pid.c


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/* $Id$
 * $URL$
 *
 * PID file handling
 *
 * Copyright (C) 1999, 2000 Michael Reinelt <michael@reinelt.co.at>
 *
 * This file is part of LCD4Linux.
 *
 * LCD4Linux is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * LCD4Linux is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */

/* 
 * exported functions:
 * 
 * int pid_init (const char *pidfile)
 *   returns 0 if PID file could be successfully created
 *   returns PID of an already running process
 *   returns -1 in case of an error

 * int pid_exit (const char *pidfile)
 *   returns 0 if PID file could be successfully deleted
 *   otherwise returns error from unlink() call
 *
 */


#include "config.h"

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "debug.h"
#include "pid.h"
#include "qprintf.h"

#ifdef WITH_DMALLOC
#include <dmalloc.h>
#endif


int pid_init(const char *pidfile)
{
    char tmpfile[256];
    char buffer[16];
    int fd, len, pid;

    qprintf(tmpfile, sizeof(tmpfile), "%s.%s", pidfile, "XXXXXX");

    if ((fd = mkstemp(tmpfile)) == -1) {
	error("mkstemp(%s) failed: %s", tmpfile, strerror(errno));
	return -1;
    }

    if (fchmod(fd, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) == -1) {
	error("fchmod(%s) failed: %s", tmpfile, strerror(errno));
	close(fd);
	unlink(tmpfile);
	return -1;
    }

    qprintf(buffer, sizeof(buffer), "%d\n", (int) getpid());
    len = strlen(buffer);
    if (write(fd, buffer, len) != len) {
	error("write(%s) failed: %s", tmpfile, strerror(errno));
	close(fd);
	unlink(tmpfile);
	return -1;
    }
    close(fd);


    while (link(tmpfile, pidfile) == -1) {

	if (errno != EEXIST) {
	    error("link(%s, %s) failed: %s", tmpfile, pidfile, strerror(errno));
	    unlink(tmpfile);
	    return -1;
	}

	if ((fd = open(pidfile, O_RDONLY)) == -1) {
	    if (errno == ENOENT)
		continue;	/* pidfile disappared */
	    error("open(%s) failed: %s", pidfile, strerror(errno));
	    unlink(tmpfile);
	    return -1;
	}

	len = read(fd, buffer, sizeof(buffer) - 1);
	if (len < 0) {
	    error("read(%s) failed: %s", pidfile, strerror(errno));
	    unlink(tmpfile);
	    return -1;
	}

	buffer[len] = '\0';
	if (sscanf(buffer, "%d", &pid) != 1 || pid == 0) {
	    error("scan(%s) failed.", pidfile);
	    unlink(tmpfile);
	    return -1;
	}

	if (pid == getpid()) {
	    error("%s already locked by us. uh-oh...", pidfile);
	    unlink(tmpfile);
	    return 0;
	}

	if ((kill(pid, 0) == -1) && errno == ESRCH) {
	    error("removing stale PID file %s", pidfile);
	    if (unlink(pidfile) == -1 && errno != ENOENT) {
		error("unlink(%s) failed: %s", pidfile, strerror(errno));
		unlink(tmpfile);
		return pid;
	    }
	    continue;
	}
	unlink(tmpfile);
	return pid;
    }

    unlink(tmpfile);
    return 0;
}


int pid_exit(const char *pidfile)
{
    return unlink(pidfile);
}