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diff --git a/man3/dbopen.3 b/man3/dbopen.3 new file mode 100644 index 0000000..a6d418a --- /dev/null +++ b/man3/dbopen.3 @@ -0,0 +1,536 @@ +.\" Copyright (c) 1990, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" SPDX-License-Identifier: BSD-4-Clause-UC +.\" +.\" @(#)dbopen.3 8.5 (Berkeley) 1/2/94 +.\" +.TH dbopen 3 2022-12-04 "Linux man-pages 6.05.01" +.UC 7 +.SH NAME +dbopen \- database access methods +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <sys/types.h> +.B #include <limits.h> +.B #include <db.h> +.B #include <fcntl.h> +.PP +.BI "DB *dbopen(const char *" file ", int " flags ", int " mode \ +", DBTYPE " type , +.BI " const void *" openinfo ); +.fi +.SH DESCRIPTION +.IR "Note well" : +This page documents interfaces provided up until glibc 2.1. +Since glibc 2.2, glibc no longer provides these interfaces. +Probably, you are looking for the APIs provided by the +.I libdb +library instead. +.PP +.BR dbopen () +is the library interface to database files. +The supported file formats are btree, hashed, and UNIX file oriented. +The btree format is a representation of a sorted, balanced tree structure. +The hashed format is an extensible, dynamic hashing scheme. +The flat-file format is a byte stream file with fixed or variable length +records. +The formats and file-format-specific information are described in detail +in their respective manual pages +.BR btree (3), +.BR hash (3), +and +.BR recno (3). +.PP +.BR dbopen () +opens +.I file +for reading and/or writing. +Files never intended to be preserved on disk may be created by setting +the +.I file +argument to NULL. +.PP +The +.I flags +and +.I mode +arguments are as specified to the +.BR open (2) +routine, however, only the +.BR O_CREAT , +.BR O_EXCL , +.BR O_EXLOCK , +.BR O_NONBLOCK , +.BR O_RDONLY , +.BR O_RDWR , +.BR O_SHLOCK , +and +.B O_TRUNC +flags are meaningful. +(Note, opening a database file +.B O_WRONLY +is not possible.) +.\"Three additional options may be specified by ORing +.\"them into the +.\".I flags +.\"argument. +.\".TP +.\"DB_LOCK +.\"Do the necessary locking in the database to support concurrent access. +.\"If concurrent access isn't needed or the database is read-only this +.\"flag should not be set, as it tends to have an associated performance +.\"penalty. +.\".TP +.\"DB_SHMEM +.\"Place the underlying memory pool used by the database in shared +.\"memory. +.\"Necessary for concurrent access. +.\".TP +.\"DB_TXN +.\"Support transactions in the database. +.\"The DB_LOCK and DB_SHMEM flags must be set as well. +.PP +The +.I type +argument is of type +.I DBTYPE +(as defined in the +.I <db.h> +include file) and +may be set to +.BR DB_BTREE , +.BR DB_HASH , +or +.BR DB_RECNO . +.PP +The +.I openinfo +argument is a pointer to an access-method-specific structure described +in the access method's manual page. +If +.I openinfo +is NULL, each access method will use defaults appropriate for the system +and the access method. +.PP +.BR dbopen () +returns a pointer to a +.I DB +structure on success and NULL on error. +The +.I DB +structure is defined in the +.I <db.h> +include file, and contains at +least the following fields: +.PP +.in +4n +.EX +typedef struct { + DBTYPE type; + int (*close)(const DB *db); + int (*del)(const DB *db, const DBT *key, unsigned int flags); + int (*fd)(const DB *db); + int (*get)(const DB *db, DBT *key, DBT *data, + unsigned int flags); + int (*put)(const DB *db, DBT *key, const DBT *data, + unsigned int flags); + int (*sync)(const DB *db, unsigned int flags); + int (*seq)(const DB *db, DBT *key, DBT *data, + unsigned int flags); +} DB; +.EE +.in +.PP +These elements describe a database type and a set of functions performing +various actions. +These functions take a pointer to a structure as returned by +.BR dbopen (), +and sometimes one or more pointers to key/data structures and a flag value. +.TP +.I type +The type of the underlying access method (and file format). +.TP +.I close +A pointer to a routine to flush any cached information to disk, free any +allocated resources, and close the underlying file(s). +Since key/data pairs may be cached in memory, failing to sync the file +with a +.I close +or +.I sync +function may result in inconsistent or lost information. +.I close +routines return \-1 on error (setting +.IR errno ) +and 0 on success. +.TP +.I del +A pointer to a routine to remove key/data pairs from the database. +.IP +The argument +.I flag +may be set to the following value: +.RS +.TP +.B R_CURSOR +Delete the record referenced by the cursor. +The cursor must have previously been initialized. +.RE +.IP +.I delete +routines return \-1 on error (setting +.IR errno ), +0 on success, and 1 if the specified +.I key +was not in the file. +.TP +.I fd +A pointer to a routine which returns a file descriptor representative +of the underlying database. +A file descriptor referencing the same file will be returned to all +processes which call +.BR dbopen () +with the same +.I file +name. +This file descriptor may be safely used as an argument to the +.BR fcntl (2) +and +.BR flock (2) +locking functions. +The file descriptor is not necessarily associated with any of the +underlying files used by the access method. +No file descriptor is available for in memory databases. +.I fd +routines return \-1 on error (setting +.IR errno ), +and the file descriptor on success. +.TP +.I get +A pointer to a routine which is the interface for keyed retrieval from +the database. +The address and length of the data associated with the specified +.I key +are returned in the structure referenced by +.IR data . +.I get +routines return \-1 on error (setting +.IR errno ), +0 on success, and 1 if the +.I key +was not in the file. +.TP +.I put +A pointer to a routine to store key/data pairs in the database. +.IP +The argument +.I flag +may be set to one of the following values: +.RS +.TP +.B R_CURSOR +Replace the key/data pair referenced by the cursor. +The cursor must have previously been initialized. +.TP +.B R_IAFTER +Append the data immediately after the data referenced by +.IR key , +creating a new key/data pair. +The record number of the appended key/data pair is returned in the +.I key +structure. +(Applicable only to the +.B DB_RECNO +access method.) +.TP +.B R_IBEFORE +Insert the data immediately before the data referenced by +.IR key , +creating a new key/data pair. +The record number of the inserted key/data pair is returned in the +.I key +structure. +(Applicable only to the +.B DB_RECNO +access method.) +.TP +.B R_NOOVERWRITE +Enter the new key/data pair only if the key does not previously exist. +.TP +.B R_SETCURSOR +Store the key/data pair, setting or initializing the position of the +cursor to reference it. +(Applicable only to the +.B DB_BTREE +and +.B DB_RECNO +access methods.) +.RE +.IP +.B R_SETCURSOR +is available only for the +.B DB_BTREE +and +.B DB_RECNO +access +methods because it implies that the keys have an inherent order +which does not change. +.IP +.B R_IAFTER +and +.B R_IBEFORE +are available only for the +.B DB_RECNO +access method because they each imply that the access method is able to +create new keys. +This is true only if the keys are ordered and independent, record numbers +for example. +.IP +The default behavior of the +.I put +routines is to enter the new key/data pair, replacing any previously +existing key. +.IP +.I put +routines return \-1 on error (setting +.IR errno ), +0 on success, and 1 if the +.B R_NOOVERWRITE +.I flag +was set and the key already exists in the file. +.TP +.I seq +A pointer to a routine which is the interface for sequential +retrieval from the database. +The address and length of the key are returned in the structure +referenced by +.IR key , +and the address and length of the data are returned in the +structure referenced +by +.IR data . +.IP +Sequential key/data pair retrieval may begin at any time, and the +position of the "cursor" is not affected by calls to the +.IR del , +.IR get , +.IR put , +or +.I sync +routines. +Modifications to the database during a sequential scan will be reflected +in the scan, that is, +records inserted behind the cursor will not be returned +while records inserted in front of the cursor will be returned. +.IP +The flag value +.B must +be set to one of the following values: +.RS +.TP +.B R_CURSOR +The data associated with the specified key is returned. +This differs from the +.I get +routines in that it sets or initializes the cursor to the location of +the key as well. +(Note, for the +.B DB_BTREE +access method, the returned key is not necessarily an +exact match for the specified key. +The returned key is the smallest key greater than or equal to the specified +key, permitting partial key matches and range searches.) +.TP +.B R_FIRST +The first key/data pair of the database is returned, and the cursor +is set or initialized to reference it. +.TP +.B R_LAST +The last key/data pair of the database is returned, and the cursor +is set or initialized to reference it. +(Applicable only to the +.B DB_BTREE +and +.B DB_RECNO +access methods.) +.TP +.B R_NEXT +Retrieve the key/data pair immediately after the cursor. +If the cursor is not yet set, this is the same as the +.B R_FIRST +flag. +.TP +.B R_PREV +Retrieve the key/data pair immediately before the cursor. +If the cursor is not yet set, this is the same as the +.B R_LAST +flag. +(Applicable only to the +.B DB_BTREE +and +.B DB_RECNO +access methods.) +.RE +.IP +.B R_LAST +and +.B R_PREV +are available only for the +.B DB_BTREE +and +.B DB_RECNO +access methods because they each imply that the keys have an inherent +order which does not change. +.IP +.I seq +routines return \-1 on error (setting +.IR errno ), +0 on success and 1 if there are no key/data pairs less than or greater +than the specified or current key. +If the +.B DB_RECNO +access method is being used, and if the database file +is a character special file and no complete key/data pairs are currently +available, the +.I seq +routines return 2. +.TP +.I sync +A pointer to a routine to flush any cached information to disk. +If the database is in memory only, the +.I sync +routine has no effect and will always succeed. +.IP +The flag value may be set to the following value: +.RS +.TP +.B R_RECNOSYNC +If the +.B DB_RECNO +access method is being used, this flag causes +the sync routine to apply to the btree file which underlies the +recno file, not the recno file itself. +(See the +.I bfname +field of the +.BR recno (3) +manual page for more information.) +.RE +.IP +.I sync +routines return \-1 on error (setting +.IR errno ) +and 0 on success. +.SS Key/data pairs +Access to all file types is based on key/data pairs. +Both keys and data are represented by the following data structure: +.PP +.in +4n +.EX +typedef struct { + void *data; + size_t size; +} DBT; +.EE +.in +.PP +The elements of the +.I DBT +structure are defined as follows: +.TP +.I data +A pointer to a byte string. +.TP +.I size +The length of the byte string. +.PP +Key and data byte strings may reference strings of essentially unlimited +length although any two of them must fit into available memory at the same +time. +It should be noted that the access methods provide no guarantees about +byte string alignment. +.SH ERRORS +The +.BR dbopen () +routine may fail and set +.I errno +for any of the errors specified for the library routines +.BR open (2) +and +.BR malloc (3) +or the following: +.TP +.B EFTYPE +A file is incorrectly formatted. +.TP +.B EINVAL +A parameter has been specified (hash function, pad byte, etc.) that is +incompatible with the current file specification or which is not +meaningful for the function (for example, use of the cursor without +prior initialization) or there is a mismatch between the version +number of file and the software. +.PP +The +.I close +routines may fail and set +.I errno +for any of the errors specified for the library routines +.BR close (2), +.BR read (2), +.BR write (2), +.BR free (3), +or +.BR fsync (2). +.PP +The +.IR del , +.IR get , +.IR put , +and +.I seq +routines may fail and set +.I errno +for any of the errors specified for the library routines +.BR read (2), +.BR write (2), +.BR free (3), +or +.BR malloc (3). +.PP +The +.I fd +routines will fail and set +.I errno +to +.B ENOENT +for in memory databases. +.PP +The +.I sync +routines may fail and set +.I errno +for any of the errors specified for the library routine +.BR fsync (2). +.SH BUGS +The typedef +.I DBT +is a mnemonic for "data base thang", and was used +because no one could think of a reasonable name that wasn't already used. +.PP +The file descriptor interface is a kludge and will be deleted in a +future version of the interface. +.PP +None of the access methods provide any form of concurrent access, +locking, or transactions. +.SH SEE ALSO +.BR btree (3), +.BR hash (3), +.BR mpool (3), +.BR recno (3) +.PP +.IR "LIBTP: Portable, Modular Transactions for UNIX" , +Margo Seltzer, Michael Olson, USENIX proceedings, Winter 1992. |