+++ /dev/null
-From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
-Subject: Tracepoints Documentation
-
-Documentation of tracepoint usage.
-
-Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
-Acked-by: 'Peter Zijlstra' <peterz@infradead.org>
-CC: Masami Hiramatsu <mhiramat@redhat.com>
-CC: "Frank Ch. Eigler" <fche@redhat.com>
-CC: 'Ingo Molnar' <mingo@elte.hu>
-CC: 'Hideo AOKI' <haoki@redhat.com>
-CC: Takashi Nishiie <t-nishiie@np.css.fujitsu.com>
-CC: 'Steven Rostedt' <rostedt@goodmis.org>
-CC: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
-Acked-by: Jan Blunck <jblunck@suse.de>
----
- Documentation/tracepoints.txt | 101 ++++++++++++++++++++++++++++++++++++++++++
- 1 file changed, 101 insertions(+)
-
-Index: linux-2.6-lttng/Documentation/tracepoints.txt
-===================================================================
---- /dev/null 1970-01-01 00:00:00.000000000 +0000
-+++ linux-2.6-lttng/Documentation/tracepoints.txt 2008-07-18 12:15:32.000000000 -0400
-@@ -0,0 +1,101 @@
-+ Using the Linux Kernel Tracepoints
-+
-+ Mathieu Desnoyers
-+
-+
-+This document introduces Linux Kernel Tracepoints and their use. It provides
-+examples of how to insert tracepoints in the kernel and connect probe functions
-+to them and provides some examples of probe functions.
-+
-+
-+* Purpose of tracepoints
-+
-+A tracepoint placed in code provides a hook to call a function (probe) that you
-+can provide at runtime. A tracepoint can be "on" (a probe is connected to it) or
-+"off" (no probe is attached). When a tracepoint 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
-+tracepoint is "on", the function you provide is called each time the tracepoint
-+is executed, in the execution context of the caller. When the function provided
-+ends its execution, it returns to the caller (continuing from the tracepoint
-+site).
-+
-+You can put tracepoints at important locations in the code. They are
-+lightweight hooks that can pass an arbitrary number of parameters,
-+which prototypes are described in a tracepoint declaration placed in a header
-+file.
-+
-+They can be used for tracing and performance accounting.
-+
-+
-+* Usage
-+
-+Two elements are required for tracepoints :
-+
-+- A tracepoint definition, placed in a header file.
-+- The tracepoint statement, in C code.
-+
-+In order to use tracepoints, you should include linux/tracepoint.h.
-+
-+In include/trace/subsys.h :
-+
-+#include <linux/tracepoint.h>
-+
-+DEFINE_TRACE(subsys_eventname,
-+ TPPTOTO(int firstarg, struct task_struct *p),
-+ TPARGS(firstarg, p));
-+
-+In subsys/file.c (where the tracing statement must be added) :
-+
-+#include <trace/subsys.h>
-+
-+void somefct(void)
-+{
-+ ...
-+ trace_subsys_eventname(arg, task);
-+ ...
-+}
-+
-+Where :
-+- subsys_eventname is an identifier unique to your event
-+ - subsys is the name of your subsystem.
-+ - eventname is the name of the event to trace.
-+- TPPTOTO(int firstarg, struct task_struct *p) is the prototype of the function
-+ called by this tracepoint.
-+- TPARGS(firstarg, p) are the parameters names, same as found in the prototype.
-+
-+Connecting a function (probe) to a tracepoint is done by providing a probe
-+(function to call) for the specific tracepoint through
-+register_trace_subsys_eventname(). Removing a probe is done through
-+unregister_trace_subsys_eventname(); it will remove the probe 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 tracepoint mechanism supports inserting multiple instances of the same
-+tracepoint, but a single definition must be made of a given tracepoint name over
-+all the kernel to make sure no type conflict will occur. Name mangling of the
-+tracepoints is done using the prototypes to make sure typing is correct.
-+Verification of probe type correctness is done at the registration site by the
-+compiler. Tracepoints can be put in inline functions, inlined static functions,
-+and unrolled loops as well as regular functions.
-+
-+The naming scheme "subsys_event" is suggested here as a convention intended
-+to limit collisions. Tracepoint names are global to the kernel: they are
-+considered as being the same whether they are in the core kernel image or in
-+modules.
-+
-+
-+* Probe / tracepoint example
-+
-+See the example provided in samples/tracepoints/src
-+
-+Compile them with your kernel.
-+
-+Run, as root :
-+modprobe tracepoint-example (insmod order is not important)
-+modprobe tracepoint-probe-example
-+cat /proc/tracepoint-example (returns an expected error)
-+rmmod tracepoint-example tracepoint-probe-example
-+dmesg
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