From mboxrd@z Thu Jan 1 00:00:00 1970 From: Al Viro Subject: Re: [RFC PATCH] vsnprintf: Remove use of %n and convert existing uses Date: Thu, 12 Sep 2013 01:19:11 +0100 Message-ID: <20130912001911.GO13318@ZenIV.linux.org.uk> References: <1378926562.4714.11.camel@joe-AO722> <1378928700.4714.17.camel@joe-AO722> <1378941761.4714.37.camel@joe-AO722> <201309120840.HHE37542.OJMFFHSOQOtVFL@I-love.SAKURA.ne.jp> <1378944257.4714.45.camel@joe-AO722> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Tetsuo Handa , linux-kernel@vger.kernel.org, kosaki.motohiro@jp.fujitsu.com, keescook@chromium.org, fweisbec@gmail.com, dan.carpenter@oracle.com, devel@driverdev.osuosl.org, gregkh@linuxfoundation.org, tushar.behera@linaro.org, lidza.louina@gmail.com, davem@davemloft.net, kuznet@ms2.inr.ac.ru, jmorris@namei.org, yoshfuji@linux-ipv6.org, kaber@trash.net, courmisch@gmail.com, vyasevich@gmail.com, nhorman@tuxdriver.com, netdev@vger.kernel.org, linux-sctp@vger.kernel.org To: Joe Perches Return-path: Received: from zeniv.linux.org.uk ([195.92.253.2]:33520 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751195Ab3ILATZ (ORCPT ); Wed, 11 Sep 2013 20:19:25 -0400 Content-Disposition: inline In-Reply-To: <1378944257.4714.45.camel@joe-AO722> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Sep 11, 2013 at 05:04:17PM -0700, Joe Perches wrote: > 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. ...) ... and most of that code proceeds to ignore pos completely. Note that ->show() is *NOT* supposed to return the number of characters it has/would like to have produced. Just return 0 and be done with that; overflows are dealt with just fine. The large amount, BTW, is below 100 lines, AFAICS, in rather few files. > There are very few that seem to use it correctly > like netfilter. > Suggestions? Just bury the cargo-culting crap. All those += seq_printf() should be simply calling it. The *only* reason to look at the return value is "if we'd already overflown the buffer, I'd rather skipped the costly generation of the rest of the record". In that case seq_printf() returning -1 means "skip it, nothing else will fit and caller will be repeating with bigger buffer anyway".