Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S978547AbdDXVr4 (ORCPT ); Mon, 24 Apr 2017 17:47:56 -0400 Received: from mail-qt0-f195.google.com ([209.85.216.195]:34767 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S978532AbdDXVrn (ORCPT ); Mon, 24 Apr 2017 17:47:43 -0400 MIME-Version: 1.0 In-Reply-To: <20170421190929.7e90e8b2@blatinox-laptop.localdomain> References: <20170419203819.21951-1-jeremy.lefaure@lse.epita.fr> <20170421190929.7e90e8b2@blatinox-laptop.localdomain> From: Andy Shevchenko Date: Tue, 25 Apr 2017 00:47:41 +0300 Message-ID: Subject: Re: [PATCH] FS-Cache: print hexadecimal value for special cookies type To: =?UTF-8?B?SsOpcsOpbXkgTGVmYXVyZQ==?= Cc: David Howells , linux-cachefs@redhat.com, "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v3OLlx6L004169 Content-Length: 1963 Lines: 50 On Sat, Apr 22, 2017 at 2:09 AM, Jérémy Lefaure wrote: > On Fri, 21 Apr 2017 22:41:54 +0300 > Andy Shevchenko wrote: >> On Wed, Apr 19, 2017 at 11:38 PM, Jérémy Lefaure >> wrote: >> > When building object-list.o, gcc 6 raises a warning on the sprintf call >> > in fscache_objlist_show: >> > >> > CC fs/fscache/object-list.o >> > fs/fscache/object-list.c: In function ‘fscache_objlist_show’: >> > fs/fscache/object-list.c:265:19: warning: ‘sprintf’ may write a >> > terminating nul past the end of the destination [-Wformat-overflow=] >> > sprintf(_type, "%02u", cookie->def->type); >> > ^~~~~~ >> > fs/fscache/object-list.c:265:4: note: ‘sprintf’ output between 3 and 4 >> > bytes into a destination of size 3 >> > sprintf(_type, "%02u", cookie->def->type); >> > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> > >> > Moreover, the documentation says that we should have an hex value for >> > special cookies (see Documentation/filesystems/caching/fscache.txt). >> > >> > Printing hexadecimal value for special cookies fixes the overflow >> > warning and complies with the documentation. >> >> If this is used by some user space tool the safest fix is to print in >> BCD and fix documentation. >> > Are you talking about the Binary Coded Decimal format ? Yes. > I don't get why > it would be better. If we change the printed format, it would break > user space tool anyway, right ? If userspace tool is bound to the format it might go crazy about hex digits in the cookie. Is that cookie important somehow? (for example, user space might request something based on it?) It might be a case when you got let say '75' and then ask for 117 (0x75), however real value is 75. So, if it's okay in this, perhaps paragraph explaining side effects in commit message would be good to have/ -- With Best Regards, Andy Shevchenko