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/*
pidfile.c - interact with pidfiles
Copyright (c) 1995 Martin Schulze <Martin.Schulze@Linux.DE>
This file is part of the sysklogd package, a kernel and system log daemon.
This program 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 of the License, or
(at your option) any later version.
This program 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., 59 Temple Place - Suite 330, Boston, MA 02111, USA
*/
/*
* Sat Aug 19 13:24:33 MET DST 1995: Martin Schulze
* First version (v0.2) released
*/
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
/* read_pid
*
* Reads the specified pidfile and returns the read pid.
* 0 is returned if either there's no pidfile, it's empty
* or no pid can be read.
*/
int read_pid (char *pidfile)
{
FILE *f;
int pid;
if (!(f=fopen(pidfile,"r")))
return 0;
fscanf(f,"%d", &pid);
fclose(f);
return pid;
}
/* check_pid
*
* Reads the pid using read_pid and looks up the pid in the process
* table (using /proc) to determine if the process already exists. If
* so 1 is returned, otherwise 0.
*/
int check_pid (char *pidfile)
{
int pid = read_pid(pidfile);
/* Amazing ! _I_ am already holding the pid file... */
if ((!pid) || (pid == getpid ()))
return 0;
/*
* The 'standard' method of doing this is to try and do a 'fake' kill
* of the process. If an ESRCH error is returned the process cannot
* be found -- GW
*/
/* But... errno is usually changed only on error.. */
if (kill(pid, 0) && errno == ESRCH)
return(0);
return pid;
}
/* write_pid
*
* Writes the pid to the specified file. If that fails 0 is
* returned, otherwise the pid.
*/
int write_pid (char *pidfile)
{
FILE *f;
int fd;
int pid;
if ( ((fd = open(pidfile, O_RDWR|O_CREAT, 0644)) == -1)
|| ((f = fdopen(fd, "r+")) == NULL) ) {
fprintf(stderr, "Can't open or create %s.\n", pidfile);
return 0;
}
if (flock(fd, LOCK_EX|LOCK_NB) == -1) {
fscanf(f, "%d", &pid);
fclose(f);
printf("Can't lock, lock is held by pid %d.\n", pid);
return 0;
}
pid = getpid();
if (!fprintf(f,"%d\n", pid)) {
printf("Can't write pid , %s.\n", strerror(errno));
close(fd);
return 0;
}
fflush(f);
if (flock(fd, LOCK_UN) == -1) {
printf("Can't unlock pidfile %s, %s.\n", pidfile, strerror(errno));
close(fd);
return 0;
}
close(fd);
return pid;
}
/* remove_pid
*
* Remove the the specified file. The result from unlink(2)
* is returned
*/
int remove_pid (char *pidfile)
{
return unlink (pidfile);
}
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