From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?utf-8?B?SsO2cm4=?= Engel Subject: Re: Proposal for "proper" durable fsync() and fdatasync() Date: Tue, 26 Feb 2008 18:02:14 +0100 Message-ID: <20080226170214.GA23829@lazybastard.org> References: <20080226072649.GB30238@shareable.org> <20080225234319.f4589ae4.akpm@linux-foundation.org> <20080226075921.GG30238@shareable.org> <200802262016.11297.nickpiggin@yahoo.com.au> <20080226140925.GB20428@lazybastard.org> <20080226152810.GB18118@shareable.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: =?utf-8?B?SsO2cm4=?= Engel , Nick Piggin , Andrew Morton , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Chris Wedgwood To: Jamie Lokier Return-path: Content-Disposition: inline In-Reply-To: <20080226152810.GB18118@shareable.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Tue, 26 February 2008 15:28:10 +0000, Jamie Lokier wrote: >=20 > > One interesting aspect of this comes with COW filesystems like btrf= s or > > logfs. Writing out data pages is not sufficient, because those wil= l get > > lost unless their referencing metadata is written as well. So eith= er we > > have to call fsync for those filesystems or add another callback an= d let > > filesystems override the default implementation. >=20 > Doesn't the ->fsync callback get called in the sys_fdatasync() case, > with appropriate arguments? My paragraph above was aimed at the sync_file_range() case. fsync and fdatasync do the right thing within the limitations you brought up in this thread. sync_file_range() without further changes will only write data pages, not the metadata required to actually access those data pages. This works just fine for non-COW filesystems, which covers all currently merged ones. With COW filesystems it is currently impossible to do sync_file_range() properly. The problem is orthogonal to your's, I just brought it up since you were already mentioning sync_file_range(). J=C3=B6rn --=20 Joern's library part 10: http://blogs.msdn.com/David_Gristwood/archive/2004/06/24/164849.aspx