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, 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 C63B4C2D0B1 for ; Thu, 6 Feb 2020 12:39:09 +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 91C9E20661 for ; Thu, 6 Feb 2020 12:39:09 +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="B3erSF5p" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 91C9E20661 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]:37918 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1izgR2-0000Ak-PY for qemu-devel@archiver.kernel.org; Thu, 06 Feb 2020 07:39:08 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:49482) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1izgQE-000859-9O for qemu-devel@nongnu.org; Thu, 06 Feb 2020 07:38:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1izgQB-000805-Sz for qemu-devel@nongnu.org; Thu, 06 Feb 2020 07:38:17 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:35123 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1izgQB-0007v6-NO for qemu-devel@nongnu.org; Thu, 06 Feb 2020 07:38:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1580992694; 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: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=pDG1ah0M9UbHGNkIJv7bMLuAazd7pqdVuDa12aLNtyo=; b=B3erSF5pJfD3DoJfj0VGWDBFuzhPuoftQgUotn5Qf+l4LVRVZdeCFh2YG0qQRqiRkGIDCZ Pb+FupXZNhkwe8HdqcWqzNf+hja96HYq4zghWWPVzTWonncQv6q1NZreCCLtctjmuRinfP uNUNVE1EvaXQO1ecqCMnEBk5yVPpbT0= 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-228-d29FFLc4NkST1JGHwE7nkg-1; Thu, 06 Feb 2020 07:38:10 -0500 X-MC-Unique: d29FFLc4NkST1JGHwE7nkg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 62C3E800D54; Thu, 6 Feb 2020 12:38:09 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.36.118.15]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8DABA87B1C; Thu, 6 Feb 2020 12:38:06 +0000 (UTC) Subject: Re: [PATCH v11 2/2] docs: qcow2: introduce compression type feature To: Vladimir Sementsov-Ogievskiy , Eric Blake , Alberto Garcia , qemu-block@nongnu.org References: <20200131142219.3264-1-vsementsov@virtuozzo.com> <20200131142219.3264-3-vsementsov@virtuozzo.com> <18578060-2c1f-6c63-31e1-dee51387210a@redhat.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: Date: Thu, 6 Feb 2020 13:38:04 +0100 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: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="vN4e0KznxX72d8vxk54VyiBeaY2RkQWVC" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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, den@openvz.org, dplotnikov@virtuozzo.com, armbru@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --vN4e0KznxX72d8vxk54VyiBeaY2RkQWVC Content-Type: multipart/mixed; boundary="1o0cWSd2UPATMBOanHn5ciAojKqssDn6j" --1o0cWSd2UPATMBOanHn5ciAojKqssDn6j Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 31.01.20 19:15, Vladimir Sementsov-Ogievskiy wrote: > 31.01.2020 20:49, Eric Blake wrote: >> On 1/31/20 11:34 AM, Alberto Garcia wrote: >>> On Fri 31 Jan 2020 03:46:12 PM CET, Eric Blake wrote: >>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 If the inc= ompatible bit "Compression type" is >>>>> set: the field >>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 must be pr= esent and non-zero (which means >>>>> non-zlib >>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 compressio= n type). Otherwise, this field must >>>>> not be present >>>>> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 or must be= zero (which means zlib). >>>> >>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 If the incompatible bit "Compress= ion type" is set: the >>>> field >>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 must be present. Otherwise, this = field must not be present >>>> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 or must be zero (which means zlib= ). >>> >>> But "not being present" and "being zero" is equivalent (as described in >>> the previous commit). >>> >>> And if the incompatible bit is not present then the field can be safely >>> ignored (i.e. whether it is zero or not is irrelevant). >>> >>> Let's try again: >>> >>> =A0=A0=A0 Defines the compression method used for compressed clusters. = All >>> =A0=A0=A0 compressed clusters in an image use the same type. >>> >>> =A0=A0=A0 The value of this field should only be used when the incompat= ible >>> bit >>> =A0=A0=A0 "Compression type" is set. If that bit is unset then this fie= ld is >>> =A0=A0=A0 not used and the compression method is zlib. This doesn=92t fully make sense to me. Maybe with s/should/must/, because as it is it means that for non-zlib compression methods, you *should* set the compression type bit and add this header extension; but you may also just add the extension and not set the compression bit. All in all, I didn=92t see anyone disagreeing on the fact that there are only two cases that make any sense: (1) Have the bit unset and the extension not present or zero: zlib. (2) Have the bit set and an extension present and non-zero: not zlib. If those are the only sensible choices, I don=92t see any practical argument for allowing anything else[1]. (However, I do see an argument for forbidding anything else, namely to ensure that everyone follows these sensible guidelines.) >> I like that wording. >> >=20 > I'm OK with it too, as well as I'm OK with the stricter variant, when we > don't allow incompatible images with zlib set. I don't see any serious > difference. >=20 > But I need this to land somehow. Max likes stricter variant and he is > maintainer of qcow2.. >=20 > Max, will you merge it as is, or did you change your mind, or should we > ask Kevin for his opinion? I=92m currently preparing a pull request (without this series), but after that I=92m planning to merge the stricter variant. As far as I=92ve seen, the argument for making it less strict was still accompanied by =93Sure, nobody would set this flag for zlib-compressed images because that doesn=92t make sense=94. So if nobody would do that, w= e might as well just forbid it and thus ensure that everyone indeed does the sensible thing. Max [1] Besides =93The specification would be one restriction shorter=94, which I don=92t think is a very good argument. Because without that sentence, anyone who implements qcow2 has to think about the problem anyway and figure out that quasi-restriction by themselves. If they don=92t, it=92d b= e a bit bad because they=92d produce incompatible zlib-compressed images for no reason. Hence why I don=92t see the restriction as a burden to the reader but as a helpful guideline (that must be followed). --1o0cWSd2UPATMBOanHn5ciAojKqssDn6j-- --vN4e0KznxX72d8vxk54VyiBeaY2RkQWVC Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl48CK0ACgkQ9AfbAGHV z0BydQf/YUdOdsgRi3LuTF8tSMOP4j0nCYqBsjv1N2yn3jSoJ/o9nBfNYK5dc/JY 4PRvMuzAyd+HmeGNr0cjp/nGH42B55DkFbTCbn0ty+HAa25/KWx4DvE/VTttRZMV VYZYwYgLZc+/bvlvd4/2OcwvycTVR3kFOZ+Uj6GLE0bdFGZqRTxeK7pzgmFoLYUy 7PI7a3eJIKK4ipXHrnmRuCDxFwOx3j0Nfn7QxMoVYjKFkSD8CbhhtTSleBoRSZwM 0tz5tn+LT9uK9xxr+1W/NhJ2PthOU+VofQqMjEk+1w6YcTPrh36iHDBnUu+YCk9/ uAxx2gdHHLoRccKMLhTmOEeJExVk9Q== =ui5t -----END PGP SIGNATURE----- --vN4e0KznxX72d8vxk54VyiBeaY2RkQWVC--