summaryrefslogtreecommitdiff
path: root/Documentation/trace/ftrace.rst
diff options
context:
space:
mode:
authorPeter Wu <peter@lekensteyn.nl>2019-08-31 18:35:00 +0300
committerJonathan Corbet <corbet@lwn.net>2019-09-02 16:14:53 +0300
commitf12fcca65369e87a078ae9d025ab0198421f5934 (patch)
tree5cf41afbe17c84de5bdc1941a6b38b65139cf893 /Documentation/trace/ftrace.rst
parent5aff7c46172b270af2a9b10eed3a8215c4ba9a87 (diff)
downloadlinux-f12fcca65369e87a078ae9d025ab0198421f5934.tar.xz
docs: ftrace: clarify when tracing is disabled by the trace file
The current text could mislead the user into believing that only read() disables tracing. Clarify that any open() call that requests read access disables tracing. Link: https://lkml.kernel.org/r/CAADnVQ+hU6QOC_dPmpjnuv=9g4SQEeaMEMqXOS2WpMj=q=LdiQ@mail.gmail.com Signed-off-by: Peter Wu <peter@lekensteyn.nl> Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/trace/ftrace.rst')
-rw-r--r--Documentation/trace/ftrace.rst13
1 files changed, 9 insertions, 4 deletions
diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index f60079259669..e3060eedb22d 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -125,7 +125,8 @@ 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 while this file is being read (opened).
+ disabled when the file is open for reading. Once all readers
+ are closed, tracing is re-enabled.
trace_pipe:
@@ -139,8 +140,9 @@ of ftrace. Here is a list of some of the key files:
will not be read again with a sequential read. The
"trace" file is static, and if the tracer is not
adding more data, it will display the same
- information every time it is read. This file will not
- disable tracing while being read.
+ information every time it is read. Unlike the
+ "trace" file, opening this file for reading will not
+ temporarily disable tracing.
trace_options:
@@ -3153,7 +3155,10 @@ different. The trace is live.
Note, reading the trace_pipe file will block until more input is
-added.
+added. This is contrary to the trace file. If any process opened
+the trace file for reading, it will actually disable tracing and
+prevent new entries from being added. The trace_pipe file does
+not have this limitation.
trace entries
-------------