From: Dave Chinner Subject: Re: [PATCH 3/3] Add timeout feature Date: Wed, 9 Jul 2008 17:13:46 +1000 Message-ID: <20080709071346.GS11558@disturbed> References: <20080708231026.GP11558@disturbed> <20080708232031.GE18195@elf.ucw.cz> <20080709005254.GQ11558@disturbed> <20080709010922.GE9957@mit.edu> <20080709061621.GA5260@infradead.org> <20080708234120.5072111f@infradead.org> <20080708235502.1c52a586@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Miklos Szeredi , hch@infradead.org, tytso@mit.edu, pavel@suse.cz, t-sato@yk.jp.nec.com, akpm@linux-foundation.org, viro@ZenIV.linux.org.uk, linux-ext4@vger.kernel.org, xfs@oss.sgi.com, dm-devel@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, axboe@kernel.dk, mtk.manpages@googlemail.com To: Arjan van de Ven Return-path: Received: from ipmail01.adl6.internode.on.net ([203.16.214.146]:38216 "EHLO ipmail01.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751119AbYGIHNv (ORCPT ); Wed, 9 Jul 2008 03:13:51 -0400 Content-Disposition: inline In-Reply-To: <20080708235502.1c52a586@infradead.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Jul 08, 2008 at 11:55:02PM -0700, Arjan van de Ven wrote: > On Wed, 09 Jul 2008 08:48:42 +0200 > Miklos Szeredi wrote: > > > On Tue, 8 Jul 2008, Arjan van de Ven wrote: > > > nah he needs to do > > > > > > make_snapshot ; backup-command ; unref_snapshot. > > > > > > freezing isn't the right solution for the backup problem ;) > > > > Confused, what's freezing _is_ for then? Patch description says: > > > > Currently, ext3 in mainline Linux doesn't have the freeze feature > > which suspends write requests. So, we cannot take a backup which > > keeps the filesystem's consistency with the storage device's features > > (snapshot and replication) while it is mounted. > > I tihnk the idea there is > > freeze . do the snapshot op . unfreeze . make backup of snapshot > > one can argue about the need of doing the first 3 steps via a userland > loop; it sure sounds like one needs to be really careful to not do any > writes to the fs from the app that does snapshots (and that includes > doing any syscalls in the kernel that allocate memory.. just because > that already could cause unrelated data to be written from inside the > app. Not fun.) Bloody hell! Doesn't *anyone* understand that a frozen filesystem is *clean*? That the process of freezing it ensures all dirty data and metadata is written out before the freeze completes? And that once frozen, it can't be dirtied until unfrozen? That's 3 (or is it 4 - maybe 5 now that I think about it) different ppl in 24 hours that have made this same broken argument about being unable to write back dirty data on a frozen filesystem...... Cheers, Dave. -- Dave Chinner david@fromorbit.com