Re: [PATCH v2] docs: ftrace: clarify when tracing is disabled by the trace file
From: Steven Rostedt
Date: Sat Aug 31 2019 - 11:58:40 EST
On Sat, 31 Aug 2019 16:35:00 +0100
Peter Wu <peter@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx
> Signed-off-by: Peter Wu <peter@xxxxxxxxxxxxx>
Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Jon care to take this in your tree?
> 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.
> @@ -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.
> @@ -3153,7 +3155,10 @@ different. The trace is live.
> Note, reading the trace_pipe file will block until more input is
> +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