tdb is a Trivial database. More...

Data Structures
struct	TDB_DATA
	The tdb data structure. More...
Defines
#define	TDB_REPLACE 1
	Flags to tdb_store()
#define	TDB_DEFAULT 0
	Flags for tdb_open()
Typedefs
typedef struct TDB_DATA	TDB_DATA
	The tdb data structure.
typedef struct tdb_context	TDB_CONTEXT
	This is the context structure that is returned from a db open.
Enumerations
enum	TDB_ERROR
	The tdb error codes.
enum	tdb_debug_level
	Debugging uses one of the following levels.
Functions
struct tdb_context *	tdb_open (const char *name, int hash_size, int tdb_flags, int open_flags, mode_t mode)
	Open the database and creating it if necessary.
struct tdb_context *	tdb_open_ex (const char name, int hash_size, int tdb_flags, int open_flags, mode_t mode, const struct tdb_logging_context log_ctx, tdb_hash_func hash_fn)
	Open the database and creating it if necessary.
void	tdb_set_max_dead (struct tdb_context *tdb, int max_dead)
	Set the maximum number of dead records per hash chain.
int	tdb_reopen (struct tdb_context *tdb)
	Reopen a tdb.
int	tdb_reopen_all (int parent_longlived)
	Reopen all tdb's.
void	tdb_set_logging_function (struct tdb_context tdb, const struct tdb_logging_context log_ctx)
	Set a different tdb logging function.
enum TDB_ERROR	tdb_error (struct tdb_context *tdb)
	Get the tdb last error code.
const char *	tdb_errorstr (struct tdb_context *tdb)
	Get a error string for the last tdb error.
TDB_DATA	tdb_fetch (struct tdb_context *tdb, TDB_DATA key)
	Fetch an entry in the database given a key.
int	tdb_parse_record (struct tdb_context tdb, TDB_DATA key, int(parser)(TDB_DATA key, TDB_DATA data, void private_data), void private_data)
	Hand a record to a parser function without allocating it.
int	tdb_delete (struct tdb_context *tdb, TDB_DATA key)
	Delete an entry in the database given a key.
int	tdb_store (struct tdb_context *tdb, TDB_DATA key, TDB_DATA dbuf, int flag)
	Store an element in the database.
int	tdb_append (struct tdb_context *tdb, TDB_DATA key, TDB_DATA new_dbuf)
	Append data to an entry.
int	tdb_close (struct tdb_context *tdb)
	Close a database.
TDB_DATA	tdb_firstkey (struct tdb_context *tdb)
	Find the first entry in the database and return its key.
TDB_DATA	tdb_nextkey (struct tdb_context *tdb, TDB_DATA key)
	Find the next entry in the database, returning its key.
int	tdb_traverse (struct tdb_context tdb, tdb_traverse_func fn, void private_data)
	Traverse the entire database.
int	tdb_traverse_read (struct tdb_context tdb, tdb_traverse_func fn, void private_data)
	Traverse the entire database.
int	tdb_exists (struct tdb_context *tdb, TDB_DATA key)
	Check if an entry in the database exists.
int	tdb_lockall (struct tdb_context *tdb)
	Lock entire database with a write lock.
int	tdb_lockall_nonblock (struct tdb_context *tdb)
	Lock entire database with a write lock.
int	tdb_unlockall (struct tdb_context *tdb)
	Unlock entire database with write lock.
int	tdb_lockall_read (struct tdb_context *tdb)
	Lock entire database with a read lock.
int	tdb_lockall_read_nonblock (struct tdb_context *tdb)
	Lock entire database with a read lock.
int	tdb_unlockall_read (struct tdb_context *tdb)
	Unlock entire database with read lock.
int	tdb_lockall_mark (struct tdb_context *tdb)
	Lock entire database with write lock - mark only.
int	tdb_lockall_unmark (struct tdb_context *tdb)
	Lock entire database with write lock - unmark only.
const char *	tdb_name (struct tdb_context *tdb)
	Get the name of the current tdb file.
int	tdb_fd (struct tdb_context *tdb)
	Get the underlying file descriptor being used by tdb.
tdb_log_func	tdb_log_fn (struct tdb_context *tdb)
	Get the current logging function.
void *	tdb_get_logging_private (struct tdb_context *tdb)
	Get the private data of the logging function.
int	tdb_transaction_start (struct tdb_context *tdb)
	Start a transaction.
int	tdb_transaction_start_nonblock (struct tdb_context *tdb)
	Start a transaction, non-blocking.
int	tdb_transaction_prepare_commit (struct tdb_context *tdb)
	Prepare to commit a current transaction, for two-phase commits.
int	tdb_transaction_commit (struct tdb_context *tdb)
	Commit a current transaction.
int	tdb_transaction_cancel (struct tdb_context *tdb)
	Cancel a current transaction.
int	tdb_get_seqnum (struct tdb_context *tdb)
	Get the tdb sequence number.
int	tdb_hash_size (struct tdb_context *tdb)
	Get the hash size.
size_t	tdb_map_size (struct tdb_context *tdb)
	Get the map size.
int	tdb_get_flags (struct tdb_context *tdb)
	Get the tdb flags set during open.
void	tdb_add_flags (struct tdb_context *tdb, unsigned flag)
	Add flags to the database.
void	tdb_remove_flags (struct tdb_context *tdb, unsigned flag)
	Remove flags from the database.
void	tdb_enable_seqnum (struct tdb_context *tdb)
	Enable sequence number handling on an open tdb.
void	tdb_increment_seqnum_nonblock (struct tdb_context *tdb)
	Increment the tdb sequence number.
unsigned int	tdb_jenkins_hash (TDB_DATA *key)
	Create a hash of the key.
int	tdb_check (struct tdb_context tdb, int(check)(TDB_DATA key, TDB_DATA data, void private_data), void private_data)
	Check the consistency of the database.

Detailed Description

tdb is a Trivial database.

In concept, it is very much like GDBM, and BSD's DB except that it allows multiple simultaneous writers and uses locking internally to keep writers from trampling on each other. tdb is also extremely small.

Interface

The interface is very similar to gdbm except for the following:

different open interface. The tdb_open call is more similar to a traditional open()
no tdbm_reorganise() function
no tdbm_sync() function. No operations are cached in the library anyway
added a tdb_traverse() function for traversing the whole database
added transactions support

A general rule for using tdb is that the caller frees any returned TDB_DATA structures. Just call free(p.dptr) to free a TDB_DATA return value called p. This is the same as gdbm.

Typedef Documentation

typedef struct tdb_context TDB_CONTEXT

This is the context structure that is returned from a db open.

Function Documentation

void tdb_add_flags	(	struct tdb_context *	tdb,
		unsigned	flag
	)

Add flags to the database.

Parameters:

[in]	tdb	The database to add the flags.
[in]	flag	The tdb flags to add.

int tdb_append	(	struct tdb_context *	tdb,
		TDB_DATA	key,
		TDB_DATA	new_dbuf
	)

Append data to an entry.

If the entry doesn't exist, it will create a new one.

Parameters:

[in]	tdb	The database to use.
[in]	key	The key to append the data.
[in]	new_dbuf	The data to append to the key.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_check	(	struct tdb_context *	tdb,
		int()(TDB_DATA key, TDB_DATA data, void private_data)	check,
		void *	private_data
	)

Check the consistency of the database.

This check the consistency of the database calling back the check function (if non-NULL) on each record. If some consistency check fails, or the supplied check function returns -1, tdb_check returns -1, otherwise 0.

Note:: The logging function (if set) will be called with additional information on the corruption found.

Parameters:

[in]	tdb	The database to check.
[in]	check	The check function to use.
[in]	private_data	the private data to pass to the check function.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_close ( struct tdb_context * tdb )

Close a database.

Parameters:

[in] tdb The database to close.

Returns:: 0 for success, -1 on error.

int tdb_delete	(	struct tdb_context *	tdb,
		TDB_DATA	key
	)

Delete an entry in the database given a key.

Parameters:

[in]	tdb	The tdb to delete the key.
[in]	key	The key to delete.

Returns:: 0 on success, -1 if the key doesn't exist.

void tdb_enable_seqnum ( struct tdb_context * tdb )

Enable sequence number handling on an open tdb.

Parameters:

[in] tdb The database to enable sequence number handling.

See also:: tdb_get_seqnum()

enum TDB_ERROR tdb_error ( struct tdb_context * tdb )

Get the tdb last error code.

Parameters:

[in] tdb The tdb to get the error code from.

Returns:: A TDB_ERROR code.

See also:: TDB_ERROR

const char* tdb_errorstr ( struct tdb_context * tdb )

Get a error string for the last tdb error.

Parameters:

[in] tdb The tdb to get the error code from.

Returns:: An error string.

int tdb_exists	(	struct tdb_context *	tdb,
		TDB_DATA	key
	)

Check if an entry in the database exists.

Note:: 1 is returned if the key is found and 0 is returned if not found this doesn't match the conventions in the rest of this module, but is compatible with gdbm.

Parameters:

[in]	tdb	The database to check if the entry exists.
[in]	key	The key to check if the entry exists.

Returns:: 1 if the key is found, 0 if not.

int tdb_fd ( struct tdb_context * tdb )

Get the underlying file descriptor being used by tdb.

This is useful for external routines that want to check the device/inode of the fd.

Parameters:

[in] tdb The database to get the fd from.

Returns:: The file descriptor or -1.

TDB_DATA tdb_fetch	(	struct tdb_context *	tdb,
		TDB_DATA	key
	)

Fetch an entry in the database given a key.

The caller must free the resulting data.

Parameters:

[in]	tdb	The tdb to fetch the key.
[in]	key	The key to fetch.

Returns:: The key entry found in the database, NULL on error with TDB_ERROR set.

See also:: tdb_error(); tdb_errorstr()

TDB_DATA tdb_firstkey ( struct tdb_context * tdb )

Find the first entry in the database and return its key.

The caller must free the returned data.

Parameters:

[in] tdb The database to use.

Returns:: The first entry of the database, an empty TDB_DATA entry if the database is empty.

int tdb_get_flags ( struct tdb_context * tdb )

Get the tdb flags set during open.

Parameters:

[in] tdb The database to get the flags form.

Returns:: The flags set to on the database.

void* tdb_get_logging_private ( struct tdb_context * tdb )

Get the private data of the logging function.

Parameters:

[in] tdb The database to get the data from.

Returns:: The private data pointer of the logging function.

See also:: tdb_log_fn()

int tdb_get_seqnum ( struct tdb_context * tdb )

Get the tdb sequence number.

Only makes sense if the writers opened with TDB_SEQNUM set. Note that this sequence number will wrap quite quickly, so it should only be used for a 'has something changed' test, not for code that relies on the count of the number of changes made. If you want a counter then use a tdb record.

The aim of this sequence number is to allow for a very lightweight test of a possible tdb change.

Parameters:

[in] tdb The database to get the sequence number from.

Returns:: The sequence number or 0.

See also:: tdb_open(); tdb_enable_seqnum()

int tdb_hash_size ( struct tdb_context * tdb )

Get the hash size.

Parameters:

[in] tdb The database to get the hash size from.

Returns:: The hash size.

void tdb_increment_seqnum_nonblock ( struct tdb_context * tdb )

Increment the tdb sequence number.

This only works if the tdb has been opened using the TDB_SEQNUM flag or enabled useing tdb_enable_seqnum().

Parameters:

[in] tdb The database to increment the sequence number.

See also:: tdb_enable_seqnum(); tdb_get_seqnum()

unsigned int tdb_jenkins_hash ( TDB_DATA * key )

Create a hash of the key.

Parameters:

[in] key The key to hash

Returns:: The hash.

int tdb_lockall ( struct tdb_context * tdb )

Lock entire database with a write lock.

Parameters:

[in] tdb The database to lock.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_lockall_mark ( struct tdb_context * tdb )

Lock entire database with write lock - mark only.

Todo:: Add more details.

Parameters:

[in] tdb The database to mark.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_lockall_nonblock ( struct tdb_context * tdb )

Lock entire database with a write lock.

This is the non-blocking call.

Parameters:

[in] tdb The database to lock.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_lockall(); tdb_error(); tdb_errorstr()

int tdb_lockall_read ( struct tdb_context * tdb )

Lock entire database with a read lock.

Parameters:

[in] tdb The database to lock.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_lockall_read_nonblock ( struct tdb_context * tdb )

Lock entire database with a read lock.

This is the non-blocking call.

Parameters:

[in] tdb The database to lock.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_lockall_read(); tdb_error(); tdb_errorstr()

int tdb_lockall_unmark ( struct tdb_context * tdb )

Lock entire database with write lock - unmark only.

Todo:: Add more details.

Parameters:

[in] tdb The database to mark.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

tdb_log_func tdb_log_fn ( struct tdb_context * tdb )

Get the current logging function.

This is useful for external tdb routines that wish to log tdb errors.

Parameters:

[in] tdb The database to get the logging function from.

Returns:: The logging function of the database.

See also:: tdb_get_logging_private()

size_t tdb_map_size ( struct tdb_context * tdb )

Get the map size.

Parameters:

[in] tdb The database to get the map size from.

Returns:: The map size.

const char* tdb_name ( struct tdb_context * tdb )

Get the name of the current tdb file.

This is useful for external logging functions.

Parameters:

[in] tdb The database to get the name from.

Returns:: The name of the database.

TDB_DATA tdb_nextkey	(	struct tdb_context *	tdb,
		TDB_DATA	key
	)

Find the next entry in the database, returning its key.

The caller must free the returned data.

Parameters:

[in]	tdb	The database to use.
[in]	key	The key from which you want the next key.

Returns:: The next entry of the current key, an empty TDB_DATA entry if there is no entry.

struct tdb_context* tdb_open	(	const char *	name,
		int	hash_size,
		int	tdb_flags,
		int	open_flags,
		mode_t	mode
	)		`[read]`

Open the database and creating it if necessary.

Parameters:

[in]	name	The name of the db to open.
[in]	hash_size	The hash size is advisory, use zero for a default value.
[in]	tdb_flags	The flags to use to open the db: TDB_CLEAR_IF_FIRST - Clear database if we are the only one with it open TDB_INTERNAL - Don't use a file, instaed store the data in memory. The filename is ignored in this case. TDB_NOLOCK - Don't do any locking TDB_NOMMAP - Don't use mmap TDB_NOSYNC - Don't synchronise transactions to disk TDB_SEQNUM - Maintain a sequence number TDB_VOLATILE - activate the per-hashchain freelist, default 5. TDB_ALLOW_NESTING - Allow transactions to nest. TDB_DISALLOW_NESTING - Disallow transactions to nest.
[in]	open_flags	Flags for the open(2) function.
[in]	mode	The mode for the open(2) function.

Returns:: A tdb context structure, NULL on error.

struct tdb_context* tdb_open_ex	(	const char *	name,
		int	hash_size,
		int	tdb_flags,
		int	open_flags,
		mode_t	mode,
		const struct tdb_logging_context *	log_ctx,
		tdb_hash_func	hash_fn
	)		`[read]`

Open the database and creating it if necessary.

This is like tdb_open(), but allows you to pass an initial logging and hash function. Be careful when passing a hash function - all users of the database must use the same hash function or you will get data corruption.

Parameters:

[in]	name	The name of the db to open.
[in]	hash_size	The hash size is advisory, use zero for a default value.
[in]	tdb_flags	The flags to use to open the db: TDB_CLEAR_IF_FIRST - Clear database if we are the only one with it open TDB_INTERNAL - Don't use a file, instaed store the data in memory. The filename is ignored in this case. TDB_NOLOCK - Don't do any locking TDB_NOMMAP - Don't use mmap TDB_NOSYNC - Don't synchronise transactions to disk TDB_SEQNUM - Maintain a sequence number TDB_VOLATILE - activate the per-hashchain freelist, default 5. TDB_ALLOW_NESTING - Allow transactions to nest. TDB_DISALLOW_NESTING - Disallow transactions to nest.
[in]	open_flags	Flags for the open(2) function.
[in]	mode	The mode for the open(2) function.
[in]	log_ctx	The logging function to use.
[in]	hash_fn	The hash function you want to use.

Returns:: A tdb context structure, NULL on error.

See also:: tdb_open()

int tdb_parse_record	(	struct tdb_context *	tdb,
		TDB_DATA	key,
		int()(TDB_DATA key, TDB_DATA data, void private_data)	parser,
		void *	private_data
	)

Hand a record to a parser function without allocating it.

This function is meant as a fast tdb_fetch alternative for large records that are frequently read. The "key" and "data" arguments point directly into the tdb shared memory, they are not aligned at any boundary.

Warning:: The parser is called while tdb holds a lock on the record. DO NOT call other tdb routines from within the parser. Also, for good performance you should make the parser fast to allow parallel operations.

Parameters:

[in]	tdb	The tdb to parse the record.
[in]	key	The key to parse.
[in]	parser	The parser to use to parse the data.
[in]	private_data	A private data pointer which is passed to the parser function.

Returns:: -1 if the record was not found. If the record was found, the return value of "parser" is passed up to the caller.

void tdb_remove_flags	(	struct tdb_context *	tdb,
		unsigned	flag
	)

Remove flags from the database.

Parameters:

[in]	tdb	The database to remove the flags.
[in]	flag	The tdb flags to remove.

int tdb_reopen ( struct tdb_context * tdb )

Reopen a tdb.

This can be used after a fork to ensure that we have an independent seek pointer from our parent and to re-establish locks.

Parameters:

[in] tdb The database to reopen.

Returns:: 0 on success, -1 on error.

int tdb_reopen_all ( int parent_longlived )

Reopen all tdb's.

If the parent is longlived (ie. a parent daemon architecture), we know it will keep it's active lock on a tdb opened with CLEAR_IF_FIRST. Thus for child processes we don't have to add an active lock. This is essential to improve performance on systems that keep POSIX locks as a non-scalable data structure in the kernel.

Parameters:

[in] parent_longlived Wether the parent is longlived or not.

Returns:: 0 on success, -1 on error.

void tdb_set_logging_function	(	struct tdb_context *	tdb,
		const struct tdb_logging_context *	log_ctx
	)

Set a different tdb logging function.

Parameters:

[in]	tdb	The tdb to set the logging function.
[in]	log_ctx	The logging function to set.

void tdb_set_max_dead	(	struct tdb_context *	tdb,
		int	max_dead
	)

Set the maximum number of dead records per hash chain.

Parameters:

[in]	tdb	The database handle to set the maximum.
[in]	max_dead	The maximum number of dead records per hash chain.

int tdb_store	(	struct tdb_context *	tdb,
		TDB_DATA	key,
		TDB_DATA	dbuf,
		int	flag
	)

Store an element in the database.

This replaces any existing element with the same key.

Parameters:

[in]	tdb	The tdb to store the entry.
[in]	key	The key to use to store the entry.
[in]	dbuf	The data to store under the key.
[in]	flag	The flags to store the key: TDB_INSERT: Don't overwrite an existing entry. TDB_MODIFY: Don't create a new entry

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_transaction_cancel ( struct tdb_context * tdb )

Cancel a current transaction.

This discards all write and lock operations that have been made since the transaction started.

Parameters:

[in] tdb The tdb to cancel the transaction on.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_transaction_commit ( struct tdb_context * tdb )

Commit a current transaction.

This updates the database and releases the current transaction locks.

Parameters:

[in] tdb The database to commit the transaction.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_transaction_prepare_commit ( struct tdb_context * tdb )

Prepare to commit a current transaction, for two-phase commits.

Once prepared for commit, the only allowed calls are tdb_transaction_commit() or tdb_transaction_cancel(). Preparing allocates disk space for the pending updates, so a subsequent commit should succeed (barring any hardware failures).

Parameters:

[in] tdb The database to prepare the commit.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_transaction_start ( struct tdb_context * tdb )

Start a transaction.

All operations after the transaction start can either be committed with tdb_transaction_commit() or cancelled with tdb_transaction_cancel().

If you call tdb_transaction_start() again on the same tdb context while a transaction is in progress, then the same transaction buffer is re-used. The number of tdb_transaction_{commit,cancel} operations must match the number of successful tdb_transaction_start() calls.

Note that transactions are by default disk synchronous, and use a recover area in the database to automatically recover the database on the next open if the system crashes during a transaction. You can disable the synchronous transaction recovery setup using the TDB_NOSYNC flag, which will greatly speed up operations at the risk of corrupting your database if the system crashes.

Operations made within a transaction are not visible to other users of the database until a successful commit.

Parameters:

[in] tdb The database to start the transaction.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr()

int tdb_transaction_start_nonblock ( struct tdb_context * tdb )

Start a transaction, non-blocking.

Parameters:

[in] tdb The database to start the transaction.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_error(); tdb_errorstr(); tdb_transaction_start()

int tdb_traverse	(	struct tdb_context *	tdb,
		tdb_traverse_func	fn,
		void *	private_data
	)

Traverse the entire database.

While travering the function fn(tdb, key, data, state) is called on each element. If fn is NULL then it is not called. A non-zero return value from fn() indicates that the traversal should stop. Traversal callbacks may not start transactions.

Warning:: The data buffer given to the callback fn does NOT meet the alignment restrictions malloc gives you.

Parameters:

[in]	tdb	The database to traverse.
[in]	fn	The function to call on each entry.
[in]	private_data	The private data which should be passed to the traversing function.

Returns:: The record count traversed, -1 on error.

int tdb_traverse_read	(	struct tdb_context *	tdb,
		tdb_traverse_func	fn,
		void *	private_data
	)

Traverse the entire database.

While traversing the database the function fn(tdb, key, data, state) is called on each element, but marking the database read only during the traversal, so any write operations will fail. This allows tdb to use read locks, which increases the parallelism possible during the traversal.

Parameters:

[in]	tdb	The database to traverse.
[in]	fn	The function to call on each entry.
[in]	private_data	The private data which should be passed to the traversing function.

Returns:: The record count traversed, -1 on error.

int tdb_unlockall ( struct tdb_context * tdb )

Unlock entire database with write lock.

Parameters:

[in] tdb The database to unlock.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_lockall(); tdb_error(); tdb_errorstr()

int tdb_unlockall_read ( struct tdb_context * tdb )

Unlock entire database with read lock.

Parameters:

[in] tdb The database to unlock.

Returns:: 0 on success, -1 on error with error code set.

See also:: tdb_lockall_read(); tdb_error(); tdb_errorstr()

The tdb API

Data Structures

Defines

Typedefs

Enumerations

Functions

Detailed Description

Interface

Typedef Documentation

Function Documentation