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=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 44855C4CECE for ; Mon, 14 Oct 2019 13:55:00 +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 193BC2133F for ; Mon, 14 Oct 2019 13:55:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 193BC2133F 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]:49930 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iK0oN-0001LV-A0 for qemu-devel@archiver.kernel.org; Mon, 14 Oct 2019 09:54:59 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42822) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iK0nS-0000Sa-9d for qemu-devel@nongnu.org; Mon, 14 Oct 2019 09:54:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iK0nQ-0003kJ-Px for qemu-devel@nongnu.org; Mon, 14 Oct 2019 09:54:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38324) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iK0nH-0003W2-5k; Mon, 14 Oct 2019 09:53:52 -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 E2DCB10DCC8F; Mon, 14 Oct 2019 13:53:43 +0000 (UTC) Received: from [10.3.116.168] (ovpn-116-168.phx2.redhat.com [10.3.116.168]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8ED185D6A7; Mon, 14 Oct 2019 13:53:43 +0000 (UTC) Subject: Re: [PATCH v3 07/16] qcow2: Write v3-compliant snapshot list on upgrade To: Max Reitz , qemu-block@nongnu.org References: <20191011152814.14791-1-mreitz@redhat.com> <20191011152814.14791-8-mreitz@redhat.com> <085c7aec-edd7-79bd-136f-5a3785a5d430@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <582dc245-8a09-f88e-d67c-9435200c327d@redhat.com> Date: Mon, 14 Oct 2019 08:53:42 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <085c7aec-edd7-79bd-136f-5a3785a5d430@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.64]); Mon, 14 Oct 2019 13:53:43 +0000 (UTC) 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: 209.132.183.28 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: Kevin Wolf , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/14/19 3:45 AM, Max Reitz wrote: >>> +=C2=A0=C2=A0=C2=A0 need_snapshot_update =3D false; >>> +=C2=A0=C2=A0=C2=A0 for (i =3D 0; i < s->nb_snapshots; i++) { >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (s->snapshots[i].extra= _data_size < >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 s= izeof_field(QCowSnapshotExtraData, vm_state_size_large) + >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 s= izeof_field(QCowSnapshotExtraData, disk_size)) >> >> Shorter as: >> if (s->snapshots[i].extra_data_size < sizeof(QCowSnapshotExtraData)) >> >> but that's stylistic, so R-b still stands. >=20 > Yes, but if we ever add fields to QCowSnapshotExtraData, we shouldn=E2=80= =99t > count them here. Therefore, I think we need to count exactly the field= s > that the standard says are mandatory in v3. If we ever add more fields, I'd prefer that we did something like: struct QCowSnapshotExtraV3Minimum { uint64_t vm_state_size_large; uint64_t disk_size; }; struct QCow3SnapshotExtraFull { struct QCowSnapshotExtraV3Minimum base; new fields...; }; and use sane naming to get at extra members based on the expected types,=20 rather than trying to piecemeal portions of a type based on size. Until we actually DO add more fields, why do we have to complicate the=20 current code? --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org