MPI_T_CVAR_GET_INFO(3)				     Open MPI				    MPI_T_CVAR_GET_INFO(3)

MPI_T see MPI-3 section 14.3.5.

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	 <#man1-ompi-info>  level.
       The nine levels are (in increasing order):

       1. MPI_T_VERBOSITY_USER_BASIC: Basic information of interest to users

       2. MPI_T_VERBOSITY_USER_DETAIL: Detailed information of interest to users

       3. MPI_T_VERBOSITY_USER_ALL: All remaining information of interest to users

       4. MPI_T_VERBOSITY_TUNER_BASIC: Basic information required for tuning

       5. MPI_T_VERBOSITY_TUNER_DETAIL: Detailed information required for tuning

       6. MPI_T_VERBOSITY_TUNER_ALL: All remaining information required for tuning

       7. MPI_T_VERBOSITY_MPIDEV_BASIC: Basic information for MPI implementors

       8. MPI_T_VERBOSITY_MPIDEV_DETAIL: Detailed information for MPI implementors

       9. MPI_T_VERBOSITY_MPIDEV_ALL: All remaining information for MPI implementors

       For more information see MPI-3 section 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 section 14.3.5.

SCOPE
       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:

       • 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 section 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 <#man1-ompi-info>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026				    MPI_T_CVAR_GET_INFO(3)
