kernel: make logging callback global #34775

1. 
   stickies-v commented at 8:35 am on March 9, 2026: contributor

   The underlying LogInstance() is a process-wide singleton, and all logging configuration (categories, levels, options) are already global. The per-connection btck_LoggingConnection handle gives the false impression of independent logger instances.

   Fix this by explicitly making the entire kernel logging interface explicitly global, simplifying its usage. Replaces btck_LoggingConnection and its {create,destroy} functions with a single btck_logging_set_callback function. The KernelLogger class is introduced to hold global kernel logging state, which will be used in future work such as #34374.

   To an extent, this approach is an alternative to #30342 which contextualizes logging. While I do believe contextualized logging would be a natural fit for the kernel interface, it seems there is currently (in my view) too little demand for the scope of changes necessary. That’s why I’ve opened this PR as a much more straightforward way to fix kernel’s current logging weirdness. If you believe kernel logging should be contextualized right away, please go review #30342 instead.

2. kernel: make logging callback global

   The underlying LogInstance() is a process-wide singleton, and all
   logging configuration (categories, levels, options) are already
   global. The per-connection btck_LoggingConnection handle gives the
   false impression of independent logger instances.
   
   Replace btck_logging_connection_create/destroy with a single
   btck_logging_set_callback that sets or clears the global callback.
   Internally, a KernelLogger singleton manages the LoggingConnection
   lifetime, intentionally leaked on exit to avoid static destruction
   order issues (matching LogInstance).

   dafe5eec14
3. DrahtBot added the label Validation on Mar 9, 2026
4. 
   DrahtBot commented at 8:36 am on March 9, 2026: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Reviews

   See the guideline for information on the review process.

   Type	Reviewers
   Concept ACK	sedited

   If your review is incorrectly listed, please copy-paste <!–meta-tag:bot-skip–> into the comment that the bot should ignore.

   LLM Linter (✨ experimental)

   Possible places where named args for integral literals may be used (e.g. func(x, /*named_arg=*/0) in C++, and func(x, named_arg=0) in Python):

   • g_kernel_logger().SetCallback(nullptr, nullptr, nullptr) in src/kernel/bitcoinkernel.cpp
   • btck_logging_set_callback(nullptr, nullptr, nullptr) in src/kernel/bitcoinkernel_wrapper.h

   2026-03-09 08:36:13

5. 
   sedited commented at 11:12 am on March 9, 2026: contributor

   While I do believe contextualized logging would be a natural fit for the kernel interface, it seems there is currently (in my view) too little demand for the scope of changes necessary.

   It really isn’t a feature/issue that is sorely missed for the foreseeable future in the kernel library. There are a few applications where it would be a nice to have. Logs coming from different sources, for example in the units tests, can be a little confusing sometimes, but even that has been manageable, and I don’t think I’ve heard many complain about that.

   Not having separate connections seems simpler. Clients of the library can still multiplex the single callback on their side in whatever fashion they wish to. There are many other (and more interesting problems imo) to be working on, so this seems like the pragmatic thing to do for now.

   Concept ACK

6. sedited requested review from alexanderwiederin on Mar 9, 2026

Contributors
stickies-v DrahtBot sedited

Review Requested
alexanderwiederin

Labels
Validation