linux-kernel - Re: [PATCH 1/2] remove all uses of printf's %n

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Message-ID: <CAGXu5jJErvcfdq0=QDd2pwCeK7kKnJ-GY2ybv9ssdkF6NjNvDw@mail.gmail.com>
Date:	Mon, 16 Sep 2013 07:59:42 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	LKML <linux-kernel@...r.kernel.org>, Joe Perches <joe@...ches.com>,
	George Spelvin <linux@...izon.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Jan Beulich <JBeulich@...e.com>,
	Motohiro KOSAKI <kosaki.motohiro@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] remove all uses of printf's %n

On Mon, Sep 16, 2013 at 4:41 AM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
> Kees Cook wrote:
>> -     seq_printf(m, "%s%d%n", con->name, con->index, &len);
>> -     len = 21 - len;
>> +     len = m->count;
>> +     seq_printf(m, "%s%d", con->name, con->index);
>> +     len = 21 - (m->count - len);
>
> Why not to create a new function which returns bytes written?
> The new function does not need to return negative value for indicating errors.

I think it's not worth it for two reasons:

- there are very few callers that need this logic
- it would require a new function for each type of function used
(right now both seq_printf and seq_puts are used).

Perhaps instead of seq->count, there should be an access function?
seq_get_count(seq) or something?

-Kees

-- 
Kees Cook
Chrome OS Security
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