Major Changes in Version 1.0.2

Implemented the shared file pointer functions and split collective I/O functions. Therefore, the main components of the MPI I/O chapter not yet implemented are file interoperability and error handling.
Added support for using ``direct I/O'' on SGI's XFS file system. Direct I/O is an optional feature of XFS in which data is moved directly between the user's buffer and the storage devices, bypassing the file-system cache. This can improve performance significantly on systems with high disk bandwidth. Without high disk bandwidth, regular I/O (that uses the file-system cache) perfoms better. ROMIO, therefore, does not use direct I/O by default. The user can turn on direct I/O (separately for reading and writing) either by using environment variables or by using MPI's hints mechanism (info). To use the environment-variables method, do
```
       setenv MPIO_DIRECT_READ TRUE
       setenv MPIO_DIRECT_WRITE TRUE
```
To use the hints method, the two keys are direct_read and direct_write. By default their values are false. To turn on direct I/O, set the values to true. The environment variables have priority over the info keys. In other words, if the environment variables are set to TRUE, direct I/O will be used even if the info keys say false, and vice versa. Note that direct I/O must be turned on separately for reading and writing. The environment-variables method assumes that the environment variables can be read by each process in the MPI job. This is not guaranteed by the MPI Standard, but it works with SGI's MPI and the ch_shmem device of MPICH.
Added support (new ADIO device, ad_pvfs) for the PVFS parallel file system for Linux clusters, developed at Clemson University (see http://www.parl.clemson.edu/pvfs). To use it, you must first install PVFS and then when configuring ROMIO, specify -file_system=pvfs in addition to any other options to configure. (As usual, you can configure for multiple file systems by using ``+''; for example, -file_system=pvfs+ufs+nfs.) You will need to specify the path to the PVFS include files via the -cflags option to configure, for example,
configure -cflags=-I/usr/pvfs/include. You will also need to specify the full path name of the PVFS library. The best way to do this is via the -lib option to MPICH's configure script (assuming you are using ROMIO from within MPICH).
Uses weak symbols (where available) for building the profiling version, i.e., the PMPI routines. As a result, the size of the library is reduced considerably.
The Makefiles use virtual paths if supported by the make utility. GNU make supports it, for example. This feature allows you to untar the distribution in some directory, say a slow NFS directory, and compile the library (create the .o files) in another directory, say on a faster local disk. For example, if the tar file has been untarred in an NFS directory called /home/thakur/romio, one can compile it in a different directory, say /tmp/thakur, as follows:
```
        cd /tmp/thakur
        /home/thakur/romio/configure
        make
```
The .o files will be created in /tmp/thakur; the library will be created in
/home/thakur/romio/lib/$ARCH/libmpio.a. This method works only if the make utility supports virtual paths. If the default make utility does not, you can install GNU make which does, and specify it to configure as
```
       /home/thakur/romio/configure -make=/usr/gnu/bin/gmake (or whatever)
```
Lots of miscellaneous bug fixes and other enhancements.
This version is included in MPICH 1.2.0. If you are using MPICH, you need not download ROMIO separately; it gets built as part of MPICH. The previous version of ROMIO is included in LAM, HP MPI, SGI MPI, and NEC MPI. NEC has also implemented the MPI-IO functions missing in ROMIO, and therefore NEC MPI has a complete implementation of MPI-IO.

Rob Latham 2016-08-01