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From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Steven Rostedt <rostedt@goodmis.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <skhan@linuxfoundation.org>
Cc:     mhiramat@kernel.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, linux-kselftest@vger.kernel.org
Subject: [PATCH v3 7/8] Documentation: tracing: boot: Add an example of tracing function-calls
Date:   Thu, 10 Sep 2020 17:56:06 +0900
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Add an example of tracing function calls on a specific function.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Documentation/trace/boottime-trace.rst |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst
index 1341b449acaa..c216f5695ae2 100644
--- a/Documentation/trace/boottime-trace.rst
+++ b/Documentation/trace/boottime-trace.rst
@@ -168,6 +168,26 @@ is for tracing functions starting with "user\_", and others tracing
 The instance node also accepts event nodes so that each instance
 can customize its event tracing.
 
+With the trigger action and kprobes, you can trace function-graph while
+a function is called. For example, this will trace all function calls in
+the pci_proc_init()::
+
+  ftrace {
+        tracing_on = 0
+        tracer = function_graph
+        event.kprobes {
+                start_event {
+                        probes = "pci_proc_init"
+                        actions = "traceon"
+                }
+                end_event {
+                        probes = "pci_proc_init%return"
+                        actions = "traceoff"
+                }
+        }
+  }
+
+
 This boot-time tracing also supports ftrace kernel parameters via boot
 config.
 For example, following kernel parameters::