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Add cdbr_open_mem.

.\"	$NetBSD: cdbr.3,v 1.4 2013/12/05 21:17:23 joerg Exp $
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.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Joerg Sonnenberger.
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.Dd December 5, 2013
.Dt CDBR 3
.Os
.Sh NAME
.Nm cdbr
.Nm cdbr_open ,
.Nm cdbr_open_mem ,
.Nm cdbr_entries ,
.Nm cdbr_get ,
.Nm cdbr_find ,
.Nm cdbr_close ,
.Nm cdbr_write
.Nd constant database access methods
.Sh SYNOPSIS
.Ft "struct cdbr *"
.Fn cdbr_open "const char *path" "int flags"
.Ft "struct cdbr *"
.Fo cdbr_open_mem
.Fa "void *base"
.Fa "size_t size"
.Fa "void (*unmap)(void *, void *, size_t)"
.Fa "void *cookie"
.Fc
.Ft uint32_t
.Fn cdbr_entries "struct cdbr *cdbr"
.Ft int
.Fn cdbr_get "struct cdbr *cdbr" "uint32_t index" "const void **data" "size_t *datalen"
.Ft int
.Fo cdbr_find
.Fa "struct cdbr *cdbr"
.Fa "const void *key"
.Fa "size_t keylen"
.Fa "const void **data"
.Fa "size_t *datalen"
.Fc
.Ft void
.Fn cdbr_close "struct cdbr *cdbr"
.Sh DESCRIPTION
The
.Nm
library provides a space efficient (key,value) database based
on perfect hashing.
.Pp
A cdb database is opened for reading by calling
.Fn cdbr_open .
The only supported value for
.Va flags
is
.Dv CDBR_DEFAULT .
The function returns a handle to pass to the other functions.
The database is closed by invoking
.Fn cdbr_close .
All resources associated with the handle are freed and the memory
returned by
.Fn cdbr_get
and
.Fn cdbr_find
is invalidated.
.Fn cdbr_open_mem
works like
.Fn cdbr_open ,
but takes a memory reference to the content of the database file.
If
.Va unmap
is not
.Dv NULL ,
it is called by
.Fn cdbr_close
with
.Va cookie ,
.Va base
and
.Va size
as arguments.
It is not called by
.Fn cdbr_open_mem
on error.
.Pp
The number of records in the database can be obtained by calling
.Fn cdbr_entries .
Records can be obtained by record number using
.Fn cdbr_get
or by key using
.Fn cdbr_find .
Both functions return 0 on success and update
.Va data
and
.Va datalen
accordingly.
The location
.Va *data
remains valid until
.Fn cdbr_close
is called.
It is the responsibility of the caller of
.Fn cdbr_find
to ensure that the key matches the returned data.
The function returns the only possible match, but the database doesn't store
the keys to minimize overhead.
.Sh SEE ALSO
.Xr nbperf 1 ,
.Xr cdbw 3 ,
.Xr db 3 ,
.Xr cdb 5
.Sh HISTORY
Support for the
.Nm cdb
format first appeared in
.Nx 6.0 .
.Sh AUTHORS
The
.Nm cdbr
and
.Nm cdbw
functions have been written by
.An Joerg Sonnenberger Aq Mt joerg@NetBSD.org .