227 lines
6 KiB
Groff
227 lines
6 KiB
Groff
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.\" $NetBSD: mpool.3,v 1.9 2003/08/07 16:42:43 agc Exp $
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.\"
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.\" 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. 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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.\"
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.Dd April 17, 2003
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.Dt MPOOL 3
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.Os
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.Sh NAME
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.Nm mpool ,
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.Nm mpool_open ,
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.Nm mpool_filter ,
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.Nm mpool_new ,
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.Nm mpool_get ,
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.Nm mpool_put ,
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.Nm mpool_sync ,
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.Nm mpool_close
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.Nd shared memory buffer pool
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.Sh SYNOPSIS
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.In db.h
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.In mpool.h
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.Ft MPOOL *
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.Fn mpool_open "DBT *key" "int fd" "pgno_t pagesize" "pgno_t maxcache"
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.Ft void
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.Fn mpool_filter "MPOOL *mp" "void (*pgin)(void *, pgno_t, void *)" \
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"void (*pgout)(void *, pgno_t, void *)" "void *pgcookie"
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.Ft void *
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.Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr"
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.Ft void *
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.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags"
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.Ft int
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.Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags"
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.Ft int
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.Fn mpool_sync "MPOOL *mp"
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.Ft int
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.Fn mpool_close "MPOOL *mp"
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.Sh DESCRIPTION
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.Nm
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is the library interface intended to provide page oriented buffer
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management 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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.Nm mpool_open
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initializes a memory pool.
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The
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.Fa 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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.Fa key
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is
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.Dv NULL ,
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the buffers are mapped into private memory.
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The
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.Fa fd
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argument is a file descriptor for the underlying file, which must be
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seekable.
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If
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.Fa key
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is
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.No non- Ns Dv NULL
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and matches a file already being mapped, the
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.Fa fd
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argument is ignored.
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.Pp
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The
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.Fa pagesize
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argument is the size, in bytes, of the pages into which the file is
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broken up.
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The
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.Fa maxcache
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argument is the maximum number of pages from the underlying file to
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cache at any one time.
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This value is not relative to the number of processes which share a
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file's buffers, but will be the largest value specified by any of the
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processes sharing the file.
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.Pp
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The
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.Nm mpool_filter
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function is intended to make transparent input and output processing
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of the pages possible.
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If the
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.Fa pgin
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function is specified, it is called each time a buffer is read into
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the memory pool from the backing file.
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If the
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.Fa pgout
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function is specified, it is called each time a buffer is written into
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the backing file.
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Both functions are are called with the
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.Fa pgcookie
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pointer, the page number and a pointer to the page to being read or
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written.
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.Pp
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The function
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.Nm 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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.Fa pgnoaddr
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address.
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Otherwise,
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.Dv NULL
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is returned and errno is set.
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.Pp
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The function
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.Nm 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,
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.Dv NULL
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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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.Nm mpool_put
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unpins the page referenced by
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.Fa pgaddr .
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.Fa pgaddr
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must be an address previously returned by
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.Nm mpool_get
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or
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.Nm mpool_new .
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The flag value is specified by or'ing any of the following values:
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.Bl -tag -width MPOOL_DIRTYX -offset indent
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.It Dv MPOOL_DIRTY
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The page has been modified and needs to be written to the backing
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file.
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.El
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.Pp
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.Nm 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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.Nm 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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.Nm 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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.Nm mpool_close
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function frees 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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.Em not
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written to the backing file.
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.Nm 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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.Nm mpool_open
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function may fail and set
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.Va errno
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for any of the errors specified for the library routine
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.Xr malloc 3 .
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.Pp
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The
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.Nm mpool_get
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function may fail and set
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.Va errno
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for the following:
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.Bl -tag -width Er -offset indent
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.It Er EINVAL
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The requested record doesn't exist.
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.El
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.Pp
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The
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.Nm mpool_new
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and
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.Nm mpool_get
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functions may fail and set
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.Va errno
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for any of the errors specified for the library routines
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.Xr read 2 ,
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.Xr write 2 ,
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and
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.Xr malloc 3 .
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.Pp
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The
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.Nm mpool_sync
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function may fail and set
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.Va errno
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for any of the errors specified for the library routine
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.Xr write 2 .
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.Pp
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The
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.Nm mpool_close
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function may fail and set
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.Va errno
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for any of the errors specified for the library routine
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.Xr free 3 .
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.Sh SEE ALSO
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.Xr btree 3 ,
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.Xr dbopen 3 ,
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.Xr hash 3 ,
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.Xr recno 3
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