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/* $Id: lock.c,v 1.1 2000/04/07 05:42:20 reinelt Exp $
*
* UUCP style locking
*
* Copyright 1999, 2000 by Michael Reinelt (reinelt@eunet.at)
*
* 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, 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., 675 Mass Ave, Cambridge, MA 02139, USA.
*
*
* $Log: lock.c,v $
* Revision 1.1 2000/04/07 05:42:20 reinelt
*
* UUCP style lockfiles for the serial port
*
*/
/*
* exported functions:
*
* pid_t lock_port (char *port)
* returns 0 if port could be successfully locked
* otherwise returns PID of the process holding the lock
*
* pid_t unlock_port (char *port)
* returns 0 if port could be successfully unlocked
* otherwise returns PID of the process holding the lock
*
*/
#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 "lock.h"
pid_t lock_port (char *port)
{
char lockfile[256];
char tempfile[256];
char buffer[16];
char *p;
int fd, len, pid;
if ((p=strrchr (port, '/'))==NULL)
p=port;
else
p++;
snprintf(lockfile, sizeof(lockfile), LOCK, p);
snprintf(tempfile, sizeof(tempfile), LOCK, "TMP.XXXXXX");
if (mktemp(tempfile)==NULL) {
fprintf(stderr, "mktemp(%s) failed.\n", tempfile);
return -1;
}
if ((fd=creat(tempfile, 0664))==-1) {
fprintf(stderr, "creat(%s) failed: %s\n", tempfile, strerror(errno));
return -1;
}
snprintf (buffer, sizeof(buffer), "%10d\n", (int)getpid());
if (write(fd, buffer, strlen(buffer))!=strlen(buffer)) {
fprintf(stderr, "write(%s) failed: %s\n", tempfile, strerror(errno));
close(fd);
unlink(tempfile);
return -1;
}
close (fd);
while (link(tempfile, lockfile)==-1) {
if (errno!=EEXIST) {
fprintf(stderr, "link(%s, %s) failed: %s\n", tempfile, lockfile, strerror(errno));
unlink(tempfile);
return -1;
}
if ((fd=open(lockfile, O_RDONLY))==-1) {
if (errno==ENOENT) continue; // lockfile disappared
fprintf (stderr, "open(%s) failed: %s\n", lockfile, strerror(errno));
unlink (tempfile);
return -1;
}
len=read(fd, buffer, sizeof(buffer)-1);
if (len<0) {
fprintf (stderr, "read(%s) failed: %s\n", lockfile, strerror(errno));
unlink (tempfile);
return -1;
}
buffer[len]='\0';
if (sscanf(buffer, "%d", &pid)!=1 || pid==0) {
fprintf (stderr, "scan(%s) failed.\n", lockfile);
unlink (tempfile);
return -1;
}
if (pid==getpid()) {
fprintf (stderr, "%s already locked by us. uh-oh...\n", lockfile);
unlink(tempfile);
return 0;
}
if ((kill(pid, 0)==-1) && errno==ESRCH) {
fprintf (stderr, "removing stale lockfile %s\n", lockfile);
if (unlink(lockfile)==-1 && errno!=ENOENT) {
fprintf (stderr, "unlink(%s) failed: %s\n", lockfile, strerror(errno));
unlink(tempfile);
return pid;
}
continue;
}
unlink (tempfile);
return pid;
}
unlink (tempfile);
return 0;
}
pid_t unlock_port (char *port)
{
char lockfile[256];
char *p;
if ((p=strrchr (port, '/'))==NULL)
p=port;
else
p++;
snprintf(lockfile, sizeof(lockfile), LOCK, p);
unlink (lockfile);
return 0;
}
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