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=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 E87AAC2D0A3 for ; Mon, 9 Nov 2020 16:36:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 81C3B206CB for ; Mon, 9 Nov 2020 16:36:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="cZrxq+j8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730218AbgKIQgs (ORCPT ); Mon, 9 Nov 2020 11:36:48 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:43033 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729875AbgKIQgr (ORCPT ); Mon, 9 Nov 2020 11:36:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604939806; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MuPzsF2/TfyPURlq9Utkh/0Cx3GjwKUOaZrivFnH40A=; b=cZrxq+j8EwFWb5QpwifpKJa2CSpWXYi/sfBm6cV8AYsK5oxh4w3W06CA/uJhJqx0FENzT7 SPr0AnJPGOzTQq3YBcKhYIvjGXKsmxnrklVrcCj/FvBwoVJPokqTsjZJptILVrHHDgtq3Y 1WuA1isqF8onh1rPsMSj95YW5nf4PEg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-582-c4OpiMA8OJOST1C66MC6dg-1; Mon, 09 Nov 2020 11:36:42 -0500 X-MC-Unique: c4OpiMA8OJOST1C66MC6dg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E74DB1074669; Mon, 9 Nov 2020 16:36:40 +0000 (UTC) Received: from horse.redhat.com (ovpn-115-201.rdu2.redhat.com [10.10.115.201]) by smtp.corp.redhat.com (Postfix) with ESMTP id A92C26EF5B; Mon, 9 Nov 2020 16:36:39 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 26279222E35; Mon, 9 Nov 2020 11:36:39 -0500 (EST) Date: Mon, 9 Nov 2020 11:36:39 -0500 From: Vivek Goyal To: Amir Goldstein Cc: Giuseppe Scrivano , Sargun Dhillon , overlayfs , Miklos Szeredi , Daniel J Walsh Subject: Re: [PATCH v7] overlayfs: Provide a mount option "volatile" to skip sync Message-ID: <20201109163639.GD1479853@redhat.com> References: <20200831181529.GA1193654@redhat.com> <20201106190325.GB1445528@redhat.com> <87o8kamfuo.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org On Sat, Nov 07, 2020 at 11:35:04AM +0200, Amir Goldstein wrote: > On Fri, Nov 6, 2020 at 9:43 PM Giuseppe Scrivano wrote: > > > > Vivek Goyal writes: > > > > > On Fri, Nov 06, 2020 at 09:58:39AM -0800, Sargun Dhillon wrote: > > > > > > [..] > > >> There is some slightly confusing behaviour here [I realize this > > >> behaviour is as intended]: > > >> > > >> (root) ~ # mount -t overlay -o > > >> volatile,index=off,lowerdir=/root/lowerdir,upperdir=/root/upperdir,workdir=/root/workdir > > >> none /mnt/foo > > >> (root) ~ # umount /mnt/foo > > >> (root) ~ # mount -t overlay -o > > >> volatile,index=off,lowerdir=/root/lowerdir,upperdir=/root/upperdir,workdir=/root/workdir > > >> none /mnt/foo > > >> mount: /mnt/foo: wrong fs type, bad option, bad superblock on none, > > >> missing codepage or helper program, or other error. > > >> > > >> From my understanding, the dirty flag should only be a problem if the > > >> existing overlayfs is unmounted uncleanly. Docker does > > >> this (mount, and re-mounts) during startup time because it writes some > > >> files to the overlayfs. I think that we should harden > > >> the volatile check slightly, and make it so that within the same boot, > > >> it's not a problem, and having to have the user clear > > >> the workdir every time is a pain. In addition, the semantics of the > > >> volatile patch itself do not appear to be such that they > > >> would break mounts during the same boot / mount of upperdir -- as > > >> overlayfs does not defer any writes in itself, and it's > > >> only that it's short-circuiting writes to the upperdir. > > > > > > umount does a sync normally and with "volatile" overlayfs skips that > > > sync. So a successful unmount does not mean that file got synced > > > to backing store. It is possible, after umount, system crashed > > > and after reboot, user tried to mount upper which is corrupted > > > now and overlay will not detect it. > > > > > > You seem to be asking for an alternate option where we disable > > > fsync() but not syncfs. In that case sync on umount will still > > > be done. And that means a successful umount should mean upper > > > is fine and it could automatically remove incomapt dir upon > > > umount. > > > > could this be handled in user space? It should still be possible to do > > the equivalent of: > > > > # sync -f /root/upperdir > > # rm -rf /root/workdir/incompat/volatile > > > > FWIW, the sync -f command above is > 1. Not needed when re-mounting overlayfs as volatile > 2. Not enough when re-mounting overlayfs as non-volatile > > In the latter case, a full sync (no -f) is required. Hi Amir, I am wondering why "sync -f upper/" is not sufficient and why full sync is required. Vivek