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/* ========================================================================
* Copyright 1988-2008 University of Washington
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
*
* ========================================================================
*/
/*
* Program: Standalone Mailbox Lock program
*
* Author: Mark Crispin
* Networks and Distributed Computing
* Computing & Communications
* University of Washington
* Administration Building, AG-44
* Seattle, WA 98195
* Internet: MRC@CAC.Washington.EDU
*
* Date: 8 February 1999
* Last Edited: 3 March 2008
*/
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <sysexits.h>
#include <syslog.h>
#include <grp.h>
#include <sys/types.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/param.h>
#include <stdlib.h>
#include <netdb.h>
#include <ctype.h>
#include <string.h>
#define LOCKTIMEOUT 5 /* lock timeout in minutes */
#define LOCKPROTECTION 0664
#ifndef MAXHOSTNAMELEN /* Solaris still sucks */
#define MAXHOSTNAMELEN 256
#endif
/* Fatal error
* Accepts: Message string
* exit code
* Returns: code
*/
int die (char *msg,int code)
{
syslog (LOG_NOTICE,"(%u) %s",code,msg);
write (1,"?",1); /* indicate "impossible" failure */
return code;
}
int main (int argc,char *argv[])
{
int ld,i;
int tries = LOCKTIMEOUT * 60 - 1;
char *s,*dir,*file,*lock,*hitch,tmp[1024];
size_t dlen,len;
struct stat sb,fsb;
struct group *grp = getgrnam ("mail");
/* get syslog */
openlog (argv[0],LOG_PID,LOG_MAIL);
if (!grp || (grp->gr_gid != getegid ()))
return die ("not setgid mail",EX_USAGE);
if (argc != 3) return die ("invalid arguments",EX_USAGE);
for (s = argv[1]; *s; s++)
if (!isdigit (*s)) return die ("invalid fd",EX_USAGE);
/* find directory */
if ((*argv[2] != '/') || !(file = strrchr (argv[2],'/')) || !file[1])
return die ("invalid path",EX_USAGE);
/* calculate lengths of directory and file */
if (!(dlen = file - argv[2])) dlen = 1;
len = strlen (++file);
/* make buffers */
dir = (char *) malloc (dlen + 1);
lock = (char *) malloc (len + 6);
hitch = (char *) malloc (len + 6 + 40 + MAXHOSTNAMELEN);
if (!dir || !lock || !hitch) return die ("malloc failure",errno);
strncpy (dir,argv[2],dlen); /* connect to desired directory */
dir[dlen] = '\0';
printf ("dir=%s, file=%s\n",dir,file);
chdir (dir);
/* get device/inode of file descriptor */
if (fstat (atoi (argv[1]),&fsb)) return die ("fstat failure",errno);
/* better be a regular file */
if ((fsb.st_mode & S_IFMT) != S_IFREG)
return die ("fd not regular file",EX_USAGE);
/* now get device/inode of file */
if (lstat (file,&sb)) return die ("lstat failure",errno);
/* does it match? */
if ((sb.st_mode & S_IFMT) != S_IFREG)
return die ("name not regular file",EX_USAGE);
if ((sb.st_dev != fsb.st_dev) || (sb.st_ino != fsb.st_ino))
return die ("fd and name different",EX_USAGE);
/* build lock filename */
sprintf (lock,"%s.lock",file);
if (!lstat (lock,&sb) && ((sb.st_mode & S_IFMT) != S_IFREG))
return die ("existing lock not regular file",EX_NOPERM);
do { /* until OK or out of tries */
if (!stat (lock,&sb) && (time (0) > (sb.st_ctime + LOCKTIMEOUT * 60)))
unlink (lock); /* time out lock if enough time has passed */
/* SUN-OS had an NFS
* As kludgy as an albatross;
* And everywhere that it was installed,
* It was a total loss.
* -- MRC 9/25/91
*/
/* build hitching post file name */
sprintf (hitch,"%s.%lu.%lu.",lock,(unsigned long) time (0),
(unsigned long) getpid ());
len = strlen (hitch); /* append local host name */
gethostname (hitch + len,MAXHOSTNAMELEN);
/* try to get hitching-post file */
if ((ld = open (hitch,O_WRONLY|O_CREAT|O_EXCL,LOCKPROTECTION)) >= 0) {
/* make sure others can break the lock */
chmod (hitch,LOCKPROTECTION);
/* get device/inode of hitch file */
if (fstat (ld,&fsb)) return die ("hitch fstat failure",errno);
close (ld); /* close the hitching-post */
/* Note: link() may return an error even if it actually succeeded. So we
* always check for success via the link count, and ignore the error if
* the link count is right.
*/
/* tie hitching-post to lock */
i = link (hitch,lock) ? errno : 0;
/* success if link count now 2 */
if (stat (hitch,&sb) || (sb.st_nlink != 2) ||
(fsb.st_dev != sb.st_dev) || (fsb.st_ino != sb.st_ino)) {
ld = -1; /* failed to hitch */
if (i == EPERM) { /* was it because links not allowed? */
/* Probably a FAT filesystem on Linux. It can't be NFS, so try
* creating the lock file directly.
*/
if ((ld = open (lock,O_WRONLY|O_CREAT|O_EXCL,LOCKPROTECTION)) >= 0) {
/* get device/inode of lock file */
if (fstat (ld,&fsb)) return die ("lock fstat failure",errno);
close (ld); /* close the file */
}
/* give up immediately if protection failure */
else if (errno != EEXIST) tries = 0;
}
}
unlink (hitch); /* flush hitching post */
}
/* give up immediately if protection failure */
else if (errno == EACCES) tries = 0;
if (ld < 0) { /* lock failed */
if (tries--) sleep (1); /* sleep 1 second and try again */
else {
write (1,"-",1); /* hard failure */
return EX_CANTCREAT;
}
}
} while (ld < 0);
write (1,"+",1); /* indicate that all is well */
read (0,tmp,1); /* read continue signal from parent */
/* flush the lock file */
if (!stat (lock,&sb) && (fsb.st_dev == sb.st_dev) &&
(fsb.st_ino == sb.st_ino)) unlink (lock);
else syslog (LOG_NOTICE,"lock file %s/%s changed dev/inode",dir,lock);
return EX_OK;
}
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