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Tue, 14 Jan 2020 14:03:34 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.36.118.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 32F7582478; Tue, 14 Jan 2020 14:03:32 +0000 (UTC) Subject: Re: [PATCH v2 1/4] qcow2: Require that the virtual size is a multiple of the sector size To: Alberto Garcia , qemu-devel@nongnu.org References: <6a1cfcbb533b487bac96e1d2282ebf210954d27a.1578596897.git.berto@igalia.com> <9f7ab60c-c9d4-527b-55dd-40f487a36895@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: <70f3996c-e62d-c560-b7a3-e0653f38493d@redhat.com> Date: Tue, 14 Jan 2020 15:03:31 +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: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ZkoeXFlmXThxGNuu9iDJfXXG4RIwCOgwI" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 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 , Nir Soffer , qemu-block@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) --ZkoeXFlmXThxGNuu9iDJfXXG4RIwCOgwI Content-Type: multipart/mixed; boundary="t264nmYKRQyn42ELXjHldthGIVUwINPIA" --t264nmYKRQyn42ELXjHldthGIVUwINPIA Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 14.01.20 14:58, Alberto Garcia wrote: > On Tue 14 Jan 2020 02:47:53 PM CET, Max Reitz wrote: >=20 >>> Yes, but does it make sense to try to support images with unaligned >>> sizes if no one is going to create them ever and QEMU cannot even >>> generate them? >> >> If nobody uses such images ever, isn=E2=80=99t the current code fine as-= is? >=20 > I'll rephrase: >=20 > 1. It is possible to have a qcow2 image with a size of 1 GB + 13 bytes > (the size field in the qcow2 header allows it). >=20 > 2. qemu-img cannot currently produce such images. >=20 > 3. QEMU can open them but it gets the size wrong. Yes, but in a safe way. The user simply doesn=E2=80=99t get access to thos= e 13 bytes. With your proposed change, it would just reject the image altogether. As a user, I=E2=80=99d prefer not being able to access 13 bytes to not bein= g able to access 1 GB + 13 bytes. Furthermore, the user couldn=E2=80=99t even fix the image then because they couldn=E2=80=99t resize it with qemu-img resize. > 4. Fixing this in QEMU involves non-trivial changes (at least at the > moment). >=20 > 5. I don't think there's any use case for such images so instead of > fixing QEMU I propose that we simply refuse to open them. If there=E2=80=99s no use case, I don=E2=80=99t see how the current behavio= r is problematic. The arguments I could immediately agree to are (1) simplicity, and (2) the image is probably corrupted. As for (1), this patch adds more lines than it removes, so from a pure quantitative standpoint, it doesn=E2=80=99t make the code simpler. As for (2), I=E2=80=99m always of the opinion we shouldn=E2=80=99t refuse t= o read corrupted images just because they are corrupted. We should open them and let the user read as much as is reasonably possible. Max --t264nmYKRQyn42ELXjHldthGIVUwINPIA-- --ZkoeXFlmXThxGNuu9iDJfXXG4RIwCOgwI Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl4dyjMACgkQ9AfbAGHV z0DuJgf/XoQ+pjIrEkZ3LPpuNnbTbOprhgF2Pqa7VNYItNeFDJuNnfc1QVjTZxkg dK9yvs4ObqyKn9SwfIFM09ZozX6YVy8Gl8EIqXKED4JqzlI50GI7KxJCeZDbD9gL w6GTuT/J8eqgjwcC/ILL1xPyFxU2dmwjkBNZNX9xLfHfWCRJs9NGmfIYhgeaD3y8 C3AfQ8sVem+nB0yKSxqdFJd1aYtFn+4zDLNWYW+a0pEsx0K9vQNrx9RqLjq3pNQO bVHReWQjLJMgVlL6Ve1Dprubr+GzJdHZh3FRrjwo26KqAnRL9p71zMOnBhi6EZ2b QCweiqqDF4N5dXmohf0QP/WbQBTuQQ== =Org8 -----END PGP SIGNATURE----- --ZkoeXFlmXThxGNuu9iDJfXXG4RIwCOgwI--