KTR(9)							   BSD Kernel Developer's Manual						    KTR(9)

NAME

     CTR0, CTR1, CTR2, CTR3, CTR4, CTR5 -- kernel tracing facility

SYNOPSIS

     #include <sys/param.h>
     #include <sys/ktr.h>

     extern int ktr_cpumask;
     extern int ktr_entries;
     extern int ktr_extend;
     extern int ktr_mask;
     extern int ktr_verbose;
     extern struct ktr_entry ktr_buf[];

     void
     CTR0(u_int mask, char *format);

     void
     CTR1(u_int mask, char *format, arg1);

     void
     CTR2(u_int mask, char *format, arg1, arg2);

     void
     CTR3(u_int mask, char *format, arg1, arg2, arg3);

     void
     CTR4(u_int mask, char *format, arg1, arg2, arg3, arg4);

     void
     CTR5(u_int mask, char *format, arg1, arg2, arg3, arg4, arg5);

     void
     CTR6(u_int mask, char *format, arg1, arg2, arg3, arg4, arg5, arg6);

DESCRIPTION

     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 CTRx macros.  The first parameter is a mask of event types (KTR_*) defined 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.  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.

     Note that the different 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);
	     ...
     }

SEE ALSO

     ktr(4), ktrdump(8)

HISTORY

     The KTR kernel tracing facility first appeared in BSD/OS 3.0 and was imported into FreeBSD 5.0.

BUGS

     Currently there is one global buffer shared among all CPUs.  It might be profitable at some point in time to use per-CPU buffers instead so
     that if one CPU halts or starts spinning, then the log messages it emitted just prior to halting or spinning will not be drowned out by
     events from the other CPUs.

     The arguments given in CTRx() macros are stored as u_long, so do not pass arguments larger than size of an u_long type.  For example passing
     64bit arguments on 32bit architectures will give incorrect results.

BSD
								 November 30, 2008							       BSD