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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]:39448 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jnJ5X-0006f8-Ux for qemu-devel@archiver.kernel.org; Mon, 22 Jun 2020 05:50:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55184) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jnJ4W-000584-Su for qemu-devel@nongnu.org; Mon, 22 Jun 2020 05:49:00 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:44547) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jnJ4T-0004kE-HZ for qemu-devel@nongnu.org; Mon, 22 Jun 2020 05:49:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592819334; 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=lkNFHI9NLAvoHsxvEp2keXZ/AHBnhF5lYNL91IteWwY=; b=UMhkFMrkKzSMGhFGFzPOI+OEJ0aLWpkEhcwkfiMMSm/7jWJsGS6njgC224HbysZu/bSCSU 1gC0szp4tPvqhkzAb1QeEAq2KKwoZjNSD8JTeJnBXrDwttIOwp3LhBLvO9q1QLomkmoGYZ h/pFrj+VCfnOA8Fu5F4Eb6ftDMmgYEQ= 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-16-viu0B_paPwmeIWyxC96sxA-1; Mon, 22 Jun 2020 05:48:50 -0400 X-MC-Unique: viu0B_paPwmeIWyxC96sxA-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4A73B100CC85; Mon, 22 Jun 2020 09:48:49 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-114-85.ams2.redhat.com [10.36.114.85]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3C58910013D2; Mon, 22 Jun 2020 09:48:48 +0000 (UTC) Subject: Re: [PATCH 1/2] qcow2: Force preallocation with data-file-raw From: Max Reitz To: Alberto Garcia , qemu-block@nongnu.org References: <20200619104012.235977-1-mreitz@redhat.com> <20200619104012.235977-2-mreitz@redhat.com> <9c14c622-eb30-4619-d33a-b59395a397be@redhat.com> 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: Mon, 22 Jun 2020 11:48:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <9c14c622-eb30-4619-d33a-b59395a397be@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="N8TnmQ5GS1sdNtag002Bzf5bzbKA6nqGC" Received-SPF: pass client-ip=205.139.110.61; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/22 03:17:49 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: Kevin Wolf , 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) --N8TnmQ5GS1sdNtag002Bzf5bzbKA6nqGC Content-Type: multipart/mixed; boundary="hLPwqsqOWuFr0PVjWsbkBvfTSQRbh0Ye0" --hLPwqsqOWuFr0PVjWsbkBvfTSQRbh0Ye0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 22.06.20 11:35, Max Reitz wrote: > On 19.06.20 18:47, Alberto Garcia wrote: >> On Fri 19 Jun 2020 12:40:11 PM CEST, Max Reitz wrote: >>> + if (qcow2_opts->data_file_raw && >>> + qcow2_opts->preallocation =3D=3D PREALLOC_MODE_OFF) >>> + { >>> + /* >>> + * data-file-raw means that "the external data file can be >>> + * read as a consistent standalone raw image without looking >>> + * at the qcow2 metadata." It does not say that the metadata >>> + * must be ignored, though (and the qcow2 driver in fact does >>> + * not ignore it), so the L1/L2 tables must be present and >>> + * give a 1:1 mapping, so you get the same result regardless >>> + * of whether you look at the metadata or whether you ignore >>> + * it. >>> + */ >>> + qcow2_opts->preallocation =3D PREALLOC_MODE_METADATA; >> >> I'm not convinced by this, >=20 > Why not? >=20 > This is how I read the spec. Furthermore, I see two problems that we > have right now that are fixed by this patch (namely (1) using a device > file as the external data file, which may have non-zero data at > creation; and (2) assigning a backing file at runtime must not show the > data). >=20 >> but your comment made me think of another >> possible alternative: in qcow2_get_cluster_offset(), if the cluster is >> unallocated and we are using a raw data file then we return _ZERO_PLAIN: >> >> --- a/block/qcow2-cluster.c >> +++ b/block/qcow2-cluster.c >> @@ -654,6 +654,10 @@ out: >> assert(bytes_available - offset_in_cluster <=3D UINT_MAX); >> *bytes =3D bytes_available - offset_in_cluster; >> =20 >> + if (type =3D=3D QCOW2_CLUSTER_UNALLOCATED && data_file_is_raw(bs)) = { >> + type =3D QCOW2_CLUSTER_ZERO_PLAIN; >> + } >> + >> return type; >> >> You could even add a '&& bs->backing' to the condition and emit a >> warning to make it more explicit. >=20 > No, this is wrong. This still wouldn=E2=80=99t fix the problem of having= a > device file as the external data file, when it already has non-zero data > during creation. (Reading the qcow2 file would return zeroes, but > reading the device would not.) >=20 > So it would need to be QCOW2_CLUSTER_NORMAL. Which is kind of the > point, when you think about it =E2=80=93 with data-file-raw, all clusters= must > always effectively be QCOW2_CLUSTER_NORMAL and be mapped 1:1. >=20 > Well, and that=E2=80=99s in turn the point of this patch. >=20 > I interpret the spec in that the metadata can be ignored, but it does > not need to be ignored. So the L1/L2 tables must be 1:1 mapping of > QCOW2_CLUSTER_NORMAL entries. >=20 > We could also choose to interpret it as =E2=80=9CWith data-file-raw, the = L1/L2 > tables must be ignored=E2=80=9D. In that case, our qcow2 driver would ne= ed to > be modified to indeed fully ignore the L1/L2 tables with data-file-raw. > (I certainly don=E2=80=99t interpret the spec this way, but I suppose we= could > call it a bug fix and amend it.) I just realized that this is not possible. data-file-raw is an autoclear flag, so the image must appear the same to qemu versions that do not support it. If we want to fully ignore the L1/L2 tables or interpret them some non-default way (like you=E2=80=99re proposing), we would have to add a new incompatible flag. 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