Re: [PATCH v2] docs: ftrace: clarify when tracing is disabled by the trace file
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2019-08-31 15:58:39
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On Sat, 31 Aug 2019 16:35:00 +0100 Peter Wu [off-list ref] wrote:
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 <redacted>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Jon care to take this in your tree? Thanks! -- Steve
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--- v2: fix typo s/trace_file/trace_pipe/ (spotted by Steven) --- Documentation/trace/ftrace.rst | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index f60079259669..e3060eedb22d 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst@@ -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 -------------