fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
255 lines
6.2 KiB
Groff
255 lines
6.2 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. 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 17, 2011
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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" "u_int flags"
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.Ft int
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.Fn mpool_delete "MPOOL *mp" "void *page"
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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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.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 currently ignored.
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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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.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 function
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.Fn mpool_new
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takes an
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.Dv MPOOL
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pointer, an address, and a set of flags 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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The flags value is formed by
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.Tn OR Ns 'ing
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the following values:
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.Bl -tag -width Ds
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.It Dv MPOOL_PAGE_REQUEST
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Allocate a new page with a specific page number.
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.It Dv MPOOL_PAGE_NEXT
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Allocate a new page with the next page number.
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.El
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.Pp
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The function
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.Fn mpool_delete
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deletes the specified page from a pool and frees the page.
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It takes an
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.Dv MPOOL
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pointer and a page as arguments.
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The page must have been generated by
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.Fn mpool_new .
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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 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_IGNOREPIN
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The page returned is not pinned;
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page will otherwise be pinned on return.
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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 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 does not 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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