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.\" $FreeBSD: src/share/man/man9/ktr.9,v 1.8 2005/03/08 01:37:36 hmp Exp $
.\" $DragonFly: src/share/man/man9/ktr.9,v 1.11 2008/01/08 17:45:43 swildner Exp $
.\"
.Dd January 8, 2008
.Dt KTR 9
.Os
.Sh NAME
.Nm KTR_INFO_MASTER ,
.Nm KTR_INFO ,
.Nm KTR_LOG ,
.Nm KTR_LOG_PTR
.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 "compile" "master" "name" "maskbit" "format" "datasize"
.Fn KTR_LOG "info" "arg ..."
.Fn KTR_LOG_PTR "info" "ptr"
.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.
.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
.Xr kprintf 9
style format string used to build the text of the event log message while
.Fa datasize
specifies the size of the data to be logged, either the total size of the
arguments required by the
.Fa format
string or the size of the data pointer
.Fa ptr .
For logging a fixed string with
.Fn KTR_INFO ,
.Fa datasize
is 0.
The
.Fa maskbit
is currently unused and can be set to 0.
.Pp
Kernel events are logged via the
.Fn KTR_LOG
and
.Fn KTR_LOG_PTR
macros.
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.
The
.Fn KTR_LOG_PTR
macro behaves similarly but takes a single data pointer
.Fa ptr
instead.
.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()", 0);
KTR_INFO(KTR_FOO, foo, func2, 1, "func2(%d)", sizeof(int));

\&...

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

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