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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 A43ACC004EF for ; Tue, 9 Jul 2019 11:28:53 +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 7D49E20844 for ; Tue, 9 Jul 2019 11:28:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7D49E20844 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]:48870 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hkoIl-00028O-V8 for qemu-devel@archiver.kernel.org; Tue, 09 Jul 2019 07:28:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44269) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hkoHz-0001Wp-EB for qemu-devel@nongnu.org; Tue, 09 Jul 2019 07:28:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hkoHy-0001eq-94 for qemu-devel@nongnu.org; Tue, 09 Jul 2019 07:28:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41964) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hkoHv-0001bi-J7; Tue, 09 Jul 2019 07:27:59 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id BEB2081F25; Tue, 9 Jul 2019 11:27:58 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-116-111.ams2.redhat.com [10.36.116.111]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6389D196EE; Tue, 9 Jul 2019 11:27:57 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 01BA61138648; Tue, 9 Jul 2019 13:27:55 +0200 (CEST) From: Markus Armbruster To: Denis Plotnikov References: <20190703110044.25610-1-dplotnikov@virtuozzo.com> <20190703110044.25610-2-dplotnikov@virtuozzo.com> Date: Tue, 09 Jul 2019 13:27:55 +0200 In-Reply-To: <20190703110044.25610-2-dplotnikov@virtuozzo.com> (Denis Plotnikov's message of "Wed, 3 Jul 2019 14:00:42 +0300") Message-ID: <878st78n2c.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 09 Jul 2019 11:27:58 +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 v1 1/3] qcow2: introduce compression type feature 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, vsementsov@virtuozzo.com, den@virtuozzo.com, qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" I'd like to recommend a few commas. Denis Plotnikov writes: > The patch adds some preparation parts for incompatible compression type > feature to QCOW2 header that indicates that *all* compressed clusters > must be (de)compressed using a certain compression type. > > It is implied that the compression type is set on the image creation and > can be changed only later by image conversion, thus compression type > defines the only compression algorithm used for the image. > > The goal of the feature is to add support of other compression algorithms > to qcow2. For example, ZSTD which is more effective on compression than ZLIB. > It works roughly x2 faster than ZLIB providing a comparable compression ratio > and therefore provide a performance advantage in backup scenarios. > > The default compression is ZLIB. Images created with ZLIB compression type > is backward compatible with older qemu versions. > > Signed-off-by: Denis Plotnikov [...] > diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt > index af5711e533..5b8a8d15fe 100644 > --- a/docs/interop/qcow2.txt > +++ b/docs/interop/qcow2.txt > @@ -109,7 +109,12 @@ in the description of a field. > An External Data File Name header extension may > be present if this bit is set. > > - Bits 3-63: Reserved (set to 0) > + Bit 3: Compression type bit. The bit must be set if > + the compression type differs from default: zlib. > + If the compression type is default the bit must > + be unset. > + > + Bits 4-63: Reserved (set to 0) > > 80 - 87: compatible_features > Bitmask of compatible features. An implementation can > @@ -165,6 +170,21 @@ in the description of a field. > Length of the header structure in bytes. For version 2 > images, the length is always assumed to be 72 bytes. > > + 104 - 107: compression_type > + Defines the compression method used for compressed clusters. > + A single compression type is applied to all compressed image > + clusters. > + The compression type is set on image creation only. > + The default compression type is zlib. > + When the deafult compression type is used the compression Comma after used, please. > + type bit (incompatible feature bit 3) must be unset. > + When any other compression type is used the compression Likewise. > + type bit must be set. > + Qemu versions older than 4.1 can use images created with > + the default compression type without any additional > + preparations and cannot use images created with any other Comma after preparations, please. > + compression type. > + > Directly after the image header, optional sections called header extensions can > be stored. Each extension has a structure like the following: > [...]