linux-kernel - Re: [RFC PATCH] vsnprintf: Remove use of %n and convert existing uses

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Date:	Wed, 11 Sep 2013 17:04:17 -0700
From:	Joe Perches <joe@...ches.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	linux-kernel@...r.kernel.org, kosaki.motohiro@...fujitsu.com,
	keescook@...omium.org, fweisbec@...il.com,
	dan.carpenter@...cle.com, devel@...verdev.osuosl.org,
	gregkh@...uxfoundation.org, tushar.behera@...aro.org,
	lidza.louina@...il.com, davem@...emloft.net, kuznet@....inr.ac.ru,
	jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net,
	courmisch@...il.com, vyasevich@...il.com, nhorman@...driver.com,
	netdev@...r.kernel.org, linux-sctp@...r.kernel.org
Subject: Re: [RFC PATCH] vsnprintf: Remove use of %n and convert existing
 uses

On Thu, 2013-09-12 at 08:40 +0900, Tetsuo Handa wrote:
> Joe Perches wrote:
> > -	seq_printf(m, "%s%d%n", con->name, con->index, &len);
> > +	len = seq_printf(m, "%s%d", con->name, con->index);
> 
> Isn't len always 0 or -1 ?

Right.  Well you're no fun...

These uses would seem broken anyway because the
seq_printf isn't itself tested for correctness.

Hmm.

Also, there's a large amount of code that appears
to do calculations with pos or len like:

	pos += seq_printf(handle, fmt. ...)

There are very few that seem to use it correctly
like netfilter.

$ grep -rP --include=*.[ch] "^[ \t]*\S[ \t\S]*\bseq_[v]?printf\b" *

Suggestions?

> int seq_vprintf(struct seq_file *m, const char *f, va_list args)
> {
> 	int len;
> 
> 	if (m->count < m->size) {
> 		len = vsnprintf(m->buf + m->count, m->size - m->count, f, args);
> 		if (m->count + len < m->size) {
> 			m->count += len;
> 			return 0;
> 		}
> 	}
> 	seq_set_overflow(m);
> 	return -1;
> }
> EXPORT_SYMBOL(seq_vprintf);
> 
> int seq_printf(struct seq_file *m, const char *f, ...)
> {
> 	int ret;
> 	va_list args;
> 
> 	va_start(args, f);
> 	ret = seq_vprintf(m, f, args);
> 	va_end(args);
> 
> 	return ret;
> }
> EXPORT_SYMBOL(seq_printf);


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