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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: Peter Wu <peter@lekensteyn.nl>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
alistair/sunxi64-5.4-dsi
Peter Wu 2019-08-31 16:35:00 +01:00 committed by Jonathan Corbet
parent 5aff7c4617
commit f12fcca653
1 changed files with 9 additions and 4 deletions
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13
Documentation/trace/ftrace.rst
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@ -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
-------------