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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 EF537C43141 for ; Fri, 22 Nov 2019 18:19:31 +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 AFC742067D for ; Fri, 22 Nov 2019 18:19:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MGndV64/" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AFC742067D 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]:53752 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iYDWk-0000gx-3E for qemu-devel@archiver.kernel.org; Fri, 22 Nov 2019 13:19:30 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36460) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iYDKc-0000pH-P4 for qemu-devel@nongnu.org; Fri, 22 Nov 2019 13:06:59 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iYDKX-0007vf-9y for qemu-devel@nongnu.org; Fri, 22 Nov 2019 13:06:55 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:33487 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iYDKU-0007us-DH for qemu-devel@nongnu.org; Fri, 22 Nov 2019 13:06:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1574446008; 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=Y0WP6QUHwtKnRXo7X2/Vcg/nhKnykLT67lSc7+bAh/I=; b=MGndV64//b3uEJTuLAdcioW3wb4NUc0yOKTh+cU9rfV/wm5lT4vOFiQRstOrepc3kObYdg Aqwl1U0mVwxuUr+a5LUL2tLDNahHfMqOZMJaGvpjyUbC8pKAWhnn6YNir7HzHx2eBtq9FP WLFD4sTEQnpWk5afAMXUNx8Luui5XRU= 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-331-95K4HtEdMROs_RMGorUoUg-1; Fri, 22 Nov 2019 13:06:46 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 83FA918B5FA0; Fri, 22 Nov 2019 18:06:45 +0000 (UTC) Received: from [10.3.116.221] (ovpn-116-221.phx2.redhat.com [10.3.116.221]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6F0265D9E1; Fri, 22 Nov 2019 18:06:42 +0000 (UTC) Subject: Re: [PATCH v3 4/8] block: truncate: Don't make backing file data visible To: Kevin Wolf , qemu-block@nongnu.org References: <20191122160511.8377-1-kwolf@redhat.com> <20191122160511.8377-5-kwolf@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <2a970e80-bed8-54ec-506a-4bff46b81577@redhat.com> Date: Fri, 22 Nov 2019 12:06:41 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191122160511.8377-5-kwolf@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-MC-Unique: 95K4HtEdMROs_RMGorUoUg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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: vsementsov@virtuozzo.com, qemu-devel@nongnu.org, stefanha@redhat.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11/22/19 10:05 AM, Kevin Wolf wrote: > When extending the size of an image that has a backing file larger than > its old size, make sure that the backing file data doesn't become > visible in the guest, but the added area is properly zeroed out. > > Consider the following scenario where the overlay is shorter than its > backing file: > > base.qcow2: AAAAAAAA > overlay.qcow2: BBBB > > When resizing (extending) overlay.qcow2, the new blocks should not stay > unallocated and make the additional As from base.qcow2 visible like > before this patch, but zeros should be read. > > A similar case happens with the various variants of a commit job when an > intermediate file is short (- for unallocated): > > base.qcow2: A-A-AAAA > mid.qcow2: BB-B > top.qcow2: C--C--C- > > After commit top.qcow2 to mid.qcow2, the following happens: > > mid.qcow2: CB-C00C0 (correct result) > mid.qcow2: CB-C--C- (before this fix) > > Without the fix, blocks that previously read as zeros on top.qcow2 > suddenly turn into A. > > Signed-off-by: Kevin Wolf > --- > block/io.c | 33 +++++++++++++++++++++++++++++++++ > 1 file changed, 33 insertions(+) Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org