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Fri, 17 Jul 2020 11:36:43 +0000 (UTC) Subject: Re: [PATCH for-5.1 v2 1/2] block: Require aligned image size to avoid assertion failure To: Kevin Wolf References: <20200716142601.111237-1-kwolf@redhat.com> <20200716142601.111237-2-kwolf@redhat.com> <7567943c-85e0-5c5b-b67e-3b915d5fa9de@redhat.com> <20200717113243.GB4550@linux.fritz.box> 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: <83a05f42-1446-6973-f2dd-05a8b37792ac@redhat.com> Date: Fri, 17 Jul 2020 13:36:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200717113243.GB4550@linux.fritz.box> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="KodLWUs3T1UTtwnqRhAjSXrZ2elmN2mel" Received-SPF: pass client-ip=207.211.31.81; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/17 05:27:47 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=ham autolearn_force=no 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: qemu-devel@nongnu.org, 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) --KodLWUs3T1UTtwnqRhAjSXrZ2elmN2mel Content-Type: multipart/mixed; boundary="ktw8DTXAShdMbXzPE01tKLo0vzMuys9oE" --ktw8DTXAShdMbXzPE01tKLo0vzMuys9oE Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 17.07.20 13:32, Kevin Wolf wrote: > Am 17.07.2020 um 13:02 hat Max Reitz geschrieben: >> On 16.07.20 16:26, Kevin Wolf wrote: >>> Unaligned requests will automatically be aligned to bl.request_alignmen= t >>> and we can't extend write requests to access space beyond the end of th= e >>> image without resizing the image, so if we have the WRITE permission, >>> but not the RESIZE one, it's required that the image size is aligned. >>> >>> Failing to meet this requirement could cause assertion failures like >>> this if RESIZE permissions weren't requested: >>> >>> qemu-img: block/io.c:1910: bdrv_co_write_req_prepare: Assertion `end_se= ctor <=3D bs->total_sectors || child->perm & BLK_PERM_RESIZE' failed. >>> >>> This was e.g. triggered by qemu-img converting to a target image with 4= k >>> request alignment when the image was only aligned to 512 bytes, but not >>> to 4k. >>> >>> Turn this into a graceful error in bdrv_check_perm() so that WRITE >>> without RESIZE can only be taken if the image size is aligned. If a use= r >>> holds both permissions and drops only RESIZE, the function will return >>> an error, but bdrv_child_try_set_perm() will ignore the failure silentl= y >>> if permissions are only requested to be relaxed and just keep both >>> permissions while returning success. >>> >>> Signed-off-by: Kevin Wolf >>> --- >>> block.c | 16 ++++++++++++++++ >>> 1 file changed, 16 insertions(+) >>> >>> diff --git a/block.c b/block.c >>> index 35a372df57..6371928edb 100644 >>> --- a/block.c >>> +++ b/block.c >>> @@ -2025,6 +2025,22 @@ static int bdrv_check_perm(BlockDriverState *bs,= BlockReopenQueue *q, >>> return -EPERM; >>> } >>> =20 >>> + /* >>> + * Unaligned requests will automatically be aligned to bl.request_= alignment >>> + * and without RESIZE we can't extend requests to write to space b= eyond the >>> + * end of the image, so it's required that the image size is align= ed. >>> + */ >>> + if ((cumulative_perms & BLK_PERM_WRITE) && >> >> What about WRITE_UNCHANGED? I think this would only matter with nodes >> that can have backing files (i.e., qcow2 in practice) because >> WRITE_UNCHANGED is only used by COR and block jobs doing something with >> a backing chain, so it shouldn=E2=80=99t matter in practice, but, well. >=20 > So basically just replacing the line with this? >=20 > if ((cumulative_perms & (BLK_PERM_WRITE | BDRV_PERM_WRITE_UNCHANGED))= && >=20 > I can do that while applying if it is what you mean. Yes. :) >> So, either way: >> >> Reviewed-by: Max Reitz >=20 > Thanks! >=20 > Kevin >=20 >>> + !(cumulative_perms & BLK_PERM_RESIZE)) >>> + { >>> + if ((bs->total_sectors * BDRV_SECTOR_SIZE) % bs->bl.request_al= ignment) { >>> + error_setg(errp, "Cannot get 'write' permission without 'r= esize': " >>> + "Image size is not a multiple of request = " >>> + "alignment"); >>> + return -EPERM; >>> + } >>> + } >>> + >>> /* Check this node */ >>> if (!drv) { >>> return 0; >>> >> >> >=20 >=20 >=20 --ktw8DTXAShdMbXzPE01tKLo0vzMuys9oE-- --KodLWUs3T1UTtwnqRhAjSXrZ2elmN2mel Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl8RjUoACgkQ9AfbAGHV z0ANkwf/b99LfjER6E2O6DvvSJu3bUWQMBxOCixghRcXwONWgb8sHIsPAw4k1whd Y8iEF0BRZ+ivVFYoD4NrxjX4G9jknBCdyn1EjT3jPyHNDVzV9efb7N6ssJq4VXOV 9TWw5agK00Jfl2Yu397qvjhVwUV31Uo1cKLQf5J7CrQ5kGJtzGWBAlrXdvplTNPF ePIGcjkAMvGEpkT3z1wPur/YwxL1GjZtBlT8/JOB+0HgzlU/y8GnxDQm706yTTx4 95BiIjvBgOiskBBD1BTRBOln8r51Y5RmYwatkeT9pIlBDlAEA9AFNwI3+x00iAdQ n2xw1MPrphUkq3z1xLHIjIrJchpPAA== =4hPj -----END PGP SIGNATURE----- --KodLWUs3T1UTtwnqRhAjSXrZ2elmN2mel--