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, 25 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 639344a4d3a2..1a3d6b329782 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -287,6 +287,7 @@ static const char *trace_options[] = {
         "annotate",
         "userstacktrace",
         "sym-userobj",
+        "printk-msg-only",
         NULL
 };
 
@@ -2265,6 +2266,25 @@ static enum print_line_t print_hex_fmt(struct trace_iterator *iter)
         return TRACE_TYPE_HANDLED;
 }
 
+static enum print_line_t print_printk_msg_only(struct trace_iterator *iter)
+{
+        struct trace_seq *s = &iter->seq;
+        struct trace_entry *entry = iter->ent;
+        struct print_entry *field;
+        int ret;
+
+        trace_assign_type(field, entry);
+
+        ret = trace_seq_printf(s, field->buf);
+        if (!ret)
+                return TRACE_TYPE_PARTIAL_LINE;
+
+        if (entry->flags & TRACE_FLAG_CONT)
+                trace_seq_print_cont(s, iter);
+
+        return TRACE_TYPE_HANDLED;
+}
+
 static enum print_line_t print_bin_fmt(struct trace_iterator *iter)
 {
         struct trace_seq *s = &iter->seq;
@@ -2345,6 +2365,11 @@ static enum print_line_t print_trace_line(struct trace_iterator *iter)
                         return ret;
         }
 
+        if (iter->ent->type == TRACE_PRINT &&
+                        trace_flags & TRACE_ITER_PRINTK &&
+                        trace_flags & TRACE_ITER_PRINTK_MSGONLY)
+                return print_printk_msg_only(iter);
+
         if (trace_flags & TRACE_ITER_BIN)
                 return print_bin_fmt(iter);