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authorFrank A. Cancio Bello <frank@generalsoftwareinc.com>2019-12-18 22:15:53 +0300
committerJonathan Corbet <corbet@lwn.net>2019-12-19 19:18:33 +0300
commitd693b2883c0b9b261d2c490a9933e703359b4542 (patch)
tree1a2602734638a47c9b47764d5282a8fa03569f95 /Documentation/trace/ftrace.rst
parentd1eef1c619749b2a57e514a3fa67d9a516ffa919 (diff)
downloadlinux-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.rst9
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