tracing: Apply tracer specific options from kernel command line.

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.

Link: http://lkml.kernel.org/r/1446599669-9294-1-git-send-email-hello.wjx@gmail.com
Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6459e141aac37734c8a1ea3865354cd73abcff0c..7fe7cc987dabcecf3ade44172c47efb81d820814 100644 (file)
--- 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);
@@ -1223,13 +1221,15 @@ static inline int run_tracer_selftest(struct tracer *type)
 
 static void add_tracer_options(struct trace_array *tr, struct tracer *t);
 
+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;
@@ -1288,6 +1288,9 @@ 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
@@ -3589,6 +3592,7 @@ 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);
 
@@ -3612,9 +3616,37 @@ 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)
@@ -7248,12 +7280,7 @@ __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();