248 lines
6.1 KiB
Groff
248 lines
6.1 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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.Dd June 4, 1993
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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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.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 "void *key" "int fd" "pgno_t pagesize" "pgno_t maxcache"
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.Ft void
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.Fo mpool_filter
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.Fa "MPOOL *mp"
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.Fa "void (*pgin)(void *, pgno_t, void *)"
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.Fa "void (*pgout)(void *, pgno_t, void *)"
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.Fa "void *pgcookie"
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.Fc
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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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The
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.Nm mpool
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library interface is 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
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.Fn mpool_open
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function 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 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 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 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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.Fn 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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.Fa 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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.Fa 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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.Fa 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
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.Fn mpool_new
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function takes an
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.Ft MPOOL
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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
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.Va errno
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is set.
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.Pp
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The
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.Fn mpool_get
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function takes a
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.Ft MPOOL
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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
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.Va errno
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is set.
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The
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.Fa flags
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argument is not currently used.
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.Pp
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The
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.Fn mpool_put
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function unpins the page referenced by
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.Fa pgaddr .
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The
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.Fa pgaddr
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argument
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must be an address previously returned by
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.Fn mpool_get
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or
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.Fn mpool_new .
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The
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.Fa flags
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argument is specified by
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.Em or Ns 'ing
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any of the following values:
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.Bl -tag -width 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 file.
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.El
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.Pp
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The
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.Fn mpool_put
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function
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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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.Fn mpool_sync
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function writes all modified pages associated with the
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.Ft MPOOL
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pointer to the
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backing file.
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The
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.Fn mpool_sync
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function
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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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.Fn 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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.Em not
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written to the backing file.
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The
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.Fn mpool_close
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function
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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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.Fn 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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.Fn 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
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.It Bq 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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.Fn mpool_new
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and
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.Fn 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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.Fn 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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.Fn 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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