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Tue, 14 Jul 2020 09:57:00 +0000 (UTC) Subject: Re: [PATCH for-5.1 1/2] block: Require aligned image size to avoid assertion failure To: Kevin Wolf References: <20200710142149.40962-1-kwolf@redhat.com> <20200710142149.40962-2-kwolf@redhat.com> <20200713142949.GD10318@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: Date: Tue, 14 Jul 2020 11:56:58 +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: <20200713142949.GD10318@linux.fritz.box> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="dKsPRmCKFBqI88YErtcs0NFlNHeS8JWgR" Received-SPF: pass client-ip=207.211.31.120; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/13 21:44:01 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 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_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: nsoffer@redhat.com, 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) --dKsPRmCKFBqI88YErtcs0NFlNHeS8JWgR Content-Type: multipart/mixed; boundary="qzTuiNTWtAfVPVeFvqLvxVCCjQHw3LkCI" --qzTuiNTWtAfVPVeFvqLvxVCCjQHw3LkCI Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 13.07.20 16:29, Kevin Wolf wrote: > Am 13.07.2020 um 13:19 hat Max Reitz geschrieben: >> On 10.07.20 16:21, Kevin Wolf wrote: >>> Unaligned requests will automatically be aligned to bl.request_alignmen= t >>> and we don't want to extend requests to access space beyond the end of >>> the image, so it's required that the image size is aligned. >>> >>> With write requests, this 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. >>> >>> Signed-off-by: Kevin Wolf >>> --- >>> block.c | 10 ++++++++++ >>> 1 file changed, 10 insertions(+) >> >> (I think we had some proposal like this before, but I can=E2=80=99t find= it, >> unfortunately...) >> >> I can=E2=80=99t see how with this patch you could create qcow2 images an= d then >> use them with direct I/O, because AFAICS, qemu-img create doesn=E2=80=99= t allow >> specifying caching options, so AFAIU you=E2=80=99re stuck with: >> >> $ ./qemu-img create -f qcow2 /mnt/tmp/foo.qcow2 1M >> Formatting '/mnt/tmp/foo.qcow2', fmt=3Dqcow2 cluster_size=3D65536 >> compression_type=3Dzlib size=3D1048576 lazy_refcounts=3Doff refcount_bit= s=3D16 >> >> $ sudo ./qemu-io -t none /mnt/tmp/foo.qcow2 >> qemu-io: can't open device /mnt/tmp/foo.qcow2: Image size is not a >> multiple of request alignment >> >> (/mnt/tmp is a filesystem on a =E2=80=9Closetup -b 4096=E2=80=9D device.= ) >=20 > Hm, that looks like some regrettable collateral damage... >=20 > Well, you could argue that we should be writing full L1 tables with zero > padding instead of just the used part. I thought we had fixed this long > ago. But looks like we haven't. That would help for the standard case. It wouldn=E2=80=99t when the cluste= r size is smaller than the request alignment, which, while maybe not important, would still be a shame. > But we should still avoid crashing in other cases, so what is the > difference between both? Is it just that qcow2 has the RESIZE permission > anyway so it doesn't matter? I assume so. > If so, maybe attaching to a block node with WRITE, but not RESIZE is > what needs to fail when the image size is unaligned? That sounds reasonable. The obvious question is what happens when the RESIZE capability is removed. Dropping capabilities may never fail =E2=80=93 I suppose we could force-keep the RESIZE capability for such nodes? Or we could immediately align such files to the block size once they are opened (with the RESIZE capability). >> Or you use blockdev-create, that seems to work (because of course you >> can set the cache mode on the protocol node when you open it for >> formatting). But, well, I think there should be a working qemu-img >> create case. >> >> Also, I=E2=80=99m afraid of breaking existing use cases with this patch = (just >> qemu-img create + using the image with cache=3Dnone). >=20 > I think for raw images, failure on start is better than crashing when > the VM is running. Agreed. > The qcow2 case needs to be fixed, of course. >=20 > Either case, I guess patch 2 can already be merged and would solve at > least the immediate bug report. Also true. Max --qzTuiNTWtAfVPVeFvqLvxVCCjQHw3LkCI-- --dKsPRmCKFBqI88YErtcs0NFlNHeS8JWgR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl8NgWoACgkQ9AfbAGHV z0CikAgAwz2xEd/mv+GM7MJXemgpbS7dy5gZhOmYEnTrh1HaaE6AveNN2pUwhktz BYeryiKexBY2OlCalpDH4pUda+rkGTB3aUH0bEEsLlm1RN6y1RI9eO2QplBw/rkZ wtyO34+9HIryebjSSbo5m+k6CcPg5AkY+S1/OLS4jLvqq1mfkvUXnkBwoyJBXhtG FP9lLOEle9bml2Mh97THhrAIisVxiiO4pTPh9oBwAPvBXkmlg43yppwZRwCJ3dhT +D1cwr9D4hHU5mypNXXsv0LsaiSpMQtidrW2BZHRc+WHODSRIPkrktzYi+BXlkEi 9sk0O1OksUtJ4Rbu1pkua+cBnaLQrQ== =xyBH -----END PGP SIGNATURE----- --dKsPRmCKFBqI88YErtcs0NFlNHeS8JWgR--