Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756458Ab3CaEhE (ORCPT ); Sun, 31 Mar 2013 00:37:04 -0400 Received: from mx1.netapp.com ([216.240.18.38]:9114 "EHLO mx1.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751333Ab3CaEhB convert rfc822-to-8bit (ORCPT ); Sun, 31 Mar 2013 00:37:01 -0400 X-IronPort-AV: E=Sophos;i="4.87,381,1363158000"; d="scan'208";a="249779997" From: "Myklebust, Trond" To: Andy Lutomirski CC: Andreas Dilger , Ric Wheeler , Pavel Machek , =?iso-8859-1?Q?J=F6rn_Engel?= , Zach Brown , Paolo Bonzini , "Linux FS Devel" , "linux-kernel@vger.kernel.org" , "Chris L. Mason" , Christoph Hellwig , Alexander Viro , "Martin K. Petersen" , Hannes Reinecke , "Joel Becker" Subject: Re: New copyfile system call - discuss before LSF? Thread-Topic: New copyfile system call - discuss before LSF? Thread-Index: AQHOECfzherspfmEjEqBTzfvhb3EUJiE2wAAgAASTQCAAFTBgIAADekAgAAaWoCABjXIAIABjuMAgDIlc4CAAAVWgIAAGvaAgAADUYCAABd/gIAAOzoAgAAQoACAAAc5gIAABS6A Date: Sun, 31 Mar 2013 04:36:59 +0000 Message-ID: <1364704619.3403.3.camel@leira.trondhjem.org> References: <512606DF.5050706@redhat.com> <4FA345DA4F4AE44899BD2B03EEEC2FA9235D998C@SACEXCMBX04-PRD.hq.netapp.com> <512635D2.4090207@redhat.com> <51267CEB.8070805@redhat.com> <4FA345DA4F4AE44899BD2B03EEEC2FA9235DAA99@SACEXCMBX04-PRD.hq.netapp.com> <20130221222449.GY22221@lenny.home.zabbo.net> <512BD44C.40907@amacapital.net> <20130226210232.GA19510@logfs.org> <20130330194933.GB1005@amd.pavel.ucw.cz> <08D26E22-3856-43A4-8835-48C86CC5F71C@dilger.ca> <20130330214509.GB4322@amd.pavel.ucw.cz> <925D663D-D8F8-4297-A642-33C732354701@netapp.com> <51577363.9060201@redhat.com> <21F42B67-1C8B-444A-899A-AE649D4043C3@dilger.ca> <1364701956.2773.12.camel@leira.trondhjem.org> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.104.60.115] Content-Type: text/plain; charset=US-ASCII Content-ID: <851AF0A2AE061B4D9362619B2270D78F@tahoe.netapp.com> Content-Transfer-Encoding: 7BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3098 Lines: 65 On Sat, 2013-03-30 at 21:18 -0700, Andy Lutomirski wrote: > On Sat, Mar 30, 2013 at 8:52 PM, Myklebust, Trond > wrote: > > On Sat, 2013-03-30 at 19:53 -0700, Andreas Dilger wrote: > >> On 2013-03-30, at 16:21, Ric Wheeler wrote: > >> > >> > On 03/30/2013 05:57 PM, Myklebust, Trond wrote: > >> >> On Mar 30, 2013, at 5:45 PM, Pavel Machek > >> >> wrote: > >> >> > >> >>> On Sat 2013-03-30 13:08:39, Andreas Dilger wrote: > >> >>>> On 2013-03-30, at 12:49 PM, Pavel Machek wrote: > >> >>>>> Hmm, really? AFAICT it would be simple to provide an > >> >>>>> open_deleted_file("directory") syscall. You'd open_deleted_file(), > >> >>>>> copy source file into it, then fsync(), then link it into filesystem. > >> >>>>> > >> >>>>> That should have atomicity properties reflected. > >> >>>> Actually, the open_deleted_file() syscall is quite useful for many > >> >>>> different things all by itself. Lots of applications need to create > >> >>>> temporary files that are unlinked at application failure (without a > >> >>>> race if app crashes after creating the file, but before unlinking). > >> >>>> It also avoids exposing temporary files into the namespace if other > >> >>>> applications are accessing the directory. > >> >>> Hmm. open_deleted_file() will still need to get a directory... so it > >> >>> will still need a path. Perhaps open("/foo/bar/mnt", O_DELETED) would > >> >>> be acceptable interface? > >> >>> Pavel > >> >> ...and what's the big plan to make this work on anything other than ext4 and btrfs? > >> >> > >> >> Cheers, > >> >> Trond > >> > > >> > I know that change can be a good thing, but are we really solving a pressing problem given that application developers have dealt with open/rename as the way to get "atomic" file creation for several decades now ? > >> > >> Using open()+rename() has side effects: > >> - changes ctime/mtime on parent directory > >> - leaves temporary file in path during creation > >> - leaves temporary file in namespace during operations, and after crash > > > > So what is the actual problem that is being solved? Yes, the above may > > be disadvantages, but none of them have proven to be show-stoppers so > > far. > > > > So far, I've seen no justification for Andy's atomicity requirement > > other than "it would be nice if...". That's not enough IMO... > > ISTM vpsendfile (or whatever it's called) plus a way to create deleted > files plus a way to relink deleted files gives atomic copies. Perhaps > this is less efficient than would be ideal for OCFS2, though. What real-life problem does the atomicity requirement solve? None of our customers have ever asked for it. They don't care... -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@netapp.com www.netapp.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/