Here is some documentation explaining what is/how to use the Linux Kernel Markers. Changelog: - Move the examples to a separate "samples" patch. Signed-off-by: Mathieu Desnoyers Acked-by: "Frank Ch. Eigler" CC: Christoph Hellwig --- Documentation/markers.txt | 81 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) Index: linux-2.6-lttng/Documentation/markers.txt =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-2.6-lttng/Documentation/markers.txt 2007-09-24 17:44:56.000000000 -0400 @@ -0,0 +1,81 @@ + Using the Linux Kernel Markers + + Mathieu Desnoyers + + +This document introduces Linux Kernel Markers and their use. It provides +examples of how to insert markers in the kernel and connect probe functions to +them and provides some examples of probe functions. + + +* Purpose of markers + +A marker placed in code provides a hook to call a function (probe) that you can +provide at runtime. A marker can be "on" (a probe is connected to it) or "off" +(no probe is attached). When a marker is "off" it has no effect, except for +adding a tiny time penalty (checking a condition for a branch) and space +penalty (adding a few bytes for the function call at the end of the +instrumented function and adds a data structure in a separate section). When a +marker is "on", the function you provide is called each time the marker is +executed, in the execution context of the caller. When the function provided +ends its execution, it returns to the caller (continuing from the marker site). + +You can put markers at important locations in the code. Markers are +lightweight hooks that can pass an arbitrary number of parameters, +described in a printk-like format string, to the attached probe function. + +They can be used for tracing and performance accounting. + + +* Usage + +In order to use the macro trace_mark, you should include linux/marker.h. + +#include + +And, + +trace_mark(subsystem_event, "%d %s", someint, somestring); +Where : +- subsystem_event is an identifier unique to your event + - subsystem is the name of your subsystem. + - event is the name of the event to mark. +- "%d %s" is the formatted string for the serializer. +- someint is an integer. +- somestring is a char pointer. + +Connecting a function (probe) to a marker is done by providing a probe (function +to call) for the specific marker through marker_probe_register() and can be +activated by calling marker_arm(). Marker deactivation can be done by calling +marker_disarm() as many times as marker_arm() has been called. Removing a probe +is done through marker_probe_unregister(); it will disarm the probe and make +sure there is no caller left using the probe when it returns. Probe removal is +preempt-safe because preemption is disabled around the probe call. See the +"Probe example" section below for a sample probe module. + +The marker mechanism supports inserting multiple instances of the same marker. +Markers can be put in inline functions, inlined static functions, and +unrolled loops as well as regular functions. + +The naming scheme "subsystem_event" is suggested here as a convention intended +to limit collisions. Marker names are global to the kernel: they are considered +as being the same whether they are in the core kernel image or in modules. +Conflicting format strings for markers with the same name will cause the markers +to be detected to have a different format string not to be armed and will output +a printk warning which identifies the inconsistency: + +"Format mismatch for probe probe_name (format), marker (format)" + + +* Probe / marker example + +See the example provided in samples/markers/src + +Compile them with your kernel. + +Run, as root : +modprobe marker-example (insmod order is not important) +modprobe probe-example +cat /proc/marker-example (returns an expected error) +rmmod marker-example probe-example +dmesg -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/