Re: [PATCH] ftrace: add kernel command line graph function filtering

[Stefan Assmann <sassmann@redhat.com>]

On 12.10.2009 11:09, Frédéric Weisbecker wrote:
> 2009/10/12 Stefan Assmann <sassmann@redhat.com>:
>> From 894e934e782ddaa33eb6d156d8326cdf479b5f62 Mon Sep 17 00:00:00 2001
>> From: Stefan Assmann <sassmann@redhat.com>
>> Date: Mon, 12 Oct 2009 09:11:47 +0200
>> Subject: [PATCH] ftrace: add kernel command line graph function filtering
>>
>> Add a command line parameter to allow limiting the function graphs that
>> are traced on boot up, when ftrace=function_graph is specified.
>>
>> This patch adds the following command line option:
>> ftrace_graph_filter=function-list
> 
> 
> If we use this parameter, we undoubtedly want to launch the function
> graph tracer.
> I'd then suggest to arm ftrace=function_graph automatically if we have
> ftrace_graph_filter
> set.
> 
> 
>>
>> Where function-list is a comma separated list of functions to filter.
>>
>> Signed-off-by: Stefan Assmann <sassmann@redhat.com>
>> ---
>>  Documentation/kernel-parameters.txt |    9 ++++++++-
>>  kernel/trace/ftrace.c               |   34 ++++++++++++++++++++++++++++++++++
>>  2 files changed, 42 insertions(+), 1 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 9107b38..144eb83 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -771,7 +771,14 @@ and is between 256 and 4096 characters. It is defined in the file
>>                        tracer at boot up. function-list is a comma separated
>>                        list of functions. This list can be changed at run
>>                        time by the set_ftrace_filter file in the debugfs
>> -                       tracing directory.
>> +                       tracing directory.
>> +
>> +       ftrace_graph_filter=[function-list]
>> +                       [FTRACE] Limit the functions traced by the function
>> +                       graph tracer at boot up. function-list is a comma
>> +                       separated list of functions. This list can be changed
>> +                       at run time by the set_graph_function file in the
>> +                       debugfs tracing directory.
> 
> 
> 
> May be you should use a more detailed definition of this parameter.
> Limiting a function traced by the function graph tracer is ambiguous.
> 
> It means we can have either:
> 
>     function_to_trace();
> 
> or:
> 
>     function_to_trace() {
>          foo() {
>              bar();
>          }
>     }
> 
> We want the second thing.
> May be instead you can write:
> 
> "Limit the top level callers functions traced by the function
>  graph tracer at boot up."
> 
> Otherwise, looks good to me:
> 
> Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
> 
> Thanks.

Thanks for reviewing Frédéric!
I hope the following is what you had in mind.

  Stefan

>From edeb75ce9c9a35d5905d45954f66a0e05d5fe8ab Mon Sep 17 00:00:00 2001
From: Stefan Assmann <sassmann@redhat.com>
Date: Mon, 12 Oct 2009 09:11:47 +0200
Subject: [PATCH] ftrace: add kernel command line graph function filtering

Add a command line parameter to allow limiting the top level callers functions
traced by the function graph tracer at boot up.

This patch adds the following command line option:
ftrace_graph_filter=function-list

Where function-list is a comma separated list of functions to filter.

Signed-off-by: Stefan Assmann <sassmann@redhat.com>
---
 Documentation/kernel-parameters.txt |    9 ++++++++-
 kernel/trace/ftrace.c               |   35 +++++++++++++++++++++++++++++++++++
 kernel/trace/trace.c                |    2 +-
 kernel/trace/trace.h                |    1 +
 4 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9107b38..539a053 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -771,7 +771,14 @@ and is between 256 and 4096 characters. It is defined in the file
 			tracer at boot up. function-list is a comma separated
 			list of functions. This list can be changed at run
 			time by the set_ftrace_filter file in the debugfs
-			tracing directory.
+			tracing directory.
+
+	ftrace_graph_filter=[function-list]
+			[FTRACE] Limit the top level callers functions traced
+			by the function graph tracer at boot up.
+			function-list is a comma separated list of functions
+			that can be changed at run time by the
+			set_graph_function file in the debugfs tracing directory.

 	ftrace_notrace=[function-list]
 			[FTRACE] Do not trace the functions specified in
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 3724756..ee9c509 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -78,6 +78,10 @@ ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
 ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
 ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;

+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+static int ftrace_set_func(unsigned long *array, int *idx, char *buffer);
+#endif
+
 static void ftrace_list_func(unsigned long ip, unsigned long parent_ip)
 {
 	struct ftrace_ops *op = ftrace_list;
@@ -2302,6 +2306,7 @@ void ftrace_set_notrace(unsigned char *buf, int len, int reset)
 #define FTRACE_FILTER_SIZE		COMMAND_LINE_SIZE
 static char ftrace_notrace_buf[FTRACE_FILTER_SIZE] __initdata;
 static char ftrace_filter_buf[FTRACE_FILTER_SIZE] __initdata;
+static char ftrace_graph_buf[FTRACE_FILTER_SIZE] __initdata;

 static int __init set_ftrace_notrace(char *str)
 {
@@ -2317,6 +2322,32 @@ static int __init set_ftrace_filter(char *str)
 }
 __setup("ftrace_filter=", set_ftrace_filter);

+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+static int __init set_graph_function(char *str)
+{
+	strncpy(ftrace_graph_buf, str, FTRACE_FILTER_SIZE);
+	return 1;
+}
+__setup("ftrace_graph_filter=", set_graph_function);
+
+static void __init set_ftrace_early_graph(char *buf)
+{
+	int ret;
+	char *func;
+
+	set_ftrace("function_graph");
+	while (buf) {
+		func = strsep(&buf, ",");
+		/* we allow only one expression at a time */
+		ret = ftrace_set_func(ftrace_graph_funcs, &ftrace_graph_count,
+				      func);
+		if (ret)
+			printk(KERN_DEBUG "ftrace: function %s not "
+					  "traceable\n", func);
+	}
+}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
 static void __init set_ftrace_early_filter(char *buf, int enable)
 {
 	char *func;
@@ -2333,6 +2364,10 @@ static void __init set_ftrace_early_filters(void)
 		set_ftrace_early_filter(ftrace_filter_buf, 1);
 	if (ftrace_notrace_buf[0])
 		set_ftrace_early_filter(ftrace_notrace_buf, 0);
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	if (ftrace_graph_buf[0])
+		set_ftrace_early_graph(ftrace_graph_buf);
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 }

 static int
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4506826..811c918 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -129,7 +129,7 @@ static int tracing_set_tracer(const char *buf);
 static char bootup_tracer_buf[MAX_TRACER_SIZE] __initdata;
 static char *default_bootup_tracer;

-static int __init set_ftrace(char *str)
+int __init set_ftrace(char *str)
 {
 	strncpy(bootup_tracer_buf, str, MAX_TRACER_SIZE);
 	default_bootup_tracer = bootup_tracer_buf;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 405cb85..4625acc 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -461,6 +461,7 @@ extern int trace_clock_id;
 extern enum print_line_t print_graph_function(struct trace_iterator *iter);
 extern enum print_line_t
 trace_print_graph_duration(unsigned long long duration, struct trace_seq *s);
+extern int set_ftrace(char *str);

 #ifdef CONFIG_DYNAMIC_FTRACE
 /* TODO: make this variable */
-- 
1.6.2.5