Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757289Ab3C3Ttg (ORCPT ); Sat, 30 Mar 2013 15:49:36 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:45408 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757193Ab3C3Ttf (ORCPT ); Sat, 30 Mar 2013 15:49:35 -0400 Date: Sat, 30 Mar 2013 20:49:33 +0100 From: Pavel Machek To: =?iso-8859-1?Q?J=F6rn?= Engel Cc: Andy Lutomirski , Zach Brown , "Myklebust, Trond" , Paolo Bonzini , Ric Wheeler , 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? Message-ID: <20130330194933.GB1005@amd.pavel.ucw.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130226210232.GA19510@logfs.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1289 Lines: 29 Hi! > > I thought the first thing people would ask for is to atomically create a > > new file and copy the old file into it (at least on local file systems). > > The idea is that nothing should see an empty destination file, either > > by race or by crash. (This feature would perhaps be described as a > > pony, but it should be implementable.) > > Having already wasted many week trying to implement your pony, I would > consider it about as possible as winning the lottery three times in a > row. It clearly is in theory and yet,... Hmm, really? AFAICT it would be simple to provide 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. Pavel (who has too many (*) ponies around) (*) 1 is sometimes too many when we talk about big mammals. -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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/