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. 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 17, 2011 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" "u_int flags" 51.Ft int 52.Fn mpool_delete "MPOOL *mp" "void *page" 53.Ft void * 54.Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags" 55.Ft int 56.Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags" 57.Ft int 58.Fn mpool_sync "MPOOL *mp" 59.Ft int 60.Fn mpool_close "MPOOL *mp" 61.Sh DESCRIPTION 62The 63.Nm mpool 64library interface is intended to provide page oriented buffer management 65of files. 66.Pp 67The 68.Fn mpool_open 69function initializes a memory pool. 70The 71.Fa key 72argument is currently ignored. 73The 74.Fa fd 75argument is a file descriptor for the underlying file, which must be seekable. 76.Pp 77The 78.Fa pagesize 79argument is the size, in bytes, of the pages into which the file is broken up. 80The 81.Fa maxcache 82argument is the maximum number of pages from the underlying file to cache 83at any one time. 84This value is not relative to the number of processes which share a file's 85buffers, but will be the largest value specified by any of the processes 86sharing the file. 87.Pp 88The 89.Fn mpool_filter 90function is intended to make transparent input and output processing of the 91pages possible. 92If the 93.Fa pgin 94function is specified, it is called each time a buffer is read into the memory 95pool from the backing file. 96If the 97.Fa pgout 98function is specified, it is called each time a buffer is written into the 99backing file. 100Both functions are called with the 101.Fa pgcookie 102pointer, the page number and a pointer to the page to being read or written. 103.Pp 104The function 105.Fn mpool_new 106takes an 107.Dv MPOOL 108pointer, an address, and a set of flags as arguments. 109If a new page can be allocated, a pointer to the page is returned and 110the page number is stored into the 111.Fa pgnoaddr 112address. 113Otherwise, 114.Dv NULL 115is returned and 116.Va errno 117is set. 118The flags value is formed by 119.Tn OR Ns 'ing 120the following values: 121.Bl -tag -width Ds 122.It Dv MPOOL_PAGE_REQUEST 123Allocate a new page with a specific page number. 124.It Dv MPOOL_PAGE_NEXT 125Allocate a new page with the next page number. 126.El 127.Pp 128The function 129.Fn mpool_delete 130deletes the specified page from a pool and frees the page. 131It takes an 132.Dv MPOOL 133pointer and a page as arguments. 134The page must have been generated by 135.Fn mpool_new . 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 specified by 151.Em or Ns 'ing 152any of the following values: 153.Bl -tag -width indent 154.It Dv MPOOL_IGNOREPIN 155The page returned is not pinned; 156page will otherwise be pinned on return. 157.El 158.Pp 159The 160.Fn mpool_put 161function unpins the page referenced by 162.Fa pgaddr . 163The 164.Fa pgaddr 165argument 166must be an address previously returned by 167.Fn mpool_get 168or 169.Fn mpool_new . 170The 171.Fa flags 172argument is specified by 173.Em or Ns 'ing 174any of the following values: 175.Bl -tag -width indent 176.It Dv MPOOL_DIRTY 177The page has been modified and needs to be written to the backing file. 178.El 179.Pp 180The 181.Fn mpool_put 182function 183returns 0 on success and -1 if an error occurs. 184.Pp 185The 186.Fn mpool_sync 187function writes all modified pages associated with the 188.Ft MPOOL 189pointer to the 190backing file. 191The 192.Fn mpool_sync 193function 194returns 0 on success and -1 if an error occurs. 195.Pp 196The 197.Fn mpool_close 198function free's up any allocated memory associated with the memory pool 199cookie. 200Modified pages are 201.Em not 202written to the backing file. 203The 204.Fn mpool_close 205function 206returns 0 on success and -1 if an error occurs. 207.Sh ERRORS 208The 209.Fn mpool_open 210function may fail and set 211.Va errno 212for any of the errors specified for the library routine 213.Xr malloc 3 . 214.Pp 215The 216.Fn mpool_get 217function may fail and set 218.Va errno 219for the following: 220.Bl -tag -width Er 221.It Bq Er EINVAL 222The requested record does not exist. 223.El 224.Pp 225The 226.Fn mpool_new 227and 228.Fn mpool_get 229functions may fail and set 230.Va errno 231for any of the errors specified for the library routines 232.Xr read 2 , 233.Xr write 2 , 234and 235.Xr malloc 3 . 236.Pp 237The 238.Fn mpool_sync 239function may fail and set 240.Va errno 241for any of the errors specified for the library routine 242.Xr write 2 . 243.Pp 244The 245.Fn mpool_close 246function may fail and set 247.Va errno 248for any of the errors specified for the library routine 249.Xr free 3 . 250.Sh SEE ALSO 251.Xr btree 3 , 252.Xr dbopen 3 , 253.Xr hash 3 , 254.Xr recno 3 255