linux-kernel - Re: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length record buffer

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Date:	Tue, 8 May 2012 21:27:12 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Kay Sievers <kay@...y.org>, Greg Kroah-Hartmann <greg@...ah.com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length
 record buffer

On Tue, May 8, 2012 at 9:11 PM, Sasha Levin <levinsasha928@...il.com> wrote:
>
> Is there a reason to keep KERN_CONT under this set of rules at all?

Yes, a very subtle and rare one.

If you want to print out a string that starts with "<%d>", you *have*
to use a prefix, in order to not make printk think that the "<*>" is
the prefix itself.

And if you don't want to start a new line, you need to use KERN_CONT.

So there is *one* case, and one case only, where KERN_CONT is useful,
and it's when the string you are printing out could otherwise be
mistaken for a prefix itself (the "<%d>" thing isn't the only such
string, of course - it could be a "%s" where the string has those
characters in it.

So think of KERN_CONT as a "quoting safety" thing. And in 99% of all
cases it is obviously not actually needed. So in general, KERN_CONT is
useless and should not be used, but that doesn't mean that it can be
removed as a _concept_.

               Linus
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