Intel Extensible Firmware Interface - Manual (Page 198)

Extensible Firmware Interface Specification
6-6 12/01/02 Version 1.10
caller may act as a filter if it chooses. Calls to SetVariable() between calls to
GetNextVariableName() may produce unpredictable results.
Once ExitBootServices() is performed, variables that are only visible during boot services
will no longer be returned. To obtain the data contents or attribute for a variable returned by
GetNextVariableName(), the GetVariable() interface is used.
Status Codes Returned
EFI_SUCCESS The function completed successfully.
EFI_NOT_FOUND The next variable was not found.
EFI_BUFFER_TOO_SMALL The VariableNameSize is too small for the result.
VariableNameSize has been updated with the size needed
to complete the request.
EFI_INVALID_PARAMETER VariableNameSize is NULL .
EFI_INVALID_PARAMETER VariableName is NULL .
EFI_INVALID_PARAMETER VendorGuid is NULL .
EFI_DEVICE_ERROR The variable name could not be retrieved due to a hardware error.