Documentation: tracing: boot: Add an example of tracing function-calls

Add an example of tracing function calls on a specific function.

Link: https://lkml.kernel.org/r/159972816669.428528.12390560334549382316.stgit@devnote2
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/Documentation/trace/boottime-trace.rst b/Documentation/trace/boottime-trace.rst
index 9bc8ace..ab3bfd6 100644 (file)
--- 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.
 
 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::
 This boot-time tracing also supports ftrace kernel parameters via boot
 config.
 For example, following kernel parameters::