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 February 25, 1999 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 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 does not 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