/*
   * 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 <paulmck@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/spinlock.h>
  #include <linux/threads.h>
  #include <linux/percpu.h>
  #include <linux/cpumask.h>
  #include <linux/seqlock.h>
  
  /**
   * 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)
  
  
  
  /* Global control variables for rcupdate callback mechanism. */
  struct rcu_ctrlblk {
  	long	cur;		/* Current batch number.                      */
  	long	completed;	/* Number of the last completed batch         */
  	int	next_pending;	/* Is the next batch already waiting?         */

  	int	signaled;

  	spinlock_t	lock	____cacheline_internodealigned_in_smp;
  	cpumask_t	cpumask; /* CPUs that need to switch in order    */
  	                         /* for current batch to proceed.        */

  } ____cacheline_internodealigned_in_smp;

  
  /* 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 {
  	/* 1) quiescent state handling : */
  	long		quiescbatch;     /* Batch # for grace period */
  	int		passed_quiesc;	 /* User-mode/idle loop etc. */
  	int		qs_pending;	 /* core waits for quiesc state */
  
  	/* 2) batch handling */
  	long  	       	batch;           /* Batch # for current RCU batch */
  	struct rcu_head *nxtlist;
  	struct rcu_head **nxttail;

  	long            qlen; 	 	 /* # of queued callbacks */

  	struct rcu_head *curlist;
  	struct rcu_head **curtail;
  	struct rcu_head *donelist;
  	struct rcu_head **donetail;

  	long		blimit;		 /* Upper limit on a processed batch */

  	int cpu;

  	struct rcu_head barrier;

  };
  
  DECLARE_PER_CPU(struct rcu_data, rcu_data);
  DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);

  
  /*
   * Increment the quiescent state counter.
   * The counter is a bit degenerated: We do not need to know
   * how many quiescent states passed, just if there was at least
   * one since the start of the grace period. Thus just a flag.
   */
  static inline void rcu_qsctr_inc(int cpu)
  {
  	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
  	rdp->passed_quiesc = 1;
  }
  static inline void rcu_bh_qsctr_inc(int cpu)
  {
  	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
  	rdp->passed_quiesc = 1;
  }

  extern int rcu_pending(int cpu);

  extern int rcu_needs_cpu(int cpu);

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

   * When synchronize_rcu() is invoked on one CPU while other CPUs

   * are within RCU read-side critical sections, then the

   * synchronize_rcu() is guaranteed to block until after all the other

   * CPUs exit their critical sections.  Similarly, if 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() \
  	do { \
  		preempt_disable(); \
  		__acquire(RCU); \
  	} while(0)

  
  /**
   * rcu_read_unlock - marks the end of an RCU read-side critical section.
   *
   * See rcu_read_lock() for more information.
   */

  #define rcu_read_unlock() \
  	do { \
  		__release(RCU); \
  		preempt_enable(); \
  	} while(0)

  
  /*
   * 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_read_lock_bh - mark the beginning of a softirq-only RCU critical section
   *
   * This is equivalent of rcu_read_lock(), but to be used when updates
   * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
   * consider completion of a softirq handler to be a quiescent state,
   * a process in RCU read-side critical section must be protected by
   * disabling softirqs. Read-side critical sections in interrupt context
   * can use just rcu_read_lock().
   *
   */

  #define rcu_read_lock_bh() \
  	do { \
  		local_bh_disable(); \
  		__acquire(RCU_BH); \
  	} while(0)

  
  /*
   * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
   *
   * See rcu_read_lock_bh() for more information.
   */

  #define rcu_read_unlock_bh() \
  	do { \
  		__release(RCU_BH); \
  		local_bh_enable(); \
  	} while(0)

  
  /**
   * 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)     ({ \
  				typeof(p) _________p1 = p; \
  				smp_read_barrier_depends(); \
  				(_________p1); \
  				})
  
  /**
   * 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); \
  					})

  /**
   * synchronize_sched - block until all CPUs have exited any non-preemptive
   * kernel code sequences.
   *
   * This means that all preempt_disable code sequences, including NMI and
   * hardware-interrupt handlers, in progress on entry will have completed
   * before this primitive returns.  However, this does not guarantee that

   * softirq handlers will have completed, since in some kernels, these
   * handlers can run in process context, and can block.

   *

   * This primitive provides the guarantees made by the (now removed)

   * synchronize_kernel() API.  In contrast, synchronize_rcu() only
   * guarantees that rcu_read_lock() sections will have completed.

   * In "classic RCU", these two guarantees happen to be one and
   * the same, but can differ in realtime RCU implementations.

   */
  #define synchronize_sched() synchronize_rcu()

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

  extern long rcu_batches_completed(void);

  extern long rcu_batches_completed_bh(void);

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

  extern void synchronize_rcu(void);
  void synchronize_idle(void);

  extern void rcu_barrier(void);

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