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=-8.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 37F8CC2D0E4 for ; Fri, 27 Nov 2020 10:34:14 +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 87F5F20885 for ; Fri, 27 Nov 2020 10:34:13 +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="ZhbZJ3Ov" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87F5F20885 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]:33816 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kib4u-0006Bi-7C for qemu-devel@archiver.kernel.org; Fri, 27 Nov 2020 05:34:12 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:58600) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kib3D-00046y-Ba for qemu-devel@nongnu.org; Fri, 27 Nov 2020 05:32:27 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:45250) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kib3A-0003fm-PT for qemu-devel@nongnu.org; Fri, 27 Nov 2020 05:32:27 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606473144; 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=YvD1Afm4U/8J4Ooypf6C8HzVqiicYxh2gBY8GU8ct2A=; b=ZhbZJ3OvW9ZFMvgaR9Jr6eABh27dPfFI7Av9sfwD0Kk7RhU28sdjg7sDWpIMnP0lwHIpA4 RbeTsBkPglBQn2lKEsFirKJCJvVPBqoDKphg0AHCM3ujrB16KCb5QIKRshhQssUAybWoKI JYVj+PXRpC3tnc2+wG174AaVwGSb34s= 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-3-4w115FVzNmKLSuBBpguXAA-1; Fri, 27 Nov 2020 05:32:20 -0500 X-MC-Unique: 4w115FVzNmKLSuBBpguXAA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F28DD185E49B; Fri, 27 Nov 2020 10:32:18 +0000 (UTC) Received: from merkur.fritz.box (ovpn-113-250.ams2.redhat.com [10.36.113.250]) by smtp.corp.redhat.com (Postfix) with ESMTPS id AFBD85D9D0; Fri, 27 Nov 2020 10:32:17 +0000 (UTC) Date: Fri, 27 Nov 2020 11:32:16 +0100 From: Kevin Wolf To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: ImageInfo oddities regarding compression Message-ID: <20201127103216.GA4736@merkur.fritz.box> References: <87r1ofru4z.fsf@dusky.pond.sub.org> <20201127101405.GA1596141@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201127101405.GA1596141@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action 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: qemu-devel@nongnu.org, Denis Plotnikov , Markus Armbruster , qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 27.11.2020 um 11:14 hat Daniel P. Berrangé geschrieben: > On Fri, Nov 27, 2020 at 11:06:36AM +0100, Markus Armbruster wrote: > > ImageInfo has an optional member @compressed: > > > > ## > > # @ImageInfo: > > [...] > > # @compressed: true if the image is compressed (Since 1.7) > > > > Doc bug: neglects to specify the default. I guess it's false. I think rather than false (definitely not compressed) it might just mean unknown, see below. > > The only user appears to be vmdk_get_extent_info(). Goes back to > > v1.7.0's commits > > > > f4c129a38a vmdk: Implment bdrv_get_specific_info > > cbe82d7fb3 qapi: Add optional field 'compressed' to ImageInfo > > > > ImageInfo also has an optional member @format-specific. > > > > Doc bug: neglects to specify when it's present. I assume it's always > > present when member @format has a value that has a non-empty variant in > > @format-specific's type ImageInfoSpecific. This seems to be the intention, yes. > > Format qcow2's variant is ImageInfoSpecificQCow2. It has a mandatory > > member @compression-type. > > > > ## > > # @Qcow2CompressionType: > > # > > # Compression type used in qcow2 image file > > # > > # @zlib: zlib compression, see > > # @zstd: zstd compression, see > > # > > # Since: 5.1 > > ## > > { 'enum': 'Qcow2CompressionType', > > 'data': [ 'zlib', { 'name': 'zstd', 'if': 'defined(CONFIG_ZSTD)' } ] } > > > > Apparently, you can't have a qcow2 image without compression. Correct? > > > > Can you imagine a use case for "without compression"? > > Yes & no. An image always has a compression type, either implicitly > zlib as the historical default, or explicitly as a type recorded in > the header. This doesn't mean compression is used. > > There may be zero or more clusters actually using compression. > Typically compression will never be used, but there's still an > associated compression type regardless. Right, so the correct answer to "is this image compressed?" is "unknown" for qcow2. Providing an answer would require checking all clusters in the image for the compression flag, which is not something we want to do for query-block. And even if we did that, it would still be unclear what to do with a partially compressed image. The @compression-type only tells you what format a compressed cluster uses if any compressed cluster exists in the image (or if a new compressed cluster is written to it). It doesn't mean that such clusters currently exist. Kevin