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| author | Frank A. Cancio Bello <frank@generalsoftwareinc.com> | 2019-12-18 22:15:53 +0300 |
|---|---|---|
| committer | Jonathan Corbet <corbet@lwn.net> | 2019-12-19 19:18:33 +0300 |
| commit | d693b2883c0b9b261d2c490a9933e703359b4542 (patch) | |
| tree | 1a2602734638a47c9b47764d5282a8fa03569f95 /Documentation/trace/ftrace.rst | |
| parent | d1eef1c619749b2a57e514a3fa67d9a516ffa919 (diff) | |
| download | linux-d693b2883c0b9b261d2c490a9933e703359b4542.tar.xz | |
docs: ftrace: Specifies when buffers get clear
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>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20191218191553.q4lwyxmquvtjzjfz@frank-laptop
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/trace/ftrace.rst')
| -rw-r--r-- | Documentation/trace/ftrace.rst | 9 |
1 files 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 |