From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753351AbZC2M0U (ORCPT ); Sun, 29 Mar 2009 08:26:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751647AbZC2M0K (ORCPT ); Sun, 29 Mar 2009 08:26:10 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:51078 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751211AbZC2M0J (ORCPT ); Sun, 29 Mar 2009 08:26:09 -0400 Date: Sun, 29 Mar 2009 14:26:00 +0200 From: Pavel Machek To: Artem Bityutskiy Cc: Linux Kernel Mailing List Subject: replace() system call needed (was Re: EXT4-ish "fixes" in UBIFS) Message-ID: <20090329122600.GA13737@elf.ucw.cz> References: <49CCCB0A.6070701@nokia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <49CCCB0A.6070701@nokia.com> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 2009-03-27 14:48:10, Artem Bityutskiy wrote: > UBIFS has exactly the same properties like ext4 - in case > of power cuts: > > 1. truncate/write/close leads to empty files > 2. create/write/rename leads to empty files > > UBIFS is used in hand-held and and power-cuts are very > often there, because users just remove battery often. > > I realize the "reality is different" argument, and already > concluded that we need a similar changes as Theo has done > for ext4: > http://git.kernel.org/?p=linux/kernel/git/tytso/ext4.git;a=commitdiff;h=bf1b69c0db7f9b9d8f02e94d40b19fca8336b991 > http://git.kernel.org/?p=linux/kernel/git/tytso/ext4.git;a=commitdiff;h=f32b730a69bd56c5c9d704d8b75f03e90e290971 > http://git.kernel.org/?p=linux/kernel/git/tytso/ext4.git;a=commitdiff;h=8411e347c3306ed36b8ca88611bf5fbf4d27d705 > > We have a problem that user-space people do not want to > use 'fsync()', even when they are pointed to their code > which is doing create/write/rename/close without fsync(). Well... they really don't want to spin the disk up for the fsync(). I'm not sure if fsync() is really sensible operation to use there. > 1. truncate/write/close leads to empty files this is buggy. > 2. create/write/rename leads to empty files ...but this should not be. If we want to make that explicit, we should provide "replace()" operation; where replace is rename that makes sure that source file is completely on media before commiting the rename. It is somehow similar to fsync()/rename(), but does not force disk spin up immediately -- it only inserts "barrier" between data blocks and rename. (And yes, it should be implemented as fsync()+rename() for filesystems like xfs. It can be implemented as plain rename for ext3 and ext4 after the fixes...) Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html