Add documentation about the newly introduced tracing remotes framework.
Signed-off-by: Vincent Donnefort <[email protected]>
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..1f9d764f69aa
--- /dev/null
+++ b/Documentation/trace/remotes.rst
@@ -0,0 +1,66 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+Tracing Remotes
+===============
+
+:Author: Vincent Donnefort <[email protected]>
+
+Overview
+========
+Firmware and hypervisors are black boxes to the kernel. Having a way to see
what
+they are doing can be useful to debug both. This is where remote tracing
buffers
+come in. A remote tracing buffer is a ring buffer executed by the firmware or
+hypervisor into memory that is memory mapped to the host kernel. This is
similar
+to how user space memory maps the kernel ring buffer but in this case the
kernel
+is acting like user space and the firmware or hypervisor is the "kernel" side.
+With a trace remote ring buffer, the firmware and hypervisor can record events
+for which the host kernel can see and expose to user space.
+
+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
+
+Once registered, an instance will appear for this remote in the Tracefs
+directory **remotes/**. Buffers can then be read using the usual Tracefs files
+**trace_pipe** and **trace**.
+
+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`.
+
+Registered events appear in the remote directory under **events/**.
+
+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
--
2.53.0.rc1.225.gd81095ad13-goog
