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

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

     #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[];

     CTR0(u_int	mask, char *format);

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

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

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

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

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

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

     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 ar-
     gument 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 argu-
     ments referenced by format.  Each event is	logged with a file name	and
     source line number	of the originating CTR call, and a timestamp in	addi-
     tion 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 ob-
     jects 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.

     This example demonstrates the use of tracepoints at the KTR_PROC logging

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

     ktr(4), ktrdump(8)

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

     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.

FreeBSD	13.0		       November	30, 2008		  FreeBSD 13.0


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