Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756649AbZIRNmp (ORCPT ); Fri, 18 Sep 2009 09:42:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754566AbZIRNmp (ORCPT ); Fri, 18 Sep 2009 09:42:45 -0400 Received: from mail1.slb.deg.dub.stisp.net ([84.203.253.98]:7350 "HELO mail1.slb.deg.dub.stisp.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754239AbZIRNmo (ORCPT ); Fri, 18 Sep 2009 09:42:44 -0400 X-Greylist: delayed 397 seconds by postgrey-1.27 at vger.kernel.org; Fri, 18 Sep 2009 09:42:44 EDT Message-ID: <4AB38C5A.4070506@draigBrady.com> Date: Fri, 18 Sep 2009 14:34:18 +0100 From: =?ISO-8859-1?Q?P=E1draig_Brady?= User-Agent: Thunderbird 2.0.0.6 (X11/20071008) MIME-Version: 1.0 To: Linus Torvalds , Mark Fasheh , Andrew Morton , Linux Kernel Mailing List , ocfs2-devel@oss.oracle.com Subject: Re: [Ocfs2-devel] [GIT PULL] ocfs2 changes for 2.6.32 References: <20090915000417.GC4507@mail.oracle.com> <20090915005417.GD4507@mail.oracle.com> <20090915040601.GE4507@mail.oracle.com> <20090915214530.GA11060@mail.oracle.com> <20090916044047.GA30453@mail.oracle.com> <20090918014333.GD15620@mail.oracle.com> In-Reply-To: <20090918014333.GD15620@mail.oracle.com> X-Enigmail-Version: 0.95.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1236 Lines: 35 Joel Becker wrote: > On Thu, Sep 17, 2009 at 09:29:14AM -0700, Linus Torvalds wrote: >> Why would anybody want to hide it at all? Why even the libc hiding? >> >> Nobody is going to use this except for special apps. Let them see what >> they can do, in all its glory. > > I expect everyone will use this through cp(1), so that cp(1) can > try to get server-side copy on the network filesystms. For reference, cp(1) has a --reflink option as of coreutils-7.5 which currently just does: ioctl (dest_fd, BTRFS_IOC_CLONE, src_fd); There is a specific option in cp to do this because a "reflink copy" was seen to have these disadvantages: 1. one copy of data blocks so more chances of data loss 2. disk head seeking deferred to modification process 3. possible fragmentation on write 4. possible ENOSPC on write Now 2. will go away with time, and 3 & 4 may be alleviated by the use of fallocate(), but 1. was deemed important enough to not enable by default. cheers, P?draig. -- 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/