Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756095Ab3CaESv (ORCPT ); Sun, 31 Mar 2013 00:18:51 -0400 Received: from mail-ve0-f171.google.com ([209.85.128.171]:49312 "EHLO mail-ve0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755274Ab3CaESt (ORCPT ); Sun, 31 Mar 2013 00:18:49 -0400 MIME-Version: 1.0 In-Reply-To: <1364701956.2773.12.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> From: Andy Lutomirski Date: Sat, 30 Mar 2013 21:18:27 -0700 Message-ID: Subject: Re: New copyfile system call - discuss before LSF? To: "Myklebust, Trond" 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 Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2726 Lines: 55 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. --Andy -- 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/