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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,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 7B529CA9EA1 for ; Fri, 18 Oct 2019 14:06:29 +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 4F60E21925 for ; Fri, 18 Oct 2019 14:06:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F60E21925 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]:40558 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iLStf-0006wB-US for qemu-devel@archiver.kernel.org; Fri, 18 Oct 2019 10:06:27 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57786) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iLSs2-000542-5V for qemu-devel@nongnu.org; Fri, 18 Oct 2019 10:04:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iLSs0-00045k-PO for qemu-devel@nongnu.org; Fri, 18 Oct 2019 10:04:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43658) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iLSry-00044E-2I; Fri, 18 Oct 2019 10:04:42 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 31EB9881363; Fri, 18 Oct 2019 14:04:41 +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 9330210013A1; Fri, 18 Oct 2019 14:04:40 +0000 (UTC) Subject: Re: [PATCH v8 3/3] docs: qcow2: introduce compression type feature To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20191018094758.7124-1-vsementsov@virtuozzo.com> <20191018094758.7124-4-vsementsov@virtuozzo.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <29df7fb8-8218-2228-9575-e84e369a7d9a@redhat.com> Date: Fri, 18 Oct 2019 09:04:40 -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: <20191018094758.7124-4-vsementsov@virtuozzo.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.69]); Fri, 18 Oct 2019 14:04:41 +0000 (UTC) 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: kwolf@redhat.com, qemu-devel@nongnu.org, armbru@redhat.com, dplotnikov@virtuozzo.com, den@openvz.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10/18/19 4:47 AM, Vladimir Sementsov-Ogievskiy wrote: > The patch add new additional field to qcow2 header: compression_type, > which specifies compression type. If field is absent or zero, default > compression type is set: ZLIB, which corresponds to current behavior. > > New compression type (ZSTD) is to be added in further commit. > > Suggested-by: Denis Plotnikov > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > docs/interop/qcow2.txt | 19 ++++++++++++++++++- > 1 file changed, 18 insertions(+), 1 deletion(-) > > diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt > index b971e59b1a..4eabd81363 100644 > --- a/docs/interop/qcow2.txt > +++ b/docs/interop/qcow2.txt > @@ -109,6 +109,12 @@ least next five fields, up to the @header_length field. > An External Data File Name header extension may > be present if this bit is set. > > + Bit 3: Compression type bit. If this bit is set, > + non-default compression is used for compressed > + clusters. In this case, @header_length must > + be at least 105 and @compression_type field > + must be non-zero. I want to insist on 8-byte alignment, so this should be at least 112. Also, as pointed out in v7, use of the decoration '@header_length' and '@compression_type' is not consistent with the rest of the document. Drop the @. > + > Bits 3-63: Reserved (set to 0) > > 80 - 87: compatible_features > @@ -183,7 +189,18 @@ It's allowed for the header end to cut some field in the middle (in this case > the field is considered as absent), but in this case the part of the field > which is covered by @header_length must be zeroed. > > - < ... No additional fields in the header currently ... > > + 104: compression_type > + Defines the compression method used for compressed clusters. > + A single compression type is applied to all compressed image > + clusters. > + If incompatible compression type bit is set: the field must > + exist (i.e. @header_length >= 105) and must be non-zero ( > + which means non-zlib compression type) > + If incompatible compression type bit is unset: the field > + may not exist (if @header_length < 105) or it must be zero > + (which means zlib). > + Available compression type values: > + 0: zlib > One byte for the field is fine, but I'd still explicitly document 7 bytes of unused padding, since I want to insist on an 8-byte multiple. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org