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-.\"
-.\" @(#)mpool.3 8.1 (Berkeley) 6/4/93
-.\"
-.TH MPOOL 3 2012-04-26 "" "Linux Programmer's Manual"
-.UC 7
-.SH NAME
-mpool \- shared memory buffer pool
-.SH SYNOPSIS
-.nf
-.B #include <db.h>
-.B #include <mpool.h>
-.sp
-.BI "MPOOL *mpool_open(DBT *" key ", int " fd ", pgno_t " pagesize \
-", pgno_t " maxcache );
-.sp
-.BI "void mpool_filter(MPOOL *" mp ", void (*pgin)(void *, pgno_t, void *),"
-.BI " void (*" pgout ")(void *, pgno_t, void *),"
-.BI " void *" pgcookie );
-.sp
-.BI "void *mpool_new(MPOOL *" mp ", pgno_t *" pgnoaddr );
-.sp
-.BI "void *mpool_get(MPOOL *" mp ", pgno_t " pgno ", unsigned int " flags );
-.sp
-.BI "int mpool_put(MPOOL *" mp ", void *" pgaddr ", unsigned int " flags );
-.sp
-.BI "int mpool_sync(MPOOL *" mp );
-.sp
-.BI "int mpool_close(MPOOL *" mp );
-.fi
-.SH DESCRIPTION
-.IR "Note well" :
-This page documents interfaces provided in glibc up until version 2.1.
-Since version 2.2, glibc no longer provides these interfaces.
-Probably, you are looking for the APIs provided by the
-.I libdb
-library instead.
-
-.I Mpool
-is the library interface intended to provide page oriented buffer management
-of files.
-The buffers may be shared between processes.
-.PP
-The function
-.BR mpool_open ()
-initializes a memory pool.
-The
-.I 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
-.I key
-is NULL, the buffers are mapped into private memory.
-The
-.I fd
-argument is a file descriptor for the underlying file, which must be seekable.
-If
-.I key
-is non-NULL and matches a file already being mapped, the
-.I fd
-argument is ignored.
-.PP
-The
-.I pagesize
-argument is the size, in bytes, of the pages into which the file is broken up.
-The
-.I 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
-.BR mpool_filter ()
-function is intended to make transparent input and output processing of the
-pages possible.
-If the
-.I pgin
-function is specified, it is called each time a buffer is read into the memory
-pool from the backing file.
-If the
-.I pgout
-function is specified, it is called each time a buffer is written into the
-backing file.
-Both functions are called with the
-.I pgcookie
-pointer, the page number and a pointer to the page to being read or written.
-.PP
-The function
-.BR mpool_new ()
-takes an
-.I 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
-.I pgnoaddr
-address.
-Otherwise, NULL is returned and
-.I errno
-is set.
-.PP
-The function
-.BR mpool_get ()
-takes an
-.I MPOOL
-pointer and a page number as arguments.
-If the page exists, a pointer to the page is returned.
-Otherwise, NULL is returned and
-.I errno
-is set.
-The
-.I flags
-argument is not currently used.
-.PP
-The function
-.BR mpool_put ()
-unpins the page referenced by
-.IR pgaddr .
-.I pgaddr
-must be an address previously returned by
-.BR mpool_get ()
-or
-.BR mpool_new ().
-The flag value is specified by ORing
-any of the following values:
-.TP
-.B MPOOL_DIRTY
-The page has been modified and needs to be written to the backing file.
-.PP
-.BR mpool_put ()
-returns 0 on success and \-1 if an error occurs.
-.PP
-The function
-.BR mpool_sync ()
-writes all modified pages associated with the
-.I MPOOL
-pointer to the
-backing file.
-.BR mpool_sync ()
-returns 0 on success and \-1 if an error occurs.
-.PP
-The
-.BR mpool_close ()
-function free's up any allocated memory associated with the memory pool
-cookie.
-Modified pages are
-.B not
-written to the backing file.
-.BR mpool_close ()
-returns 0 on success and \-1 if an error occurs.
-.SH ERRORS
-The
-.BR mpool_open ()
-function may fail and set
-.I errno
-for any of the errors specified for the library routine
-.BR malloc (3).
-.PP
-The
-.BR mpool_get ()
-function may fail and set
-.I errno
-for the following:
-.TP 15
-.B EINVAL
-The requested record doesn't exist.
-.PP
-The
-.BR mpool_new ()
-and
-.BR mpool_get ()
-functions may fail and set
-.I errno
-for any of the errors specified for the library routines
-.BR read (2),
-.BR write (2),
-and
-.BR malloc (3).
-.PP
-The
-.BR mpool_sync ()
-function may fail and set
-.I errno
-for any of the errors specified for the library routine
-.BR write (2).
-.PP
-The
-.BR mpool_close ()
-function may fail and set
-.I errno
-for any of the errors specified for the library routine
-.BR free (3).
-.SH CONFORMING TO
-Not in POSIX.1-2001.
-Present on the BSDs.
-.SH SEE ALSO
-.BR btree (3),
-.BR dbopen (3),
-.BR hash (3),
-.BR recno (3)
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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