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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 9550DC2D0CE for ; Tue, 21 Jan 2020 16:22:13 +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 64ED524653 for ; Tue, 21 Jan 2020 16:22:13 +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="iiF2UkcC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 64ED524653 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]:57616 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1itwI8-0008AR-Ei for qemu-devel@archiver.kernel.org; Tue, 21 Jan 2020 11:22:12 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:35822) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1itwGQ-0006O2-Hd for qemu-devel@nongnu.org; Tue, 21 Jan 2020 11:20:28 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1itwGP-0007om-9u for qemu-devel@nongnu.org; Tue, 21 Jan 2020 11:20:26 -0500 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:36456 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 1itwGP-0007nW-3E for qemu-devel@nongnu.org; Tue, 21 Jan 2020 11:20:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579623621; 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=+WAv0MYtdqKI1zjEAfNKbrmaveVAT3YOotRA2IVpeBc=; b=iiF2UkcCupH8wdiXUeC4XCiGkX2kWw28wtNBt6sFKk1j34k1d6wlOQtPhq8Ks+7KIISleg /sFtbrJ+TLdSCh9KdTdxjMDSMGfxf3lF9LP/HOhSnwzAqKK9Ia7j6B/tgdqxYySxa5vb8L 3NQZ8EFAyC/EJOpKl9VP76xjtbGVrmw= 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-156-xFlAZ3irN3CGVM-aHZECQA-1; Tue, 21 Jan 2020 11:20:17 -0500 X-MC-Unique: xFlAZ3irN3CGVM-aHZECQA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F0E1C8017CC; Tue, 21 Jan 2020 16:20:15 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-116.ams2.redhat.com [10.36.117.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4025F7DB34; Tue, 21 Jan 2020 16:20:14 +0000 (UTC) Subject: Re: [PATCH v10 2/2] docs: qcow2: introduce compression type feature To: Eric Blake , Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20200120171345.24345-1-vsementsov@virtuozzo.com> <20200120171345.24345-3-vsementsov@virtuozzo.com> <679ba957-0b47-27ab-0684-e066ca8a6196@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: Tue, 21 Jan 2020 17:20:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <679ba957-0b47-27ab-0684-e066ca8a6196@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="AyK8HeigY3oMsJ1q4q0lqysMbSrd4nXZ4" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] 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, qemu-devel@nongnu.org, armbru@redhat.com 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) --AyK8HeigY3oMsJ1q4q0lqysMbSrd4nXZ4 Content-Type: multipart/mixed; boundary="4vrppqaMj5YxarihldW79FJTzItYBiZNf" --4vrppqaMj5YxarihldW79FJTzItYBiZNf Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 20.01.20 20:46, Eric Blake wrote: > On 1/20/20 11:13 AM, Vladimir Sementsov-Ogievskiy wrote: >> The patch add new additional field to qcow2 header: compression_type, >=20 > s/add/adds a/ > s/to/to the/ >=20 >> 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. >=20 > It would be nice to have that patch as part of the same series, but it > has already been posted to the list separately, so I'm okay with this > series as just doc word-smithing while we get that patch series in soon. >=20 >> >> Suggested-by: Denis Plotnikov >> Signed-off-by: Vladimir Sementsov-Ogievskiy >> --- >> =A0 docs/interop/qcow2.txt | 16 +++++++++++++++- >> =A0 1 file changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt >> index 355925c35e..4569f0dba3 100644 >> --- a/docs/interop/qcow2.txt >> +++ b/docs/interop/qcow2.txt >> @@ -109,6 +109,11 @@ the next fields through header_length. >> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0 An External Data File Name header >> extension may >> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0=A0 be present if this bit is set. >> =A0 +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 Bit 3:=A0= =A0=A0=A0=A0 Compression type bit.=A0 If this bit >> is set, >> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0 a non-default compression is used for >> compressed >> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0 clusters. The compression_type field >> must be >> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0=A0 present and not zero. >=20 > Why must the compression_type field be non-zero?=A0 If this bit is set, a= n > older qemu cannot use the image, regardless of the contents of the > compression_type field, so for maximum back-compat, a sane app will > never set this bit when compression_type is zero.=A0 But there is nothing > technically wrong with setting this bit even when compression_type is 0, > and newer qemu would still manage to use the image correctly with zlib > compression if it were not for this arbitrary restriction. There is something technically wrong if the specification demands otherwise= . As you yourself say, no sane software would deviate from this behavior anyway. If that is so, I don=92t see why we shouldn=92t specify it this way. I see no benefit in allowing this bit be set for zlib images. Max --4vrppqaMj5YxarihldW79FJTzItYBiZNf-- --AyK8HeigY3oMsJ1q4q0lqysMbSrd4nXZ4 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl4nJLwACgkQ9AfbAGHV z0C9JAf8DODrGyCL7mehicMmRwwI2mHKz8E065R9S292LGztwSnWgl2LkVvzDZXU ftpGVZMrM4bMmm6g1Im5sXJZpWLbm1BMpsZfLy6ynapYqIhLD685ALrV/Gd6M7NC RyHj0RKpJlR9yk3iboAe+9GDablg7CEWrPOBVz1bWGViWozHa5m1iZMdkxboPjHm fcbClXQDSNuyfinlyhriS3VsJXJ8TNaf+mixe7FzwxCWLUkE3cwWd5vvwHWZm2DJ 1C6UKYniUw/ATkkTnFLal49s/3IVaOLAqefHJ/6DL77xZzmaMJGdmjU3Ocgpaf4i UoiefbwQNlGbdmCcjuD+deDAR4s4+g== =Z9kv -----END PGP SIGNATURE----- --AyK8HeigY3oMsJ1q4q0lqysMbSrd4nXZ4--