Driver Logging

Caution: This page may contain information that is specific to the legacy version of the driver framework (DFv1).

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 platform configuration in product assembly. An assembly platform configuration can be specified in either the product or through developer overrides for product assembly.

To set this through developer overrides for product assembly, use the following in //local/BUILD.gn:

# //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.

Note: There is both producer and consumer filtering applied to logs. The above covers the producer-side, for more information on the consumer-side, and on how to view driver logs, see viewing logs.