File: daemon_init.c

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/** @file
 * daemon_init function, does sanity checks and calls daemon().
 *
 * Author: Jeff Moyer <jmoyer@redhat.com>
 */
/*
 * TODO: Clean this up so that only one function constructs the 
 *       pidfile /var/run/loggerd.PID, and perhaps only one function
 *       forms the /proc/PID/ path.
 *
 *       Also need to add file locking for the pid file.
 */

#include "config.h"

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <fcntl.h>
#include <dirent.h>
#include <sys/mman.h>
#include <sys/errno.h>
#include <libgen.h>
#include <signal.h>
#include <syslog.h>


/*
 * This should ultimately go in a header file.
 */
void daemon_init(const char *prog, const char *pid_file, int nofork);
void daemon_cleanup(void);
int check_process_running(const char *cmd, const char *pid_file, pid_t * pid);

/*
 * Local prototypes.
 */
static void update_pidfile(const char *filename);
static int setup_sigmask(void);
static char pid_filename[PATH_MAX];

static int
check_pid_valid(pid_t pid, const char *prog)
{
	FILE *fp;
	DIR *dir;
	char filename[PATH_MAX];
	char dirpath[PATH_MAX];
	char proc_cmdline[64];	/* yank this from kernel somewhere */
	char *s = NULL;

	memset(filename, 0, PATH_MAX);
	memset(dirpath, 0, PATH_MAX);

	snprintf(dirpath, sizeof (dirpath), "/proc/%d", pid);
	if ((dir = opendir(dirpath)) == NULL) {
		return 0;	/* Pid has gone away. */
	}
	closedir(dir);

	/*
	 * proc-pid directory exists.  Now check to see if this
	 * PID corresponds to the daemon we want to start.
	 */
	snprintf(filename, sizeof (filename), "/proc/%d/cmdline", pid);
	fp = fopen(filename, "r");
	if (fp == NULL) {
		perror("check_pid_valid");
		return 0;	/* Who cares.... Let's boogy on. */
	}

	if (!fgets(proc_cmdline, sizeof (proc_cmdline) - 1, fp)) {
		/*
		 * Okay, we've seen processes keep a reference to a
		 * /proc/PID/stat file and not let go.  Then when
		 * you try to read /proc/PID/cmline, you get either
		 * \000 or -1.  In either case, we can safely assume
		 * the process has gone away.
		 */
		fclose(fp);
		return 0;
	}
	fclose(fp);

	s = &(proc_cmdline[strlen(proc_cmdline)]);
	if (*s == '\n')
		*s = 0;

	/*
	 * Check to see if this is the same executable.
	 */
	if (strstr(proc_cmdline, prog) == NULL) {
		return 0;
	} else {
		return 1;
	}
}


int
check_process_running(const char *cmd, const char *filename, pid_t * pid)
{
	pid_t oldpid;
	FILE *fp;
	int ret;
	struct stat st;

	*pid = -1;

	/*
	 * Now see if there is a pidfile associated with this cmd in /var/run
	 */
	fp = NULL;
	ret = stat(filename, &st);
	if ((ret < 0) || (!st.st_size))
		return 0;

	/*
	 * Read the pid from the file.
	 */
	fp = fopen(filename, "r");
	if (fp == NULL) {	/* error */
		return 0;
	}

	ret = fscanf(fp, "%d\n", &oldpid);
	fclose(fp);

	if ((ret == EOF) || (ret != 1))
		return 0;

	if (check_pid_valid(oldpid, cmd)) {
		*pid = oldpid;
		return 1;
	}
	return 0;
}


static void
update_pidfile(const char *filename)
{
	FILE *fp = NULL;

	strncpy(pid_filename, filename, PATH_MAX - 1);

	fp = fopen(pid_filename, "w");
	if (fp == NULL) {
		syslog(LOG_ERR, "daemon_init: Unable to create pidfile %s: %s\n",
			filename, strerror(errno));
		exit(1);
	}

	fprintf(fp, "%d", getpid());
	fclose(fp);
}


static int
setup_sigmask(void)
{
	sigset_t set;

	sigfillset(&set);

	/*
	 * Dont't block signals which would cause us to dump core.
	 */
	sigdelset(&set, SIGQUIT);
	sigdelset(&set, SIGILL);
	sigdelset(&set, SIGTRAP);
	sigdelset(&set, SIGABRT);
	sigdelset(&set, SIGFPE);
	sigdelset(&set, SIGSEGV);
	sigdelset(&set, SIGBUS);

	/*
	 * Don't block SIGTERM or SIGCHLD
	 */
	sigdelset(&set, SIGTERM);
	sigdelset(&set, SIGINT);
	sigdelset(&set, SIGQUIT);
	sigdelset(&set, SIGCHLD);

	return (sigprocmask(SIG_BLOCK, &set, NULL));
}


void
daemon_init(const char *prog, const char *pid_file, int nofork)
{
	pid_t pid;

	if (check_process_running(prog, pid_file, &pid) && (pid != getpid())) {
		syslog(LOG_ERR,
			"daemon_init: Process \"%s\" already running.\n",
			prog);
		exit(1);
	}

	if (setup_sigmask() < 0) {
		syslog(LOG_ERR, "daemon_init: Unable to set signal mask.\n");
		exit(1);
	}

	if (!nofork && daemon(0, 0)) {
		syslog(LOG_ERR, "daemon_init: Unable to daemonize.\n");
		exit(1);
	}

	update_pidfile(pid_file);
}


void
daemon_cleanup(void)
{
	if (strlen(pid_filename))
		unlink(pid_filename);
}