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.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)mpool.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd June 4, 1993 36.Dt MPOOL 3 37.Os 38.Sh NAME 39.Nm mpool 40.Nd "shared memory buffer pool" 41.Sh SYNOPSIS 42.In db.h 43.In mpool.h 44.Ft MPOOL * 45.Fn mpool_open "void *key" "int fd" "pgno_t pagesize" "pgno_t maxcache" 46.Ft void 47.Fo mpool_filter 48.Fa "MPOOL *mp" 49.Fa "void (*pgin)(void *, pgno_t, void *)" 50.Fa "void (*pgout)(void *, pgno_t, void *)" 51.Fa "void *pgcookie" 52.Fc 53.Ft void * 54.Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr" 55.Ft void * 56.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags" 57.Ft int 58.Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags" 59.Ft int 60.Fn mpool_sync "MPOOL *mp" 61.Ft int 62.Fn mpool_close "MPOOL *mp" 63.Sh DESCRIPTION 64The 65.Nm mpool 66library interface is intended to provide page oriented buffer management 67of files. 68The buffers may be shared between processes. 69.Pp 70The 71.Fn mpool_open 72function initializes a memory pool. 73The 74.Fa key 75argument is the byte string used to negotiate between multiple 76processes wishing to share buffers. 77If the file buffers are mapped in shared memory, all processes using 78the same key will share the buffers. 79If 80.Fa key 81is 82.Dv NULL , 83the buffers are mapped into private memory. 84The 85.Fa fd 86argument is a file descriptor for the underlying file, which must be seekable. 87If 88.Fa key 89is 90.No non\- Ns Dv NULL 91and matches a file already being mapped, the 92.Fa fd 93argument is ignored. 94.Pp 95The 96.Fa pagesize 97argument is the size, in bytes, of the pages into which the file is broken up. 98The 99.Fa maxcache 100argument is the maximum number of pages from the underlying file to cache 101at any one time. 102This value is not relative to the number of processes which share a file's 103buffers, but will be the largest value specified by any of the processes 104sharing the file. 105.Pp 106The 107.Fn mpool_filter 108function is intended to make transparent input and output processing of the 109pages possible. 110If the 111.Fa pgin 112function is specified, it is called each time a buffer is read into the memory 113pool from the backing file. 114If the 115.Fa pgout 116function is specified, it is called each time a buffer is written into the 117backing file. 118Both functions are called with the 119.Fa pgcookie 120pointer, the page number and a pointer to the page to being read or written. 121.Pp 122The 123.Fn mpool_new 124function takes an 125.Ft MPOOL 126pointer and an address as arguments. 127If a new page can be allocated, a pointer to the page is returned and 128the page number is stored into the 129.Fa pgnoaddr 130address. 131Otherwise, 132.Dv NULL 133is returned and 134.Va errno 135is set. 136.Pp 137The 138.Fn mpool_get 139function takes a 140.Ft MPOOL 141pointer and a page number as arguments. 142If the page exists, a pointer to the page is returned. 143Otherwise, 144.Dv NULL 145is returned and 146.Va errno 147is set. 148The 149.Fa flags 150argument is not currently used. 151.Pp 152The 153.Fn mpool_put 154function unpins the page referenced by 155.Fa pgaddr . 156The 157.Fa pgaddr 158argument 159must be an address previously returned by 160.Fn mpool_get 161or 162.Fn mpool_new . 163The 164.Fa flags 165argument is specified by 166.Em or Ns 'ing 167any of the following values: 168.Bl -tag -width indent 169.It Dv MPOOL_DIRTY 170The page has been modified and needs to be written to the backing file. 171.El 172.Pp 173The 174.Fn mpool_put 175function 176returns 0 on success and -1 if an error occurs. 177.Pp 178The 179.Fn mpool_sync 180function writes all modified pages associated with the 181.Ft MPOOL 182pointer to the 183backing file. 184The 185.Fn mpool_sync 186function 187returns 0 on success and -1 if an error occurs. 188.Pp 189The 190.Fn mpool_close 191function free's up any allocated memory associated with the memory pool 192cookie. 193Modified pages are 194.Em not 195written to the backing file. 196The 197.Fn mpool_close 198function 199returns 0 on success and -1 if an error occurs. 200.Sh ERRORS 201The 202.Fn mpool_open 203function may fail and set 204.Va errno 205for any of the errors specified for the library routine 206.Xr malloc 3 . 207.Pp 208The 209.Fn mpool_get 210function may fail and set 211.Va errno 212for the following: 213.Bl -tag -width Er 214.It Bq Er EINVAL 215The requested record doesn't exist. 216.El 217.Pp 218The 219.Fn mpool_new 220and 221.Fn mpool_get 222functions may fail and set 223.Va errno 224for any of the errors specified for the library routines 225.Xr read 2 , 226.Xr write 2 , 227and 228.Xr malloc 3 . 229.Pp 230The 231.Fn mpool_sync 232function may fail and set 233.Va errno 234for any of the errors specified for the library routine 235.Xr write 2 . 236.Pp 237The 238.Fn mpool_close 239function may fail and set 240.Va errno 241for any of the errors specified for the library routine 242.Xr free 3 . 243.Sh SEE ALSO 244.Xr btree 3 , 245.Xr dbopen 3 , 246.Xr hash 3 , 247.Xr recno 3 248