/* 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"
//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 option -d to 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_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 <syslog.h>

/* glibc frees previous setenv'ed value when we do next setenv()
 * of the same variable. uclibc does not do this! */
#if (defined(__GLIBC__) && !defined(__UCLIBC__)) /* || OTHER_SAFE_LIBC... */
# define SETENV_LEAKS 0
#else
# define SETENV_LEAKS 1
#endif


#define CRON_DIR        CONFIG_FEATURE_CROND_DIR
#define CRONTABS        CONFIG_FEATURE_CROND_DIR "/crontabs"
#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 */
#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
	/* 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,
};
#if ENABLE_FEATURE_CROND_D
# define DebugOpt (option_mask32 & OPT_d)
#else
# define DebugOpt 0
#endif


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


/* 0 is the most verbose, default 8 */
#define LVL5  "\x05"
#define LVL7  "\x07"
#define LVL8  "\x08"
#define WARN9 "\x49"
#define DIE9  "\xc9"
/* level >= 20 is "error" */
#define ERR20 "\x14"

static void crondlog(const char *ctl, ...) __attribute__ ((format (printf, 1, 2)));
static void crondlog(const char *ctl, ...)
{
	va_list va;
	int level = (ctl[0] & 0x1f);

	va_start(va, ctl);
	if (level >= (int)G.log_level) {
		/* Debug mode: all to (non-redirected) stderr, */
		/* Syslog mode: all to syslog (logmode = LOGMODE_SYSLOG), */
		if (!DebugOpt && G.log_filename) {
			/* Otherwise (log to file): we reopen log file at every write: */
			int logfd = open_or_warn(G.log_filename, O_WRONLY | O_CREAT | O_APPEND);
			if (logfd >= 0)
				xmove_fd(logfd, STDERR_FILENO);
		}
		/* When we log to syslog, level > 8 is logged at LOG_ERR
		 * syslog level, level <= 8 is logged at LOG_INFO. */
		if (level > 8) {
			bb_verror_msg(ctl + 1, va, /* strerr: */ NULL);
		} else {
			char *msg = NULL;
			vasprintf(&msg, ctl + 1, va);
			bb_info_msg("%s: %s", applet_name, msg);
			free(msg);
		}
	}
	va_end(va);
	if (ctl[0] & 0x80)
		exit(20);
}

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:
		crondlog(WARN9 "user %s: parse error at %s", user, base);
		return;
	}

	if (DebugOpt && (G.log_level <= 5)) { /* like LVL5 */
		/* can't use crondlog, it inserts '\n' */
		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

	delete_cronfile(fileName);

	if (!getpwnam(fileName)) {
		crondlog(LVL7 "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) {
				crondlog(WARN9 "user %s: too many lines", fileName);
				break;
			}

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

			if (DebugOpt)
				crondlog(LVL5 "user:%s entry:%s", fileName, parser->data);

			/* check if line is setting MAILTO= */
			if (0 == strncmp(tokens[0], "MAILTO=", 7)) {
#if ENABLE_FEATURE_CROND_CALL_SENDMAIL
				free(mailTo);
				mailTo = (tokens[0][7]) ? xstrdup(&tokens[0][7]) : NULL;
#endif /* otherwise just ignore such lines */
				continue;
			}
//TODO: handle SHELL=, 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.
			/* check if a minimum of tokens is specified */
			if (n < 6)
				continue;
			*pline = line = xzalloc(sizeof(*line));
			/* 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
			/* copy command */
			line->cl_cmd = xstrdup(tokens[5]);
			if (DebugOpt) {
				crondlog(LVL5 " command:%s", 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);
}

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 */
	if (chdir(G.crontab_dir_name) < 0) {
		crondlog(DIE9 "chdir(%s)", G.crontab_dir_name);
	}

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

		if (!dir)
			crondlog(DIE9 "chdir(%s)", "."); /* exits */
		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)
{
#if SETENV_LEAKS
	safe_setenv(&G.env_var_user, "USER", pas->pw_name);
	safe_setenv(&G.env_var_home, "HOME", pas->pw_dir);
	/* if we want to set user's shell instead: */
	/*safe_setenv(G.env_var_shell, "SHELL", pas->pw_shell);*/
#else
	xsetenv("USER", pas->pw_name);
	xsetenv("HOME", pas->pw_dir);
#endif
	/* currently, we use constant one: */
	/*setenv("SHELL", DEFAULT_SHELL, 1); - done earlier */
}

static void change_user(struct passwd *pas)
{
	/* careful: we're after vfork! */
	change_identity(pas); /* - initgroups, setgid, setuid */
	if (chdir(pas->pw_dir) < 0) {
		crondlog(WARN9 "chdir(%s)", pas->pw_dir);
		if (chdir(CRON_DIR) < 0) {
			crondlog(DIE9 "chdir(%s)", CRON_DIR); /* exits */
		}
	}
}

// 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,
		const char *prog,
		const char *shell_cmd /* if NULL, we run sendmail */
) {
	struct passwd *pas;
	pid_t pid;

	/* prepare things before vfork */
	pas = getpwnam(user);
	if (!pas) {
		crondlog(WARN9 "can't get uid for %s", user);
		goto err;
	}
	set_env_vars(pas);

	pid = vfork();
	if (pid == 0) {
		/* CHILD */
		/* initgroups, setgid, setuid, and chdir to home or CRON_DIR */
		change_user(pas);
		if (DebugOpt) {
			crondlog(LVL5 "child running %s", prog);
		}
		if (mailFd >= 0) {
			xmove_fd(mailFd, shell_cmd ? 1 : 0);
			dup2(1, 2);
		}
		/* crond 3.0pl1-100 puts tasks in separate process groups */
		bb_setpgrp();
		execlp(prog, prog, (shell_cmd ? "-c" : SENDMAIL_ARGS), shell_cmd, (char *) NULL);
		crondlog(ERR20 "can't execute '%s' for user %s", prog, user);
		if (shell_cmd) {
			fdprintf(1, "Exec failed: %s -c %s\n", prog, shell_cmd);
		}
		_exit(EXIT_SUCCESS);
	}

	if (pid < 0) {
		crondlog(ERR20 "can't 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 void 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 {
			crondlog(ERR20 "can't create mail file %s for user %s, "
					"discarding output", mailFile, user);
		}
	}

	line->cl_pid = fork_job(user, mailFd, DEFAULT_SHELL, line->cl_cmd);
	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);
		}
	}
}

/*
 * 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, SENDMAIL, NULL);
}

#else /* !ENABLE_FEATURE_CROND_CALL_SENDMAIL */

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

	pas = getpwnam(user);
	if (!pas) {
		crondlog(WARN9 "can't get uid for %s", user);
		goto err;
	}

	/* Prepare things before vfork */
	set_env_vars(pas);

	/* 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);
		if (DebugOpt) {
			crondlog(LVL5 "child running %s", DEFAULT_SHELL);
		}
		/* crond 3.0pl1-100 puts tasks in separate process groups */
		bb_setpgrp();
		execl(DEFAULT_SHELL, DEFAULT_SHELL, "-c", line->cl_cmd, (char *) NULL);
		crondlog(ERR20 "can't execute '%s' for user %s", DEFAULT_SHELL, user);
		_exit(EXIT_SUCCESS);
	}
	if (pid < 0) {
		/* FORK FAILED */
		crondlog(ERR20 "can't vfork");
 err:
		pid = 0;
	}
	line->cl_pid = 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) {
			if (DebugOpt)
				crondlog(LVL5 "file %s:", file->cf_username);
			if (file->cf_deleted)
				continue;
			for (line = file->cf_lines; line; line = line->cl_next) {
				if (DebugOpt)
					crondlog(LVL5 " 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]
				) {
					if (DebugOpt) {
						crondlog(LVL5 " job: %d %s",
							(int)line->cl_pid, line->cl_cmd);
					}
					if (line->cl_pid > 0) {
						crondlog(LVL8 "user %s: process already running: %s",
							file->cf_username, line->cl_cmd);
					} else if (line->cl_pid == 0) {
						line->cl_pid = -1;
						file->cf_wants_starting = 1;
					}
				}
			}
		}
	}
}

static void start_jobs(void)
{
	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 >= 0)
				continue;

			start_one_job(file->cf_username, line);
			pid = line->cl_pid;
			crondlog(LVL8 "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;
}

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();

	/* "-b after -f is ignored", and so on for every pair a-b */
	opt_complementary = "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+");
	opts = getopt32(argv, "l:L:fbSc:" 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;
	}

	xchdir(G.crontab_dir_name);
	//signal(SIGHUP, SIG_IGN); /* ? original crond dies on HUP... */
	xsetenv("SHELL", DEFAULT_SHELL); /* once, for all future children */
	crondlog(LVL8 "crond (busybox "BB_VER") started, log level %d", G.log_level);
	rescan_crontab_dir();
	write_pidfile(CONFIG_PID_FILE_PATH "/crond.pid");

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

		t1 = t2;

		/* Synchronize to 1 minute, minimum 1 second */
		sleep(sleep_time - (time(NULL) % sleep_time) + 1);

		t2 = time(NULL);
		dt = (long)t2 - (long)t1;

		/*
		 * 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();
		if (DebugOpt)
			crondlog(LVL5 "wakeup dt=%ld", dt);
		if (dt < -60 * 60 || dt > 60 * 60) {
			crondlog(WARN9 "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();
			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 */
}