[RFC][PATCH] tracing: Make branch trace display correct header

[Zhaolei <zhaolei@cn.fujitsu.com>]

Before patch:
  # tracer: branch
  #
  #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
  #              | |       |          |         |
             <...>-2981  [000] 24008.872738: [  ok  ] trace_irq_handler_exit:irq_event_types.h:41
             <...>-2981  [000] 24008.872742: [  ok  ] note_interrupt:spurious.c:229
  ...

After patch:
# tracer: branch
#
#           TASK-PID    CPU#    TIMESTAMP  CORRECT  FUNC:FILE:LINE
#              | |       |          |         |       |
           <...>-2985  [000] 26329.142970: [  ok  ] slab_free:slub.c:1776
           <...>-2985  [000] 26329.142972: [  ok  ] trace_kmem_cache_free:kmem_event_types.h:191
  ...

But it is not the best fix way.
When format(length) of TASK-PID, CPU and TIMESTAMP chanegd in trace.c,
other files who uses there fields need to changed for print right header line.

Maybe we can make a function to print header line of these 3 field:
print_common_head()
{
	seq_puts(s, "#           TASK-PID    CPU#    TIMESTAMP");
}

and call this function in other files' print_header:
static void branch_print_header(struct seq_file *s)
{
	print_common_head();
	seq_puts(s, "  CORRECT  FUNC:FILE:LINE\n");
}

But if header line is multi-line, this way can't work.

Another way is to export specific header-line content in other files:
static void branch_print_header(char *buf, int len)
{
	strcpy(buf, "  CORRECT  FUNC:FILE:LINE\n"
		    "     |            |\n"
		    );
}
And combile common-header and specific header in trace.c, then do seq_puts.
But this seems too complex for tracing framework.

Similar problem exists in other tracers as sched_switch.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 kernel/trace/trace_branch.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index 8e64e60..7a7a9fd 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -157,6 +157,13 @@ static enum print_line_t trace_branch_print(struct trace_iterator *iter,
 	return TRACE_TYPE_HANDLED;
 }
 
+static void branch_print_header(struct seq_file *s)
+{
+	seq_puts(s, "#           TASK-PID    CPU#    TIMESTAMP  CORRECT"
+		"  FUNC:FILE:LINE\n");
+	seq_puts(s, "#              | |       |          |         |   "
+		"    |\n");
+}
 
 static struct trace_event trace_branch_event = {
 	.type		= TRACE_BRANCH,
@@ -171,6 +178,7 @@ static struct tracer branch_trace __read_mostly =
 #ifdef CONFIG_FTRACE_SELFTEST
 	.selftest	= trace_selftest_startup_branch,
 #endif /* CONFIG_FTRACE_SELFTEST */
+	.print_header	= branch_print_header,
 };
 
 __init static int init_branch_tracer(void)
-- 1.5.5.3