From mboxrd@z Thu Jan 1 00:00:00 1970 From: Conor Murphy Subject: virtio-blk.c handling of i/o which is not a 512 multiple Date: Wed, 30 Mar 2011 08:15:38 +0000 (UTC) Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit To: kvm@vger.kernel.org Return-path: Received: from lo.gmane.org ([80.91.229.12]:60800 "EHLO lo.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752925Ab1C3IP6 (ORCPT ); Wed, 30 Mar 2011 04:15:58 -0400 Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1Q4qZF-000825-NZ for kvm@vger.kernel.org; Wed, 30 Mar 2011 10:15:53 +0200 Received: from 95.45.199.134 ([95.45.199.134]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 30 Mar 2011 10:15:53 +0200 Received: from conor_murphy_virt by 95.45.199.134 with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 30 Mar 2011 10:15:53 +0200 Sender: kvm-owner@vger.kernel.org List-ID: Hi, I'm trying to write a virtio-blk driver for Solaris. I've gotten it to the point where Solaris can see the device and create a ZFS file system on it. However when I try and create a UFS filesystem on the device, the VM crashed with the error *** glibc detected *** /usr/bin/qemu-kvm: double free or corruption (!prev): 0x00007f2d38000a00 *** I can reproduce the problem with a simple dd, i.e. dd if=/dev/zero of=/dev/rdsk/c2d10p0 bs=5000 count=1 My driver will create a virtio-blk request with two elements in the sg list, one for the first 4096 byes and the other for the remaining 904. >>From stepping through with gdb, virtio_blk_handle_write will sets n_sectors to 9 (5000 / 512). Later on the code, n_sectors is used the calculate the size of the buffer required but 9 * 512 is too small and so when the request is process it ends up writing past the end of the buffer and I guest this triggers the glibc error. Is there a requirement for virtio-blk guest drivers that all i/o requests are sized in multiples of 512 bytes?