tracepoint: Have tracepoints created with DECLARE_TRACE() have _tp suffix

Most tracepoints in the kernel are created with TRACE_EVENT(). The
TRACE_EVENT() macro (and DECLARE_EVENT_CLASS() and DEFINE_EVENT() where in
reality, TRACE_EVENT() is just a helper macro that calls those other two
macros), will create not only a tracepoint (the function trace_<event>()
used in the kernel), it also exposes the tracepoint to user space along
with defining what fields will be saved by that tracepoint.

There are a few places that tracepoints are created in the kernel that are
not exposed to userspace via tracefs. They can only be accessed from code
within the kernel. These tracepoints are created with DEFINE_TRACE()

Most of these tracepoints end with "_tp". This is useful as when the
developer sees that, they know that the tracepoint is for in-kernel only
(meaning it can only be accessed inside the kernel, either directly by the
kernel or indirectly via modules and BPF programs) and is not exposed to
user space.

Instead of making this only a process to add "_tp", enforce it by making
the DECLARE_TRACE() append the "_tp" suffix to the tracepoint. This
requires adding DECLARE_TRACE_EVENT() macros for the TRACE_EVENT() macro
to use that keeps the original name.

Link: https://lore.kernel.org/all/20250418083351.20a60e64@gandalf.local.home/

Cc: netdev <netdev@vger.kernel.org>
Cc: Jiri Olsa <olsajiri@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: David Ahern <dsahern@kernel.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Breno Leitao <leitao@debian.org>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Gabriele Monaco <gmonaco@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/20250510163730.092fad5b@gandalf.local.home
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 11 insertions, 6 deletions

diff --git a/Documentation/trace/tracepoints.rst b/Documentation/trace/tracepoints.rst
index decabcc77b56..b35c40e3abbe 100644
--- a/Documentation/trace/tracepoints.rst
+++ b/Documentation/trace/tracepoints.rst
@@ -71,7 +71,7 @@ In subsys/file.c (where the tracing statement must be added)::
 	void somefct(void)
 	{
 		...
-		trace_subsys_eventname(arg, task);
+		trace_subsys_eventname_tp(arg, task);
 		...
 	}
 
@@ -129,12 +129,12 @@ within an if statement with the following::
 		for (i = 0; i < count; i++)
 			tot += calculate_nuggets();
 
-		trace_foo_bar(tot);
+		trace_foo_bar_tp(tot);
 	}
 
-All trace_<tracepoint>() calls have a matching trace_<tracepoint>_enabled()
+All trace_<tracepoint>_tp() calls have a matching trace_<tracepoint>_enabled()
 function defined that returns true if the tracepoint is enabled and
-false otherwise. The trace_<tracepoint>() should always be within the
+false otherwise. The trace_<tracepoint>_tp() should always be within the
 block of the if (trace_<tracepoint>_enabled()) to prevent races between
 the tracepoint being enabled and the check being seen.
 
@@ -143,7 +143,10 @@ the static_key of the tracepoint to allow the if statement to be implemented
 with jump labels and avoid conditional branches.
 
 .. note:: The convenience macro TRACE_EVENT provides an alternative way to
-      define tracepoints. Check http://lwn.net/Articles/379903,
+      define tracepoints. Note, DECLARE_TRACE(foo) creates a function
+      "trace_foo_tp()" whereas TRACE_EVENT(foo) creates a function
+      "trace_foo()", and also exposes the tracepoint as a trace event in
+      /sys/kernel/tracing/events directory.  Check http://lwn.net/Articles/379903,
       http://lwn.net/Articles/381064 and http://lwn.net/Articles/383362
       for a series of articles with more details.
 
@@ -159,7 +162,9 @@ In a C file::
 
 	void do_trace_foo_bar_wrapper(args)
 	{
-		trace_foo_bar(args);
+		trace_foo_bar_tp(args); // for tracepoints created via DECLARE_TRACE
+					//   or
+		trace_foo_bar(args);    // for tracepoints created via TRACE_EVENT
 	}
 
 In the header file::