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SubjectRe: [PATCH] docs: ftrace: clarify when tracing is disabled by the trace file
On Fri, 23 Aug 2019 00:48:23 +0100
Peter Wu <peter@lekensteyn.nl> 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 <peter@lekensteyn.nl>
> ---
> 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..965be5c9afb3 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_file file does

I was just about to ack this, and then I saw the above.

s/trace_file/trace_pipe/

Other than that, it looks good!

-- Steve

> +not have this limitation.
>
> trace entries
> -------------

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