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=-3.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 48856C63777 for ; Tue, 17 Nov 2020 05:42:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ECF6C24198 for ; Tue, 17 Nov 2020 05:42:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="YIt1jnPD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726316AbgKQFlw (ORCPT ); Tue, 17 Nov 2020 00:41:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726274AbgKQFlv (ORCPT ); Tue, 17 Nov 2020 00:41:51 -0500 Received: from mail-il1-x144.google.com (mail-il1-x144.google.com [IPv6:2607:f8b0:4864:20::144]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BBF9FC0613CF; Mon, 16 Nov 2020 21:41:51 -0800 (PST) Received: by mail-il1-x144.google.com with SMTP id y18so10240864ilp.13; Mon, 16 Nov 2020 21:41:51 -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=4uP0R4NMek+c9p+edkiMYaC2lOlHd67i9h4rSBZ4QGE=; b=YIt1jnPD4pcSqM6gNNrslEYZqoa3Wm8d4SYuvafhQWRR0bNNdIiBKkGFz3mLsZjiw3 XovPQMcH1m2EZ7Cs+Ifs6YPdroHxMzwxd6nicwF11L1rxHiUCB493IJvdJMUpvaRNg3L 8SOBy8NVKl1+teRICIP2SVo2B7+DXnZ5QwWE2TnEgcC8e4RYz+WMtXGuakpF/aH0AUKT C4lumr3ipiz1trXE3IfBHbbU4UcLYqF5/JhIhwERAnhoZm9Dwya/H2GN40jYyBdjOIxq sFjhQSc910VRZhYkcqG2vozEyh4S6oqbA5HAECeKOqkeQtOhJn3ZdeRSYKkY4ZYK0nU9 AcJQ== 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=4uP0R4NMek+c9p+edkiMYaC2lOlHd67i9h4rSBZ4QGE=; b=jo6z2G/8RwGv2MIrrh2oMOqiQksXJNAin1/zPrXGzUtZnkk15XsHBJjtS8kaz2tcRs hSGTUZd/1Q/8YCK226YWaZlI410VOXfzS7xMT4TzvI0BE71KMs9ptsODetvqKZ4H0HMW WOs6Ds0ydq0l4sqDlCwFHWs8pA27HqX2ztwjLR+VA6wFXn0GhALdEepvlEyxXpTsPTJO wjhpnGk3izAONv6rZEqDIun9buaY6LsadkXITxq5zbhvySTBGor6EwzzcKsOcfNpjZTH BcGp8yQZ9qzCA21zYSwv1HiTMh9A9DraxfRjklw5LTKOiVmq+hYa6xfjrnaTX4JbBxMR N0vA== X-Gm-Message-State: AOAM5332m661LrPpnaT9XPO2chYyMRy6Vb3LxEaLz1R8A3E8z5Gn2eNP cu6wO4LcxI/KXVHpHFwOEqABD5ICmc71vak4/v4= X-Google-Smtp-Source: ABdhPJw1PmowWRS71CiSsLwz4ShaMDnkL1iLcri2fbmdXbqb9K34Ui9UH2LpgeTnv8pCeUoaXqMwdOltuo6tw/feqtg= X-Received: by 2002:a92:bac5:: with SMTP id t66mr11045762ill.250.1605591711122; Mon, 16 Nov 2020 21:41:51 -0800 (PST) MIME-Version: 1.0 References: <20201116045758.21774-1-sargun@sargun.me> <20201116045758.21774-4-sargun@sargun.me> <20201116144240.GA9190@redhat.com> <20201116163615.GA17680@redhat.com> <20201116212644.GE9190@redhat.com> <20201116221401.GA21744@ircssh-2.c.rugged-nimbus-611.internal> In-Reply-To: <20201116221401.GA21744@ircssh-2.c.rugged-nimbus-611.internal> From: Amir Goldstein Date: Tue, 17 Nov 2020 07:41:39 +0200 Message-ID: Subject: Re: [RFC PATCH 3/3] overlay: Add the ability to remount volatile directories when safe To: Sargun Dhillon Cc: Vivek Goyal , overlayfs , Miklos Szeredi , Alexander Viro , Giuseppe Scrivano , Daniel J Walsh , David Howells , linux-fsdevel , Chengguang Xu Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org > > > I think upper files data can "evaporate" even as the overlay is still mounted. > > > > I think assumption of volatile containers was that data will remain > > valid as long as machine does not crash/shutdown. We missed the case > > of possibility of writeback errors during those discussions. > > > > And if data can evaporate without anyway to know that somehthing > > is gone wrong, I don't know how that's useful for applications. > > > > Also, first we need to fix the case of writeback error handling > > for volatile containers while it is mounted before one tries to fix it > > for writeback error detection during remount, IMHO. > > > > Thanks > > Vivek > > > > I feel like this is an infamous Linux problem, and lots[1][2][3][4] has been said > on the topic, and there's not really a general purpose solution to it. I think that > most filesystems offer a choice of "continue" or "fail-stop" (readonly), and if > the upperdir lives on that filesystem, we will get the feedback from it. > > I can respin my patch with just the "boot id" and superblock ID check if folks > are fine with that, and we can figure out how to resolve the writeback issues > later. > On the contrary. Your code for error check is very valuable and more important than the remount feature. If you change ovl_should_sync() to check for error since mount and return error in that case, which all callers will check, then I think you fix the evaporating files issue and that needs to come first with stable kernel backport IMO. Thanks, Amir.