mars/kernel/lamport.c
2018-01-31 08:09:00 +01:00

98 lines
2.4 KiB
C

/*
* MARS Long Distance Replication Software
*
* This file is part of MARS project: http://schoebel.github.io/mars/
*
* Copyright (C) 2010-2014 Thomas Schoebel-Theuer
* Copyright (C) 2011-2014 1&1 Internet AG
*
* 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.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/semaphore.h>
#include "lamport.h"
struct semaphore lamport_sem = __SEMAPHORE_INITIALIZER(lamport_sem, 1); // TODO: replace with spinlock if possible (first check)
struct timespec lamport_now = {};
void get_lamport(struct timespec *now)
{
int diff;
down(&lamport_sem);
*now = CURRENT_TIME;
diff = timespec_compare(now, &lamport_now);
if (diff >= 0) {
timespec_add_ns(now, 1);
memcpy(&lamport_now, now, sizeof(lamport_now));
timespec_add_ns(&lamport_now, 1);
} else {
timespec_add_ns(&lamport_now, 1);
memcpy(now, &lamport_now, sizeof(*now));
}
up(&lamport_sem);
}
EXPORT_SYMBOL_GPL(get_lamport);
void set_lamport(struct timespec *old)
{
int diff;
protect_timespec(old);
down(&lamport_sem);
diff = timespec_compare(old, &lamport_now);
if (diff >= 0) {
memcpy(&lamport_now, old, sizeof(lamport_now));
timespec_add_ns(&lamport_now, 1);
}
up(&lamport_sem);
}
EXPORT_SYMBOL_GPL(set_lamport);
/* Protect against illegal values, e.g. from currupt filesystems etc.
*/
int max_lamport_future = 30 * 24 * 3600;
bool protect_timespec(struct timespec *check)
{
struct timespec limit = CURRENT_TIME;
bool res = false;
limit.tv_sec += max_lamport_future;
if (unlikely(check->tv_sec >= limit.tv_sec)) {
down(&lamport_sem);
timespec_add_ns(&lamport_now, 1);
memcpy(check, &lamport_now, sizeof(*check));
if (unlikely(check->tv_sec > limit.tv_sec))
max_lamport_future += check->tv_sec - limit.tv_sec;
up(&lamport_sem);
res = true;
}
return res;
}