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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 28F60C7618F for ; Tue, 16 Jul 2019 16:55:19 +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 015E5205ED for ; Tue, 16 Jul 2019 16:55:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 015E5205ED 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]:51282 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnQjV-0001mC-So for qemu-devel@archiver.kernel.org; Tue, 16 Jul 2019 12:55:17 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59673) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnQjL-0001JQ-9M for qemu-devel@nongnu.org; Tue, 16 Jul 2019 12:55:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hnQjK-0001AS-E9 for qemu-devel@nongnu.org; Tue, 16 Jul 2019 12:55:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50916) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hnQjI-00018a-Ff; Tue, 16 Jul 2019 12:55:04 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E70813082B6D; Tue, 16 Jul 2019 16:55:02 +0000 (UTC) Received: from linux.fritz.box (ovpn-117-24.ams2.redhat.com [10.36.117.24]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 82E735D72E; Tue, 16 Jul 2019 16:55:01 +0000 (UTC) Date: Tue, 16 Jul 2019 18:54:59 +0200 From: Kevin Wolf To: Max Reitz Message-ID: <20190716165459.GI7297@linux.fritz.box> References: <20190715104508.7568-1-mreitz@redhat.com> <20190715104508.7568-2-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190715104508.7568-2-mreitz@redhat.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Tue, 16 Jul 2019 16:55:03 +0000 (UTC) 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 for-4.1? 1/4] qcow2: Fix .bdrv_has_zero_init() 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: Jeff Cody , Stefan Weil , qemu-devel@nongnu.org, qemu-block@nongnu.org, Stefano Garzarella Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 15.07.2019 um 12:45 hat Max Reitz geschrieben: > If a qcow2 file is preallocated, it can no longer guarantee that it > initially appears as filled with zeroes. > > So implement .bdrv_has_zero_init() by checking whether the file is > preallocated; if so, forward the call to the underlying storage node, > except for when it is encrypted: Encrypted preallocated images always > return effectively random data, so .bdrv_has_zero_init() must always > return 0 for them. > > Reported-by: Stefano Garzarella > Signed-off-by: Max Reitz Hm... This patch only really works directly after image creation (which is indeed where .bdrv_has_zero_init is used). Why do we have to have a full qcow2_is_zero() that loops over the whole image just to find out whether it's preallocated? Wouldn't looking at a single data cluster be enough? Kevin