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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 76BE4C2BA2B for ; Thu, 9 Apr 2020 13:49:31 +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 4206020678 for ; Thu, 9 Apr 2020 13:49:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LQ/KngXJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4206020678 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]:49650 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jMXYg-00014C-Bb for qemu-devel@archiver.kernel.org; Thu, 09 Apr 2020 09:49:30 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60824) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jMXWy-0007ed-7O for qemu-devel@nongnu.org; Thu, 09 Apr 2020 09:47:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jMXWx-0001RD-9V for qemu-devel@nongnu.org; Thu, 09 Apr 2020 09:47:44 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:31194 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jMXWx-0001R2-6a for qemu-devel@nongnu.org; Thu, 09 Apr 2020 09:47:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586440062; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ehoOSQ7bqGYev3slS73lHjePd8DvkKgdfmQv+zGW9OI=; b=LQ/KngXJJcGGWTk6bAeOxmOtDDpTfMd5hGkHbNIImIz9PfTUrOB+/TMKceTqVBYt5ao5Nm i/EyrtYmZQxdFCGwWaaCRfYIf7876q5XMVyWKbS403pMd58qkNYHVAHGR66qoH2t+/pZ3T lIuB7Sicl8UYIPbw07nIQg/7SzbtKRA= 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-195-HcdxK1HjOneXL4pAjBxgGw-1; Thu, 09 Apr 2020 09:47:40 -0400 X-MC-Unique: HcdxK1HjOneXL4pAjBxgGw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A73C6107ACCC; Thu, 9 Apr 2020 13:47:39 +0000 (UTC) Received: from [10.3.114.49] (ovpn-114-49.phx2.redhat.com [10.3.114.49]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 509C728579; Thu, 9 Apr 2020 13:47:39 +0000 (UTC) Subject: Re: qcow2: Zero-initialization of external data files From: Eric Blake To: Max Reitz , Qemu-block , Kevin Wolf References: <50080252-ff22-78ed-0002-1742c694471b@redhat.com> <8b4bc264-7bce-c9c1-1905-a22b4c61cae4@redhat.com> Organization: Red Hat, Inc. Message-ID: Date: Thu, 9 Apr 2020 08:47:38 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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: , Cc: "qemu-devel@nongnu.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/9/20 8:42 AM, Eric Blake wrote: >>> I'd argue that requiring the user to pre-zero the raw data file is >>> undesirable; and that we should instead fix our code to not report the >>> image as reading all zeroes when creating with data_file_raw=3Don. >> >> OK.=C2=A0 I think that could be achieved by just enforcing @preallocatio= n to >> be at least =E2=80=9Cmetadata=E2=80=9D whenever @data-file-raw is set.= =C2=A0 Would that make >> sense? >=20 > Is a preallocation of metadata sufficient to report things correctly? If= =20 > so, it seems like a reasonable compromise to me.=C2=A0 I was more envisio= ning=20 > a fix elsewhere: if we are reporting block status of what looks like an= =20 > unallocated cluster, but data-file-raw is set, we change our answer to=20 > instead report it as allocated with unknown contents.=C2=A0 But with=20 > preallocation, you either force the qcow2 file to list no cluster as=20 > unallocated (which matches the fact that the raw image really is fully=20 > allocated) while not touching the raw image, or you can go one step=20 > further and request full preallocation to wipe the raw image to 0 in the= =20 > process. What happens when an operation attempts to unmap things? Do we reject=20 all unmap operations when data-file-raw is set (thus leaving a cluster=20 marked as allocated at all times, if we can first guarantee that=20 preallocation set things up that way)? --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org