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Fri, 17 Jul 2020 11:32:44 +0000 (UTC) Date: Fri, 17 Jul 2020 13:32:43 +0200 From: Kevin Wolf To: Max Reitz Subject: Re: [PATCH for-5.1 v2 1/2] block: Require aligned image size to avoid assertion failure Message-ID: <20200717113243.GB4550@linux.fritz.box> References: <20200716142601.111237-1-kwolf@redhat.com> <20200716142601.111237-2-kwolf@redhat.com> <7567943c-85e0-5c5b-b67e-3b915d5fa9de@redhat.com> MIME-Version: 1.0 In-Reply-To: <7567943c-85e0-5c5b-b67e-3b915d5fa9de@redhat.com> 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="82I3+IH0IqGh5yIs" Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=kwolf@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" --82I3+IH0IqGh5yIs Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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. > >=20 > > Failing to meet this requirement could cause assertion failures like > > this if RESIZE permissions weren't requested: > >=20 > > 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. > >=20 > > 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. > >=20 > > 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. > >=20 > > Signed-off-by: Kevin Wolf > > --- > > block.c | 16 ++++++++++++++++ > > 1 file changed, 16 insertions(+) > >=20 > > 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) && >=20 > 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. So basically just replacing the line with this? if ((cumulative_perms & (BLK_PERM_WRITE | BDRV_PERM_WRITE_UNCHANGED)) &= & I can do that while applying if it is what you mean. > So, either way: >=20 > Reviewed-by: Max Reitz Thanks! Kevin > > + !(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 --82I3+IH0IqGh5yIs Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE3D3rFZqa+V09dFb+fwmycsiPL9YFAl8RjFoACgkQfwmycsiP L9bbLhAAjOgXa4bwwmPjDEaKJSAYRgGIiVkHQkXce28u8cCatcNb/xWRKaDs8Exz ZtIsKjA9LaQa/zRnbvUHrt/suQmeT7qopQG8kB+AFW1m9EBXQHsvt2WbOzqlBLy4 4/wDAQBeKVWGxKCS5IRpUluFyHp3nXV2QaC5/xIPb8Sl/FwJ6ewmNI3VxB8Ha+Au AVSZ8yFqi6eU67+mmno4ZR9mn3dhS3yQgpDmgaHd7NqXUHuIAg2OOBk0evkG//PR OaEOelHFHoKg3yi5eMnVxW6hTChDqDxtSIZ6NFmNPRfQ/fQ8A+9X46laQerv1uAH Shsez7zE/Ou5Hzm/V0imZwH5bnCLjuq3U8q9Gd8XeA319dd6PpeFHqtwwGXn81u5 YFU2vqNoAjYkyhtXYtWRzTDBjR2IxNiYE8/x1d7U8oFzZs3fr8U2milj6LBU9gSW oKJFHbiHcL+M8ZdVISLILhL9AuAxF03G+QM83H/iEzlg39x1eRm8GsmugK6V7L9A 6y5obA5u+fnj5o6y7qh4fYX5VuA3GKNB9qJgv2IXxZLWfKoIVigBkbkEvC6ddc/g 31qklpoNGK57kFVctnoqSl6wk0AH4dWXb0XSxR7EoW8RA8IivoUYRATVGGoxPl13 74RxbK/RLe2pN+nPS1Q8cX/rDy2y3+a9C2jRoXsPmAq9wNf0sXM= =zbvG -----END PGP SIGNATURE----- --82I3+IH0IqGh5yIs--