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