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Wed, 15 Jul 2020 07:03:59 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwnvS+jkoqVDZ00eut04A4TpreVEl0/pYkfKRcYukwGivF7r2SQmWIXvuZ6239t/SY8V4v0ELRSgjSh0BsQQ9E= X-Received: by 2002:a05:6830:309b:: with SMTP id f27mr9276688ots.315.1594821839577; Wed, 15 Jul 2020 07:03:59 -0700 (PDT) MIME-Version: 1.0 References: <20200710142149.40962-1-kwolf@redhat.com> <20200710142149.40962-2-kwolf@redhat.com> <20200713165637.GH10318@linux.fritz.box> <20200715134229.GB8833@linux.fritz.box> In-Reply-To: <20200715134229.GB8833@linux.fritz.box> From: Nir Soffer Date: Wed, 15 Jul 2020 17:03:43 +0300 Message-ID: Subject: Re: [PATCH for-5.1 1/2] block: Require aligned image size to avoid assertion failure To: Kevin Wolf Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=nsoffer@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Received-SPF: pass client-ip=207.211.31.120; envelope-from=nsoffer@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/15 05:07:28 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: QEMU Developers , qemu-block , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 15, 2020 at 4:42 PM Kevin Wolf wrote: > > Am 15.07.2020 um 15:22 hat Nir Soffer geschrieben: > > On Mon, Jul 13, 2020 at 7:56 PM Kevin Wolf wrote: > > > > > > Am 13.07.2020 um 18:33 hat Nir Soffer geschrieben: > > > > On Fri, Jul 10, 2020 at 5:22 PM Kevin Wolf wrote: > > > > > > > > > > Unaligned requests will automatically be aligned to bl.request_alignment > > > > > 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_sector <= bs->total_sectors || child->perm & BLK_PERM_RESIZE' failed. > > > > > > > > > > This was e.g. triggered by qemu-img converting to a target image with 4k > > > > > request alignment when the image was only aligned to 512 bytes, but not > > > > > to 4k. > > > > > > > > Was it on NFS? Shouldn't this be fix by the next patch then? > > > > > > Patch 2 makes the problem go away for NFS because NFS doesn't even > > > require the 4k alignment. But on storage that legitimately needs 4k > > > alignment (or possibly other filesystems that are misdetected), you > > > would still hit the same problem. > > > > I want to add oVirt point of view on this. We enforce raw image > > alignment of 4k on file based storage, and 128m on block storage, so > > our raw images cannot have this issue. > > Yes, then you won't hit the problem. > > > We have an issue with empty qcow2 images which are unaligned size, but > > we don't create such images in normal flows. > > Can you give a reproducer where qcow2 images would be affected? > Generally speaking, the qcow2 driver either takes both WRITE and RESIZE > permissions or neither. So it should just automatically resize the image > as needed instead of crashing. I think this is a theoretical issue in other programs trying to access the unaligned images using direct I/O.