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.\" $FreeBSD: src/share/man/man9/ktr.9,v 1.8 2005/03/08 01:37:36 hmp Exp $
.\"
.Dd August 22, 2012
.Dt KTR 9
.Os
.Sh NAME
.Nm KTR_INFO_MASTER ,
.Nm KTR_INFO_MASTER_EXTERN ,
.Nm KTR_INFO ,
.Nm KTR_LOG ,
.Nm KTR_COND_LOG
.Nd kernel tracing facility
.Sh SYNOPSIS
.In sys/ktr.h
.Vt "extern int ktr_entries" ;
.Vt "extern int ktr_verbose" ;
.Vt "extern struct ktr_entry *ktr_buf[MAXCPU]" ;
.Fn KTR_INFO_MASTER "master"
.Fn KTR_INFO_MASTER_EXTERN "master"
.Fn KTR_INFO "compile" "master" "name" "maskbit" "format" "type name" "..."
.Fn KTR_LOG "info" "arg ..."
.Fn KTR_COND_LOG "info" "cond" "arg ..."
.Sh DESCRIPTION
The
.Nm ktr
facility provides a circular buffer of events that can be logged in a
.Xr kprintf 9
style fashion.
These events can then be dumped with
.Xr ddb 4 ,
.Xr gdb 1
or
.Xr ktrdump 8 .
.Pp
.Fn KTR_INFO_MASTER
declares a new master variable
.Dv ktr Ns _ Ns Fa master Ns _ Ns Dv enable
that is used to turn on and off event logging.
.Fn KTR_INFO_MASTER_EXTERN
is a convenience macro for declaring a master variable
.Sy extern .
.Pp
The
.Fn KTR_INFO
macro registers a new event
.Fa name
that will be controlled by the
.Fa master
enable variable.
Code for logging this event will be compiled in when
.Fa compile
is defined.
The
.Fa format
argument is a format string in the manner of
.Xr kprintf 9
used to build the text of the event log message.
The arguments required by the format string have to be specified with a
.Fa type
and a
.Fa name .
The
.Fa maskbit
is a bit number that determines which of the corresponding
.Va debug.ktr.*_enable
sysctl's bits will enable logging of this event.
.Pp
Kernel events are logged via the
.Fn KTR_LOG
macro.
The
.Fa info
parameter is an identifier of the format
.Fa master Ns _ Ns Fa name .
.Fn KTR_LOG
accepts zero or more additional
.Fa arg
arguments as required by the
.Fa format
string passed to the associated
.Fn KTR_INFO
call.
.Pp
The
.Fn KTR_COND_LOG
macro is equivalent to
.Fn KTR_LOG
except it logs only when the condition specified in
.Fa cond
evaluates to true.
.Pp
The
.Va ktr_entries
variable contains the number of entries in the
.Va 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.
.Pp
The
.Va ktr_verbose
variable stores the verbose flag that controls whether events are logged to
the console in addition to the event buffer.
.Sh EXAMPLES
This example demonstrates a simple usage of the KTR facility:
.Pp
.Bd -literal -compact
#include <sys/ktr.h>

\&...

#if !defined(KTR_FOO)
#define KTR_FOO		KTR_ALL
#endif
KTR_INFO_MASTER(foo);
KTR_INFO(KTR_FOO, foo, func1, 0, "func1()");
KTR_INFO(KTR_FOO, foo, func2, 1, "func2(%d)", int arg);
KTR_INFO(KTR_FOO, foo, func3, 2, "func3: arg positive: %d", int arg);

\&...

void
func1(void)
{
	KTR_LOG(foo_func1);
	...
}

void
func2(int arg)
{
	KTR_LOG(foo_func2, arg);
	...
}

void
func3(int arg)
{
	KTR_COND_LOG(foo_func3, arg >= 0, arg);
	...
}
.Ed
.Sh SEE ALSO
.Xr gdb 1 ,
.Xr ddb 4 ,
.Xr ktr 4 ,
.Xr ktrdump 8 ,
.Xr kprintf 9
.Sh HISTORY
The
.Nm ktr
kernel tracing facility first appeared in
.Bsx 3.0
and was imported into
.Fx 5.0
and
.Dx 1.1 .
It was completely rewritten by Matthew Dillon in
.Dx 1.3 .