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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 0337FC2BA19 for ; Wed, 15 Apr 2020 21:14:26 +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 BFF132051A for ; Wed, 15 Apr 2020 21:14:25 +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="b3Q5ToIM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BFF132051A 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]:55122 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jOpMW-0001ty-WA for qemu-devel@archiver.kernel.org; Wed, 15 Apr 2020 17:14:25 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42481) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jOpLl-0001MY-2H for qemu-devel@nongnu.org; Wed, 15 Apr 2020 17:13:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jOpLk-0002Oq-2h for qemu-devel@nongnu.org; Wed, 15 Apr 2020 17:13:37 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:39492 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 1jOpLj-0002Om-W1 for qemu-devel@nongnu.org; Wed, 15 Apr 2020 17:13:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586985215; 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=TMtWp2gDGLilPtjVfNp/Cp00peq/A8WQOL/noCDI+xQ=; b=b3Q5ToIMzlyiESibrN8rGhSHg7dEgNQcZs61HjpWn3KmbgiVD0BTxsmYBJld9F6bQGgTQK QN0maivHVJRX8xmKwdR1fV0umwDkbAS2r2inqElkOUaYV4I3A5fADxw325jRUFa1BViPSv T3aZokb0ss7fitFxhstO+0iDrXs77OQ= 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-488-3ElCn3rlNuqelXoyVTStSg-1; Wed, 15 Apr 2020 17:13:31 -0400 X-MC-Unique: 3ElCn3rlNuqelXoyVTStSg-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9184B107ACC4; Wed, 15 Apr 2020 21:13:29 +0000 (UTC) Received: from [10.3.115.59] (ovpn-115-59.phx2.redhat.com [10.3.115.59]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C2215116D95; Wed, 15 Apr 2020 21:13:28 +0000 (UTC) Subject: Re: [PATCH v4 07/30] qcow2: Document the Extended L2 Entries feature To: Alberto Garcia , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org References: <8c88b96f-c6f5-e06c-73e1-56001089a7ca@redhat.com> <781c734c-e53c-76ae-74de-26d9e827e1a2@virtuozzo.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <9b1aabf7-ed8b-28b1-578a-373f1d897c53@redhat.com> Date: Wed, 15 Apr 2020 16:13:28 -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 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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 , "Denis V . Lunev" , Anton Nefedov , qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/15/20 2:11 PM, Alberto Garcia wrote: > On Fri 10 Apr 2020 11:29:59 AM CEST, Vladimir Sementsov-Ogievskiy wrote: >>> Should we also document that extended L2 entries are incompatible >>> with raw external files? [...] After all, when raw external file is >>> enabled, the entire image is allocated, at which point subclusters >>> don't make much sense. >> >> It still may cache information about zeroed subclusters: gives more >> detailed block-status. That's a good point about one reason why it might be useful. > > So shall I forbid extended_l2 + data_file_raw then? > > I wonder, if the only problem is that it's just not very useful, does it > make sense to add additional complexity and restrictions to the code > simply to prevent the user from making a sub-optimal choice? At this point, I'm not seeing a technical reason why we have to forbid subclusters with data-file-raw. Mixing may be inefficient compared to using raw-data-file without subclusters, but inefficiencies are not worth the code bloat to forbid the combination. If we come up with a scenario where the mix would cause data corruption, that's a different story, but I'm not seeing such a reason at the moment. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org