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/*
* lockfile.c Safely creates a lockfile, also over NFS.
* This file also holds the implementation for
* the Svr4 maillock functions.
*
* Version: @(#)lockfile.c 0.1.1 19-Feb-1998 miquels@cistron.nl
*
* Copyright (C) Miquel van Smoorenburg 1997,1998.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*/
#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <utime.h>
#include <paths.h>
#include <errno.h>
#include <lockfile.h>
#include <maillock.h>
static char mlockfile[MAXPATHLEN];
static int islocked = 0;
/*
* Create a lockfile.
*/
int lockfile_create(const char *lockfile, int retries)
{
struct stat st, st1;
time_t now;
int sleeptime = 5;
int statfailed = 0;
int fd;
int i, e;
char tmplock[MAXPATHLEN];
char sysname[256];
char buf[4];
char *p;
/*
* Safety measure.
*/
if (strlen(lockfile) + 32 > MAXPATHLEN) {
errno = ENAMETOOLONG;
return L_ERROR;
}
/*
* Create a temp lockfile (hopefully unique) and
* write 0\0 into the lockfile for svr4 compatibility.
*/
if (gethostname(sysname, sizeof(sysname)) < 0)
return L_ERROR;
if ((p = strchr(sysname, '.')) != NULL)
*p = 0;
strcpy(tmplock, lockfile);
if ((p = strrchr(tmplock, '/')) == NULL)
p = tmplock;
else
p++;
sprintf(p, ".lk%05d%x%s",
getpid(), (int)time(NULL) & 15, sysname);
i = umask(022);
fd = open(tmplock, O_WRONLY|O_CREAT|O_EXCL, 0644);
e = errno;
umask(i);
if (fd < 0) {
errno = e;
return L_TMPLOCK;
}
i = write(fd, "0", 2);
e = errno;
if (close(fd) != 0) {
e = errno;
i = -1;
}
if (i != 2) {
unlink(tmplock);
errno = i < 0 ? e : EAGAIN;
return L_TMPWRITE;
}
/*
* Now try to link the temporary lock to the lock.
*/
for (i = 0; i < retries && retries > 0; i++) {
sleeptime = i > 12 ? 60 : 5 * i;
if (sleeptime > 0)
sleep(sleeptime);
/*
* KLUDGE: some people say the return code of
* link() over NFS can't be trusted.
* EXTRA FIX: the value of the nlink field
* can't be trusted (may be cached).
*/
(void)link(tmplock, lockfile);
if (lstat(tmplock, &st1) < 0)
return L_ERROR; /* Can't happen */
if (lstat(lockfile, &st) < 0) {
if (statfailed++ > 5) {
/*
* Normally, this can't happen; either
* another process holds the lockfile or
* we do. So if this error pops up
* repeatedly, just exit...
*/
e = errno;
(void)unlink(tmplock);
errno = e;
return L_MAXTRYS;
}
continue;
}
/*
* See if we got the lock.
*/
if (st.st_rdev == st1.st_rdev &&
st.st_ino == st1.st_ino) {
(void)unlink(tmplock);
return L_SUCCESS;
}
statfailed = 0;
/*
* Locks are invalid after 5 minutes.
* Use the time of the file system.
*/
time(&now);
if ((fd = open(lockfile, O_RDONLY)) >= 0) {
if (read(fd, buf, 1) >= 0 && fstat(fd, &st1) == 0)
now = st1.st_atime;
close(fd);
}
if (now < st.st_ctime + 300)
continue;
(void)unlink(lockfile);
}
(void)unlink(tmplock);
errno = EAGAIN;
return L_MAXTRYS;
}
/*
* Remove a lock.
*/
int lockfile_remove(const char *lockfile)
{
return unlink(lockfile);
}
/*
* Touch a lock.
*/
int lockfile_touch(const char *lockfile)
{
return utime(lockfile, NULL);
}
/*
* Lock a mailfile. This looks a lot like the SVR4 lockmbox() thingy.
* Arguments: lusername, retries.
*/
int maillock(const char *name, int retries)
{
int i;
if (islocked) return 0;
snprintf(mlockfile, MAXPATHLEN, "%s/%s.lock", _PATH_MAILDIR, name);
i = lockfile_create(mlockfile, retries);
if (i == 0) islocked = 1;
return i;
}
void mailunlock(void)
{
if (!islocked) return;
lockfile_remove(mlockfile);
islocked = 0;
}
void touchlock(void)
{
lockfile_touch(mlockfile);
}
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