[PATCH v2] tracing: Apply tracer specific options from kernel command line.

[Jiaxing Wang <hello.wjx@gmail.com>]

Currently, the trace_options parameter is only applied in
tracer_alloc_buffers() when global_trace.current_trace is nop_trace,
so a tracer specific option will not be applied even when the specific
tracer is also enabled from kernel command line. For example, the
'func_stack_trace' option can't be enabled with the following kernel
parameter:

  ftrace=function ftrace_filter=kfree trace_options=func_stack_trace

We can enable tracer specific options by simply apply the options again
if the specific tracer is also supplied from command line and started
in register_tracer().

To make trace_boot_options_buf can be parsed again, a comma and a space
is put back if they were replaced by strsep and strstrip respectively.

Also make register_tracer() be __init to access the __init data, and
in fact register_tracer is only called from __init code.

Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com>
---
 kernel/trace/trace.c | 45 ++++++++++++++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6dd064e..689886c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -214,12 +214,10 @@ __setup("alloc_snapshot", boot_alloc_snapshot);
 
 
 static char trace_boot_options_buf[MAX_TRACER_SIZE] __initdata;
-static char *trace_boot_options __initdata;
 
 static int __init set_trace_boot_options(char *str)
 {
 	strlcpy(trace_boot_options_buf, str, MAX_TRACER_SIZE);
-	trace_boot_options = trace_boot_options_buf;
 	return 0;
 }
 __setup("trace_options=", set_trace_boot_options);
@@ -1204,13 +1202,15 @@ static inline int run_tracer_selftest(struct tracer *type)
 }
 #endif /* CONFIG_FTRACE_STARTUP_TEST */
 
+static void __init apply_trace_boot_options(void);
+
 /**
  * register_tracer - register a tracer with the ftrace system.
  * @type - the plugin for the tracer
  *
  * Register a new plugin tracer.
  */
-int register_tracer(struct tracer *type)
+int __init register_tracer(struct tracer *type)
 {
 	struct tracer *t;
 	int ret = 0;
@@ -1268,6 +1268,9 @@ int register_tracer(struct tracer *type)
 	/* Do we want this tracer to start on bootup? */
 	tracing_set_tracer(&global_trace, type->name);
 	default_bootup_tracer = NULL;
+
+	apply_trace_boot_options();
+
 	/* disable other selftests, since this will break it. */
 	tracing_selftest_disabled = true;
 #ifdef CONFIG_FTRACE_STARTUP_TEST
@@ -3577,6 +3580,7 @@ static int trace_set_options(struct trace_array *tr, char *option)
 	int neg = 0;
 	int ret = -ENODEV;
 	int i;
+	size_t orig_len = strlen(option);
 
 	cmp = strstrip(option);
 
@@ -3600,9 +3604,37 @@ static int trace_set_options(struct trace_array *tr, char *option)
 
 	mutex_unlock(&trace_types_lock);
 
+	/*
+	 * If the first trailing whitespace is replaced with '\0' by strstrip,
+	 * turn it back into a space.
+	 */
+	if (orig_len > strlen(option))
+		option[strlen(option)] = ' ';
+
 	return ret;
 }
 
+static void __init apply_trace_boot_options(void)
+{
+	char *buf = trace_boot_options_buf;
+	char *option;
+
+	while (true) {
+		option = strsep(&buf, ",");
+
+		if (!option)
+			break;
+		if (!*option)
+			continue;
+
+		trace_set_options(&global_trace, option);
+
+		/* Put back the comma to allow this to be called again */
+		if (buf)
+			*(buf - 1) = ',';
+	}
+}
+
 static ssize_t
 tracing_trace_options_write(struct file *filp, const char __user *ubuf,
 			size_t cnt, loff_t *ppos)
@@ -7153,12 +7185,7 @@ __init static int tracer_alloc_buffers(void)
 	INIT_LIST_HEAD(&global_trace.events);
 	list_add(&global_trace.list, &ftrace_trace_arrays);
 
-	while (trace_boot_options) {
-		char *option;
-
-		option = strsep(&trace_boot_options, ",");
-		trace_set_options(&global_trace, option);
-	}
+	apply_trace_boot_options();
 
 	register_snapshot_cmd();
 
-- 
2.1.4