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 CB18AC352A3 for ; Tue, 11 Feb 2020 15:37:09 +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 982C62051A for ; Tue, 11 Feb 2020 15:37:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="BpjRZv+p" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 982C62051A 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]:51668 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1Xb2-0006t8-Pt for qemu-devel@archiver.kernel.org; Tue, 11 Feb 2020 10:37:08 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:44730) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j1XZI-0004ZV-W1 for qemu-devel@nongnu.org; Tue, 11 Feb 2020 10:35:22 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j1XZH-00048R-QB for qemu-devel@nongnu.org; Tue, 11 Feb 2020 10:35:20 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:41867 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 1j1XZH-00048K-Mg for qemu-devel@nongnu.org; Tue, 11 Feb 2020 10:35:19 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1581435319; 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=CB7sZAqTkFI88bV54qWIx5RAQXb390dPiYTE7mKqv9c=; b=BpjRZv+pbrZ8RdXKVO9hT0w0CDPYr9CUP1ep2hCSSUTEQbWDoZQazT/lj0jeurEAjaLG1F DBMIr4n+432tz7gLPJOA4pMcf+BOKSSEsO2uA2BNWStmYryzkGRtjAZnV/7DGWTsEh7ZTr Y9uOD2gA8A5vl07zVC67DM76mnWh+2g= 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-357-7ZYV3ajFPBKkxxg5NgH_wA-1; Tue, 11 Feb 2020 10:35:02 -0500 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 A6362107ACC4; Tue, 11 Feb 2020 15:35:01 +0000 (UTC) Received: from [10.3.116.180] (ovpn-116-180.phx2.redhat.com [10.3.116.180]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3CC1B384; Tue, 11 Feb 2020 15:35:01 +0000 (UTC) Subject: Re: [PATCH v2 03/33] block: Add BdrvChildRole To: Max Reitz , qemu-block@nongnu.org References: <20200204170848.614480-1-mreitz@redhat.com> <20200204170848.614480-4-mreitz@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Tue, 11 Feb 2020 09:35:00 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: 7ZYV3ajFPBKkxxg5NgH_wA-1 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: 207.211.31.120 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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/6/20 4:49 AM, Max Reitz wrote: >>>> + >>>> +=C2=A0=C2=A0=C2=A0 /* Filtered child */ >>>> +=C2=A0=C2=A0=C2=A0 BDRV_CHILD_FILTERED=C2=A0=C2=A0=C2=A0=C2=A0 =3D (1= << 2), >>> >>> I'm not sure this comment does justice for what the flag represents, bu= t >>> am not sure of what longer comment to put in its place. >> >> You=E2=80=99re right. I thought I could just rely on our .is_filter >> documentation (at least after >> https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg01721.html), >> but that doesn=E2=80=99t really apply here. >> >> For example, this series makes raw (without further parameters) have a >> CHILD_FILTERED child, without raw being a filter itself. >> >> So there should indeed be some definition here. >> >> Maybe: >> >> A child to which the parent forwards all reads and writes. Therefore, >> this child presents exactly the same visible data as the parent. >=20 > On second thought, the =E2=80=9Ctherefore=E2=80=9D is wrong, because the = first sentence > applies to quorum, but the logical conclusion does not. >=20 > So maybe rather: >=20 > A child to which the parent forwards all reads and writes. It must > present exactly the same visible data as the parent. > Any node may have at most one filtered child at a time. Yes, this works for me. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org