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

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Date:	Tue, 17 Sep 2013 22:06:02 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	keescook@...omium.org, geert@...ux-m68k.org
Cc:	linux-kernel@...r.kernel.org, joe@...ches.com, linux@...izon.com,
	dan.carpenter@...cle.com, viro@...iv.linux.org.uk,
	JBeulich@...e.com, kosaki.motohiro@...il.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/2] remove all uses of printf's %n

Kees Cook wrote:
> On Mon, Sep 16, 2013 at 1:09 AM, Geert Uytterhoeven
> <geert@...ux-m68k.org> wrote:
> > On Mon, Sep 16, 2013 at 9:43 AM, Kees Cook <keescook@...omium.org> wrote:
> >> All users of %n are calculating padding size when using seq_file, so
> >> instead use the new last_len member for discovering the length of the
> >> written strings.
> >
> > Would it make sense to provide a seq_pad(...) function instead, to avoid
> > exposing more seq_file internals to its callers?
> 
> We'd still need to track how much to pad.

If we add "size_t pad_until;" to "struct seq_file", we can do

void seq_setwidth(struct seq_file *m, size_t size)
{
	m->pad_until = m->count + size;
}

void seq_pad(struct seq_file *m, char c)
{
	int size = m->pad_until - m->count;
	if (size > 0)
		seq_printf(m, "%*s", size, "");
	if (c)
		seq_putc(m, c);
}

and use like

  seq_setwidth(m, 21);
  seq_printf(m, "%s%d", con->name, con->index);
  seq_pad(m, '\n');

.
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