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>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9776f06..2b48c52 100644 (file)
--- 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 37d1c70..c1434b5 100644 (file)
--- 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: