#34038 logging: replace -loglevel with -trace, expose trace logging via RPC

Replaces the `-loglevel` startup and configuration option with `-trace`, allowing `-trace=<category>` to enable both debug and trace logging using syntax identical to `-debug`. Extends the `logging` RPC to accept a `trace` parameter and updates its return object to categorize log settings into `excluded`, `debug`, and `trace` string arrays, providing `-deprecatedrpc=logging` for backwards compatibility.

Problem: Configuring trace-level logging required combining `-debug=<category>` with `-loglevel=<category>:trace`, while specifying `-loglevel` alone silently had no effect. Additionally, node operators could not inspect or dynamically change trace-level logging at runtime via the `logging` RPC.

Evidence of importance:

• Commit 2708138613 notes that previously 'trace logging for a category was enabled by saying "-debug=net -loglevel=net:trace" and saying "-loglevel=net:trace" (without "-debug" or "-debug=net") would silently do nothing.'
• Release notes highlight that 'The -loglevel configuration option has been removed' and the 'logging RPC command is now able to switch trace level logs on and off, via its third parameter' while changing the output format.

Scope: Completely removes the `-loglevel` configuration argument in favor of `-trace`, and alters the default output schema of the `logging` RPC (retaining the old schema behind `-deprecatedrpc=logging`).

Risk of a mistake: medium (rpc_api, other). A breaking change to the logging RPC output schema and the removal of the -loglevel startup argument could disrupt external monitoring tools or configuration scripts.

Changed since the previous assessment: Added dedicated release notes documenting the removal of `-loglevel` and the `logging` RPC format change.

Ready

Nothing known that would invalidate a review now.

Waiting on (from the thread read):

• decision: decision on approach: this PR's interacting -trace flag model versus ryanofsky's unified -loglevel proposal in #35387 2026-08-21
• decision: approach conflict between parallel flags (-debug/-trace) and unified -loglevel (#35387) 2026-08-21
• reviewer: re-review after rebase in c:6363461488 2026-10-23

Disputed

objection that needs a change, the objector pushed back after a reply (ryanofsky)

Thread notes: Re-classified ryanofsky's scope request as a suggestion (fixed by splitting PRs). Split ryanofsky's approach NACK into two parts (confusing interacting flags and impossible configurations), both marked contested following his pushback during milestone review. / Converted ryanofsky's scope objection to a suggestion, added part 2 to rc:2928796887 for stickies-v's suggestion on info terminology, and updated ryanofsky's approach NACK to contested following his pushback in c:5369066469.

Objections, suggestions, and questions:

Support:

• stickies-v (member) (Concept ACK, 2025-12-10) [read: -loglevel, BCLog::NO_RATE_LIMIT]: Both the new `BCLog::NO_RATE_LIMIT` and `-loglevel` changes make for a more natural and ergonomic interface for both developers and users, and the changes required are limited enough.
• stickies-v (member) (ACK, 2026-04-02) [read: -debug, -trace, RPC, rpc]: The new `-debug` and `-trace` startup options are a lot easier to use, and although I think the RPC interface is getting increasingly unwieldy, this seems to be the best approach minimizing breaking changes to expose the trace level there too.
• sedited (member) (Tested ACK, 2026-05-11) [tested]: tACK 5b114839c24f2298cd57c3d724f85f39400d6832 [not substantive]

Participants:

• stickies-v (member, support, 49 statements 2025-12-10 to 2026-07-04): ACKed after earlier concerns about PR scope and RPC interface complexity were resolved
• abo-L (none, neutral, 1 statements 2025-12-15 to 2025-12-15): posted a Bitcoin address
• ryanofsky (member, objection, 6 statements 2026-03-10 to 2026-08-21): approach NACK advocating for a unified -loglevel model in #35387 instead of interacting flags
• sedited (member, support, 4 statements 2026-05-11 to 2026-08-09): tested ACK and agreed with the current parallel flag design
• maflcko (member, neutral, 2 statements 2026-08-21 to 2026-08-21): process inquiry, moved PR milestone from 32.0 to 33.x

Enables:

• #35355

Base for: #35355

153 lines under test/bench/ci.

• src/rpc/node.cpp +74/-20
• test/functional/feature_logging.py +37/-22
• src/logging.cpp +48/-5
• src/test/logging_tests.cpp +29/-24
• src/init/common.cpp +18/-27
• test/functional/rpc_misc.py +21/-8
• src/logging.h +12/-14
• doc/release-notes-34038.md +13/-0
• doc/developer-notes.md +4/-5
• test/functional/test_framework/test_node.py +4/-1
• src/bench/logging.cpp +2/-2
• src/test/util/setup_common.cpp +1/-2
• src/rpc/client.cpp +2/-0
• src/wallet/sqlite.cpp +1/-1
• src/init.cpp +0/-1
• src/init/common.h +0/-1

The short text the ranking pass compares across PRs.

Replaces the -loglevel configuration option with -trace and exposes trace logging controls in the logging RPC. Previously, enabling trace logging required using both -debug and -loglevel options together because -loglevel alone silently did nothing, and trace logging could not be toggled at runtime via RPC. The logging RPC now supports a trace parameter and groups categories into excluded, debug, and trace arrays, preserving legacy output format under -deprecatedrpc=logging. PR #35355 builds on top of this change.

P3 · new feature (ranking pass: Moved down 12: competing with #35387 on the same problem and admin-only in scope, so it ranks below the correctness fixes despite unblocking #35355.)

Extending the logging RPC allows dynamic runtime inspection and toggling of trace-level logging, but alters the return schema requiring a deprecation path. While breaking changes to RPC output require reviewer scrutiny under RPC compatibility criteria, the logging endpoint is an administrative tool rather than a hot method used by downstream application infrastructure.

Membership: Updates src/rpc/node.cpp to accept a trace parameter in the logging RPC and alters its return object format, introducing a deprecation flag.

Factors: security/stability 0, bug 1, performance 0, user value 2, leverage 1

P3 · user request (ranking pass: Lowered within band: the -loglevel confusion is real but competing proposal #35387 means a decision, not just review, is needed.)

Resolves confusing logging configuration behavior where -loglevel alone would silently fail without -debug. Within the utilities rubric, addressing confusing logging options is explicitly valued, though the issue is not critical to node operation and is reasonably deferrable.

Membership: src/logging.cpp and src/init/common.cpp changes overhaul logging options and configuration handling by replacing -loglevel with -trace.

Factors: security/stability 0, bug 1, performance 0, user value 2, leverage 1