1.\" Copyright (c) 2001 John H. Baldwin <jhb@FreeBSD.org> 2.\" 3.\" Redistribution and use in source and binary forms, with or without 4.\" modification, are permitted provided that the following conditions 5.\" are met: 6.\" 1. Redistributions of source code must retain the above copyright 7.\" notice, this list of conditions and the following disclaimer. 8.\" 2. Redistributions in binary form must reproduce the above copyright 9.\" notice, this list of conditions and the following disclaimer in the 10.\" documentation and/or other materials provided with the distribution. 11.\" 12.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 13.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 14.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 15.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 16.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 17.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 18.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 19.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 20.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 21.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 22.\" SUCH DAMAGE. 23.\" 24.\" $FreeBSD$ 25.\" 26.Dd April 12, 2022 27.Dt KTR 9 28.Os 29.Sh NAME 30.Nm CTR0 , CTR1 , CTR2 , CTR3 , CTR4 , CTR5 31.Nd kernel tracing facility 32.Sh SYNOPSIS 33.In sys/param.h 34.In sys/ktr.h 35.Vt "extern int ktr_cpumask" ; 36.Vt "extern int ktr_entries" ; 37.Vt "extern int ktr_extend" ; 38.Vt "extern int ktr_mask" ; 39.Vt "extern int ktr_verbose" ; 40.Vt "extern struct ktr_entry ktr_buf[]" ; 41.Ft void 42.Fn CTR "u_int mask" "char *format" "..." 43.Ft void 44.Fn CTR0 "u_int mask" "char *format" 45.Ft void 46.Fn CTR1 "u_int mask" "char *format" "arg1" 47.Ft void 48.Fn CTR2 "u_int mask" "char *format" "arg1" "arg2" 49.Ft void 50.Fn CTR3 "u_int mask" "char *format" "arg1" "arg2" "arg3" 51.Ft void 52.Fn CTR4 "u_int mask" "char *format" "arg1" "arg2" "arg3" "arg4" 53.Ft void 54.Fn CTR5 "u_int mask" "char *format" "arg1" "arg2" "arg3" "arg4" "arg5" 55.Ft void 56.Fn CTR6 "u_int mask" "char *format" "arg1" "arg2" "arg3" "arg4" "arg5" "arg6" 57.Sh DESCRIPTION 58KTR provides a circular buffer of events that can be logged in a 59.Xr printf 9 60style 61fashion. 62These events can then be dumped with 63.Xr ddb 4 , 64.Xr gdb 1 65or 66.Xr ktrdump 8 . 67.Pp 68Events are created and logged in the kernel via the 69.Dv CTR 70and 71.Dv CTR Ns Ar x 72macros. 73The first parameter is a mask of event types 74.Pq Dv KTR_* 75defined in 76.In sys/ktr_class.h . 77The event will be logged only if any of the event types specified in 78.Fa mask 79are enabled in the global event mask stored in 80.Va ktr_mask . 81The 82.Fa format 83argument is a 84.Xr printf 9 85style format string used to build the text of the event log message. 86Following the 87.Fa format 88string are zero to six arguments referenced by 89.Fa format . 90Each event is logged with a file name and source line number of the 91originating CTR call, and a timestamp in addition to the log message. 92.Pp 93The event is stored in the circular buffer with supplied arguments as is, 94and formatting is done at the dump time. 95Do not use pointers to the objects with limited lifetime, for instance, 96strings, because the pointer may become invalid when buffer is printed. 97.Pp 98The 99.Dv CTR Ns Ar x 100macros differ only in the number of arguments each 101one takes, as indicated by its name. 102.Pp 103The 104.Va ktr_entries 105variable contains the number of entries in the 106.Va ktr_buf 107array. 108These variables are mostly useful for post-mortem crash dump tools to locate 109the base of the circular trace buffer and its length. 110.Pp 111The 112.Va ktr_mask 113variable contains the run time mask of events to log. 114.Pp 115The CPU event mask is stored in the 116.Va ktr_cpumask 117variable. 118.Pp 119The 120.Va ktr_verbose 121variable stores the verbose flag that controls whether events are logged to 122the console in addition to the event buffer. 123.Sh EXAMPLES 124This example demonstrates the use of tracepoints at the 125.Dv KTR_PROC 126logging level. 127.Bd -literal 128void 129mi_switch() 130{ 131 ... 132 /* 133 * Pick a new current process and record its start time. 134 */ 135 ... 136 CTR3(KTR_PROC, "mi_switch: old proc %p (pid %d)", p, p->p_pid); 137 ... 138 cpu_switch(); 139 ... 140 CTR3(KTR_PROC, "mi_switch: new proc %p (pid %d)", p, p->p_pid); 141 ... 142} 143.Ed 144.Sh SEE ALSO 145.Xr ktr 4 , 146.Xr ktrdump 8 147.Sh HISTORY 148The KTR kernel tracing facility first appeared in 149.Bsx 3.0 150and was imported into 151.Fx 5.0 . 152.Pp 153The 154.Fn CTR 155macro accepting a variable number of arguments first appeared in 156.Fx 14.0 . 157.Sh BUGS 158Currently there is one global buffer shared among all CPUs. 159It might be profitable at some point in time to use per-CPU buffers instead 160so that if one CPU halts or starts spinning, then the log messages it 161emitted just prior to halting or spinning will not be drowned out by events 162from the other CPUs. 163.Pp 164The arguments given in 165.Fn CTRx 166macros are stored as 167.Vt u_long , 168so do not pass arguments larger than size of an 169.Vt u_long 170type. 171For example passing 64bit arguments on 32bit architectures will give incorrect 172results. 173