freebsd/share/man/man9/ktr.9

.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org>
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.Dd February 15, 2001
.Dt KTR 9
.Os
.Sh NAME
.Nm CTR0 , CTR1 , CTR2 , CTR3 , CTR4 , CTR5
.Nd kernel tracing facility
.Sh SYNOPSIS
.In sys/param.h
.In sys/ktr.h
.Vt "extern int ktr_cpumask" ;
.Vt "extern int ktr_entries" ;
.Vt "extern int ktr_extend" ;
.Vt "extern int ktr_mask" ;
.Vt "extern int ktr_verbose" ;
.Vt "extern struct ktr_entry ktr_buf[]" ;
.Ft void
.Fn CTR0 "u_int mask" "char *format"
.Ft void
.Fn CTR1 "u_int mask" "char *format" "arg1"
.Ft void
.Fn CTR2 "u_int mask" "char *format" "arg1" "arg2"
.Ft void
.Fn CTR3 "u_int mask" "char *format" "arg1" "arg2" "arg3"
.Ft void
.Fn CTR4 "u_int mask" "char *format" "arg1" "arg2" "arg3" "arg4"
.Ft void
.Fn CTR5 "u_int mask" "char *format" "arg1" "arg2" "arg3" "arg4" "arg5"
.Sh DESCRIPTION
KTR provides a circular buffer of events that can be logged in a
.Xr printf 9
style
fashion.
These events can then be dumped either via
.Xr ddb 4
or
.Xr gdb 1 .
.Pp
Events are created and logged in the kernel via the
.Dv CTR Ns Ar x
macros.
The first parameter is a mask of event types
.Pq Dv KTR_*
defined in
.Aq Pa sys/ktr.h .
The event will be logged only if any of the event types specified in
.Fa mask
are enabled in the global event mask stored in
.Va ktr_mask .
The
.Fa format
argument is a
.Xr printf 9
style format string used to build the text of the event log message.
Following the
.Fa format
string are zero to five arguments referenced by
.Fa format .
Note that the different macros differ only in the number of arguments each
one takes, as indicated by its name.
Each event is logged with a timestamp in addition to the log message.
.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_mask
variable contains the run time mask of events to log.
.Pp
The kernel can be configured to compile with several extensions to the base
functionality.
These extensions can be checked for at runtime via the
.Va ktr_extend
variable.
It will be set to zero if the extensions are not compiled in and non-zero
if they are compiled in.
This is useful for post-mortem debugging tools such as
.Xr gdb 1
that are used to analyze kernel crash dumps.
.Pp
The CPU event mask is stored in the
.Va ktr_cpumask
variable.
.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 the use of tracepoints at the
.Dv KTR_PROC
logging level.
.Bd -literal -offset indent
void
mi_switch()
{
	...
	/*
	 * Pick a new current process and record its start time.
	 */
	...
	CTR3(KTR_PROC, "mi_switch: old proc %p (pid %d, %s)", p, p->p_pid,
	    p->p_comm);
	...
	cpu_switch();
	...
	CTR3(KTR_PROC, "mi_switch: new proc %p (pid %d, %s)", p, p->p_pid,
	    p->p_comm);
	...
}
.Ed
.Sh SEE ALSO
.Xr ktr 4
.Sh HISTORY
The KTR kernel tracing facility first appeared in
.Bsx 3.0
and was imported into
.Fx 5.0 .
.Sh 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.