From: Frank A. Cancio Bello Date: Wed, 18 Dec 2019 19:15:53 +0000 (-0500) Subject: docs: ftrace: Specifies when buffers get clear X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=d693b2883c0b9b261d2c490a9933e703359b4542;p=linux.git 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 Reviewed-by: Steven Rostedt (VMware) Link: https://lore.kernel.org/r/20191218191553.q4lwyxmquvtjzjfz@frank-laptop Signed-off-by: Jonathan Corbet --- diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index d2b5657ed33e9..46df39300d22a 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