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