fmpio(3) fmpio(3)
NAME
MPset, MPget, MPopen, MPclose, MPflush, MPseek, MPread, MPwrite - File
Memory Buffer Pool Stdio Interface
SYNOPSIS
#include <fmpio.h>
extern int MPset
(
int pagesize,
int maxcache,
int flags
);
extern int MPget
(
int *pagesize,
int *maxcache,
int flags
);
extern MPFILE *MPopen
(
const char *path,
int flags
);
extern int MPclose(MPFILE *mpfs);
extern int MPflush(MPFILE *mpfs);
extern int MPseek
(
MPFILE *mpfs,
off_t offset,
int whence
);
extern int MPread
(
MPFILE *mpfs,
void *buf,
size_t nbytes
);
extern int MPwrite
(
MPFILE *mpfs,
void *buf,
size_t nbytes
);
PARAMETERS
int pagesize
IN: pagesize to use for next open/create.
int maxcache
IN: max number of pages to cache.
int flags (MPset)
IN: flags = 0, MP_PAGEALL.
int *pagesize
OUT: pagesize to used in last open/create.
int *maxcache
OUT: max number of pages cached in last open/create.
int flags (MPget)
IN:.
const char *path
IN: filename.
int flags (MPopen)
IN: DFACC_CREATE, DFACC_READ, DFACC_WRITE, DFACC_RDWR,
DFACC_ALL.
MPFILE *mpfs
IN: File Memory pool handle.
off_t offset
IN: Offset into the file.
int whence
IN: SEEK_CUR, SEEK_SET, SEEK_END.
void *buf (MPread)
IN: User buffer to read data into.
size_t nbytes (MPread)
IN: number of bytes to read in.
void *buf (MPwrite)
IN: User buffer to write data from.
size_t nbytes (MPwrite)
IN: number of bytes to write out.
DESCRIPTION
MPset
Set the pagesize and maximum number of pages to cache on the next
open/create of a file. A pagesize that is a power of 2 is recommended.
The values set here only affect the next open/creation of a file and do
not change a particular file's paging behaviour after it has been
opened or created. This maybe changed in a later release.
Use flags arguement of 'MP_PAGEALL' if the whole file is to be cached
in memory otherwise passs in zero.
MPget
This gets the last pagesize and maximum number of pages cached for the
last open/create of a file.
MPopen
Open/Create the file for reading/writing and create a memory pool for
the file. Currently we let the library decide whether to use the
default PAGESIZE for creating pages and MAXCACHE for number of pages to
cache in the pool.
MPclose
First sync the file memory pool to disk. Next close the file memory
pool. Finally close the file.
MPflush
Flushes the file memory pool to disk.
MPseek
Seeks to the correct page in the file depending upon the offset and the
flag 'whence'. Similiar to the stdio routine. Assumes the flags values
for SEEK_SET, SEEK_CUR and SEEK_END are universal. May not be true for
non-Unix OS's.
MPread
This routine handles getting the correct pages to read to satisfy the
request. The data is then copied from the memory pool into the user's
buffer.
MPwrite
This routine handles getting the correct pages to write to satisfy the
request. The data is then copied from the user's buffer to the memory
pool.
RETURNS
MPset
Returns SUCCEED if successful and FAIL otherwise.
MPget
Returns SUCCEED.
MPopen
Pointer to MPFILE struct if successful and NULL otherwise.
MPclose
Returns SUCCEED on success and FAIL otherwise.
MPflush
Returns SUCCEED on success and FAIL otherwise.
MPseek
Returns offset into the file on success and FAIL otherwise.
MPread
Returns number of bytes read if successful and FAIL otherwise.
MPwrite
Returns number of bytes written if successful and FAIL otherwise.
NAME
MPset
MPset - set pagesize and maximum number of pages to cache on next
open/create.
MPget
MPget - get last pagesize and max number of pages cached for open/cre-
ate.
MPopen
MPopen - open/create the file and create a memory pool for file.
MPclose
MPclose - close the file, sync the file memory pool to disk and close
it.
MPflush
MPflush - flush file memory pool to disk.
MPseek
MPseek - seek to the specified file offset in the memory pool.
MPread
MPread - read 'nbytes' from file memory pool into 'buf'.
MPwrite
MPwrite - write 'nbytes' form 'buf' to the file memory pool.
NOTE
MPset
Currently 'maxcache' has to be greater than 1. Maybe use special case
of 0 to specify you want to turn page buffering off or use the flags
arguement.
Current memory usage overhead for the Memory Pool is approximately ~(2k
+ maxcache*(28+pagesize) + npages*20) bytes.
MPseek
Note that it returns an 'int' as opposed to 'off_t'. This is because
the HDF library still deals with file offsets in terms of signed inte-
gers....*sigh*...hopefully This will be changed in a future release.
MPread
The memcpy from the buffer pool to the users buffer is an expensive
operation.
MPwrite
The memcpy from the the users buffer to the memory pool is an expensive
operation.
CONTACT
George Velamparampil <georgev@ncsa.uiuc.edu>
NCSA Software Development Group
HDF Group
152 Computing Applications Bldg.
605 E. Springfield Ave.
Champaign, IL 61820
c2man fmpio.h 2 February 1996 fmpio(3)
hdf 4.2r4 - Generated Fri Feb 6 07:42:16 CST 2009