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>

2 files changed, 14 insertions, 0 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
 =======================================