[RFC PATCH 1/1] tracefs: add TP_printk_no_nl - RFC

[Jim Cromie <jim.cromie@gmail.com>]

This variant of TP_printk() does *not* add the trailing newline.

https://lore.kernel.org/lkml/20200825153338.17061-1-vincent.whitchurch@axis.com/

taught dyndbg to send pr_debug() msgs to tracefs, via -x/T flag.

It "reused" the include/trace/events/printk.h console event,
which does the following:

	TP_fast_assign(
		/*
		 * Each trace entry is printed in a new line.
		 * If the msg finishes with '\n', cut it off
		 * to avoid blank lines in the trace.
		 */
		if ((len > 0) && (text[len-1] == '\n'))
			len -= 1;

		memcpy(__get_str(msg), text, len);
		__get_str(msg)[len] = 0;
	),

That trim work could be avoided, *iff* all pr_debug() callers are
known to have no '\n' to strip.  While thats not true for *all*
callsites, it is 99+% true for DRM.debug callsites, and can be made
true for some subsets of prdbg/dyndbg callsites.

WANTED: macros to validate that a literal format-str has or doesn't
have a trailing newline, or to provide or trim trailing newline(s?).
Should be usable in TP_printk* defns, for use in new event defns.

Cc: <rostedt@goodmis.org>
Cc: Vincent Whitchurch <vincent.whitchurch@axis.com>
Cc: <daniel@ffwll.ch>
Cc: <pmladek@suse.com>
Cc: <sergey.senozhatsky@gmail.com>
Cc: <john.ogness@linutronix.de>
Cc: Simon Ser <contact@emersion.fr>
Cc: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 include/trace/stages/stage3_trace_output.h | 3 +++
 include/trace/stages/stage7_class_define.h | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/include/trace/stages/stage3_trace_output.h b/include/trace/stages/stage3_trace_output.h
index c1fb1355d309..5f5c1374fa10 100644
--- a/include/trace/stages/stage3_trace_output.h
+++ b/include/trace/stages/stage3_trace_output.h
@@ -8,6 +8,9 @@
 #undef TP_printk
 #define TP_printk(fmt, args...) fmt "\n", args
 
+#undef TP_printk_no_nl
+#define TP_printk_no_nl(fmt, args...) fmt, args
+
 #undef __get_dynamic_array
 #define __get_dynamic_array(field)	\
 		((void *)__entry + (__entry->__data_loc_##field & 0xffff))
diff --git a/include/trace/stages/stage7_class_define.h b/include/trace/stages/stage7_class_define.h
index bcb960d16fc0..8247e4478f19 100644
--- a/include/trace/stages/stage7_class_define.h
+++ b/include/trace/stages/stage7_class_define.h
@@ -37,3 +37,6 @@
 
 #undef TP_printk
 #define TP_printk(fmt, args...) "\"" fmt "\", "  __stringify(args)
+
+#undef TP_printk_no_nl
+#define TP_printk_no_nl(fmt, args...) "\"" fmt "\", "  __stringify(args)
-- 
2.41.0