| MPOOL(3) | Library Functions Manual | MPOOL(3) | 
mpool, mpool_open,
  mpool_filter, mpool_new,
  mpool_get, mpool_put,
  mpool_sync, mpool_close
  —
#include <db.h>
#include <mpool.h>
MPOOL *
  
  mpool_open(DBT
    *key, int fd,
    pgno_t pagesize,
    pgno_t maxcache);
void
  
  mpool_filter(MPOOL
    *mp, void (*pgin)(void *,
    pgno_t, void *), void
    (*pgout)(void *, pgno_t, void *),
    void *pgcookie);
void *
  
  mpool_new(MPOOL
    *mp, pgno_t
    *pgnoaddr);
void *
  
  mpool_get(MPOOL
    *mp, pgno_t pgno,
    u_int flags);
int
  
  mpool_put(MPOOL
    *mp, void *pgaddr,
    u_int flags);
int
  
  mpool_sync(MPOOL
    *mp);
int
  
  mpool_close(MPOOL
    *mp);
mpool is the library interface intended to provide page
  oriented buffer management of files. The buffers may be shared between
  processes.
The function mpool_open() initializes a
    memory pool. The 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 key is
    NULL, the buffers are mapped into private memory.
    The fd argument is a file descriptor for the
    underlying file, which must be seekable. If key is
    non-NULL and matches a file
    already being mapped, the fd argument is ignored.
The pagesize argument is the size, in bytes, of the pages into which the file is broken up. The 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.
The mpool_filter() function is intended to
    make transparent input and output processing of the pages possible. If the
    pgin function is specified, it is called each time a
    buffer is read into the memory pool from the backing file. If the
    pgout function is specified, it is called each time a
    buffer is written into the backing file. Both functions are called with the
    pgcookie pointer, the page number and a pointer to the
    page to being read or written.
The function 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
    pgnoaddr address. Otherwise,
    NULL is returned and errno is set.
The function mpool_get() takes a MPOOL
    pointer and a page number as arguments. If the page exists, a pointer to the
    page is returned. Otherwise, NULL is returned and
    errno is set. The flags parameter is not currently used.
The function mpool_put() unpins the page
    referenced by pgaddr. pgaddr
    must be an address previously returned by
    mpool_get() or mpool_new().
    The flag value is specified by or'ing any of the following values:
MPOOL_DIRTYmpool_put() returns 0 on success and -1 if
    an error occurs.
The function mpool_sync() writes all
    modified pages associated with the MPOOL pointer to the backing file.
    mpool_sync() returns 0 on success and -1 if an error
    occurs.
The mpool_close() function frees up any
    allocated memory associated with the memory pool cookie. Modified pages are
    not written to the backing file.
    mpool_close() returns 0 on success and -1 if an
    error occurs.
mpool_open() function may fail and set
  errno for any of the errors specified for the library
  routine malloc(3).
The mpool_get() function may fail and set
    errno for the following:
EINVALThe mpool_new() and
    mpool_get() functions may fail and set
    errno for any of the errors specified for the library
    routines read(2),
    write(2), and
    malloc(3).
The mpool_sync() function may fail and set
    errno for any of the errors specified for the library
    routine write(2).
The mpool_close() function may fail and
    set errno for any of the errors specified for the
    library routine free(3).
| December 16, 2010 | NetBSD 9.3 |