From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kay Sievers Subject: Re: [dm-devel] linux-next - WARNING: at fs/block_dev.c:824 bd_link_disk_holder+0x92/0x1ac() Date: Thu, 13 Jan 2011 17:10:02 +0100 Message-ID: References: <4D2EE156.1050006@redhat.com> <20110113122701.GG16523@nb.net.home> <20110113131216.GF30719@htj.dyndns.org> <20110113132637.GH16523@nb.net.home> <20110113133722.GG30719@htj.dyndns.org> <4D2F04FF.1070309@redhat.com> <20110113141107.GI30719@htj.dyndns.org> <4D2F0B6A.6010201@redhat.com> <20110113155955.GI16523@nb.net.home> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Tejun Heo , Milan Broz , device-mapper development , "Jun'ichi Nomura" , Valdis.Kletnieks@vt.edu, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Alexander Viro , linux-fsdevel@vger.kernel.org To: Karel Zak Return-path: In-Reply-To: <20110113155955.GI16523@nb.net.home> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Jan 13, 2011 at 16:59, Karel Zak wrote: > On Thu, Jan 13, 2011 at 03:43:38PM +0100, Kay Sievers wrote: >> On Thu, Jan 13, 2011 at 15:30, Tejun Heo wrote: >> > On Thu, Jan 13, 2011 at 3:25 PM, Milan Broz wro= te: >> >> Maybe, but this was not invented in DM/MD camp:-) >> >> Probably Kay or Greg can answer why it was done this way? >> >> It's not from Greg or Kay. It just appeared some day in the context = of dm. :) >> >> And yes, symlinks *look* nice and simple for the outside, but they a= re >> not, and have all sorts of problems like non-atomic updates, make it > > =C2=A0Sounds like sysfs implementation problem, right? It's a normal multi-file problem. It can by-definition not be atomic without doing really weird locking things. > =C2=A0If there is noway to fix sysfs then we can add a generic ioctl = or > =C2=A0/sys/block//{slave,holder}_list files with list of > =C2=A0holders/slaves. Yeah, we've been there with the btrfs problem. For btrfs it woud probably need to be something statfs()-like. > =C2=A0But please, don't force userspace to use *claimer-specific* > =C2=A0methods to answer *generic questions* like slave/holder depende= ncies > =C2=A0between devices. The links exist only for dm and md so far, I think. It's the classical multiple-parents-in-a-tree problem. We have that for bonded network devices and some IO buses too. There is no nice representation for these reversed-trees-in-the-tree so far. Kay