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Fri, 11 Oct 2019 14:57:15 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-116-40.ams2.redhat.com [10.36.116.40]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 522805D71C; Fri, 11 Oct 2019 14:57:14 +0000 (UTC) Subject: Re: [PATCH v2 04/16] qcow2: Keep unknown extra snapshot data From: Max Reitz To: Eric Blake , qemu-block@nongnu.org References: <20190819185602.4267-1-mreitz@redhat.com> <20190819185602.4267-5-mreitz@redhat.com> <72822609-d767-ace1-4a0c-6f6d0d7a361d@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: <45f90b77-14c5-eec9-4298-abdcc22adb62@redhat.com> Date: Fri, 11 Oct 2019 16:57:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <72822609-d767-ace1-4a0c-6f6d0d7a361d@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="YHEU6r5ZUy2VOszPtVTtE3Iwi5NFvjMWK" X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Fri, 11 Oct 2019 14:57:15 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 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) --YHEU6r5ZUy2VOszPtVTtE3Iwi5NFvjMWK Content-Type: multipart/mixed; boundary="mm649bOThEhm7Yg6FwdKJewv8AP8CAjjh" --mm649bOThEhm7Yg6FwdKJewv8AP8CAjjh Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 20.08.19 13:42, Max Reitz wrote: > On 19.08.19 21:23, Eric Blake wrote: >> On 8/19/19 1:55 PM, Max Reitz wrote: >>> The qcow2 specification says to ignore unknown extra data fields in >>> snapshot table entries. Currently, we discard it whenever we update = the >>> image, which is a bit different from "ignore". >>> >>> This patch makes the qcow2 driver keep all unknown extra data fields >>> when updating an image's snapshot table. >>> >>> Signed-off-by: Max Reitz >>> --- >>> block/qcow2.h | 5 ++++ >>> block/qcow2-snapshot.c | 61 +++++++++++++++++++++++++++++++++++-----= -- >>> 2 files changed, 56 insertions(+), 10 deletions(-) >>> >> >>> @@ -162,7 +184,7 @@ static int qcow2_write_snapshots(BlockDriverState= *bs) >>> sn =3D s->snapshots + i; >>> offset =3D ROUND_UP(offset, 8); >>> offset +=3D sizeof(h); >>> - offset +=3D sizeof(extra); >>> + offset +=3D MAX(sizeof(extra), sn->extra_data_size); >> >> Why would we ever have less than sizeof(extra) bytes to write on outpu= t, >> since we always produce the fields on creation and synthesize the >> missing fields of extra on read? Can't you rewrite this as: >> >> assert(sn->extra_data_size >=3D sizeof(extra)); >> offset +=3D sn->extra_data_size; >=20 > Hm, but I don=E2=80=99t prop up extra_data_size to be at least sizeof(e= xtra). I > can do that, but it would add a few extra lines here and there. On second thought, it doesn=E2=80=99t work at all because then there is n= o way to later detect whether the image is compliant or not. Max --mm649bOThEhm7Yg6FwdKJewv8AP8CAjjh-- --YHEU6r5ZUy2VOszPtVTtE3Iwi5NFvjMWK Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl2gmEgACgkQ9AfbAGHV z0D7Ogf9F+lCgLbAnbdwUeeKnIk4fJtwoOhm7BSzOMFhR8jxXU4bwltXWzQbhSFA 7u7NbNlCBFXe1aB7cEvNmt3sVDLqAJsXz9dSPMxkj1QTnIN+vEKcaXBvDBrljHKE cScV2uaWcSMoMAGPCbRUDSlRWFrNNykKStC3+qcTyktwII9kwI9sWB42nzYJtqUE L/KHfQI2OivwnTD9FK3Bdg4A7/GGCf2jCYSPjYVmhKmNah3eKldvPRcI9W8DqRC4 ZiYbg9BNoNsgaJzMly2d5TcksnizuvABLfpW3oLW4j9wZeBY4bxT4fM24D/vkm8t rRcGTg+y13GztgrvFVXz75jfKodNRg== =F7X6 -----END PGP SIGNATURE----- --YHEU6r5ZUy2VOszPtVTtE3Iwi5NFvjMWK--