docs: ftrace: Specifies when buffers get clear (d693b288) · Commits · 戴 / test

Clarify a few places where the ring buffer and the "snapshot" buffer are cleared as a side effect of an operation. This will avoid users lost of tracing data because of these so far undocumented behavior. Signed-off-by:

Frank A. Cancio Bello <frank@generalsoftwareinc.com> Reviewed-by:

Steven Rostedt (VMware) <rostedt@goodmis.org> Link: https://lore.kernel.org/r/20191218191553.q4lwyxmquvtjzjfz@frank-laptop Signed-off-by:

Jonathan Corbet <corbet@lwn.net>

Documentation/trace/ftrace.rst

+7 −2

Original line number	Diff line number	Diff line
		@@ -95,7 +95,8 @@ of ftrace. Here is a list of some of the key files:
		current_tracer:

		This is used to set or display the current tracer
		that is configured.
		that is configured. Changing the current tracer clears
		the ring buffer content as well as the "snapshot" buffer.

		available_tracers:

		@@ -126,7 +127,8 @@ of ftrace. Here is a list of some of the key files:
		This file holds the output of the trace in a human
		readable format (described below). Note, tracing is temporarily
		disabled when the file is open for reading. Once all readers
		are closed, tracing is re-enabled.
		are closed, tracing is re-enabled. Opening this file for
		writing with the O_TRUNC flag clears the ring buffer content.

		trace_pipe:

		@@ -490,6 +492,9 @@ of ftrace. Here is a list of some of the key files:

		# echo global > trace_clock

		Setting a clock clears the ring buffer content as well as the
		"snapshot" buffer.

		trace_marker:

		This is a very useful file for synchronizing user space

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