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Revision 1.9, Thu Aug 7 16:42:43 2003 UTC (18 years, 5 months ago) by agc
Move UCB-licensed code from 4-clause to 3-clause licence. Patches provided by Joel Baker in PR 22280, verified by myself.
.\" $NetBSD: mpool.3,v 1.9 2003/08/07 16:42:43 agc Exp $ .\" .\" Copyright (c) 1990, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)mpool.3 8.1 (Berkeley) 6/4/93 .\" .Dd April 17, 2003 .Dt MPOOL 3 .Os .Sh NAME .Nm mpool , .Nm mpool_open , .Nm mpool_filter , .Nm mpool_new , .Nm mpool_get , .Nm mpool_put , .Nm mpool_sync , .Nm mpool_close .Nd shared memory buffer pool .Sh SYNOPSIS .In db.h .In mpool.h .Ft MPOOL * .Fn mpool_open "DBT *key" "int fd" "pgno_t pagesize" "pgno_t maxcache" .Ft void .Fn mpool_filter "MPOOL *mp" "void (*pgin)(void *, pgno_t, void *)" \ "void (*pgout)(void *, pgno_t, void *)" "void *pgcookie" .Ft void * .Fn mpool_new "MPOOL *mp" "pgno_t *pgnoaddr" .Ft void * .Fn mpool_get "MPOOL *mp" "pgno_t pgno" "u_int flags" .Ft int .Fn mpool_put "MPOOL *mp" "void *pgaddr" "u_int flags" .Ft int .Fn mpool_sync "MPOOL *mp" .Ft int .Fn mpool_close "MPOOL *mp" .Sh DESCRIPTION .Nm is the library interface intended to provide page oriented buffer management of files. The buffers may be shared between processes. .Pp The function .Nm mpool_open initializes a memory pool. The .Fa key argument is the byte string used to negotiate between multiple processes wishing to share buffers. If the file buffers are mapped in shared memory, all processes using the same key will share the buffers. If .Fa key is .Dv NULL , the buffers are mapped into private memory. The .Fa fd argument is a file descriptor for the underlying file, which must be seekable. If .Fa key is .No non- Ns Dv NULL and matches a file already being mapped, the .Fa fd argument is ignored. .Pp The .Fa pagesize argument is the size, in bytes, of the pages into which the file is broken up. The .Fa maxcache argument is the maximum number of pages from the underlying file to cache at any one time. This value is not relative to the number of processes which share a file's buffers, but will be the largest value specified by any of the processes sharing the file. .Pp The .Nm mpool_filter function is intended to make transparent input and output processing of the pages possible. If the .Fa pgin function is specified, it is called each time a buffer is read into the memory pool from the backing file. If the .Fa pgout function is specified, it is called each time a buffer is written into the backing file. Both functions are are called with the .Fa pgcookie pointer, the page number and a pointer to the page to being read or written. .Pp The function .Nm mpool_new takes an MPOOL pointer and an address as arguments. If a new page can be allocated, a pointer to the page is returned and the page number is stored into the .Fa pgnoaddr address. Otherwise, .Dv NULL is returned and errno is set. .Pp The function .Nm mpool_get takes a MPOOL pointer and a page number as arguments. If the page exists, a pointer to the page is returned. Otherwise, .Dv NULL is returned and errno is set. The flags parameter is not currently used. .Pp The function .Nm mpool_put unpins the page referenced by .Fa pgaddr . .Fa pgaddr must be an address previously returned by .Nm mpool_get or .Nm mpool_new . The flag value is specified by or'ing any of the following values: .Bl -tag -width MPOOL_DIRTYX -offset indent .It Dv MPOOL_DIRTY The page has been modified and needs to be written to the backing file. .El .Pp .Nm mpool_put returns 0 on success and \-1 if an error occurs. .Pp The function .Nm mpool_sync writes all modified pages associated with the MPOOL pointer to the backing file. .Nm mpool_sync returns 0 on success and \-1 if an error occurs. .Pp The .Nm mpool_close function frees up any allocated memory associated with the memory pool cookie. Modified pages are .Em not written to the backing file. .Nm mpool_close returns 0 on success and \-1 if an error occurs. .Sh ERRORS The .Nm mpool_open function may fail and set .Va errno for any of the errors specified for the library routine .Xr malloc 3 . .Pp The .Nm mpool_get function may fail and set .Va errno for the following: .Bl -tag -width Er -offset indent .It Er EINVAL The requested record doesn't exist. .El .Pp The .Nm mpool_new and .Nm mpool_get functions may fail and set .Va errno for any of the errors specified for the library routines .Xr read 2 , .Xr write 2 , and .Xr malloc 3 . .Pp The .Nm mpool_sync function may fail and set .Va errno for any of the errors specified for the library routine .Xr write 2 . .Pp The .Nm mpool_close function may fail and set .Va errno for any of the errors specified for the library routine .Xr free 3 . .Sh SEE ALSO .Xr btree 3 , .Xr dbopen 3 , .Xr hash 3 , .Xr recno 3