Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755707Ab2FTSH2 (ORCPT ); Wed, 20 Jun 2012 14:07:28 -0400 Received: from mail-qa0-f50.google.com ([209.85.216.50]:61000 "EHLO mail-qa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752139Ab2FTSH0 (ORCPT ); Wed, 20 Jun 2012 14:07:26 -0400 Message-ID: <1340215644.6961.12.camel@cwalton-XPS-8300> Subject: Re: [PATCH] Allow cross subvolume reflinks (2nd attempt) From: Calvin Walton To: Alexander Block Cc: kreijack@inwind.it, linux-btrfs@vger.kernel.org, dave@jikos.cz, hch@infradead.org, linux-fsdevel@vger.kernel.org, chris.mason@fusionio.com, linux-kernel@vger.kernel.org Date: Wed, 20 Jun 2012 14:07:24 -0400 In-Reply-To: References: <1340188512-5761-1-git-send-email-ablock84@googlemail.com> <4FE205CF.9020509@libero.it> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 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: 1823 Lines: 44 On Wed, 2012-06-20 at 19:27 +0200, Alexander Block wrote: > On Wed, Jun 20, 2012 at 7:18 PM, Goffredo Baroncelli wrote: > > Hi Alexander, > > > > On 06/20/2012 12:35 PM, Alexander Block wrote: > >> The patch also does proper vfs mount checks, so cross mount > >> point reflinks are not possible with this patch. It only allows cross > >> reflinks between two subvolumes which are in the same mount point. > > > > Thanks for working on that. What happens if two subvolumes of the same > > filesystem are mounted on two different places ? > > > > I usually do: > > mount -o subvol=__active /dev/sdX / > > mount -o subvol=. /dev/sdX /var/btrfs > > > > So two different subvolumes of the same filesystem (the one on /dev/sdX) > > are mounted on two different places. > > > > Is it possible to do > > cp --reflink /tmp/foo /var/btrfs/tmp/foo2 > This will fail with -EXDEV. The patch explicitly forbids reflinks crossing vfs > mount boundaries. Which means that if I want to do a reflink copy between two separately mounted subvolumes, I will have to go and do a third mount with a common subvolume above those two, then do the reflink operation within this extra mount? This seems slightly impractical. Is it any extra code to enable doing cross-mount reflinks? Why was the decision made not to allow them? Is there some particular opposition to supporting cross-mount operations on multiple mounts of the same filesystem in general? (I'd love to have rename() work across bind mounts, for example...) -- Calvin Walton -- 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/