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=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED 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 C22C9C433DB for ; Mon, 15 Feb 2021 06:13:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A9FD64E51 for ; Mon, 15 Feb 2021 06:13:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229578AbhBOGM4 (ORCPT ); Mon, 15 Feb 2021 01:12:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229486AbhBOGMz (ORCPT ); Mon, 15 Feb 2021 01:12:55 -0500 Received: from mail-il1-x135.google.com (mail-il1-x135.google.com [IPv6:2607:f8b0:4864:20::135]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 594EFC061574; Sun, 14 Feb 2021 22:12:15 -0800 (PST) Received: by mail-il1-x135.google.com with SMTP id o15so4608944ilt.6; Sun, 14 Feb 2021 22:12:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=AIfzBFyCNv86KZ5EeKdCATv8zV74pSszmiyVwnpE6Nc=; b=k0IBTbrK0ESj9dqk3Z3e4KEyh1g/vcsSuFVfp1fSer/oIilr0RdHix+c2QAgcoPE9p QMFfuNTMqtPcZncO6cLPA9nlKIOr6rqGaPVVlKM1g/mUpgATLpepq4fnrX7xlzlWoPO6 CaChIG7Up1dRFW+7LgvDOVR97E91Tw4aJgHMErvwWBwVhW0lqJ2U6pvkK/t2TbBMyZWu jaPIJhV7jBgD8aiJTU9PbiOrZry46KkC8ROXITo1ZFVVRA06KabcbK2Hi3tbxQ765Oqj Y101ZFwTzkwnuv89UxKYAoTwqEcYVsnwCINgnzWXiaLKS43NZR1W3NknAr3CfzMPQUpW NHyA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=AIfzBFyCNv86KZ5EeKdCATv8zV74pSszmiyVwnpE6Nc=; b=gk1OlE1lQVCP9lusdKStgu6VTU0YDuUyq03ApKLUOZTYYziSFYbA9R0Ndt5jA+Qfzy UCeZR7QvukbnnY4xAs4iu4FjmZnPBAkPPRkOs5nW2nACAoEzOIBp1X0g+qspug4PyTys 5EJdKPC+lAMyFh5+0WMdHjdLoilwwMABApUe4I4O+y/UikK9gX6Ix6fYpzuJGSPfGlQj t8ed0igp5mQbv8kIyjwHSA0IKpgJT+xFZ8D4o+btHEP3Ro73fof90f3hcTeCkqAjwmh+ 7lW7YswQhOqeloDZ3Lg4RbL0ILcY4XiTTRJFQV0G/uCYsMePeVMsQm5crHvW2H+yb4Je BLOg== X-Gm-Message-State: AOAM533JE7JWzidYX338mTERhbblEf72BkgwbVlaCzaLSeoDF7gsFoJM MnmOt0KPvkZJyRT2sOkdcQeDiDs3C3H/Wu8WNcI= X-Google-Smtp-Source: ABdhPJyb23eBt7g724jOrO2qq+oMbkHZIz8bp0GNBdYcDx3Cy3rmgj4gyvL7c1Co5feWV7tFpRi2Qd/lsAnw+J53Hp8= X-Received: by 2002:a92:8e42:: with SMTP id k2mr12099589ilh.250.1613369534723; Sun, 14 Feb 2021 22:12:14 -0800 (PST) MIME-Version: 1.0 References: <20210212044405.4120619-1-drinkcat@chromium.org> <20210212124354.1.I7084a6235fbcc522b674a6b1db64e4aff8170485@changeid> <871rdljxtx.fsf@suse.de> <87sg61ihkj.fsf@suse.de> In-Reply-To: <87sg61ihkj.fsf@suse.de> From: Amir Goldstein Date: Mon, 15 Feb 2021 08:12:03 +0200 Message-ID: Subject: Re: [PATCH 1/6] fs: Add flag to file_system_type to indicate content is generated To: Luis Henriques Cc: Greg KH , Jeff Layton , Nicolas Boichat , "Darrick J . Wong" , Alexander Viro , Ian Lance Taylor , Luis Lozano , Dave Chinner , linux-fsdevel , linux-kernel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Feb 12, 2021 at 2:40 PM Luis Henriques wrote: > > 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); > } > Which kernel is this patch based on? At this point, I am with Dave and Darrick on not falling back to generic_copy_file_range() at all. We do not have proof of any workload that benefits from it and the above patch does not protect from a wierd use case of trying to copy a file from sysfs to sysfs. I am indecisive about what should be done with generic_copy_file_range() called as fallback from within filesystems. I think the wise choice is to not do the fallback in any case, but this is up to the specific filesystem maintainers to decide. Thanks, Amir.