFd >= 0) {
                close(mailFd);
        }
        return pid;
}

static pid_t start_one_job(const char *user, CronLine *line)
{
        char mailFile[128];
        int mailFd = -1;

        line->cl_pid = 0;
        line->cl_empty_mail_size = 0;

        if (line->cl_mailto) {
                /* Open mail file (owner is root so nobody can screw with it) */
                snprintf(mailFile, sizeof(mailFile), "%s/cron.%s.%d", CRON_DIR, user, getpid());
                mailFd = open(mailFile, O_CREAT | O_TRUNC | O_WRONLY | O_EXCL | O_APPEND, 0600);

                if (mailFd >= 0) {
                        fdprintf(mailFd, "To: %s\nSubject: cron: %s\n\n", line->cl_mailto,
                                line->cl_cmd);
                        line->cl_empty_mail_size = lseek(mailFd, 0, SEEK_CUR);
                } else {
                        bb_error_msg("can't create mail file %s for user %s, "
                                        "discarding output", mailFile, user);
                }
        }

        line->cl_pid = fork_job(user, mailFd, line, /*sendmail?*/ 0);
        if (mailFd >= 0) {
                if (line->cl_pid <= 0) {
                        unlink(mailFile);
                } else {
                        /* rename mail-file based on pid of process */
                        char *mailFile2 = xasprintf("%s/cron.%s.%d", CRON_DIR, user, (int)line->cl_pid);
                        rename(mailFile, mailFile2); // TODO: xrename?
                        free(mailFile2);
                }
        }

        return line->cl_pid;
}

/*
 * process_finished_job - called when job terminates and when mail terminates
 */
static void process_finished_job(const char *user, CronLine *line)
{
        pid_t pid;
        int mailFd;
        char mailFile[128];
        struct stat sbuf;

        pid = line->cl_pid;
        line->cl_pid = 0;
        if (pid <= 0) {
                /* No job */
                return;
        }
        if (line->cl_empty_mail_size <= 0) {
                /* End of job and no mail file, or end of sendmail job */
                return;
        }

        /*
         * End of primary job - check for mail file.
         * If size has changed and the file is still valid, we send it.
         */
        snprintf(mailFile, sizeof(mailFile), "%s/cron.%s.%d", CRON_DIR, user, (int)pid);
        mailFd = open(mailFile, O_RDONLY);
        unlink(mailFile);
        if (mailFd < 0) {
                return;
        }

        if (fstat(mailFd, &sbuf) < 0
         || sbuf.st_uid != DAEMON_UID
         || sbuf.st_nlink != 0
         || sbuf.st_size == line->cl_empty_mail_size
         || !S_ISREG(sbuf.st_mode)
        ) {
                close(mailFd);
                return;
        }
        line->cl_empty_mail_size = 0;
        /* if (line->cl_mailto) - always true if cl_empty_mail_size was nonzero */
                line->cl_pid = fork_job(user, mailFd, line, /*sendmail?*/ 1);
}

#else /* !ENABLE_FEATURE_CROND_CALL_SENDMAIL */

static pid_t start_one_job(const char *user, CronLine *line)
{
        const char *shell;
        struct passwd *pas;
        pid_t pid;

        pas = getpwnam(user);
        if (!pas) {
                bb_error_msg("can't get uid for %s", user);
                goto err;
        }

        /* Prepare things before vfork */
        shell = line->cl_shell ? line->cl_shell : G.default_shell;
        set_env_vars(pas, shell);

        /* Fork as the user in question and run program */
        pid = vfork();
        if (pid == 0) {
                /* CHILD */
                /* initgroups, setgid, setuid, and chdir to home or CRON_DIR */
                change_user(pas);
                log5("child running %s", shell);
                /* crond 3.0pl1-100 puts tasks in separate process groups */
                bb_setpgrp();
                execl(shell, shell, "-c", line->cl_cmd, (char *) NULL);
                bb_error_msg_and_die("can't execute '%s' for user %s", shell, user);
        }
        if (pid < 0) {
                bb_simple_perror_msg("vfork");
 err:
                pid = 0;
        }
        line->cl_pid = pid;
        return pid;
}

#define process_finished_job(user, line)  ((line)->cl_pid = 0)

#endif /* !ENABLE_FEATURE_CROND_CALL_SENDMAIL */

/*
 * Determine which jobs need to be run.  Under normal conditions, the
 * period is about a minute (one scan).  Worst case it will be one
 * hour (60 scans).
 */
static void flag_starting_jobs(time_t t1, time_t t2)
{
        time_t t;

        /* Find jobs > t1 and <= t2 */

        for (t = t1 - t1 % 60; t <= t2; t += 60) {
                struct tm *ptm;
                CronFile *file;
                CronLine *line;

                if (t <= t1)
                        continue;

                ptm = localtime(&t);
                for (file = G.cron_files; file; file = file->cf_next) {
                        log5("file %s:", file->cf_username);
                        if (file->cf_deleted)
                                continue;
                        for (line = file->cf_lines; line; line = line->cl_next) {
                                log5(" line %s", line->cl_cmd);
                                if (line->cl_Mins[ptm->tm_min]
                                 && line->cl_Hrs[ptm->tm_hour]
                                 && (line->cl_Days[ptm->tm_mday] || line->cl_Dow[ptm->tm_wday])
                                 && line->cl_Mons[ptm->tm_mon]
                                ) {
                                        log5(" job: %d %s",
                                                        (int)line->cl_pid, line->cl_cmd);
                                        if (line->cl_pid > 0) {
                                                log8("user %s: process already running: %s",
                                                        file->cf_username, line->cl_cmd);
                                        } else if (line->cl_pid == 0) {
                                                line->cl_pid = START_ME_NORMAL;
                                                file->cf_wants_starting = 1;
                                        }
                                }
                        }
                }
        }
}

#if ENABLE_FEATURE_CROND_SPECIAL_TIMES
static int touch_reboot_file(void)
{
        int fd = open(CRON_REBOOT, O_WRONLY | O_CREAT | O_EXCL | O_TRUNC, 0000);
        if (fd >= 0) {
                close(fd);
                return 1;
        }
        /* File (presumably) exists - this is not the first run after reboot */
        return 0;
}
#endif

static void start_jobs(int wants_start)
{
        CronFile *file;
        CronLine *line;

        for (file = G.cron_files; file; file = file->cf_next) {
                if (!file->cf_wants_starting)
                        continue;

                file->cf_wants_starting = 0;
                for (line = file->cf_lines; line; line = line->cl_next) {
                        pid_t pid;
                        if (line->cl_pid != wants_start)
                                continue;

                        pid = start_one_job(file->cf_username, line);
                        log8("USER %s pid %3d cmd %s",
                                file->cf_username, (int)pid, line->cl_cmd);
                        if (pid < 0) {
                                file->cf_wants_starting = 1;
                        }
                        if (pid > 0) {
                                file->cf_has_running = 1;
                        }
                }
        }
}

/*
 * Check for job completion, return number of jobs still running after
 * all done.
 */
static int check_completions(void)
{
        CronFile *file;
        CronLine *line;
        int num_still_running = 0;

        for (file = G.cron_files; file; file = file->cf_next) {
                if (!file->cf_has_running)
                        continue;

                file->cf_has_running = 0;
                for (line = file->cf_lines; line; line = line->cl_next) {
                        int r;

                        if (line->cl_pid <= 0)
                                continue;

                        r = waitpid(line->cl_pid, NULL, WNOHANG);
                        if (r < 0 || r == line->cl_pid) {
                                process_finished_job(file->cf_username, line);
                                if (line->cl_pid == 0) {
                                        /* sendmail was not started for it */
                                        continue;
                                }
                                /* else: sendmail was started, job is still running, fall thru */
                        }
                        /* else: r == 0: "process is still running" */
                        file->cf_has_running = 1;
                }
//FIXME: if !file->cf_has_running && file->deleted: delete it!
//otherwise deleted entries will stay forever, right?
                num_still_running += file->cf_has_running;
        }
        return num_still_running;

}

static void reopen_logfile_to_stderr(void)
{
        if (G.log_filename) {
                int logfd = open_or_warn(G.log_filename, O_WRONLY | O_CREAT | O_APPEND);
                if (logfd >= 0)
                        xmove_fd(logfd, STDERR_FILENO);
        }
}

int crond_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int crond_main(int argc UNUSED_PARAM, char **argv)
{
        time_t t2;
        unsigned rescan;
        unsigned sleep_time;
        unsigned opts;

        INIT_G();

        opts = getopt32(argv, "^"
                        "l:L:fbSc:" IF_FEATURE_CROND_D("d:")
                        "\0"
                        /* "-b after -f is ignored", and so on for every pair a-b */
                        "f-b:b-f:S-L:L-S" IF_FEATURE_CROND_D(":d-l")
                        /* -l and -d have numeric param */
                        ":l+" IF_FEATURE_CROND_D(":d+")
                        ,
                        &G.log_level, &G.log_filename, &G.crontab_dir_name
                        IF_FEATURE_CROND_D(,&G.log_level)
        );
        /* both -d N and -l N set the same variable: G.log_level */

        if (!(opts & OPT_f)) {
                /* close stdin, stdout, stderr.
                 * close unused descriptors - don't need them. */
                bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
        }

        if (!(opts & OPT_d) && G.log_filename == NULL) {
                /* logging to syslog */
                openlog(applet_name, LOG_CONS | LOG_PID, LOG_CRON);
                logmode = LOGMODE_SYSLOG;
        }

        //signal(SIGHUP, SIG_IGN); /* ? original crond dies on HUP... */

        reopen_logfile_to_stderr();
        xchdir(G.crontab_dir_name);
        /* $SHELL, or current UID's shell, or DEFAULT_SHELL */
        /* Useful on Android where DEFAULT_SHELL /bin/sh may not exist */
        G.default_shell = xstrdup(get_shell_name());

        log8("crond (busybox "BB_VER") started, log level %d", G.log_level);
        rescan_crontab_dir();
        write_pidfile_std_path_and_ext("crond");
#if ENABLE_FEATURE_CROND_SPECIAL_TIMES
        if (touch_reboot_file())
                start_jobs(START_ME_REBOOT); /* start @reboot entries, if any */
#endif

        /* Main loop */
        t2 = time(NULL);
        rescan = 60;
        sleep_time = 60;
        for (;;) {
                struct stat sbuf;
                time_t t1;
                long dt;

                /* Synchronize to 1 minute, minimum 1 second */
                t1 = t2;
                sleep(sleep_time - (time(NULL) % sleep_time));
                t2 = time(NULL);
                dt = (long)t2 - (long)t1;

                reopen_logfile_to_stderr();

                /*
                 * The file 'cron.update' is checked to determine new cron
                 * jobs.  The directory is rescanned once an hour to deal
                 * with any screwups.
                 *
                 * Check for time jump.  Disparities over an hour either way
                 * result in resynchronization.  A negative disparity
                 * less than an hour causes us to effectively sleep until we
                 * match the original time (i.e. no re-execution of jobs that
                 * have just been run).  A positive disparity less than
                 * an hour causes intermediate jobs to be run, but only once
                 * in the worst case.
                 *
                 * When running jobs, the inequality used is greater but not
                 * equal to t1, and less then or equal to t2.
                 */
                if (stat(G.crontab_dir_name, &sbuf) != 0)
                        sbuf.st_mtime = 0; /* force update (once) if dir was deleted */
                if (G.crontab_dir_mtime != sbuf.st_mtime) {
                        G.crontab_dir_mtime = sbuf.st_mtime;
                        rescan = 1;
                }
                if (--rescan == 0) {
                        rescan = 60;
                        rescan_crontab_dir();
                }
                process_cron_update_file();
                log5("wakeup dt=%ld", dt);
                if (dt < -60 * 60 || dt > 60 * 60) {
                        bb_info_msg("time disparity of %ld minutes detected", dt / 60);
                        /* and we do not run any jobs in this case */
                } else if (dt > 0) {
                        /* Usual case: time advances forward, as expected */
                        flag_starting_jobs(t1, t2);
                        start_jobs(START_ME_NORMAL);
                        sleep_time = 60;
                        if (check_completions() > 0) {
                                /* some jobs are still running */
                                sleep_time = 10;
                        }
                }
                /* else: time jumped back, do not run any jobs */
        } /* for (;;) */

        return 0; /* not reached */
}