[for-next][PATCH 19/26] Documentation: tracing: boot: Add an example of tracing function-calls

Steven Rostedt
2020-09-22T01:25:44Z

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>
---
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 9bc8aceb8c0a..ab3bfd67197c 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::
--
2.28.0