Commit f12fcca6 authored by Peter Wu's avatar Peter Wu Committed by Jonathan Corbet
Browse files

docs: ftrace: clarify when tracing is disabled by the trace file 

The current text could mislead the user into believing that only read()
disables tracing. Clarify that any open() call that requests read access
disables tracing.

Link: https://lkml.kernel.org/r/CAADnVQ+hU6QOC_dPmpjnuv=9g4SQEeaMEMqXOS2WpMj=q=LdiQ@mail.gmail.com


Signed-off-by: default avatarPeter Wu <peter@lekensteyn.nl>
Acked-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 5aff7c46

Documentation/trace/ftrace.rst

+9 −4
Original line number Diff line number Diff line
@@ -125,7 +125,8 @@ 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 while this file is being read (opened).

	disabled when the file is open for reading. Once all readers

	are closed, tracing is re-enabled.



  trace_pipe:
@@ -139,8 +140,9 @@ of ftrace. Here is a list of some of the key files: 
	will not be read again with a sequential read. The

	"trace" file is static, and if the tracer is not

	adding more data, it will display the same

	information every time it is read. This file will not

	disable tracing while being read.

	information every time it is read. Unlike the

	"trace" file, opening this file for reading will not

	temporarily disable tracing.



  trace_options:
@@ -3153,7 +3155,10 @@ different. The trace is live. 




Note, reading the trace_pipe file will block until more input is

added.

added. This is contrary to the trace file. If any process opened

the trace file for reading, it will actually disable tracing and

prevent new entries from being added. The trace_pipe file does

not have this limitation.



trace entries

-------------

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