/*!

\mainpage

SIONlib is a small library for writing and reading binary data
to/from from several thousands of processors into one or a small number of
physical files. The library provides global open and close functions
for accessing one file for writing and reading in parallel. Only these
function are collective, writing and reading to/from this file can be
done asynchronously.  sionlib provides a sion file handle and also an
file pointer (FILE *) which allows to use the standard C file I/O
operations (POSIX). This file pointer points to a unique position in
the file.

SIONlib provides a simplified file handling for a parallel program
that formerly had to read or write binary data in parallel into
separate files (task-local files). After opening the file with
sionlib, the I/O can be done with the standard C-I/O functionality
(fwrite, fread) without changing the existing program. Instead of
maintaining thousands of separate files for storing the data, there is
only one large file containing all the data.

SIONlib requires information on the BLOCKSIZE of the underlying filesystem, 
i.e., the BLOCKSIZE is the smallest part of a file which can be locked. For
instance, IBM GPFS has blocksizes of one ore two Megabytes.  

Given that each processor writes its data to same file, sionlib
assigns different regions (e.g., data blocks) of the file to a
processor. Hence, for each processor, sionlib needs the estimated data
size which would be written to the file (chunk size). sionlib can also
handle extensions (additional chunks), if the end of a data block is
reached.

Both, the estimated chunk size and filesystem's blocksize are
used to calculate the individual start position in the file for each
processor. While a certain block of the file is locked only by one
processor, efficient parallel writing and reading is feasible.

*/

