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.TH "MPI_T_CVAR_GET_INFO" "3" "May 30, 2025" "" "Open MPI"
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.sp
MPI_T see MPI\-3 section 14.3.5.
.sp
\fI\%MPI_T_cvar_get_info\fP — Query information from a control variable
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

int MPI_T_cvar_get_info(int cvar_index, char *name, int *name_len,
                        int *verbosity, MPI_Datatype *datatype, MPI_T_enum *enumtype,
                        const *desc, int *desc_len, int *bind, int *scope)
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBcvar_index\fP: Index of the control variable to be queried.
.UNINDENT
.SH INPUT/OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBname_len\fP: Length of the string and/or buffer for name.
.IP \(bu 2
\fBdesc_len\fP: Length of the string and/or buffer for desc.
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBname\fP: Buffer to return the string containing the name of the control variable.
.IP \(bu 2
\fBverbosity\fP: Verbosity level of this variable.
.IP \(bu 2
\fBdatatype\fP: MPI datatype of the information stored in the control variable.
.IP \(bu 2
\fBenumtype\fP: Optional descriptor for enumeration information.
.IP \(bu 2
\fBdesc\fP: Buffer to return the string containing the description of the control variable.
.IP \(bu 2
\fBbind\fP: Type of MPI object to which this variable must be bound.
.IP \(bu 2
\fBscope\fP: Scope of when changes to this variable are possible.
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_T_cvar_get_info\fP can be used to query information about a control
variable. The function returns the verbosity, datatype, enumeration
type, binding, and scope of the queried control variable in the
arguments \fIverbosity\fP, \fIdatatype\fP, \fIenumtype\fP, \fIbind\fP, and \fIscope\fP,
respectively. Control variables in Open MPI are the same as MCA
parameters.
.SH VERBOSITY
.sp
As Open MPI exposes a very large number of MCA parameters (control
variables), control variables are categorized into nine verbosity
levels corresponding to the equivalent \fI\%ompi_info\fP level. The nine levels are (in increasing order):
.INDENT 0.0
.IP 1. 3
\fBMPI_T_VERBOSITY_USER_BASIC\fP: Basic information of interest to users
.IP 2. 3
\fBMPI_T_VERBOSITY_USER_DETAIL\fP: Detailed information of interest to users
.IP 3. 3
\fBMPI_T_VERBOSITY_USER_ALL\fP: All remaining information of interest to users
.IP 4. 3
\fBMPI_T_VERBOSITY_TUNER_BASIC\fP: Basic information required for tuning
.IP 5. 3
\fBMPI_T_VERBOSITY_TUNER_DETAIL\fP: Detailed information required for tuning
.IP 6. 3
\fBMPI_T_VERBOSITY_TUNER_ALL\fP: All remaining information required for tuning
.IP 7. 3
\fBMPI_T_VERBOSITY_MPIDEV_BASIC\fP: Basic information for MPI implementors
.IP 8. 3
\fBMPI_T_VERBOSITY_MPIDEV_DETAIL\fP: Detailed information for MPI implementors
.IP 9. 3
\fBMPI_T_VERBOSITY_MPIDEV_ALL\fP: All remaining information for MPI implementors
.UNINDENT
.sp
For more information see MPI\-3 section 14.3.1.
.SH DATATYPE
.sp
The datatype returned by \fI\%MPI_T_cvar_get_info\fP is restricted to
one of the following datatypes: \fBMPI_INT\fP, \fBMPI_UNSIGNED\fP,
\fBMPI_UNSIGNED_LONG\fP, \fBMPI_UNSIGNED_LONG_LONG\fP, \fBMPI_COUNT\fP,
\fBMPI_CHAR\fP, and \fBMPI_DOUBLE\fP\&. For more information on datatypes in
MPI_T see MPI\-3 section 14.3.5.
.SH SCOPE
.sp
The scope describes when and how changes can be made to a control
variable. From MPI\-3 section 14.3.6, the scope may be any of the following:
.INDENT 0.0
.IP \(bu 2
\fBMPI_T_SCOPE_CONSTANT\fP: read\-only, value is constant
.IP \(bu 2
\fBMPI_T_SCOPE_READONLY\fP: read\-only, cannot be written, but can change
.IP \(bu 2
\fBMPI_T_SCOPE_LOCAL\fP: may be writeable, writing is a local operation
.IP \(bu 2
\fBMPI_T_SCOPE_GROUP\fP: may be writeable, must be done to a group of
processes, all processes in a group must be set to consistent
values
.IP \(bu 2
\fBMPI_T_SCOPE_GROUP_EQ\fP: may be writeable, must be done to a group
of processes, all processes in a group must be set to the same value
.IP \(bu 2
\fBMPI_T_SCOPE_ALL\fP: may be writeable, must be done to all
processes, all connected processes must be set to consistent values
.IP \(bu 2
\fBMPI_T_SCOPE_ALL_EQ\fP: may be writeable, must be done to all
processes, all connected processes must be set to the same value
.UNINDENT
.sp
For more information see MPI\-3 section 14.3.6 Table 14.4.
.SH NOTES
.sp
This MPI tool interface function returns two strings. This function
takes two argument for each string: a buffer to store the string, and a
length which must initially specify the size of the buffer. If the
length passed is n then this function will copy at most n \- 1 characters
of the string into the corresponding buffer and set the length to the
number of characters copied \- 1. If the length argument is NULL or the
value specified in the length is 0 the corresponding string buffer is
ignored and the string is not returned.
.sp
Open MPI does not currently support binding control variables to MPI
objects.
.SH ERRORS
.sp
\fI\%MPI_T_cvar_get_info\fP will fail if:
.INDENT 0.0
.IP \(bu 2
\fBMPI_T_ERR_NOT_INITIALIZED\fP: The MPI Tools interface not initialized
.IP \(bu 2
\fBMPI_T_ERR_INVALID_INDEX\fP: The control variable index is invalid
.UNINDENT
.sp
\fBSEE ALSO:\fP
.INDENT 0.0
.INDENT 3.5
\fI\%ompi_info\fP
.UNINDENT
.UNINDENT
.SH COPYRIGHT
2003-2025, The Open MPI Community
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