Return-Path: Received: from fieldses.org ([173.255.197.46]:56426 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725951AbeJCBMm (ORCPT ); Tue, 2 Oct 2018 21:12:42 -0400 Date: Tue, 2 Oct 2018 14:28:00 -0400 To: Andreas Dilger Cc: Eric Sandeen , Qu Wenruo , Joshi , linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org Subject: Re: cross-fs copy support Message-ID: <20181002182800.GA8364@fieldses.org> References: <2a92fff4-d005-835a-3bd7-a328b008857f@gmx.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: From: bfields@fieldses.org (J. Bruce Fields) Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Oct 01, 2018 at 01:51:09PM -0600, Andreas Dilger wrote: >    On Oct 1, 2018, at 9:49 AM, Eric Sandeen wrote: > > Yes, I would expect there to be problems with his modified kernel > > for a filesystem that supports clone_file_range, because > > vfs_copy_file_range() will clone if possible, and this should fail across > > filesystems. > > > > In general, though, I don't know for sure why we don't fall back to > > do_splice_direct() across filesystems, although the filesystems that > > implement their own ->copy_file_range ops may have their own, > > further restrictions within their implementations. > > > > This call /is/ documented in the manpage as only being valid for > > files on the same filesystem, though: > > http://man7.org/linux/man-pages/man2/copy_file_range.2.html > > There was a patch to allow cross-mount copy for NFS, but it hasn't landed > yet. I thought Christoph Hellwig vetoed it partly because he thought NFS server-to-server copy is too complicated. Which perhaps it is, but I suspect we'll do it anyway because the benefit seems obvious. --b.