Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <b867ee8a02043ec6b18c9330bfe3a091d66c816c.camel@perches.com>
Subject: Re: [PATCH] pwm: Add missing '\n' in log messages
From:   Joe Perches <joe@perches.com>
To:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Thierry Reding <thierry.reding@gmail.com>,
        paul@crapouillou.net, Dan Carpenter <dan.carpenter@oracle.com>
Cc:     u.kleine-koenig@pengutronix.de, linux-pwm@vger.kernel.org,
        linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org
Date:   Tue, 14 Apr 2020 12:04:32 -0700
In-Reply-To: <f13a8754-3866-d3d2-eaff-29cb6d14ff8d@wanadoo.fr>
References: <20200411153528.30130-1-christophe.jaillet@wanadoo.fr>
         <20200414135827.GB3593749@ulmo>
         <f13a8754-3866-d3d2-eaff-29cb6d14ff8d@wanadoo.fr>
Content-Type: text/plain; charset="ISO-8859-1"
User-Agent: Evolution 3.34.1-2 
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 2020-04-14 at 20:30 +0200, Christophe JAILLET wrote:
> Being able to detect early missing trailing '\n' would help maintainers 
> and patch providers.
> 
> You are the 2nd person (I've added Paul Cercueil in copy of my reply) 
> who reports that he is thinking that it is no more required to add a '\n'.

The printk subsystem will, for every printk, check
if the last printk has a newline termination and if
it doesn't and the current printk does not start with
KERN_CONT will insert a newline.

The negative to this approach is the last printk,
if it does not have a newline, is buffered and not
emitted until another printk occurs.

There is also the (now small) possibility that
multiple concurrent kernel threads or processes
could interleave printks without a terminating
newline and a different process could emit a
printk that starts with KERN_CONT and the emitted
message could be garbled.

See:

commit 4bcc595ccd80decb4245096e3d1258989c50ed41
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat Oct 8 20:32:40 2016 -0700

    printk: reinstate KERN_CONT for printing continuation lines