Logging
Consistent logging makes debugging tractable across a large kernel codebase.
Use log crate macros exclusively (log-crate-only)
The project standardizes on the
log crate’s macros:
trace!, debug!, info!, warn!, error!.
Custom output functions, println!,
and hand-rolled serial print macros
are not acceptable in production code.
Exception: code that runs before the logging subsystem
is initialized may use early-boot output helpers.
// Good
log::info!("VirtIO block device initialized: {} sectors", num_sectors);
// Bad
println!("VirtIO block device initialized: {} sectors", num_sectors);Choose appropriate log levels (log-levels)
| Level | Use for |
|---|---|
trace! | High-frequency events: every interrupt, every packet, every page fault. |
debug! | Development diagnostics: state transitions, intermediate values. |
info! | Rare, noteworthy events: subsystem initialization, configuration changes. |
warn! | Recoverable problems: fallback paths taken, deprecated usage detected. |
error! | Serious failures: resource exhaustion, invariant violations caught at runtime. |
A log statement that fires on every syscall
or every timer tick must use trace!, not debug!.
See also: PR #2260.