All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
$FreeBSD: head/share/man/man4/ktr.4 74013 2001-03-09 03:43:18Z jhb $
.Dd February 16, 2001 .Dt KTR 4 .Os .Sh NAME .Nm ktr .Nd kernel tracing facility .Sh SYNOPSIS .Cd options KTR .Cd options KTR_COMPILE=(KTR_LOCK|KTR_INTR|KTR_PROC) .Cd options KTR_CPUMASK=0x3 .Cd options KTR_ENTRIES=8192 .Cd options KTR_EXTEND .Cd options KTR_MASK=(KTR_INTR|KTR_PROC) .Cd options KTR_VERBOSE .Sh DESCRIPTION The .Nm facility allows kernel events to be logged while the kernel executes so that they can be examined later when debugging. The only mandatory option to enable .Nm is "options KTR".
p The "KTR_ENTRIES" option sets the size of the buffer of events. It should be a power of two. The size of the buffer in the currently running kernel can be found via the read-only sysctl .Sy debug.ktr.entries . By default the buffer contains 1024 entries. .Ss Event Masking Event levels can be enabled or disabled to trim excessive and overly verbose logging. First, a mask of events is specified at compile time via the "KTR_COMPILE" option to limit which events are actually compiled into the kernel. The default value for this option is for all events to be enabled.
p Secondly, the actual events logged while the kernel runs can be further masked via the run time event mask. The "KTR_MASK" option sets the default value of the run time event mask. The runtime event mask can also be set by the .Xr loader 8 via the .Sy debug.ktr.mask environment variable. It can also be examined and set after booting via the .Sy debug.ktr.mask sysctl. By default the run time mask is set to log only .Dv KTR_GEN events. The definitions of the event mask bits can be found in .Aq Pa sys/ktr.h . .Ss Extensions The kernel can be configured to compile with several extensions to the base functionality via the "KTR_EXTEND" option. These extensions can be checked for via the .Sy debug.ktr.extend read-only sysctl. It will be set to zero if the extensions are not compiled in and non-zero if they are compiled in. If the extensions are compiled in, then each event entry includes the filename and line number that the event was logged from as well as the CPU on which the current thread was executing when the event was logged.
p One extension is a CPU event mask whose default value can be changed via the "KTR_CPUMASK" option. A CPU must have the bit corresponding to its logical id set in this bitmask for events that occur on it to be logged. This mask can be set by the .Xr loader 8 via the .Sy debug.ktr.cpumask environment variable. It can also be examined and set after booting via the .Sy debug.ktr.cpumask sysctl. By default events on all CPUs are enabled.
p The log messages go through more processing at log time when the extensions are enabled as well. In the basic mode, the format string and arguments are stored directly in the event entry. In the extended mode, .Xr snprintf 9 is invoked and the resulting string is stored directly in the event entry. This extra processing is more expensive in terms of execution but produces events that are arguably more readable and easier to parse for some utilities such as .Xr ddb 4 .
p By default, events are only logged to the internal buffer for examination later, but if the verbose flag is set then they are dumped to the kernel console as well. This flag can also be set from the loader via the .Sy debug.ktr.verbose environment variable, or it can be examined and set after booting via the .Sy debug.ktr.verbose sysctl. If the flag is set to zero, which is the default, then verbose output is disabled. If the flag is set to one, then the contents of the log message and the CPU number are printed to the kernel console. If the flag is greater than one, then the filename and line number of the event are output to the console in addition to the log message and the CPU number. The "KTR_VERBOSE" option sets the flag to one. .Ss Examining the Events
p The KTR buffer can be examined from within .Xr ddb 4 via the c show ktr Op Ic /v command. This command displays the contents of the trace buffer one page at a time. At the .Dq --more-- prompt, the Enter key displays one more entry and prompts again. The spacebar displays another page of entries. Any other key quits. By default the timestamp, filename, and line number are not displayed with each log entry. If the .Op Ic /v modifier is specified, then they are displayed in addition to the normal output. Note that the events are displayed in reverse chronological order. That is, the most recent events are displayed first. .Sh SEE ALSO .Xr ktr 9 .Sh HISTORY The KTR kernel tracing facility first appeared in .Tn BSD/OS and was imported into .Fx 5.0 . .Sh BUGS Currently there is no userland utility outside of a gdb script to extract the event buffer from a kernel crash dump or a running kernel.