* [PATCH v2] docs: ftrace: Specifies when buffers get clear
@ 2019-12-18 19:15 Frank A. Cancio Bello
2019-12-18 19:33 ` Steven Rostedt
0 siblings, 1 reply; 3+ messages in thread
From: Frank A. Cancio Bello @ 2019-12-18 19:15 UTC (permalink / raw)
To: Steven Rostedt, Ingo Molnar, Jonathan Corbet, linux-doc, linux-kernel
Cc: joel, nachukannan, saiprakash.ranjan
Clarify a few places where the ring buffer and the "snapshot" buffer
are cleared as a side effect of an operation.
This will avoid users lost of tracing data because of these so far
undocumented behavior.
Signed-off-by: Frank A. Cancio Bello <frank@generalsoftwareinc.com>
---
Changes in v2:
- Per Steven comment correct the fact that the "snapshot" buffer is
not touched when writing in the "trace" file.
- Use tab instead of spaces for alignment.
Documentation/trace/ftrace.rst | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index d2b5657ed33e..46df39300d22 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -95,7 +95,8 @@ of ftrace. Here is a list of some of the key files:
current_tracer:
This is used to set or display the current tracer
- that is configured.
+ that is configured. Changing the current tracer clears
+ the ring buffer content as well as the "snapshot" buffer.
available_tracers:
@@ -126,7 +127,8 @@ 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 when the file is open for reading. Once all readers
- are closed, tracing is re-enabled.
+ are closed, tracing is re-enabled. Opening this file for
+ writing with the O_TRUNC flag clears the ring buffer content.
trace_pipe:
@@ -490,6 +492,9 @@ of ftrace. Here is a list of some of the key files:
# echo global > trace_clock
+ Setting a clock clears the ring buffer content as well as the
+ "snapshot" buffer.
+
trace_marker:
This is a very useful file for synchronizing user space
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] docs: ftrace: Specifies when buffers get clear
2019-12-18 19:15 [PATCH v2] docs: ftrace: Specifies when buffers get clear Frank A. Cancio Bello
@ 2019-12-18 19:33 ` Steven Rostedt
2019-12-18 19:38 ` Jonathan Corbet
0 siblings, 1 reply; 3+ messages in thread
From: Steven Rostedt @ 2019-12-18 19:33 UTC (permalink / raw)
To: Frank A. Cancio Bello
Cc: Ingo Molnar, Jonathan Corbet, linux-doc, linux-kernel, joel,
nachukannan, saiprakash.ranjan
On Wed, 18 Dec 2019 14:15:53 -0500
"Frank A. Cancio Bello" <frank@generalsoftwareinc.com> wrote:
> Clarify a few places where the ring buffer and the "snapshot" buffer
> are cleared as a side effect of an operation.
>
> This will avoid users lost of tracing data because of these so far
> undocumented behavior.
>
> Signed-off-by: Frank A. Cancio Bello <frank@generalsoftwareinc.com>
Thanks for the update.
Jon, do you want to take this?
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-- Steve
> ---
> Changes in v2:
> - Per Steven comment correct the fact that the "snapshot" buffer is
> not touched when writing in the "trace" file.
> - Use tab instead of spaces for alignment.
>
> Documentation/trace/ftrace.rst | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
> index d2b5657ed33e..46df39300d22 100644
> --- a/Documentation/trace/ftrace.rst
> +++ b/Documentation/trace/ftrace.rst
> @@ -95,7 +95,8 @@ of ftrace. Here is a list of some of the key files:
> current_tracer:
>
> This is used to set or display the current tracer
> - that is configured.
> + that is configured. Changing the current tracer clears
> + the ring buffer content as well as the "snapshot" buffer.
>
> available_tracers:
>
> @@ -126,7 +127,8 @@ 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 when the file is open for reading. Once all readers
> - are closed, tracing is re-enabled.
> + are closed, tracing is re-enabled. Opening this file for
> + writing with the O_TRUNC flag clears the ring buffer content.
>
> trace_pipe:
>
> @@ -490,6 +492,9 @@ of ftrace. Here is a list of some of the key files:
>
> # echo global > trace_clock
>
> + Setting a clock clears the ring buffer content as well as the
> + "snapshot" buffer.
> +
> trace_marker:
>
> This is a very useful file for synchronizing user space
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] docs: ftrace: Specifies when buffers get clear
2019-12-18 19:33 ` Steven Rostedt
@ 2019-12-18 19:38 ` Jonathan Corbet
0 siblings, 0 replies; 3+ messages in thread
From: Jonathan Corbet @ 2019-12-18 19:38 UTC (permalink / raw)
To: Steven Rostedt
Cc: Frank A. Cancio Bello, Ingo Molnar, linux-doc, linux-kernel,
joel, nachukannan, saiprakash.ranjan
On Wed, 18 Dec 2019 14:33:51 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> Jon, do you want to take this?
Sure, will do.
jon
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-12-18 19:15 [PATCH v2] docs: ftrace: Specifies when buffers get clear Frank A. Cancio Bello
2019-12-18 19:33 ` Steven Rostedt
2019-12-18 19:38 ` Jonathan Corbet
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