From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:36074 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725836AbeH3WFd (ORCPT ); Thu, 30 Aug 2018 18:05:33 -0400 Date: Thu, 30 Aug 2018 14:02:05 -0400 From: Brian Foster Subject: Re: [PATCH, RFC] xfs: re-enable FIBMAP on reflink; disable for swap Message-ID: <20180830180204.GC2853@bfoster> References: <2eb759e5-2faa-67fd-5c16-c1d8edc42d02@redhat.com> <20180830162545.GA26816@lst.de> <20180830163614.GA27069@lst.de> <65e818f2-885d-50a4-0d4a-7700c703c2af@sandeen.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <65e818f2-885d-50a4-0d4a-7700c703c2af@sandeen.net> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Eric Sandeen Cc: Christoph Hellwig , Eric Sandeen , linux-xfs On Thu, Aug 30, 2018 at 11:35:46AM -0500, Eric Sandeen wrote: > On 8/30/18 11:36 AM, Christoph Hellwig wrote: > > On Thu, Aug 30, 2018 at 11:31:40AM -0500, Eric Sandeen wrote: > >> That's no reason to uniquely disallow it for reflinked files, though; > >> the problem is universal. It's true for fiemap as well. So I'm not sure > >> that's an argument against the patch? > > > > fiemap at least tells you an extent is shared, bmap does not. > > yes, so bmap is clearly the wrong interface to use if you want to > write directly to a file's blocks. But if you know enough to check > the fiemap shared flag, you know enough to not use fibmap for that purpose... > FWIW, this patch seems reasonable to me. To Christoph's point, I don't think either interface really grants license to write to the underlying blocks, so either way it's technically being abused for this purpose. Unless there's a clear way to return an error for a particular type of file, I think it's reasonable behavior for fibmap to expose the data it supports (i.e., block maps) and drop the data it doesn't (reflink state). Brian > -Eric