Driver Logging

You can have a driver send log messages to the syslog through the use of the zxlogf(<log_level>,...) macro, which is defined in lib/ddk/debug.h.

Depending on the type of log level, by default, log messages are sent to the following logs:

• syslog:
  • ERROR
  • WARNING
  • INFO

To control which log levels are sent to the syslog, you can use the assembly platform configuration . An assembly platform configuration can be specified in either the product or via assembly overrides.

For example, you can make a //local/BUILD.gn file:

# //local/BUILD.gn:
assembly_developer_overrides("sdhci-debug-logs") {
    platform = {
        diagnostics = {
            component_log_initial_interests = [
                {
                    component = "fuchsia-boot:///sdhci#meta/sdhci.cm"
                    log_severity = "debug"
                },
            ]
        }
    }
}

Then use fx set to set the assembly-override:

fx set <product.board> --assembly-override=//local:sdhci-debug-logs

Additionally, this enables DEBUG and TRACE logs for the sdhci driver, as we are setting a minimum log level, and TRACE is lower than DEBUG.

A driver's logs are tagged with the process name, "driver", and the driver name. This can be used to filter the output of the syslog whilst searching for particular logs.