/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*-
*
* Author: Michael Zucchi <notzed@helixcode.com>
*
* Copyright (C) 1999 Helix Code (http://www.helixcode.com/).
*
* 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 02111-1307
* USA
*/
#include <config.h>
/* need configure checks or some configurable thingy here */
#define USE_DOT
#define USE_FCNTL
#define USE_FLOCK
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <alloca.h>
#include <time.h>
#ifdef USE_DOT
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#endif
#ifdef USE_FCNTL
#include <unistd.h>
#include <fcntl.h>
#endif
#ifdef USE_FLOCK
#include <sys/file.h>
#endif
#include "camel-lock.h"
/* dunno where this fucking thing is got from */
#define _(x) (x)
#define d(x) (printf("%s(%d): ", __FILE__, __LINE__),(x))
/**
* camel_lock_dot:
* @path:
* @ex:
*
* Create an exclusive lock using .lock semantics.
* All locks are equivalent to write locks (exclusive).
*
* Return value: -1 on error, sets @ex appropriately.
**/
int
camel_lock_dot(const char *path, CamelException *ex)
{
#ifdef USE_DOT
char *locktmp, *lock;
int retry = 0;
int fdtmp;
struct stat st;
/* TODO: Is there a reliable way to refresh the lock, if we're still busy with it?
Does it matter? We will normally also use fcntl too ... */
/* use alloca, save cleaning up afterwards */
lock = alloca(strlen(path) + strlen(".lock") + 1);
sprintf(lock, "%s.lock", path);
locktmp = alloca(strlen(path) + strlen("XXXXXX") + 1);
#ifndef HAVE_MKSTEMP
sprintf(locktmp, "%sXXXXXX", path);
if (mktemp(locktmp) == NULL) {
/* well, this is really only a programatic error */
camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Could not create lock file for %s: %s"), path, strerror(errno));
return -1;
}
#endif
while (retry < CAMEL_LOCK_DOT_RETRY) {
d(printf("trying to lock '%s', attempt %d\n", lock, retry));
if (retry > 0)
sleep(CAMEL_LOCK_DOT_DELAY);
#ifdef HAVE_MKSTEMP
sprintf(locktmp, "%sXXXXXX", path);
fdtmp = mkstemp(locktmp);
#else
fdtmp = open(locktmp, O_RDWR|O_CREAT|O_EXCL, 0600);
#endif
if (fdtmp == -1) {
camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Could not create lock file for %s: %s"), path, strerror(errno));
return -1;
}
close(fdtmp);
/* apparently return code from link can be unreliable for nfs (see link(2)), so we ignore it */
link(locktmp, lock);
/* but we check stat instead (again, see link(2)) */
if (stat(locktmp, &st) == -1) {
d(printf("Out lock file %s vanished!?\n", locktmp));
/* well that was unexpected, try cleanup/retry */
unlink(locktmp);
unlink(lock);
} else {
d(printf("tmp lock created, link count is %d\n", st.st_nlink));
unlink(locktmp);
/* if we had 2 links, we have created the .lock, return ok, otherwise we need to keep trying */
if (st.st_nlink == 2)
return 0;
}
/* check for stale lock, kill it */
if (stat(lock, &st) == 0) {
time_t now = time(0);
d(printf("There is an existing lock %ld seconds old\n", now-st.st_ctime));
if (st.st_ctime < now - CAMEL_LOCK_DOT_STALE) {
d(printf("Removing it now\n"));
unlink(lock);
}
}
retry++;
}
d(printf("failed to get lock after %d retries\n", retry));
camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Timed out trying to get lock file on %s. Try again later."), path);
return -1;
#else /* ! USE_DOT */
return 0;
#endif
}
/**
* camel_unlock_dot:
* @path:
*
* Attempt to unlock a .lock lock.
**/
void
camel_unlock_dot(const char *path)
{
#ifdef USE_DOT
char *lock;
lock = alloca(strlen(path) + strlen(".lock") + 1);
sprintf(lock, "%s.lock", path);
d(printf("unlocking %s\n", lock));
(void)unlink(lock);
#endif
}
/**
* camel_lock_fcntl:
* @fd:
* @type:
* @ex:
*
* Create a lock using fcntl(2).
*
* @type is CAMEL_LOCK_WRITE or CAMEL_LOCK_READ,
* to create exclusive or shared read locks
*
* Return value: -1 on error.
**/
int
camel_lock_fcntl(int fd, CamelLockType type, CamelException *ex)
{
#ifdef USE_FCNTL
struct flock lock;
d(printf("fcntl locking %d\n", fd));
memset(&lock, 0, sizeof(lock));
lock.l_type = type==CAMEL_LOCK_READ?F_RDLCK:F_WRLCK;
if (fcntl(fd, F_SETLK, &lock) == -1) {
camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Failed to get lock using fcntl(2): %s"), strerror(errno));
return -1;
}
#endif
return 0;
}
/**
* camel_unlock_fcntl:
* @fd:
*
* Unlock an fcntl lock.
**/
void
camel_unlock_fcntl(int fd)
{
#ifdef USE_FCNTL
struct flock lock;
d(printf("fcntl unlocking %d\n", fd));
memset(&lock, 0, sizeof(lock));
lock.l_type = F_UNLCK;
fcntl(fd, F_SETLK, &lock);
#endif
}
/**
* camel_lock_flock:
* @fd:
* @type:
* @ex:
*
* Create a lock using flock(2).
*
* @type is CAMEL_LOCK_WRITE or CAMEL_LOCK_READ,
* to create exclusive or shared read locks
*
* Return value: -1 on error.
**/
int
camel_lock_flock(int fd, CamelLockType type, CamelException *ex)
{
#ifdef USE_FLOCK
int op;
d(printf("flock locking %d\n", fd));
if (type == CAMEL_LOCK_READ)
op = LOCK_SH|LOCK_NB;
else
op = LOCK_EX|LOCK_NB;
if (flock(fd, op) == -1) {
camel_exception_setv(ex, CAMEL_EXCEPTION_SYSTEM, _("Failed to get lock using flock(2): %s"), strerror(errno));
return -1;
}
#endif
return 0;
}
/**
* camel_unlock_flock:
* @fd:
*
* Unlock an flock lock.
**/
void
camel_unlock_flock(int fd)
{
#ifdef USE_FLOCK
d(printf("flock unlocking %d\n", fd));
(void)flock(fd, LOCK_UN);
#endif
}
/**
* camel_lock_folder:
* @path: Path to the file to lock (used for .locking only).
* @fd: Open file descriptor of the right type to lock.
* @type: Type of lock, CAMEL_LOCK_READ or CAMEL_LOCK_WRITE.
* @ex:
*
* Attempt to lock a folder, multiple attempts will be made using all
* locking strategies available.
*
* Return value: -1 on error, @ex will describe the locking system that failed.
**/
int
camel_lock_folder(const char *path, int fd, CamelLockType type, CamelException *ex)
{
int retry = 0;
while (retry < CAMEL_LOCK_RETRY) {
if (retry > 0)
sleep(CAMEL_LOCK_DELAY);
camel_exception_clear(ex);
if (camel_lock_fcntl(fd, type, ex) == 0) {
if (camel_lock_flock(fd, type, ex) == 0) {
if (camel_lock_dot(path, ex) == 0)
return 0;
camel_unlock_flock(fd);
}
camel_unlock_fcntl(fd);
}
retry++;
}
return -1;
}
/**
* camel_unlock_folder:
* @path: Filename of folder.
* @fd: Open descrptor on which locks were placed.
*
* Free a lock on a folder.
**/
void
camel_unlock_folder(const char *path, int fd)
{
camel_unlock_dot(path);
camel_unlock_flock(fd);
camel_unlock_fcntl(fd);
}
#if 0
int main(int argc, char **argv)
{
CamelException *ex;
int fd1, fd2;
ex = camel_exception_new();
#if 0
if (camel_lock_dot("mylock", ex) == 0) {
if (camel_lock_dot("mylock", ex) == 0) {
printf("Got lock twice?\n");
} else {
printf("failed to get lock 2: %s\n", camel_exception_get_description(ex));
}
camel_unlock_dot("mylock");
} else {
printf("failed to get lock 1: %s\n", camel_exception_get_description(ex));
}
camel_exception_clear(ex);
#endif
fd1 = open("mylock", O_RDWR);
fd2 = open("mylock", O_RDWR);
if (camel_lock_fcntl(fd1, CAMEL_LOCK_WRITE, ex) == 0) {
printf("got fcntl write lock once\n");
sleep(5);
if (camel_lock_fcntl(fd2, CAMEL_LOCK_WRITE, ex) == 0) {
printf("got fcntl write lock twice!\n");
} else {
printf("failed to get write lock: %s\n", camel_exception_get_description(ex));
}
camel_exception_clear(ex);
if (camel_lock_fcntl(fd2, CAMEL_LOCK_READ, ex) == 0) {
printf("got fcntl read lock as well?\n");
camel_unlock_fcntl(fd2);
} else {
printf("failed to get read lock: %s\n", camel_exception_get_description(ex));
}
camel_exception_clear(ex);
camel_unlock_fcntl(fd1);
} else {
printf("failed to get write lock at all: %s\n", camel_exception_get_description(ex));
}
if (camel_lock_fcntl(fd1, CAMEL_LOCK_READ, ex) == 0) {
printf("got fcntl read lock once\n");
sleep(5);
if (camel_lock_fcntl(fd2, CAMEL_LOCK_WRITE, ex) == 0) {
printf("got fcntl write lock too?!\n");
} else {
printf("failed to get write lock: %s\n", camel_exception_get_description(ex));
}
camel_exception_clear(ex);
if (camel_lock_fcntl(fd2, CAMEL_LOCK_READ, ex) == 0) {
printf("got fcntl read lock twice\n");
camel_unlock_fcntl(fd2);
} else {
printf("failed to get read lock: %s\n", camel_exception_get_description(ex));
}
camel_exception_clear(ex);
camel_unlock_fcntl(fd1);
}
close(fd1);
close(fd2);
return 0;
}
#endif
