SyslogBackend

SyslogBackend implements mw::log::detail::Backend and is the Linux counterpart of the QNX SlogBackend: it is selected by SyslogRecorderFactory when the configured log mode contains kSystem and the target platform is Linux (target_compatible_with = ["@platforms//os:linux"]), wrapping it in a TextRecorder the same way SlogBackend is wrapped on QNX.

Like SlogBackend, it stores LogRecords in a CircularAllocator between ReserveSlot() and FlushSlot(). ReserveSlot() and GetLogRecord() only hand out and look up slots in that buffer; no data leaves the process until FlushSlot() is called.

FlushSlot() converts the LogRecord’s LogLevel to a syslog(3) priority via ConvertMwLogLevelToSyslogPriority() and forwards the record’s app ID, context ID and payload to the injected score::os::Syslog seam as a single syslog(priority, "%.*s,%.*s: %.*s", ...) call, which glibc delivers through vsyslog(3). LogLevel::kOff (and any out-of-range level) maps to SyslogPriority::kInvalid and is dropped instead of being forwarded, mirroring SlogBackend’s handling of its own invalid level.

The score::os::Syslog seam is opened once, in the constructor’s Init(), via openlog(app_id, LOG_PID | LOG_NDELAY, LOG_USER); the object-seam wrapper (Syslog interface / SyslogImpl / MockSyslog) is what makes SyslogBackend host-unit-testable without a real syslog daemon.

The sequence below shows a single log call from LogStream construction through to the syslog(3) call made when the stream is destroyed and the slot is flushed: