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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. .\" %%%LICENSE_END .\" .\" @(#)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 .B #include .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. 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 4.10 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 \%https://www.kernel.org/doc/man\-pages/.