From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:42207) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1URdGq-0007EH-Vn for qemu-devel@nongnu.org; Mon, 15 Apr 2013 02:52:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1URdGp-0006eq-Q7 for qemu-devel@nongnu.org; Mon, 15 Apr 2013 02:52:08 -0400 Received: from mail-wi0-x236.google.com ([2a00:1450:400c:c05::236]:34379) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1URdGp-0006ec-KF for qemu-devel@nongnu.org; Mon, 15 Apr 2013 02:52:07 -0400 Received: by mail-wi0-f182.google.com with SMTP id m6so142973wiv.9 for ; Sun, 14 Apr 2013 23:52:06 -0700 (PDT) Date: Mon, 15 Apr 2013 08:52:03 +0200 From: Stefan Hajnoczi Message-ID: <20130415065203.GA13418@stefanha-thinkpad.redhat.com> References: <5167F641.8090004@cybercom.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5167F641.8090004@cybercom.com> Subject: Re: [Qemu-devel] qemu-img: error while compressing, Input/output error List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ilkka Tengvall Cc: qemu-devel@nongnu.org On Fri, Apr 12, 2013 at 02:55:45PM +0300, Ilkka Tengvall wrote: > I run into an issue where qemu-img convert fails repeatedly on > compressing a raw disk image. It's not all broken, since it many > times also works. When it fails, it fails always to the same sector. > > I run into problem using f18 qemu-img-1.2.2-6.fc18.x86_64, and > repeated it with the latest qemu-img from qemu git as of 12th of > April 2013: > last git log: 93b48c201eb6c0404d15550a0eaa3c0f7937e35e > > I discussed the problem on IRC on qemu channel with stefanha, and he > asked me to provide the info here. Thanks for you help stefanha! > > Here is some background snipplets: > > " > anyone having idea why "qemu-img convert -c -O qcow2 -f raw > file1 file1.qcow2" would fail to: > qemu-img: error while compressing sector 1842944: Input/output error > ikke: My guess is that > qcow2_alloc_compressed_cluster_offset() is failing > Compressed writes cannot overwrite existing sectors, > perhaps there's a bug in qemu-img convert that causes it > to touch the same sector twice. > We wouldn't notice it when compression is disabled. > But when it's enabled you get a failure. > stefanha: by the way, is it right that qemu-img.c:1372 > calculates cluster_sectors from cluster_size by rounding down rather > than up? I know nothing about this code but that looks a little > suspicious > And the contents of the input image affect the I/O > pattern during conversion > which would explain why you always get the problem with > certain images. > pm215: That should be okay. cluster_size is a power of 2 > and multiple of 512. > For qcow2 the default cluster_size is 64 KB. > ikke: A post to the mailing list with a link to the file > and a description of how to trigger the failure would be fine. > I think it won't take long to fix. > " > > The image for repeating this is available here (~230MB): > > http://hard.ware.fi/~ikke/stuff/ubuntufs.raw.img.gzip > > and the command to reproduce the error is here: > > $ qemu-img convert -c -O qcow2 -f raw root.fs.copy root.fs.small.new > qemu-img: error while compressing sector 1842944: Input/output error I discussed the bug with kwolf on Friday. Although I sent a patch to add an error message when the input image length is not a multiple of cluster_size, Kevin pointed out that we can allow the final cluster to be zero-padded beyond the end of the virtual disk. I'll try to send a patch for that this week. Stefan