/*
 * Read-Copy Update mechanism for mutual exclusion 
 *
 * 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.
 *
 * Copyright (c) IBM Corporation, 2001
 *
 * Author: Dipankar Sarma <dipankar@in.ibm.com>
 * 
 * Based on the original work by Paul McKenney <paul.mckenney@us.ibm.com>
 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 * Papers:
 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
 *
 * For detailed explanation of Read-Copy Update mechanism see -
 * 		http://lse.sourceforge.net/locking/rcupdate.html
 *
 */

#ifndef __LINUX_RCUPDATE_H
#define __LINUX_RCUPDATE_H

#ifdef __KERNEL__

#include <linux/cache.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <linux/percpu.h>

/**
 * struct rcu_head - callback structure for use with RCU
 * @list: list_head to queue the update requests
 * @func: actual update function to call after the grace period.
 * @arg: argument to be passed to the actual update function.
 */
struct rcu_head {
	struct list_head list;
	void (*func)(void *obj);
	void *arg;
};

#define RCU_HEAD_INIT(head) \
		{ list: LIST_HEAD_INIT(head.list), func: NULL, arg: NULL }
#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head)
#define INIT_RCU_HEAD(ptr) do { \
       INIT_LIST_HEAD(&(ptr)->list); (ptr)->func = NULL; (ptr)->arg = NULL; \
} while (0)



/* Control variables for rcupdate callback mechanism. */
struct rcu_ctrlblk {
	spinlock_t	mutex;		/* Guard this struct                  */
	long		curbatch;	/* Current batch number.	      */
	long		maxbatch;	/* Max requested batch number.        */
	unsigned long	rcu_cpu_mask; 	/* CPUs that need to switch in order  */
					/* for current batch to proceed.      */
};

/* Is batch a before batch b ? */
static inline int rcu_batch_before(long a, long b)
{
        return (a - b) < 0;
}

/* Is batch a after batch b ? */
static inline int rcu_batch_after(long a, long b)
{
        return (a - b) > 0;
}

/*
 * Per-CPU data for Read-Copy UPdate.
 * nxtlist - new callbacks are added here
 * curlist - current batch for which quiescent cycle started if any
 */
struct rcu_data {
	long		qsctr;		 /* User-mode/idle loop etc. */
        long            last_qsctr;	 /* value of qsctr at beginning */
                                         /* of rcu grace period */
        long  	       	batch;           /* Batch # for current RCU batch */
        struct list_head  nxtlist;
        struct list_head  curlist;
};

DECLARE_PER_CPU(struct rcu_data, rcu_data);
extern struct rcu_ctrlblk rcu_ctrlblk;

#define RCU_qsctr(cpu) 		(per_cpu(rcu_data, (cpu)).qsctr)
#define RCU_last_qsctr(cpu) 	(per_cpu(rcu_data, (cpu)).last_qsctr)
#define RCU_batch(cpu) 		(per_cpu(rcu_data, (cpu)).batch)
#define RCU_nxtlist(cpu) 	(per_cpu(rcu_data, (cpu)).nxtlist)
#define RCU_curlist(cpu) 	(per_cpu(rcu_data, (cpu)).curlist)

#define RCU_QSCTR_INVALID	0

static inline int rcu_pending(int cpu) 
{
	if ((!list_empty(&RCU_curlist(cpu)) &&
	     rcu_batch_before(RCU_batch(cpu), rcu_ctrlblk.curbatch)) ||
	    (list_empty(&RCU_curlist(cpu)) &&
			 !list_empty(&RCU_nxtlist(cpu))) ||
	    test_bit(cpu, &rcu_ctrlblk.rcu_cpu_mask))
		return 1;
	else
		return 0;
}

#define rcu_read_lock()		preempt_disable()
#define rcu_read_unlock()	preempt_enable()

extern void rcu_init(void);
extern void rcu_check_callbacks(int cpu, int user);

/* Exported interfaces */
extern void FASTCALL(call_rcu(struct rcu_head *head, 
                          void (*func)(void *arg), void *arg));
extern void synchronize_kernel(void);

#endif /* __KERNEL__ */
#endif /* __LINUX_RCUPDATE_H */