tracing/ftrace: add the printk-msg-only option

Impact: display ftrace_printk messages "as is"

By default, ftrace_printk() messages find their output with some other
informations like pid, caller, ...
Sometimes a developer just want to have the ftrace_printk left "as is", without
other information.

This is done by providing a default-off option called printk-msg-only.
To enable it, just do `echo printk-msg-only > /debugfs/tracing/trace_options`

Before the patch:

           <...>-2739  [000]   145.692153: __might_sleep: I'm an ftrace_printk msg in __might_sleep
           <...>-2739  [000]   145.692155: __might_sleep: I'm another ftrace_printk msg in __might_sleep

After the patch and the printk-msg-only option enabled:

I'm an ftrace_printk msg in __might_sleep
I'm another ftrace_printk msg in __might_sleep

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f07c246dd73d..fc75dce7a664 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -578,7 +578,8 @@ enum trace_iterator_flags {
         TRACE_ITER_BRANCH               = 0x1000,
         TRACE_ITER_ANNOTATE             = 0x2000,
         TRACE_ITER_USERSTACKTRACE       = 0x4000,
-        TRACE_ITER_SYM_USEROBJ          = 0x8000
+        TRACE_ITER_SYM_USEROBJ          = 0x8000,
+        TRACE_ITER_PRINTK_MSGONLY       = 0x10000
 };
 
 /*