mars/kernel/lamport.h

169 lines
5.3 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.
*/
#ifndef LAMPORT_H
#define LAMPORT_H
#include <linux/time.h>
#include <linux/ktime.h>
#ifndef CURRENT_TIME
#include <linux/timekeeping.h>
#endif
/* Adapt to upstream commits
* 8758a240e2d74c5932ab51a73377e6507b7fd441
* bfe1c566453a0979c0b3cd3728d0de962272f034
*/
#ifndef CURRENT_TIME
# include <linux/time64.h>
# define lamport_time timespec64
# define lamport_time_to_ns timespec64_to_ns
# define ns_to_lamport_time ns_to_timespec64
# define lamport_time_compare timespec64_compare
# define lamport_time_add timespec64_add
# define lamport_time_add_ns timespec64_add_ns
# define lamport_time_sub timespec64_sub
# define get_real_lamport current_kernel_time64
#else /* deprecated */
# define lamport_time timespec
# define lamport_time_to_ns timespec_to_ns
# define ns_to_lamport_time ns_to_timespec
# define lamport_time_compare timespec_compare
# define lamport_time_add timespec_add
# define lamport_time_add_ns timespec_add_ns
# define lamport_time_sub timespec_sub
# define get_real_lamport() CURRENT_TIME
#endif
#include <linux/rwsem.h>
struct lamport_clock {
struct rw_semaphore lamport_sem;
struct lamport_time lamport_stamp;
};
extern struct lamport_clock global_lamport;
/* Protect against illegal values, e.g. from currupt filesystems etc.
*/
extern int max_lamport_future;
/*
* We always get both the local real time and the Lamport time in parallel,
* consistently.
*
* The implementation ensures that the distributed Lamport timestamp can
* never fall behind the local real time.
*
* When not interested in real time, you can simply leave real_now at NULL.
*/
extern void _get_lamport(struct lamport_clock *clock,
struct lamport_time *real_now,
struct lamport_time *lamport_now);
/* This ensures _strict_ monotonicity of the Lamport clock */
extern void _set_lamport(struct lamport_clock *clock,
struct lamport_time *lamport_advance);
/* Non-strict version.
* Use this for better performance when strictness is not needed.
*/
extern void _set_lamport_nonstrict(struct lamport_clock *clock,
struct lamport_time *lamport_advance);
/* After strictly advancing the Lamport time, re-get the new values.
* This is almost equivalent to a sequence of set_lamport() ; get_lamport()
* but (1) atomic and (2) more efficient
* because the internal lock is taken only once.
*/
extern void _set_get_lamport(struct lamport_clock *clock,
struct lamport_time *lamport_advance,
struct lamport_time *real_now,
struct lamport_time *lamport_now);
extern bool _protect_lamport_time(struct lamport_clock *clock,
struct lamport_time *check);
/* Usually the following versions are the preferred ones for working
* on the single global lamport clock instance.
*/
#define get_lamport(real_now,lamport_now) \
_get_lamport(&global_lamport,real_now,lamport_now)
#define set_lamport(lamport_advance) \
_set_lamport(&global_lamport,lamport_advance)
#define set_lamport_nonstrict(lamport_advance) \
_set_lamport_nonstrict(&global_lamport,lamport_advance)
#define set_get_lamport(lamport_advance,real_now,lamport_now) \
_set_get_lamport(&global_lamport,lamport_advance,real_now,lamport_now)
#define protect_lamport_time(check) \
_protect_lamport_time(&global_lamport,check)
/*
* Here is a very general lockless version for inlining.
* Typical usage is when no true concurrency can happen, or when
* some other embracing locks are already protecting the scene.
* All pointers except clock may be NULL, then no code
* will be generated.
*/
static inline
void __lamport_op(struct lamport_time *clock,
struct lamport_time *lamport_prev,
struct lamport_time *lamport_advance,
struct lamport_time *real_now,
struct lamport_time *lamport_now)
{
/* Remember the old clock value. */
if (lamport_prev)
*lamport_prev = *clock;
/* Advance the clock when necessary. */
if (lamport_advance)
if (lamport_time_compare(lamport_advance, clock) > 0)
*clock = *lamport_advance;
else
*clock = lamport_time_add(*clock,
(struct lamport_time){0, 1});
else
*clock = lamport_time_add(*clock,
(struct lamport_time){0, 1});
/* Get and handle realtime */
if (real_now) {
*real_now = get_real_lamport();
if (lamport_time_compare(real_now, clock) > 0)
*clock = *real_now;
}
/* Finally, retrieve new lamport stamp */
if (lamport_now)
*lamport_now = *clock;
}
#endif