linux-kernel - Re: printk: what is going on with additional newlines?

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Date:   Tue, 29 Aug 2017 09:48:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Pavel Machek <pavel@....cz>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>, Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jiri Slaby <jslaby@...e.com>, Andreas Mohr <andi@...as.de>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: printk: what is going on with additional newlines?

On Mon, Aug 28, 2017 at 2:05 AM, Pavel Machek <pavel@....cz> wrote:
> Hi!
>
> In 4.13-rc, printk("foo"); printk("bar"); seems to produce
> foo\nbar. That's... quite surprising/unwelcome. What is going on
> there? Are timestamps responsible?

No.

It's actively trying to treach you not to do shit.

If you want to continue a line, you NEED to use KERN_CONT.

That has always been true. It hasn't always been enforced, though.

If you do two printk's and the second one doesn't say "I'm a
continuation", the printk logic assumes you're just confused and
wanted two lines.

And no, we are *NOT* adding code to printk to help people avoid this.
Quite the reverse.

Stop doing continuations at all please. But if you do, you'd better
use KERN_CONT. And if you don't, and you get multiple lines, it's your
own damn fault.

                 Linus