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=-2.2 required=3.0 tests=FROM_EXCESS_BASE64, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 3C16CC74A54 for ; Thu, 11 Jul 2019 13:57:27 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 14A5720872 for ; Thu, 11 Jul 2019 13:57:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 14A5720872 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41990 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlZZe-0001Rd-Cw for qemu-devel@archiver.kernel.org; Thu, 11 Jul 2019 09:57:26 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51989) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlZYq-0000Zm-98 for qemu-devel@nongnu.org; Thu, 11 Jul 2019 09:56:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hlZYn-0006ro-V5 for qemu-devel@nongnu.org; Thu, 11 Jul 2019 09:56:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56648) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hlZYl-0006np-3d; Thu, 11 Jul 2019 09:56:31 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id 09DFE85550; Thu, 11 Jul 2019 13:56:30 +0000 (UTC) Received: from redhat.com (unknown [10.42.17.95]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1AA7860633; Thu, 11 Jul 2019 13:56:26 +0000 (UTC) Date: Thu, 11 Jul 2019 14:56:24 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Eric Blake Message-ID: <20190711135624.GN11930@redhat.com> References: <20190710170349.1548-1-mlevitsk@redhat.com> <84232589-627a-8151-a3d5-84c053d9a257@redhat.com> <3e82ff24-6f84-9de8-d3ab-c34966f875f0@redhat.com> <096a8bcf57997c594e1d5d7ea9606029909b81fc.camel@redhat.com> <1bdb9136-ae97-7bf3-762e-0774b0980160@redhat.com> <45b56973-cc6c-2968-e758-7e10734b75bf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <45b56973-cc6c-2968-e758-7e10734b75bf@redhat.com> User-Agent: Mutt/1.12.0 (2019-05-25) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 11 Jul 2019 13:56:30 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH] LUKS: support preallocation in qemu-img X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Kevin Wolf , Maxim Levitsky , qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jul 11, 2019 at 08:50:56AM -0500, Eric Blake wrote: > On 7/11/19 7:24 AM, Max Reitz wrote: >=20 > >>> So it isn=E2=80=99t just me who expects these to pre-initialize the= image to 0. > >>> Hm, although... I suppose @falloc technically does not specify wh= ether > >>> the data reads as zeroes. I kind of find it to be implied, but, we= ll... > >> > >> I personally don't really think that zeros are important, but rather= the level of allocation. > >> posix_fallocate probably won't write the data blocks but rather only= the inode metadata / used block bitmap/etc. > >> > >> On the other hand writing zeros (or anything else) will force the bl= ock layer to actually write to the underlying > >> storage which could trigger lower layer allocation if the underlying= storage is thin-provisioned. > >> > >> In fact IMHO, instead of writing zeros, it would be better to write = random garbage instead (or have that as an even 'fuller' > >> preallocation mode), since underlying storage might 'compress' the z= eros.=20 > >=20 > > Which is actually an argument why you should just write zeroes on the > > LUKS layer, because this will then turn into quasi-random data on the > > protocol layer. >=20 > We want preallocation to be fast (insofar as possible). Writing zeroes > in LUKS is not fast, because it forces random data on the protocol > layer; while writing zeroes on the protocol layer can be fast, even if > it reads back as random on the LUKS layer. If you WANT to guarantee > reading zeroes, that's image scrubbing, not preallocation. I think thi= s > patch is taking the right approach, of letting the underlying layer > allocate data efficiently (but the burden is then on the underlying > layer to actually allocate data, and not optimize by compressing zeroes > into non-allocated storage). On the topic of scrubbing, it would actually be nice to have a "secure delete" for QEMU block driver formats that can do some level of scrubbing in software and/or calling out to hardware support. Similarly to prealloc a choice of 'metadata' or 'full'. Wwith LUKS you can do well by just scrubbing the image header (which kills the master decryption key rendering payload useless). Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|