[PATCH][RFC] tracing: Enable tracepoints via module parameters

[Steven Rostedt]

A few months ago it was suggested to have a way to enable tracepoints in
a module when it is loaded. I tried various methods, but this one seems
to be the least intrusive. In fact, it requires no modification to the
module code.

The trace event now adds its own MODULE_INFO() and kernel_param_ops that
and links the information about a tracepoint into the module's __param
section. A module can be loaded with a tracepoint active by adding
trace_<tracepoint>=1 as one of the parameters.

The following patch is in:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git

    branch: rfc/trace


Steven Rostedt (1):
      tracing: Enable tracepoints via module parameters

----
 include/linux/ftrace_event.h |    4 +++
 include/trace/ftrace.h       |   22 ++++++++++++++++-
 kernel/trace/trace_events.c  |   52 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 76 insertions(+), 2 deletions(-)
---------------------------
commit b514aa1b59148994a47086cdd46db7f994b4789e
Author: Steven Rostedt <srostedt@xxxxxxxxxx>
Date:   Tue Mar 8 17:06:14 2011 -0500

    tracing: Enable tracepoints via module parameters
    
    Add the tracepoints within the module to the module info section
    and allow the tracepoints to be enabled when the module is loaded.
    
    For example:
    
    [root]# modinfo samples/trace_events/trace-events-sample.ko
    filename:       samples/trace_events/trace-events-sample.ko
    license:        GPL
    description:    trace-events-sample
    author:         Steven Rostedt
    tracepoint:     foo_bar
    srcversion:     F6AC4B8D911A5C5B9CCDD7B
    depends:
    vermagic:       2.6.38-rc5+ SMP preempt mod_unload
    
    Notice that the trace-events-sample tracepoint "foo_bar" shows
    up in the modinfo. When loading the module with:
    
     # insmod trace-events-sample.ko trace_foo_bar=1
    
    The tracepoint "foo_bar" will be enabled.
    
    Cc: Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx>
    Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
    Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxxx>
    Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 47e3997..b672889 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -124,6 +124,8 @@ void tracing_record_cmdline(struct task_struct *tsk);
 
 struct event_filter;
 
+extern struct kernel_param_ops ftrace_mod_ops;
+
 enum trace_reg {
 	TRACE_REG_REGISTER,
 	TRACE_REG_UNREGISTER,
@@ -155,6 +157,7 @@ enum {
 	TRACE_EVENT_FL_FILTERED_BIT,
 	TRACE_EVENT_FL_RECORDED_CMD_BIT,
 	TRACE_EVENT_FL_CAP_ANY_BIT,
+	TRACE_EVENT_FL_MOD_ENABLE_BIT,
 };
 
 enum {
@@ -162,6 +165,7 @@ enum {
 	TRACE_EVENT_FL_FILTERED		= (1 << TRACE_EVENT_FL_FILTERED_BIT),
 	TRACE_EVENT_FL_RECORDED_CMD	= (1 << TRACE_EVENT_FL_RECORDED_CMD_BIT),
 	TRACE_EVENT_FL_CAP_ANY		= (1 << TRACE_EVENT_FL_CAP_ANY_BIT),
+	TRACE_EVENT_FL_MOD_ENABLE	= (1 << TRACE_EVENT_FL_MOD_ENABLE_BIT),
 };
 
 struct ftrace_event_call {
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 3e68366..3d4a6ee 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -561,6 +561,22 @@ static inline void ftrace_test_probe_##call(void)			\
 #undef __get_dynamic_array
 #undef __get_str
 
+/*
+ * Add ftrace trace points in modules to be set by module
+ * parameters. This adds "trace_##call" as a module parameter.
+ * The user could enable trace points on module load with:
+ *  trace_##call=1 as a module parameter.
+ */
+#undef ftrace_mod_params
+#ifdef MODULE
+#define ftrace_mod_params(call)				\
+	module_param_cb(trace_##call, &ftrace_mod_ops,	\
+			&event_##call, 0644);		\
+	MODULE_INFO(tracepoint, #call)
+#else
+#define ftrace_mod_params(call)
+#endif
+
 #undef TP_printk
 #define TP_printk(fmt, args...) "\"" fmt "\", "  __stringify(args)
 
@@ -588,7 +604,8 @@ static struct ftrace_event_call __used event_##call = {			\
 	.print_fmt		= print_fmt_##template,			\
 };									\
 static struct ftrace_event_call __used					\
-__attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
+__attribute__((section("_ftrace_events"))) *__event_##call = &event_##call;\
+ftrace_mod_params(call)
 
 #undef DEFINE_EVENT_PRINT
 #define DEFINE_EVENT_PRINT(template, call, proto, args, print)		\
@@ -602,7 +619,8 @@ static struct ftrace_event_call __used event_##call = {			\
 	.print_fmt		= print_fmt_##call,			\
 };									\
 static struct ftrace_event_call __used					\
-__attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
+__attribute__((section("_ftrace_events"))) *__event_##call = &event_##call; \
+ftrace_mod_params(call)
 
 #include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
 
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 5f499e0..5223751 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1285,6 +1285,7 @@ static void trace_module_add_events(struct module *mod)
 {
 	struct ftrace_module_file_ops *file_ops = NULL;
 	struct ftrace_event_call **call, **start, **end;
+	int ret;
 
 	start = mod->trace_events;
 	end = mod->trace_events + mod->num_trace_events;
@@ -1300,6 +1301,14 @@ static void trace_module_add_events(struct module *mod)
 		__trace_add_event_call(*call, mod,
 				       &file_ops->id, &file_ops->enable,
 				       &file_ops->filter, &file_ops->format);
+		/* If the module tracepoint parameter was set */
+		if ((*call)->flags & TRACE_EVENT_FL_MOD_ENABLE) {
+			(*call)->flags = 0;
+			ret = ftrace_event_enable_disable(*call, 1);
+			if (ret < 0)
+				pr_warning("unable to enable tracepoint %s",
+					   (*call)->name);
+		}
 	}
 }
 
@@ -1457,6 +1466,49 @@ static __init int event_trace_init(void)
 }
 fs_initcall(event_trace_init);
 
+/* Allow modules to load with enabled trace points */
+int ftrace_mod_param_set(const char *val, const struct kernel_param *kp)
+{
+	struct ftrace_event_call *call = kp->arg;
+
+	/* This is set like param_set_bool() */
+
+	/* No equals means "set"... */
+	if (!val)
+		val = "1";
+
+	/* One of =[yYnN01] */
+	switch (val[0]) {
+	case 'y': case 'Y': case '1':
+		break;
+	case 'n': case 'N': case '0':
+		/* Do nothing */
+		return 0;
+	default:
+		return -EINVAL;
+	}
+
+	/* Set flag to tell ftrace to enable this event on init */
+	call->flags = TRACE_EVENT_FL_MOD_ENABLE;
+
+	return 0;
+}
+
+int ftrace_mod_param_get(char *buffer, const struct kernel_param *kp)
+{
+	struct ftrace_event_call *call = kp->arg;
+
+	return sprintf(buffer, "%d",
+		   !!(call->flags &
+		     (TRACE_EVENT_FL_MOD_ENABLE | TRACE_EVENT_FL_ENABLED)));
+}
+
+struct kernel_param_ops ftrace_mod_ops = {
+	.set = ftrace_mod_param_set,
+	.get = ftrace_mod_param_get,
+};
+EXPORT_SYMBOL(ftrace_mod_ops);
+
 #ifdef CONFIG_FTRACE_STARTUP_TEST
 
 static DEFINE_SPINLOCK(test_spinlock);


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