KTR provides a circular buffer of events that can be logged in a printf(9) style fashion. These events can then be dumped with ddb(4), gdb(1) or ktrdump(8).
Events are created and logged in the kernel via the CTR x macros. The first parameter is a mask of event types (KTR_*) defined in
.In sys/ktr.h . The event will be logged only if any of the event types specified in mask are enabled in the global event mask stored in ktr_mask. The format argument is a printf(9) style format string used to build the text of the event log message. Following the format string are zero to five arguments referenced by format. Note that the different macros differ only in the number of arguments each one takes, as indicated by its name. Each event is logged with a timestamp in addition to the log message.
The ktr_entries variable contains the number of entries in the ktr_buf array. These variables are mostly useful for post-mortem crash dump tools to locate the base of the circular trace buffer and its length.
The ktr_mask variable contains the run time mask of events to log.
The CPU event mask is stored in the ktr_cpumask variable.
The ktr_verbose variable stores the verbose flag that controls whether events are logged to the console in addition to the event buffer.
This example demonstrates the use of tracepoints at the KTR_PROC logging level.
* Pick a new current process and record its start time.
CTR3(KTR_PROC, "mi_switch: old proc %p (pid %d, %s)", p, p->p_pid,
CTR3(KTR_PROC, "mi_switch: new proc %p (pid %d, %s)", p, p->p_pid,