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Message-ID: <1379346277.1934.9.camel@joe-AO722>
Subject: Re: [PATCH 1/2] remove all uses of printf's %n
From: Joe Perches <joe@perches.com>
To: Kees Cook <keescook@chromium.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        LKML <linux-kernel@vger.kernel.org>,
        George Spelvin <linux@horizon.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Al Viro <viro@zeniv.linux.org.uk>, Jan Beulich <JBeulich@suse.com>,
        Motohiro KOSAKI <kosaki.motohiro@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
Date: Mon, 16 Sep 2013 08:44:37 -0700
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On Mon, 2013-09-16 at 08:25 -0700, Kees Cook wrote:
> On Mon, Sep 16, 2013 at 8:09 AM, Joe Perches <joe@perches.com> wrote:
> > On Mon, 2013-09-16 at 07:59 -0700, Kees Cook wrote:
> >> Perhaps instead of seq->count, there should be an access function?
> >> seq_get_count(seq) or something?
> >
> > My thought was to add a seq_last_len()
> 
> That would mean growing the size of the seq_file structure and adding
> instructions for all users. While I personally have no problem with
> that, I worry others might.

I don't think adding an int and a size_t is a big deal.

I'm still hoping to hear from Al if expanding the struct
is OK and race-free.

> If we just use seq->count (or equivalent
> function), then only those that want length will use it. I actually
> think this uses fewer instructions than %n. Especially in the case
> where seq_printf got replaced by seq_puts. :)

Shrug.  None of these are inline uses so the overall
code size doesn't change much.

I have patches that make seq_overflow public and replace
the current uses of the seq_printf/seq_puts/seq_putc
returns where appropriate.

Given that I was already touching a lot of the
seq_<foo> calls, I also have patches that convert all
the seq_printf(fmt) (no additional args) to seq_puts()
and all the seq_puts("[single char]") to seq_putc() as
separate patches.