mpi_io - Introduction to the ROMIO implementation of MPI
I/O routines
DESCRIPTION
MPI I/O routines are based on MPI-2 MPI I/O routines, in
which derived data types are used to express data
partitioning. These MPI-2 I/O routines are derived from
the ROMIO 1.0.1 source code. The current IRIX
implementation contains all interfaces defined in the
MPI-2 I/O chapter of the MPI-2 standard except shared file
pointer functions (Sec. 9.4.4), split collective data
access functions (Sec. 9.4.5), support for file
interoperability (Sec. 9.5), I/O error handling (Sec.
9.7), and I/O error classes (Sec. 9.8). Because shared
file pointer functions are not supported, the
MPI_MODE_SEQUENTIAL file access mode to MPI_File_open is
also not supported.
Limitations
The MPI I/O routines have the following limitations:
* Beginning with MPT 1.6, the status argument is set
following all read, write, MPIO_Test, and MPIO_Wait
functions. Consequently, MPI_Get_count and
MPI_Get_elements will now work when passed the status
object from these operations. Previously, they did
not.
* All nonblocking I/O functions use a MPIO_Request
object instead of the usual MPI_Request object.
Accordingly, two functions, MPIO_Test and MPIO_Wait
are provided to wait and test on these MPIO_Request
objects. They have the same semantics as MPI_Test and
MPI_Wait, as shown in the following synopsis:
int MPIO_Test(MPIO_Request *request, int *flag,
MPI_Status *status);
int MPIO_Wait(MPIO_Request *request, MPI_Status *status);
The usual functions, MPI_Test, MPI_Wait, MPI_Testany,
and so on, do not work for nonblocking I/O.
* All functions return only two possible error codes:
MPI_SUCCESS on success and MPI_ERR_UNKNOWN on failure.
* End-of-file is not detected. The individual file
pointer is increased by the requested amount of data
and not by the actual amount of data read. Therefore,
after end-of-file is reached, MPI_File_get_position(3)
returns a wrong offset.
MPI I/O supports direct access to files stored in XFS
filesystems. Direct access bypasses the system's buffer
cache, leading to better performance in some specialized
cases. You can enable direct I/O for read and write
operations by setting the appropriate environment
variable(s), MPIO_DIRECT_READ or MPIO_DIRECT_WRITE, to the
string "TRUE," as in the following example: setenv
MPIO_DIRECT_READ TRUE setenv MPIO_DIRECT_WRITE TRUE
List of Routines
The MPI I/O routines are as follows:
MPI_File_c2f(3)
MPI_File_close(3)
MPI_File_delete(3)
MPI_File_f2c(3)
MPI_File_get_amode(3)
MPI_File_get_atomicity(3)
MPI_File_get_byte_offset(3)
MPI_File_get_group(3)
MPI_File_get_info(3)
MPI_File_get_position(3)
MPI_File_get_size(3)
MPI_File_get_type_extent(3)
MPI_File_get_view(3)
MPI_File_iread(3)
MPI_File_iread_at(3)
MPI_File_iwrite(3)
MPI_File_iwrite_at(3)
MPI_File_open(3)
MPI_File_preallocate(3)
MPI_File_read(3)
MPI_File_read_all(3)
MPI_File_read_at(3)
MPI_File_read_at_all(3)
MPI_File_seek(3)
MPI_File_set_atomicity(3)
MPI_File_set_info(3)
MPI_File_set_size(3)
MPI_File_set_view(3)
MPI_File_sync(3)
MPI_File_write(3)
MPI_File_write_all(3)
MPI_File_write_at(3)
MPI_File_write_at_all(3)
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