path: root/db/dbinc/region.h

/*-
 * See the file LICENSE for redistribution information.
 *
 * Copyright (c) 1998,2007 Oracle.  All rights reserved.
 *
 * $Id: region.h,v 12.14 2007/05/17 15:15:05 bostic Exp $
 */

#ifndef _DB_REGION_H_
#define	_DB_REGION_H_

/*
 * The DB environment consists of some number of "regions", which are described
 * by the following four structures:
 *
 *	REGENV	   -- shared information about the environment
 *	REGENV_REF -- file describing system memory version of REGENV
 *	REGION	   -- shared information about a single region
 *	REGINFO	   -- per-process information about a REGION
 *
 * There are three types of memory that hold regions:
 *	per-process heap (malloc)
 *	file mapped into memory (mmap, MapViewOfFile)
 *	system memory (shmget, CreateFileMapping)
 *
 * By default, regions are created in filesystem-backed shared memory.  They
 * can also be created in system shared memory (DB_SYSTEM_MEM), or, if private
 * to a process, in heap memory (DB_PRIVATE).
 *
 * Regions in the filesystem are named "__db.001", "__db.002" and so on.  If
 * we're not using a private environment allocated in heap, "__db.001" will
 * always exist, as we use it to synchronize on the regions, whether they are
 * in filesystem-backed memory or system memory.
 *
 * The file "__db.001" contains a REGENV structure and an array of REGION
 * structures.  Each REGION structures describes an underlying chunk of
 * shared memory.
 *
 *	__db.001
 *	+---------+
 *	|REGENV  |
 *	+---------+   +----------+
 *	|REGION   |-> | __db.002 |
 *	|	  |   +----------+
 *	+---------+   +----------+
 *	|REGION   |-> | __db.003 |
 *	|	  |   +----------+
 *	+---------+   +----------+
 *	|REGION   |-> | __db.004 |
 *	|	  |   +----------+
 *	+---------+
 *
 * The tricky part about manipulating the regions is creating or joining the
 * database environment.  We have to be sure only a single thread of control
 * creates and/or recovers a database environment.  All other threads should
 * then join without seeing inconsistent data.
 *
 * We do this in two parts: first, we use the underlying O_EXCL flag to the
 * open system call to serialize creation of the __db.001 file.  The thread
 * of control creating that file then proceeds to create the remaining
 * regions in the environment, including the mutex region.  Once the mutex
 * region has been created, the creating thread of control fills in the
 * __db.001 file's magic number.  Other threads of control (the ones that
 * didn't create the __db.001 file), wait on the initialization of the
 * __db.001 file's magic number.  After it has been initialized, all threads
 * of control can proceed, using normal shared mutex locking procedures for
 * exclusion.
 *
 * REGIONs are not moved or removed during the life of the environment, and
 * so processes can have long-lived references to them.
 *
 * One of the REGION structures describes the environment region itself.
 *
 * The REGION array is not locked in any way.  It's an array so we don't have
 * to manipulate data structures after a crash -- on some systems, we have to
 * join and clean up the mutex region after application failure.  Using an
 * array means we don't have to worry about broken links or other nastiness
 * after the failure.
 *
 * All requests to create or join a region return a REGINFO structure, which
 * is held by the caller and used to open and subsequently close the reference
 * to the region.  The REGINFO structure contains the per-process information
 * that we need to access the region.
 *
 * The one remaining complication.  If the regions (including the environment
 * region) live in system memory, and the system memory isn't "named" somehow
 * in the filesystem name space, we need some way of finding it.  Do this by
 * by writing the REGENV_REF structure into the "__db.001" file.  When we find
 * a __db.001 file that is too small to be a real, on-disk environment, we use
 * the information it contains to redirect to the real "__db.001" file/memory.
 * This currently only happens when the REGENV file is in shared system memory.
 *
 * Although DB does not currently grow regions when they run out of memory, it
 * would be possible to do so.  To grow a region, allocate a new region of the
 * appropriate size, then copy the old region over it and insert the additional
 * memory into the already existing shalloc arena.  Region users must reset
 * their base addresses and any local pointers into the memory, of course.
 * This failed in historic versions of DB because the region mutexes lived in
 * the mapped memory, and when it was unmapped and remapped (or copied),
 * threads could lose track of it.  Also, some systems didn't support mutex
 * copying, e.g., from OSF1 V4.0:
 *
 *	The address of an msemaphore structure may be significant.  If the
 *	msemaphore structure contains any value copied from an msemaphore
 *	structure at a different address, the result is undefined.
 *
 * All mutexes are now maintained in a separate region which is never unmapped,
 * so growing regions should be possible.
 */

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

#define	DB_REGION_PREFIX	"__db"		/* DB file name prefix. */
#define	DB_REGION_FMT		"__db.%03d"	/* Region file name format. */
#define	DB_REGION_ENV		"__db.001"	/* Primary environment name. */
#define	DB_REGION_NAME_LENGTH	8		/* Length of file names. */

#define	INVALID_REGION_ID	0	/* Out-of-band region ID. */
#define	REGION_ID_ENV		1	/* Primary environment ID. */

typedef enum {
	INVALID_REGION_TYPE=0,		/* Region type. */
	REGION_TYPE_ENV,
	REGION_TYPE_LOCK,
	REGION_TYPE_LOG,
	REGION_TYPE_MPOOL,
	REGION_TYPE_MUTEX,
	REGION_TYPE_TXN } reg_type_t;

#define	INVALID_REGION_SEGID	-1	/* Segment IDs are either shmget(2) or
					 * Win16 segment identifiers.  They are
					 * both stored in a "long", and we need
					 * an out-of-band value.
					 */
/*
 * Nothing can live at region offset 0, because, in all cases, that's where
 * we store *something*.  Lots of code needs an out-of-band value for region
 * offsets, so we use 0.
 */
#define	INVALID_ROFF		0

/* Reference describing system memory version of REGENV. */
typedef struct __db_reg_env_ref {
	roff_t	   size;		/* Region size. */
	long	   segid;		/* UNIX shmget ID, VxWorks ID. */
} REGENV_REF;

/* Per-environment region information. */
typedef struct __db_reg_env {
	/*
	 * !!!
	 * The magic, panic, version and envid fields of the region are fixed
	 * in size, the timestamp field is the first field which is variable
	 * length.  These fields must never change in order, to guarantee we
	 * can always read them, no matter what Berkeley DB release we have.
	 *
	 * !!!
	 * The magic and panic fields are NOT protected by any mutex, and for
	 * this reason cannot be anything more complicated than zero/non-zero.
	 */
	u_int32_t magic;		/* Valid region magic number. */
	u_int32_t panic;		/* Environment is dead. */

	u_int32_t majver;		/* Major DB version number. */
	u_int32_t minver;		/* Minor DB version number. */
	u_int32_t patchver;		/* Patch DB version number. */

	u_int32_t envid;		/* Unique environment ID. */

	time_t	  timestamp;		/* Creation time. */

	u_int32_t init_flags;		/* Flags environment initialized with.*/

	/*
	 * The mtx_regenv mutex protects the environment reference count and
	 * memory allocation from the primary shared region (the crypto, thread
	 * control block and replication implementations allocate memory from
	 * the primary shared region).
	 *
	 * The rest of the fields are initialized at creation time, and don't
	 * need mutex protection.  The flags, op_timestamp and rep_timestamp
	 * fields are used by replication only and are protected by the
	 * replication mutex.  The rep_timestamp is is not protected when it
	 * is used in recovery as that is already single threaded.
	 */
	db_mutex_t mtx_regenv;		/* Refcnt, region allocation mutex. */
	u_int32_t  refcnt;		/* References to the environment. */

	u_int32_t region_cnt;		/* Number of REGIONs. */
	roff_t	  region_off;		/* Offset of region array */

	roff_t	  cipher_off;		/* Offset of cipher area */

	roff_t	  thread_off;		/* Offset of the thread area. */

	roff_t	  rep_off;		/* Offset of the replication area. */
#define	DB_REGENV_REPLOCKED	0x0001	/* Env locked for rep backup. */
	u_int32_t flags;		/* Shared environment flags. */
#define	DB_REGENV_TIMEOUT	30	/* Backup timeout. */
	time_t	  op_timestamp;		/* Timestamp for operations. */
	time_t	  rep_timestamp;	/* Timestamp for rep db handles. */

	size_t	pad;			/* Guarantee that following memory is
					 * size_t aligned.  This is necessary
					 * because we're going to store the
					 * allocation region information there.
					 */
} REGENV;

/* Per-region shared region information. */
typedef struct __db_region {
	u_int32_t	id;		/* Region id. */
	reg_type_t	type;		/* Region type. */

	roff_t	size_orig;		/* Region size in bytes (original). */
	roff_t	size;			/* Region size in bytes (adjusted). */

	roff_t	primary;		/* Primary data structure offset. */

	long	segid;			/* UNIX shmget(2), Win16 segment ID. */
} REGION;

/*
 * Per-process/per-attachment information about a single region.
 */
struct __db_reginfo_t {		/* __env_region_attach IN parameters. */
	DB_ENV	   *dbenv;		/* Enclosing environment. */
	reg_type_t  type;		/* Region type. */
	u_int32_t   id;			/* Region id. */

				/* env_region_attach OUT parameters. */
	REGION	   *rp;			/* Shared region. */

	char	   *name;		/* Region file name. */

	void	   *addr_orig;		/* Region address (original). */
	void	   *addr;		/* Region address (adjusted). */
	void	   *primary;		/* Primary data structure address. */

	size_t	    max_alloc;		/* Maximum bytes allocated. */
	size_t	    allocated;		/* Bytes allocated. */

#ifdef DB_WIN32
	HANDLE	wnt_handle;		/* Win/NT HANDLE. */
#endif

#define	REGION_CREATE		0x01	/* Caller created region. */
#define	REGION_CREATE_OK	0x02	/* Caller willing to create region. */
#define	REGION_JOIN_OK		0x04	/* Caller is looking for a match. */
	u_int32_t   flags;
};

/*
 * R_ADDR	Return a per-process address for a shared region offset.
 * R_OFFSET	Return a shared region offset for a per-process address.
 */
#define	R_ADDR(reginfop, offset)					\
	(F_ISSET((reginfop)->dbenv, DB_ENV_PRIVATE) ? (void *)(offset) :\
	(void *)((u_int8_t *)((reginfop)->addr) + (offset)))
#define	R_OFFSET(reginfop, p)						\
	(F_ISSET((reginfop)->dbenv, DB_ENV_PRIVATE) ? (roff_t)(p) :	\
	(roff_t)((u_int8_t *)(p) - (u_int8_t *)(reginfop)->addr))

/*
 * PANIC_ISSET, PANIC_CHECK:
 *	Check to see if the DB environment is dead.
 */
#define	PANIC_ISSET(dbenv)						\
	((dbenv)->reginfo != NULL && ((REGENV *)			\
	    ((REGINFO *)(dbenv)->reginfo)->primary)->panic != 0 &&	\
	    !F_ISSET((dbenv), DB_ENV_NOPANIC))

#define	PANIC_CHECK(dbenv)						\
	if (PANIC_ISSET(dbenv))						\
		return (__db_panic_msg(dbenv));

#if defined(__cplusplus)
}
#endif
#endif /* !_DB_REGION_H_ */