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Mon, 30 Mar 2020 10:05:05 +0000 (UTC) Subject: Re: [PATCH v4] qcow2: Forbid discard in qcow2 v2 images with backing files To: Alberto Garcia , qemu-devel@nongnu.org References: <20200327185930.19493-1-berto@igalia.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: <81e31d93-8bd6-476b-ff92-080da8a2cd67@redhat.com> Date: Mon, 30 Mar 2020 12:05:03 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200327185930.19493-1-berto@igalia.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="rQFnKquS4irUhbkqjPWBkbVcaB8Dj5guh" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 216.205.24.74 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 , =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= , 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) --rQFnKquS4irUhbkqjPWBkbVcaB8Dj5guh Content-Type: multipart/mixed; boundary="7rWjHRDAWQiQh5cy4mYVBO3Q2lYs00eoe" --7rWjHRDAWQiQh5cy4mYVBO3Q2lYs00eoe Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 27.03.20 19:59, Alberto Garcia wrote: > A discard request deallocates the selected clusters so they read back > as zeroes. This is done by clearing the cluster offset field and > setting QCOW_OFLAG_ZERO in the L2 entry. >=20 > This flag is however only supported when qcow_version >=3D 3. In older > images the cluster is simply deallocated, exposing any possible stale > data from the backing file. >=20 > Since discard is an advisory operation it's safer to simply forbid it > in this scenario. >=20 > Note that we are adding this check to qcow2_co_pdiscard() and not to > qcow2_cluster_discard() or discard_in_l2_slice() because the last > two are also used by qcow2_snapshot_create() to discard the clusters > used by the VM state. In this case there's no risk of exposing stale > data to the guest and we really want that the clusters are always > discarded. >=20 > Signed-off-by: Alberto Garcia > --- > v4: > - Show output of qemu-img map when there's no backing file [Eric] >=20 > v3: > - Rebase and change iotest number > - Show output of qemu-img map in iotest 290 [Kevin] > - Use the l2_offset and rb_offset variables in iotest 060 >=20 > v2: >=20 > - Don't create the image with compat=3D0.10 in iotest 060 [Max] > - Use $TEST_IMG.base for the backing image name in iotest 289 [Max] > - Add list of unsupported options to iotest 289 [Max] >=20 > block/qcow2.c | 6 +++ > tests/qemu-iotests/060 | 12 ++--- > tests/qemu-iotests/060.out | 2 - > tests/qemu-iotests/290 | 97 ++++++++++++++++++++++++++++++++++++++ > tests/qemu-iotests/290.out | 61 ++++++++++++++++++++++++ > tests/qemu-iotests/group | 1 + > 6 files changed, 170 insertions(+), 9 deletions(-) > create mode 100755 tests/qemu-iotests/290 > create mode 100644 tests/qemu-iotests/290.out Thanks, applied to my block branch: https://git.xanclic.moe/XanClic/qemu/commits/branch/block Max --7rWjHRDAWQiQh5cy4mYVBO3Q2lYs00eoe-- --rQFnKquS4irUhbkqjPWBkbVcaB8Dj5guh Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl6BxE8ACgkQ9AfbAGHV z0Ag2Af9HiCaluxDv8xE/lrjm0FgAJDJcM3UMcw0wcVaI4Kugt7NICYsWKaC6nJ6 OH5h6A7OSguz5wcZU2Xeup+5VcDpoTJabYnmUVrvHwNwMQgC6cvv6coMazm0pHz6 XDSu2OaKg5qbir6McLYlmOePkgIVMSVVeysTuqXWGBOgGKsDfrKjLR0bmDVG+SUE EtGdTLj3cn+a3MuHZtZlug75T8Op3aTRR4wztL3PXXKH5vMbqwEPsO4SVcI6sCVb m/NjgnXwr53NltmuhNTEtQAn1PbEz+xFiWA4ZGaONLzEUjxnfrQ9QfOOs10r9UJu 8qeczkkHCLkSIC3jkcHldQsNkq0FeA== =TI+h -----END PGP SIGNATURE----- --rQFnKquS4irUhbkqjPWBkbVcaB8Dj5guh--