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