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Message-ID: <87y1iwlc80.fsf@jogness.linutronix.de>
Date: Mon, 31 Jul 2023 10:31:03 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Jim Cromie <jim.cromie@...il.com>, rostedt@...dmis.org,
linux-kernel@...r.kernel.org
Cc: Jim Cromie <jim.cromie@...il.com>,
Vincent Whitchurch <vincent.whitchurch@...s.com>,
daniel@...ll.ch, pmladek@...e.com, sergey.senozhatsky@...il.com,
Simon Ser <contact@...rsion.fr>,
Sean Paul <seanpaul@...omium.org>
Subject: Re: [RFC PATCH 1/1] tracefs: add TP_printk_no_nl - RFC
On 2023-07-30, Jim Cromie <jim.cromie@...il.com> wrote:
> 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.
Note that the trailing '\n' in printk messages has a purpose. It
finalizes commitment of the message to the ringbuffer so that the
message cannot be extended by any LOG_CONT printk's that may come along
(from any context).
If it is not intended that a message is extended, then that message
should include a trailing '\n'.
Grepping through the kernel, I am surprised how many messages are
missing the trailing newline when it is obvious they are not intended to
be extended. I consider these bugs.
John Ogness
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