Returning Errors

Device drivers do not usually print messages, except for unexpected errors such as data corruption. Instead, the driver entry points should return error codes so that the application can determine how to handle the error. If the driver must print a message, it should use cmn_err(9F) to do so. This is similar to the C function printf(3C), which prints to the console, to the message buffer, or both.

The format string specifier interpreted by cmn_err(9F) is similar to the printf(3C) format string, with the addition of the format %b, which prints bit fields. Callers to cmn_err(9F) also specify the level, which indicates the label to be printed. The first character of the format string is treated specially. See the cmn_err(9F) man page for more details.

The level CE_PANIC has the side effect of crashing the system. This level should be used only if the system is in such an unstable state that to continue would cause more problems. It can also be used to get a system core dump when debugging. It should not be used in production device drivers.