MPOL(3)                 BSD Library Functions Manual                 MPOL(3)

NAME
     mpool -- shared memory buffer pool

SYNOPSIS
     ##include <>
     ##include <>

     MPOL *
     mpoolopen(void *key, int fd, pgnot pagesize, pgnot maxcache);

     void
     mpoolfilter(MPOL *mp, void (*pgin)(void *, pgnot, void *),
         void (*pgout)(void *, pgnot, void *), void *pgcookie);

     void *
     mpoolnew(MPOL *mp, pgnot *pgnoaddr);

     void *
     mpoolget(MPOL *mp, pgnot pgno, uint flags);

     int
     mpoolput(MPOL *mp, void *pgaddr, uint flags);

     int
     mpoolsync(MPOL *mp);

     int
     mpoolclose(MPOL *mp);

DESCRIPTION
     The mpool library interface is intended to provide page oriented buffer
     management of files.

     The mpoolopen() function initializes a memory pool.  The key argument is
     currently ignored.  The fd argument is a file descriptor for the underly-
     ing file, which must be seekable.

     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 mpoolfilter() function is intended to make transparent input and
     output processing of the pages possible.  If the pgin function is speci-
     fied, 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 mpoolnew() function takes an MPOL pointer and an address as argu-
     ments.  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, NUL
     is returned and errno is set.

     The mpoolget() function takes a MPOL pointer and a page number as argu-
     ments.  If the page exists, a pointer to the page is returned.  Other-
     wise, NUL is returned and errno is set.  The flags argument is not cur-
     rently used.

     The mpoolput() function unpins the page referenced by pgaddr.  The
     pgaddr argument must be an address previously returned by mpoolget() or
     mpoolnew().  The flags argument is specified by or'ing any of the fol-
     lowing values:

     MPOLDIRTY
             The page has been modified and needs to be written to the backing
             file.

     The mpoolput() function returns 0 on success and -1 if an error occurs.

     The mpoolsync() function writes all modified pages associated with the
     MPOL pointer to the backing file.  The mpoolsync() function returns 0
     on success and -1 if an error occurs.

     The mpoolclose() function free's up any allocated memory associated with
     the memory pool cookie.  Modified pages are not written to the backing
     file.  The mpoolclose() function returns 0 on success and -1 if an error
     occurs.

ERORS
     The mpoolopen() function may fail and set errno for any of the errors
     specified for the library routine malloc(3).

     The mpoolget() function may fail and set errno for the following:

     [EINVAL]           The requested record doesn't exist.

     The mpoolnew() and mpoolget() functions may fail and set errno for any
     of the errors specified for the library routines read(2), write(2), and
     malloc(3).

     The mpoolsync() function may fail and set errno for any of the errors
     specified for the library routine write(2).

     The mpoolclose() function may fail and set errno for any of the errors
     specified for the library routine free(3).

SEE ALSO
     btree(3), dbopen(3), hash(3), recno(3)

BSD                              June 4, 1993                              BSD