[PATCH v7 16/28] Documentation: tracing: Add tracing remotes
From: Vincent Donnefort <hidden>
Date: 2025-10-03 13:39:14
Also in:
kvmarm, linux-arm-kernel, lkml
Subsystem:
documentation, the rest, tracing · Maintainers:
Jonathan Corbet, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
Add documentation about the newly introduced tracing remotes framework. Signed-off-by: Vincent Donnefort <redacted>
diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index b4a429dc4f7a..d77ffb7e2d08 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst@@ -90,6 +90,17 @@ interactions. user_events uprobetracer +Remote Tracing +-------------- + +This section covers the framework to read compatible ring-buffers, written by +entities outside of the kernel (most likely firmware or hypervisor) + +.. toctree:: + :maxdepth: 1 + + remotes + Additional Resources --------------------
diff --git a/Documentation/trace/remotes.rst b/Documentation/trace/remotes.rst
new file mode 100644
index 000000000000..e7fb3ee96c30
--- /dev/null
+++ b/Documentation/trace/remotes.rst@@ -0,0 +1,59 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +Tracing Remotes +=============== + +:Author: Vincent Donnefort <vdonnefort@google.com> + +Overview +======== +A trace remote relies on ring-buffer remotes to read and control compatible +tracing buffers, written by entity such as firmware or hypervisor. + +Once registered, a tracefs instance will appear for this remote in the Tracefs +directory **remotes/**. This remote can be read and controlled using the same +files as regular Tracefs instances such as **trace_pipe**, **tracing_on** or +**trace**. + +Register a remote +================= +A remote must provide a set of callbacks `struct trace_remote_callbacks` whom +description can be found below. Those callbacks allows Tracefs to enable and +disable tracing and events, to load and unload a tracing buffer (a set of +ring-buffers) and to swap a reader page with the head page, which enables +consuming reading. + +.. kernel-doc:: include/linux/trace_remote.h + +Declare a remote event +====================== +Macros are provided to ease the declaration of remote events, in a similar +fashion to in-kernel events. A declaration must provide an ID, a description of +the event arguments and how to print the event: + +.. code-block:: c + + REMOTE_EVENT(foo, EVENT_FOO_ID, + RE_STRUCT( + re_field(u64, bar) + ), + RE_PRINTK("bar=%lld", __entry->bar) + ); + +Then those events must be declared in a C file with the following: + +.. code-block:: c + + #define REMOTE_EVENT_INCLUDE_FILE foo_events.h + #include <trace/define_remote_events.h> + +This will provide a `struct remote_event remote_event_foo` that can be given to +`trace_remote_register`. + +Simple ring-buffer +================== +A simple implementation for a ring-buffer writer can be found in +kernel/trace/simple_ring_buffer.c. + +.. kernel-doc:: include/linux/simple_ring_buffer.h
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