thermferm/lock.c

/*****************************************************************************
 * Copyright (C) 2014
 *   
 * Michiel Broek <mbroek at mbse dot eu>
 *
 * This file is part of the mbsePi-apps
 *
 * This 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.
 *
 * mbsePi-apps 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 ThermFerm; see the file COPYING.  If not, write to the Free
 * Software Foundation, 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
 *****************************************************************************/

#include "lock.h"
#include "thermferm.h"

/*
 *  Put a lock on this program.
 */
int lockprog(char *name)
{
    char    *tempfile, *lockfile;
    FILE    *fp;
    pid_t   oldpid;

    tempfile = calloc(PATH_MAX, sizeof(char));
    lockfile = calloc(PATH_MAX, sizeof(char));

    snprintf(tempfile, PATH_MAX, "/var/run/%s.tmp", name);
    snprintf(lockfile, PATH_MAX, "/var/run/%s.pid", name);

    if ((fp = fopen(tempfile, "w")) == NULL) {
	perror(name);
	printf("Can't create lockfile \"%s\"\n", tempfile);
	free(tempfile);
	free(lockfile);
	return 1;
    }
    fprintf(fp, "%10u\n", getpid());
    fclose(fp);

    while (TRUE) {
	if (link(tempfile, lockfile) == 0) {
	    unlink(tempfile);
	    free(tempfile);
	    free(lockfile);
	    return 0;
	}
	if ((fp = fopen(lockfile, "r")) == NULL) {
	    perror(name);
	    printf("Can't open lockfile \"%s\"\n", tempfile);
	    unlink(tempfile);
	    free(tempfile);
	    free(lockfile);
	    return 1;
	}
	if (fscanf(fp, "%u", &oldpid) != 1) {
	    perror(name);
	    printf("Can't read old pid from \"%s\"\n", tempfile);
	    fclose(fp);
	    unlink(tempfile);
	    free(tempfile);
	    free(lockfile);
	    return 1;
	}
	fclose(fp);
	if (kill(oldpid,0) == -1) {
	    if (errno == ESRCH) {
		printf("Stale lock found for pid %u\n", oldpid);
		unlink(lockfile);
		/* no return, try lock again */  
	    } else {
		perror(name);
		printf("Kill for %u failed\n",oldpid);
		unlink(tempfile);
		free(tempfile);
		free(lockfile);
		return 1;
	    }
	} else {
	    printf("Another %s is already running, pid=%u\n", name, oldpid);
	    unlink(tempfile);
	    free(tempfile);
	    free(lockfile);
	    return 1;
	}
    }
}


void ulockprog(char *name)
{
    char	    *lockfile;
    pid_t	    oldpid;
    FILE	    *fp;

    lockfile = calloc(PATH_MAX, sizeof(char));
    snprintf(lockfile, PATH_MAX, "/var/run/%s.pid", name);

    if ((fp = fopen(lockfile, "r")) == NULL) {
	syslog(LOG_NOTICE, "Can't open lockfile \"%s\"", lockfile);
	free(lockfile);
	return;
    }

    if (fscanf(fp, "%u", &oldpid) != 1) {
	syslog(LOG_NOTICE, "Can't read old pid from \"%s\"", lockfile);
	fclose(fp);
	unlink(lockfile);
	free(lockfile);
	return;
    }

    fclose(fp);

    if (oldpid == getpid()) {
	(void)unlink(lockfile);
    }

    free(lockfile);
}