From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756156Ab3CaCxN (ORCPT ); Sat, 30 Mar 2013 22:53:13 -0400 Received: from mail-oa0-f48.google.com ([209.85.219.48]:48248 "EHLO mail-oa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755481Ab3CaCxL convert rfc822-to-8bit (ORCPT ); Sat, 30 Mar 2013 22:53:11 -0400 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> Mime-Version: 1.0 (1.0) In-Reply-To: <51577363.9060201@redhat.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8BIT Message-Id: <21F42B67-1C8B-444A-899A-AE649D4043C3@dilger.ca> Cc: "Myklebust, Trond" , Pavel Machek , =?utf-8?Q?J=C3=B6rn_Engel?= , Andy Lutomirski , 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 X-Mailer: iPhone Mail (10B146) From: Andreas Dilger Subject: Re: New copyfile system call - discuss before LSF? Date: Sat, 30 Mar 2013 19:53:06 -0700 To: Ric Wheeler Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cheers, Andreas