LTTng » Babeltrace

This is a follow up on https://review.lttng.org/c/babeltrace/+/3045 now that end users are starting to contact us wondering why up-to-date lttng and babeltrace2 show incomplete information for bitwise enums.

I think we should implement a better stop-gap solution while awaiting CTF2. I recommend that we specialize the babeltrace2 CTF input plugin to detect traces produced by the lttng-modules kernel tracer, for specific known (hardcoded) events and fields which have a bitwise enum semantic, and use this hardcoded knowledge to print the correct bitwise enum to the end user rather than "<unknown>".

This should ensure the current producer/consumer tools work well together (show complete information about those bitwise enums) without requiring to modify tons of documentation about the specific flags needed for bt2 to handle lttng traces appropriately. And this would not lead to misleading scenarios where we print an unknown value as a bitwise enum by mistake.

Hardcoded producer detection/event/fields is of course a last resort solution awaiting proper self-description in the upcoming CTF2 spec.