1.\" $NetBSD: mpool.3,v 1.8 2003/04/17 19:35:03 wiz Exp $ 2.\" 3.\" Copyright (c) 1990, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)mpool.3 8.1 (Berkeley) 6/4/93 35.\" 36.Dd April 17, 2003 37.Dt MPOOL 3 38.Os 39.Sh NAME 40.Nm mpool , 41.Nm mpool_open , 42.Nm mpool_filter , 43.Nm mpool_new , 44.Nm mpool_get , 45.Nm mpool_put , 46.Nm mpool_sync , 47.Nm mpool_close 48.Nd shared memory buffer pool 49.Sh SYNOPSIS 50.In db.h 51.In mpool.h 52.Ft MPOOL * 53.Fn mpool_open "DBT *key" "int fd" "pgno_t pagesize" "pgno_t maxcache" 54.Ft void 55.Fn mpool_filter "MPOOL *mp" "void (*pgin)(void *, pgno_t, void *)" \ 56"void (*pgout)(void *, pgno_t, void *)" "void *pgcookie" 57.Ft void * 58.Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr" 59.Ft void * 60.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags" 61.Ft int 62.Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags" 63.Ft int 64.Fn mpool_sync "MPOOL *mp" 65.Ft int 66.Fn mpool_close "MPOOL *mp" 67.Sh DESCRIPTION 68.Nm 69is the library interface intended to provide page oriented buffer 70management of files. 71The buffers may be shared between processes. 72.Pp 73The function 74.Nm mpool_open 75initializes a memory pool. 76The 77.Fa key 78argument is the byte string used to negotiate between multiple 79processes wishing to share buffers. 80If the file buffers are mapped in shared memory, all processes using 81the same key will share the buffers. 82If 83.Fa key 84is 85.Dv NULL , 86the buffers are mapped into private memory. 87The 88.Fa fd 89argument is a file descriptor for the underlying file, which must be 90seekable. 91If 92.Fa key 93is 94.No non- Ns Dv NULL 95and matches a file already being mapped, the 96.Fa fd 97argument is ignored. 98.Pp 99The 100.Fa pagesize 101argument is the size, in bytes, of the pages into which the file is 102broken up. 103The 104.Fa maxcache 105argument is the maximum number of pages from the underlying file to 106cache at any one time. 107This value is not relative to the number of processes which share a 108file's buffers, but will be the largest value specified by any of the 109processes sharing the file. 110.Pp 111The 112.Nm mpool_filter 113function is intended to make transparent input and output processing 114of the pages possible. 115If the 116.Fa pgin 117function is specified, it is called each time a buffer is read into 118the memory pool from the backing file. 119If the 120.Fa pgout 121function is specified, it is called each time a buffer is written into 122the backing file. 123Both functions are are called with the 124.Fa pgcookie 125pointer, the page number and a pointer to the page to being read or 126written. 127.Pp 128The function 129.Nm mpool_new 130takes an MPOOL pointer and an address as arguments. 131If a new page can be allocated, a pointer to the page is returned and 132the page number is stored into the 133.Fa pgnoaddr 134address. 135Otherwise, 136.Dv NULL 137is returned and errno is set. 138.Pp 139The function 140.Nm mpool_get 141takes a MPOOL pointer and a page number as arguments. 142If the page exists, a pointer to the page is returned. 143Otherwise, 144.Dv NULL 145is returned and errno is set. 146The flags parameter is not currently used. 147.Pp 148The function 149.Nm mpool_put 150unpins the page referenced by 151.Fa pgaddr . 152.Fa pgaddr 153must be an address previously returned by 154.Nm mpool_get 155or 156.Nm mpool_new . 157The flag value is specified by or'ing any of the following values: 158.Bl -tag -width MPOOL_DIRTYX -offset indent 159.It Dv MPOOL_DIRTY 160The page has been modified and needs to be written to the backing 161file. 162.El 163.Pp 164.Nm mpool_put 165returns 0 on success and \-1 if an error occurs. 166.Pp 167The function 168.Nm mpool_sync 169writes all modified pages associated with the MPOOL pointer to the 170backing file. 171.Nm mpool_sync 172returns 0 on success and \-1 if an error occurs. 173.Pp 174The 175.Nm mpool_close 176function frees up any allocated memory associated with the memory pool 177cookie. 178Modified pages are 179.Em not 180written to the backing file. 181.Nm mpool_close 182returns 0 on success and \-1 if an error occurs. 183.Sh ERRORS 184The 185.Nm mpool_open 186function may fail and set 187.Va errno 188for any of the errors specified for the library routine 189.Xr malloc 3 . 190.Pp 191The 192.Nm mpool_get 193function may fail and set 194.Va errno 195for the following: 196.Bl -tag -width Er -offset indent 197.It Er EINVAL 198The requested record doesn't exist. 199.El 200.Pp 201The 202.Nm mpool_new 203and 204.Nm mpool_get 205functions may fail and set 206.Va errno 207for any of the errors specified for the library routines 208.Xr read 2 , 209.Xr write 2 , 210and 211.Xr malloc 3 . 212.Pp 213The 214.Nm mpool_sync 215function may fail and set 216.Va errno 217for any of the errors specified for the library routine 218.Xr write 2 . 219.Pp 220The 221.Nm mpool_close 222function may fail and set 223.Va errno 224for any of the errors specified for the library routine 225.Xr free 3 . 226.Sh SEE ALSO 227.Xr btree 3 , 228.Xr dbopen 3 , 229.Xr hash 3 , 230.Xr recno 3 231