From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 677C0C433E0 for ; Fri, 12 Feb 2021 12:43:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3B62964DA5 for ; Fri, 12 Feb 2021 12:43:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231922AbhBLMna (ORCPT ); Fri, 12 Feb 2021 07:43:30 -0500 Received: from mx2.suse.de ([195.135.220.15]:59872 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231797AbhBLMlc (ORCPT ); Fri, 12 Feb 2021 07:41:32 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E8239AC90; Fri, 12 Feb 2021 12:40:47 +0000 (UTC) Received: from localhost (brahms [local]) by brahms (OpenSMTPD) with ESMTPA id 0e6ddaf3; Fri, 12 Feb 2021 12:41:49 +0000 (UTC) From: Luis Henriques To: Greg KH Cc: Jeff Layton , Amir Goldstein , Nicolas Boichat , "Darrick J . Wong" , Alexander Viro , Ian Lance Taylor , Luis Lozano , Dave Chinner , linux-fsdevel , linux-kernel Subject: Re: [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated References: <20210212044405.4120619-1-drinkcat@chromium.org> <20210212124354.1.I7084a6235fbcc522b674a6b1db64e4aff8170485@changeid> <871rdljxtx.fsf@suse.de> Date: Fri, 12 Feb 2021 12:41:48 +0000 In-Reply-To: (Greg KH's message of "Fri, 12 Feb 2021 13:18:13 +0100") Message-ID: <87sg61ihkj.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Greg KH writes: > On Fri, Feb 12, 2021 at 12:05:14PM +0000, Luis Henriques wrote: >> Greg KH writes: >> >> > On Fri, Feb 12, 2021 at 10:22:16AM +0200, Amir Goldstein wrote: >> >> On Fri, Feb 12, 2021 at 9:49 AM Greg KH wrote: >> >> > >> >> > On Fri, Feb 12, 2021 at 12:44:00PM +0800, Nicolas Boichat wrote: >> >> > > Filesystems such as procfs and sysfs generate their content at >> >> > > runtime. This implies the file sizes do not usually match the >> >> > > amount of data that can be read from the file, and that seeking >> >> > > may not work as intended. >> >> > > >> >> > > This will be useful to disallow copy_file_range with input files >> >> > > from such filesystems. >> >> > > >> >> > > Signed-off-by: Nicolas Boichat >> >> > > --- >> >> > > I first thought of adding a new field to struct file_operations, >> >> > > but that doesn't quite scale as every single file creation >> >> > > operation would need to be modified. >> >> > >> >> > Even so, you missed a load of filesystems in the kernel with this patch >> >> > series, what makes the ones you did mark here different from the >> >> > "internal" filesystems that you did not? >> >> > >> >> > This feels wrong, why is userspace suddenly breaking? What changed in >> >> > the kernel that caused this? Procfs has been around for a _very_ long >> >> > time :) >> >> >> >> That would be because of (v5.3): >> >> >> >> 5dae222a5ff0 vfs: allow copy_file_range to copy across devices >> >> >> >> The intention of this change (series) was to allow server side copy >> >> for nfs and cifs via copy_file_range(). >> >> This is mostly work by Dave Chinner that I picked up following requests >> >> from the NFS folks. >> >> >> >> But the above change also includes this generic change: >> >> >> >> - /* this could be relaxed once a method supports cross-fs copies */ >> >> - if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb) >> >> - return -EXDEV; >> >> - >> >> >> >> The change of behavior was documented in the commit message. >> >> It was also documented in: >> >> >> >> 88e75e2c5 copy_file_range.2: Kernel v5.3 updates >> >> >> >> I think our rationale for the generic change was: >> >> "Why not? What could go wrong? (TM)" >> >> I am not sure if any workload really gained something from this >> >> kernel cross-fs CFR. >> > >> > Why not put that check back? >> > >> >> In retrospect, I think it would have been safer to allow cross-fs CFR >> >> only to the filesystems that implement ->{copy,remap}_file_range()... >> > >> > Why not make this change? That seems easier and should fix this for >> > everyone, right? >> > >> >> Our option now are: >> >> - Restore the cross-fs restriction into generic_copy_file_range() >> > >> > Yes. >> > >> >> Restoring this restriction will actually change the current cephfs CFR >> behaviour. Since that commit we have allowed doing remote copies between >> different filesystems within the same ceph cluster. See commit >> 6fd4e6348352 ("ceph: allow object copies across different filesystems in >> the same cluster"). >> >> Although I'm not aware of any current users for this scenario, the >> performance impact can actually be huge as it's the difference between >> asking the OSDs for copying a file and doing a full read+write on the >> client side. > > Regression in performance is ok if it fixes a regression for things that > used to work just fine in the past :) > > First rule, make it work. Sure, I just wanted to point out that *maybe* there are other options than simply reverting that commit :-) Something like the patch below (completely untested!) should revert to the old behaviour in filesystems that don't implement the CFR syscall. Cheers, -- Luis diff --git a/fs/read_write.c b/fs/read_write.c index 75f764b43418..bf5dccc43cc9 100644 --- a/fs/read_write.c +++ b/fs/read_write.c @@ -1406,8 +1406,11 @@ static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in, file_out, pos_out, len, flags); - return generic_copy_file_range(file_in, pos_in, file_out, pos_out, len, - flags); + if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb) + return -EXDEV; + else + generic_copy_file_range(file_in, pos_in, file_out, pos_out, len, + flags); } /*