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docs: ftrace: Specifies when buffers get clear

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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>
This commit is contained in:
Frank A. Cancio Bello 2019-12-18 14:15:53 -05:00 committed by Jonathan Corbet
parent d1eef1c619
commit d693b2883c
1 changed files with 7 additions and 2 deletions
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9
Documentation/trace/ftrace.rst
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@ -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