The current value of the trace variable tracevar is used to control whether or not a particular trace operation takes place. The trace variable values can be set at system build time (see Section 12). The following defined constants are suggestive of how to use trace levels.
TR_NEVER for debugging statements that are unused (noop)TR_FULL_TRACE every subroutine entry and exit
TR_DETAILED all functions plus dumps of data structures at strategic points
TR_FUNCTIONAL_TRACE all the functions of the module and their parameters
TR_MORE_EVENTS even more detail on events
TR_EVENTS more detail than major events
TR_SOFT_ERRORS mild warnings
TR_MAJOR_EVENTS open, close, etc.
TR_GROSS_EVENTS the coarsest tracing level
TR_ERRORS serious non-fatal errors; some residual event traces
TR_ALWAYS normally only used during protocol development