tdb2: typesafe traverse function

[ccan] / ccan / tdb2 / tdb2.h

#ifndef CCAN_TDB2_H
#define CCAN_TDB2_H

/*
   TDB version 2: trivial database library

   Copyright (C) Andrew Tridgell 1999-2004
   Copyright (C) Rusty Russell 2010-2011

     ** NOTE! The following LGPL license applies to the tdb
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/

#ifdef  __cplusplus
extern "C" {
#endif

#ifndef _SAMBA_BUILD_
/* For mode_t */
#include <sys/types.h>
/* For O_* flags. */
#include <sys/stat.h>
/* For sig_atomic_t. */
#include <signal.h>
/* For uint64_t */
#include <stdint.h>
#endif
#include <ccan/compiler/compiler.h>
#include <ccan/typesafe_cb/typesafe_cb.h>

union tdb_attribute;
struct tdb_context;

/**
 * tdb_open - open a database file
 * @name: the file name (can be NULL if flags contains TDB_INTERNAL)
 * @tdb_flags: options for this database
 * @open_flags: flags argument for tdb's open() call.
 * @mode: mode argument for tdb's open() call.
 * @attributes: linked list of extra attributes for this tdb.
 *
 * This call opens (and potentially creates) a database file.
 * Multiple processes can have the TDB file open at once.
 *
 * On failure it will return NULL, and set errno: it may also call
 * any log attribute found in @attributes.
 *
 * See also:
 *      union tdb_attribute
 */
struct tdb_context *tdb_open(const char *name, int tdb_flags,
                             int open_flags, mode_t mode,
                             union tdb_attribute *attributes);


/* flags for tdb_open() */
#define TDB_DEFAULT 0 /* just a readability place holder */
#define TDB_INTERNAL 2 /* don't store on disk */
#define TDB_NOLOCK   4 /* don't do any locking */
#define TDB_NOMMAP   8 /* don't use mmap */
#define TDB_CONVERT 16 /* convert endian */
#define TDB_NOSYNC   64 /* don't use synchronous transactions */

/**
 * tdb_close - close and free a tdb.
 * @tdb: the tdb context returned from tdb_open()
 *
 * This always succeeds, in that @tdb is unusable after this call.  But if
 * some unexpected error occurred while closing, it will return non-zero
 * (the only clue as to cause will be via the log attribute).
 */
int tdb_close(struct tdb_context *tdb);

/**
 * struct tdb_data - representation of keys or values.
 * @dptr: the data pointer
 * @dsize: the size of the data pointed to by dptr.
 *
 * This is the "blob" representation of keys and data used by TDB.
 */
typedef struct tdb_data {
        unsigned char *dptr;
        size_t dsize;
} TDB_DATA;

/**
 * enum TDB_ERROR - error returns for TDB
 *
 * See Also:
 *      tdb_errorstr()
 */
enum TDB_ERROR {
        TDB_SUCCESS     = 0,    /* No error. */
        TDB_ERR_CORRUPT = -1,   /* We read the db, and it was bogus. */
        TDB_ERR_IO      = -2,   /* We couldn't read/write the db. */
        TDB_ERR_LOCK    = -3,   /* Locking failed. */
        TDB_ERR_OOM     = -4,   /* Out of Memory. */
        TDB_ERR_EXISTS  = -5,   /* The key already exists. */
        TDB_ERR_NOEXIST = -6,   /* The key does not exist. */
        TDB_ERR_EINVAL  = -7,   /* You're using it wrong. */
        TDB_ERR_RDONLY  = -8,   /* The database is read-only. */
        TDB_ERR_LAST = TDB_ERR_RDONLY
};

/**
 * tdb_store - store a key/value pair in a tdb.
 * @tdb: the tdb context returned from tdb_open()
 * @key: the key
 * @dbuf: the data to associate with the key.
 * @flag: TDB_REPLACE, TDB_INSERT or TDB_MODIFY.
 *
 * This inserts (or overwrites) a key/value pair in the TDB.  If flag
 * is TDB_REPLACE, it doesn't matter whether the key exists or not;
 * TDB_INSERT means it must not exist (returns TDB_ERR_EXISTS otherwise),
 * and TDB_MODIFY means it must exist (returns TDB_ERR_NOEXIST otherwise).
 *
 * On success, this returns TDB_SUCCESS.
 *
 * See also:
 *      tdb_fetch, tdb_transaction_start, tdb_append, tdb_delete.
 */
enum TDB_ERROR tdb_store(struct tdb_context *tdb,
                         struct tdb_data key,
                         struct tdb_data dbuf,
                         int flag);

/* flags to tdb_store() */
#define TDB_REPLACE 1           /* A readability place holder */
#define TDB_INSERT 2            /* Don't overwrite an existing entry */
#define TDB_MODIFY 3            /* Don't create an existing entry    */

/**
 * tdb_fetch - fetch a value from a tdb.
 * @tdb: the tdb context returned from tdb_open()
 * @key: the key
 * @data: pointer to data.
 *
 * This looks up a key in the database and sets it in @data.
 *
 * If it returns TDB_SUCCESS, the key was found: it is your
 * responsibility to call free() on @data->dptr.
 *
 * Otherwise, it returns an error (usually, TDB_ERR_NOEXIST) and @data is
 * undefined.
 */
enum TDB_ERROR tdb_fetch(struct tdb_context *tdb, struct tdb_data key,
                         struct tdb_data *data);

/**
 * tdb_errorstr - map the tdb error onto a constant readable string
 * @ecode: the enum TDB_ERROR to map.
 *
 * This is useful for displaying errors to users.
 */
const char *tdb_errorstr(enum TDB_ERROR ecode);

/**
 * tdb_append - append a value to a key/value pair in a tdb.
 * @tdb: the tdb context returned from tdb_open()
 * @key: the key
 * @dbuf: the data to append.
 *
 * This is equivalent to fetching a record, reallocating .dptr to add the
 * data, and writing it back, only it's much more efficient.  If the key
 * doesn't exist, it's equivalent to tdb_store (with an additional hint that
 * you expect to expand the record in future).
 *
 * See Also:
 *      tdb_fetch(), tdb_store()
 */
enum TDB_ERROR tdb_append(struct tdb_context *tdb,
                          struct tdb_data key, struct tdb_data dbuf);

/**
 * tdb_delete - delete a key from a tdb.
 * @tdb: the tdb context returned from tdb_open()
 * @key: the key to delete.
 *
 * Returns TDB_SUCCESS on success, or an error (usually TDB_ERR_NOEXIST).
 *
 * See Also:
 *      tdb_fetch(), tdb_store()
 */
enum TDB_ERROR tdb_delete(struct tdb_context *tdb, struct tdb_data key);

/**
 * tdb_transaction_start - start a transaction
 * @tdb: the tdb context returned from tdb_open()
 *
 * This begins a series of atomic operations.  Other processes will be able
 * to read the tdb, but not alter it (they will block), nor will they see
 * any changes until tdb_transaction_commit() is called.
 *
 * See Also:
 *      tdb_transaction_cancel, tdb_transaction_commit.
 */
enum TDB_ERROR tdb_transaction_start(struct tdb_context *tdb);

/**
 * tdb_transaction_cancel - abandon a transaction
 * @tdb: the tdb context returned from tdb_open()
 *
 * This aborts a transaction, discarding any changes which were made.
 * tdb_close() does this implicitly.
 */
void tdb_transaction_cancel(struct tdb_context *tdb);

/**
 * tdb_transaction_commit - commit a transaction
 * @tdb: the tdb context returned from tdb_open()
 *
 * This completes a transaction, writing any changes which were made.
 *
 * fsync() is used to commit the transaction (unless TDB_NOSYNC is set),
 * making it robust against machine crashes, but very slow compared to
 * other TDB operations.
 *
 * A failure can only be caused by unexpected errors (eg. I/O or
 * memory); this is no point looping on transaction failure.
 *
 * See Also:
 *      tdb_transaction_prepare_commit()
 */
enum TDB_ERROR tdb_transaction_commit(struct tdb_context *tdb);

/**
 * tdb_transaction_prepare_commit - prepare to commit a transaction
 * @tdb: the tdb context returned from tdb_open()
 *
 * This ensures we have the resources to commit a transaction (using
 * tdb_transaction_commit): if this succeeds then a transaction will only
 * fail if the write() or fsync() calls fail.
 *
 * See Also:
 *      tdb_transaction_commit()
 */
enum TDB_ERROR tdb_transaction_prepare_commit(struct tdb_context *tdb);

/**
 * tdb_traverse - traverse a TDB
 * @tdb: the tdb context returned from tdb_open()
 * @fn: the function to call for every key/value pair (or NULL)
 * @p: the pointer to hand to @f
 *
 * This walks the TDB until all they keys have been traversed, or @fn
 * returns non-zero.  If the traverse function or other processes are
 * changing data or adding or deleting keys, the traverse may be
 * unreliable: keys may be skipped or (rarely) visited twice.
 *
 * There is one specific exception: the special case of deleting the
 * current key does not undermine the reliability of the traversal.
 *
 * On success, returns the number of keys iterated.  On error returns
 * a negative enum TDB_ERROR value.
 */
#define tdb_traverse(tdb, fn, p)                                        \
        tdb_traverse_(tdb, typesafe_cb_preargs(int, (fn), (p),          \
                                               struct tdb_context *,    \
                                               TDB_DATA, TDB_DATA), (p))

int64_t tdb_traverse_(struct tdb_context *tdb,
                      int (*fn)(struct tdb_context *,
                                TDB_DATA, TDB_DATA, void *), void *p);

/**
 * tdb_firstkey - get the "first" key in a TDB
 * @tdb: the tdb context returned from tdb_open()
 * @key: pointer to key.
 *
 * This returns an arbitrary key in the database; with tdb_nextkey() it allows
 * open-coded traversal of the database, though it is slightly less efficient
 * than tdb_traverse.
 *
 * It is your responsibility to free @key->dptr on success.
 *
 * Returns TDB_ERR_NOEXIST if the database is empty.
 */
enum TDB_ERROR tdb_firstkey(struct tdb_context *tdb, struct tdb_data *key);

/**
 * tdb_nextkey - get the "next" key in a TDB
 * @tdb: the tdb context returned from tdb_open()
 * @key: a key returned by tdb_firstkey() or tdb_nextkey().
 *
 * This returns another key in the database; it will free @key.dptr for
 * your convenience.
 *
 * Returns TDB_ERR_NOEXIST if there are no more keys.
 */
enum TDB_ERROR tdb_nextkey(struct tdb_context *tdb, struct tdb_data *key);

/**
 * tdb_chainlock - lock a record in the TDB
 * @tdb: the tdb context returned from tdb_open()
 * @key: the key to lock.
 *
 * This prevents any changes from occurring to a group of keys including @key,
 * even if @key does not exist.  This allows primitive atomic updates of
 * records without using transactions.
 *
 * You cannot begin a transaction while holding a tdb_chainlock(), nor can
 * you do any operations on any other keys in the database.  This also means
 * that you cannot hold more than one tdb_chainlock() at a time.
 *
 * See Also:
 *      tdb_chainunlock()
 */
enum TDB_ERROR tdb_chainlock(struct tdb_context *tdb, TDB_DATA key);

/**
 * tdb_chainunlock - unlock a record in the TDB
 * @tdb: the tdb context returned from tdb_open()
 * @key: the key to unlock.
 */
enum TDB_ERROR tdb_chainunlock(struct tdb_context *tdb, TDB_DATA key);

/**
 * tdb_check - check a TDB for consistency
 * @tdb: the tdb context returned from tdb_open()
 * @check: function to check each key/data pair (or NULL)
 * @private_data: pointer for @check
 *
 * This performs a consistency check of the open database, optionally calling
 * a check() function on each record so you can do your own data consistency
 * checks as well.  If check() returns an error, that is returned from
 * tdb_check().
 */
enum TDB_ERROR tdb_check(struct tdb_context *tdb,
                         enum TDB_ERROR (*check)(TDB_DATA key,
                                                 TDB_DATA data,
                                                 void *private_data),
                         void *private_data);

/**
 * enum tdb_summary_flags - flags for tdb_summary.
 */
enum tdb_summary_flags {
        TDB_SUMMARY_HISTOGRAMS = 1 /* Draw graphs in the summary. */
};

/**
 * tdb_summary - return a string describing the TDB state
 * @tdb: the tdb context returned from tdb_open()
 * @flags: flags to control the summary output.
 * @summary: pointer to string to allocate.
 *
 * This returns a developer-readable string describing the overall
 * state of the tdb, such as the percentage used and sizes of records.
 * It is designed to provide information about the tdb at a glance
 * without displaying any keys or data in the database.
 *
 * On success, sets @summary to point to a malloc()'ed nul-terminated
 * multi-line string.  It is your responsibility to free() it.
 */
enum TDB_ERROR tdb_summary(struct tdb_context *tdb,
                           enum tdb_summary_flags flags,
                           char **summary);

/**
 * enum tdb_attribute_type - descriminator for union tdb_attribute.
 */
enum tdb_attribute_type {
        TDB_ATTRIBUTE_LOG = 0,
        TDB_ATTRIBUTE_HASH = 1,
        TDB_ATTRIBUTE_SEED = 2,
        TDB_ATTRIBUTE_STATS = 3
};

/**
 * struct tdb_attribute_base - common fields for all tdb attributes.
 */
struct tdb_attribute_base {
        enum tdb_attribute_type attr;
        union tdb_attribute *next;
};

/**
 * enum tdb_log_level - log levels for tdb_attribute_log
 * @TDB_LOG_ERROR: used to log unrecoverable errors such as I/O errors
 *                 or internal consistency failures.
 * @TDB_LOG_USE_ERROR: used to log usage errors such as invalid parameters
 *                 or writing to a read-only database.
 * @TDB_LOG_WARNING: used for informational messages on issues which
 *                   are unusual but handled by TDB internally, such
 *                   as a failure to mmap or failure to open /dev/urandom.
 */
enum tdb_log_level {
        TDB_LOG_ERROR,
        TDB_LOG_USE_ERROR,
        TDB_LOG_WARNING
};

/**
 * struct tdb_attribute_log - log function attribute
 *
 * This attribute provides a hook for you to log errors.
 */
struct tdb_attribute_log {
        struct tdb_attribute_base base; /* .attr = TDB_ATTRIBUTE_LOG */
        void (*log_fn)(struct tdb_context *tdb,
                       enum tdb_log_level level,
                       void *log_private,
                       const char *message);
        void *log_private;
};

/**
 * struct tdb_attribute_hash - hash function attribute
 *
 * This attribute allows you to provide an alternative hash function.
 * This hash function will be handed keys from the database; it will also
 * be handed the 8-byte TDB_HASH_MAGIC value for checking the header (the
 * tdb_open() will fail if the hash value doesn't match the header).
 *
 * Note that if your hash function gives different results on
 * different machine endians, your tdb will no longer work across
 * different architectures!
 */
struct tdb_attribute_hash {
        struct tdb_attribute_base base; /* .attr = TDB_ATTRIBUTE_HASH */
        uint64_t (*hash_fn)(const void *key, size_t len, uint64_t seed,
                            void *priv);
        void *hash_private;
};

/**
 * struct tdb_attribute_seed - hash function seed attribute
 *
 * The hash function seed is normally taken from /dev/urandom (or equivalent)
 * but can be set manually here.  This is mainly for testing purposes.
 */
struct tdb_attribute_seed {
        struct tdb_attribute_base base; /* .attr = TDB_ATTRIBUTE_SEED */
        uint64_t seed;
};

/**
 * struct tdb_attribute_stats - tdb operational statistics
 *
 * This attribute records statistics of various low-level TDB operations.
 * This can be used to assist performance evaluation.
 *
 * New fields will be added at the end, hence the "size" argument which
 * indicates how large your structure is.  If your size is larger than
 * that known about by this version of tdb, the size will be reduced to
 * the known structure size.  Thus you can detect older versions, and
 * thus know that newer stats will not be updated.
 */
struct tdb_attribute_stats {
        struct tdb_attribute_base base; /* .attr = TDB_ATTRIBUTE_STATS */
        size_t size; /* = sizeof(struct tdb_attribute_stats) */
        uint64_t allocs;
        uint64_t   alloc_subhash;
        uint64_t   alloc_chain;
        uint64_t   alloc_bucket_exact;
        uint64_t   alloc_bucket_max;
        uint64_t   alloc_leftover;
        uint64_t   alloc_coalesce_tried;
        uint64_t     alloc_coalesce_lockfail;
        uint64_t     alloc_coalesce_race;
        uint64_t     alloc_coalesce_succeeded;
        uint64_t        alloc_coalesce_num_merged;
        uint64_t compares;
        uint64_t   compare_wrong_bucket;
        uint64_t   compare_wrong_offsetbits;
        uint64_t   compare_wrong_keylen;
        uint64_t   compare_wrong_rechash;
        uint64_t   compare_wrong_keycmp;
        uint64_t expands;
        uint64_t frees;
        uint64_t locks;
        uint64_t    lock_lowlevel;
        uint64_t    lock_nonblock;
};

/**
 * union tdb_attribute - tdb attributes.
 *
 * This represents all the known attributes.
 *
 * See also:
 *      struct tdb_attribute_log, struct tdb_attribute_hash,
 *      struct tdb_attribute_seed, struct tdb_attribute_stats.
 */
union tdb_attribute {
        struct tdb_attribute_base base;
        struct tdb_attribute_log log;
        struct tdb_attribute_hash hash;
        struct tdb_attribute_seed seed;
        struct tdb_attribute_stats stats;
};

/**
 * tdb_null - a convenient value for errors.
 */
extern struct tdb_data tdb_null;

#ifdef  __cplusplus
}
#endif

#endif /* tdb2.h */