/*

 * 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, see <http://www.gnu.org/licenses/>.

 *

 * 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 __XEN_RCUPDATE_H

#define __XEN_RCUPDATE_H

#include <xen/cache.h>

#include <xen/spinlock.h>

#include <xen/percpu.h>

#include <xen/cpumask.h>

#include <xen/preempt.h>

#define __rcu

/**

 * struct rcu_head - callback structure for use with RCU

 * @next: next update requests in a list

 * @func: actual update function to call after the grace period.

 */

struct rcu_head {

    struct rcu_head *next;

    void (*func)(struct rcu_head *head);

};

#define RCU_HEAD_INIT   { .next = NULL, .func = NULL }

#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT

#define INIT_RCU_HEAD(ptr) do { \

       (ptr)->next = NULL; (ptr)->func = NULL; \

} while (0)

int rcu_pending(int cpu);

int rcu_needs_cpu(int cpu);

/*

 * Dummy lock type for passing to rcu_read_{lock,unlock}. Currently exists

 * only to document the reason for rcu_read_lock() critical sections.

 */

struct _rcu_read_lock {};

typedef struct _rcu_read_lock rcu_read_lock_t;

#define DEFINE_RCU_READ_LOCK(x) rcu_read_lock_t x

/**

 * rcu_read_lock - mark the beginning of an RCU read-side critical section.

 *

 * When call_rcu() is invoked

 * on one CPU while other CPUs are within RCU read-side critical

 * sections, invocation of the corresponding RCU callback is deferred

 * until after the all the other CPUs exit their critical sections.

 *

 * Note, however, that RCU callbacks are permitted to run concurrently

 * with RCU read-side critical sections.  One way that this can happen

 * is via the following sequence of events: (1) CPU 0 enters an RCU

 * read-side critical section, (2) CPU 1 invokes call_rcu() to register

 * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,

 * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU

 * callback is invoked.  This is legal, because the RCU read-side critical

 * section that was running concurrently with the call_rcu() (and which

 * therefore might be referencing something that the corresponding RCU

 * callback would free up) has completed before the corresponding

 * RCU callback is invoked.

 *

 * RCU read-side critical sections may be nested.  Any deferred actions

 * will be deferred until the outermost RCU read-side critical section

 * completes.

 *

 * It is illegal to block while in an RCU read-side critical section.

 */

#define rcu_read_lock(x)       ({ ((void)(x)); preempt_disable(); })

/**

 * rcu_read_unlock - marks the end of an RCU read-side critical section.

 *

 * See rcu_read_lock() for more information.

 */

#define rcu_read_unlock(x)     ({ ((void)(x)); preempt_enable(); })

/*

 * So where is rcu_write_lock()?  It does not exist, as there is no

 * way for writers to lock out RCU readers.  This is a feature, not

 * a bug -- this property is what provides RCU's performance benefits.

 * Of course, writers must coordinate with each other.  The normal

 * spinlock primitives work well for this, but any other technique may be

 * used as well.  RCU does not care how the writers keep out of each

 * others' way, as long as they do so.

 */

/**

 * rcu_dereference - fetch an RCU-protected pointer in an

 * RCU read-side critical section.  This pointer may later

 * be safely dereferenced.

 *

 * Inserts memory barriers on architectures that require them

 * (currently only the Alpha), and, more importantly, documents

 * exactly which pointers are protected by RCU.

 */

#define rcu_dereference(p)     (p)

/**

 * rcu_assign_pointer - assign (publicize) a pointer to a newly

 * initialized structure that will be dereferenced by RCU read-side

 * critical sections.  Returns the value assigned.

 *

 * Inserts memory barriers on architectures that require them

 * (pretty much all of them other than x86), and also prevents

 * the compiler from reordering the code that initializes the

 * structure after the pointer assignment.  More importantly, this

 * call documents which pointers will be dereferenced by RCU read-side

 * code.

 */

#define rcu_assign_pointer(p, v) ({ smp_wmb(); (p) = (v); })

void rcu_init(void);

void rcu_check_callbacks(int cpu);

/* Exported interfaces */

void call_rcu(struct rcu_head *head, 

              void (*func)(struct rcu_head *head));

int rcu_barrier(void);

void rcu_idle_enter(unsigned int cpu);

void rcu_idle_exit(unsigned int cpu);

void rcu_idle_timer_start(void);

void rcu_idle_timer_stop(void);

#endif /* __XEN_RCUPDATE_H */