The mpool library interface is intended to provide page oriented buffer management of files.
The mpool_open function initializes a memory pool. The key argument is currently ignored. The fd argument is a file descriptor for the underlying 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 files 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 mpool_new function 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 mpool_get function 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 argument is not currently used.
The mpool_put function unpins the page referenced by pgaddr. The pgaddr argument must be an address previously returned by mpool_get or mpool_new. The flags argument is specified by or ing any of the following values: