linux-kernel - [PATCH v1 05/12] tracefs: add TP_printk_no_nl

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Date:   Fri,  3 Nov 2023 14:10:04 +0100
From:   Łukasz Bartosik <lb@...ihalf.com>
To:     Jason Baron <jbaron@...mai.com>, Jim Cromie <jim.cromie@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Douglas Anderson <dianders@...omium.org>
Cc:     Guenter Roeck <groeck@...gle.com>,
        Yaniv Tzoreff <yanivt@...gle.com>,
        Benson Leung <bleung@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        upstream@...ihalf.com, pmladek@...e.com,
        sergey.senozhatsky@...il.com, john.ogness@...utronix.de,
        Simon Ser <contact@...rsion.fr>
Subject: [PATCH v1 05/12] tracefs: add TP_printk_no_nl - RFC

From: Jim Cromie <jim.cromie@...il.com>

This variant of TP_printk() does *not* add the trailing newline.  It
is for use by printk/debug-ish events which already have a trailing
newline.  Its here to support:

https://lore.kernel.org/lkml/
20200825153338.17061-1-vincent.whitchurch@...s.com/
which 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@...dmis.org>
Cc: Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc: <daniel@...ll.ch>
Cc: <pmladek@...e.com>
Cc: <sergey.senozhatsky@...il.com>
Cc: <john.ogness@...utronix.de>
Cc: Simon Ser <contact@...rsion.fr>
Cc: Sean Paul <seanpaul@...omium.org>
Signed-off-by: Jim Cromie <jim.cromie@...il.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)
-- 
2.42.0.869.gea05f2083d-goog