tracing/events: Add trace_event boot option

We already have ftrace= boot option, and this adds a similar
boot option for trace events, so allow trace events to be
enabled at boot, for boot debugging purpose.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4A4ACE29.3010407@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

5 files changed, 52 insertions, 6 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index d3f41db3ed49..2582e7aea29f 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2478,6 +2478,11 @@ and is between 256 and 4096 characters. It is defined in the file
         trace_buf_size=nn[KMG]
                         [FTRACE] will set tracing buffer size.
 
+        trace_event=[event-list]
+                        [FTRACE] Set and start specified trace events in order
+                        to facilitate early boot debugging.
+                        See also Documentation/trace/events.txt
+
         trix=           [HW,OSS] MediaTrix AudioTrix Pro
                         Format:
                         <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq>
diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
index f157d7594ea7..2bcc8d4dea29 100644
--- a/Documentation/trace/events.txt
+++ b/Documentation/trace/events.txt
@@ -83,6 +83,15 @@ When reading one of these enable files, there are four results:
  X - there is a mixture of events enabled and disabled
  ? - this file does not affect any event
 
+2.3 Boot option
+---------------
+
+In order to facilitate early boot debugging, use boot option:
+
+        trace_event=[event-list]
+
+The format of this boot option is the same as described in section 2.1.
+
 3. Defining an event-enabled tracepoint
 =======================================
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3aa0a0dfdfa8..bdb3afc8b306 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -49,7 +49,7 @@ unsigned long __read_mostly	tracing_thresh;
  * On boot up, the ring buffer is set to the minimum size, so that
  * we do not waste memory on systems that are not using tracing.
  */
-static int ring_buffer_expanded;
+int ring_buffer_expanded;
 
 /*
  * We need to change this state when a selftest is running.
@@ -63,7 +63,7 @@ static bool __read_mostly tracing_selftest_running;
 /*
  * If a tracer is running, we do not want to run SELFTEST.
  */
-static bool __read_mostly tracing_selftest_disabled;
+bool __read_mostly tracing_selftest_disabled;
 
 /* For tracers that don't implement custom flags */
 static struct tracer_opt dummy_tracer_opt[] = {
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 3548ae5cc780..52eb0d8dcd75 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -517,6 +517,9 @@ extern unsigned long ftrace_update_tot_cnt;
 extern int DYN_FTRACE_TEST_NAME(void);
 #endif
 
+extern int ring_buffer_expanded;
+extern bool tracing_selftest_disabled;
+
 #ifdef CONFIG_FTRACE_STARTUP_TEST
 extern int trace_selftest_startup_function(struct tracer *trace,
                                            struct trace_array *tr);
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 53c8fd376a88..fecac1314cbe 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -17,6 +17,8 @@
 #include <linux/ctype.h>
 #include <linux/delay.h>
 
+#include <asm/setup.h>
+
 #include "trace_output.h"
 
 #define TRACE_SYSTEM "TRACE_SYSTEM"
@@ -1133,6 +1135,18 @@ struct notifier_block trace_module_nb = {
 extern struct ftrace_event_call __start_ftrace_events[];
 extern struct ftrace_event_call __stop_ftrace_events[];
 
+static char bootup_event_buf[COMMAND_LINE_SIZE] __initdata;
+
+static __init int setup_trace_event(char *str)
+{
+        strlcpy(bootup_event_buf, str, COMMAND_LINE_SIZE);
+        ring_buffer_expanded = 1;
+        tracing_selftest_disabled = 1;
+
+        return 1;
+}
+__setup("trace_event=", setup_trace_event);
+
 static __init int event_trace_init(void)
 {
         struct ftrace_event_call *call;
@@ -1140,6 +1154,8 @@ static __init int event_trace_init(void)
         struct dentry *entry;
         struct dentry *d_events;
         int ret;
+        char *buf = bootup_event_buf;
+        char *token;
 
         d_tracer = tracing_init_dentry();
         if (!d_tracer)
@@ -1185,6 +1201,19 @@ static __init int event_trace_init(void)
                                  &ftrace_event_format_fops);
         }
 
+        while (true) {
+                token = strsep(&buf, ",");
+
+                if (!token)
+                        break;
+                if (!*token)
+                        continue;
+
+                ret = ftrace_set_clr_event(token, 1);
+                if (ret)
+                        pr_warning("Failed to enable trace event: %s\n", token);
+        }
+
         ret = register_module_notifier(&trace_module_nb);
         if (ret)
                 pr_warning("Failed to register trace events module notifier\n");
@@ -1392,10 +1421,10 @@ static __init void event_trace_self_test_with_function(void)
 
 static __init int event_trace_self_tests_init(void)
 {
-
-        event_trace_self_tests();
-
-        event_trace_self_test_with_function();
+        if (!tracing_selftest_disabled) {
+                event_trace_self_tests();
+                event_trace_self_test_with_function();
+        }
 
         return 0;
 }