NAME

       MPI_T_cvar_get_info - Query information from a control variable

SYNTAX

C Syntax

       #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)

INPUT PARAMETERS

       cvar_index
                 Index of the control variable to be queried.

INPUT/OUTPUT PARAMETERS

       name_len  Length of the string and/or buffer for name.

       desc_len  Length of the string and/or buffer for desc.

OUTPUT PARAMETERS

       name      Buffer to return the string containing the name of the control variable.

       verbosity Verbosity level of this variable.

       datatype  MPI datatype of the information stored in the control variable.

       enumtype  Optional descriptor for enumeration information.

       desc      Buffer to return the string containing the description of the control variable.

       bind      Type of MPI object to which this variable must be bound.

       scope     Scope of when changes to this variable are possible.

DESCRIPTION

       MPI_T_cvar_get_info  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 verbosity, datatype, enumtype, bind, and scope, respectively. Control variables in Open MPI are
       the same as MCA parameters.

VERBOSITY

       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 ompi_info level. The  nine  levels
       are (in increasing order):

       MPI_T_VERBOSITY_USER_BASIC
                 Basic information of interest to users

       MPI_T_VERBOSITY_USER_DETAIL
                 Detailed information of interest to users

       MPI_T_VERBOSITY_USER_ALL
                 All remaining information of interest to users

       MPI_T_VERBOSITY_TUNER_BASIC
                 Basic information required for tuning

       MPI_T_VERBOSITY_TUNER_DETAIL
                 Detailed information required for tuning

       MPI_T_VERBOSITY_TUNER_ALL
                 All remaining information required for tuning

       MPI_T_VERBOSITY_MPIDEV_BASIC
                 Basic information for MPI implementors

       MPI_T_VERBOSITY_MPIDEV_DETAIL
                 Detailed information for MPI implementors

       MPI_T_VERBOSITY_MPIDEV_ALL
                 All remaining information for MPI implementors

                 For more information see MPI-3 § 14.3.1.

DATATYPE

       The  datatype  returned  by MPI_T_cvar_get_info is restricted to one of the following datatypes: MPI_INT,
       MPI_UNSIGNED, MPI_UNSIGNED_LONG, MPI_UNSIGNED_LONG_LONG, MPI_COUNT, MPI_CHAR, and  MPI_DOUBLE.  For  more
       information on datatypes in MPI_T see MPI-3 § 14.3.5.

SCOPE

       The  scope  describes  when  and  how changes can be made to a control variable. From MPI-3 § 14.3.6, the
       scope may be any of the following:

       MPI_T_SCOPE_CONSTANT
                 read-only, value is constant

       MPI_T_SCOPE_READONLY
                 read-only, cannot be written, but can change

       MPI_T_SCOPE_LOCAL
                 may be writeable, writing is a local operation

       MPI_T_SCOPE_GROUP
                 may be writeable, must be done to a group of processes, all processes in a group must be set to
                 consistent values

       MPI_T_SCOPE_GROUP_EQ
                 may be writeable, must be done to a group of processes, all processes in a group must be set to
                 the same value

       MPI_T_SCOPE_ALL
                 may be writeable, must be done to all  processes,  all  connected  processes  must  be  set  to
                 consistent values

       MPI_T_SCOPE_ALL_EQ
                 may  be  writeable,  must  be done to all processes, all connected processes must be set to the
                 same value

                 For more information see MPI-3 § 14.3.6 Table 14.4.

NOTES

       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.

       Open MPI does not currently support binding control variables to MPI objects.

ERRORS

       MPI_T_cvar_get_info() will fail if:

       [MPI_T_ERR_NOT_INITIALIZED]
                 The MPI Tools interface not initialized

       [MPI_T_ERR_INVALID_INDEX]
                 The control variable index is invalid

SEE ALSO

       ompi_info

4.1.6                                             Sep 30, 2023                            MPI_T_cvar_get_info(3)