1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
221 lines
5.9 KiB
Groff
221 lines
5.9 KiB
Groff
.\" Copyright (c) 1990, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mpool.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.TH MPOOL 3 "June 4, 1993"
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.UC 7
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.SH NAME
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mpool \- shared memory buffer pool
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.SH SYNOPSIS
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.nf
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.ft B
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#include <db.h>
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#include <mpool.h>
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MPOOL *
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mpool_open (DBT *key, int fd, pgno_t pagesize, pgno_t maxcache);
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void
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mpool_filter (MPOOL *mp, void (*pgin)(void *, pgno_t, void *),
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.ti +5
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void (*pgout)(void *, pgno_t, void *), void *pgcookie);
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void *
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mpool_new (MPOOL *mp, pgno_t *pgnoaddr);
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void *
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mpool_get (MPOOL *mp, pgno_t pgno, u_int flags);
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int
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mpool_put (MPOOL *mp, void *pgaddr, u_int flags);
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int
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mpool_sync (MPOOL *mp);
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int
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mpool_close (MPOOL *mp);
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.ft R
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.fi
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.SH DESCRIPTION
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.IR Mpool
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is the library interface intended to provide page oriented buffer management
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of files.
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The buffers may be shared between processes.
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.PP
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The function
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.I mpool_open
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initializes a memory pool.
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The
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.I key
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argument is the byte string used to negotiate between multiple
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processes wishing to share buffers.
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If the file buffers are mapped in shared memory, all processes using
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the same key will share the buffers.
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If
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.I key
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is NULL, the buffers are mapped into private memory.
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The
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.I fd
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argument is a file descriptor for the underlying file, which must be seekable.
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If
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.I key
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is non-NULL and matches a file already being mapped, the
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.I fd
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argument is ignored.
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.PP
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The
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.I pagesize
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argument is the size, in bytes, of the pages into which the file is broken up.
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The
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.I maxcache
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argument is the maximum number of pages from the underlying file to cache
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at any one time.
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This value is not relative to the number of processes which share a file's
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buffers, but will be the largest value specified by any of the processes
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sharing the file.
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.PP
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The
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.I mpool_filter
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function is intended to make transparent input and output processing of the
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pages possible.
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If the
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.I pgin
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function is specified, it is called each time a buffer is read into the memory
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pool from the backing file.
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If the
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.I pgout
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function is specified, it is called each time a buffer is written into the
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backing file.
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Both functions are called with the
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.I pgcookie
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pointer, the page number and a pointer to the page to being read or written.
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.PP
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The function
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.I mpool_new
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takes an MPOOL pointer and an address as arguments.
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If a new page can be allocated, a pointer to the page is returned and
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the page number is stored into the
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.I pgnoaddr
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address.
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Otherwise, NULL is returned and errno is set.
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.PP
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The function
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.I mpool_get
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takes a MPOOL pointer and a page number as arguments.
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If the page exists, a pointer to the page is returned.
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Otherwise, NULL is returned and errno is set.
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The flags parameter is not currently used.
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.PP
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The function
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.I mpool_put
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unpins the page referenced by
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.IR pgaddr .
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.I Pgaddr
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must be an address previously returned by
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.I mpool_get
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or
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.IR mpool_new .
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The flag value is specified by
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.IR or 'ing
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any of the following values:
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.TP
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MPOOL_DIRTY
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The page has been modified and needs to be written to the backing file.
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.PP
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.I Mpool_put
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returns 0 on success and -1 if an error occurs.
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.PP
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The function
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.I mpool_sync
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writes all modified pages associated with the MPOOL pointer to the
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backing file.
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.I Mpool_sync
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returns 0 on success and -1 if an error occurs.
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.PP
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The
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.I mpool_close
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function free's up any allocated memory associated with the memory pool
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cookie.
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Modified pages are
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.B not
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written to the backing file.
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.I Mpool_close
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returns 0 on success and -1 if an error occurs.
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.SH ERRORS
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The
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.I mpool_open
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function may fail and set
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.I errno
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for any of the errors specified for the library routine
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.IR malloc (3).
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.PP
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The
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.I mpool_get
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function may fail and set
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.I errno
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for the following:
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.TP 15
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[EINVAL]
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The requested record doesn't exist.
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.PP
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The
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.I mpool_new
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and
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.I mpool_get
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functions may fail and set
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.I errno
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for any of the errors specified for the library routines
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.IR read (2) ,
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.IR write (2) ,
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and
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.IR malloc (3).
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.PP
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The
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.I mpool_sync
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function may fail and set
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.I errno
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for any of the errors specified for the library routine
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.IR write (2).
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.PP
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The
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.I mpool_close
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function may fail and set
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.I errno
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for any of the errors specified for the library routine
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.IR free (3).
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.SH "SEE ALSO"
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.IR dbopen (3),
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.IR btree (3),
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.IR hash (3),
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.IR recno (3)
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