/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1996, 2012 Oracle and/or its affiliates.  All rights reserved.
 *
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 * $Id$
 */

#ifndef	_DB_MP_H_
#define	_DB_MP_H_

#include "dbinc/atomic.h"

#if defined(__cplusplus)
extern "C" {
#endif

struct __bh;		typedef struct __bh BH;
struct __bh_frozen_p;	typedef struct __bh_frozen_p BH_FROZEN_PAGE;
struct __bh_frozen_a;	typedef struct __bh_frozen_a BH_FROZEN_ALLOC;
struct __db_mpool_hash; typedef struct __db_mpool_hash DB_MPOOL_HASH;
struct __db_mpool_fstat_int;
typedef struct __db_mpool_fstat_int DB_MPOOL_FSTAT_INT;
struct __db_mpreg;	typedef struct __db_mpreg DB_MPREG;
struct __mpool;		typedef struct __mpool MPOOL;

				/* We require at least 20KB of cache. */
#define	DB_CACHESIZE_MIN	(20 * 1024)

/*
 * DB_MPOOLFILE initialization methods cannot be called after open is called,
 * other methods cannot be called before open is called
 */
#define	MPF_ILLEGAL_AFTER_OPEN(dbmfp, name)				\
	if (F_ISSET(dbmfp, MP_OPEN_CALLED))				\
		return (__db_mi_open((dbmfp)->env, name, 1));
#define	MPF_ILLEGAL_BEFORE_OPEN(dbmfp, name)				\
	if (!F_ISSET(dbmfp, MP_OPEN_CALLED))				\
		return (__db_mi_open((dbmfp)->env, name, 0));

/*
 * Cache flush operations, plus modifiers.
 */
#define	DB_SYNC_ALLOC		0x0001	/* Flush for allocation. */
#define	DB_SYNC_CACHE		0x0002	/* Flush entire cache. */
#define	DB_SYNC_CHECKPOINT	0x0004	/* Checkpoint. */
#define	DB_SYNC_FILE		0x0008	/* Flush file. */
#define	DB_SYNC_INTERRUPT_OK	0x0010	/* Allow interrupt and return OK. */
#define	DB_SYNC_QUEUE_EXTENT	0x0020	/* Flush a queue file with extents. */
#define	DB_SYNC_SUPPRESS_WRITE	0x0040	/* Ignore max-write configuration. */
#define	DB_SYNC_TRICKLE		0x0080	/* Trickle sync. */

/*
 * DB_MPOOL --
 *	Per-process memory pool structure.
 */
struct __db_mpool {
	/* These fields need to be protected for multi-threaded support. */
	db_mutex_t mutex;		/* Thread mutex. */

	/*
	 * DB_MPREG structure for the DB pgin/pgout routines.
	 *
	 * Linked list of application-specified pgin/pgout routines.
	 */
	DB_MPREG *pg_inout;
	LIST_HEAD(__db_mpregh, __db_mpreg) dbregq;

					/* List of DB_MPOOLFILE's. */
	TAILQ_HEAD(__db_mpoolfileh, __db_mpoolfile) dbmfq;

	/*
	 * The env and reginfo fields are not thread protected, as they are
	 * initialized during mpool creation, and not modified again.
	 */
	ENV	   *env;		/* Enclosing environment. */
	REGINFO	   *reginfo;		/* Underlying cache regions. */
};

/*
 * DB_MPREG --
 *	DB_MPOOL registry of pgin/pgout functions.
 */
struct __db_mpreg {
	LIST_ENTRY(__db_mpreg) q;	/* Linked list. */

	int32_t ftype;			/* File type. */
					/* Pgin, pgout routines. */
	int (*pgin) __P((DB_ENV *, db_pgno_t, void *, DBT *));
	int (*pgout) __P((DB_ENV *, db_pgno_t, void *, DBT *));
};

/*
 * File hashing --
 *	We hash each file to hash bucket based on its fileid
 *	or, in the case of in memory files, its name.
 */

/* Number of file hash buckets, a small prime number */
#define	MPOOL_FILE_BUCKETS	17

#define	FHASH(id, len)	__ham_func5(NULL, id, (u_int32_t)(len))

#define	FNBUCKET(id, len)						\
	(FHASH(id, len) % MPOOL_FILE_BUCKETS)

/* Macros to lock/unlock the mpool region as a whole. */
#define	MPOOL_SYSTEM_LOCK(env)						\
	MUTEX_LOCK(env, ((MPOOL *)					\
	    (env)->mp_handle->reginfo[0].primary)->mtx_region)
#define	MPOOL_SYSTEM_UNLOCK(env)					\
	MUTEX_UNLOCK(env, ((MPOOL *)					\
	    (env)->mp_handle->reginfo[0].primary)->mtx_region)

/* Macros to lock/unlock a specific mpool region. */
#define	MPOOL_REGION_LOCK(env, infop)					\
	MUTEX_LOCK(env, ((MPOOL *)(infop)->primary)->mtx_region)
#define	MPOOL_REGION_UNLOCK(env, infop)					\
	MUTEX_UNLOCK(env, ((MPOOL *)(infop)->primary)->mtx_region)

/*
 * MPOOL --
 *	Shared memory pool region.
 */
struct __mpool { /* SHARED */
	/*
	 * The memory pool can be broken up into individual pieces/files.
	 * There are two reasons for this: firstly, on Solaris you can allocate
	 * only a little more than 2GB of memory in a contiguous chunk,
	 * and I expect to see more systems with similar issues.  Secondly,
	 * applications can add / remove pieces to dynamically resize the
	 * cache.
	 *
	 * While this structure is duplicated in each piece of the cache,
	 * the first of these pieces/files describes the entire pool, the
	 * second only describe a piece of the cache.
	 */
	db_mutex_t	mtx_region;	/* Region mutex. */
	db_mutex_t	mtx_resize;	/* Resizing mutex. */

	/*
	 * The lsn field and list of underlying MPOOLFILEs are thread protected
	 * by the region lock.
	 */
	DB_LSN	  lsn;			/* Maximum checkpoint LSN. */

	/* Configuration information: protected by the region lock. */
	u_int32_t max_nreg;		/* Maximum number of regions. */
	u_int32_t gbytes;		/* Number of gigabytes in cache. */
	u_int32_t bytes;		/* Number of bytes in cache. */
	u_int32_t pagesize;		/* Default page size. */
	db_size_t mp_mmapsize;		/* Maximum file size for mmap. */
	int32_t mp_maxopenfd;		/* Maximum open file descriptors. */
	int32_t mp_maxwrite;		/* Maximum buffers to write. */
	db_timeout_t mp_maxwrite_sleep;	/* Sleep after writing max buffers. */

	/*
	 * The number of regions and the total number of hash buckets across
	 * all regions.
	 * These fields are not protected by a mutex because we assume that we
	 * can read a 32-bit value atomically.  They are only modified by cache
	 * resizing which holds the mpool resizing mutex to ensure that
	 * resizing is single-threaded.  See the comment in mp_resize.c for
	 * more information.
	 */
	u_int32_t nreg;			/* Number of underlying REGIONS. */
	u_int32_t nbuckets;		/* Total number of hash buckets. */

	/*
	 * The regid field is protected by the resize mutex.
	 */
	roff_t	  regids;		/* Array of underlying REGION Ids. */

	roff_t	  ftab;			/* Hash table of files. */

	/*
	 * The following fields describe the per-cache portion of the region.
	 *
	 * The htab and htab_buckets fields are not thread protected as they
	 * are initialized during mpool creation, and not modified again.
	 *
	 * The last_checked, lru_priority, and lru_generation fields are thread
	 * protected by the region lock.
	 */
	roff_t	  htab;			/* Hash table offset. */
	u_int32_t htab_buckets;		/* Number of hash table entries. */
	u_int32_t last_checked;		/* Last bucket checked for free. */
	u_int32_t lru_priority;		/* Priority counter for buffer LRU. */
	u_int32_t lru_generation;	/* Allocation race condition detector. */
	u_int32_t htab_mutexes;		/* Number of hash mutexes per region. */

	 /*
	  * The pages field keeps track of the number of pages in the cache
	  * and is protected by the region lock.  It is accessed for reading
	  * without the lock to return statistics.
	  */
	u_int32_t pages;		/* Number of pages in the cache. */

	/*
	 * The stat fields are not thread protected, and cannot be trusted.
	 */
	DB_MPOOL_STAT stat;		/* Per-cache mpool statistics. */

	/*
	 * We track page puts so that we can decide when allocation is never
	 * going to succeed.  We don't lock the field, all we care about is
	 * if it changes.
	 */
	u_int32_t  put_counter;		/* Count of page put calls. */

	/*
	 * Cache flush operations take a long time...
	 *
	 * Some cache flush operations want to ignore the app's configured
	 * max-write parameters (they are trying to quickly shut down an
	 * environment, for example).  We can't specify that as an argument
	 * to the cache region functions, because we may decide to ignore
	 * the max-write configuration after the cache operation has begun.
	 * If the variable suppress_maxwrite is set, ignore the application
	 * max-write config.
	 *
	 * We may want to interrupt cache flush operations in high-availability
	 * configurations.
	 */
#define	DB_MEMP_SUPPRESS_WRITE	0x01
#define	DB_MEMP_SYNC_INTERRUPT	0x02
	u_int32_t config_flags;

	/* Free frozen buffer headers, protected by the region lock. */
	SH_TAILQ_HEAD(__free_frozen) free_frozen;

	/* Allocated blocks of frozen buffer headers. */
	SH_TAILQ_HEAD(__alloc_frozen) alloc_frozen;
};

/*
 * NREGION --
 *	Select a cache region given the bucket number.
 */
#define	NREGION(mp, bucket)						\
	((bucket) / (mp)->htab_buckets)

/*
 * MP_HASH --
 *	 We make the assumption that early pages of the file are more likely
 *	 to be retrieved than the later pages, which means the top bits will
 *	 be more interesting for hashing as they're less likely to collide.
 *	 That said, as 512 8K pages represents a 4MB file, so only reasonably
 *	 large files will have page numbers with any other than the bottom 9
 *	 bits set.  We XOR in the MPOOL offset of the MPOOLFILE that backs the
 *	 page, since that should also be unique for the page.  We don't want
 *	 to do anything very fancy -- speed is more important to us than using
 *	 good hashing.
 *
 *	 Since moving to a dynamic hash, which boils down to using some of the
 *	 least significant bits of the hash value, we no longer want to use a
 *	 simple shift here, because it's likely with a bit shift that mf_offset
 *	 will be ignored, and pages from different files end up in the same
 *	 hash bucket.  Use a nearby prime instead.
 */
#define	MP_HASH(mf_offset, pgno)					\
	((((pgno) << 8) ^ (pgno)) ^ (((u_int32_t) mf_offset) * 509))

/*
 * Inline the calculation of the mask, since we can't reliably store the mask
 * with the number of buckets in the region.
 *
 * This is equivalent to:
 *     mask = (1 << __db_log2(nbuckets)) - 1;
 */
#define	MP_MASK(nbuckets, mask) do {					\
	for (mask = 1; mask < (nbuckets); mask = (mask << 1) | 1)	\
		;							\
} while (0)

#define	MP_HASH_BUCKET(hash, nbuckets, mask, bucket) do {		\
	(bucket) = (hash) & (mask);					\
	if ((bucket) >= (nbuckets))					\
		(bucket) &= ((mask) >> 1);				\
} while (0)

#define	MP_BUCKET(mf_offset, pgno, nbuckets, bucket) do {		\
	u_int32_t __mask;						\
	MP_MASK(nbuckets, __mask);					\
	MP_HASH_BUCKET(MP_HASH(mf_offset, pgno), nbuckets,		\
	    __mask, bucket);						\
} while (0)

/*
 * MP_GET_REGION --
 *	Select the region for a given page.
 */
#define	MP_GET_REGION(dbmfp, pgno, infopp, ret) do {			\
	DB_MPOOL *__t_dbmp;						\
	MPOOL *__t_mp;							\
									\
	__t_dbmp = dbmfp->env->mp_handle;				\
	__t_mp = __t_dbmp->reginfo[0].primary;				\
	if (__t_mp->max_nreg == 1) {					\
		*(infopp) = &__t_dbmp->reginfo[0];			\
	} else								\
		ret = __memp_get_bucket((dbmfp)->env,			\
		    (dbmfp)->mfp, (pgno), (infopp), NULL, NULL);	\
} while (0)

/*
 * MP_GET_BUCKET --
 *	Select and lock the bucket for a given page.
 */
#define	MP_GET_BUCKET(env, mfp, pgno, infopp, hp, bucket, ret) do {	\
	DB_MPOOL *__t_dbmp;						\
	MPOOL *__t_mp;							\
	roff_t __t_mf_offset;						\
									\
	__t_dbmp = (env)->mp_handle;					\
	__t_mp = __t_dbmp->reginfo[0].primary;				\
	if (__t_mp->max_nreg == 1) {					\
		*(infopp) = &__t_dbmp->reginfo[0];			\
		__t_mf_offset = R_OFFSET(*(infopp), (mfp));		\
		MP_BUCKET(__t_mf_offset,				\
		    (pgno), __t_mp->nbuckets, bucket);		\
		(hp) = R_ADDR(*(infopp), __t_mp->htab);			\
		(hp) = &(hp)[bucket];				\
		MUTEX_READLOCK(env, (hp)->mtx_hash);			\
		ret = 0;						\
	} else								\
		ret = __memp_get_bucket((env),				\
		    (mfp), (pgno), (infopp), &(hp), &(bucket));		\
} while (0)

struct __db_mpool_hash {
	db_mutex_t	mtx_hash;	/* Per-bucket mutex. */

	DB_HASHTAB	hash_bucket;	/* Head of bucket. */

	db_atomic_t	hash_page_dirty;/* Count of dirty pages. */

#ifndef __TEST_DB_NO_STATISTICS
	u_int32_t	hash_io_wait;	/* Count of I/O waits. */
	u_int32_t	hash_frozen;	/* Count of frozen buffers. */
	u_int32_t	hash_thawed;	/* Count of thawed buffers. */
	u_int32_t	hash_frozen_freed;/* Count of freed frozen buffers. */
#endif

	DB_LSN		old_reader;	/* Oldest snapshot reader (cached). */

	u_int32_t	flags;
};

/*
 * Mpool file statistics structure for use in shared memory.
 * This structure must contain the same fields as the __db_mpool_fstat struct
 * except for any pointer fields that are filled in only when the struct is
 * being populated for output through the API.
 */
struct __db_mpool_fstat_int { /* SHARED */
	u_int32_t st_pagesize;		/* Page size. */
#ifndef __TEST_DB_NO_STATISTICS
	u_int32_t st_map;		/* Pages from mapped files. */
	uintmax_t st_cache_hit;	/* Pages found in the cache. */
	uintmax_t st_cache_miss;	/* Pages not found in the cache. */
	uintmax_t st_page_create;	/* Pages created in the cache. */
	uintmax_t st_page_in;		/* Pages read in. */
	uintmax_t st_page_out;		/* Pages written out. */
	uintmax_t st_backup_spins;	/* Number of spins by a backup. */
#endif
};

/*
 * The base mpool priority is 1/4th of the name space, or just under 2^30. When
 * the LRU priority counter is about to wrap (within a 128-entry 'red zone'
 * area) we adjust everybody down so that no one is larger than the new LRU
 * priority.
 */
#define	MPOOL_LRU_MAX		UINT32_MAX
#define	MPOOL_LRU_REDZONE	(MPOOL_LRU_MAX - 128)
#define	MPOOL_LRU_BASE		(MPOOL_LRU_MAX / 4)
#define	MPOOL_LRU_DECREMENT	(MPOOL_LRU_MAX - MPOOL_LRU_BASE)

/*
 * Mpool priorities from low to high.  Defined in terms of fractions of the
 * buffers in the pool.
 */
#define	MPOOL_PRI_VERY_LOW	-1	/* Dead duck.  Check and set to 0. */
#define	MPOOL_PRI_LOW		-2	/* Low. */
#define	MPOOL_PRI_DEFAULT	0	/* No adjustment -- special case.*/
#define	MPOOL_PRI_HIGH		10	/* With the dirty buffers. */
#define	MPOOL_PRI_DIRTY		10	/* Dirty gets a 10% boost. */
#define	MPOOL_PRI_VERY_HIGH	1	/* Add number of buffers in pool. */

/*
 * MPOOLFILE --
 *	Shared DB_MPOOLFILE information.
 */
struct __mpoolfile { /* SHARED */
	db_mutex_t mutex;		/* MPOOLFILE mutex. */

#ifndef HAVE_ATOMICFILEREAD
	/* Information to synchronize backups. */
	u_int32_t   backup_in_progress;	/* Backup running. */
	pid_t       pid;		/* Process doing backup. */
	db_threadid_t tid;		/* Thread doing backup. */
	db_atomic_t writers;		/* Number of current writers. */
	db_mutex_t  mtx_write;		/* block writers while updating.*/
	db_pgno_t   low_pgno, high_pgno;/* Low and high backup range.*/
#endif
	
	/* Protected by MPOOLFILE mutex. */
	u_int32_t revision;		/* Bumped on any movement subdbs. */
	u_int32_t mpf_cnt;		/* Ref count: DB_MPOOLFILEs. */
	u_int32_t neutral_cnt;		/* Ref count: refs that don't care about
					 * MVCC or DURABLE.  That is, read-only
					 * or write behind references.
					 */
	u_int32_t block_cnt;		/* Ref count: blocks in cache. */
	db_pgno_t last_pgno;		/* Last page in the file. */
	db_pgno_t last_flushed_pgno;	/* Last page flushed to disk. */
	db_pgno_t orig_last_pgno;	/* Original last page in the file. */
	db_pgno_t maxpgno;		/* Maximum page number. */
	u_int8_t excl_lockout;		/* Internal exclusive db lockout. */

	roff_t	  path_off;		/* File name location. */

	/* Protected by hash bucket mutex. */
	SH_TAILQ_ENTRY q;		/* List of MPOOLFILEs */

	/*
	 * The following are used for file compaction processing.
	 * They are only used when a thread is in the process
	 * of trying to move free pages to the end of the file.
	 * Other threads may look here when freeing a page.
	 * Protected by a lock on the metapage.
	 */
	u_int32_t free_ref;		/* Refcount to freelist. */
	u_int32_t free_cnt;		/* Count of free pages. */
	db_size_t free_size;		/* Allocated size of free list. */
	roff_t	  free_list;		/* Offset to free list. */

	/*
	 * We normally don't lock the deadfile field when we read it since we
	 * only care if the field is zero or non-zero.  We do lock on read when
	 * searching for a matching MPOOLFILE -- see that code for more detail.
	 */
	int32_t	  deadfile;		/* Dirty pages can be discarded. */

	u_int32_t bucket;		/* hash bucket for this file. */

	/*
	 * None of the following fields are thread protected.
	 *
	 * There are potential races with the ftype field because it's read
	 * without holding a lock.  However, it has to be set before adding
	 * any buffers to the cache that depend on it being set, so there
	 * would need to be incorrect operation ordering to have a problem.
	 */
	int32_t	  ftype;		/* File type. */

	/*
	 * There are potential races with the priority field because it's read
	 * without holding a lock.  However, a collision is unlikely and if it
	 * happens is of little consequence.
	 */
	int32_t   priority;		/* Priority when unpinning buffer. */

	/*
	 * There are potential races with the file_written field (many threads
	 * may be writing blocks at the same time), and with no_backing_file
	 * and unlink_on_close fields, as they may be set while other threads
	 * are reading them.  However, we only care if the field value is zero
	 * or non-zero, so don't lock the memory.
	 *
	 * !!!
	 * Theoretically, a 64-bit architecture could put two of these fields
	 * in a single memory operation and we could race.  I have never seen
	 * an architecture where that's a problem, and I believe Java requires
	 * that to never be the case.
	 *
	 * File_written is set whenever a buffer is marked dirty in the cache.
	 * It can be cleared in some cases, after all dirty buffers have been
	 * written AND the file has been flushed to disk.
	 */
	int32_t	  file_written;		/* File was written. */
	int32_t	  no_backing_file;	/* Never open a backing file. */
	int32_t	  unlink_on_close;	/* Unlink file on last close. */
	db_atomic_t	  multiversion;	/* Number of DB_MULTIVERSION handles. */

	/*
	 * We do not protect the statistics in "stat" because of the cost of
	 * the mutex in the get/put routines.  There is a chance that a count
	 * will get lost.
	 */
	DB_MPOOL_FSTAT_INT stat;	/* Per-file mpool statistics. */

	/*
	 * The remaining fields are initialized at open and never subsequently
	 * modified.
	 */
	int32_t	  lsn_off;		/* Page's LSN offset. */
	u_int32_t clear_len;		/* Bytes to clear on page create. */

	roff_t	  fileid_off;		/* File ID string location. */

	u_int32_t pagesize;		/* Underlying pagesize. */
	roff_t	  pgcookie_len;		/* Pgin/pgout cookie length. */
	roff_t	  pgcookie_off;		/* Pgin/pgout cookie location. */

	/*
	 * The flags are initialized at open and never subsequently modified.
	 */
#define	MP_CAN_MMAP		0x001	/* If the file can be mmap'd. */
#define	MP_DATABASE_LOCKING	0x002	/* Lock in exclusive mode. */
#define	MP_DIRECT		0x004	/* No OS buffering. */
#define	MP_DURABLE_UNKNOWN	0x008	/* We don't care about durability. */
#define	MP_EXTENT		0x010	/* Extent file. */
#define	MP_FAKE_DEADFILE	0x020	/* Deadfile field: fake flag. */
#define	MP_FAKE_FILEWRITTEN	0x040	/* File_written field: fake flag. */
#define	MP_FAKE_NB		0x080	/* No_backing_file field: fake flag. */
#define	MP_FAKE_UOC		0x100	/* Unlink_on_close field: fake flag. */
#define	MP_NOT_DURABLE		0x200	/* File is not durable. */
#define	MP_TEMP			0x400	/* Backing file is a temporary. */
	u_int32_t  flags;

	db_pgno_t  fe_watermark;	/* File extension watermark. */
	u_int32_t  fe_txnid;		/* Transaction that set watermark. */
	u_int32_t  fe_nlws;		/* Number of log writes suppressed. */
};

/*
 * Flags to __memp_bh_free.
 */
#define	BH_FREE_FREEMEM		0x01
#define	BH_FREE_REUSE		0x02
#define	BH_FREE_UNLOCKED	0x04

/*
 * BH --
 *	Buffer header.
 */
struct __bh { /* SHARED */
	db_mutex_t	mtx_buf;	/* Shared/Exclusive mutex */
	db_atomic_t	ref;		/* Reference count. */
#define	BH_REFCOUNT(bhp)	atomic_read(&(bhp)->ref)

#define	BH_CALLPGIN	0x001		/* Convert the page before use. */
#define	BH_DIRTY	0x002		/* Page is modified. */
#define	BH_DIRTY_CREATE	0x004		/* Page is modified. */
#define	BH_DISCARD	0x008		/* Page is useless. */
#define	BH_EXCLUSIVE	0x010		/* Exclusive access acquired. */
#define	BH_FREED	0x020		/* Page was freed. */
#define	BH_FROZEN	0x040		/* Frozen buffer: allocate & re-read. */
#define	BH_TRASH	0x080		/* Page is garbage. */
#define	BH_THAWED	0x100		/* Page was thawed. */
	u_int16_t	flags;

	u_int32_t	priority;	/* Priority. */
	SH_TAILQ_ENTRY	hq;		/* MPOOL hash bucket queue. */

	db_pgno_t	pgno;		/* Underlying MPOOLFILE page number. */
	roff_t		mf_offset;	/* Associated MPOOLFILE offset. */
	u_int32_t	bucket;		/* Hash bucket containing header. */
	int		region;		/* Region containing header. */

	roff_t		td_off;		/* MVCC: creating TXN_DETAIL offset. */
	SH_CHAIN_ENTRY	vc;		/* MVCC: version chain. */
#ifdef DIAG_MVCC
	u_int16_t	align_off;	/* Alignment offset for diagnostics.*/
#endif

	/*
	 * !!!
	 * This array must be at least size_t aligned -- the DB access methods
	 * put PAGE and other structures into it, and then access them directly.
	 * (We guarantee size_t alignment to applications in the documentation,
	 * too.)
	 */
	DB_ALIGN8	u_int8_t buf[1];	/* Variable length data. */
};

/*
 * BH_FROZEN_PAGE --
 *	Data used to find a frozen buffer header.
 */
struct __bh_frozen_p {
	BH header;
	db_pgno_t	spgno;		/* Page number in freezer file. */
};

/*
 * BH_FROZEN_ALLOC --
 *	Frozen buffer headers are allocated a page at a time in general.  This
 *	structure is allocated at the beginning of the page so that the
 *	allocation chunks can be tracked and freed (for private environments).
 */
struct __bh_frozen_a {
	SH_TAILQ_ENTRY links;
};

#define	MULTIVERSION(dbp)	atomic_read(&(dbp)->mpf->mfp->multiversion)

#define	PAGE_TO_BH(p)	(BH *)((u_int8_t *)(p) - SSZA(BH, buf))
#define	IS_DIRTY(p)							\
    (F_ISSET(PAGE_TO_BH(p), BH_DIRTY|BH_EXCLUSIVE) == (BH_DIRTY|BH_EXCLUSIVE))

#define	BH_OWNER(env, bhp)		((TXN_DETAIL *) NULL)

#define	BH_OWNED_BY(env, bhp, txn)	FALSE

#define	VISIBLE_LSN(env, bhp)						\
    (&BH_OWNER(env, bhp)->visible_lsn)

/*
 * Make a copy of the buffer's visible LSN, one field at a time.  We rely on the
 * 32-bit operations being atomic.  The visible_lsn starts at MAX_LSN and is
 * set during commit or abort to the current LSN.
 *
 * If we race with a commit / abort, we may see either the file or the offset
 * still at UINT32_MAX, so vlsn is guaranteed to be in the future.  That's OK,
 * since we had to take the log region lock to allocate the read LSN so we were
 * never going to see this buffer anyway.
 */
/* Without transactions -- and hence MVCC -- buffers are always visible. */
#define	BH_VISIBLE(env, bhp, read_lsnp, vlsn)	TRUE

#define	BH_OBSOLETE(bhp, old_lsn, vlsn)		FALSE

#define	MVCC_SKIP_CURADJ(dbc, pgno) 		FALSE

#if defined(DIAG_MVCC) && defined(HAVE_MPROTECT)
#define	VM_PAGESIZE 4096
#define	MVCC_BHSIZE(mfp, sz) do {					\
	sz += VM_PAGESIZE + sizeof(BH);					\
	if (mfp->pagesize < VM_PAGESIZE)				\
		sz += VM_PAGESIZE - mfp->pagesize;			\
} while (0)

#define	MVCC_BHALIGN(p) 	NOP_STATEMENT

#define	MVCC_BHUNALIGN(bhp) 	NOP_STATEMENT

#ifdef linux
#define	MVCC_MPROTECT(buf, sz, mode) do {				\
	int __ret = mprotect((buf), (sz), (mode));			\
	DB_ASSERT(env, __ret == 0);					\
} while (0)
#else
#define	MVCC_MPROTECT(buf, sz, mode) do {				\
	if (!F_ISSET(env, ENV_PRIVATE | ENV_SYSTEM_MEM)) {		\
		int __ret = mprotect((buf), (sz), (mode));		\
		DB_ASSERT(env, __ret == 0);				\
	}								\
} while (0)
#endif /* linux */

#else /* defined(DIAG_MVCC) && defined(HAVE_MPROTECT) */
#define	MVCC_BHSIZE(mfp, sz) do {} while (0)
#define	MVCC_BHALIGN(p) do {} while (0)
#define	MVCC_BHUNALIGN(bhp) do {} while (0)
#define	MVCC_MPROTECT(buf, size, mode) do {} while (0)
#endif

/*
 * Flags to __memp_ftruncate.
 */
#define	MP_TRUNC_NOCACHE	0x01
#define	MP_TRUNC_RECOVER	0x02

#if defined(__cplusplus)
}
#endif

#include "dbinc_auto/mp_ext.h"
#endif /* !_DB_MP_H_ */