From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755607AbaJWM4i (ORCPT ); Thu, 23 Oct 2014 08:56:38 -0400 Received: from relay1.mentorg.com ([192.94.38.131]:64386 "EHLO relay1.mentorg.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755296AbaJWM4h (ORCPT ); Thu, 23 Oct 2014 08:56:37 -0400 Message-ID: <5448FB01.1090108@mentor.com> Date: Thu, 23 Oct 2014 15:56:33 +0300 From: Vladimir Zapolskiy User-Agent: Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Icedove/31.0 MIME-Version: 1.0 To: Greg Kroah-Hartman CC: Tejun Heo , Subject: Re: [PATCH RESEND] fs: sysfs: return EFBIG on write if offset is larger than binary file size References: <1412876515-12057-1-git-send-email-vladimir_zapolskiy@mentor.com> <20141009184631.GA17554@mtj.dyndns.org> In-Reply-To: <20141009184631.GA17554@mtj.dyndns.org> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [137.202.0.76] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Greg, On 09.10.2014 21:46, Tejun Heo wrote: > Hello, Vladimir. > > On Thu, Oct 09, 2014 at 08:41:55PM +0300, Vladimir Zapolskiy wrote: >> According to the user expectations common utilities like dd or sh >> redirection operator '>' should work correctly over binary files from >> sysfs. At the moment doing excessive write can not be ever completed >> (no error is returned), e.g. for 4-byte file: >> >> write(1, "\0\0\0\0\0\0\0\0", 8) = 4 >> write(1, "\0\0\0\0", 4) = 0 >> write(1, "\0\0\0\0", 4) = 0 >> write(1, "\0\0\0\0", 4) = 0 >> write(1, "\0\0\0\0", 4) = 0 >> write(1, "\0\0\0\0", 4) = 0 >> ....... >> >> This is not a successful completion of write(2), so fix the problem by >> returning EFBIG as described in POSIX.1-2001: >> >> [EFBIG] >> The file is a regular file, nbyte is greater than 0, and the >> starting position is greater than or equal to the offset maximum >> established in the open file description associated with fildes. >> >> Note, the write(2) ABI is changed, however >> 1) write(2) behaviour is corrected in conformance to POSIX, the >> existing userspace applications must be aware of possible errors on >> a syscall, >> 2) the return value is changed on error path, so it is an exceptional >> situation, >> 3) the change is related only to binary sysfs files, which is a very >> small class of files, mainly representing non-volatile registers or >> ram, eeproms etc, many of such files are read-only. >> >> Presumably it is safe to apply the change, the described problem is >> definitely in the kernel and userspace utilities can not be changed to >> process 0 return value as an error, because it is just not an error >> according to POSIX. >> >> Signed-off-by: Vladimir Zapolskiy >> Cc: Greg Kroah-Hartman >> Cc: Tejun Heo > > This is a bit risky but the current behavior is problematic and as you > pointed out the danger of actual breakge is relatively low. We might > as well give it a shot. > > Cautiously-acked-by: Tejun Heo > > Please also cc stable. > > Thanks. have you had time to look at the problem? Understanding the risk of the change, should the inconsistency with POSIX be documented in Documentation/ABI/stable/syscalls instead? With best wishes, Vladimir