tracing: Add trace_options kernel command line parameter

Add trace_options to the kernel command line parameter to be able to
set options at early boot. For example, to enable stack dumps of
events, add the following:

  trace_options=stacktrace

This along with the trace_event option, you can get not only
traces of the events but also the stack dumps with them.

Requested-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 55 insertions, 15 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9776f068306b..2b48c52464a1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2859,6 +2859,22 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         to facilitate early boot debugging.
                         See also Documentation/trace/events.txt
 
+        trace_options=[option-list]
+                        [FTRACE] Enable or disable tracer options at boot.
+                        The option-list is a comma delimited list of options
+                        that can be enabled or disabled just as if you were
+                        to echo the option name into
+
+                            /sys/kernel/debug/tracing/trace_options
+
+                        For example, to enable stacktrace option (to dump the
+                        stack trace of each event), add to the command line:
+
+                              trace_options=stacktrace
+
+                        See also Documentation/trace/ftrace.txt "trace options"
+                        section.
+
         transparent_hugepage=
                         [KNL]
                         Format: [always|madvise|never]
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 37d1c703e3ec..c1434b5ce4d1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -155,6 +155,18 @@ static int __init set_ftrace_dump_on_oops(char *str)
 }
 __setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);
 
+
+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)
+{
+        strncpy(trace_boot_options_buf, str, MAX_TRACER_SIZE);
+        trace_boot_options = trace_boot_options_buf;
+        return 0;
+}
+__setup("trace_options=", set_trace_boot_options);
+
 unsigned long long ns2usecs(cycle_t nsec)
 {
         nsec += 500;
@@ -2838,24 +2850,14 @@ static void set_tracer_flags(unsigned int mask, int enabled)
                 trace_printk_start_stop_comm(enabled);
 }
 
-static ssize_t
-tracing_trace_options_write(struct file *filp, const char __user *ubuf,
-                        size_t cnt, loff_t *ppos)
+static int trace_set_options(char *option)
 {
-        char buf[64];
         char *cmp;
         int neg = 0;
-        int ret;
+        int ret = 0;
         int i;
 
-        if (cnt >= sizeof(buf))
-                return -EINVAL;
-
-        if (copy_from_user(&buf, ubuf, cnt))
-                return -EFAULT;
-
-        buf[cnt] = 0;
-        cmp = strstrip(buf);
+        cmp = strstrip(option);
 
         if (strncmp(cmp, "no", 2) == 0) {
                 neg = 1;
@@ -2874,10 +2876,25 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
                 mutex_lock(&trace_types_lock);
                 ret = set_tracer_option(current_trace, cmp, neg);
                 mutex_unlock(&trace_types_lock);
-                if (ret)
-                        return ret;
         }
 
+        return ret;
+}
+
+static ssize_t
+tracing_trace_options_write(struct file *filp, const char __user *ubuf,
+                        size_t cnt, loff_t *ppos)
+{
+        char buf[64];
+
+        if (cnt >= sizeof(buf))
+                return -EINVAL;
+
+        if (copy_from_user(&buf, ubuf, cnt))
+                return -EFAULT;
+
+        trace_set_options(buf);
+
         *ppos += cnt;
 
         return cnt;
@@ -5133,6 +5150,13 @@ __init static int tracer_alloc_buffers(void)
 
         register_die_notifier(&trace_die_notifier);
 
+        while (trace_boot_options) {
+                char *option;
+
+                option = strsep(&trace_boot_options, ",");
+                trace_set_options(option);
+        }
+
         return 0;
 
 out_free_cpumask: