On Wed, 18 Dec 2019 14:15:53 -0500 "Frank A. Cancio Bello" <frank@xxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxx> Thanks for the update. Jon, do you want to take this? Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> -- 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
