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/* -*- 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