CTR69

Usage

Overview

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) (ports/devel/gdb) or ktrdump(8).

Events are created and logged in the kernel via the CTR and CTRx macros. The first parameter is a mask of event types (KTR_*) defined in ⟨sys/ktr_class.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 six arguments referenced by format. Each event is logged with a file name and source line number of the originating CTR call, and a timestamp in addition to the log message.

The event is stored in the circular buffer with supplied arguments as is, and formatting is done at the dump time. Do not use pointers to the objects with limited lifetime, for instance, strings, because the pointer may become invalid when buffer is printed.

The CTRx macros differ only in the number of arguments each one takes, as indicated by its name.

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.

Examples

This example demonstrates the use of tracepoints at the KTR_PROC logging level.

void
mi_switch()
{
	...
	/*
	 * Pick a new current process and record its start time.
	 */
	...
	CTR3(KTR_PROC, "mi_switch: old proc %p (pid %d)", p, p->p_pid);
	...
	cpu_switch();
	...
	CTR3(KTR_PROC, "mi_switch: new proc %p (pid %d)", p, p->p_pid);
	...
}