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

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Message-ID: <CA+55aFyzR4LKhJKLFgvvd9OTsos2_g4-9fova782BX4kyA3bLA@mail.gmail.com>
Date:   Tue, 29 Aug 2017 10:12:22 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Pavel Machek <pavel@....cz>,
        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>
Subject: Re: printk: what is going on with additional newlines?

On Tue, Aug 29, 2017 at 10:00 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I refuse to help those things. We mis-designed things

Actually, let me rephrase that:

It might actually be a good idea to help those things, by making
helper functions available that do the marshalling.

So not calling "printk()" directly, but having a set of simple
"buffer_print()" functions where each user has its own buffer, and
then the "buffer_print()" functions will help people do nicely output
data.

So if the issue is that people want to print (for example) hex dumps
one character at a time, but don't want to have each character show up
on a line of their own, I think we might well add a few functions to
help dop that.

But they wouldn't be "printk". They would be the buffering functions
that then call printk when tyhey have buffered a line.

That avoids the whole nasty issue with printk - printk wants to show
stuff early (because _maybe_ it's critical) and printk wants to make
log records with timestamps and loglevels. And printk has serious
locking issues that are really nasty and fundamental.

A private buffer has none of those issues.

                 Linus